Conference Agenda

Lightning strikes to conductors of overhead lines may cause high transient induced voltages at neighboring pipelines. Thus, the computation of these voltages is important for the safe and reliable pipeline operation. This work investigates the effects of line parameters and soil modelling on the transient voltages induced at an aboveground pipeline due to lightning strikes to a phase conductor of a nearby overhead transmission line. Three different earth formulations are evaluated: the Carson, Wise, and the method of moments with surface operator combined with the extended transmission line approaches. Computations are performed using both frequency- and time-domain models, as well as constant and frequency-dependent soil electrical properties. CIGRE lightning current waveforms are employed in simulations derived on the basis of the statistical distributions of their parameters for negative first return-strokes. Transient induced voltage waveforms differ among the evaluated lightning currents, with higher peak values for shorter and steeper current wavefronts. Conservative results are obtained for the constant soil properties and Carson’s earth formulations, which neglect, respectively, the dispersion of soil electrical properties and displacement current.

This paper investigates the numerical performance of the Wedepohl series and of the Gauss-Kronrod quadrature to calculate ground- and sea-return impedances of power cables. Many computational routines to calculate ground-return impedances of cables used in EMTP-type programs have been proposed without technical justification of their application range. In this paper, we explore the convergence and accuracy of the Wedepohl series based on the number of terms in the series and as a ratio test. As a result, an accurate and stable numerical algorithm to compute ground- and sea-return impedances is proposed. The proposed method is capable of accounting for very low resistivity values and large depths.

This paper presents a three-parameter transmission line high impedance fault (HIF) model for the Alternative Transients Program (ATP)/ATPDraw. Real-world HIFs caused by vegetation contact on lines belonging to a Brazilian utility are firstly investigated to identify representative features of the fault resistance behavior during the disturbance period. Then, a data regression method is applied to obtain a time-domain function which emulates the fault resistance. Finally, an ATP/ATPDraw transmission line HIF model is developed and described in detail. For the sake of simplicity, only three parameters are proposed to be used in the model, namely: Initial resistance, final resistance and resistance decaying time constant. To prove the proposed model is representative, real HIF records are compared against ATP/ATPDraw simulated ones. The obtained results show the proposed model satisfactorily emulates the effects of real HIFs.

This paper proposes a tower-foot grounding system model compatible with EMT programs which might be useful for the simulation of lightning transients in overhead lines. The proposed model is based on the solution of the telegrapher’s equations and the application of the classical Marti’s
transmission line model. The model is implemented in the Alternative Transients Program (ATP) and validated considering a benchmark electromagnetic model. Its accuracy is evaluated and shown both in terms of the simulated ground potential rise (GPR) and line overvoltages developed through the insulator strings due to lightning currents. Finally, the model accuracy is also demonstrated in terms of the line backflashover outage rate.

This paper presents a new modeling approach based on idempotent decomposition of the nodal admittance matrix for representation of cables and overhead lines (OHL). By subjecting the idempotent matrices rather than the nodal admittance matrix to rational fitting, the poor observability of the smallest eigenvalues in the lower frequency range is overcome. Unlike the well-known method of characteristics (MoC), this alternative representation yields a so general fully-coupled admittance matrix suitable to tackle scenarios encompassing short and long lengths. Besides retaining the frequency dependence of parameters, the proposed phase-domain model showed to be accurate and suitable to circumvent the requirement of small time-steps.

This paper proposes small-argument approximations for two closed-form equations that were recently derived for the calculation of the ground-return impedance and admittance of underground cables. The proposed expressions are shown to be accurate up to 1 MHz for a typical cable configuration and frequency-dependent ground parameters. Their accuracy is also demonstrated in the calculation of transients on underground cables taking as reference results obtained with more general formulations.

This paper presents techniques to interface a Transient Stability Analysis (TSA) based model to an ElectroMagnetic Transient (EMT) based model running on a Real Time Digital Simulator. Practical challenges of implementing such an interface are discussed. The proposed TSA model can be simulated using a substantially larger time-step compared to the EMT model. The interface between the EMT model and the TSA model is implemented using a transmission line modeled using Dynamic Phasors (DP). Time-step delay is the primary cause of numerical instability in co-simulations. In this work, a traveling wave model of a transmission line is used to decouple the EMT and TSA networks. The interface requires that the propagation delay of the interfaced transmission lines be greater than the EMT time-step even though the TSA is simulated using a much larger time-step than the EMT model. The proposed technique is validated using the IEEE 39 bus system and a power system with 500 buses.

The main purpose of this research is to speed-up real-time simulations of electromagnetic transients (EMTs) using sparse linear solver techniques. This paper presents the integration of a direct sparse linear solver (KLU) into a real-time software for EMT simulation. This solver is combined with parallelization of network solution. Fill-in reduction techniques are investigated as well as partial refactorization to speed-up computations. The pivoting technique during refactorization is asserted in terms of simulation stability as compared to existing sparse solver based on code generation without pivoting. Performance and validation are studied on practical power system cases with real-time Hardware-In-the-Loop (HIL) simulation. Substantial performance gains, up to 50%, are obtained using fill-in reduction and partial refactorization. Pivoting is necessary to maintain numerical stability.

This paper proposes a one-stage and oscillation free numerical integration method using the compact scheme for electromagnetic transient simulations. Since the compact scheme becomes L-stable at a moment when a circuit suddenly changes to a stiff system, the method is capable of suppressing the spurious numerical oscillations. Moreover, the compact scheme, which is a one-stage method, does not produce spurious spikes due to nonlinear elements. The compact scheme is compared with the trapezoidal method, the two-stage diagonally implicit Runge-Kutta (2S-DIRK) and the trapezoidal method with the second order backward difference formula (TR-BDF2). It follows from the comparison that the compact scheme does not produce the spurious numerical oscillations and spikes.

Hydro-Québec built two static var compensators at the 735-kV La Verendrye substation in 1985. Each has a capacity of +330/-110 Mvar to help regulate system voltage and power system dynamic. They exceeded their useful life, and their operation was becoming challenging due to the aging control technology. Spare part availability and cost were also becoming an issue. A refurbishment project was thus undertaken. Due to design constraints, a hybrid SVC was selected: traditional thyristor-switched capacitors are used, but thyristor-controlled inductors are replaced by full-bridge modular multilevel converters. Throughout the ongoing project, hardware-in-the-loop real-time simulation was used for dynamic performance testing, factory acceptance tests and pre-commissioning studies. Two modeling approaches were used to represent the hybrid SVC: conventional electromagnetic transient simulation and small time-step approach. As this paper demonstrates, both approaches are valid in this case and produce matching results if simulation contrivances are not neglected.

At Hydro-Québec, power system studies are mainly done with offline electromagnetic transient simulation tools and real-time simulation is typically reserved for hardware-in-the-loop studies related to HVDC and compensation system commissioning. However, there is a growing internal need to pursue large-scale power studies incorporating physical systems to explore wide-area monitoring, protection, and control strategies: large power systems must then be ported from offline software to the real-time environment. The current paper presents lessons learned over the years about the offline to real-time porting process. As Hydro-Québec is involved in simulation tool development, software-related issues and challenges are presented and discussed. Details are then provided regarding the porting process of a large-scale power system required for wide-area control explorations. Prior to waveform comparison and performance assessment, modeling details and required modifications on the original simulation schematic are presented. In closing, electromagnetic transient modeling best practices and tricks to facilitate porting offline simulations to real-time are reported here to help users increase the efficiency and performance of their offline simulations and prepare them for real-time operation.

This paper aims to present a guideline formodeling and normative instructions for short-circuit (SC)and transient recovery voltage (TRV) analysis of mediumvoltage circuit-breakers installed in a real industrial system.The Alternative Transient Program (ATP) through its graphicalinterface ATPDraw was used in the work. The criteria usedfor modeling the analyzed industrial system are presented indetail. For a better understanding of the technical informationrequired for the modeling employed in TRV and SC studies,a set of detailed and typical data used is presented in orderto contribute to the reproduction of this case study in otherexpanding industrial power systems. The instructions for SCand TRV evaluation of circuit-breakers are based on the limitsdescribed by IEC standards and other references. The resultsare presented by discussing the effects of industrial expansionon the evaluated medium-voltage circuit breakers.

The development of accurate equivalent models of distribution networks (DNs) is one of the most important aspects for power system dynamic analysis. Consequently, during the last decades, several equivalent models have been proposed to analyze the dynamic behavior of DNs. However, the performance of existing models is sensitive to several factors such as the pre-disturbance operating conditions and the penetration level of distributed generators. Scope of this paper is to evaluate the applicability range of conventional equivalent models for the dynamic analysis of modern DNs by using a recently proposed performance assessment method. Towards this objective, the performance, in terms of accuracy and generalization capability, of 22 conventional equivalent models is assessed. Finally, the most critical parameters of all examined equivalents are identified by applying a variance-based sensitivity analysis.

Distribution feeders are prone to different types of events, such as disturbances and faults. Since these events are both unwanted and unexpected, their detection is essential for prompt system restoration, ensuring its reliability. This paper proposes the use of a power component, defined for non-sinusoidal conditions, as a disturbance detection index, which is estimated using the real-time stationary discrete wavelet packet transform. The proposed method analyzes the voltage and current of each phase separately, which are acquired at a single upstream measurement point, the substation. The performance and effectiveness of the proposed method are evaluated using events simulated in a test system based on a real distribution network. The results attest that the proposed method is suitable for detecting non-stationary disturbances.

Thereplacement of conventional synchronous gener-ators with converter-interfaced renewable energy sources (RESs)reduces the overall inertia levels of modern power systems,leading to frequency stability issues. Moreover, the intermittentnature of RESs constitutes system inertia variable during the day,further complicating the frequency control procedure. Therefore,power system operators shall estimate close to real-time theoverall inertia levels of their grids in order to ensure theirsecure and reliable operation. In this context, in this paper, anew methodology for the inertia estimation of multi-area powersystems is formulated. The proposed method uses the modalsensitivity matrix to obtain a linear approximation of the relationbetween modal parameters and inertia constants. During thereal-time operation, modal parameters are identified via systemresponses using the Matrix Pencil method. The identified modesand the derived sensitivity matrix are used to estimate the overallinertia of the examined power system. The effectiveness of theproposed method is validated by means of simulations performedin one-area, two-area, and three-area power system models.

Electricity is currently one of the most promising components for the future growth of our communities. Energy consumption will skyrocket in the near future, necessitating massive reforms in the energy industry to ensure that contemporary cities have enough electricity. Furthermore, climate change necessitates a greater than ever before energy transition from fossil fuels to greener power generating sources such as wind, solar power, or other more newly discovered technologies such as hydrogen. However, significant improvements to the power distribution and transmission grids are required for high - RES penetration in the energy system. To illustrate, power networks have been built radially, with energy flowing in just one direction, from the original power source to the consumer, with no provision for the penetration of independent power producers (ipps) across power grids. As a result, studying and developing such significant components, including power protection systems, is now seen as a critical undertaking in order to minimize unanticipated breakdowns and optimize grid availability. The goal of this work is to analyze a novel and promising technology in the power protection industry known as Solid State Breakers (SSB) and its contribution to the efficient operation of power distribution networks with high-RES penetration.

This paper evaluates the modeling of guyed towers of transmission lines in EMT-type programs to assess the backflashover occurrence of transmission lines and proposes a new modeling approach for this kind of towers. Two approaches to model the guyed towers by the revised Jordan model were evaluated: (i) the approach suggested by CIGRE Brochure 63 that represents the tower surge impedance as the parallel of the surge impedances of the mast and the guyed wires, disregarding the mutual coupling among them, and (ii) a new approach assuming the surge impedance of all the conductors in the tower section, guyed and mast conductors, and their mutual effect. The evaluations assumed the results provided by the Hybrid Electromagnetic Model (HEM) as reference for assessing the quality of the approaches. The approach (i) provided results of lightning overvoltage significantly lower than the reference, HEM model, leading to an underestimation of the probability of backflashover of the line. On the other hand, the approach (ii) was responsible for the results closest to those provided by HEM, indicating its quality, and the recommendation of applying this proposed approach for modeling guyed towers in the evaluations of backflashover occurrence.

Massive integration of power electronic devices with multiple control schemes in a wide frequency range pose new challenges regarding systems stability and reliability. Interactions between the fast control loops or between the fast control loops and passive elements of the grid, have been reported in literature and have led to introducing a new type of stability: the Fast-Interaction Converter-driven Stability (FICDS). In this paper, factors affecting the FICDS, such as tuning controller parameters, line parameters, number of interconnected inverters, are explored in four microgrid topologies, operating in grid connected and islanded mode. With the use of an impedance based model which tracks the poles of the CDS transfer functions of each system, their stability has been assessed. The obtained results have been verified via timedomain simulations. Simulations from the islanded microgrid of Gaidouromantra in Greece showcase the impact of the control parameters on the operation of the system and indicate the need for further investigation.

Some petrochemical plants (low density polyethylene type) always require the use of big synchronous motors to feed large power compressors (typically from 10 to 30 MW).
In certain supply network conditions, it could happen that the motor undergoes a critical starting which takes several tens of seconds to be completed. “Critical” means that the starting time is higher than the time the rotor can withstand in blocked condition: therefore, it is necessary to assess the actual motor rotation to be sure that the motor is being self-ventilating during its acceleration and can survive the critical starting. By means of numerical simulations, it is demonstrated that the solution of using an under-impedance relay (ANSI code 21) for starting supervision, as is proposed in technical literature since many years, gives some troubles for the correct and safe protection of the starting of the motor, with respect to the most common solution of adopting a supervision switch relay (ANSI code 14) based on rotor speed measurement.

