Basically the induction motor has the stationary stator and the rotor is the rotating part. General operation shows the stator takes supply from the AC mains. In the inverted or rotor fed induction motor the rotor has three phase winding where supply of three phase AC is fed. The winding of this rotor must be in star configuration. This inverted or rotor fed induction motor is used experimentally as it has mechanical revolving characteristics in stator and rotor both.
Connection of Inverted or Rotor Fed Induction Motor
The stator has three phases winding where the three phase supply is to be fed. The rotor has also three phases winding in star configuration. The end of each coil terminates to the slip ring. In the rotor three slip rings are there as rotor winding is in three phase configuration. The slip rings are mounted on rotor shaft. The brushes ride on the slip rings.
The measurement coils are placed in the slots of rotor and taken out to the additional slip rings on the shaft. Same number of measurement coils is placed in the stator winding slots also.
This motor can be driven from the stator or the rotor side.
Mechanical sensitive balance can be observed without any centrifugal force as this type of motor is so designed.
The rotor current can be induced by changing the stator current or magnetic fields.
Operational Principle Inverted or Rotor Fed Induction Motor
When the rotor winding and stator winding are fed to different three phase supply with same frequency (say 50 Hz), stator sets up a rotating magnetic field and along with that a rotating magnetic field is established in the rotor. Rotor will rotate in the direction of the magnetic field direction of rotor.
By transformer action Rotor magnetic field will create an induced EMF and current in the Stator such that a magnetic field created in stator will come to an action of opposition of the stator magnetic field. Rotor frequency will be linked in the stator with slip. As two magnetic fields tries to oppose each other their rotor motion goes to be slow or to be stopped.
This motion of the rotor totally depends on the phase difference between stator and rotor applied voltage. It can be said that the speed of the rotor depends on the difference between rotor and stator frequency i.e. (fs – fr). Some harmonics will be induced in both stator and rotor as the rotor acts as the frequency converter in the magnitude.
Purpose of Use of Inverted or Rotor Fed Induction Motor
- Voltage variation analysis of the measurement coils on the inverted rotor induction motor.
- Measurement circuits voltage analysis for no-load operation of the inverted rotor induction motor.
- Measurement circuits voltage analysis for load operation of the inverted rotor induction motor.