Buchholz Relay for Power Transformer Protection Device

How does a Buchholz Relay Protect Power Transformer?

A Buchholz relay is a protective device used to protect power transformers from internal faults and incipient failures. It is an essential component of a power transformer's protection and monitoring system. The Buchholz relay operates on the principle of detecting abnormal conditions within the transformer's oil-filled tank. Here's how it works and how it protects power transformers:

Automatic Transfer Switch Diagram And Operation Procedure

What Is Transfer Automatic Transfer Switch and How Does Work?

A transfer switch is nothing but an electrical device that allows transferring of electrical flow safely from multiple sources to load. On the other way, the load can trans-receive electrical energy from multiple sources safely.

To prevent a power outage from the main utility power supply a transfer switch can take power from an alternate utility source or standby generator source or even an emergency power backup source.

Transfer Switch can operate automatically as soon as a failure of the main source or after a certain period of time to reinstate the main source. This type of transfer switch is known as Auto Transfer Switch or in short ATS.

Another Transfer Switch is known as a manual transfer switch which operates manually. When the utility power goes out, it simply needs to plug the alternate source into the transfer switch to start it up and flip the transfer switch from the main source position to the alternate source position.

In very basic, transfer switches are two types-

1. Auto Transfer Switch, &
2. Manual Transfer Switch.

In common transfer switch is known as ATS or Change Over Switch.

What is the main feature of ATS (Automatic Transfer Switch)?

The principal purpose of an ATS (Automatic Transfer Switch) is to ensure the continuous delivery of electrical power from one of two power sources to a connected load circuit. 

The main elements of an ATS are-

01. Normal grid supply;

02. Emergency supply.

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Why Transfer Switch Is Needed

You can use your generator power in your home to feed your TV, Refrigerator, or Internet while utility power or main power is outage, just change over the switch from utility to generator. Life becomes easier and faster;

In industry, each minute is seeking production. To continue a production chain break-less, the uninterrupted power supply is very essential, and ATS takes a vital role in this case;

In data processing or data storage centers, a continuous power supply is essential to back up important data. ATS plays the main rules in keeping the power supply alive;

Signal controlling stations like airports, metro, fire-department, defiance, etc. need a troubleless power supply to transfer important information; ATS needs to ensure uninterrupted power supply;

In the hospital, so many life-supporting types of equipment are operating and can not be off for a moment. ATS works to continue the life-supporting power supply.

Wiring Diagram for Change Over Switch or Transfer Switch

In the schematic line, the diagram shows how to wire the Transfer Switch with the main service disconnect switch for the utility power source and generator power source along with your load disconnecting circuit breakers.

Here, in Line-1 & Line-2, the neutral and grounding connection is shown perfectly which will help to work with your own job.

This is not followed by any specific regulation, this is demonstrated just to improve your basic knowledge. Before performing your practical job must follow the local safety rules and regulations. 

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Transfer Switch Operation Modes

A Transfer switch has the ability to operate in different modes of operation. In a given mode of operation, the transfer system will respond in a given way to changing system conditions. The transfer system will respond differently to the selection of different modes of operation.

The basic mode of operation of a transfer switch is as below:

01. Manual Mode;

02. Automatic Mode.

Manual mode: Selected via a selector switch position or other pre-determined user input via the user interface into manual mode position, the automatic mode will be inactive and the switch will able to operate manually.

 Automatic Mode: When the sector switch is selected in automatic position or other pre-determined user input via the user interface. The switch will be able to act in automatic mode.

What is the nominal capacity of an ATS?

The nominal capacity of an ATS (Automatic Transfer Switch) is designed to meet the continuous current carrying capacity from 30-4000 amperes. Typically, the most commonly used ampere ratings include 30, 40, 70, 80, 100, 150, 225, 260, 400, 600, 800, 1000, 1200, 1600, 2000, 3000, and 4000 amperes.

Why Earthing Switch or Disconnector is Used in Transmission Line?

How Earthing or Disconnector Switch Play Rule to Personnel Safety Even in a Isolated Disconnected Line? 

The function of earth or disconnector switch is to discharge the capacitive voltage that stored in generator side or long transmission line conductors in the isolated system just after opening the CB (Circuit Breaker) and Isolator.

So, we understand that the main purpose of earth switch is to ground the isolated bus/conductor. Generally earth switch is mechanically interlinked with isolator. Means when isolator opens the circuit then earth-switch closes & vice-vars.

When earth switch is connected to the isolated but charged system it discharges the stored energy to earth, so that maintenance work can be carried out either in line on generator side.

So earth switch provides extra safety to the working personnel during transmission line maintenance.

You may interrelated to read:

01. What is the Function of Earthing or Grounding Transformer?

02. Equipment Grounding for De-energized Construction and Maintenance.

In my practical experiences I found three cases regarding the necessity of earthing in dead line too.

Case-1:

When the line crews working a dead line where parallel another line is alive. The line crews experienced the voltage exist and they felt some electrical shook.

Case-2:

When we construct parallel two circuits high voltage transmission line and energized a single circuit first. We found that other circuit also experiencing around 1kV in control panel metering system. This happened due to induced voltage.

Case-3:

When we construct a long overhead transmission and it was causing electric shook before touching with any energized line. Finally we discovered the voltage developed in it due to conductor capacitive behavior.

When Earthing Switch or Disconnector Should be Operated?

Operating the earth switch in an energized line may causes sever accident. The condition of earth switch operation is as below;

1. Earth switches should be operated only when the isolators are in open;
2. All earth switches can be operated manually. Semaphore indicator can be seen for position feedback (on/off) in switch yard control panel.

Latest Earth Switch or Dis-connector

What we discussed is for maintenance purpose earth switch mainly, but in latest GIS (Gas Insulated Switch) system switch-gear used automatic high speed earth switch. In this system when any fault occurred the faulty part automatically isolated and earthed by high speed auto earth switch and protect the equipment immediately.