A substation is a critical component of electrical generation, transmission, and distribution systems that facilitates voltage transformation and power flow management. Key components include transformers, circuit breakers, isolators, current transformers, and earthing systems, each fulfilling specific roles in safety and operational efficiency. Various bus systems such as single bus, double bus, and ring bus configurations enable varying levels of flexibility and reliability in maintaining power distribution without interruptions during maintenance.

1. SUBSTATION
COMPONENTS

2. WHAT IS SUBSTATION…?
 A substation is a part of an electrical generation, transmission,
and distribution system.
 Between the generating station and consumer, electric power may flow
through several substations at different voltage levels.

3.  Transmission substation
 Distribution substation
 Converter substations
 Switching substation
 Classification by insulation
 Classification by structure
CLASSIFICATION

4. MAIN COMPONENTS
TRANSFORMER
CIRCUIT BREAKER
LIGHTING ARRESTER
CURRENT TRANSFORMER

5. BUS BAR ISOLATOR
POTENTIAL WAVE TRAP

6. INSULATOR EARTH SWITCH
EARTHING SYSTEM CONTROL PANEL

7. TRANSFORMER
• Power transformers are used in transmission network of higher voltages for step-
up and step down application (400 kV, 200 kV, 110 kV, 66 kV, 33kV) and are
generally rated above 200MVA.
• Distribution transformers are used for lower voltage distribution networks as a
means to end user connectivity. (11kV, 6.6 kV, 3.3 kV, 440V, 230V) and are
generally rated less than 200 MVA.

8. BUS BARS
• a bus bar is a thick strip of copper or aluminium that conducts electricity.
• Bus bars are used to carry very large currents, or to distribute current to
multiple devices within switchgear or equipment.

9. CIRCUIT BREAKER
•It designed to protect an electrical
circuit from damage caused by
overload or short circuit.
•Its basic function is to detect a fault
condition and discontinue the
electric flow
.

10. BULK OIL CB MINIMUM OIL AIR BLAST
AUXIAL BLAST CROSS BLAST SF 6

11. 1. Actuator lever - used to manually
trip and reset the circuit breaker.
2. Actuator mechanism - forces the
contacts together or apart
3. Contacts - Allow current when
touching and break the current when
moved apart
4. Terminals
5. Bimetallic strip.
6. Calibration screw - allows the
manufacturer to precisely adjust the
trip current of the device after
assembly.
7. Solenoid
8. Arc divider/extinguisher
CIRCUIT BREAKER

12. ISOLATOR
•It is a disconnection
switch and to be operated
on no load.
•It is used to make sure
that an electrical circuit can
be completely de-energized
for service or maintenance.
• It provide electrical
isolation of the equipment .

13. CURRENT TRANSFORMER
•CT is a type of instrument transformer
that is used in power system for
measurement, detection, protection of the
system.
•Current transformers are used extensively
for measuring current and monitoring the
operation of the power grid.

14. POTENTIAL TRANSFORMER
 Potential transformers are instrument
transformers. They have a large number of
primary turns and a few number of
secondary turns.
 It converts voltages from high to low. It
will take the thousands of volts behind
power transmission systems and step the
voltage down to something that meters can
handle.

15. LIGHTING ARRESTER
It discharge the over voltage surges to earth
and protect the equipment insulation from
switching surges and lightning surges.
It located at the starting of the substation as
seen from incoming transmission lines and is
the first equipment of the substation

16. INSULATOR
 An insulator, also called a dielectric,
is a material that resists the flow of
electric current.
Insulators are used in electrical
equipment to support and separate
electrical conductors without allowing
current through themselves.

17. PIN TYPE SUSPENSION TYPE STRAIN TYPE
STRAIN TYPE SHACKLE TYPE

18. WAVE TRAP
 It trap the high frequency communication
signals sent on the line from the remote
substation and diverting them to the telecom/
teleprotection panel in the substation control
room .
 The Line trap offers high impedance to the
high frequency communication signals thus
obstructs the flow of these signals in to the
substation bus bars.
 The signals are primarily teleprotection
signals and in addition, voice and data
communication signals.

