Switchgear and protection

In this modern era, Switchgear and protection become a important aspect of power system, as demand of electrical energy has increased very much. Electrical energy is much needed in almost every field and purposes like heating, lighting, industries, hospitals, domestic applications, and electric traction (term used for electric trains).

Therefore, In order to provide such a large amount of electrical energy efficiently, three things switching, controlling and protection should be taken care of ,otherwise if there is a failure in transferring the energy, then it may cause damage to appliances and equipment of power system. so we have to introduce Switchgear.

I will also provide you switch and protection handwritten notes.

Definition of switchgear

The apparatus and method use for switching, controlling and protection of the electrical circuits and equipment is known as switchgear and protection.

During the normal operation of power system, switchgear (fuse, circuit breaker, relay etc.) permits to switch-off or switch-on the generators, transmission lines, distributors, and other electrical equipments.

If a failure occurs on any part of power system for example: a short circuit, then a heavy current will pass through the equipment and it can aslo damage the equipment or can interrupt the service to costumers.

Therefore, to protect the system and equipment from such failures, we install switchgear which detects the fault and prevent the healthy part of system.

I have also made videos on Switchgear and protection in detail on my youtube channel.

Features of switchgear

  1. Complete reliabilityBy the term Reliability we mean how smooth or trustworthy a system is , it means whenever a fault occurs on any part of the power system, the switchgear must operate in order to isolate the healthy part of system from faulty section. If a system is less reliable then it may or may not operate during a fault, whereas if a system is highly reliable, then it will definitely operate as soon as a fault occur.
  2. Quick operationwhenever a fault occurs on any part of the power system, the switchgear must operate very quickly to prevent various equipment of power system like transformers, and other electrical appliances.
  3. Discrimination It must be able to discriminate between the faulty section and healthy section accurately. A smart switchgear will discriminate automatically and accurately.
  4. Provision for instruments and manual control It has to be adaptive , if any instrument needs to be installed like voltmeter, ammeter. Then, it must also have a provision for manual control on switching and controlling.

Switchgear and protection Equipments

There are various types of switchgear and protection devices in power system. See our further post also for detailed knowledge of these devices.

Switches :

A switch is a static device, which is use to open or close an electrical circuit in a convenient way. You may have seen switches at homes, industries, etc. they all comes in category of switchgear. But there are more types of Switches of which you might not yet aware, We will discuss them all, Switch can be classified into

  1. Air break switch : they operate in air, means no medium is needed for them.
  2. oil switches: they operate in a oil, which is use to quench (finish) the arc that occurs when joints of switch got separated.

Use of switch is limited to a particular range, we can not use switch for large voltage range. Also, operation of a switch is not automatic. It is manual, It means when a fault occur then we have to open the switch manually in order to prevent the switch. This is a big disadvantage as it may damage the precious appliances and equipment.

we will discuss them in next blog and on our YouTube channel also in detail

Fuses :

A fuse is a thin piece of wire, which melts when excessive current flows through it for sufficient time. It is basically inserted in series with the circuit which is to be protected.

Under normal condition, the fuse element is at a temperature below its melting point (it means that it will not melt upto that temperature) therefore, it carries the normal load current without over heating.

However, when a short circuit or any fault occurs the current through the fuse becomes high and the wire gets melted due to overheating and hence it trips the circuit and prevent the healthy part from faulty section.

Once a fuse gets used in a fault, then we have to replace it with the new one. This is the big disadvantage of a fuse that it can not recover automatically.

There are many types of fuse which we will discuss in upcoming sections. Read the detailed working and explanation of fuse here : Types of fuses and their uses

Circuit breakers :

As far, we have studied that switch can disconnect the circuit but it is done manually.

A Fuse disconnects the circuit automatically but it will not connect the circuit again and service to the costumer will be interrupted until the next fuse is employed.

So we want a equipment which can do switching automatically and manually when a fault occurs, and also able to connect the circuit automatically when a fault removed, hence circuit breakers gets introduced.

Oil circuit breaker
132kV oil filled circuit breaker

A circuit breaker is an equipment which can open or close a circuit under all conditions like no load, full load and fault conditions. A circuit breaker can operate both manually and automatically.

Manually under normal conditions for maintenance and other work, and automatically under fault conditions.

Circuit breaker can operate under high voltages. there are many type of circuit breakers like air circuit breaker, oil circuit breaker, vacuum circuit breaker, SF6 . we will all discuss them in detail in upcoming post.

under normal conditions for maintenance and other work, and automatically under fault conditions. circuit breaker can operate under high voltages. there are many type of circuit breakers like air circuit breaker, oil circuit breaker, vacuum circuit breaker, SF6. . We have discussed them one by one in detail in upcoming sections. please check other post aslo.

Relays :

Relay is basically a device or switch which detects the fault in the system, then it provides the information to circuit breaker. So that a circuit breaker can operate to prevent the healthy parts from faulty section.

Primary side of a relay is connected to a current transformer. Secondary side of current transformer is connected to the operating coil of relay as shown in fig. below.

When the faulty current comes, the value of current in the primary as well as in the secondary side of Current transformer increases. Hence, the operating coil of Relay gets energized and it closes the trip circuit by pulling the rod below and this completes the circuit. Now the Trip circuit is in operating condition with the connected battery. Now the trip coil will also gets energized and it will pull the rod toward it, which is connected to circuit breaker for completing the circuit. But now the connection through the circuit breaker will get open and it will interrupt the flow of current.

Relay trip circuit

There are many types of relays electromagnetic relay, induction relay etc. we will discuss them in a separate section.

Types of Switchgear

There are two types of Switchgear:

  1. Outdoor type
  2. Indoor type

Outdoor type

For voltages beyond 66kV, switchgear Equipment installation is done outdoor. Because for such high voltages, the clearance between conductors and the equipments such as switches, circuit breakers, transformers and other equipment is large. A sufficient gap should be there between conductors and other switchgear equipments.

Outdoor type switchgear arrangement
Outdoor type switchgear arrangement

Indoor type :

For voltages below 66kV, Indoor type switchgear are install due to economic considerations. It is a metal clad type in which all live parts are completely enclose in an earthed metal casing.

Indoor type switchgear arrangement
Indoor type switchgear arrangement

We have seen the introduction of switchgear and protection. We have created a full playlist, on our youtube channel in Hindi and English both.