Abstract

Capacitor voltage transformers (CVT) have been widely used in 220kV, 500kV HVDC transmission lines. The transient characteristics of CVT mainly show that when the primary side fails,the secondary side voltage can no longer be obtained simply from the primary side voltage according to the intermediate transformer conversion ratio, which will affect the commutation process of HVDC transmission system and even the frequency of commutation failure. This paper first establishes a simulation model in PSCAD/EMTDC with the actual parameters of the 500kV fast-saturated CVT, verifies its transient characteristics, and proposes a built-in series low-voltage capacitor C3 in the CVT to eliminate the output voltage error. The principle of commutation failure predictive control (CFPREV) is analyzed, and its input voltage has an impact on the commutation process of the DC system. Based on the Yi-hua DC model of East China Power Grid, the output voltages of CVT and CVT with C3 are used as input voltages for CFPREV. Simulation results show that the commutation results of CVT with C3 can be more accurate reflects the impact of AC bus faults on the inverter side on the DC system, and improves the speed and effectiveness of DC system recovery.

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