Due to the vast number of substations at the distribution level and increased costs of differential busbar protection, DSOs are in search of cost-effective protection schemes for busbar protection. This includes the use of various communication-based protection schemes, such as the reverse-blocking schemes used at Stedin. However, due to impedance grounding, the single-phase-to-ground short circuit currents have small values in medium voltage impedance-earthed distribution grids. As a result, the reverse-blocking scheme fails to detect this type of fault. This paper introduces a novel distributed protection scheme based on the detection of zero-sequence components of the currents and voltages and the negative-sequence current component. The proposed scheme successfully detects single-phase-to-ground busbar faults by using the standard settings of the widely available overcurrent IEDs, and an IEC 61850 communication between them. Firstly, the detection of the zero- and negative-sequence current components is used to distinguish between a busbar and a feeder fault. Secondly, zero-sequence voltage detection is used to distinguish between the faulty and healthy sections of the busbar when the busbar coupler is opened. This also increases the proposed scheme’s reliability by avoiding miss-operation due to human errors during maintenance or testing. The grid is modeled in a Real Time Digital Simulator (RTDS), and a Hardware-in-the-Loop (HiL) simulation is carried out to test the protection scheme. The extensive simulations show the strengths and the limitations of the proposed scheme. Based on the research results, the developed protection scheme is implemented as a standard protection scheme in all of Stedin’s new distribution substations.

With increased integration of renewable energy resources, FACTs devices and series compensation, sub-synchronous oscillations (SSO) have become more common in electrical power systems in recent years. Specially designed relaying devices are often employed to detect and isolate harmful SSO conditions as when unconstrained, they can lead to widespread equipment damage and system instability. This paper presents design and implementation of a SSO relay model that can effectively extract sub-synchronous components in system measurements to quickly detect SSO conditions. Dependability and security of the developed relay model are validated using electro-magnetic transient (EMT) type simulations. In addition, performance of the developed relay model is compared against a commercial (physical) SSO relay. Obtained results demonstrate the effectiveness of the implemented relay model in detecting SSO and protecting electrical power systems against SSO conditions.

Unearthed neutral is often used in industrial networks, which require continuous power supply, and indistribution networks where the network capacitive current is not too high; or it is uneconomical to move to compensated grounding. Unearthed networks can remain in operation during an earth-fault, but fast determination of the faulty line is the key for prevention of further fault escalation. Signal injection is one of the fault location methods often used in LV unearthed networks. The possibility of application of this method in MV networks isdependent on how to inject the signal into unearthed phases with voltages ranging from 10 to 35 kV. This paper presents the signal injection circuit, which consist of three inductive voltage transformers (IVTs). The specifics of IVT design for signal injection are discussed. The application of the LF signal injection during an earth-fault was simulated on the model of an unearthed distribution network in EMTP. An intermittent fault and ring-type network connection were considered as possible cases.

This paper presents a two-terminal traveling-wave-based protection algorithm applied to non-homogeneous transmission lines comprising any number of sections with different topologies and considering the effect of the sampling rate. Existing two-terminal traveling wave protection functions cannot protect the line under close-in faults and present limitations in non-homogeneous transmission lines. However, the effects of the sampling rate, considered in the proposed method, result in well-defined protection and unprotected zones, essential for protection security and coordination to deal with the issue of close-in faults in non-homogeneous transmission lines. Furthermore, the algorithm can accurately detect the faulted section, allowing its use in advanced protection functions such as adaptive automatic auto-reclosing and high-speed protection schemes. A protection device was modeled considering a sampling frequency equal to 1 MHz, including functions to detect traveling waves via wavelet transform, and the proposed protection algorithm to discriminate line internal from external faults, and to select the faulted section. The algorithm was evaluated using a large number of ATP fault simulations. The results show that the algorithm is robust and reliable for protection devices installed in non-homogeneous lines.

In this paper, the performances of fixed and variable window size phasor-based techniques reported in the literature are evaluated on a classical one-terminal impedance-based fault locator, pointing out the challenges and alternatives for applications in transmission systems equipped with high-speed protection functions. To do so, several Alternative Transients Program (ATP) fault simulations were carried out in a 230 kV/60 Hz power network, varying their parameters such as type, location,
inception angle and resistance. The obtained results attest that phasors estimated from variable window size strategies may improve the fault locator performance, even in the first cycles after
the disturbance occurrence, appearing themselves as potential alternatives to be applied in combination with high-speed phasorbased protection routines.

Detailed Equivalent Models (DEMs) of Modular Multilevel Converters (MMCs) are generally developed based on Thevenin equivalent circuits with a time-varying resistor. This approach may become computationally inefficient, specifically for the simulation of large power systems with many nodes, where the network admittance matrix needs to be frequently re-inverted every time a switching event occurs. This paper proposes a novel strategy to eliminate admittance matrix re-inversions during the converter's normal operation and restrict it only to when the converter undergoes blocking. The proposed DEM thus yields marked reductions in the simulation time of MMC circuits, and is particularly useful in studies wherein repetitive simulations are necessary. Models are implemented for MMCs with half-bridge (HBSM) and full-bridge (FBSM) sub-modules in the PSCAD/EMTDC simulator, and their accuracy is thoroughly validated for normal and blocked operating conditions. It is shown that the developed models are 30% and 60% more computationally efficient, respectively, for HBSM and FBSM MMCs in comparison to existing DEMs.

This work analyses a voltage source back-to-back converter interfacing two alternating current systems from a multivariable perspective. Since the plant is not functionally controllable, frequency-dependent relative gain array analysis is carried out to aid in the choice of the most suitable variables to be controlled in a specific frequency range. This analysis is crucial to choose the low- and high-frequency controllers. A systematic approach is developed to tune a centralized optimal control. Validation of theoretical analysis and proposed multiple-input multiple-output (MIMO) control law is performed through experimental results.

This paper presents an equivalent time-domaingrid-following inverter-based generator model, which can be usedin Electromagnetic Transients Programs (EMTP). It is developedin the Alternative Transients Program (ATP) using the ATPDrawgraphical interface. A complete benchmark photovoltaic modelavailable in ATP/ATPDraw environment is taken as referenceto evaluate the proposed model under steady-state and faultscenarios. The obtained results showed that the proposedmodel is simpler and less time-consuming than the completemodel, being capable of easily consider the implementation ofdifferent components/controls of Inverter-Based Resources (IBR)in EMTP. The settings used in the implemented control schemesproved to be effective, resulting in an average error of about2.33% during fault conditions. Also, a reduction of about 70 % inthe execution time was achieved when compared to the analyzedbenchmark one, attesting its usefulness for power system studieswith high presence of grid-following IBRs

Recently, many high voltage direct current (HVdc) transmission lines are being constructed with the intention of becoming “backbones” of future power grids. Grid-Forming (GFM) controlled Voltage Source Converters (VSCs) are anticipated to provide significant stability advantages compared with Grid-Following (GFL) VSCs in HVdc converters connected to weak ac grids or to grids with high penetration of renewable inverter-based resources (IBRs). This paper proposes an adaptive fault ride through controller for Virtual Synchronous Machine (VSM) GFM control, which has significantly improved fault ride through capability over the more conventional GFM with cascaded or switchable current limiting. The performance of the proposed adaptive control is investigated using Electromagnetic Transient (EMT) simulation. The results show that the proposed adaptive control has superior post disturbance recovery from ac faults as well as phase angle shifts, and overcomes the instability reported in GFMs connected to strong ac networks.

This paper proposes a method for detecting,classifying and locating incident faults on transmission line (TL)of a bipolar HVDC system. This method is based on the travelingwaves theory and uses the redundant discrete wavelet transformto filter voltage signals monitored at only one system terminal.The model represents the Brazilian HVDC system of the MadeiraRiver, which is simulated in the Alternative Transient Program(ATP). Different fault scenarios are analyzed, being generatedby varying type, resistance and fault location. Moreover, inorder to make the simulation more realistic, the TL is modeledbased on frequency dependent parameters. Thereby, the impactsof line parameter uncertainties and transient attenuation onthe proposed method are analyzed. From the obtained results,it is concluded that the method correctly detects all faulttypes through the use of a self-adaptive detection threshold.Furthermore, it is verified that the self-adaptive threshold detectsthe fault times instants with an efficiency superior to the fixedthreshold. In the classification step, all faults were correctlyclassified through rules elaborated based on the voltage variationlevel. Finally, the total average errors of fault location representsonly 0.047% of the TL extension. Moreover, it is verified thatfault location errors for pole:pole faults were inferior to thoseobtained for pole:ground faults, being the efficiency of the methodinversely proportional to the fault resistance.

This paper focuses on a specific issue of bipolar HVDC lines with a dedicated metallic return (DMR). DMR is insulated to a lower level than the pole and its insulators are shorter. One event, for example, pole-to-groundfault will cause a fault on both the pole insulation and the DMR insulation simultaneously because the DMR insulation fault will be supported by the DC current and will turn into a DC arc. To ensure independent pole operation, these types of events should be avoided or, if the DMR does flashover, to extinguish the fault as soon as possible. This is studied through the paper and different solutions are tested to protect the DMR.

This paper proposes a comprehensive process for analyzing accurate transformer inrush current by elaborately controlling the closing instant of a circuit breaker and the level of residual flux in the iron core. The effectiveness of the proposed analyzing process is verified with a laboratory-scaled test system consisting of a 100 kVA 380/320 V Dyn11 three-phase dry-type transformer and a thyristor-based point-on-wave device. Moreover, the measured inrush currents by the proposed process are compared with those calculated by widely accepted inrush current equations. The proposed analyzing process is highly effective to demonstrate the inrush current under the specified energizing condition concerning the closing instant of the voltage and the residual flux in the iron core. The results show that there is a big difference between the measured and calculated inrush currents under the identical energizing condition of the voltage angle with 0° and the residual flux density with approximately 70 %.

An accurate representation of the transformer saturation curve is essential for calculations of low frequency transients (inrush current, ferroresonance, load rejection) and steady states (power quality problems, harmonics and subharmonics). This paper presents an original extraction methodology for determining the transformer saturation curve from the measured ferroresonant current and voltage waveforms. The proposed method is based on the formulation of a novel multiobjective function, using current and voltage obtained from the measurement. The proposed simulation-optimization method is based on the Backward Differentiation Method for solving the very stiff differential equation system that describes the ferroresonance as well as the Nelder-Mead optimization method used to minimize the proposed multiobjective function. Five functions are proposed for approximating the saturation curve. The best ferroresonance simulation results are obtained with the inverse extended Frolich function. The validity of the proposed methodology has been confirmed by a very good agreement between the measured and simulated results of the ferroresonant current and voltage under different ferroresonance scenarios (three different values of series capacitances).

This paper presents the implementation of a nonlinear model of a Capacitive Voltage Transformer (CVT) to evaluate the transient response in conformity with the international standard IEC 61869-5. The work is divided into three main steps: electrical tests to measure the CVT parameters and frequency response; implementation of linear mathematical modeling and an optimization algorithm to estimate unmeasured parameters; and implementation of nonlinear modeling in a simulation program for electromagnetic transients. First, the requirements of the IEC standard about the transient response of CVT are presented. Then, some important aspects of CVT modeling are discussed. Afterward, a linear model of a CVT is used to estimate the parameter not measured in the laboratory. Then, a nonlinear model is implemented in ATP. The model is validated in the time domain by comparing the simulation results with some signals measured in the laboratory. Finally, simulations of the transient response tests are made following the IEC 61869-5. The results show that the model developed in this work is reliable and can be used for the simulation of ferroresonance and transient response tests following the IEC 61869-5 when no laboratory structure is available.

One of the main causes forincorrect operation of the transformer relay protection are inrush currents. The transient inrush currentsoccur when energizing the unloaded transformer, and it is a consequence of the transformer core saturation. This paper presents an analysis of transients caused by energization ofthree-phase autotransformer 300 MVA,with rated voltages400/115/10.5kV. Using the EMTsoftware with parametric toolbox,a large number of simulations isperformed to show the impact of model parameters on the amplitude and duration of inrush currents as well as the probability of differential current 2ndharmonic amplitude occurrence. Based on the simulation results, the optimal differential protection settings are determined, and the probability of a false relay protection operation is determined.

Phasor models have been widely used inshort-circuit simulations, in which system operators verify thebehaviour of the grid over thousands of different contingencies.However, it is still unclear if phasor models can still be usedin fault studies in modern or future power grids dominated byrenewable generation with power electronics and converters.Therefore, this paper analyses the suitability of phasor modelsto simulate short-circuit transients in grids with grid-following(GFL) and grid-forming (GFM) voltage-source converters (VSC).Phasor models of GFL and GFM were developed and tested intwo test systems, one with 50% of converters in the generationmix and another powered 100% by converters. Asymmetricaland symmetrical faults were applied at different points of thesystems and key variables were used to compare the phasormodels against EMT models during the transients. The resultsshowed that, despite neglecting transients in the grid, phasormodels could be used in a preliminary stage of short-circuitstudies as it was capable of tracking the steady-state valueof almost all variables analysed. In this case, detailed EMTsimulations, although necessary, would be used only at moreadvanced stages of the studies.

