Test Circuit for Evaluation of Breaking Capacity of Motor Starters

Series RL circuits having a power factor between 40 and 50 percent with a resistor shunting the inductor and drawing one percent of the power are presently used for evaluating breaking capacity of motor starters. Transient recovery voltages of these circuits show anomalies which indicate that test circuits in different laboratories may have widely different characteristics and produce different test results. It is shown that important differences in the transient recovery voltage may be caused by differences in the effective capacitance shunting the series inductor and parasitic inductance in the shunt resistor. Test circuit recovery voltages are compared with representative recovery voltages of induction motors.