As technology advances, new challenges arise for power systems engineers in terms of EMT modeling and simulation. A good example is the HVDC transmission system under construction between France and Ireland [1]. The French and Irish transmission system operators (RTE and EirGrid) have been working together to build this 575km length, 700MW HVDC link to connect the two countries.
The involved parties have been performing feasibility studies to evaluate the behavior of the HVDC system using EMTP®. Given the project's relevance, accurate and reliable simulation tools are required for modeling both underground and submarine cable sections, including an optical fiber cable.
Illustration of the cross-section HVDC cable layout modeled in EMTP.
The cable impedance must be accurately modeled from DC up to switching frequencies, which is a very large band of frequencies. Cable models may display wrong behavior for DC phenomena and/or high frequencies without proper care.
Line/Cable Data Module
To fulfill the abovementioned requirements, EMTP® offers the Line/Cable Data calculation module, which is a state-of-the-art tool for transmission line and cable modeling. This module is suitable for modeling both overhead lines and underground/ submarine cables. The Line/Cable Data module applies the Method-Of Moments and Surface Operator (MoM-SO) technique for calculating the longitudinal impedance accounting for skin, proximity, and ground-return effects. The MoM-SO method is reported to achieve accurate results compared to Finitre-Element-Method solvers. As for the shunt admittance (transversal) electromagnetic effects, the so-called "Extended Transmission Line Theory" is applied to calculate the capacitance and line-to-ground losses [2]. As for the transient model representation, the EMTP Wideband model is applied.
Wideband Model and Advantages
The Wideband model in EMTP® is the preferred option since it achieves accurate fitting of the line mathematical functions (characteristic admittance and propagation function). Unlike other models, the Wideband model is computed in the phase-domain; therefore, it does not involve errors due to any assumptions in transformation matrices. This feature is particularly important to evaluate sheath induced voltages in cables.
Studies and Assessments
Among the studies achieved for this project by RTE are:
Assessment of transient overvoltages due to energization
DC transient overvoltages due to enerization
Short-circuit arrester capability assessment
DC surge arrester capability assessment
Evaluation of the transient overvoltage on the optical fiber repeater caused by a fault on the HVDC cable
Current stress on the optical fiber repeater power supply cable caused by a fault on the HVDC cable
EMTP® offers a robust solution for evaluating existing and new power system facilities with up-to-date models. A unique advantage is the capability to initialize transient simulations with realistic conditions using the EMTP Multiphase Load-Flow module. The initialization procedure is also capable of initializing HVDC converters and IBRs.
References:
[1] https://www.rte-france.com/en/projects/celtic-interconnector-interconnection-between-france-ireland
[2] H. Xue, A. Ametani, J. Mahseredjian, I. Kocar, "Generalized Formulation of Earth-Return Impedance/Admittance and Surge Analysis on Underground Cables," IEEE Transactions on Power Delivery, vol. 33, no. 6, pp. 2654-2663, Dec. 2018, doi: 10.1109/tpwrd.2018.2796089
[3] N. Jiang, C. Yang, H. Xue, J. Mahseredjian, "An investigation of electromagnetic transient characteristics on a practical 500 kV submarine cable system," Electric Power Research, vol. 223, Oct. 2023, 109615, doi: 10.1016/j.epsr.2023.109615
[4] J. Morales, H. Xue, J. Mahseredjian, I. Kocar, "A new tool for calculation of line and cable parameters," Electric Power Systems Research, vol. 220, July 2023, 109314, doi: 10.1016/j.epsr.2023.109314.
[5]H. Xue, J. Mahseredjian, J. Morales, H. Saad, S. Dennetiere, T. Xue, "An Investigation of Frequency and Electromagnetic Transient Responses on VSC-HVDC Cable Network," Accepted for publication in IEEE Trans. on Power Delivery.
Author: Jesus Morales
Date: 2024-04-10