substation of ac transmission and distribution

1. A
PRESENTATION
ON
Sub-Stations
GTU, Ahmedabad
Venus
International
College Of Technology
Prepared
by
V EEE
Patel Akash R En.120810108014
Patel Uttam En.120810108006
Patel Yash En.120810108011
Patel Sujal En.120810108004

2. Flow of Presentation
 Substation Introduction
 Classification of substations
 Transformer substation
 Pole mounted substation
 Underground substation
 Power factor correction substation
 Frequency changer substation
 SUB-STATION EQUIPMENTS & ITS FUNCTIONS
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3. Introduction
Sub-stations:- The assembly of
apparatus used to change some
characteristic (voltage ,a.c to d.c,
frequency, power factor, etc)of electrical
supply is called a Sub-stations.
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4. A Substation should be-
Located at a proper site and at the center of gravity
of load.
Easily operated and maintained.
Involve minimum capital cost.
For safety, consideration must be given to the
maintenance of regulation clearances, facilities for
carrying out repairs and maintenance, abnormal
occurrences such as possibility of explosion or fire
etc .
For reliability, consideration must be given for good
design and construction, the provision of suitable
protective gear etc.
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5. Classification of sub-
stations
According to service requirement
Transformer sub-stations.
Switching sub-stations.
Power factor correction sub-stations.
Frequency changer sub-stations.
converting sub-stations.
Industrial sub-stations
According to construction
Indoor sub-stations.
Outdoor sub-stations.
Underground sub-stations.
Pole-mounted sub-station.
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6. Transformer sub-stations
They are concern with the
changing of voltage level
The majority of sub-stations in
power system are or transformer
type
Types
1. Step up sub-stations
2. Primary grid sub-stations
3. Secondary sub-stations
4. Distribution sub-stations
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7. 7
Gs
11 kv
Step up sub-
stations
11/220kv
Primary grid
Substations
220/66kv
Secondary sub-
stations
66/11kv
Secondary sub-
stations
66/11kv
Distribution
sub-stations
11/0.4kv
Distribution
sub-
stations
11/0.4kv
Distribution
sub-
stations
11/0.4kv
High voltage
11kv consumer
High voltage
11kv consumer
Typical electrical supply system

8. Step Up Substation
Step up substations are associated with generating stations. Generation
of power is limited to low voltage levels due to limitations of the rotating
alternators. These generating voltages must be stepped up for
economical transmission of power over long distance. So there must be a
step up substation associated with generating station.
Primary Step Down Substation:
The primary step down sub stations are created nearer to load center
along the primary transmission lines. Here primary transmission voltages
are stepped down to different suitable voltages for secondary
transmission purpose.
Secondary Step Down Substation
Along the secondary transmission lines, at load center, the secondary
transmission voltages are further stepped down for primary distribution
purpose. The stepping down of secondary transmission voltages to
primary distribution levels are done at secondary step down substation.
Distribution Substation
Distribution substation are situated where the primary distribution
voltages are stepped down to supply voltages for feeding the actual
consumers through a distribution network. 8

9. Pole-mounted sub-station
Pole mounted substation are mainly
distribution substation constructed
on two pole, four pole and
sometime six or more poles
structures.
In these type of substation fuse
protected distribution transformer
are mounted on poles along with
electrical isolator switches.
The 11 kV line is connected to the
transformer through gang isolator
and fuses.
The lightning arresters are installed
on the H.T. side to protect the sub-
station from lightning strokes. The
transformer steps down the voltage
to 400V, 3-phase, 4-wire supply
. The oil circuit breaker (O.C.B.)
installed on the L.T. side
automatically isolates the
transformer from
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10. Underground Substation
Underground sub-ststion
The substation are
situated at underground
is called underground
substation.
In congested places
where place for
constructing distribution
substation is difficult to
find out, one can go for
underground sub –
station scheme.
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11. The following points must be kept in view while laying
out underground sub-station
1. Size of station should be as minimum as possible.
2. There should be reasonable access for both
equipment and personnel.
3. There should be good ventilation.
4. There should be provision for remote indication of
excessive rise in temperature so that H.V.
5. The transformers, switches and fuses should be air
cooled to avoid bringing oil into the premises.
6. There should be provision for emergency lighting and
protection against fire.
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12. Power factor correction sub-
stations. Those sub-stations which
improve the power factor of
the system are called power
factor correction sub-stations.
Such sub-stations are
generally located at the
receiving end of transmission
lines. These sub-stations
generally use synchronous
condensers as the power
factor improvement
equipment.
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Power factor correction sub-stations

13. Frequency changer substation
. Those sub-stations
which change the
supply frequency are
known as frequency
changer sub-
stations. Such a
frequency change
may be required for
industrial utilisation.
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14. SUB-STATION EQUIPMENTS & ITS
FUNCTIONS
Lightening Arrester
Lightening arrestors are the instrument that are used in
the incoming feeders so that to prevent the high voltage
entering the main station. This high voltage is very
dangerous to the instruments used in the substation.
Even the instruments are very costly, so to prevent any
damage lightening arrestors are used. The lightening
arrestors do not let the lightening to fall on the station.
Bus-bars.
When a number of lines operating at the same voltage
have to be directly connected electrically, bus-bars are
used as the common electrical component. Bus-bars are
copper or aluminium bars (generally of rectangular x-
section) and operate at constant voltage. The incoming
and outgoing lines in a sub-station are connected to the
bus-bars. 14

15. Isolator
The use of this isolator is to protect the transformer
and the other instrument in the line. The isolator
isolates the extra voltage to the ground and thus any
extra voltage cannot enter the line. Thus an isolator is
used after the bus also for protection.
Circuit Breaker
The circuit breakers are used to break the circuit if
any fault occurs in any of the instrument. These circuit
breaker breaks for a fault which can damage other
instrument in the station. For any unwanted fault over
the station we need to break the line current. This is
only done automatically by the circuit breaker. There
are mainly two types of circuit breakers used for any
substations. They are
a. SF6 circuit breakers
b. Spring circuit breakers.
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16. Potential Transformer
There are two potential transformers used in the bus
connected both side of the bus. The potential
transformer uses a bus isolator to protect itself. The
main use of this transformer is to measure the voltage
through the bus. This is done so as to get the detail
information of the voltage passing through the bus to
the instrument.
Voltage transformer.
It is essentially a step down transformer and steps
down the voltage to a known ratio. The primary of this
transformer consists of a large number of turns of fine
wire connected across the line. The secondary winding
consists of a few turns and provides for measuring
instruments and relays a voltage which is a known
fraction of the line voltage.
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17. Current transformer (C.T.).
A current transformer in essentially a step-up
transformer which steps down the current to a known
ratio. The primary of this transformer consists of one or
more turns of thick wire connected in series with the
line. The secondary consists of a large number of turns
of fine wire and provides for the measuring instruments
and relays a current which is a constant fraction of the
current in the line.
. Miscellaneous equipment.
In addition to above, there may be following
equipment in a sub-station :
( i) fuses
( ii) carrier-current equipment
( iii) sub-station auxiliary supplies
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18. THE
END
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