大型水轮发电机消弧线圈接地方式下的注入式定子接地保护新方案

在中性点经消弧线圈接地的大型水轮发电机的定子接地保护中，从消弧线圈附带的仪表线圈注入20 Hz信号是一种常规方案。为了提升保护效果并克服大型水轮发电机定子绕组对地电容增大带来的困难，提出了一种从消弧线圈串接电阻两端注入20 Hz信号的新方案。与常规方案对比，分析了应用新方案时从注入端口看进去的20 Hz等值电路，研究了相应的接地故障过渡电阻计算方法。以天生桥二级水电站发电机为研究对象，参照其消弧线圈的参数定制了试验专用消弧线圈，并在动模发电机上进行了定子接地故障试验，检验了2种保护方案的效果。动模试验结果表明，新方案相比常规方案，接地故障过渡电阻测量最大值由5.6 kΩ提高到20 kΩ，测量误差在±6%以内。

A New Method for Stator Ground Fault Protection with Voltage Injection on Large Hydro Generators Grounded by Arc Suppression Coils

For stator ground fault protection of large hydro-generators grounded with arc suppression coil at neutral point, the conventional method is to inject 20 Hz signal from the instrument coil attached to the arc suppression coil. In order to improve the effect of the protection and to overcome the difficulties caused by the increase of stator-to-ground capacitance, a new method is proposed to inject the 20 Hz signal from the resistor in series with the arc suppression coil. The proposed method is compared with the conventional one in terms of the 20 Hz equivalent circuit viewed from the injection port, and the corresponding calculation method for transition resistance is also studied. Taking a generator of Tianshengqiao-Ⅱ Hydro Power Station as the research object, an arc suppression coil based on the parameters of the real generators’ arc suppression coil is customized for test, and the stator ground fault experiment is conducted on a dynamic simulation generator to test the effectiveness of the two methods. The results of the experiment show that, compared with the conventional method, the proposed new method has the maximum measured ground fault transition resistance increasing from 5.6 kΩ to 20 kΩ with an error within ±6%.