An electrical substation receives power from generating stations via transmission lines and distributes power via outgoing transmission lines. It performs several key functions: - Transforming voltage levels for efficient long-distance transmission and local distribution using step-up and step-down transformers. - Balancing loads, switching circuits, detecting and isolating faults to maintain stable grid operations. - Regulating voltage, monitoring and controlling parameters, and implementing protection systems to safeguard equipment. Substations can be indoor or outdoor and are classified by their service (e.g. distribution, industrial) or design (e.g. pole-mounted, foundation-mounted). They facilitate renewable energy integration and allow remote control and monitoring for efficient power system

1. Electrical substation:
An electrical substation is an assemblage of electrical components including busbars,
switchgear, power transformers, auxiliaries etc. These components are connected in a definite
sequence such that a ckt. can be switched off during normal operation by manual command
and also automatically during abnormal conditions such as short-circuit.
Basically an electrical substation consists of number of incoming ckt. and outgoing ckt.
connected to a common Bus-bar system. A substation receives electrical power from
generating station via incoming transmission lines and delivers elect. power via the outgoing
transmission lines.
Substation is integral part of a power system and form important links between the generating
station, transmission systems, distribution systems and the load points.
Function of Substation:
1. Voltage Transformation: Substations transform voltage levels to facilitate efficient long-distance
transmission and local distribution.
2. Step-Up Transformers: Substations step up voltage for long-distance transmission to reduce
energy loss.
3. Step-Down Transformers: Substations step down voltage for local distribution and end-user
consumption.
4. Load Balancing: Substations help balance the load on different circuits to prevent overloading
and ensure stable operation.
5. Circuit Switching: Substations enable the switching of circuits for maintenance, repair, or to
reroute power in case of faults.
6. Fault Detection and Isolation: Substations include protective devices to detect and isolate faults
in the power system to minimize disruptions.
7. Power Factor Correction: Substations may include equipment to improve the power factor and
increase the efficiency of power transmission.

2. 8. Voltage Regulation: Substations regulate voltage levels to ensure that power quality meets
acceptable standards for end-users.
9. Bus bar Arrangement: Substations use busbars to connect and distribute power to different
circuits and transformers.
10. Control and Monitoring: Substations are equipped with control and monitoring systems to
manage and supervise various parameters of the power system.
11. Protection Systems: Substations implement protection systems to safeguard equipment and the
power grid from overcurrent, overvoltage, and other anomalies.
12. Remote Control: Some substations allow remote control and monitoring for efficient operation
and maintenance.
13. Transformer Cooling: Substations employ cooling systems to maintain the optimal temperature
of transformers, ensuring their proper functioning.
14. Switchgear Operation: Substations use switchgear to control the flow of electricity and protect
equipment during normal operation and fault conditions.
15. Grounding: Substations include grounding systems to provide a safe path for fault currents and
protect equipment and personnel.
16. Metering: Substations have metering equipment to measure and record parameters like voltage,
current, and power for billing and monitoring purposes.
17. Harmonic Filtering: Substations may include filters to mitigate harmonics and improve power
quality.
18. Emergency Power Supply: Some substations have backup power systems to ensure continuity of
service during power outages.
19. Integration of Renewable Energy: Substations facilitate the integration of renewable energy
sources into the power grid.
20. Data Communication: Substations use communication systems to exchange data with other
substations, control centers, and monitoring stations for coordinated grid management.

3. Types of Substation
1) According to service
2) According to Design
1) Substations According to The Service:
Here are types of substations according to the service
1. Step-Up Transformer Substation:
 This type of substation is designed to increase the voltage of electricity generated at
power plants before it is transmitted over long distances. It typically contains step-up
transformers.
2. Transmission or Primary Substation:
 Positioned near the power generation source, the primary substation receives high-
voltage power and may involve voltage transformation for efficient transmission.
3. Sub- Transmission or Secondary Substation:
 Receives power from a primary substation and steps down the voltage for local
distribution to end-users.
4. Distribution Substation:
 Connected to the distribution network, this substation further steps down voltage for
local distribution to homes, businesses, and other consumers.
5. Industrial Substation:
 Serves industrial facilities and is designed to meet the specific power requirements of
industrial processes. It may include equipment for power factor correction and other
industrial needs.
6. Switching Substation:
 Primarily used for switching operations, isolating faulty equipment or rerouting power
to ensure continuous and reliable service.
7. Power Factor Correction Substation:
 Focuses on improving the power factor of the electrical system, ensuring that the ratio
of real power to apparent power is optimized for efficiency.
8. Frequency Substation:
 Monitors and controls the frequency of the electrical system. Frequency substations are
important in maintaining system stability, especially in interconnected grids.
9. Converting Substation:
 Converts electrical power between different forms, such as AC to DC or vice versa. This
is common in High Voltage Direct Current (HVDC) systems.

