What function does a secondary resistance starter serve?

A secondary resistance starter is primarily used to limit the starting current of an electric motor, particularly in applications involving large induction motors. When an electric motor starts, it draws a much higher current than its normal operating current, which can be several times higher. This high inrush current can lead to voltage drops in the power supply system and may damage the motor or other components connected to it.

The secondary resistance is introduced into the circuit at startup. By increasing the resistance in the motor circuit when the motor is starting, the starting current is reduced, allowing the motor to start more gently. As the motor accelerates and reaches a certain speed, this resistance can be removed from the circuit, allowing the motor to run efficiently at its rated speed with a normal operating current.

While enhancing torque, increasing maximum speed, and improving thermal efficiency are important aspects of motor performance, they are not the primary functions of a secondary resistance starter. The main goal is to manage the starting current effectively, ensuring safe and reliable operation of the motor for its intended application.