Magnetic Circuit Calculation And Operation Characteristics Analysis Of Powerformer

Powerformer is a novel high voltage generator. It has similar rotor structure as traditional generator, but uses concentric high-voltage cables as its stator windings. Since the using of new winding system, its rate voltage can be several times larger than traditional generator. The change of the stator structure not only gives it the property to generate high voltage electricity, but also changes its other performances, which will produce new problems in the design and performances analyses of it. So take a high voltage prototype of 162.5kVA/5kV as the investigated subject,the problems related to its design and performances is studied.Firstly, slot shape and its impact on magnetic circuit calculation is stated and analyzed. After saturation characteristic of stator teeth due to slot shape is illustrated, width formula about the special shaped tooth is deduced. Then by comparison with finite element calculation results, approximate calculation method of the tooth magnetomotive force is determined. Besides, the variation rules of main magnetic gap coefficients with the saturation are also calculated and given.Secondly, problems on accurately calculating parameters of steady operation points are discussed. Three parts contents about them are analyzed, which includes magnetic field calculation, electric potential calculation and iteration. Then, method about magnetic permeability modification, electric potential computation process under both flux density method and flux linkage method, as well as iteration steps for magnetic field calculation are given one by one.Thirdly, based on the method of calculating induced electric potential that can adapt to the complex slot shape, several important steady operation characteristics are calculated with finite element method under the special structure of Powerformer. Then no-load characteristic, short-circuit characteristic, power-angle characteristic, and v-shape characteristic are calculated, and detail results of the characteristics are analyzed.Finally, after the reactances calculation model considering cross-magnetizing phenomenon is given, reactances variation rules corresponding to each steady operation point of both power-angle characteristics and v-shape characteristics are calculated, which can provide theoretical basis for operation analysis of Powerformer.In conclusion, the work in this paper can be important reference for further design and analysis of Powerformer. The methods used in calculating magnetic circuit and operation characteristics, as well as the calculated variation rules of reactances and magnetic circuit parameters will also do favor in the design and analysis of other generators.