35kV电磁式电压互感器连续爆炸事故探讨

Analysis of Successive Explosions of a 35 kV Electromagnetic Potential Transformer

运行于海拔1000 m左右山区地形的35 kV中性点不接地系统,其I母电磁式电压互感器(PT)在只带空母线的状态下发生爆炸,更换电磁式PT并安装消谐器后不久再次爆炸。事故后进行了高压诊断性试验和油化试验,结合交接试验数据分析了事故前后电气性能和绝缘性能的变化,研究了故障录波图波形的特点,发现电磁式PT一次公共N端对地放电,三相电压相位差发生了明显变化。认为由于电磁式PT与消谐器绝缘配合不当,发生单相弧光接地时,N端耐受电压过高而将对地绝缘击穿,使得消谐器失去作用,进而诱发较少见的单相(A相)基频并联谐振和B相1/2分频谐振,产生的大电流使得一次保险管熔断,电磁式PT过热而爆炸。通过合理的选型,可以避免事故的发生。

This paper investigates a failure of a 35 kV neutral point unearthed system in a hilly territory at the altitude about 1 000 m. The system＇s No. 1 busbar electromagnetic voltage transformer （PT）had exploded with an open-circuit bus connected. Then the PT was replaced and a harmonic eliminating device was installed. However,the PT exploded again soon after the replacement. High voltage diagnostic tests conducted,and the changes of electric properties comparing with historical data. Waveform recorded and insulation strength after the failure during found at the common terminal of the PT＇s primary three-phase voltage were observed in the waveform. and oil tests were were obtained by the failure was also analyzed. Discharge to earth was side,and apparent changes in the phase difference of the The cause of the failure is summarized to be improper insulation match between the PT and the harmonic eliminating device. As a result of the poor match, single-phase arc grounding occurred to cause over-voltage on the N-terminal and subsequent breakdown of its insulation to earth,which resulted in malfunction of the harmonic eliminating device,and subsequently resulted in rare fundamental frequency parallel resonance of single-phase （phase A） and 1/2 fundamental frequency resonance of phase B. The induced heavy current ,blew the primary side fuse to make the PT overheat and then explode. The investigation result suggests that this kind of failure can be avoided by proper selection of the device type.