中压配电网单相接地故障熄弧后的电气特征分析

配电网单相接地故障熄弧后的电气变化规律不仅决定过电压水平、电弧是否重燃以及重燃时的电气特征,更将对故障诊断方法的适应性与可靠性产生影响。利用配电网单相接地故障等值电路对系统故障恢复过程进行了分析,发现不同接地方式系统的零序网络在熄弧后均存在衰减的振荡过程。其中不接地系统的零序电压幅值大、振荡频率远低于工频、持续时间长,相电压存在较长时间的过电压。经消弧线圈接地系统的零序电压幅值大、振荡频率略大于工频、持续时间一般在5个周期以上。由于拍频现象会导致故障相1.1倍以内的过电压,经小电阻接地系统振荡频率远高于工频且幅值小、衰减速度快。利用ATP-EMTP验证了3种配电网接地方式下系统单相接地熄弧后恢复过程符合上述规律。

Electrical Characteristics of Medium-voltage Distribution Network with Single-phase-to-ground Fault After Arc Extinction

The electrical variation law of the single-phase-to-ground fault in distribution network after arc extinction do not only determines the over-voltage level whether the arc is re-ignited or the re-ignition electrical characteristics, but also affects the adaptability and reliability of the fault diagnosis method. The system fault recovery process is analyzed based on the single-phase-to-ground fault equivalent circuit of distribution network. It is found that the zero-sequence network in different grounding systems have an attenuated oscillation process after arc extinction. For ungrounded system, the zero-sequence voltage amplitude is large. The oscillation frequency is much lower than the power frequency and the oscillation time is long. The phase overvoltage will last for a long time. For arc suppression coil grounding system, the zero sequence voltage amplitude is large. The oscillation frequency is slightly larger than the power frequency, and the duration is generally above 5 cycles. The beat frequency phenomenon will cause overvoltage whose amplitude is within 1. 1 times of the normal level on the fault phase. For low resistance grounding system, the oscillation frequency is much higher than the power frequency. Its amplitude is small and the attenuation speed is fast. The correctness of the recovery process of single-phase-to-ground fault after are extinction in three types of grounding systems is verified by ATP-EMTP.