4. 2) SUBSTATIONS ACCORDING TO THE DESIGN:
Here are types of substations according to the Design
1) Indoor substation
2) Outdoor substation
1) Indoor substation:
Definition: A substation in which the apparatus is equipped inside the substation building
is called indoor substation. Such type of substation is mainly used for the voltage up to
11000 v
The indoor substation is subdivided into several compartments like control compartment,
indicating and metering instruments and protective device compartment main bus-bar
compartment, current transformer and cable sealing box compartment as shown in the figure
below.
The switch gear on the supply or primary side will consist of oil circuit breaker only. The high
voltage supply is given to the primary of the transformer through a circuit breaker. From the bus
bar, various feeders emerge out. The panel on each feeder consists of an isolator switch and a
circuit breaker. In addition to isolator and circuit breaker, the panel also provided the measuring
instrument.
For the protection of feeders usually, reverse power relay is used. For the protection of oil filled
transformer Buchholz relay is used. The accessories of the indoors type substations are a storage
battery, firefighting equipment such as water, buckets, and fire extinguisher, etc., The battery is

5. used for the operation of protective gear and switching operating solenoids and emergency
lighting in substations in the case of failure of supply.
Indoor substations and transformer substation, as well as, high voltage switchboards consist of a
series of open and enclosed chamber or compartments. The main equipment for this installation
is arranged in these compartments. The chamber space within which the equipment of the main
bus-bar is connected is called a compartment or a cubical cell.
Substations of the Integrity Built Type:
In such type of substation, the device is equipped on site. In such substation, the cell structure
is constructed of concrete or bricks.
Substations of the Composite Built-Up Type:
In such type of substations factory or workshop are built but are assembled on site within a
substation switch gear room. The compartments of such substations take the form of metal
cabinets or enclosures, each of which contains the equipment of one main connection cell. In
such cabinets, an oil circuit breaker, a load interrupter switch, and one or more voltage
transformers may be mounted.
Unit Type Factory Fabricated Substations and Metal Clad Switchboards:
These are built in electrical workshops and are carried to the site of installations fully pre-
assembled. After installations of substations and switchboards only connection to the incoming
and outgoing power circuits are required to be made.
General View of A Unit -Type Metal-Clad Switchboard

6. Advantages of Indoor Substations:
1. Space Efficiency: Indoor substations save space and are suitable for urban areas with limited
room.
2. Environmental Protection: Enclosed environments shield equipment from weather, extending
their lifespan.
3. Reduced Maintenance: Less exposure to external elements leads to lower maintenance needs.
4. Enhanced Security: Indoor substations, being enclosed, offer better security against
unauthorized access.
5. Improved Personnel Safety: Controlled indoor environments enhance safety by minimizing
exposure to live electrical components.
Disadvantages of Indoor Substations:
1. Initial Cost: Constructing enclosed structures may involve higher initial costs.
2. Limited Cooling Options: Cooling systems may be required, adding complexity and potential
cost.
3. Space Constraints: Indoor substations may face challenges accommodating larger equipment in
some situations.
4. Ventilation Requirements: Adequate ventilation needs to be ensured to dissipate heat
generated by equipment.
5. Potential Fire Hazard: The risk of fire needs careful management due to the presence of
electrical equipment and transformers.
2) Outdoor substation:
Definition:
The substation which installs for high voltage requirements outside the building
construction is called an outdoor substation.
Or
A substation which is used for all voltage levels between 55 KV to 765 KV is called outdoor
substation. Such type of substation requires less time for construction but uses more
space.
The outdoor substations are mainly classified into two types, namely pole-mounted substation
and foundation-mounted substations.

7. Pole Mounted Substation:
Such substations are used for supporting distribution transformers having the capacity up to 250
KVA. Such types of transformers are the cheapest, simplest, and smallest of distributions. All the
equipment is the outdoor type and mounted on the supporting structures of high tension
distribution line. Triple pole mechanically operated switch used for switching on and off the high
tension transmission line.
HT fuse is used for protection of the high tension transmission line. For controlling the low
tension lines, low tension switches along with fuses is equipped. Lightning arresters are equipped
over the high tension line for the protection of the transformers from the surges. Pole-Mounted
substations are earthed at two or more places.
Pole-Mounted Outdoor Substation
The transformers having a capacity up to 125 KVA are mounted on the double pole structure and
for the transformer having a capacity between 125 to 250 KVA 4-pole structure with the suitable
platform is used. Such types of the substation are placed in very thickly populated location.
Their maintenance cost is low, and by using a large number of the substation in a town, it is
desirable to lay the distributors at a lower cost. But when the number of transformers is
increasing, total KVA is increased, no load losses in increases and the cost per KVA increases.
Foundation Mounted Substation:
In foundation mounted substation all the equipment area assembled and the substations are
embedded by the fence for safety purpose. The equipment required for such type of substations
are heavy, and hence the site selected for such type of substation must have a good path for
heavy transport. Foundation mounted outdoor substation is shown in the figure below.

8. Foundation-Mounted Outdoor Substation
Advantages of Outdoor Substation:
The outdoor substations have the following main advantages. These are
 All the equipment in the outdoor substations is within view, and therefore fault location is
easier.
 The expansion of the installation is easier in the outdoor substations.
 The time requires in the construction of such substations is lesser.
 The smaller amount of building material like steel, concrete is required.
 The construction work required is comparatively less, and the cost of the switchgear
installation is also very low.
 Repairing work is easy, and proper space is provided between the apparatus so that the
fault occur at one point will not be carried over to another point.
Disadvantages of Outdoor Substation:
 More space is required for the outdoor substations.
 Protection devices are required to be installed for the protection against lightning surges.
 The length of the control cables increases which increase the cost of the substation.
 Equipment designed for outdoor substation are more costly because outdoor door
substation equipment required additional protection from the dirt and dust.