An Experimental Study of Induction Machine End-Turn Leakage Reactance

There are a number of empirical and rationally derived methods described in the technical literature for the predetermination of the end-turn leakage reactance of an induction machine stator winding. The use of these calculation methods will yield widely different results when applied to a particular machine winding. Since the isolation of the end-turn leakage reactance from test results requires extensive and tedious experimental work, the designer seldom, if ever, has the opportunity to verify the accuracy of the calculation method which he uses. It is the object of the subject study to determine experimentally the actual endturn leakage reactance for a limited size range and variety of 3-phase squirrel-cage induction motor winding conditions. The experimental data are used to evaluate the relative accuracy of several published calculation methods, and to suggest refinements in one of these methods which will permit attainment of practical degrees of accuracy in design calculations. An empirical calculation method published by Alexander Gray is found to be more accurate in its predictions for the range of machine sizes involved than any of the other methods considered, however, it is limited to use with stator windings having only full pole pitch coils. Since modern design practice dictates, from several considerations, the use of fractional pitch coils, it is necessary to develop additional empirical data to enable calculation of end-turn leakage reactance for this condition.