What is Induction Generator

here present the artice about the inducion generator and principal of operation and advantages and application of induction generator

👉Induction Generator

defination :when the slip of the induction motor is less than zero, i.e. when the induction motor runs above the synchronous a speed then it runs as a generator called induction generator.

• the negetive slip indicates that the rotor of induction motor is running faster than synchronous speed. 
• hence to run the induction machine as an induction generator, its slip must be negative 

• show the induction generator which is driven by the prime mover such as engine or wind turbine and is comnected to a 3-phase load.
• when the speed of induction generator is above its synchronous speed the active power(p) is delivered by the generator to the 3-phase load and the corresponding mode of operation to the induction machine is called generating mode and the slip of induction machine will be negative.
• however for creating its own magnetic field, it absorbs reactive power(Q) from the 3- phase line or capacitor bank.

touque - speed characteristics

• the touque- speed characteristics for motoring and generating mode of induction machine is show in figure.
• the construction of induction generator is the same as that of induction motor.
• the only difference in case of induction generator is that the direction of rotation or induced torque is reversed.

principle of operation

• when the 3- phase induction motor is driven at a speed greater than synchronous speed by an external prime mover with exciting current provided either from 3- phase line or capacitor bank, the emf and current of slip frequency will appear in the rotor winding. but the direction of this emf and current will be opposite, as compared to the direction when it is operating below the synchronous speed.
• In generating mode of operation,an external prime mover drives the rotor above the synchronous speed.The stator flux induces currents in the rotor,but since the opposing rotor flux in now cutting the stator coils,an active current is produced in stator coils and the motor operates as a generator,sending power back to the grid.

Advantages of induction generator

1. they are mechanically and electrically simpler than other type of generators.
2. simple robust and rugged in construction.
3. relatively cheaper.
4. Requires no brushes and commutator.
5. Easy in maintenance.
6. they do not have to be synchronised to the supply lines as does a synchronous generator.

Applications of induction generator

• Iduction generator are often used in wind turbines and small hydro power station due to their ability to produce usefull power at varying rotor speeds.
• induction generators are particulary suitable for wind generating station as in this case speed is always a variable factor.
• they are also very useful in automatic dynamic braking such as for braking purposes in case of railways.

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