<p> Conventional method for testing the total power loss and internal temperature rise of induction motors under full load can often be a complex and costly process. The new phase modulation method for synthetic full-load testing of induction machines has been proven viable, provided the power oscillation in this method can be minimized. This thesis explores two techniques for stabilizing power fluctuation in the new method, and determines the test system's power sensitivities to parameter changes in the equivalent circuit of the induction motors under test.</p> <p> A computer simulation representing the test system used in the new phase modulation method was developed, and an experimental testing facility was built to test the technique devised for suppressing power oscillation in the test system.</p> <p> The results from simulations are analyzed and compared to those obtained from the actual experiments in order to identify the feasible power-suppressing technique, and determine the induction machine parameters responsible for causing power unbalance in the test system.</p> / Thesis / Master of Applied Science (MASc)

This thesis describes new methods of evaluating the efficiency of three-phase induction machines using synthetic loading. Synthetic loading causes the induction machine to draw full-load current without the need to connect a mechanical load to the machine's drive shaft. The synthetic loading methods cause the machine to periodically accelerate and decelerate, producing an alternating motor-generator action. This action causes the machine, on average over each synthetic loading cycle, to operate at rated rms current, rated rms voltage and full-load speed, thereby producing rated copper losses, iron loss and friction and windage loss. The excitation voltages are supplied from a PWM inverter with a large capacity DC bus capable of supplying rated rms voltage. The synthetic loading methods of efficiency evaluation are verified in terms of the individual losses in the machine by using a new dynamic model that accounts for iron loss and all parameter variations. The losses are compared with the steady-state loss distribution determined using very accurate induction machine parameters. The parameters were identified using a run-up-to-speed test at rated voltage and the locked rotor and synchronous speed tests conducted with a variable voltage supply. The latter tests were used to synthesise the variations in stator leakage reactance, magnetising reactance and the equivalent iron loss resistance over the induction machine's speed range. The run-up-to-speed test was used to determine the rotor resistance and leakage reactance variations over the same speed range. The test method results showed for the first time that the rotor leakage reactance varied in the same manner as the stator leakage and magnetising reactances with respect to current. When all parameter variations are taken into account there is good agreement between theoretical and measured results for the synthetic loading methods. The synthetic loading methods are applied to three-phase induction machines with both single- and double-cage rotors to assess the effect of rotor parameter variations in the method. Various excitation waveforms for each method were used and the measured and modelled efficiencies compared to conventional efficiency test results. The results verify that it is possible to accurately evaluate the efficiency of three-phase induction machines using synthetic loading.