Development Of Generator Stator And Rotor Ground Fault Protection With Voltage Injection

With the application of giant hydro-generator and 1000MW thermal-generator, higher request has been put on the performance of generator stator and rotor ground fault protection. The generator stator winding phase-to-ground fault is common fault for a generator which is the indication of more serious generator internal short-circuit fault. And generator rotor winding one-point ground fault is also common fault for a generator, although the rotor one-point ground fault won't cause great harm, but if ensued second ground fault, it will be a serious threat on generator's safety. At present, the traditional generator stator and rotor ground fault protection have not fully satisfied demands. While the generator stator and rotor ground fault protection with voltage injection are promising new protections, due to their good reliability and sensitivity, which could provide reliable ground fault monitoring in generator downtime, startup and normal operation, and become research focus of generator protection.The principle, software and hardware design scheme of generator stator and rotor ground fault protection with voltage injection are deeply studied in this paper. Firstly the principle of the generator stator and rotor ground fault protection with voltage injection is analyzed, and the judgments in the protection are given. The characteristics of the generator stator and rotor ground fault protection with voltage injection are described. Then, in the rotor grounding protection, the feature of the injection from double sides and injection from one-side are compared. The software realization method of the protection and the hardware realization scheme of square-wave injection source and the coupling unit are given. In the stator ground fault protection, protection logic and auxiliary criterion in 20Hz low-frequency injection protection is studied, considering the influence of the distribution transformer parameters on the calculation results. The hardware design of 20Hz signal source and 20Hz band pass filter are described. Besides the injection source attachment hardware design, the protective device hardware design is also given in this paper. Finally, the test result of the generator stator and rotor ground fault protection with voltage injection is introduced. The protection scheme studied in this paper has been applied in a 300MW generator.