Question

Draw neat sketch of pantograph type of isolator. State the sequence of operation of circuit breaker, isolator and earthing switch while opening and closing.

Answer 1

### Pantograph Type Isolator

A pantograph type isolator is a device used in electrical systems, particularly in substations, to isolate a section of a circuit from the rest of the system. It features a unique design that resembles a pantograph (a device used for drawing or transferring designs), allowing for effective operation in high-voltage applications. Here’s a neat sketch of a pantograph type isolator:

```plaintext
    (Phase Conductor)
           ||
           ||      
           ||    
           ||        ____
           ||      //    \\
           ||____//        \\_____
           ||    //          \\    |
           ||   //            \\   |
           ||  //              \\  |
           || //                \\ |
           ||/                   \|
           ||                     |
           ||                     |
           ||                     |
           ||                     |
           ||                     |
           ||                     |
         __||_____________________||__
       (Isolator Contacts)    (Ground)
```

### Sequence of Operations

Understanding the sequence of operations for a circuit breaker, isolator, and earthing switch is essential in power systems for maintaining safety and ensuring reliability. Here’s how these devices typically operate when opening and closing:

#### 1. **Opening Operation**

- **Circuit Breaker:**
  - The circuit breaker is designed to protect electrical circuits from overloads and short circuits. When an overload condition is detected, it trips and opens the circuit.
  - **Sequence:**
    - The sensing mechanism detects an abnormal condition (overload/short circuit).
    - The trip mechanism is activated, causing the contacts to separate, interrupting the flow of current.

- **Isolator:**
  - The isolator is operated only after the circuit breaker has successfully opened the circuit. It is used to isolate a part of the circuit for maintenance or repair.
  - **Sequence:**
    - Ensure the circuit breaker is open.
    - The isolator is manually operated (or remotely, depending on design) to open the contacts, providing a visible break in the circuit.

- **Earthing Switch:**
  - The earthing switch is used to connect the isolated part of the circuit to the ground, ensuring that any residual charge is safely discharged.
  - **Sequence:**
    - Once the isolator is open, the earthing switch is closed.
    - This connects the isolated equipment to the ground, providing a safe path for any fault currents or residual voltage.

#### 2. **Closing Operation**

- **Earthing Switch:**
  - Before closing the isolator or circuit breaker, the earthing switch must be opened to ensure that the isolated section is not grounded.
  - **Sequence:**
    - The earthing switch is opened, removing the ground connection from the isolated circuit.

- **Isolator:**
  - With the earthing switch open, the isolator can be closed to restore the connection.
  - **Sequence:**
    - The isolator is operated to close the contacts, re-establishing the connection to the circuit.

- **Circuit Breaker:**
  - Finally, the circuit breaker can be closed to restore the circuit.
  - **Sequence:**
    - The circuit breaker is closed, allowing current to flow again into the circuit.

### Summary of the Sequence:

1. **Opening:**
   - **Circuit Breaker** opens → isolates the load.
   - **Isolator** opens → provides a visible break.
   - **Earthing Switch** closes → grounds the isolated section.

2. **Closing:**
   - **Earthing Switch** opens → removes the ground.
   - **Isolator** closes → reconnects the circuit.
   - **Circuit Breaker** closes → restores current flow.

### Conclusion

The pantograph type isolator, along with the circuit breaker and earthing switch, plays a critical role in electrical systems. The sequence of operations ensures safety during maintenance and repair by properly isolating circuits and grounding equipment when necessary. This careful coordination helps to prevent accidents and ensures the integrity of electrical installations.

Answer 2

Sure! Let's break this down into two parts: the sketch of the pantograph-type isolator and the sequence of operation for the circuit breaker, isolator, and earthing switch.

### 1. **Sketch of Pantograph-Type Isolator**

The pantograph-type isolator is used in electrical systems to isolate a section of the circuit for maintenance or safety purposes. Here’s a textual description of its sketch:

- **Base Frame**: A sturdy frame that supports the entire isolator mechanism.
- **Pantograph Mechanism**: This consists of a set of articulated arms that resemble the pantograph used in trains. The arms pivot and slide to open and close the isolator.
- **Isolator Blades**: These are the contact points that open and close to disconnect or connect the circuit. They are typically positioned at the ends of the pantograph arms.
- **Operating Mechanism**: This could be a manual handle or a motorized device that moves the pantograph arms.
- **Insulators**: Positioned between the base frame and the isolator blades to support the isolator and ensure electrical isolation.

For a visual representation, you can imagine the pantograph mechanism looking like a pair of scissors, but with a more complex arrangement of arms and links.

### 2. **Sequence of Operation**

Here’s the sequence of operations for opening and closing an electrical circuit, considering a typical setup involving a circuit breaker, an isolator (like a pantograph-type), and an earthing switch:

#### **Opening Sequence**

1. **Circuit Breaker Operation**:
   - The circuit breaker is first opened to disconnect the live electrical circuit. This step is crucial to ensure that no current flows through the isolator when it is being opened.
   - The circuit breaker typically trips and separates its contacts, effectively isolating the section of the circuit.

2. **Isolator Operation**:
   - Once the circuit breaker is open, the isolator is operated to physically disconnect the electrical circuit. In the case of a pantograph-type isolator, this involves moving the pantograph arms to separate the isolator blades.
   - The isolator should now be fully open, providing a visible gap and ensuring that the section is fully isolated.

3. **Earthing Switch Operation**:
   - After the isolator is open, the earthing switch can be operated. This step involves connecting the earthing switch to the isolated section of the circuit to ground it.
   - This is important for safety, as it ensures that the isolated section is at earth potential, preventing any potential electric shock hazards for maintenance personnel.

#### **Closing Sequence**

1. **Earthing Switch Operation**:
   - Before closing the isolator, the earthing switch should be removed or opened to ensure that the circuit is no longer grounded.
   - This step prevents any potential short circuits or faults when the isolator and circuit breaker are closed.

2. **Isolator Operation**:
   - The isolator is then closed by moving the pantograph arms back to their original position, which allows the isolator blades to come together and reconnect the circuit.
   - Ensure that the isolator is fully closed, with no gaps between the blades.

3. **Circuit Breaker Operation**:
   - Finally, the circuit breaker is closed to restore power to the circuit.
   - The circuit breaker contacts close, allowing current to flow through the now reconnected circuit.

### Summary

- **Opening**: Circuit breaker → Isolator → Earthing switch.
- **Closing**: Earthing switch → Isolator → Circuit breaker.

This sequence ensures that maintenance can be performed safely and that the circuit is properly reconnected when necessary.