Load testing of induction machines without torque measurements

Direct load testing of induction motors, together with data from variable voltage no load testing, is currently used in IEEE Standard 112B to establish efficiency as a function of load. An accurate torque transducer is necessary for this load testing. In an attempt to reduce both the testing time and the required equipment, the present paper proposes to eliminate the torque transducer by loading the induction motor under test with a dynamometer based on an induction motor fed from a power electronic converter with fully bidirectional power flow. The induction motor is loaded both as a motor and as a generator at the same slip speed and also is driven at exact synchronism to separate the no load core losses, thus eliminating the need for an adjustable voltage source (autotransformer) of the conventional no-load saturation test. Only a full voltage no load (uncoupled) motoring test is required to determine the mechanical losses. Experimental results from a 75 hp induction motor are given both for the standard (IEEE 112B) and proposed method. Although more verifications are required, it seems that the method holds real potential for electric machine and drive manufacturers