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Induction Generator

Induction Generator:
Induction Generator is a asynchronous Generator that uses the principle of induction motor to generate electricity.

Induction Motor as Induction Generator:

The induction motor can be used as Induction Generator by making its speed greater than synchronous speed by using Prime mover

Conditions for motor to act as generator:


  • Slip produced should be Negative
  • Prime mover torque should be opposite to electrical torque


Working:
Induction motor can be used as Induction generator by rotating its rotor more than synchronous speed. This  can be attained by using a Prime mover. 

In normal motor, the stator is provided with supply, where it produces stator flux, which produces rotor current. Rotor current produces rotor flux opposite to stator flux. This difference produces a positive slip where the stator flux is greater than rotor flux.

In Generator, Prime mover is used to rotate rotor greater than synchronous speed with DC excitation. Now the rotor rotates and produces rotor flux which induces Current in stator. This difference produces a Negative slip as the rotor flux is greater than stator flux. Hence the motor Works as 
generator.

Capacitor bank:

While connecting induction generator to the electrical grid, capacitor bank are required. When the DC Source is removed capacitor provide magnetization current to produce Voltage. Induction machine always require armature current as rotor lags stator field it produces reactive power so capacitor is used to provide reactive power.
Active power is directly proportional to slip greater than synchronous speed.

Grid connection:

For the Induction generator to connect with grid, the Voltage and frequency of machine should be decided by the electrical grid. Voltage and frequency of induction generator should match with electrical grid

Squirrel cage induction motor can be used as squirrel generator with speed greater than synchronous speed with high efficiency
Induction generator 

Advantages:


  • Robustconstruction 
  • Small size per KW
  • Runs in parallel without hunting
  • Does not require synchronous generator 

Disadvantages:

  • When the load current becomes greater than capability of generator the motor will stop and need to be restarted 

Application:

  • Mini hydro power plant
  • Wound turbines
  • Gas stream to reduce high pressure to low pressure 

Induction  Generator VS Synchronous Generator:


  • Induction generator rotates at speed greater than synchronous speed where as synchronous generator rotates at synchronous speed.
  • Induction generator has Negative slip where as in synchronous generator slip is always unit
  • Seperate DC excitation is needed for stand alone in synchronous generator where as capacitor bank is also needed for stand alone induction generator 
  • Synchronous Generator requires slip Things and brushes where as Induction generator is free from slip rings and brushes 

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