目前,对基波谐振和单相接地故障判据的主要区别在于零序电压U0的高低。通常,基频谐振定为当U0≥150V时;当30V≤U0<145V时定为单相接地故障。为了防止在单相接地时由于装置误动使TV长时间过负荷而烧毁的情况发生,通常将该装置基频谐振的判据电压定得比较高。
At present, the main difference between the criterion of fundamental resonance and single-phase grounding fault lies in the level of zero-sequence voltage U0. Usually, the fundamental frequency resonance is defined as a single-phase ground fault when U0 < 150V and 30V < U0 < 145V. In order to prevent the burnout of TV due to device misoperation during single-phase grounding, the criterion voltage of fundamental frequency resonance of the device is usually set relatively high.
这样,在工频位移电压不是很高的情况下(如空母线合闸)装置将无法动作,就可能使某些励磁特性欠佳、铁心易饱和TV的熔丝熔断。而且这种装置当电网对地电容较大时,它对防止间歇性接地或接地消失瞬间互感器因瞬时饱和涌流而造成熔丝熔断的事故无能为力。此外,在持续时间较长的间歇电弧过电压激发下,流过TV高压绕组的电流将显著增大,仍可能会烧坏TV。
In this way, if the power frequency displacement voltage is not very high (such as empty bus closing), the device will not be able to operate, which may cause some fuses with poor excitation characteristics and saturable core TV to fuse. Moreover, when the capacitance of the power grid to the ground is large, the device can do nothing to prevent the fuse fusing accident caused by the instantaneous saturated inrush of the transformer when the intermittent grounding or grounding disappears. In addition, the current flowing through the high voltage winding of TV will increase significantly under the excitation of long duration intermittent arc overvoltage, which may still burn the TV.