WOUND ROTOR MOTOR 

Wound rotor motor is an induction motor which was developed for variable speed applications it is also called a slip ring AC motor. This 3-phase induction motor has high starting torque and because of this torque it can be used for many applications such as it can be used for high inertia loads having a long acceleration time. It is because we can control the speed, torque and resulting heating of the wound rotor motor

Stator winding of the wound rotor motor is identical to those of squirrel cage motor the conductor bar of squirrel cage motor is replaced by three-phase windings wound the wound rotor windings terminate in slip rings mounted on to the rotor shaft and while during the start-up they are connected in series to a three-phase resistor bank externally these motors are the first to allow variable-speed operations the rotor winding is connected in series with variable resistors and thus the speed of the motor can be controlled wound rotor motor are very useful because of their high starting torque without overloading the electrical supply by the added resistance in the wound rotor motor it makes the rotor current in phase with the stator current which increases the torque due to the added resistance the secondary unit current is decreased so high starting torque can be produced with low starting current


The slots of the stator are placed with windings the windings can be wound in either a wye or a delta configuration. It can be wound to run on a single voltage or dual voltage


The rotor is constructed by placing insulated coils of wire in the slots instead of the conductor bars and thus it is different from squirrel cage motor by using coils of wire in the windings instead of conductor bars, and it also uses the resistance bank and the three slip rings on the shaft


The slip ring in the wound motor is mounted on the shaft, slip rings are electrically insulated from the shaft brushes are used to connect the rotor to the external set of resistors and the graphite in the brush provides lubrication


Brushes will connect the rotor to the external resistors, external resistors carry the entire rotor current and thus it will be helpful for the troubleshooting by the help of an ammeter the current can be easily measured any differences in current in the different phases show the problem in the resistor bank


Three phase power will be applied to the stator through the motor leads T1, T2, T3 and it will create a magnetic field in the stator this motor starts with full resistance in the circuit, resistance will be switched out of the rotor circuit when the motor accelerates when the motor gains the full speed all the resistance are switched out and the rotor windings are shorted Wound rotor motors are not started with slip ring shunted, as the rotor resistance is low and the starting current would be too high. By adding resistance in the ring circuit starting currents are decreased and the starting torque is increased