Abstract
Insulation failures in dry-type distribution transformers occur frequently and severely when 12-kV vacuum circuit breakers are applied to switch shunt reactors. However, the reason for this phenomenon is unclear. Based on the test platform for the failure circuit of a running 10-kV power system, a series of field tests was conducted to investigate the overvoltage mechanism of this type of failure. Field tests successfully recorded the prestrike and reignition waveforms during the transient processes of switching shunt reactors, based on which transient process and phenomena were analyzed. The prestrike probability was as high as 60% during the transient process of switching on shunt reactors. However, the probability of reignition was significantly lower than that of prestrike. The phase-to-ground and interphase maximum overvoltages during the switching transient processes have approximately the same amplitude. The prestrike caused phase-to-ground overvoltages beyond 6.0 p.u., whereas the reignition caused overvoltage beyond 8.0 p.u. The mechanisms of overvoltage generation of the switching transient processes were analyzed based on circuit analysis. Multiprestrikes and multireignitions, cable length, switching conditions, and system configurations were the main reasons for severe overvoltages.
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