Study On Stator Ground Fault Simulation And Monitoring Online For Generators

Generator, as one of the most important and costly major apparatuses in the power system, whose running state will affect the safety and stability of the electric power network. With the rapid development of industry and economy, the capacity of generator is growing. Today the generators in huge hydro power stations have already been beyond 700MW, and the generators of AP1000 being built in china have arrived on 1250MW. The generator is so expensive that it will cost much money and manpower to repair after fault. Therefore more severe request is presented to the relay protection and condition monitoring for generators.These years, perfect protection algorithms of stator ground fault protection are proposed constantly. But the algorithms based on transient analysis can't monitor the insulation of stator winding, and the safety of protections based on injecting electric source signal is doubted for the injecting source. So, it is very important to monitor the ground fault resistance, combined with generator protection and condition monitoring.The paper firstly introduces the existing generator stator ground protection and their shortages, and then summarizes the new ideas of stator ground protection.The shortage of existing generator stator ground fault simulation model is analyzed. In order to tally with the actual situation, a simulation model, based on multi-loop analysis presented by Tsinghua University, regarded one winding cell as a unit, considered distributed capacity and simplified damping winding, is tried to set up.To apply the simulation model by MATLAB, the mean of three-dimensional matrix in MATLAB is used to calculate time-variable inductance parameter. Two generators are simulated by the model programmed with MATLAB. Good performance of the model and program is shown from the simulation data and dynamic simulation test.Combined with traveling wave location, a method, based on first-harmonic zero sequence and third-harmonic equivalent circuits of generator, to calculate the stator ground fault resistance online is proposed. The accuracy of the method is shown by a large amount of digital simulation and dynamic imitation experiments.