A Method of Calculating Starting Performance of PM Motor

Abstract

This paper describes a new method which predicts the starting performance of a PM motor (double squirrel-cage permanent magnet motor).
As the motor has the field excitation at standstill, it's impossible to determine several constants (synchronous reactance, sub-transient reactance, etc) and the performances using the method of IEC Pub. 34-4 or JEC-114.
This method, named a D. C. decay measurement, is applied to the armature winding of a PM motor at standstill. That is to say, by means of Fourier transformation of the D. C. decay current which is measured when the two terminals of the star-connected armature winding are short-circuited, the direct- and quadratureaxis impedance loci are obtained, and the starting performance is calculated on the basis of two-reaction theory. The starting performance of a PM motor calculated by this method agrees with experimental result. The method can easily calculate the performance of middle and large PM motors in factories, because the capacity of this equipment is very small.