Synthetic loading of three-phase induction motors by magnetic field magnitude modulation

The paper describes a novel method of loading three-phase induction motors, without the need to connect a load to the machine´s drive shaft. The proposed new method uses microprocessor controlled power electronics to produce a rotating magnetic field which rotates at constant speed but with sinusoidally varying magnitude. The new method substantially reduces the magnitude of the oscillating torque during the test while at the same time achieving the same accuracy as with the authors´ existing dual frequency and sweep frequency methods. The various power losses and their distribution in the machine are calculated taking into account rotor parameter variations with frequency. If full load temperature rise is measured using the method described, results are obtained which are close to, but always higher than, those measured when using a conventional generator load and a 50 Hz inverter supply