The Study of VFTO Distribution in the Insulation System of IOCT Used in Traction Network

The FDS (Frequency-domain Dielectric Spectroscopy) of oil-immersed insulation paper, and semi-conductive paper with different moisture content, has been measured. The data measured are fitted as a function of frequency and moisture content using the amendatory Cole–Cole model utilizing the least square technique. Then, the broadband MTL model of the insulation system of IOCT (Inverted-type Oil-immersed Current Transformer) is established considering the capacitive electrodes thin layer, and the distribution parameters consider the moisture and frequency dependence. A new method for VFTO (Very Fast Transient Overvoltage) distribution calculation of insulation systems is proposed.

Research on Parameter Optimization Based on Genetic Algorithm to Suppress Transient Overvoltage of LCC-HVDC System

Since the 1980s, the direct current (DC) transmission technology has developed rapidly in China. However, with the large-scale application of DC transmission technology, new problems are brought to the power system. Commutation failure of the DC system will cause overvoltage in the alternating current (AC) power network, which will cause great harm to the weak AC system with wind power access. Therefore, it is urgent to carry out research on overvoltage suppression at the sending end of AC system. This paper reveals the formation mechanism of transient overvoltage and confirms that the control parameters of DC system influence the voltage at the sending end directly. And the appropriate control parameters were selected to suppress the overvoltage by the parameter optimization based on genetic algorithm (GA).

Transient overvoltage characteristics in submarine cables of multi-terminal flexible HVDC transmission system

The overvoltage transient characteristics of submarine cables are one of the key technologies for submarine power transmission. This article takes the submarine cable of Zhoushan Multi-terminal Flexible HVDC Transmission Project as the research object. The MMC-HVDC simulation models at both ends of converter stations are built in PSCAD. The parameters and equivalent models of the flexible HVDC cables are determined, and the submarine DC cable operating overvoltage is calculated by using statistical methods. The simulation results show that the maximum overvoltage of the submarine cable, that is, the maximum overvoltage of the conductor to sheath, the sheath to the armour, and the armour to the ground are 400 kV, 7.27 kV and 0.45kV respectively. The maximum overvoltage when it occurs faults on grid-side or valve-side appears in the middle of the submarine cable. Maximum overvoltage of HVDC single pole grounding fault appears at the connection point of land cable and submarine cable. The simulation results and the discovery of features in this article provide reference in the design, selection, and testing of submarine power transmission equipment.