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1. SWITCHING OVERVOLTAGE CHARACTERISTICS OF ±1100-KV UHVDC
CONVERTER STATION
ABSTRACT
The present study analyzed the characteristics of switching overvoltage, and discussed in
detail the main influencing factors and worst-case conditions of switching overvoltage in the
±1100-kV ultra-high-voltage direct-current (UHVDC) converter station. The results showed that
ac bus overvoltage was produced by oscillation, and would not be a threat to the equipment in
the converter station. The results also showed there were two cases for overvoltage on related
valves. In the first case, the valve overvoltage was on converter valves in the upper three-pulse
group of the 12-pulse converter, and was caused by the voltage difference between the dc line
and ac bus at the valve side under a specific fault. In the second case, the overvoltage was on
other valves, and was caused by a phase-to-phase switching surge that penetrated into the valve
hall. Other results were that overvoltage on the dc bus was mainly caused by the full reflection of
the wave, and overvoltage on the neutral bus was caused by high-voltage sources, such as the dc
source creating stress on the neutral bus under specific faults, or the freewheeling current of the
metal return line and the smoothing reactors.