Multi-loop model and simulation research of turbine generator with inter-turn short circuits fault of field windings

The inter-turn short circuits fault of field windings is one common fault in generators. It will cause serious damages if such faults are not handled properly in time?For this reason, according to the multi-loop method of AC machines this paper proposes multi-loop mathematical model of turbine generators with inter-turn short circuits fault of field windings. The inductance parameters are calculated by air-gap permeance method and the calculated wave-form of inductance parameters shows reasonable. Combining with the actual structure of a 300MW turbine generator, the normal rated load operation and the short circuits fault operation of generator have been simulated based on the model. The normal stator winding currents and the fault currents difference in stator winding parallel branches of same phase were obtained. The currents of normal and fault field winding are calculated. The model considers the different structure and the harmonics in air gap magnetic field, which provides the basis for further fault analysis for turbine generator with inter-turn short circuits of field winding.

I. Introduction

The inter-turn short circuits fault of field windings, which often happen in turbine generators, will cause serious damages that the field current increases, the reactive power output decreases, and the rotor vibration aggravate [1] [2] [3]. So it is very important for the safe operation of generators to know fault characteristic of inter-turn short circuit of field windings. Existing research followed the experimental research, the qualitative analysis approaches and the numerical simulation method [2] [3] [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 the cost of the experiment, and does not have 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] [6][7] [8].