The rising renewable energy in-feed in power systems entails wider presence of power electronic devices (PEDs). Consequently, adverse dynamic phenomena can be observed in power systems, as a result of the interaction between different controllers or between controllers and existing power grid equipment in the close vicinity. This paper aims to outline the key contributing factors of controller interactions with focus on HVDC-connected offshore wind farms (OWF) by proposing a comprehensive methodology to identify system topologies and conditions that can instigate interactions in the onshore system. In this regard, a benchmark model has been developed in an EMT-type tool comprising three generic HVDC-connected OWFs, a fourth OWF connected through an AC cable and a STATCOM. Moreover, two different versions of the control system of the HVDC links were developed to study interactions between controllers from different manufacturers. Parametric EMT-type simulations were performed for various system conditions and topologies to provide a wider view on the risk of interaction between multi-infeed HVDC links and OWF systems. Harmonic stability is also studied to illustrate the risk of resonance between two HVDC links connected in the network.

The solid-state transformer (SST) is being presented as a technology that enables the construction of new power systems due to its many advantages. These benefits include reduced weight and volume compared to traditional transformers, power factor compensation, accurate output voltage regulation, harmonic mitigation, short-circuit current limitation, and voltage dip immunity, under certain conditions. Unlike other studies that only demonstrated the effectiveness of Model Predictive Control (MPC) in individual parts of the SST, this study shows the control of an entire SST using the MPC strategy. The performance of the SST during power system transients is evaluated to showcase the features of the SST by predictive control.

Transient simulations are usually carried out to analyze the behavior of control and protection systems when performing switching action in power transformers. For this reason, the saturation curve and/or the hysteresis curve of the transformer must be properly modelled. However, in most of the cases the real saturation/hysteresis curve of a transformer is not known, because such measurements are not carried out as part of the factory tests of a transformer. This article describes a method to measure the hysteresis- and saturation curve with a portable measuring system on-site. The added value of the measured saturation curve is illustrated through an example, in which a
single-phase low voltage transformer is modelled. This example shows the added value of a measurement-based modelling. An additional example illustrates measurement of the hysteresis curve of 350 MVA, 420/110 kV power transformers.

Timely detection and classification of power system events are essential for situation awareness and reliable electricity grid operation. It is also a crucial step with regard to synchrophasor network data management and archiving. In this paper, an event detection and classification method based on the singular value decomposition (SVD) of synchrophasor data is proposed. The detection algorithm exploits the low-dimensionality characteristics of synchrophasor data and identifies the changes in the dimensionality of a sliding data matrix. The SVD-based method assigns several detection flags indicating events and outliers in voltage magnitude, phase angle and frequency data. The proposed classification algorithm comprises a decision tree employing detection flags and singular values to classify events into several categories, e.g., fault, voltage magnitude and phase angle events, and generation-load mismatch events. Moreover, the proposed algorithm identifies whether events are spatially correlated. Field synchrophasor data collected from a smart grid are used to evaluate the performance of the proposed method. The numerical results show that the proposed method can successfully detect and classify different types of events even in the presence of measurement uncertainty.

In today's grid reinforcement in Germany, more and more underground cable sections are being installed at the 400-kV level. They are mostly used near cities or to overcome other obstacles. Consequently, mixed transmission lines are formed, which include overhead line and cable sections at this voltage level. Typically, shunt reactors are used on such lines to compensate the capacitive reactive power. In addition to the compensation degree, the type of the reactor is also important. These can be realized as an air core coil or as a coil with iron core. Especially when using iron core coils there are additional effects like saturation or zero-missing effects, which have to be investigated before erecting a mixed transmission line. These effects are numerically simulated and validated and explained using an analytical method. With the aid of a simplified model, the system properties have been investigated and applied to the transmission line.

A phase-domain synchronous machine modeling technique by using only basic circuit components and applying the magnetic circuit representation used for transformer modeling is proposed in this paper. The model based on the proposed technique is implemented into XTAP, one of the electromagnetic transient analysis programs, and the accuracy of the proposed model is validated through simulation in an infinite-bus case system by comparing it with some conventional synchronous machine models in this paper.

In this paper, a new method for on-line inertiaestimation is developed. The proposed method is based onthe sliding window concept and uses ambient responses, i.e.,responses obtained during the normal operation of the powersystem, to identify inertia constants of generation devices. Theeffectiveness of the developed method is evaluated by means ofsimulations on two benchmark power system models, namelythe IEEE 9-Bus Test System and the IEEE 39-Bus Test System.The conducted analysis reveals that the proposed method canaccurately identify inertia constants of conventional synchronousgenerators (SGs), converter-interfaced units operated as virtualSGs, and virtual power plants. The performance of the proposedmethod is also evaluated under noisy conditions, by performingMonte Carlo simulations. Finally, comparisons with conventionalmethods are performed, demonstrating the superior performanceof the developed method.

Voltage dividers are devices designed to reduce high voltages according to a transformation ratio to facilitate their measurement for different purposes. Among them is the detection of transient overvoltages in medium voltage lines. It is convenient to know the transformation ratio of the sensor and its working frequency range for the correct measurement of overvoltages. This article shows the characterization process of an air-insulated capacitive voltage divider used to measure induced voltages in distribution networks. A detailed description of the device is shown, such as how it works and the tests carried out for its characterization. The parameters of its equivalent circuit are obtained by modeling the voltage divider in the CST Studio 2021 software; through laboratory tests, its experimental transformation ratio is obtained; and through a frequency sweep applied to the divider, its frequency response is determined. Indeed, the experimental transformation ratio is 10667.46:1, and the frequency range obtained experimentally is between 60 Hz and 4 MHz, different data from those given by the manufacturer. These experimental data can be used as a reference for the capacitive voltage divider.

In islanded hybrid AC/DC multi-microgrids (MMGs), interconnected AC microgrids (ACMGs) can operate with their own frequency and power sharing strategy. Hence, to formulate the load-flow problem of multi-frequency islanded MMGs, conventional single-frequency load-flow approaches are
not applicable. To this aim, in this paper a novel unified load-flow framework for AC/DC hybrid MMGs, is proposed. The principles of the proposed method are based on the modified augmented
nodal analysis (MANA) formulation, which can be utilized for an arbitrary number of interconnected multiphase MGs. Then, an unbalanced MMG, which includes two ACMGs, one DC MG (DCMG), and two interlink converters (ICs), is used to verify the validity of the proposed MANA-based formulation.

The Delta-connected STATCOM is regarded as the most advantageous topology for STATCOMs based on the Modular Multilevel Converter (MMC) technology. Embedding energy storage devices into the MMCs has gained significant research interest in recent years. This paper focuses on modeling of MMC-based Delta-STATCOMs with embedded energy storage. A flexible modeling approach is proposed, which allows easy interfacing of various converter models with various energy storage device models. Four commonly used types of MMC models are applied to STATCOM modeling: detailed, detailed equivalent, arm equivalent, and average value. Supercapacitors and batteries are used as energy storage devices. Dynamic performances of the models are compared in transient simulation cases using EMTP.

Power-electronic converters are essential elements for the effective interconnection of renewable energy sources to the power grid, as well as to include energy storage units, vehicle charging stations, microgrids, etc. Converter models that provide an accurate representation of their wideband operation and interconnection with other active and passive grid components and systems are necessary for reliable steady state and transient analyses during normal or abnormal grid operating conditions. This paper introduces two Laplace domain-based approaches to model buck and boost DC-DC converters for electromagnetic transient studies. The first approach is an analytical one, where the converter is represented by a two-port admittance model via mode averaging and inclusion of switching effects. The second approach consists of reconstructing the two-port admittance model of the converter from terminal measurements for a series of tests. The performance of both approaches is evaluated against EMTP simulations, with very close results.

Parallel operation of grid-forming inverters (GFMIs) is often achieved using droop characteristics implemented in converter controllers. Converters’ recovery after a disturbance depends on the dynamics of each individual GFMI, and the droop characteristic alone is unable to ensure successful parallel operation. This work proposes a dynamic-phasor based modeling approach that enables eigenvalue analysis of multi-converter systems to identify the underlying factors that affect the interactions among parallel GFMIs. Network dynamics are included through dynamic phasor modeling of its elements, and controller dynamics are fully included. Modeling modularity is preserved, which allows to easily extend the test system to any topology of interest. The results presented for an exemplar two-converter system prove that the virtual inertia time-constant plays a significant role in exciting interactions, and that network and control system parameters are vital in extending the stability margins of the systems. EMT simulation results from PSCAD/EMTDC are included to verify the validity of the predictions of the dynamic-phasor based model.

Weak grid sub-synchronous oscillation (SSO) is an important research topic. Although some analysis and mitigation schemes have been conducted, misperceptions still exist. This paper first aims to update the understanding of weak grid instability of voltage source converters (VSCs) and then points out that instability risks originate in the super-synchronous frequency range rather than in the sub-synchronous frequency range. Moreover, the resonance frequency can be even larger than the double fundamental frequency under certain parameter conditions. This paper also refines the impacts of VSC control parameters on weak grid instability mechanism andresonance frequency. Based on the results, the classification of this phenomenon should be revised.

In this paper, the behavior of traveling waves (TWs) on transmission lines which interconnect inverter-based resources (IBRs) is investigated, assessing the performance of well-known TW functions applied in protection and fault location schemes. To do so, traditional synchronous generators and wind turbine-based IBRs of types III and IV are investigated, allowing comparative studies regarding the shape of fault-induced transients measured at the monitored line terminals. Then, the impacts of typical terminations of IBR-interconnecting lines on the classical double-ended TW-based fault location method, as well as on directional, overcurrent and differential TW-based protections are analyzed, highlighting the effects of busbar and transformer stray capacitances on the performance of these functions. The obtained results reveal that TW solutions are promising for IBR-interconnecting lines. However, a significant influence of busbar and transformer stray capacitances on the performance of TW functions is also identified, revealing the need for taking these capacitances into account during the definition of settings used in TW protection and fault location schemes.

Electromagnetic transient (EMT) simulations are often performed to analyze disturbances which occur during a steady-state operation of the power grid. In modern transmission and distribution power grids, a number of voltage-source converters (VSCs) are used for renewable energy interconnections and system control. To perform EMT simulations with such VSCs, a time step of the order of microseconds is used to represent the switching operations of the VSCs. In order to avoid a prohibitively-long computation time, a steady-state initialization method is required to directly start from a steady state. This paper proposes a systematic and heuristic procedure for the steady-state initialization of generic VSCs. Using an AC steady-state solution, detailed portions in the circuit part and the control-system part of a VSC are systematically initialized. For validation, EMT simulations of a 6.6-kV distribution grid with two VSCs are performed with and without the proposed initialization procedure in this paper. Practically no transient is observed in the result with the proposed procedure, and therefore it is confirmed that directly starting from a steady state is made possible. On the other hand, the result without the proposed procedure does not reach the steady state even after continuing the EMT simulation for 300 ms.

Dimensioning, testing and maintenance of the lightning protection system of wind turbines can be improved using the local distributions of lightning current parameters instead of those on which lightning protection standards rely. This paper presents a prototype system for measuring lightning currents’ waveforms on wind turbines. The prototype is being developed at the Faculty of Electrical Engineering and Computing, University of Zagreb, Croatia. The system’s fundamental components are two Rogowski coils and their corresponding integrators. One coil is optimized for lower frequencies and amplitudes, while the other is for higher ones. The cRIO real-time controller is used as an acquisition system, with acquisition logic developed using LabVIEW. The controller has one digitizer for each coil and a GPS synchronization module. The system was tested in the High Voltage Laboratory at University. It was recently installed on an actual wind turbine in Croatia, located in an area characterized by high winter lightning activity. Simultaneously with the prototype measurement system, the lightning activity in the wind turbine micro-location will be monitored by three other systems: the lightning location system, additional lightning monitoring sensors installed in the blades of the same wind turbine and a high-speed camera installed at the wind turbine location.

This paper presents a new aspect of shield wire (SW) modeling for assessing the indirect lightning performance of overhead medium-voltage distribution lines: a flashover (FO) between an SW and the reinforcing bars of a distribution pole or a crossarm (SWFO). In general, an SW is periodically grounded approximately every four to ten poles and not grounded at the other poles. However, owing to lightning-induced overvoltages, the voltage difference between the SW and the distribution pole may even exceed 100 kV, and the SWFO can occur. In this paper, we evaluate the effect of the SWFO on the number of FO occurrences of phase-conductor insulators by the Monte Carlo method using a 2D finite-difference time-domain-based indirect lightning surge analysis program. The effect of the SWFO is more significant in lines with high soil resistivity (a soil resistivity of 1000 m was assumed) regardless of the installation of surge arresters: the total number of FO occurrences markedly differs by up to 50% between cases in which the SWFO is considered and not considered. The analysis presented in this paper will assist the formulation of lightning protection measures particularly, in regions with high-resistivity soils.

This paper investigates the effect of the impulse corona inside the cross-arm on the lightning performance of a Y-shaped composite pylon with a cable as an internal down-lead through the hollow cross-arm. First, the electromagnetic transient model for the down-lead system of the composite pylon is built. The simplified steps for calculating the surge impedance of the cable down-lead are given. In addition, the mutual coupling between two down-leads is considered. Through a laboratory test on coaxial cylinders resembling the structure of the cable and cross-arm, the dynamic capacitance of the corona on the surface of the cable is obtained and included in the electromagnetic transient model. Then, the effect of the corona on the traveling waveform and mutual capacitance is discussed. Furthermore, the influences of the ground electrode length and the phase voltage on lightning performance are also studied. Finally, the backflash rates of the composite pylon with cable as down-lead are calculated. The results show that the impulse corona has a limited impact on the critical current, and the composite pylon with cable as down-lead shows a promising lightning performance.

In this work, the authors model the number of lightning flashes in transmission structures with Ground Flash Density, height tower, and elevation above sea level as variables. 333transmission structures were located in the northeast of Colombia, where an influence radius of 150 meters was established for each one. Cloud-to-ground lightning strokes detected by the LINET network between 2014 and 2021 in the studied area were grouped into flashes and counted for each radius. Likewise, each structure was characterized by its height, elevation above sea level, and GFD of the area where it is located. In this way, a model that describes 75.66 % of flashes in transmission structures with a standard deviation of 0.32 flashes was built. It is concluded that there is a linear relationship between the dependent variable and all the independent variables.

