大型发电机注入式定子接地保护判据的改进

Improvement on Criterions of Stator Earth Fault Protection with Voltage Injection for Large-sized Generators

大型发电机对定子接地保护提出了更高的性能要求,倾向于在静止无励磁状态下也要有定子接地保护,因此装设注入式定子接地保护成为一种趋势。文中对注入式定子接地保护的2个判据进行了改进。接地过渡电阻判据跳闸段增加安全电流限制,并给出安全电流限制定值的整定方法;通过分析传递过电压对零序电流判据的影响,零序电流判据增设为2段,高定值段快速跳闸,低定值(灵敏)段增加主变高压侧接地闭锁。改进后的判据避免了接地故障电流很小的情况下不必要的跳闸停机对系统造成冲击,同时避免了传递过电压引起保护误动,进一步提高了注入式定子接地保护的可靠性和快速性。

Much higher performance of the stator earth fault （SEF） protection is required on the large-sized generator. It inclines to use SEF protection even though generator is at stand-still without excitation in rotor. Therefore, it is a trend to install the SEF protection by sub-harmonic voltage injecting. Two criterions of the SEF protection with voltage injection are improved. Firstly, a safe current restriction is added in the fault resistance criterion for the trip stage. And, the setting method of the safe current restriction is given. Secondly, the effects of the transitive over-voltage on the zero-sequence current criterion are analyzed. The zero-sequence current criterion is set into two stages. One is the high value stage used to fast trip, and another is the low value （sensitive） stage with a block criterion of the main transformer ear thing on the HV side. By improving the criterions, there is no trip while the earth fault current is too small even though the fault resistance is zero, so that there is no impact on the power system. And there is no mis-operation caused by the transitive over-voltage. The reliability and the response speed of the SEF protection by sub-harmonic voltage injecting are improved.