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 Line. Also, we will see what is the proper sequence of operation of 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 which is designed to open or break an electric circuit under No load condition. Breaking of an electrical circuit by the Isolator is more secure than Circuit Breaker. We can also open or break the circuit by 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 which breaks the circuit automatically under fault conditions. It can be operated manually to close or open a circuit under normal condition. Circuit breaker mainly used to close or open a circuit when the load is connected (that means when the circuit carrying current).

The other properties of 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 which is designed for No-Load operation.	A circuit breaker is a device which 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 Isolator.	The circuit breaker cannot work without Relay.
6.	Generally, the breaking capacity of the Isolator is very low.	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 source. When a circuit is broken or open 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 condition, 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 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 Isolator, Circuit Breaker, and Earthing Switch:

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

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

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

We know that the Isolator is designed to operate under no load condition, so if we open the isolator before the circuit breaker, that means we open the isolator under live condition. 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 line. 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 complete 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:

• Application, Advantages, and Disadvantages of all types of Circuit Breaker
• Working and connection diagram of Single Phasing Preventer.
• All about Current Transformer(CT) and Potential Transformer(PT)
• Which side of Transformer is provided for Tapping and Why?All reasons explained.
• [Three Reasons] Why Transformer is Rated in KVA - Full Explained
• Direct Online Starter[DOL Starter] Diagram Full Explained
• Why we use 220V, 50Hz AC at home instead of DC or other voltage?Full Explanation.

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