The paper focuses on evaluating the stress on distribution class surge arresters (SAs) caused by lightning strikes. It proposes a procedure for estimating the statistical distribution of energy absorbed by SAs due to both indirect and direct lightning strikes, which is a crucial step for assessing the probability of SA failure. Two different SA representations are considered, namely, a static nonlinear resistance and a dynamic, frequency dependent model. After analyzing the overvoltage and current waveforms caused by lightning strikes and considering the effect of flashover occurrence, the paper assesses the effect of several factors on the current and energy absorption, namely the presence of a periodically grounded shield wire, of the grounding resistance value, and of the distance between subsequent SAs. The analysis shows that the static model can be considered accurate enough for evaluating the stress originated by direct and indirect lightnings on distribution class SAs.

The differences on the lightning response of transmission lines, whose towers are subjected to the impression of pulses of current of first negative return strokes and of positive flashes, are determined by computational simulation. It is shown that the amplitude of the resulting transient overvoltages across insulators per unit of impressed current is much larger for negative return strokes. As most of the traditional procedures for assessing lightning performance of transmission lines ignore these differences, their results can exhibit significant errors.

In a multi-terminal direct current (MTdc) system based on a modular multilevel converter (MMC), high-speed and large interruption capability direct current circuit breakers (de CDs) are required for de fault interruption. However, the commercialisation of these breakers is challenging, especially offshore, due to the large footprint of the surge arrester.Hence, a supplementary control is required to limit the rate of current rise along with the fault current limiter.Furthermore, the operation of the de CB is not frequent, thus, it can lead to delays in fault interruption. This study proposes the indirect model predictive control (MPC)-based zero-current control. This control provides de fault current suppression by continuously controlling the zero-sequence current component using circulating current suppression control (CCSC), and by providing feedback to the outer voltage loop and inner current loop of MMCs. The proposed control is simulated for pole-to-pole and pole-to-ground faults at the critical fault location of an MTdc system. The simulation is performed in Real Time Digital Simulator (RTDS) environment, which shows that the predictive control reduces the rate of rise of the fault current, and in this way provides an additional 3 ms after the de fault occurrence for the de CB to clear the fault. Besides, the energy absorbed by the de CB's surge arrester during the pole-to-pole and pole-to-ground fault remains the same with the proposed control

This paper presents a tool developed in EMTP to automatically determine model parameters for matching existing field measurements. The tool uses the particle swarm optimization (PSO) algorithm to calibrate or update existing models. To enhance the performance of the tool, a technique used to improve PSO efficiency is also proposed. Two test cases are presented. The first case aims to determine the parameters of the reactive power control loop in a PV park controller model. The second case finds the unknown parameters in an exciter model of a synchronous machine connected to a grid.

Deep learning techniques have recently demonstrated outstanding success when used for Power Quality Disturbance (PQD) classification. However, a core obstacle is that deep neural networks (DNN)s are complex models, and their architecture is designed using trial and error processes. Accordingly, the problem of finding the optimal architecture can be considered as a problem that consists of high-dimensional solutions. Meanwhile, in the last couple of years, Neural Architecture Search (NAS) techniques have been developed to efficiently find the best possible performance architecture for a specific task. In this light, the goal of this research is to develop a method to find optimal PQD classifiers using the NAS technique, based on an evolutionary algorithm. This method can converge efficiently to an optimal DNN architecture. Thus, a classifier that achieves high accuracy for PQDs classification is provided using limited resources and with minimal human intervention. This idea is demonstrated on two different DNN typologies- convolutional neural networks (CNN) and Bi-directional long short-term memory (Bi-LSTM). By adopting this method, the results of the generated PQD classifiers are more accurate when compared to recently developed classifiers.

This paper develops a novel multi-rate, multi-solverco-simulation framework combining dynamic phasors, transientstability, base-frequency dynamic phasors for frequency-adaptivesimulation of transients, and electromagnetic transient (EMT)models. This framework subdivides a given power network intoseveral types of subsystems based on the connected devices,required accuracy in representing dynamic details, electricaldistance from perturbations, and the intended purpose of thestudy; as such, the paper describes methods and guidelines tosimulate each subsystem using the most appropriate solver andtime-step size to maximize simulation efficiency and accuracy.It also addresses the tasks of multiple interfacing and solverinteractions that are essential in coupling different solvers. Theproposed framework is built around an industrial-grade EMTsimulator, to which other solvers are interfaced, enabling accessto a variety of power system models and distinct features. Theaccuracy and efficiency of the framework are demonstratedthrough co-simulations carried out on a modified version of the118-bus network, which includes an MMC-HVDC system.

This paper analyzes the use of fitting techniques based on partial fraction expansions in the fitting of modal transmission line functions and the assumption of constant and real transformation matrix (constant T) in the transformation of modal functions into phase domain. The focus is on the fitting of the propagation function due to its complexity compared to the characteristic admittance function. It is demonstrated for the first time that using a constant T can intrinsically violate the passivity of the transmission line system depending on the choice of frequency point for assigning the constant T. Consequently, the final rational model violates passivity at certain frequency intervals. Second contribution is the evaluation of the fitting performance with a new solution strategy based on the recently introduced rational Krylov fitting (RKF). The case studies suggest that RKF results in accurate and less order models compared to the vector fitting (VF) algorithm which is the de facto method in electromagnetic transient-type models. Finally, the fitting accuracy of the legacy constant T model based on Bode fitting is presented in the phase frame giving a clear picture of its poor fitting performance compared to modern methods and explaining its inaccuracies in the time domain.

In this paper, an alternative approach to power loss calculation in a transformer supplying a nonlinear load is presented. The advantage of the proposed approach is that it relies on readily available transformer technical data in contrast to the data required by the methodology described in IEEE std. C57.110-2018. Experimental verification of the proposed approach was carried out using a 4.5kVA laboratory dry type power transformer. The results obtained experimentally show
high compatibility with theoretical model featuring an error margin smaller than 0.2%.

Installing cables in the power system results in a shift of resonances to lower frequencies, and possibly introduces problems associated with near fundamental frequency resonance overvoltages. These overvoltages were found to prevail especially during switching events in weak systems. This paper has studied a utility case by using PSCAD software as well as the sequence network method. The industry practice demonstrates that several mitigation methods exist to deal with resonance problems. These can be classified into (i) installing direct transfer trip functions for contingencies, (ii) suppressing the phenomenon (e.g. specifying surge arresters), (iii) adding interlocking between the associated circuit breakers to prevent mis-operations or (iv) avoiding the problem (e.g. using alternative system connections). Some of the mitigation methods may not be recommended according to the Safety-by-Design initiative of the utility. The surge arrester (ii) itself cannot provide full protection and should be used together with other mitigation measures. To balance the risk against cost and ensure the cables can be operated safely, this paper recommends (iv) of planning an alternative system connection to avoid the residual risk of overvoltages.

The paper investigates overvoltage propagation in a 400kV network within the National Grid Electricity Transmission system in the UK. The studies were triggered by a replacement project for two parallel 400 kV cables and the installation of an additional one. The network in the vicinity of the cables has historical issues of flashover and circuit breaker failures. Electromagnetic transient studies were performed to simulate energisation and fault inception and clearance for the three new cables to examine compliance against overvoltage standards and limits. Studies were performed using the DIgSILENT analysis tool. Studies show that due to resonance in a specific frequency range, switching overvoltage propagated and amplified at remote nodes to a level close to the equipment's rated switching voltage. As mitigation, surge arresters with characteristics different from the National Grid recommended surge arresters were proposed and found suitable to bring the overvoltage values within the design limits for temporary overvoltage.

Inan ungrounded electrical system, successive reignitions and extinctions of a single-phase to ground fault is known to potentially generate a voltage escalation phenomenon.This is the so-called arcing ground fault whose theory has been thoroughly described in literature, even though very few practical occurrences have been experienced in existing electrical systems due to the specific and rare conditions that cause its appearance. This paper studies the risk of appearance of voltage escalation inthe 10 kV auxiliary system of an industrial plant. It describes the physical principles at the origin of voltage escalation and presents a study conducted using an EMT-like program. The results show that, thanks to the presence of a permanent insulation monitor (PIM) connected to the system through voltage transformers, the successive reignitions and extinctions of single-phase faults cannot cause severe overvoltages or voltage escalation. The paper ends with some general conclusions.

This paper studies the voltages developed on a wind turbine (WT) and a medium-voltage distribution line (MVDL) connected to a wind farm subjected to lightning strikes and located on FD (FD) soils. The ground potential rise (GPR), voltages at the blade tip and on phase conductors of the MVDL are calculated using the full-wave electromagnetic software XGSLab® employing the rigorous Partial Element Equivalent Circuit (PEEC) method. The wind farm comprises four wind turbines with interconnected grounding systems using cables buried in resistivity soils of 1,000 and 5,000 Ω.m. The voltages are computed for the first positive impulse (FPI) of 100-kA 10/350 μs and for the subsequent negative impulse (SNI) of 50-kA, 1/200μs. Results have shown that voltage peaks increase notably as the soil resistivity increases. When the WTs are assumed, oscillations in the GPR waveforms for the SNI occur due to the multiple reflections between the blade and the turbine’s base. However, the voltages for the FPI present smooth time-domain responses. Furthermore, the overvoltages developed at the MVDL are significantly dependent on the soil resistivity and lightning current waveform.

In half-wavelength (HWL) transmission lines, severe temporary overvoltages are usually observed during the occurrence of line-to-line faults in specific critical locations, and it is unrealistic to ignore the impact of the corona phenomenon. To represent the corona effect, an accurate Suliciu corona model was adopted and implemented in PSCAD software, and a new technique based on the genetic algorithm (GA) was proposed to fit the model parameters. Furthermore, the paper evaluated the performance of the overvoltage mitigation method based on the installation of two spark gaps (SGs) at strategic points to detune the resonance condition. As shown, the SGs turn the HWL line
overvoltage levels similar to those observed in conventional AC lines, and the corona modelling further reduces the severity of the overvoltages.

In high-voltage industrial electrical power systems it is common to ground the neutral of the generators by high resistance to control the ground-fault currents. Grounding resistors are sized so that transient overvoltages remain at controlled amplitudes, and, for this, it is considered as a basic criterion to set the resistive component of the ground-fault current greater than or equal to the total capacitive current. Although this criterion is widespread in the literature, when the resistor is connected to the secondary of a grounding transformer this criterion can be different. Normally, the works found in the literature does not consider the transformer parameters, however, for large industrial power systems which have a high capacitive current, the transformer parameters need to be considered, hence a new criterion to keep the overvoltages at safe levels must be investigated. Thus, in this work, it is proposed a transient model to study intermittent-ground faults in a typical industrial power system. Furthermore, many simulations are performed to investigate which parameters affect the overvoltages when the grounding transformer parameters are considered.

A novel, simple and fast method to identify the faulted phases using the maximum rate of change of incremental current (ROCOIC) is proposed. Six indices are calculated considering a pairwise comparison of ROCOIC. The decision-making process is based on selecting which two indices are the largest among all. The algorithm requires only three thresholds to detect fault inception and to identify the ground and three-phase faults. Simulation studies show that the method is robust and not affected by fault inception angle, fault location, and fault resistance. The proposed method only requires locally measured current signals. Since the method relies on the fundamental component of instantaneous incremental current, the proposed method can be implemented in systems with low sampling rates and avoids the need to use transducers with high bandwidth.

Faulty feeder selection is a challenging task for distribution system operator due to the low earth fault current magnitudes in compensated networks. However, extensive cable usages, especially in metropolitan cities causes unintentional resonance in the network earthed through inductance or grounding transformer. The unintentionally resonated networks are not designed like intentionally compensated networks where faulty feeder should be isolated in a predetermined time. There are transient zero sequence current based methods, particularly synthesized for compensated networks to identify faulty feeders. However, zero sequence-based faulty feeder selection methods have drawbacks in the presence of underground cables. Further, transient zero sequence current is prone to many parameters such as capacitive imbalance and fault resistance. In this study, a transient negative sequence current based faulty feeder selection method is proposed. The effectiveness of the proposed method is demonstrated in a simulated 151-node distribution network. EMTP simulations are carried out by considering different fault inception times, fault resistance and capacitive imbalance of the system. Results show that negative sequence current offers selective faulty feeder selection and no false trip is observed in unintentionally resonating distribution network.

The condition where the load angle of a generatorchanges rapidly with respect to another generator or portion ofa system is called Generator Out-of-Step (OOS). The traditionalway of detecting an OOS condition is to analyze the trajectoryof the impedance seen from the generator terminals. Therefore,setting calculations for these impedance-based methods becomemore challenging and time consuming. Detailed time domainsimulations, which required both generator and system data, arenecessary to set up these relays. This paper proposes a novelmethod to detect an OOS condition of a generator using itsrelative rotor speed. The inputs for the proposed algorithm arethe terminal voltage, current and machine parameters whichare readily available for typical synchronous generators. Theproposed algorithm monitors the change of relative rotor speedfollowing a fault and declares the OOS condition if the relativespeed tends to increase during a swing cycle. This technique iscomputationally simple, easy to implement, and fast comparedto impedance-based methods. The application of the proposedmethod is investigated using time domain simulations. Also, thesensitivity and security of the proposed method are analyzedunder various power system conditions.

