Conference Agenda

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.