转子接地保护相关二次回路对地过电压的分析

乒乓式或注入式发电机转子接地保护的二次回路需接到转子绕组的正负两端。600 MW及以上容量的大型发电机的额定励磁电压普遍较高，且运行中会有各种过电压，因而担心二次回路绝缘等级偏低，不能承受足够的过电压。分析了在差模和共模电压作用下及转子绕组发生一点接地故障时，二次回路可能出现的严重过电压。研究结果表明，直接和间接与转子绕组相连接的二次回路电缆的耐压要求不同，宜采用独立的注入式转子一点接地保护并就地安装在励磁系统屏柜内，缩短直接与转子绕组连接的二次回路电缆;转子电压的信号采集宜采用具有隔离作用的变送器。

Analysis of Over-voltage to Ground on Secondary Circuit of Rotor Earth Fault Protection

Two schemes of generator rotor earth fault protection(REFP),named "ping-pong" and "voltage injection",are often applied.The secondary circuit of the REFP must be connected to the positive and negative terminals of rotor field windings.The rated field voltage of 600 MW or larger generator is commonly higher,and there are various over-voltages in the process of operation.Therefore,it is worried that the low-level insulation of the secondary circuit cannot withstand over-voltages.The over-voltages in the secondary circuit under the effects of common-mode and differential-mode voltages,while one-point rotor earth fault occurs,are analyzed.The results show that the demands on voltage withstanding capability of the secondary circuits,which are directly and non-directly connected to rotor field windings,are different.It suggests installing an independent relay of REFP in the cabinet of excitation system,so that the length of the directly connecting secondary circuit can be shortened.It is proper to use a transducer with galvanic insulation to measure the field voltage.