Conference Agenda

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.