Simulation research on field windings inter-turn short circuits fault of turbine generator with no load based on multi-loop model

The inter-turn short circuits fault of field windings is a common fault in generators. According to the multi-loop method of AC machines, this paper proposes multi-loop mathematical model of turbine generator with inter-turn short circuits fault of field windings. Based on the model, the normal operation and the short circuits fault operation of generator with no load have been simulated combining with the actual structure of a 300MW turbine generator. The time-varying mutual inductances between stator and rotor winding are calculated, from simulation results, the field current and stator voltages show the model reasonable under normal operation, After the field windings short faults, the field current increases gradually to a new constant value under the constant field voltage, the transient feature of stator voltage are obtained, which provides the basis for further fault analysis and fault diagnosis of turbine generator with field winding inter-turn short circuits.

I. Introduction

The inter-turn short circuits fault of field windings, which often happens in turbine generators, can cause serious damages [1]–[3]. The National Standards contains the gap detector coil method that detects the inter-turn circuits fault in China. However, there is not the detector equipment in a part of electric power plants [4]. So it is necessary for studying new diagnosis method to further know fault feature of inter-turn short circuit of field windings. Existing research followed the experimental research, the qualitative analysis approaches and the numerical simulation method [2]–[4]. Some useful results have been achieved up to now. The qualitative analysis can get fault characteristic, the experimental research is closer to the actual situation, but for large-scale units, the experimental research needs the higher cost of the experiment and it is lack of universality, which has limitations in practical applications. The numerical simulation method can obtain accurately the distribution and the value of fault current in the loops [4] by simulating different operations of different structure machines with less cost [5]–[7].