A substation is an important part of an electrical power system where voltage is transformed from high to low levels or vice versa. Electric power may pass through multiple substations between generation and consumption. Main components of a substation include transformers to step up or down voltages, circuit breakers, switches, protective relays, surge arrestors, and other equipment. Substations can be indoor, outdoor, underground or pole-mounted depending on construction, and serve purposes like transmission, distribution, power factor correction or frequency changing. Careful consideration is given to site selection, environmental factors and layout of a substation.

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

1.
2.
3.
4.
Classified by their main two features.
According to constructional features:Are of four type.
Indoor Sub-station
Outdoor Sub-station
Underground Sub-station
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
B: Secondary power lines' side
1.Primary power lines
7.Current transformer
2.Ground wire
8.Lightning arrester
3.Overhead lines
9.Main transformer
4.Transformer for measurement
10.Control building
of electric voltage
11.Security fence
5.Disconnect switch
12.Secondary power lines
6.Circuit breaker
7.Current transformer
8.Lightning arrester

10. Plan & Section of a Substation