The document outlines the importance of switchgear and protection in modern electrical energy management systems, detailing their roles in normal operations and during fault conditions. It defines key components of switchgear, such as circuit breakers, fuses, and lightning arresters, and explains their functions in protecting and managing electrical power systems. The document also covers the fault-clearing process of circuit breakers and the significance of arc suppression for safe and efficient operation.

1. Switchgear And Protection

2. Introduction
• Electrical energy management system ensures supply of energy to every customers at all time at rated
voltage, rated frequency and specified waveform.
• Switchgear, protection and network automation are integral part of modern energy management
system.
• Switchgear and protection/control panels are installed at each voltage level for:
Normal switching, control and monitoring and
Automatic switching during abnormal and faulty operating conditions such as short circuits, under
voltage, overloads.

3. Electrical Switchgear
• Definition of Switchgear
• A switchgear or electrical switchgear is a generic term
which includes all the switching devices associated with
mainly power system protection. It also includes all
devices associated with control, metering and
regulating of electrical power system. Assembly of such
devices in a logical manner forms a switchgear. This is
very basic definition of switchgear.

4. Electrical Switchgear

5. SWITCHGEAR AND PROTECTION
Switchgear protection plays a vital role in modern power
system network, right from generation through
transmission to distribution end. The current interruption
device or switching device is called circuit breaker in
Switchgear protection system.

6. Type of faults
 Single line to ground fault
 Line to line fault
 Double line to ground fault
 Open circuit fault
 Three phase fault
 Simultaneous fault

7. Sr. No Switchgear Equipment Function
1. Fuse To Protect circuit against over current and short circuit currents.
2. Circuit breaker To make or break the circuit manually or remotely under normal
condition and automatically under fault condition.
3. Isolator To disconnect the part of the system for maintenance from live
circuit under no current condition.
4. Earthing Switch To discharge the voltage on the line ( due to charges of line
capacitance to earth) after disconnecting line from live section.
5. Lightning arrester To divert high voltage surge towards the earth, due to lighting stroke
or switching surges.
6. Current transformer To stepping down the magnitude of current for measurement,
protection and control.
7. Potential transformer To stepping down the magnitude of line voltage for measurement,
protection and control.
8. Relay To disconnect the abnormally operating part so as to prevent the
subsequent faults eg. Overload protection of a machine protects the
machine and prevent insulation failure.

9. Lightening Arrestor
• A lightning arrester is a device used on electrical systems and telecommunication systems to protect the insulation and
conductors of the system from the damaging effects of lightning. The typical lightning arrester has a high voltage terminal and a
ground terminal.
• When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from
the surge is diverted through the arrestor, in most cases to earth.
• In telephony, a lightning arrestor is placed where wires enter a structure, preventing damage to electronic instruments within
and ensuring the safety of individuals near them. Smaller versions of lightning arresters, also called surge arrestors, are devices
that are connected between each conductor in power and communications systems and the Earth. These prevent the flow of the
normal power or signal currents to ground, but provide a path over which high-voltage lightning current flows, bypassing the
connected equipment. Their purpose is to limit the rise in voltage when a communications or power line is struck by lightning
or is near to a lightning strike.
• If protection fails or is absent, lightning that strikes the electrical system introduces thousands of kilovolts that may damage the
transmission lines, and can also cause severe damage to transformers and other electrical or electronic devices. Lightning-
produced extreme voltage spikes in incoming power lines can damage electrical home appliances or even produce death

10. Switch gear - It's function
SWITCHGEAR : Gear for Switching
Switching Devices Control & Sensing Devices Decision Making Devices
Circuit breakers
Isolators
Switches
Current Transformers;
Voltage Transformers;
Reactors;
Tripping Units.
Protective Relays
Lightning Arresters
Fuses

11. FAULT-CLEARING PROCESS OF A
CIRCUIT BREAKERS
• If we consider a fault occurrence and clearing process of a circuit breaker,
the following order or sequence of operation is observed.
• FAULT OCCURS: As the fault occurs, the fault impedance being low, the
currents increases and the relay gets actuated. The moving parts of the relay
move because of the increase in the operating torque. The relay takes some
time to close its contacts.

12. • RELAY CONTACT CLOSES: The relay contacts closes the trip – circuit of
the circuit breaker and the trip-coil is energised from the control voltage
supply from a battery bank of tripping unit.
• OPERATING MECHANISM OPERATES:
As the trip – coil is energized, which enables the actuation of the operating
mechanism for the opening operation to separate the circuit breaker
contacts.
FAULT-CLEARING PROCESS OF A
CIRCUIT BREAKERS

13. • ARCING: Arc is drawn between the separating contacts, because the
charged electrons surrounding the separating contacts tries to re-establish
potential between the contacts.
• When a fault occurs in the protective
circuit, relay connected to CT and PT
actuate and close its contacts. Current
flows from battery in trip circuit. As the
trip coil is energized the cb operating
mechasm is actuated and it operates for
opening operation.

14. • CLEARANCE: ISOLATION: The arc is extinguished in the
circuit breaker by appropriate suitable techniques at some natural
currents zero of a.c. wave. The process of current interruption is
completed when the arc is extinguished, current reaches final zero
value and the arc does not restrike again. The fault is said to be
cleared.

15. Arc in Circuit Breaker
What is arc ?
• During opening of current carrying contacts in a circuit
breaker the medium in between opening contacts become
highly ionized through which the interrupting current gets
low resistive path and continues to flow through this path
even the contacts are physically separated. During the
flowing of current from one contact to other the path
becomes so heated that it glows.This is called arc.

16. • Whenever, on load current contacts of circuit breaker open there is an arc
in circuit breaker, established between the separating contacts.
• As long as this arc is sustained in between the contacts the current
through the circuit breaker will not be interrupted finally as because arc is
itself a conductive path of electricity.
• For total interruption of current the circuit breaker it is essential to quench
the arc as quick as possible.
• The main designing criteria of a circuit breaker is to provide appropriate
technology of arc quenching in circuit breaker to fulfill quick and safe
current interruption. So before going through different arc quenching
techniques employed in circuit breaker, we should try to understand the
basic theory of arc in circuit breaker.

17. Electrical Circuit Breaker
 Definition of Circuit Breaker : -
Electrical Circuit Breaker is a switching device which can be
operated manually as well as automatically for controlling and
protection of electrical power system respectively. As the modern power
system deals with huge currents, the special attention should be given
during designing of circuit breaker to safe interruption of arc produced
during the operation of circuit breaker. This was the basic definition of
circuit breaker.
 Types of Circuit Breaker
1) Oil Circuit Breaker
2) Air Circuit Breaker
3) SF6 Circuit Breaker
4) Vacuum Circuit Breaker