Analysis And Diagnosis On The Internal Faults In Stator Windings Of The Synchronous Machine

As the basic equipment of electric energy production, synchronous machines play very important role in safety and stability of the whole power system. With the rapid development of electric utility industry and the increasing capacity of generator, increasing reliability for safe operation of generator is required. Internal faults in stator windings are the common electrical fault of a generator. It includes turn-to-turn short circuit, phase-to-phase short circuit, sealing off and loss of phase fault. Most of these faults are initiated from failure of monitoring the turn-to-turn short circuit in time. If the internal faults are developed without control, there will be disaster to the stator windings. Fault analysis and diagnosis have essential meaning in theory and practical value in engineering.Based on the multi-loop theory (MLT), fault mechanism of stator winding for the synchronous generator is analyzed; this paper establishes the mathematical model of stator windings under faults. Conventional analysis for internal fault is mainly on the steady changing situation of current and voltage. Because internal faults of the stator winding have great impact on the generator's start-up process, this paper begins with the analysis of start-up process, then introduce the motion equation into multi-loop model, the focus is on the analysis of changing situation of all kinds of parameters during start-up after internal faults.Accurate inductance calculation is the basis of MLT, by using air-gap conductance method; respective inductance parameters after fault are calculated. Starting from single coil, the inductance and resistance of the single coil are first got, and then according to the real composition of respective loop, loop parameters are calculated. The impact of iron core conductance is reduced to the air gap; the impact of harmonic and slot coefficient on machine's winding coefficient, self-inductance and mutual inductance is fully considered.According to the simulation results of MLT, the impacts of stator winding internal fault on the interconnected electric parameters are systematically analyzed. The changing situation of current, torque under different fault location, different short circuit turn ratio is described; thus the fault rules are found.The impact of harmonic on the simulation results of stator winding internal fault is further analyzed.The time-domain and frequency-domain current signal's changing situation after fault is analyzed; proper fault characteristic is extracted and used for fault diagnosis.