19. EARTH SWITCH
 Earth Switch is used to discharge the voltage on the circuit to
the earth for safety.
 Earth switch is mounted on the frame of the isolators.
 Earth Switch is located for each incomer transmission line and
each side of the bus-bar section

20. EARTHING SYSTEM
 Station Earthing System includes Earth Mat and Earth electrodes
placed below ground level
Function earthing system is to provide low resistance earthing for
 Discharging currents from the surge arresters, overhead shielding,
earthing switches
 For equipment body earthing
 For safe touch potential and step potential in substation.

21. METERING, CONTROL AND
RELAY PANELS
To house various measuring Instruments, control Instruments, Protective relays.
They are located in air-conditioned building. Control Cables are laid between
Switchyard equipment and these panels.

22. Some very commonly used bus bar arrangement are discussed
below
Single Bus System
Single Bus System is simplest and cheapest one. In this scheme all
the feeders and transformer bay are connected to only one single
bus as show.
Advantages of Single Bus System
1) This is very simple in design.
2) This is very cost effective scheme.
3) This is very convenient to operate.
Bus bar arrangements

23. Single Bus System

24. Disadvantages of Single Bus System
1) One but major difficulty of these type of
arrangement is that, maintenance of equipment
of any bay cannot be possible without
interrupting the feeder or transformer connected
to that bay.
2) The indoor 11KV switchboards have quite often
single bus bar arrangement.

25. Single Bus System with Bus
Sectionalizer
Some advantages are realized if a
single bus bar is sectionalized with
circuit breaker. If there are more than
one incoming and the incoming sources
and outgoing feeders are evenly
distributed on the sections as shown in
the figure, interruption of system can be
reduced to a good extent.

26. Single Bus System with Bus
Sectionalizer

27. Advantages of Single
Bus System with Bus
Sectionalizer
If any of the sources is out of system, still all
loads can be fed by switching on the
sectional circuit breaker or bus coupler breaker.
If one section of the bus bar system is under
maintenance, part load of the substation can be
fed by energizing the other section of bus bar.

28. Disadvantages of Single
Bus System with Bus
Sectionalizer
1) As in the case of single bus system,
maintenance of equipment of any bay cannot
be possible without interrupting the feeder or
transformer connected to that bay.
2) The use of isolator for bus sectionalizing
does not fulfill the purpose. The isolators
have to be operated ‘off circuit’ and which is
not possible without total interruption of bus
– bar. So investment for bus-coupler breaker
is required.

29. Double Bus System
1) In double bus bar system two identical bus bars
are used in such a way that any outgoing or
incoming feeder can be taken from any of the bus.
2)Actually every feeder is connected to both of the
buses in parallel through individual isolator as shown
in the figure.

31. By closing any of the isolators one can put the
feeder to associated bus. Both of the buses are
energized and total feeders are divided into two
groups, one group is fed from one bus and other
from other bus. But any feeder at any time can be
transferred from one bus to other. There is one bus
coupler breaker which should be kept close during
bus transfer operation. For transfer operation, one
should first close the bus coupler circuit
breaker then close the isolator associated with the
bus to where the feeder would be transferred and
then open the isolator associated with the bus from
where feeder is transferred. Lastly after this transfer
operation he or she should open the bus coupler
breaker.

32. Advantages of Double Bus System
Double Bus Bar Arrangement increases the
flexibility of system.
Disadvantages of Double Bus System
The arrangement does not permit breaker
maintenance with out interruption.

33. Double Breaker Bus System
In double breaker bus bar system two identical bus bars are
used in such a way that any outgoing or incoming feeder can
be taken from any of the bus similar to double bus bar system.
Only difference is that here every feeder is connected to both
of the buses in parallel through individual breaker instead only
isolator as shown in the figure. By closing any of the breakers
and its associated isolators, one can put the feeder to
respective bus. Both of the buses are energized and total
feeders are divided into two groups, one group is fed from one
bus and other from other bus similar to previous case. But any
feeder at any time can be transferred from one bus to other.
There is no need of bus coupler as because the operation is
done by breakers instead of isolator. For transfer operation,
one should first close the isolators and then the breaker
associated with the bus to where the feeder would be
transferred and then he or she opens the breaker and then
isolators associated with the bus from where feeder is