This paper investigates the effects of communicationchannel latency (CCHL) on time-domain line protectionfunctions. The Alternative Transients Program (ATP) was usedto simulate the monitored power system and to model boththe analyzed relays and communication channels via MODELSlanguage. By doing so, the need for extra long optical fibers forlaboratory tests is overcome. To provide a reliable investigationon the CCHL effects, a time-domain relay model is firstlyimplemented and validated by comparing its response against anactual device. Then, the communication channel is set to properlyrepresent practical CCHL values under different fault scenariosfor transmission lines with different lengths. The obtained resultsshow that including the CCHL effects on time-domain protectiontesting procedures is of utmost importance because, depending onthe data propagation time through the communication channel,it may have a relevant influence in what we call here “race ofprotection functions”.

In this paper, the performances of one-ended and two-ended traveling wave (TW)-based fault location techniques in series compensated transmission lines (SCTLs) are thoroughly investigated, highlighting the impact of the series capacitors (SCs) and their associated overvoltage protection on such routines. To do so, a diversity of fault simulations were carried out on a realistic Alternative Transients Program (ATP) power system model of a 500 kV/60 Hz double-circuit SCTL located in the north region of Brazil. From the carried out studies, it is demonstrated that the two-ended algorithm is not impacted when the SCs are installed at the line ends, but the single-ended routines based on correlation functions are more affected by the SCs banks, even though some promising results may be obtained depending on their adjustments.

The algorithms for the correction of transients in coupling capacitor voltage transformers (CCVTs) are generally designed from processing samples in the time domain. Therefore, they need to be embedded in the measurement, protection, and control devices, because in these instruments only the phasors are available for the development of dedicated applications. In this paper, as an extension of a method originally developed by these authors for the time domain correction of CCVT secondary voltage samples, a mathematical formulation is developed that demonstrates the applicability of the existing method for phasor compensation, regardless of the phasor estimation algorithm used. Three phasor estimation algorithms and two CCVTs with different topologies and voltage levels are used to evaluate the method's performance. ATP (Alternative Transients Program) was used to generate the oscillographic records, while the phasor estimation algorithms and their corrections were implemented in MatLab. From the results, it can be inferred that the evaluated method can be used to correct voltage phasor disturbances, providing more suitable signals for protection algorithms.

This paper proposes a new resonance-type FCL, which is designed specifically for DFIG-based wind turbines. The proposed topology overcomes the well-documented drawbacks associated with conventional resonance-based FCLs while preserving the advantages of this topology. The proposed circuit limits the fault current for the entire fault period independently of the reactor’s charging state and significantly reduces the wind turbine’s torque oscillations during a fault. The proposed FCL is simulated as part of a power system that includes a wind turbine, synchronous generator, and two step-up transformers. The results show that during a three-phase to-ground fault, the proposed FCL significantly improves the system’s stability, and leads to improved fault current, voltage, active power, reactive power, and torque transients.

The rapid proliferation of wind power plants has generated an increasing demand to modify the series-compensated network sections in Sweden. Moreover, the network planning must consider factors such as the expected load increase and series-capacitor refurbishments or renewal. This work discusses the Swedish transmission system operator’s perspective on planning series-compensated network sections containing wind power plants, providing in-depth summaries of essential studies conducted using frequency domain- and electromagnetic transient tools. Such studies include transient overvoltages, temporary overvoltages, and subsynchronous oscillation studies. However, the initial planning that determines the series capacitor’s design parameters is also covered to capture the entire system design chain. The initial planning consists of steady-state calculations, phasor-based transient simulations, and relay protection considerations, such as current inversion. Finally, this work thoroughly discusses how the study results are incorporated into the series capacitor design specification to achieve the best possible system solution.

This paper presents a model for photovoltaic (PV) distributed generators that operates in abnormal electrical voltage scenarios - Voltage Ride Through (VRT), following the Brazilian standard NBR 16149 of 2013. The model includes various modes of operation, such as interruption of energy supply, disconnection, and reconnection of the PV system to the grid. Two types of simulations were performed to test the model’s performance: the first involved using a ramp function to test
the activation of different operating modes, while the second connected the PV model to a distribution feeder and tested its response to a short circuit. The results showed that the model met
the requirements established by the standard and was efficient in representing the behavior of the PV system in real-world scenarios.

Fault signatures of doubly fed induction generator (DFIG) based wind turbine generators (WTGs) are different and more complex than that of synchronous generators (SGs). This paper proposes a new approach to elaborate the formation of the fault signatures of DFIG-based WTGs under asymmetrical faults and various fault ride through control. The proposed internal voltage vectors and equivalent circuit enable reorganizing the control schemes, electric and magnetic circuits of DFIG in terms of transient, positive- and negative-sequence components. This way, the characteristics of DFIG-based WTGs and SGs can be compared in a similar frame through their internal voltage
vectors. The differences and similarities are summarized in support of protection and control designs.

This paper presents a case study of measurements of switching transient overvoltages using a capacitive electric field sensor. The system was developed and installed in a substation after the failure of a surge arrester during the energization of a 420 kV transmission line. First, the closing operation was simulated in an electromagnetic transient simulation program to estimate the switching transient overvoltages for this event. Then, the concept and design of the measurement system are explained. The system calibration performed in the high-voltage laboratory is presented. Afterward, the installation of the measurement system in the substation is discussed, with a special focus on the calibration of the voltage ratio considering the physical configuration where it is installed. Finally, the measurement results are presented and compared with simulations. The results show that the transient overvoltages caused by the energization of the transmission line should not cause the failure of the surge arrester. The measurement system has been demonstrated to be capable of measuring switching transient voltages of a 420 kV transmission line and can be considered a flexible solution for the long-term monitoring of transient overvoltages in substatio

The transmission system expansion plan of Germany foresees several new EHV (Extra High Voltage) transmission lines to transmit bulk power generated by wind farms in the north of Germany to the South. Some of these EHV lines will be so called "mixed lines" consisting of several underground cable and overhead line sections. The high charging current of XLPE cables has to be compensated by shunt reactors. A planned double-circuit 380-kV transmission line with total length of ca. 110 km is ofinterest for the analysis of SPAR (single-phase autoreclosure)operation in this paper, where a cable section along the line has alength of 5.5 km. By means of electromagnetic transientssimulations the maximum secondary arc duration will bedetermined for the mixed line under various operating conditions.

Transient events that result from the incorporation of HVDC into the HVAC power transmission system make fault identification a difficult task. To minimize transient power outages, anomalies must be identified and categorized as quickly as feasible using robust schemes. In the proposed scheme, the multi-classification of AC faults in hybrid transmission lines is performed. A neural network has been employed for the correct recognition and classification of AC faults. The proposed scheme initially uses squaring and lowpass filtering techniques along with, transient energy, negative sequence of voltage, and current as features to pre-process the fault voltage and current signals. The extracted features are then used to form the neural network's input for training and testing. We performed a complete assessment study on the developed ac/dc test system employing MATLAB/Simulink software to ensure the stability and reliability of the presented technique. The technique is verified under noise-added data and compared with other schemes to ensure efficacy. The test result shows that the proposed technique has successfully classified the AC faults with an accuracy of 99.3% in ac/dc transmission lines.

A fault current limiter (FCL) is an economical option to limit the increased fault current levels, which may also improve the rotor angle stability. Previous studies on this topic mainly focused on the FCLs with quick recovery and concluded that the FCL improves the rotor angle stability. However, some
commercially available FCLs have delayed recovery, which may pose different challenges and need to be studied. This paper studies the impact of a superconducting fault current limiter (SCFCL) with delayed recovery on transient rotor angle stability. This paper first develops an analytical understanding of the stability of a system with SCFCL using the equal area criterion. Later, time-domain simulations are employed to demonstrate the impacts of the SCFCL on the rotor angle stability of a single-machine infinite-bus system. The results show that the SCFCL with delayed recovery leads to rotor angle instability in some cases.

Non-intrusive load monitoring is one of the key tools in demand-side management (DSM). Recent advancements in the computational power of processors have accentuated the role of machine learning algorithms e.g., clustering, as a key function in the NILM solutions applied on power grids. In event-based NILM methods, the algorithm detects the transient states (load events) and clusters them based on the similarity of different features of the transient state. In this study, the performances of eight clustering algorithms are comprehensively investigated and the impact of choosing different input signals, e.g., P , Q, and I, on transient states clustering is analyzed. Various input signals from the BLUED dataset are fed to the clustering algorithms. By comparing the evaluation metrics including shape-based and ground-truth-based metrics, it is observed that the OPTICS algorithm fed by dual-stream input streams outperformed the rest of the investigated clustering algorithms and input sets. OPTICS algorithm groups load events based on their density in multi-dimensional space, using a dynamic radius. The OPTICS algorithm, as the best-performing transient state clustering algorithm for the low-frequency NILM purpose, is then tested with the downsampled input data in a wide frequency range, to observe the impact of the data-sampling frequency on the results, which simplifies the use of clustering algorithms in future studies.

Offline electromagnetic transient (EMT) simulation is a very time-consuming activity for large-scale and complex power systems. Hydro-Québec (HQ) is involved in the development of EMT simulation tools, one of which can operate both in real-time (RT) and offline. This software heavily relies on parallel processing to achieve high-level performance. However, the offline mode is currently limited as it targets only single system image computers. As the offline mode uses the Message Passing Interface (MPI) standard to implement its parallel processing, porting the offline mode to PC clusters is the logical step to increase the offline simulation capabilities of HQ EMT simulation software. This paper evaluates the performance of different communication fabrics for the execution of offline EMT simulation operating in parallel with MPI. The performance metrics used for this evaluation are first discussed. The evaluated communication fabrics are then presented and tested with an offline simulation of the HQ power transmission system.

This paper introduces new techniques for efficientuse of electromagnetic transient simulators combined withoptimization algorithms to optimize power systems withconverter-tied renewable resources. This work is motivated byseveral challenges that must be overcome for simulation-basedoptimal design, including high computational burden ofsimulating large switching systems, repetitive nature of thedesign cycle, and large number of variables that need to behandled. Two screening methods are proposed in this paper toidentify the parameters that do not influence the optimal solutionsignificantly and hence can be ignored. Moreover, hybridizationof optimization algorithms and parallel processing techniquesare explored to achieve additional computational benefits. Casestudies of systems with different complexity and number ofvariables are used to demonstrate the effectiveness of theproposed techniques.

This paper presents a new tool for the computation of per-unit-length parameters for transmission line and cable models used for simulating electromagnetic transients (EMT). The proposed methodology is based on the MoM-SO theory and state-of-the-art formulations for the computation of the series impedance and shunt admittance parameters. The new tool has major advantages compared to traditional approaches available in EMT-type software. These advantages include accurate skin and proximity effect modeling, above-ground cable modeling, modeling of stranded wires in cables, representation of multilayer soil, coupled overhead lines and underground cables, etc. This paper presents the new tool together with demonstrations of transient simulations for practical examples.

Modern power grids incorporating inverter-based resources (IBRs) may be liable to persistent oscillations and instability incidents, which jeopardize the reliable operation of the power system. Due to the high number and the complexity of the involved components, an analytical stability assessment of modern power grids is infeasible. A viable approach is the impedancebased stability analysis (ISBA) using impedances extracted from manufacturer-specific electro-magnetic transient (EMT) models via frequency scanning. This paper reviews the EMT-level positive-sequence, dq-frame and αβ-frame frequency scanning techniques and compares their computational efficiencies. The impact of the model reference frame on IBSA precision is also examined on two test cases: I - a full-size converter (FSC)-based wind park (WP) interacts with transmission grid in the supersynchronous frequency range; II - a doubly-fed induction generator (DFIG)-based WP interacts with transmission grid in the sub-synchronous frequency range. Among the compared techniques, ISBA using dq-frame impedance models features the highest accuracy. However, IBSA using positive-sequence or αβ-frame impedance models is sufficiently accurate. The computational speed of the ps-scan is fastest among the presented
techniques. Using αβ-frame models has the slowest computational speed and is, therefore, is not recommended.

Electrical systems have been facing transformations, such as distributed generation insertion, system expansion and regulatory standards in order to increase reliability and quality of
the power supply. Thus, fault location methods must be updated to ensure accuracy in estimating the location of electrical faults. The delay in restoring the system causes damage to utilities and
consumers. Considering this, the current work presents an approach capable of locating faults accurately in radial distribution systems. At first, the distance is estimated using the
travelling wave theory with data from measurements from two terminals. Next, due to the radial characteristic of the system, the proposal aims to mitigate the problem of multiple estimation of
faults. Thus, features are extracted from the voltage and current signals, which are used as inputs of decision trees to identify the fault region. The proposed approach was validated in a medium voltage distribution system, in which the results presented an average error of 0.79% (with a standard deviation of 0.4%) in estimating the fault distances and an average accuracy above 88.7% in identifying the region under fault. Thus, it was demonstrated that the proposed methodology is efficient to locate faults, mitigating the problem of multiple estimation.

This paper presents an Electromagnetic Transient (EMT)-based study about the IEEE 2800-2022 standard benefits for transmission line protection functionalities in the presence of Inverter-Based Resources (IBR). Seven functions are evaluated, namely: 1) Self-polarized distance protection, 2) Memory-polarized distance protection, 3) Memory-Cross-polarized distance protection, 4) Negative sequence-based directional function, 5) Zero sequence-based directional function, 6) Incremental phasor-based phase-selection function, and 7) Current angle-based phase-selection function. To do so, massive EMT simulations are carried out in the PSCAD environment to emulate contingency scenarios in a typical transmission circuit that interconnects an IBR to a synchronous power grid. The evaluated protection functions are implemented and validated with the routines applied in commercial relays, providing a practical perspective on the importance of recent advances in IBR control standards, such as the IEEE 2800-2022. The results demonstrate that the IEEE 2800-2022 significantly improves the transmission line protection performance, being the EMT-based analysis crucial to provide a detailed study on these benefits.

