采用三相共箱GIS的中性点非有效接地系统中工频铁磁谐振的判别方法

Criterion for Judging Power Frequency Ferroresonance in Neutral Point Ungrounded GIS System

铁磁谐振过电压是影响电气设备内部绝缘的重要因素之一,在中性点不接地GIS系统中,因铁磁谐振过电压造成的设备损坏占有相当的比例。为了方便地判断系统在转换工作方式时是否有可能发生工频铁磁谐振,详细推导了中性点不接地系统发生工频铁磁谐振的判据,该判据是利用解析法推导出了回路等效电阻与临界电阻的关系式,根据此判别式还可以选择消除谐振的电压互感器二次开口零序电阻的阻值。通过实例,在两种工况下,验证了该方法的有效性。最后,分析了系统中性点接消弧线圈对铁磁谐振的影响。

Ferroresonance overvoltage is one of the most harmful faetors to inner insulation of eleetrieal equipment. For neutral-ungrounded GIS system, the failures caused by ferroresonance overvoltage account for a large proportion. In this paer, a criterion of power frequency ferroresonance in neutral-ungrounded GIS system is deduced by means of analytical method to estimate whether the ferroresonance will occour when a GIS system is switching from one working manner to another. This criterion describes the relationship between equavilent resistance of circuit and critical resistance. It can also be used to determine the zero-sequence resistance of the secondary coil of potential transformer for eliminating the ferroresonance overvohage. The availability of this criterion is verified via a praetical application to a gas insulated substation in two working conditions. In addition, the effeet of-connecting an are suppression coil to neutral point of GIS system on ferroresonance overvohage is analyzed.