电气系统的内部过电压触发的原因很多，既有线路参数匹配引起的工频过电压，也有开关操作时电弧复燃引起的操作过电压；此外还有电感负载负荷截流引起的过电压和电感电容串联引起的谐振过电压。内部过电压，特别是操作过电压引起的事故时有发生；据统计资料，一般工频过电压不会超过2倍相电压，切除空载线路引起的操作过电压和间歇性电弧引起的过电压不会超过3． 5倍相电压，铁磁谐振过电压不会超过3倍相电压。但是，实际运行经验证明，事故的发生往往是几种过电压叠加在一起， 过电压倍数有时高达额定相电压的7～8倍。
There are many reasons for triggering the internal over-voltage of the electrical system, including the power frequency over-voltage caused by the line parameter matching, the operation over-voltage caused by the arc reignition during the switching operation, the over-voltage caused by the closure of the inductive load and the resonance over-voltage caused by the series connection of the inductive capacitance. Internal over-voltage, especially operation over-voltage accidents occur from time to time; according to statistics, generally, power frequency over-voltage will not exceed 2 times of phase voltage, operation over-voltage caused by switching off no-load lines and intermittent arc will not exceed 3.5 times of phase voltage, and ferroresonance over-voltage will not exceed 3 times of phase voltage. However, the actual operation experience shows that the occurrence of the accident is often several kinds of over-voltage superimposed together, and the over-voltage multiple is sometimes as high as 7-8 times of the rated phase voltage.