Induction Generator : Definition, Working, Applications, Pros & Cons [PDF]

In this article we will discuss about induction generators in detail. But before you dive into the details let us first understand about the definition of Induction Generators.

What Is an Induction Generator?

An induction generator, a type of AC electrical generator, operates like an induction motor initially. When connected to a power system and driven above its synchronous speed by a prime mover (turbine, engine, windmill), it transforms into a generator. Its performance differs slightly from a motor, with lower slip RPM, power factor, and higher efficiency. Notably, induction generators offer frequency regulation advantages, making them ideal for applications like mini-hydropower plants and wind turbines, providing energy recovery with simple controls.

Working of Induction Generator

In the previous section, we introduced Induction Generators. Now, let’s delve into how they operate in four steps:

#1 Connect an AC supply to the stator terminals, creating a rotating magnetic field that drives the rotor as a motor.

#2 Accelerate the rotor to synchronous speed using a prime mover, reducing slip to zero and rotor current to zero.

#3 Rotate the rotor beyond synchronous speed, creating negative slip and generating rotor current in the opposite direction.

#4 The generated rotor current produces a counteracting magnetic field, inducing a stator voltage that turns the machine into an induction generator, also known as an asynchronous generator.

Applications of Induction Generator

1. Paper Mills
   Induction generators find application in paper mills with ample bark and wood scrap fuel. Utilizing a boiler, this can produce 4000 HP of excess steam. Connecting a 4000 HP turbine and a 2000 HP Induction Generator to a 2000 HP pump enables the generation of 2000 HP electricity. In steam failure, the generator functions as a motor to drive the pump, preventing system over-speed in electrical load loss.
2. Windmills
   Harnessing constant desert-to-mountain winds, towers with windmills connected to Induction Generators through gearboxes generate power proportional to wind velocity, sellable to the local utility.

1. Water Companies
   Water companies benefit from buying low-rate nighttime power and selling high-rate daytime power. With low and high storage basins and pumps, they pump water at night and use it to generate power during peak periods, selling it back to utilities. This remotely operable system is simple yet effective.

Limitations of an Induction Generator

Now, let’s explore the limitations of Induction Generators:

1. Reactive Power Dependency:
   Induction generators connected to a capacitor system can generate ample reactive power within their capabilities. However, surpassing the generator’s capacity to supply both magnetization reactive power and load power causes an immediate halt in power production.
2. Restarting Protocol:
   In case of a shutdown due to excessive load, the induction generator requires a restart. This involves removing the load and restarting with either a DC source or utilizing residual magnetism in the core.

1. Wind-Generating Station Suitability:
   Induction generators find particular suitability in wind-generating stations where speed is variable. Their capacity to adapt to changing speeds aligns well with the dynamic conditions of wind power generation.
2. Load-Dependent Nature:
   Unlike synchronous motors, induction generators are load-dependent. This characteristic restricts their ability to contribute independently to grid frequency control.

Understanding these limitations is crucial for optimizing the performance and application of Induction Generators in various contexts.

Advantages and Disadvantages of Induction Generator

In our final section, we’ll highlight key advantages and disadvantages of Induction Generators:

Advantages:

1. Low maintenance requirements.
2. Cost-effective compared to alternatives.
3. High energy density with a compact size per kW output.
4. Smooth parallel operation without hunting.
5. No synchronization needed with the supply line, similar to synchronous generators.

Disadvantage:

1. Dependent on reactive volt-amperes from the supply line for excitation.

Conclusion

In this article, we’ve covered crucial aspects of induction generators, from their basic definition to their working principles and various applications. The final section highlights key advantages and disadvantages. If you have firsthand experience or additional insights on asynchronous generators, we welcome your opinions in the comments.