Switchgear By Dr. Nivedita Singh

1. Switchgear &
Maintenance

2. SWITCHGEAR
switchgear is the combination of
electrical disconnect
switches, fuses or circuit breakers used
to control, protect and isolate electrical
equipment. Switchgear is used both to
de-energize equipment to allow work to
be done and to
clear faults downstream.

3. Switchgear

4. Types:
LV Switchgear
MV Switchgear
Generally electrical
switchgear rated upto 1 KV is
termed as low voltage switchgear
The most common use of LV
switchgear is in LV distribution
board.

7. THE ROLE OF SWITCHGEAR IS :
ELECTRICAL PROTECTION
SAFE ISOLATION FROM LIVE PARTS
LOCAL OR REMOTE SWITCHING
The basic functions of
Switchgear

8. Periodic Maintenance
Preventive Maintenance
a) 2 yearly Maintenance
b) 4 yearly Maintenance
Importance Of PM
Through such PM, troubles can be detected in the
Early stages and corrective actions can be taken
before extensive damage occurs.

9. The most common use of LV switchgear is in
LV distribution board.
This system has the following parts
Incomer
The incomer feeds incoming electrical
power to the incomer bus.
The switchgear used in the incomer should
have a main switching device.
The switchgear devices attached with incomer
should be capable of withstanding
abnormal current for a short specific duration
in order to allow downstream devices to
operate.
Generally Air Circuit Breakers are preferably
used as interrupting device.
Sub – Incomer
These sub – incomers draw power from main
incomer bus and feed this power to feeder bus
Feeders
Different feeders are connected to the feeder
bus to feeds different loads like, motor loads,
lighting loads, industrial machinery loads, air
conditioner loads, transformer cooling
system loads etc.

10. Main Transformer Incomer

11. Main Components Of Switchgears

12. Busbar
Busbar is a strip or bar of copper, brass or aluminium that conducts
electricity within a switchboard, distribution board, substation,
The cross-sectional size of the busbar determines the maximum amount
of current
Used to interconnect the loads and sources of electrical power.

13. Busbar Specification
Manufacturer: Nova Magrini Gallilio
Type of Busbar : Copper ( Insulated with Silver coated joints)
Busbar Rating : 1500 Amp
Method Of Cleaning : Clean with Lint Free Cloth
Busbar Dimensions : 2*100*8 mm
Busbar Maintenance
Full Bus Bar Inspection check for overheating signs, visual
inspection of Cu plate and nut bolts. cleaning of incoming/outgoing
spouts.
Remove dust with vacuum cleaner.
Cleaning and lubricating mechanical links with contact grease.
Check operating mechanism of shutter.
Contact Resistance of Electrical joints.
Check IR to earth and between phases on busbar and outgoing
circuits @ 2500V

18. Air Circuit Breaker (ACB)
A circuit breaker is an automatically operated electrical switch designed to protect
an electrical circuit from damage caused by overload or short circuit. Its basic
function is to detect a fault condition and interrupt current flow

19. This type of circuit breakers, is those kind
of circuit breaker which operates in air at
atmospheric pressure.
 ACBs are still preferable choice up
to voltage 15 KV
It is also good choice to avoid the risk of oil fire,
in case of oil circuit breaker.
Operation Of ACB
The first objective is usually achieved by forcing
the arc into contact with as large an area as
possible of insulating material. Every air circuit
breaker is fitted with a chamber surrounding the
contact. This chamber is called ‘arc chute’. The
arc is driven into it. If inside of the arc chute is
suitably shaped, and if the arc can be made
conform to the shape, the arc chute wall will help
to achieve cooling.

20. Air Circuit Breakers : Charging method
Circuit breaker closing springs may be compressed manually or by means
of a small electric motor.
The closing coil is charged by manual charging handle. For closing, first
charge the spring by using the charging handle

21. Maintenance of Air Circuit Breaker
LV Circuit Breakers operating at 600 volt and
below, should be inspected
Maintained every 1 to 4 years depending on their
services and operating
Conditions.
Conditions that make frequency maintenance and
inspection are necessary:
High humidity and High temp
Dusty or Dirty Atmosphere
Corrosive Atmosphere

22. Inspection & Cleaning
Insulating parts including bushing should be cleaned
of dust
Clean & inspect Arc Chutes for Cracks, Broken Parts
. Replace Damage Parts
Inspect Breaker Operating Mechanism for loose
hardware & missing or broken etc
Examine for wears
Check Rack in/ out mechanism for normel operation
Lubricate if necessary
Check tightness of all terminations
Contacts maintenance
Arcing contacts to be verified for burn off
To be adjusted or exchanged that arc contacts
simultaneoslu when closing
Permissible tolerance 1mm
Adjust lead of arcing contacts from main contacts such
that when arc contacts
Meet then distance between

23. Insulation Resistance Test (Megger)
Load and line conductors should disconnected from the breaker to make
Test. IR between phases and phases w.r.t ground with breaker closed.
the result is compared against manufacturer/ pervious data
For breaker being tested.
Cycling the breaker
On & Off the breaker several times to check the correct operation
Of breaker.
Verify For Loop Check
Insert circuit breaker at test position and on & off the breaker
from remote location

24. Current Transformer
A current transformer (CT) is used for
measurement of alternating electric
currents

25. Current transformer are used in electrical power system for stepping down
currents of the system for metering and protection purpose.
power
A CT functions with the same basic working principle of electrical
transformer
CT steps down rated system current to 1 Amp or 5 Amp.
Because the relays and meters are generally designed for 1 Amp, 5 Amp and
110V

26. Relay
Relays is automatic device which senses an abnormal condition of
electrical circuit and closes its contacts. these contacts in turns close
and complete the circuit breaker trip coil circuit hence make the circuit
breaker tripped

27. Protective Relay Testing
Why do we use protective relays?
Their main duty is to isolate a faulty section within few cycles
Periodic Maintenance Testing
After a relay is commissioned it’s important to carry out regular
maintenance tests.
Some of the advantages of such testing can be stated as, it will pin point
a defective relay before it fails to act during a fault
Methods of Testing
Steady State: steady state testing is for checking the relay pick up.
Injected current, voltage. when the current is raised and then
fluctuated around pick up.
Dynamic state Time for relay operation is measured.

28. Freja 300
The FREJA 300 relay testing system is a computer-aided relay testing
system by injecting current and voltage.

29. Testing Principles
There are two main principles as primary injection and secondary
injection.
• Primary injection- High current is injected to primary side of
the CT. Test carried out covers CT, conductors, relay and
sometimes circuit breaker as well. The relay unit has to be
isolated from the power system. Usually this principle is used at
commissioning and also if the secondary of the CT is not
accessible.
• Secondary injection - Relay is disconnected from the CT and
the stepped down current is
directly injected to relay.

30. General Precautions to be taken
Check the Electrical Isolation First
During maintenance Earth MUST be connected
Before maintenance of breaker spring must be discharge.
Don’t use compressed air on breaker
Don’t use file or emery paper for contacts cleaning
Inspection Inside Switchgear Room
Switchgear environment (switch room access and surrounds,
including fence and external walls if outdoors.
Signs of water
Signs of unauthorized access
Condition of firefighting equipment and warning notices
General Housekeeping