Inverted or Rotor Fed Induction Motor

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Key learnings:
  • Inverted Induction Motor Definition: An inverted induction motor is defined as a motor where the rotor has a three-phase winding that receives power supply, creating mechanical revolving characteristics in both the stator and rotor.
  • Connection Setup: The stator and rotor both have three-phase windings, with the rotor winding in a star configuration connected to slip rings.
  • Operational Principle: The motor operates by setting up rotating magnetic fields in both the stator and rotor, with the rotor’s speed depending on the phase difference between their applied voltages.
  • Rotor Frequency: The rotor’s speed is influenced by the difference in frequency between the rotor and the stator.
  • Purpose of Use: The motor is used for voltage variation analysis and measurement circuit analysis in both no-load and load conditions.

An induction motor has a stationary stator and a rotating rotor. Typically, the stator receives power from the AC mains supply. In an inverted induction motor, the rotor has a three-phase winding that receives power. This winding must be in a star configuration. This type of motor is used experimentally because it has mechanical revolving characteristics in both the stator and rotor.

Connection of Inverted or Rotor Fed Induction Motor

The stator has a three-phase winding that receives the three-phase supply. The rotor also has a three-phase winding in a star configuration, with each coil ending at a slip ring. The rotor has three slip rings, mounted on its shaft, where brushes make contact.

Measurement coils are placed in the rotor slots and connected to additional slip rings on the shaft. An equal number of measurement coils are placed in the stator winding slots as well.

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 and stator windings are fed with a three-phase supply at the same frequency (like 50 Hz), the stator sets up a rotating magnetic field , and a similar field is established in the rotor. The rotor then rotates in the direction of its magnetic field.

The rotor’s magnetic field induces an EMF and current in the stator through transformer action, creating a magnetic field that opposes the stator’s field. The rotor frequency links with the stator frequency through slip. As the two magnetic fields oppose each other, the rotor motion slows down or stops.

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

  1. Voltage variation analysis of the measurement coils on the inverted rotor induction motor.
  2. Measurement circuits voltage analysis for no-load operation of the inverted rotor induction motor.
  3. Measurement circuits voltage analysis for load operation of the inverted rotor induction motor.
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