35. One and A Half Breaker Bus System
This is an improvement on the double breaker scheme to effect
saving in the number of circuit breakers. For every two circuits
only one spare breaker is provided. The protection is however
complicated since it must associate the central breaker with the
feeder whose own breaker is taken out for maintenance. For the
reasons given under double breaker scheme and because of the
prohibitory costs of equipment even this scheme is not much
popular. As shown in the figure that it is a simple design, two
feeders are fed from two different buses through their
associated breakers and these two feeders are coupled by a
third breaker which is called tie breaker. Normally all the three
breakers are closed and power is fed to both the circuits from
two buses which are operated in parallel. The tie breaker acts as
coupler for the two feeder circuits.
During failure of any feeder breaker, the power is fed through
the breaker of the second feeder and tie breaker, therefore each
feeder breaker has to be rated to feed both the feeders, coupled
by tie breaker.

37. Advantages of One and A Half Breaker Bus
System
During any fault on any one of the buses, that
faulty bus will be cleared instantly without
interrupting any feeders in the system since all
feeders will continue to feed from other healthy
bus.
Disadvantages of One and A Half Breaker
Bus System
This scheme is much expensive due to investment
for third breaker.

38. Main and Transfer Bus System
This is an alternative of double bus system. The main conception
of Main and Transfer Bus System is, here every feeder line is
directly connected through an isolator to a second bus called
transfer bus. The said isolator in between transfer bus and
feeder line is generally called bypass isolator. The main bus is as
usual connected to each feeder through a bay consists of circuit
breaker and associated isolators at both side of the breaker.
There is one bus coupler bay which couples transfer bus and
main bus through a circuit breaker and associated isolators at
both sides of the breaker. If necessary the transfer bus can be
energized by main bus power by closing the transfer bus coupler
isolators and then breaker. Then the power in transfer bus can
directly be fed to the feeder line by closing the bypass isolator. If
the main circuit breaker associated with feeder is switched off or
isolated from system, the feeder can still be fed in this way by
transferring it to transfer bus.

40. Switching Operation for Transferring a Feeder to Transfer Bus
from Main Bus without Interruption of Power
(i) First close the isolators at both side of the bus coupler breaker.
(ii) Then close the bypass isolator of the feeder which is to be transferred
to transfer bus.
(iii) Now energized the transfer bus by closing the bus coupler circuit
breaker from remote.
(iv) After bus coupler breaker is closed, now the power from main bus
flows to the feeder line through its main
breaker as well as bus coupler breaker via transfer bus.
(v) Now if main breaker of the feeder is switched off, total power flow will
instantaneously shift to the bus coupler breaker and hence this breaker
will serve the purpose of protection for the feeder.
(vi) At last the operating personnel open the isolators at both sides of the
main circuit breaker to make it isolated from rest of the live system.
So it can be concluded that in Main & Transfer Bus System the
maintenance of circuit breaker is possible without any interruption of
power. Because of this advantage the scheme is very popular for 33KV
and 13KV system.

41. Double Bus System with Bypass
Isolators

42. This is combination of the double bus system and
main and transfer bus system. In Double Bus System
with Bypass Isolators either bus can act as main bus
and second bus as transfer bus. It permits breaker
maintenance without interruption of power which is
not possible in double bus system but it provides all
the advantages of double bus system. It however
requires one additional isolator (bypass isolator) for
each feeder circuit and introduces slight
complication in system layout. Still this scheme is
best for optimum economy of system and it is best
optimum choice for 220KV system.

43. Ring Bus System
The schematic diagram of the system is given in the
figure. It provides a double feed to each feeder
circuit, opening one breaker under maintenance or
otherwise does not affect supply to any feeder. But
this system has two major disadvantages. One as it
is closed circuit system it is next to impossible to
extend in future and hence it is unsuitable for
developing system. Secondly, during maintenance
or any other reason if any one of the circuit
breaker in ring loop is switch of reliability of system
becomes very poor as because closed loop becomes
opened. Since, at that moment for any tripping of
any breaker in the open loop causes interruption in
all the feeders between tripped breaker and open
end of the loop.