Question

What is the difference between synchronous generator & asynchronous generator?

Answer 1

Synchronous and asynchronous generators are two types of electrical generators that operate on different principles. Here’s a detailed comparison of the two:

### Synchronous Generator

**1. Operating Principle:**
   - A synchronous generator operates at a constant speed, which is synchronized with the frequency of the electrical grid to which it is connected. This means that the rotor of the generator rotates at a speed directly proportional to the frequency of the electrical grid.

**2. Rotor and Stator:**
   - The rotor in a synchronous generator is equipped with windings that produce a rotating magnetic field. This magnetic field synchronizes with the rotating magnetic field of the stator (the stationary part) to produce electricity.

**3. Speed and Frequency:**
   - The speed of a synchronous generator is fixed and directly related to the frequency of the grid. For example, in a 50 Hz grid, the rotor speed must be 3000 RPM (Revolutions Per Minute) if there are 2 poles (the speed depends on the number of poles and the frequency of the grid).

**4. Power Factor Control:**
   - Synchronous generators can control the power factor of the system. They can operate at lagging, leading, or unity power factor, depending on the excitation of the rotor windings.

**5. Applications:**
   - They are commonly used in large power plants where they are connected to the grid, such as hydroelectric, thermal, and nuclear power plants.

**6. Excitation:**
   - They require an external excitation system to provide the necessary current to the rotor windings to maintain the magnetic field.

### Asynchronous Generator (or Induction Generator)

**1. Operating Principle:**
   - An asynchronous generator operates at a speed slightly higher than the synchronous speed of the rotating magnetic field in the stator. This difference in speed is called slip. The rotor of an asynchronous generator does not rotate in synchronization with the stator's magnetic field.

**2. Rotor and Stator:**
   - The rotor of an asynchronous generator is usually a squirrel-cage type or wound rotor. The stator generates a rotating magnetic field, which induces current in the rotor.

**3. Speed and Frequency:**
   - The speed of an asynchronous generator varies with the load and is always slightly higher than the synchronous speed. The slip (the difference between the synchronous speed and the rotor speed) changes with the load.

**4. Power Factor Control:**
   - Asynchronous generators generally have less control over the power factor compared to synchronous generators. They are more often used in applications where power factor control is less critical.

**5. Applications:**
   - They are often used in wind turbines and small-scale hydroelectric plants. They are well-suited for applications where the generator can run at varying speeds.

**6. Excitation:**
   - Asynchronous generators do not require an external excitation system. They can generate power without needing an external source of magnetizing current.

### Summary

- **Speed and Synchronization:** Synchronous generators operate at a constant speed synchronized with the grid frequency, while asynchronous generators operate at variable speeds slightly above the synchronous speed.
- **Power Factor Control:** Synchronous generators can control the power factor, whereas asynchronous generators have less flexibility in this regard.
- **Excitation:** Synchronous generators require an external excitation system; asynchronous generators do not.

Each type of generator has its advantages and is chosen based on the specific requirements of the application, such as the need for speed control, power factor correction, or the nature of the power generation source.

Answer 2

The main difference between a **synchronous generator** and an **asynchronous generator** (also called an induction generator) lies in how they operate and maintain their speed in relation to the power grid's frequency.

### 1. **Synchronous Generator**:
   - **Speed Relation**: The rotor of a synchronous generator spins at a speed that is directly proportional to the frequency of the electrical grid. This is called **synchronous speed**. The rotor and the magnetic field rotate at the same speed.
   - **Working Principle**: It uses a DC current in the rotor winding to produce a magnetic field, and this field rotates in sync with the grid's frequency.
   - **Excitation Requirement**: Requires an external DC supply (excitation) for the rotor to maintain the magnetic field.
   - **Power Factor Control**: Can supply both active and reactive power, allowing control of power factor.
   - **Applications**: Used in large power plants where a stable frequency is critical, like hydroelectric and thermal power stations.

### 2. **Asynchronous Generator (Induction Generator)**:
   - **Speed Relation**: The rotor of an asynchronous generator spins at a speed slightly different (usually faster) than the synchronous speed. This difference is called **slip**.
   - **Working Principle**: It operates by utilizing the slip between rotor speed and stator field to induce current in the rotor, hence it doesn’t require an external excitation source for magnetic fields.
   - **Excitation Requirement**: Does not need a separate DC excitation as the magnetic field is induced by the rotating stator.
   - **Power Factor Control**: Cannot independently control reactive power, so it usually absorbs reactive power from the grid.
   - **Applications**: Commonly used in wind turbines and small-scale power generation where fluctuations in speed are acceptable.

### Summary:
- **Synchronous Generator**: Operates at a constant speed (synchronous speed), requires external excitation, and can control reactive power.
- **Asynchronous Generator**: Operates at varying speeds, doesn’t require external excitation, and typically consumes reactive power from the grid.