The apparatus used for switching, controlling and protecting the electrical circuits and equipment is known as switchgear. The switchgear equipment is essentially concerned with switching and interrupting currents either under normal or abnormal operating conditions. The tumbler switch with ordinary fuse is the simplest form of switchgear and is used to control and protect lights and other equipment in homes, offices etc. For circuits of higher rating, a high-rupturing capacity (H.R.C.) fuse in conjuction with a switch may serve the purpose of controlling and protecting the circuit. However, such a switchgear cannot be used profitably on high voltage system (3·3 kV) for two reasons. Firstly, when a fuse blows, it takes sometime to replace it and consequently there is interruption of service to the customers. Secondly, the fuse cannot successfully interrupt large fault currents that result from the faults on high voltage system. With the advancement of power system, lines and other equipments operate at high voltages and carry large currents. When a short circuit occurs on the system, heavy current flowing through the equipment may cause considerable damage. In order to interrupt such heavy fault currents, automatic circuit breakers (or simply circuit breakers) are used. A circuit breaker is a switchgear which can open or close an electrical circuit under both normal and abnormal conditions. Even in instances where a fuse is adequate, as regards to breaking capacity, a circuit breaker may be preferable. It is because a circuit breaker can close circuits, as well as break them without replacement and thus has wider range of use altogether than a fuse

1. Switchgear Operation
EEE-4822 General Viva Voice
Name: Md. Mobasher Karim
ID: ET183058
Section: 8B
Presented By:
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2. Table of Contents
 Introduction
 Essential Features of Switchgear
 Working
 Components of Switchgear
 Functions of Switchgear
 Switchgear Types
 Questions
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3. Introduction
 A device that is used to switch, control and protect the circuits as well as
devices. This is anxious about switching as well as interrupting currents under
different operating conditions like normal or abnormal. In an electric power
system, it is an arrangement of electrical disconnect switches, circuit
breakers, fuses which are used to protect, control & separate electrical
device. The switchgear diagram is shown below.
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4. Essential Features of Switchgear
i. Complete reliability:
 Increasing capacity of generating stations.
 Switchgear is added to the power system to improve the reliability.
 When fault occurs on any part of the power system, the switchgear must operate
to isolate the faulty section from the remainder circuit.
ii. Absolutely certain discrimination: When fault occurs on any section of the
power system, the switchgear must be able to discriminate between the
faulty section and the healthy section.
iii. Quick operation: When fault occurs on any part of the power system, the
switchgear must operate quickly so that no damage is done to generators,
transformers and other equipment by the short-circuit currents.
iv. Provision for manual control: A switchgear must have provision for manual
control.
v. Provision for instruments: There must be provision for instruments which
may be required.
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5. Working
 Switchgear includes switching & protecting devices like fuses, switches,
relays, circuit breakers, etc. This device allows operating devices like
electrical equipment, generators, distributors, transmission lines, etc. Once
the short circuit occurs within the power system, then a huge current will
flow through the devices. So that the equipment can be damaged & the
interruption will occur to the operators. To overcome this problem, it is used
to detect the fault in the power system. In this way, this is works to protect
the equipment from the damage.
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6. Components of Switchgear
 It includes two components namely power conducting and control systems.
The components of power conducting include fuses, switches, circuit
breakers, lightning arrestors which are used for interrupting the flow of
electric power.
 Control systems like control panels, transformers like potential, current
protective relays & connected circuitry that controls, monitors & protect the
components of power conducting.
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7. Functions of Switchgear
The main functions of this equipment include the following.
 It protects the equipment from short-circuits & fault currents.
 This device gives isolation to the circuits from power supplies.
 It increases the availability of the system by allowing more than one source to
feed a load.
 It can open & close the electrical circuits under the conditions of normal &
abnormal.
 In normal conditions, it can operate manually so it ensures the safety of the
operator & also proper electrical energy utilization.
 In abnormal conditions, it operates mechanically. Once a fault happens this device
detects the fault & detaches the damaged part in the power system. So it protects
the power system from damage.
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8. Switchgear Types
There are three types of switch gears namely LV (Low voltage), MV (Medium voltage)
and HV (High voltage) Switchgear.
1. Low Voltage Switchgear (LV): The power system which deals up to 1KV is called as
LV or low voltage switchgear. This kind of equipment mainly includes switches, LV
circuit breakers, HRC fuses, earth leakage (EL) circuit breakers, offload electrical
isolators, MCBs (miniature circuit breakers) and MCCBs (molded case circuit
breakers), etc.
2. Medium Voltage Switchgear (MV): The power system which deals up to 36 kV is
called MV (medium voltage switchgear). These are available in different types like
without metal enclosure outdoor type, metal-enclosed indoor & outdoor type, etc.
This kind of equipment includes substation devices like minimum oil CBs, bulk oil
CBs, SF6 gas-insulated, air magnetic, gas-insulated, vacuum, etc.
3. High Voltage Switchgear (HV): The power system which deals above 36KV is called
HV (high voltage) switchgear. When the level of voltage increases then the arcing
will be generated as the switching operation is extremely high. As a result, during
the designing of this equipment, special care has to be taken. The main
component of this equipment is the High Voltage (HV) circuit breaker.
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9. Switchgear Types (Continued)
Low Voltage Switchgear (LV) Medium Voltage
Switchgear (MV)
High Voltage
Switchgear (HV)
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10. Questions
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