SUBSTATIONS
The present day the electrical
power is generated, transmitted and distributed in the form of alternating
current. The power is produced at the power stations which are located at
favorable locations generally quiet away from the consumers. It is delivered to
the consumers through a large network of transmission and distribution lines.
At many places in the lines of the power system it is necessary to change
voltage or frequency or power factor of electric supply. This is done by
substations.
Substations receive power from incoming lines , the power is
transformed to desired voltage by transformers and is then supplied to outgoing
lines. The generating voltage (11 KV or 6.6 KV) at the power station is stepped
up to high voltage ( 220 KV or 110 KV or
66 KV ) for primary transmission of electric power. This voltage is stepped
down to lower voltages at receiving substation and is further stepped down for
distribution. Substations are important part of power system. The continuity of
supply depends to a considerable extend up on the successful operation of
substations.
Classification of substations
1) According to service requirement:
A) Transformer substations : In these substations the
voltage level of electric supply is changed by using power transformers. They
receive power at some voltage and
deliver it at some other voltages.
B)
Switching substations : They simply
perform the switching operations of power lines.
C) Power-factor correction substations : They are used
to improve power factor of the system .
D) Frequency changer substations : They change the
supply frequency for various purposes.
E) Converting substations : They are used to convert ac into DC
F). Industrial substations: They are used to supply power to individual
industrial consumers.
G) Distribution substations : They are for distribution
of power at low voltage to various consumers.
2) According to construction:
a Indoor substations : They are used up to 33 KV, all
the substation equipments are installed indoor .
b. Outdoor substations : For voltages above 33 KV all equipments are installed outdoor, because
for such voltages the clearance required is large and is not economical for
installed indoor.
c. Under ground substations : All equipments are
installed in under ground. It is advantages in thickly populated areas.
d. Pole mounted substations : It is an out door
substation in which the equipments are installed on H pole or 4 pole structure.
These are used for distribution purposes . These are cheap.
e. Gas insulated Substations (indoor) : In GIS the
various equipments are housed in separate metal enclosed modules filled with
SF6 gas. The gas provides sufficient insulation. As SF6 gas has high dielectric
strength than air the clearances required are smaller. Hence the overall size
of equipments and substation are reduced. These substations are highly useful
in town areas because less space is required. These can be also used in highly
polluted areas. The pressure of gas is generally 4 Kg/ sq.cm.
Comparison between outdoor and indoor
substations
Sl no.
|
Particulars
|
Outdoor substations
|
Indoor substations
|
1
|
Space required
|
More
|
Less
|
2
|
Time required for erection
|
Less
|
More
|
3
|
Future extension
|
Easy
|
Difficult
|
4
|
Fault location
|
Easy
|
Difficult
|
5
|
Capital cost
|
Low
|
High
|
6
|
Operation
|
Difficult
|
Easy
|
7
|
System voltage
|
Used for voltage above 11 KV
|
Used for voltage up to 11 KV ( GIS up to 400 KV )
|
