Measurement of stray load losses in squirrel-cage induction motors

The paper begins by considering the reliability of two low-power methods of measuring stray load losses: the first of these methods is the well known reverse-rotation test and the second a relatively unknown test called the d.c. excitation test. The development of a new and accurate full-load method of measuring stray load losses in squirrel-cage induction motors is then discussed, and the results obtained from this test are compared with the low-power test results. Fifteen motors in all were tested. The paper also deals with the effect on stray load losses of speed, current and the m.m.f. harmonic contents of the stator winding. The magnitudes of the measured stray load losses are compared with the amounts allowed by British Standard 269: 1927.