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Laboratory Manual for Substation Design EET 414/4
Name:_______________________________ Matrix No:___________ Date:_________
EXPERIMENT 1.
INTRODUCTION TO SUBSTATIONS
Objective:
To introduce classifications, functions, works and supporting installations, design of grid
resistance, operation and maintenance of substations.
Introduction
What is a substation?
Substations are integral parts of a power system and form important link between the
generating stations, transmission systems, distribution systems and the load points such
as Figure 1.
The substation’s function is to support the system, providing points of delivery in the
transmission system. Substations meter distribution equipment and power lines step down
voltage for distribution to homes, and maintain voltage at a constant level.
This constant level of voltage is particularly important. To travel long distances over
wires, electric power must be much higher voltage than the level at which it is actually
produced by a power plant. The higher the voltage, the lower the line loss and voltage
drop and the greater the system’s efficiency. As the power gets closer to its destinations,
voltage is gradually decreased to a level safe for consumers. Transmission substations
give the power its first step down, and distribution substation step it down father, so it
may be sent on the consumer.
The lines leaving a distribution substation are owned and maintained by the local utility.
These lines carry the power to homes, businesses, schools and industries. A multitude of
equipment is contained in substations: transformers, circuit breakers insulators, reactors,
lightning arrester and more. A transformer performs the main function of a substation,
which is to reduce the voltage to an acceptable level for distribution. The voltage
regulator maintains a constant outgoing voltage.
Laboratory Manual for Substation Design EET 414/4
FIGURE 1. SUBSTATION
Laboratory Manual for Substation Design EET 414/4
FIGURE 2. ONE LINE DIAGRAM OF ELECTRIC POWER SYSTEM
FIGURE 3. ELECTRICAL POWER GENERATION SYSTEMS
Classification of Substations (S/S)
A. Classification based on functions

Step-up Substation (generation substation)

Transmission substation

Sub-transmission Substation

Distribution Substation
B. Classification based on constructions

Air Insulated Substation (AIS):
Outdoor installations S/S (Switchyard)
Indoor installations S/S

Gas insulated S/S
Outdoor installations S/S (Switchyard)
In such substations bus-bar and connector can be seen by naked eye. In such
substations main equipment like, circuit breakers, isolator, bus-bar, power
Laboratory Manual for Substation Design EET 414/4
transformer, lightning arrester etc, are installed out door, whereas controls,
measurement, and auxiliary equipment are installed in buildings.
Indoor installations S/S., entire of main equipments and controls, measurement,
and auxiliary equipment are installed in buildings.
Six types of bus/switching arrangements commonly used in AIS design.
FIGURE 4. CONFIGURATION OF BUSBARS

Gas insulated substations, There are several equipments inside like, Circuit
breakers, switches, instrument transformer, lightning arrester and so on are in
the form of metal enclosed SF6 gas filled modules. The modules are assembled
in accordance with the required configuration.
The various live parts are
enclosed inside the enclosures and are supported on epoxy post insulator or disc
insulator or disc insulators.
Laboratory Manual for Substation Design EET 414/4
FIGURE 5. GAS INSULATION SUBSTATION
1. CIRCUIT BREAKER
2. DISCONECTOR (ISOLATOR)
3. EARTHING (GROUNDING) SWITCH
4. CURRENT TRANSFORMER
5. VOLTAGE TRANSFORMER
6. CABLE SEALING END CHAMBER
7. GAS BARRIER
8. SUPPORTING INSULATOR
9. MAIN BUSBAR
10. RESERVE BUSBAR
C. Parts of the Works