Half-wavelength transmission line protection is a challenge that hinders the implementation of this technology. However, this line is considered an interesting alternative to transmit bulk power blocks over very long distances and to connect wind and photovoltaic generation to an electrical power system. This study introduces a method to protect a half-wavelength transmission line. The proposed complex plane-based protection algorithm uses a differential complex power in the sequence domain to detect faults along the entire line. The embedded spark-gap mitigation device is properly considered because it is a necessary apparatus to remove severe resonant fault conditions. A time-domain analysis shows that the proposed algorithm achieves robust performance for both internal and external faults.

Overvoltage protection of substations connecting hydro power plants (HPP) to the transmission network depends on numerous factors such as: type of HPP connection (air-insulated substation AIS or gas insulated substation GIS), overhead line/cable connection, location, and characteristics of installed equipment, specific operating conditions, and topology. This paper deals with analysis of overvoltage protection in the underground located HPP considering AIS and GIS connection to 220 kV transmission network with specific emphasis on lightning overvoltages. Detailed model for analysis of lightning overvoltages was developed, and simulations are carried out to determine optimum overvoltage protection configuration. Due to specific topology of HPP connection and underground location of step-up transformer, it is necessary to determine the level of transferred overvoltages over transformer to check the necessity for installing additional surge arresters for protection of generator.

Microgrids emerged as an efficient way to integrate distributed energy resources and local loads into power distribution systems, allowing the local system operation in gridconnected and islanded modes. However, the microgrids imply several challenges for the protection systems, such as the changes in fault current path and the decrease of the fault current amplitude during islanded operation. Therefore, conventional overcurrent protection does not guarantee selectivity, coordination, reliability, and adequate trip time in AC microgrids. Under this perspective, voltage-based relays have been widely investigated as a potential protection for AC microgrids. Thus, this paper critically reviews voltage-based protection and proposes improvements to an existing technique, aiming to simplify the settings and guarantee reliability and selectivity among various voltage-based protection devices. The results showed that our modifications improved the selectivity and reliability of the voltage-based protection compared with the original technique and the traditional overcurrent protection devices for different topologies of an AC microgrid.

This paper proposes a one-terminal traveling wave (TW)-based transmission line protection for line commutated converter (LCC) of high-voltage direct current (HVDC) systems. The method requires the first and second wavefronts to reach the local bus and considers the boundary conditions of the system. A detailed mathematical analysis of the sampling frequency effects, as the basis for a number of innovations of practical interest, is presented here. Firstly, a definition of a minimum sampling frequency is formulated. This is crucial when dealing with the high sampling frequencies traditionally needed by TW-based methods. Secondly, mathematical expressions of protected, unprotected, and uncertainty zones on the transmission line are defined. Thanks to these calculations, the method is also capable of distinguishing faults at the line terminals from faults on the protected transmission line. Thirdly, the non-requirement for the TW propagation speed estimation is proven. Some TW-based protection elements require knowledge of the TW propagation speed, which is a source of errors. The proposed function presented good dependability and was able to operate below 15 ms for a transmission line of 2900 km in length.

Digital fault recorders (DFRs) and some conventional relays operate typically with sampling frequencies up to a few kHz. Conversely, traveling wave (TW)-based methods are usually designed to operate at sampling frequencies in the order of MHz. However, this paper demonstrates that two-terminal TW-based protection that considers the effects of the sampling frequency and TW propagation velocity uncertainties can protect transmission lines using sampling frequencies of a few kHz instead of MHz. This demonstration considers a performance validation based on challenging real-world faults recorded in transmission lines equipped with DFRs operating with a sampling frequency of 15,360 Hz. The low-sampling frequency two-terminal TW protection was
implemented in hardware as a protective relay to evaluate actual data in real-time analysis, representing a significant step towards the practical application of the TW concept readily available in real protection devices with a low-sampling frequency.

High local electric field intensity in transformer windings originating from transient signals is one of the reasons for transformer failures. Due to the integration of renewable energy sources into the power grids and the increased number of transients, the likelihood of transformer catastrophic failure increases accordingly. Therefore, to ensure the reliable performance of transformers and associated power networks studying their behavior during these events is required. Accordingly, there is a need for accurate modeling of transformer windings capable of simulating electromagnetic transients. Using these models, it is possible to identify frequencies that can be dangerous to the transformer windings and to study different protection schemes. This paper aims to find an accurate analytical model of transformer winding validated by experimental measurements and to study the performance of the R-L protection device during the transient phenomena. The protection device is designed based on the winding model to introduce an impedance comparable to that of the transformer winding at critical frequencies where voltage amplification in the winding is significant. This approach ensures enhanced protection against potential transformer damage to the transformer. By using this protection scheme, the high inter-turn voltage originating from transient signals may be mitigated. At the same time, it does not affect the grid's performance during normal conditions.

Transient Recovery Voltage (TRV) analysis is a type of electromagnetic study that proves if the circuit breaker (CB) can withstand switching transients. Switching transients’ incidence and severeness is determined by surrounding electrical system, hence special locations of CB installation require more attention. This paper shows TRV calculations on a CB that is placed at HV terminals of a step-up transformer in a hydro power plant. Since there is no classical generator CB placed on the MV terminals of the step-up transformer, the breaker placed on the HV terminals is used for synchronizations to the grid. The requirements for HV CB placed in such locations are given in IEC 62271-100, where it is stated that proximity of a generator is regarded as a special case. For TRV analysis, the CB and surrounding network were modeled in EMT-like software. TRVs are calculated for terminal faults, short-line faults, capacitive current and out-of-phase switching. Power-frequency voltage stress and arc influence on the short-circuit DC component are discussed. Due to the exceeded TRV envelopes and lack of their definition for out-of-phase switching, a CB of a higher voltage level is recommended for installation in the case study considered in this paper.

This paper presents a summary of significant contributions on research on power system transients performed by Prof. Akihiro Ametani at Polytechnique Montréal, Canada. The contents of the paper are based on the results published by Prof. Ametani, his former colleagues and students at Polytechnique Montréal. The paper involves three parts: theoretical innovation and implementation, field measurements and numerical electromagnetic analysis. The major contributions are related to line/cable modeling. The important impact of each part is also highlighted in this paper.

Switching of (small) inductive currents by means of vacuum circuit breakers may lead to multiple re-ignitions. This is the result of the ability of the interrupter’s quenching capability, which generates steep overvoltages that can stress the equipment insulation. Should no mitigation measures be applied, the equipment is exposed to a high risk of failure. In this paper, the findings and conclusions of a such a failure investigation and mitigation analysis are presented, referring to multiple cable connector failures in 33 kV shunt reactor installations in the Netherlands.

Meshed bipolar High Voltage Direct Current grids are considered as one of the preferable solutions for integration of renewable energy sources and increasing the security of power systems on a continental scale. In this context, several fault current studies are proposed in the literature, considering different grounding methods for modular multilevel converter neutral points. But these studies often focus on fault current paths to the fault location, and none of them analyzes the return
paths of fault current from the fault location. This article deals with fault currents return paths in case of pole-to-ground fault in a grounding configuration using surge arresters in all stations
except one, which is solidly grounded. The influence of this solidly grounded point location on the return paths of fault currents is evaluated. With these results, a modelling simplification is considered for HVDC protection studies. Specifically, the discussion investigates whether all MMC neutral points can be solidly grounded.

Grid-forming converters operate as voltage sources behind impedance. This property makes them robust against Short-Circuit Ratio (SCR) variation, but vulnerable against large grid disturbances. As a precaution, grid-forming converters have to embed adequate control algorithms to ensure a stable system operation under various grid conditions, to deal with excessive overloadings mainly caused by faults, and to guarantee a stable re-synchronization after fault clearance. These expectations have been met in previous works considering balanced conditions. Nevertheless, the extension of the grid-forming control to deal with unbalanced grid conditions considering current limitation and angular stability is a point rarely discussed in the literature. To fill this research gap, this paper proposes an Extended Power Synchronization Method (EPSM) that allows the system to operate under balanced and unbalanced grid conditions while meeting the Fault Ride-Through requirements (FRT). The proposed method is a direct voltage control-based, which embeds a threshold current control loop, which is enabled only when a fault is detected. Additionally, the control is equipped with an algorithm that modifies the active power control during faults to aid the power converter to be remain synchronized after fault clearance. The effectiveness of the proposed control has been demonstrated through time-domain simulations.

The growth and integration of renewable energy and control systems in the utility grid represents a challenge for the electric power industry. Power quality monitoring plays a critical role in modern electrical systems for both standards compliance and system security reasons. This paper presents a novel technique for calculating subharmonics, harmonics, interharmonics, supraharmonics, and DC offset in electrical systems. This extended spectral fitting (ESF) approach is a combination of the numerical Laplace transform (NLT) and a modified vector fitting (VF) which we have denominated extended vector fitting (EVF). In this novel approach, it is assumed that frequencies of the harmonics and supraharmonics are known poles and that frequencies of the subharmonics and interharmonics are unknown poles in the frequency domain (FD), resulting in a rational approximation that considers known poles and unknown poles. The advantages of the proposed methodology are demonstrated (1) for synthetic test signals and (2) in an AC-DC-AC converter simulation. Results show that the ESF approach can fully decompose a signal into the aforementioned components with a high degree of accuracy.

This paper presents a solution to the observed ferroresonance (FRR) phenomenon for both energization switching and load shedding conditions in an unconventional rural electrification system. The energy is extracted from the electric field surrounding an extrahigh voltage transmission
line. Ferroresonance occurs in the power transformers of the distribution substation, and the existing solution cannot be directly applied. The mitigation method consists of the insertion of a shunt resistor when the FRR starts. The robustness of the method is shown in a time-domain simulation implemented in PSCAD/EMTDC.

In the design phase of connecting wind power plants (WPPs) to the transmission network, harmonics amplification due to different system parameters (e.g. the long HVAC cable connection) need tobe determined. Not all parameters tocalculate the harmonic voltage distortion gain are known indetail. The aim of this paper is to analyze the impact of some uncertainties on the harmonic voltage distortion gain by the use of a real case study. Impacts of several aspects, such asnetwork condition (e.g. transmission network contingencies and WPP contingencies), modeling approach (cable modeling) and parameter uncertainties (e.g. cable capacitance), are investigated via simulations. It can be concluded that the transmission network contingencies as well as the Windfarm contingencies have the most significant effect on harmonic amplification. The effect of the export cable modeling is also noticeable while the cable capacitance uncertainties have a less critical effect onharmonic amplification.

Ferroresonance in single-phase,line-to-line con-nectedtransformers in an ungrounded distribution system with delta-connected capacitors is possible but has not been reported in recent literature. In this paper, a high voltage event that actually occurred in an ungrounded distribution network with multiple distribution transformers has been simulated for lessons learned. The hypothesis was that ferroresonance was the cause of the overvoltage event in the network after a single-phase event led to sustained voltages of 1.45 p.u. Simulations were performed and ferroresonance was found to be the possible cause for the overvoltages. One of the prevention solutions found to avoid the overvoltages was to balance the loads on the three phases. The increased deployment of CVR/VVO strategies leads to circuit configurations similar to that studied in this paper and could lead to an increased likelihood of ferroresonance, if it is not fully understood and addressed. The impact of additional single-phasesolar inverters on the low voltage side of the transformers was also studied. The results obtained show that the effective loading of the transformers, which is the difference in the actual load connected and the output from the DER, proved to be the deciding factor for initiation of ferroresonance in such networks.

The use of solar photovoltaic (PV) in distribution networks has increased considerably in recent years. Although they have many advantages, PV systems can also result in complex power quality issues in distribution networks, like harmonic distortion, that can interfere with loads and controllers. Harmonic emission from different inverters and their aggregation is thus of interest. In this work, harmonic emission of two PV string inverters and two substations operating in a large PV power plant is presented. The distribution of the full range of current harmonics is analyzed, as well as the correlation between the values of each harmonic and the power level produced, by the inverter or substation, and the correlation between voltage and current harmonics. Significant differences are observed in the harmonic emission of the inverters, despite being under the same operating loading and grid conditions. The results obtained for the substations are in line to those for the inverters. This study was performed in a grid connected 12 MW PV power plant operating in Europe.

To achieve carbon neutrality by 2050, electric vehicles (EVs) are promoted and EV fast chargers are expected to become part of the public infrastructure. To feed power to EV fast chargers installed in highway rest areas, the authors have proposed a 33-kV dedicated cable supply system installed along the highway. Due to the large capacitance of a cable system, harmonics may be of concerns for the operation of the proposed system. Therefore, this paper presents a study of harmonics occurring in the 33-kV dedicated cable supply system to feed EV fast chargers. First, the cause of the harmonics is identified by deriving resonance frequencies of the equivalent circuit of the cable supply system. Then, the harmonic resonance phenomenon is verified by electromagnetic transient (EMT) simulations. The results indicate conditions with which harmonic resonance may occur in the cable supply system. To perform the simulations, the EMT simulation models of distribution substations and EV fast chargers are picked up from the generic EMT simulation models prepared in XTAP (eXpandable Transient Analysis Program) for distribution and microgrid simulations. It should be noted that the harmonics simulations mentioned above can readily be performed by picking up necessary models from the model library.

