SYNTHETIC LOADING OF 3-PHASE INDUCTION-MOTORS BY MAGNETIC-FIELD MAGNITUDE MODULATION

The paper describes a novel method of loading three-phase induction mo tors, without the need to connect a load to the machine's drive shaft. The proposed new method uses microprocessor controlled power electron ics to produce a rotating magnetic field which rotates at constant spe ed but with sinusoidally varying magnitude. The new method substantial ly reduces the magnitude of the oscillating torque during the test whi le at the same time achieving the same accuracy as with the authors' e xisting dual frequency and sweep frequency methods. The various power losses and their distribution in the machine are calculated taking int o account rotor parameter variations with frequency. If full load temp erature rise is measured using the method described, results are obtai ned which are close to, but always higher than, those measured when us ing a conventional generator load and a 50 Hz inverter supply.