This paper investigates the switching impulse and temporary overvoltage (TOV) duty for 400 kV underground power cables using ATP. This work together with the work reported in [I], investigates the f i l l range of transient overvoltages due to lightning, switching and other temporary overvoltages (TOVs) using ATP.[ I ] re-assesses the basic insulation level (BIL) for 400 kV oil-filled cables. The objective of this work was to check the impact of switching surges on the choice of BIL and to re-assess the switching impulse insulation level (SIL) and TOV withstand level for 400 kV cables. A comprehensive study of the transient overvoltages experienced by cables within National Grid's transmission system has been pegormed. This paper provides an argument, for reducing the BIL and SIL for 400 kV cables.
Hybrid circuit breakers (CBs) are the most promising technology to isolate DC faults in modular multilevel converter (MMC)-based DC grids. However, they consist of expensive power electronic components that are sensitive to high overvoltage and overcurrent. This study proposes a hybrid high-voltage DC circuit breaker with an energy absorption branch of a parallel arrester structure, and investigates the possibility of reducing the fault current and the switching overvoltage. First, the basic principle of an energy absorption branch with a parallel arrester structure is presented. Then, the simultaneous and sequential insertion strategies are illustrated. Second, each strategy and each structure are combined separately to analyse their respective characteristics in reducing the overvoltage, the fault current, the energy absorption and the fault clearance time. The sequential insertion strategy of the proposed energy absorption branch is proved to have the best performance. Finally, the trade-offs between these four metrics are achieved through the non-dominated sorting genetic algorithm II (NSGA-II). A general method to determine the parameters of the proposed energy absorption branch from the Pareto front based on different preferences is provided. Simulations on PSCAD show that sequential insertion of the proposed energy absorption branch with the optimal parameters is able to suppress the switching overvoltage and limit the fault current to a relatively low extent simultaneously.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Offshore wind farms (OWFs) integration are attractive extensively for furnishing more robust power than land wind farms. This paper introduces a modular combined DC-DC autotransformer (MCAT), which contributes to the offshore wind power integration of DC grids with different voltage levels. Traditional DC transformers contains medium- or high-frequency converter transformers, which have the disadvantages of high manufacturing difficulty and cost. These shortcomings seriously affect the progress of commercial application of DC transformers. To solve these problems, in the proposed MCAT, converter transformers are replaced with a DC-isolation capacitor and a compensation inductor in series to reduce the footprint of offshore platforms and improve economy. Theoretical analysis is carried out for the MCAT operation principle. Selection methods of main circuit parameters for the MCAT are discussed in detail. Then, corresponding control strategies of the MCAT are proposed. Finally, the effectiveness of the proposed MCAT and its control strategies are validated by time domain simulations in PSCAD/EMTDC. The time-domain simulation results show the correctness of the main circuit parameters and the rationality of the MCAT control strategies.
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