Based on the nonlinear PT(Potential Transformer) model including losses,the instantaneous symmetrical component method is applied to deduce the expressions of PT transient over-current during single phase grounding fault and after its removal for the ungrounded-neutral power system.It is found that the PT transient over-current consists of the positive-sequence exciting current in normal operating condition and the decaying zero-sequence over-current.The PT transient over-currents during single phase grounding fault and after its removal are analyzed with MATLAB/Simulink for different arc suppression coil compensation modes.The simulative results show that,when single phase grounding fault occurs,the PT transient overcurrent is mainly related to its nonlinear excitation characteristics;when the fault is removed,larger exciting over-current is generated in PT,which contains the steady-state component and the decaying transient component,greatly influenced by the zero-sequence network.Therefore,it is proposed to restrain the PT damage by changing the zero-sequence parameters of system.%引入计及损耗的电压互感器非线性模型,采用瞬时对称分量法推导了中性点不接地电网发生单相接地故障期间和故障消失后电压互感器的暂态过电流表达式,发现该电流由正常运行状态下的正序励磁电流和衰减的零序过电流组成.通过MATLAB/Simulink仿真分析了系统在单相接地故障期间及故障消失后、不同消弧线圈补偿方式下的电压互感器暂态过电流.仿真结果表明,系统发生单相接地故障时,电压互感器中的暂态过电流主要与其励磁特性的非线性有关;单相接地故障消失后,在电压互感器中产生较大的励磁过电流,包含受系统零序网络影响较大的稳态分量和衰减暂态分量.由此提出可通过改变系统的零序参数来抑制电压互感器的损坏.
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