INDUCTION GENERATORS

Generally INDUCTION GENERATOR is defined as the machine with "NEGATIVE SLIP".
When the induction motor runs at above synchronous speed (i.e >1500 rpm) then it is called as "INDUCTION GENERATOR".   (OR)
                If a poly phase induction motor while connected to a constant voltage or frequency mains is mecanically coupled to a prime mover and is driven by it at a speed higher than synchronous speed, the rotor overtakes the rotating magnetic field and the rotor conductors cut the magnetic flux in the reverse direction to the motor rotation
                           We know SLIP= synchronous speed - speed / synchronous speed
                                                 
let us cosider NS = 1500 , N = 1650 then slip becomes negitive so it is called as machine with a negitive slip.
        An induction generator supplies an active current to the mains, but at the same time, it recieves lagging reactive current from the mains as same as motor.That is why, it requires a source of reactive energy to obtain this current.       
       Therefore INDUCTION GENERATOR cannot operate independently.
However, the necessary reactive current may be supplied to an induction generator by static capacitor connected in parallel with it.

 
  ADVANTAGES:-

1. It does not hunt or drop out of synchronism.
2. Simple and rugged in construction.
3. cheaper in cost and easy maintenance.
4. Induction regulator provides a constant voltage adjustments depends on the loading of the line.

DISADVANTAGES:-   

1. Cannot be operated independently.
2. Can deliver only leading current.
3. These are helpful in system stability.

APPLICATIONS:-           

1. For installation in small power station where it can be operated in parallel and feeding into a common mains without attendant.
2. For breaking purpose in railway work.
3. Now a days these induction generators are also used in wind power plants as shown in below figure.

In the above figure static capacitors are added to improve power factor and reactive power in parallel to the induction motor.

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