配电网低频非线性振荡引发PT保险熔断的机理及抑制措施

Mechanism and suppression of PT fuse caused by low‑frequency nonlinear oscillation in distribution network

电缆的接入使配电网中性点不接地系统对地电容电流增大,产生由单相接地故障引发的低频非线性振荡,导致电磁式电压互感器(potential transformer,PT)保险熔断,严重影响系统安全运行。首先,分析了低频非线性振荡导致PT保险熔断的原理,并基于ATP⁃EMTP平台对10 kV中性点不接地系统进行了仿真计算,计算表明,低频非线性振荡最大过电压小于2.0 p.u.,故障0.1 s后电流接近熔断器熔断电流,系统对地电容增大、零序电阻减小,保险熔断风险增大;然后,仿真验证了4PT接线和PT高压侧中性点串接压敏电阻抑制措施的有效性,并计算了零序电压测量误差;最后,建立10 kV系统的低频非线性振荡试验平台,验证仿真的有效性,对提高配电网PT运行安全性具有参考价值。

The capacitance current to ground in a non-earthing system is increased due to cables,which results in the low-frequency nonlinear oscillation caused by the single-phase earthing fault and hence leads to the fuse of potential transformer(PT),seriously affect the safe operation.The principle of PT fuse caused by low-frequency nonlinear oscillation is analyzed,and a 10 kV neutral point ungrounded system is simulated with ATP-EMTP software.Calculations show that the maximum overvoltage of low-frequency nonlinear oscillation is less than 2.0 p.u.;after 0.1 s of fault occurse,the capacitance relative to the earth increases,the zero-sequence resistance decreases,and the fuse risk increases.Simulation results show the effectiveness of suppression measures for PT with four wires and the neutral point at its high voltage side in series with a varistor.Measurement errors of the zero-sequence voltage are also calculated.Finally,the platform of a 10 kV system for low-frequency nonlinear oscillation tests is built to verify the validity.It is valuable to improve the safety of PT operation in distribution network.