A substation is a part of an electrical distribution system where voltage is transformed from high to low or low to high. Electric power may pass through multiple substations between generation and consumption. Substations are classified as indoor, outdoor, underground, or pole-mounted. They can serve to transform voltage, switch circuits, correct power factors, change frequencies, or supply industrial facilities. Key components include transformers, circuit breakers, surge arrestors, switchgear, and relays. Substations have layouts with primary and secondary sides separated by transformers, circuit breakers, and other equipment.

1. by Towfiqur Rahman
(towfiq.eee@gmail.com)

2. What is a Sub-station?
A substation is a part of an
electrical generation, transmission, and distribution
system, where voltage is transformed from high to low,
or low to high, or many other important functions.
Electric power may flow through several substations
between generating plant and consumer, and may be
changed in voltage in several steps.
Mainly Sub-station is defined as “The
assembly of apparatus used to same some
characteristics (e.g. Voltage, AC to DC, P.F. , Frequency
etc.) of electric supply is called Substation.”

3. Types of Sub-station
 Classified by their main two features.
According to constructional features:-
Are of four type.
1. Indoor Sub-station
2. Outdoor Sub-station
3. Underground Sub-station
4. Pole-mounted Sub-station

4. According to service requirement
features:- Are of six types.
 Transformer Sub-station:- Divided into two
different sub types:-
i. Transmission Sub-station
ii. Distribution Sub-station
 Switching Sub-stations
 Power factor correction Sub-station
 Frequency Changing Sub-station
 Converting Sub-station
 Industrial Sub-station

5. Design Considerations
Site Considerations:- Location place, Access road,
present and future load center, existing and future
sources of power etc.
Environmental Considerations:- Weather,
Temperature, Wind, Appearance, Public Safety,
Audible Noise, Electrostatic and Electromagnetic
Effects, Effluent, Ice etc.

6. Components of a Substation
 Transformer:- Main
component. It is classified by
two type.
 Power Transformer:-
A power transformer is
used in a substation to step
up or step down the voltage
 Instrument Transformer
i. Current Transformer
ii. Voltage Transformer

7.  Insulator
 Earthing system
 Isolation Switches
 Circuit breakers

8.  Surge arrestor
 Switchgear
 Relay

9. Sub-station Layout
A:Primary power lines' side
1.Primary power lines
2.Ground wire
3.Overhead lines
4.Transformer for measurement
of electric voltage
5.Disconnect switch
6.Circuit breaker
7.Current transformer
8.Lightning arrester
B: Secondary power lines' side
7.Current transformer
8.Lightning arrester
9.Main transformer
10.Control building
11.Security fence
12.Secondary power lines

10. Plan & Section of a Substation