Importance and Operation Sequence of Isolator, Circuit Breaker, Earthing Switch

Isolator, Circuit Breaker, Earthing Switch

Today we are going to know what is the Function and importance of Isolator, Circuit Breaker, and Earthing Switch in Electrical Transmission and Distribution Lines. Also, we will see what is the proper sequence of operation of the Isolator, Circuit Breaker, and Earthing Switch, because we cannot operate or ON/OFF them in any manner.

What is Isolator?

An isolator is nothing but a switch that is designed to open or break an electric circuit under No load conditions. Breaking of an electrical circuit by the Isolator is more secure than Circuit Breaker. We can also open or break the circuit with the Circuit breaker but it is not more secure because of the closing and breaking mechanism cannot see directly. After OFF the circuit breaker, current may flow for the ARC phenomenon.

What is Circuit Breaker?

A circuit breaker is a device that breaks the circuit automatically under fault conditions. It can be operated manually to close or open a circuit under normal conditions. Circuit breakers are mainly used to close or open a circuit when the load is connected (that means when the circuit carries current).

The other properties of the Isolator and Circuit breaker are given in the below comparison table,

Difference Between Isolator and Circuit Breaker:

SL NO.	Isolator	Circuit Breaker
1.	An isolator is a switch that is designed for No-Load operation.	A circuit breaker is a device that is designed for On load operation.
2.	The isolator cannot break the circuit when faults occur	The circuit breaker can break the circuit when faults occur
3.	There is no ARC is produce in the Isolator as it operated at No load condition.	ARC is produced in the Circuit Breaker as it operated at On Load condition.
4.	Isolators are operated manually	Circuit breakers are operated automatically as well as manually
5.	There is no Relay is required for the operation of the Isolator.	The circuit breaker cannot work without Relay.
6.	Generally, the breaking capacity of the Isolator is very low.	The breaking capacity of the circuit breaker is very high.

What is Earthing Switch?

Earthing switch is used to ground the residual charge in power lines after disconnecting the line from the source. When a circuit is broken or opened by the circuit breaker and Isolator, there is a residual charge remaining in the circuit. So to discharge the charge Earthing switch is used.

In normal conditions, the isolators and circuit breakers are closed but the earthing switch is closed. During the maintenance period, the circuit breakers and isolators are kept open, and earthing switch is kept closed.

In the Substations circuit breakers, isolators, and earthing switches are connected. For the maintenance or any other purpose if we need to open or break the circuit then we should follow a proper sequence for the operations of circuit breakers, isolators, and earthing switches. If we follow the wrong sequence then it will be a danger for us as well as equipment and circuits.

The sequence of operation of the Isolator, Circuit Breaker, and Earthing Switch:

While we opening a circuit we should follow the below sequence,

So, First, the Circuit Breaker should be open, then the isolator should be open and at last, the earthing switch is to be closed.

While we closing a circuit we should follow the below sequence,

So, first, the Earthing Switch is to be open, then the isolator is to be closed and at last, the circuit breaker is to be closed.

What happened if we open the isolator before the circuit breaker?

We know that the Isolator is designed to operate under no load conditions, so if we open the isolator before the circuit breaker, that means we open the isolator under live conditions. So there will be huge sparking between the contacts of the Isolator which is very dangerous for us.

Understanding the sequence with an Example:

Here a circuit diagram of 11KV/400V substation is shown. Here is one incoming line and two outgoing lines. Suppose we need to the maintenance of the Transformer of the second outgoing line.

So for the maintenance, first the transformer is to be disconnected from the circuit. So below sequence should be followed,

1. First circuit breakers A, B should be open.

2. Then the isolators C and D should be open.

3. Then the earthing switches E and F should be closed.

Now after completing the maintenance, to connect again the Transformer to the line we should follow the below sequence,

1. First Open the earthing switches E and F

2. Then close the isolators C and D

3. Then close the circuit breakers A and B

Read Also:

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• Main Purpose of Using Neutral Grounding Resistor
• Different Types of Protection for Capacitor Bank Explained
• List of Overvoltage Protection Devices and Their Function
• Series and Shunt Reactor Difference, Applications, Use

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