This article presents a non-conventional voltage-transforming system that extracts energy from transmission line (TL) electrical field. The generation system consists in a 20 km collector line built within the right-of-way of a 230 kV transmission line to attend a 100 kW load. A non-conventional substation is conceived to provide adequate voltage regulation. This voltage-transforming system can be replicated at both sides of the TL to feed small remote loads or become an additional supply source for existing rural systems. No intervention on the existent line is necessary. Important results regarding transient, quality and reliability indexes cost evaluation of the system are provided.

This paper proposes an improved method to enhance the dc response of a frequency-dependent transmission line model used in EMT studies. A modification to the rational function approximation of propagation and characteristic admittance matrices of a transmission line is introduced to enforce exact dc values at 0 Hz. Furthermore, weighting factors are applied to improve accuracy at low frequencies. Finally, the order of the propagation function is reduced to decrease the computational effort. The validity of the proposed approach is demonstrated using examples involving underground cables and overhead lines. First, the effect of dc correction is demonstrated by comparing transmission line frequency domain characteristics. In addition, time domain simulations via open and short circuit conditions show a more accurate simulation of HVDC transmission lines with the proposed method.

This paper proposes an inverter control strategy that combines virtual synchronous generator control with harmonic detection based on Fourier linear combiners with adaptive gain. In the proposed strategy, the virtual synchronous generator control calculates the current in the fundamental frequency component, responsible for the control inertial characteristic, and harmonic voltage detector based on Fourier linear combiners selectively detects the harmonic voltages to be damped. The 5th harmonic order adaptive gain is calculated from voltage and current measurements on a bus of interest in the system. Real-time simulation results were developed in a hardware-in-the-loop test-bench to show that the proposed control can simultaneously mitigate the grid voltage and current harmonics and reduce the peaks of frequency oscillations after transients.

This paper presents a co-simulation tool to link multiple instances of an electromagnetic transient (EMT) simulation tool for parallel and fast computations. The tool exploits the propagation delays of transmission lines and cables to create network decoupling into several smaller sub-networks. These sub-networks are solved in parallel without approximations. A multi-rate option is also incorporated, in which the sub-networks can use different numerical integration time-steps. The Functional Mock-up Interface (FMI) is used for creating the co-simulation interface between multiple instances according to a master-slave communication scheme and the data sharing method is implemented using low-level synchronization primitives called semaphores. The interfaces between each subnetwork are automatically initialized for time-domain simulations using load-flow results.

The simulation of electromagnetic transients may suffer from inaccuracies due to a phenomenon known as frequency warping (FW). This paper presents an analysis of the effects of FW on the accuracy of digital simulations, demonstrating that the use of the trapezoidal integration rule (TR), commonly employed in many electromagnetic transients simulators, is the root cause of such inaccuracies. Although FW is considered a major problem in digital signal processing, it is often overlooked when simulating electrical transients. The analysis is carried out in a fourth-order RLC circuit, from which the analytic solution is derived. The circuit is solved using the combined state-space nodal method, considering the TR or recursive convolutions as solution methods for the state-space representation. It was observed that the FW caused a change in the natural oscillation frequency of the system, causing a pulsating behavior of absolute error. The accumulation of errors over time can result in deteriorated solutions when either the time steps are not sufficiently small or the simulation runs for a long enough duration. This paper emphasizes the significance of accounting for the FW phenomenon in digital simulations that rely on integration methods, such as the TR.

Passive component models are necessary to ensure numerical stability in the simulation of electromagnetic transients in power systems. However, it is challenging to represent transmission lines and cables with frequency-dependent wideband models that are accurate, efficient, and passive. This paper proposes a new method for the passivity enforcement of wideband line and cable models. The wideband models rely on pole-residue identification of characteristic admittance and propagation function in rational forms. In case the resulting models are not passive, the proposed method simultaneously applies perturbation to the residue matrices of characteristic admittance and propagation function. The set of equations related to passivity enforcement through the residues of propagation function in phase domain is complex and presented for the first time in this paper. The proposed approach minimizes the overall perturbation for maintaining passivity as opposed to the existing simplified approaches that rely on the perturbation of the residues of either characteristic admittance or diagonal elements of propagation function. The performance of the method is validated with application cases, and it is shown that it outperforms the existing methods that seek simplification in problem formulation.

This paper presents a new approach for protecting microgrids based on multi-agent systems and using the angular variation of currents. The multi-agent system was structured using a congregation organization with three agents: section agent, circuit breaker agent, and switch agent. In this proposal, section agents are located at the microgrid lines, obtaining the difference in current angles between the buses. Then, if a threshold is reached, it sends a trip signal to the circuit breaker agent. This agent is responsible for receiving the trip signals and determining the correct line to be isolated. Finally, the switch agent is responsible for monitoring the microgrid operating scenario and updating the adequate thresholds of the agents. The proposed method was assessed firstly using simulations in PSCAD. Next, the multi-agent strategy was embedded into a low-cost microcontroller unit and tested through hardware-in-the-loop (HIL) experiments using the Real-Time Digital Simulator (RTDS). The experimental and simulation results indicated the feasibility of the proposed method.

New grid elements such as Voltage Source Converters (VSC) and cables are being increasingly used in today’s power grid. These new grid elements behave differently compared to synchronous machines and overhead lines during transients and faults, impacting the present system’s legacy protection. An increased share of underground cables affects the system’s resonance frequencies whereas VSCs introduce actively controlled current phase shifts during short-circuit faults. Existing research mainly focuses on VSC impacts on phasor-based legacy protection. This paper studies the impact of these new grid elements on incremental quantity-based directional protection, which operates in the time domain, using EMT-type models and hardware experiments. First, cables introduce low frequency oscillations for remote, single phase faults and additionally under weak grid conditions. At low frequencies, these oscillations are not filtered out by the protection, which may result in a decrease of dependability margin (23% of the tested cases) and potential security issues. For the majority of studied cases, the relays worked correctly. Second, fast reactive current injection by a VSC can cause malfunction of incremental quantity protection. Malfunction occurred in 1 case and a decrease of dependability in 10% of the tested cases. This is especially problematic for grids with relatively low synchronous infeed.

Transient-based earth fault protection is widelyused in all types of resonant grounded networks, and thoughthe operating principles of the commonly available relays areusually derived from radial networks, manufacturers claimapplicability in meshed networks as well. This paper utilizesa laboratory setup to study the directional indication of fourtransient earth fault relays in non-radial resonant groundednetworks. Two of the relays considered are widely used analogsingle-purpose transient earth fault relays, whereas the other tworelays represent two transient-based earth fault functions foundin modern protective devices. The paper verifies the locationof crossover points according to the presented theory, i.e. faultlocations for which relays transition between seeing faults asforward and reverse faults, and demonstrates the viability ofthe proposed theoretical analysis of crossover points. However,presented analytical formulae only describe the two analog relaysaccurately, whereas the two modern relays have a more complexoperating principle which requires further analysis to quantifyproperly. Finally, it is shown that relay misoperation which isnot easily fixed by communication between relays can occur, andit is suggested that network operators conduct detailed relaycoordination when applying transient earth fault relays insteadof relying on standardized settings.

Due tothe unavailabilityof asuitablerelay for microgrid protection,various utilities are fitting available IEDs for the protection of microgrids. At present,microgrid protection is achievedusing a combination of conventional numerical relays. These numerical relays are not suitable for all kinds of microgrid architecturesand do not provide complete protection with inverter-based generators. Since these relays were designed considering the fault characteristics of synchronous generators, they fail to respond to the fault characterized by inverter-based generators. This paper proposes a new protection techniquethat is independent of the type of generating sources, control philosophyof inverters as well asmicrogrid architecture. Simulations are performed using PSCAD/EMTDCand performance of the protection scheme is also evaluated in real-time usingRTDS. Pertinentresults are presentedwhich demonstratethe effectiveness of the proposed scheme.

Detecting and recognizing the secondary arc extinction is considered as a backbone of the single pole auto reclosing schemes. This paper proposes a multi-channel convolutional network to detect the secondary arc extinction during in a long AC power transmission line arc fault. In contrast to the conventional methods, the proposed Machin learning-based method can automatically learn the features from the raw data given as input. Multivariate time series data of phase voltage, current and neutral reactor signals were used as the input to the proposed model. The features are extracted in the convolution layer instead of using hand-crafted feature extraction like most of the existing research. The softmax classifier is used to detect the fault and secondary arc extinction. Matlab Simulink is used to simulate the test system and collect the dataset to evaluate the proposed neural network model. To verify the generalizability of the proposed architecture datasets were collected at different locations and different phase lines. The proposed algorithm was able to detect the secondary arc extinction with 98.26% accuracy and able to give signal for auto-recloser logic with the maximum window length of three cycle. The result shows that the proposed neural network architecture is accurate and robust to detect the secondary arc extinction further can be used as a signal for a single pole adaptive auto recloser scheme.

This article investigates the use of the distance function to protect shunt reactors. For this purpose, mho phase comparator is assessed. To carry out a comparative evaluation, the distance function performance was further compared with the differential function performance. Moreover, the Alternative Transit Program (ATP) was applied to model an electrical system, in which the reactor is subjected to different faults, including phase-to-phase, phase-to-ground, turn-to-ground and turn-to-turn faults. The performance of the evaluated distance function was also investigated against the number of turns involved and the leakage factor. From the results obtained, it is suggested the joint use of the distance function with the differential protection, because if the differential function does
not operate, distance function would guarantee the operation for internal faults, including turn-to-ground and turn-to-turn faults, increasing reliability of protection scheme for shunt reactors.
Also, the present study may serve as a guide for further studies, for example, that evaluate the use of distance function to protect iron-core reactors.

This work provides a simplified transient model for low-voltage DIN rail surge protective devices (SPDs), accounting for their resistive, inductive, and capacitive behavior. The time-domain modeling approach is based on impulse current and sinusoidal voltage experiments. The lumped-circuit model is implemented in the ATP-EMTP environment and yields results in satisfactory agreement with the experimentally derived residual voltage and energy absorption of commercially available DIN rail SPDs for single- and three-phase installations. The proposed model can be used for evaluating the protection level and maximum residual voltage of SPDs under standard and non-standard surge currents and can be an effective tool employed in insulation coordination studies of power systems.

This paper presents a systematic investigation of equivalent homogeneous earth method (EHEM) for calculation of earth-return impedance of overhead conductors above a multi-layer earth. The recently developed EHEM is based on the concept of equivalent propagation constant of earth. The characteristics of equivalent propagation constant of earth and integrand convergences of EHEM are further studied. The parametric studies of accuracy on earth-return impedance between exact formula (EF) and EHEM are also presented in this paper.

Power systems are exposed to different types of electromagnetic transients, which involve a large spectrum of signals whose duration can range from several nanoseconds to several milliseconds, and whose peak values can also cover a wide range of values. Therefore, measuring electromagnetic transients in power systems is a challenging task. Fast front transients caused by lightning events are especially dangerous, and improved knowledge about them is essential for better protection design. The development of measuring systems for such phenomenon is important. This paper is dedicated to the development of a measuring system for lightning and line surge arrester currents. Modern electronic tools and equipment, as well as cutting-edge communication and information technologies, constitute the foundation of the proposed system. This includes the most recent models of acquisition units and GPS devices that are now available on the market, as well as communication networks including 4G, 5G, and WiFi. Software and hardware components of the system are described. The paper presents laboratory tests conceived to prove that the system operates correctly and provides accurate results. The measurements are compared to EMTP and MATLAB simulations. Both are in agreement.

A methodology is proposed for estimating the shielding failure flashover rate (SFFOR) of single-circuit overhead lines with horizontal phase configuration. An application to a 66 kV overhead line is presented. A stochastic lightning attachment model is employed, based on the concept of fractal structures, to compute the probability of shielding failure to the line. Results of stochastic modeling are combined with those of an ATP-EMTP model for estimating the critical lightning currents causing flashover of the line insulation. Shielding failure results of the proposed methodology are compared and discussed with results obtained employing the methodology of the IEEE Std 1243. Innovation of this work lies in estimating the SFFOR of overhead lines by considering the stochastic nature of lightning attachment, physical criteria associated with leader discharges’ inception and propagation, as well as electromagnetic transient simulations to predict lightning-related flashover to overhead lines accurately

This paper assesses the influence of corona effect on the overvoltages developed across the insulator strings of overhead transmission lines due to lightning. The influence of corona is investigated considering lightning strikes to the tower top and shielding wires at midspan. A large range of soil resistivity and lightning currents peaks are evaluated in the analysis, and the
stress across the insulator strings is evaluated applying the integration method. Simulations are carried out in the Alternative Transient Program (ATP/EMTP), wherein the corona effect is
represented through the accurate Suliciu corona model, which was implemented using the MODELS interface and combined with J. Marti line model. Furthermore, it was also represented the wideband behavior of tower grounding system. Results showed that corona effect has a minor influence in the overvoltages across the insulator string for strikes to the tower top. However, it strongly influences the overvoltages across line insulators ensuing from a lightning strike to the shielding wire at the midspan, leading to a decrease in the peak value of the lightning current that causes line flashover.

In mixed/Syphon connections, the cable system as a whole can be subjected to fast-front overvoltages due to lightning strikes, either directly on the phase conductors or on the shield
wires of the overhead line(s) connected to the cable. In this paper, a methodology is presented that facilitates the calculation of the failure rate performance of a cable’s sheath bonding system due to
lightning strikes on the connected overhead line(s).

