基于比率制动特性的电压互感器中线断线判别方法

Identification of PT neutral line break based on percentage restraint

分析了电压互感器(TV)中线断线时的电气特征,即三相电压中将产生3次谐波分量,且大小相等、方向相同。试验结果表明,TV中线断线时,相电压和自产零序电压中的3次谐波幅值随TV原边输入电压增大而增大。在理论分析和模拟试验的基础上,提出了一种基于比率制动特性的TV中线断线判别新方法,在没有保护元件启动的情况下,当TV自产零序电压3次谐波幅值与三相电压最大基波幅值的比值大于比率定值时,判为TV中线断线,延时动作于报警。理论分析和现场数据表明:该方法能够真实反映TV中线断线的电气特征,可以准确判断TV中线断线,并且具有运算量小、易于程序实现等特点。

The electrical characteristic of PT with broken neutral line is analyzed：the third harmonics of three-phase voltages are enhanced,with same amplitude and direction.Test shows that,when PT neutral line is broken,the third harmonics of phase voltage and generated zero-sequence voltage increase along with the increase of input voltage.Therefore,it is proposed to identify the PT neutral line break according to the ratio of zero-sequence voltage third harmonic to maximal phase voltage.Theoretical analysis and site data indicate that,the proposed method detects PT neutral line break accurately,with small computation and suitable for programming.