One of the major and common applications of industrial resistors is the control of motors used in compressors, blowers, cranes, elevators, forklifts, conveyors and etc. The Motor Starting Resistor limits the inrush current of the motor and adjusts its torque-velocity characteristic.
- In Wound Rotor Induction Motors, the Motor Starting Resistor is connected to rotor’s slip rings in star connection. By reducing the resistance steps, a smooth start is provided for the motor. This equipment is utilized in the motors with high starting torque.
- In squirrel-cage induction motors, the Motor Starting Resistor is located in the supply path of the stator winding and it will reduce the starting current by reducing the starting voltage. In this case, by reducing the resistance steps, a smooth start is provided for the motor.
- In star-delta starting procedure, motor is started via star-connection and subsequently, the connection will be changed to delta-connection. In this method, in order to reduce the sparks and balance the Counter-electromotive force (EMF), the Motor Starting Resistor is added to the circuit which eventually leads to soft starting of the motor.
- In DC series motors, the Motor Starting Resistor is added to the armature winding during starting and it will bring about reduction of voltage and starting current. Therefore, the starting toque will be reduced and afterward, by reducing the resistance steps, a smooth start is provided for the motor.