The growing penetration of converter-interfaced renewable energy sources (CI-RES) has revealed several challenges related to the stability of the electrical grids. To mitigate these issues, there is an ongoing research regarding the concept of virtual synchronous generators, where new control schemes are employed to enable CI-RES with integrated fast-acting energy storage system (ESS) to provide ancillary services to the grid, e.g., inertial response (IR). Although several solutions have been proposed in the literature, the proper integration and energy management of the ESS towards IR provision remains an open research topic. In this paper, an holistic control approach is presented regarding IR provision by a system comprising of a CI-RES and an ultracapacitor (UC). The proposed approach is supplemented by an efficient energy management system allowing the UC to release/absorb energy during IR provision while always ensuring the operation of the UC voltage within its technical limits. The robustness and the performance of the proposed method are experimentally evaluated in a lab setup, where all the components of the proposed system, i.e., CI-RES and UC have been analytically implemented.

The advent of renewable energy sources (RESs) has posed several technical challenges related to the operation of modern power systems. These can be classified into two main categories: a) problems at the power system level, and b) local problems at the distribution network (DN). To solve these issues, there is a strong need for the development of innovative control schemes that can be employed by converter-based network assets, e.g., battery energy storage (BES) systems and distributed RES. In this context, a unified control system (UCS) for the provision of ancillary services (ASs) by distributed RES-BES systems within a multi-services perspective is introduced in this paper. The proposed UCS comprises different algorithms to provide ASs related to voltage regulation, voltage unbalance mitigation and frequency support. The UCS is implemented in 3-phase, 4-leg converters (3Ph4LCs) to ensure the provision of ASs in unbalanced DNs. In addition, at the dc side of the 3Ph4LC a series dc-dc converter for BES support allows the implementation of the proposed UCS in weak DNs. The transient operational performance of the proposed UCS is evaluated by conducting time-domain simulations.

Grid forming converters are expected to become the main voltage source for electrical power systems in future grids, as many of the conventional power plants based on synchronous generators are being replaced by renewable generating plants interfacing with grids via converters. This paper evaluates network energisation via grid forming converter based on multi-loop droop control, focusing on transformer inrush and switching overvoltages. The evaluation utilizes simulation conducted in PSCAD-EMTDC to investigate the scenarios of using a 50 MVA battery energy storage plant with grid forming converters to sequentially energise part of a 132 kV network. The results are analysed and compared with those obtained under the scenario of energising the same network via a 50 MVA synchronous generator. The studies serve to identify the potential differences between grid forming converters and synchronous generators in terms of their impacts on transformer inrush transients and cable switching overvoltages. In addition, the influences of grid forming converter aggregation, controller parameter settings and current limiter settings on the inrush and switching transients are investigated.

This paper introduces a grid forming (GFM) control method – detailed synchronous machine emulation virtual synchronous generator (VSG). The proposed method makes a voltage source converter exactly emulate a synchronous generator (SG), using a current source interface. The precise emulation of an SG gives tighter control over overcurrent and improved transient damping. Electromagnetic Transients (EMT) simulation is used to demonstrate the operation, and small signal model is used to assess the stability performance. Small signal analysis shows that the resulting VSG operates stably, and oscillatory modes can be damped by appropriate optimization of the virtual damping windings resistances.

The growing use of renewable energy sources such as wind and solar in distribution networks (DNs) poses a challenge for DN protection. Inverter-based resources (IBRs) have fault responses that differ from conventional generators, which can have a significant impact on how the DN is protected and lead to misoperations, such as blinding. Use of simplified inverter models may result in incorrect relay settings and relay misoperations. This paper leverages a comprehensive grid-following inverter with dynamic reactive current (DRC) limiting model. The inverter with DRC model is combined with distribution system equations, to form a nonlinear differential and algebraic equations (NDAE) model, in which the fault response is verified. The grid-following inverter with DRC limiting is then implemented in a distribution system with protection elements and compared with a simplified fault response model based on frozen control. The system is tested under varying irradiance conditions, as well as varying dynamic factor K of the DRC limiting model. The effect of the DRC current limiting model on protection blinding is investigated as well. The case study reveals that precise modeling of the PV inverter including the DRC limiter is indeed required to properly identify and predict blinding scenarios in the DN.

In this paper, a rigorous and independent validation of two different approaches for calculating the ground-return impedance and admittance of multiconductor underground cable systems using the transmission line theory is carried out. Furthermore, analyses are performed to evaluate the accuracy of a closed-form approximation for the calculation of the groundreturn admittance of underground cable systems. The validations are based on the full-wave finite-difference time-domain (FDTD) method and consider the calculation of transients on flat and trefoil underground cable arrangements for different excitation types. Short cable lengths of 50 m and 100 m and soil resistivities of up to 1000 Ωm are considered. The results demonstrate the validity of the transmission line theory for the calculation of fast transients (with risetimes as low as 0.2 μs) on underground cables provided the ground-return parameters are rigorously determined, with the advantage of presenting much greater efficiency and easiness to implement in electromagnetic transient simulators compared to the full-wave FDTD method. Lastly, it is shown that the ground-return admittance approximation, despite its simplicity, leads to results comparable to those obtained through more complete formulations for the calculation of transients in underground cables, but more efficiently and without significant loss of accuracy.

Geomagnetic disturbances (GMD) affect power systems by causing transformer saturation. The primary impacts of transformer saturation are increased harmonic current injections and var losses, which may lead to damage of high-voltage transformers and/or voltage collapse. The investigation of GMD risks and mitigation strategies requires accurate modeling of a GMD. This paper firstly presents the requirements in terms of modeling components to correctly simulate GMD in EMTP, and secondly the impacts of GMD on Hydro-Québec transmission system, which is fully represented in EMTP, a GMD-EMT simulation world premiere.

Cables used in offshore windfarms are usually three-core (3C) with metallic armour. The series impedance at power frequency is necessary to estimate cable steady-state and fault condition performances, e.g., by calculating sequence impedances. The impedance at higher frequencies is also needed for transient analysis. Three-dimensional (3D) effects, being inevitably present in 3C cables, such as twisting effects, may be treated in a two-and-a-half-dimensional (2.5D) fashion. Although fast, this approach cannot account for the full 3D effects since it ignores solenoid effects. Thus, the calculated impedance may be inaccurate, potentially compromising the cable performance. 3D models based on finite element method are developed in this paper to consider the full 3D effects. The impedance is derived at power and higher frequencies. The proposed 3D method is evaluated against 2.5D methods. Solenoid effects appear to have a remarkable influence on impedance. Design aspects, such as the magnetic permeability and the pitch angle of the armour, are also examined. Finally, the effect on modal propagation characteristics is highlighted and the transient response is simulated.

This paper performs an investigation on electromagnetic transients for a practical 500 kV cable system. The system consists of 500 kV overhead lines, submarine and underground cables. In order to study the insulation coordination of the cable system, the transient simulations are performed using EMTP. The modal propagation constants of submarine cable are also investigated. Moreover, the cable series and shunt parameters are calculated using the newly developed Line/Cable Data Module in EMTP. The voltage and current characteristics of the cable system in steady-state, and for switching, fault and lightning transients, are studied. The transient overvoltage levels are also compared with requirements of insulation coordination in local standards. The work shown in this paper could provide a reference for the insulation design of 500 kV cable system.

Buried pipeline systems benefit from mitigation wires (earthing systems) in order to be protected against electric shock hazards. Moreover, cathodic protection (CP) systems are incorporated into pipeline systems to provide protection against corrosion by injecting an impressed DC current. DC decoupling devices are normally installed between the pipeline’s metallic wall and the earthing wire, functioning as a filter that blocks the DC component (of the CP system) while allowing the hazardous AC interference current to be dissipated into the earth. However, the internal capacitance of the DC decoupling devices introduces an error in the routine survey measurement of the CP effectiveness, as frequently reported by pipelines’ system operators. In this paper, the factors influencing this measurement error are investigated by modeling the electrical behavior of the CP-pipeline system. This investigation concluded that the capacitive discharge time constant and by extension, the measurement error highly depends on the pipeline resistance to remote earth (coating resistance), as well as on the number and the capacitance C of the capacitive DC decoupling devices. To this extent, methods for minimizing Eoff measurement error are proposed.

We present a positive and zero sequence line parameter estimation method, that is robust to systematic errors in the instrument transformers, especially when they are within the specified tolerance as per standards. Using Monte Carlo simulations, it is shown that the proposed approach is robust and accurate for all operating conditions, specifically for short length and lightly loaded transmission lines. We also validate the proposed approach on 400 kV and 765 kV transmission lines using actual field phasor measurement unit (PMU) data. Further, estimation of zero sequence line parameter values is somewhat tricky because not enough unbalance exists during the normal operation of the power grid. Therefore, we quantify the minimum percentage unbalance needed in currents to determine zero sequence line parameter values within 1% tolerance.We also present the line length and line loading effects in estimating zero sequence line parameter values using simulations. Simulation and field PMU data results on 765 kV and 400 kV lines of different lengths and loading levels show that the proposed method estimates accurate positive and zero sequence line parameter values.

Numerous factors, including sudden load reductions, switching transient loads, lightning strikes, and malfunctions of control devices, can result in overvoltage. Overvoltage can harm associated power supply components and result in insulation failure, electronic component damage, flashovers, etc. A machine learning technique called a "neural network" estimates computation results that depend on a lot of inputs. For a variety of reasons, neural networks have recently been used to manage and optimize the power system. This paper presents an artificial neural network (ANN)-based approach to determining overvoltages in power systems. To simulate overvoltages, many simulations were performed in Electromagnetic Transient Program (EMTP). Variations of parameters ofinterest that have an influence on overvoltages were made using JavaScript that was connected to EMTP models. The extraction of characteristic parameters from overvoltage waveshape is a demanding task, and it was conducted in MATLAB, as was a overvoltage classification methodology based on neural networks. Results were presented and discussed.

As more power electronics are introduced into the power system, its stability is impacted, e.g., through undesired interactions. One such interaction is called sub-synchronous control interaction (SSCI), an example being an interaction between a DFIG wind farm and a series compensated line. In this paper, two methods are used to assess the risk of SSCI: the reactance crossover method, and the Nyquist criterion. The analysis is performed on three case studies: one system based on the IEEE First Benchmark System, and the other system is modelled as a typical Swedish transmission system with two different degrees of series compensation. Both methods predict SSCI in all three case studies, with the Nyquist criterion being able to predict the oscillation frequency more accurately. To mitigate the sub-synchronous oscillations, a PV farm is implemented and placed in parallel to the wind farm. The performed simulations show that it is able to damp the oscillations successfully in all case studies.

This paper presents an interpolation-based solutionthat allows the application of traveling wave (TW)-basedalgorithms even using sampling rates lower than those typicallyconsidered as a requirement for classical approaches. Twophasor (PH)-based and one TW-based fault location methodsare compared with the proposed technique and applied throughAlternative Transients Program (ATP) fault simulations ina 500 kV/60 Hz Brazilian double circuit series-compensatedtransmission lines with high-voltage direct current lines (HVDCs)and static var compensators (SVCs) in the vicinity. The resultsshow that the proposed interpolation-based technique is reliableand suitable for TW-based fault location using data records withsampling rates lower than those used in commercially availableequipment. Moreover, its accuracy is comparable to classicalTW-based fault location solutions, revealing its usefulness forpractical application when only traditional digital fault recorders(DFRs) are available.

This paper presents an interpolation with Backward Euler (BE) method that enhances the switching simulations accuracy in an electromagnetic transient (EMT) simulation with a fixed time-step. Because of the switching operations on discrete instants, the simulations can show artificial voltage spikes and numerical oscillations (chatter), compromising the accuracy and producing misleading results. We thus present a method that eliminates the spurious switching losses and improves the accuracy by combining interpolation and extrapolation with a half-time-step BE solution over existing interpolation-based approaches to resolve the issues above. In addition, this improved method requires the same calculation steps as the industry-accepted instantaneous interpolation. Analytical discussion reinforced by the simulation studies for a simple and complex power electronic circuits demonstrates the accuracy and efficacy of the proposed interpolation with BE method.

The impedance-based stability analysis (IBSA) is an effective method for identifying instability issues caused by gridconnected inverter-based resources (IBRs). The electromagnetic transient (EMT)-level positive sequence and dq-frame frequency scanning methods (p-scan and dq-scan, respectively) are widely used to measure the impedance models of IBRs. The p-scan is easier to implement but has inaccuracy issue because it ignores the mirror frequency effect (MFE). The dq-scan is accurate but cannot differentiate the resonance and mirror frequencies. This paper proposes a new EMT-level coupled sequence domain (CSD) multi-input multi-output (MIMO) frequency scanning method (CSD-scan) in stationary frame. The CSD-scan usage in IBSA 1) accounts for the MFE; 2) differentiates the resonance and mirror frequencies; 3) requires no coordinates transformation for perturbation and measurement signals; 4) significantly reduces computational burden compared to the existing coupled sequence scanning method. This paper also demonstrates the impedance transformation relation between dq-domain and stationary frame CSD. The accuracy and time efficiency of the proposed CSD-scan is validated in both IBSA and EMT simulations on a weak grid test case incorporating full-size converter (FSC)-based wind park (WP) by comparing with p- and dq-scans.

This paper presents an accuracy analysis from the application of techniques for the extraction of characteristic data from current and voltage signals in transmission line fault location based on traveling wave theory. The techniques used were the empirical mode decomposition and the variational mode decomposition associated with Teager energy operator, which helps to identify the instantaneous energy of the first intrinsic mode function. The simulation of the power system was carried out using the MATLAB/Simulink® software, for a test system consisting of a 200 km long transmission line between two Thevenin equivalents. Data is obtained from both terminals. The
fault resistance was fixed at 100 Ω, but the incidence angle, the sampling rate and the fault location were varied for all fault types. The numerical and graphical results proved that the techniques can extract the characteristic data of the current and voltage signals and estimate the fault distance to the terminal with high accuracy, depending only on the sampling rate adopted.