小电流接地系统压变熔丝熔断导致的电压异常研究

Study on voltage abnormity caused by fuse broken of potential transformer in small current grounding system

小电流接地系统通常采用四压变接线模式。四压线接线的电压异常事故分析难度较大,容易出现误判。通过对一起两相压变熔丝熔断导致电压显示异常事故的计算与分析,发现了已有研究的局限性,建立了考虑辅助绕组环流对压变阻抗值影响的四压变分析模型,对传统分析方法进行了完善。通过试验验证了辅助绕组环流的存在会减小未熔断相压变的阻抗值,进而影响其与零序压变的分压比、相角差,产生电压显示上的差异。结合现场事故与实物试验的结果,确定了单相熔丝熔断、两相熔丝熔断时后台母线电压及录波器波形的特征。

4PT connection mode is widely adopted in small current grounding system.However,it is difficult to analyze the Voltage Abnormity of 4PT connection mode,and erroneous judgement is prone to happen.This paper starts with the analysis on a voltage abnormity accident caused by fuse broken of two-phase potential transformers.Compared with previous studies,this paper notes the influence of the current circulation in the auxiliary winding of potential transformers on its impedance value.The experiment proves that the current circulation in the auxiliary winding of potential transformers reduces the impedance value of the fuse-unbroken PT.The amplitude distribution and phase difference of fuse-unbroken PT between zero-sequence PT is also influenced,finally leading to the diversity of voltage display.Characteristics of bus voltage and waveform of wave recorder when single-phase or two-phase fuse is fused were summarized.