三峡大型发电机中性点接地电阻的合理选择

通过分析中性点接地电阻对定子绕组单相接地保护、重燃弧过电压以及接地故障电流的影响,认为适当地提高中性点接地电阻有助于提高外加20Hz电源定子单相接地保护的灵敏度、有利于减小接地故障电流和中性点接地电流,且不会带来威胁发电机安全的过电压。结合三峡发电机的特点———定子绕组绝缘等级高、定子绕组对地电容大,认为中性点接地电阻取3~5倍的对地容抗值比较合适。

Proper selection of neutral grounding resistor of the large-sized hydro-generator in Three Gorges Power Plant

The grounding method of distribution transformer with secondary resistor, high resistance grounding method, is used on the large-sized hydro-generators in Three Gorges Power Plant. However, the value of the grounding resistor is not proper. This paper analyzes the effects of neutral grounding resistor on the ground fault protection, on the transient over voltage caused by arcing restrike, and on the ground fauh current. Studies show that properly increasing resistor is better for increasing the sensitivity of ground fault protection with 20Hz voltage source, better for limiting ground fault current and neutral grounding current. In addition, it will not bring any very. high ovelwohage. Considering that the generator in Three Gorges Power Plant has high insulation level and high single-phase to ground capacitance, it should be proper that the primary value of neutral resistance is 3 to 5 times of the system to ground capacitive reactance