Electrical Works
Civil works
Installation supports

Electrical works consist of:
1. Transformer
5. Grounding systems
2. Bus-bar
6. Cable installations
3. Circuit Breaker
7. Control panel
Laboratory Manual for Substation Design EET 414/4
4. Protective relay
8. etc
FIGURE 6.
BUS-BAR ERECTIONS
FIGURE 7 : Substation Equipment Parts
Laboratory Manual for Substation Design EET 414/4
Control Panel
FIGURE 8. CONTROL PANEL
Cable Installations
FIGURE 9. CABLE DUCT INSTALLATIONS
Laboratory Manual for Substation Design EET 414/4
Grounding System
1. Equipment Grounding (Body Grounding)
2. System grounding (Neutral grounding)
3.
Substation grounding
There are two main design goals to be achieved by any substation ground system
under normal as well as fault conditions. These are:
i). To provide means to dissipate electric currents into the earth without exceeding any
operating and equipment limits.
ii). To assure that a person in the vicinity of grounded facilities is not exposed to the
danger of critical electric shock.
The grounding system includes all of the interconnected grounding facilities in
the substation area, including the ground grid, overhead ground wires, neutral conductor,
underground cables, foundations, deep well, etc.
FIGURE 10: SUBSTATIONS GROUNDING SYSTEMS
1.
2.
3.
4.
5.
Grounding electrodes (spike)
Grounding conductor
Risers
Shielding wire
Surge arrester
6. Grounding switch
7. Transformer neutral
8. Cable
9. Equipment body or frame
Laboratory Manual for Substation Design EET 414/4

Civil Works
1. Control Building, officer building, auxiliary building
2. Road Entrance
3. Foundation and support pillar: Building foundations, switchyard foundation,
transformer foundations.
4. Drainage
5. Cable duct
6. etc
FIGURE 11. CIVIL WORKS
Laboratory Manual for Substation Design EET 414/4

Installation supports
1. Fire protections
2. Battery system
3. Water pump house
Substation Functions for The Electric Power System
1. Voltage change from one level to another
2. Voltage regulated to compensate for system voltage change
3. Electric transmission and distribution circuits switched into and out of the system
4. Electric power qualities flowing in the transmission and distribution circuits
measured
5. Communication signals connected to the circuits
6. Lightning and switching surges eliminated from electric system
7. Electric generators connected to the transmission and distributions
8. Interconnection between the electric systems of various companies completed
9. Reactive kVA supplied to the transmission and distributions circuits and the flow
reactive kVA on the transmission and distributions circuits controlled.
Substation Equipment Major Components and its Functions.
There are various of substation main equipments as shown Figure 6.
1. Power transformer: to change ac electric energy at one voltage level to another
voltage level base upon electromagnetic principle.
2. Current instrument: are used for reducing/stepping down a.c. current from higher
value to lower suitable value for measuring, protection and control.
3. Voltage transformer is used for stepping down voltage from higher value to lower
suitable value for measurement, protection and control.
4,5 Bus-bars: connected location the incoming and out going circuit.
6. Circuit Breaker: is device capable of making and breaking and electric circuit
under normal and abnormal conditions such as short circuits. It can operate
automatically and clear fault currents safely and quickly.
Laboratory Manual for Substation Design EET 414/4
7. Isolator (disconnecting switch): A switching device which can be opened or
closed only under no load conditions.
8. Earthing Switch: that connects a conductor to the earth so as to discharge the
charge on the conductor to ground.
9. Shunt capacitor: power factor improvement by mean of reactive kVA supplied
10. Shunt reactor: to raise voltage
11. Lightning arrester: to protect the substation equipment from lightning and
switching over voltage surges.
FIGURE 12. SINGLE LINE DIAGRAM SHOWING SUBSTATION
EQUIPMENT
Single Line Diagram
SUBSTATION ‘A’
MAIN INTAKE
EARTH
EARTH
EARTH
EARTH
EARTH
SUBSTATION ‘B’
EARTH
RING MAIN UNIT
EARTH
Out
In
Step-up Transformer
Step-down Transformer
EARTH
EARTH
FIGURE 13. One line diagram of Modular Power system
Laboratory Manual for Substation Design EET 414/4
Name:__________________________________ Matrix No:________ Date:______
DISCUSSION
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CONCLUSION
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Instructor Approval:_______________________________ Date:______________