Induction Motor Performance Calculations

By means of solutions of the induction motor exact equivalent circuit in the form of infinite power series, approximate formulas for the important motor characteristics are derived. These formulas enable the effects of magnetizing current, core loss, and primary resistance on maximum torque, starting current, and so forth, to be readily taken into account with engineering accuracy. A new form of power factor chart is presented, which enables the power factor-load curve of any motor to be conveniently determined from no load test data. Exact values of power factor can be obtained from the chart by applying differential corrections, formulas for which are given. The methods outlined were developed to secure an optimum combination of speed, accuracy, and consistency in design calculations, and have been in regular use for the past seven years.