Calculation of single phase series motor control characteristics

CALCULATION of the characteristics of a-c equipments as applied to locomotives and cars presents difficulties not found when dealing with d-c equipments due to the additional variables involved. Characteristics of the motors are usually presented on the basis of constant voltages at the motor terminals. However, the motors operate in service from an assumed constant voltage power source with a certain amount of impedance such as transformer, preventive coil, and bus bar or cable resistance and reactance in series with the motors. Not only does the vector relation of the impedance drop to the motor voltage vary with motor power factor, but the impedance itself varies depending upon the combination of contactors and transformer taps being used.