Analysis and Comparison of Sensors for Measurements of Partial Discharges in Hydrogenerator Stator Windings

Abstract In order to measure electrical signals produced by partial discharges in hydrogenerators stator windings, capacitive couplers are regularly used. They are electrically connected to the windings and therefore, require undesired insulation intrusion. For avoiding such an intrusion, a microstrip directional coupler is used, which is experimentally and numerically investigated in this work. This electromagnetic field sensor is analyzed initially via computer simulation using the finite-difference time-domain method. This numerical analysis is fulfilled considering the coupler placed over a stator bar. Experimental high-voltage tests with generator windings were also performed. We compare the results of the measurements obtained by using various sensors and show that the microstrip directional coupler has some important advantages over traditional capacitive sensors such as complete conductive insulation from the windings and the capacity of detecting shorter PD pulses due to their wider bandwidth.摘要 为检测水轮发电机定子绕组局部放电（partial discharges）产生的电信号，电容式耦合器（capacitive couplers）是常用的检测设备。此类耦合器需与绕组直接实现电气连接，因此会引入不必要的绝缘侵入问题。为规避该类问题，本研究采用微带定向耦合器（microstrip directional coupler），并通过实验与数值模拟对其展开系统性研究。 本研究首先借助时域有限差分法（finite-difference time-domain method）开展计算机仿真，对置于定子线棒上方的微带定向耦合器这一电磁场传感器（electromagnetic field sensor）进行分析。随后，针对发电机绕组完成了高压测试实验。 本研究对比了不同传感器的实测结果，结果表明，相较于传统电容式传感器，微带定向耦合器具备两项核心优势：一是可实现与绕组之间完全的导电绝缘；二是凭借更宽的带宽，能够检测到幅值更短的局部放电（PD）脉冲。