introduction to transmission and distribution of electrical power

1. Introduction to Electric Power
Transmission and Distribution

2. Introduction
 Electric power transmission is the bulk movement of
electrical energy from a generating site, such as a
power plant, to an electrical substation. The
interconnected lines which facilitate this movement are
known as a transmission network.
 The combined transmission and distribution network is
known as the "National Grid".
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3. Power System
 The generation, transmission and distribution of electric power is
called power system.
A power system has the following stages:
- Generation of electric power
- Transmission of electric power.
- Distribution of electric power.
 Most transmission lines are high-voltage three-phase alternating
current (AC).
 High-voltage direct-current (HVDC) technology is used for greater
efficiency over very long distances (typically hundreds of miles).
 Electricity is transmitted at high voltages (115 kV or above) to
reduce the energy loss which occurs in long-distance transmission.
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4. Layout of Power System
A power system is consist of the following stages:
1. Power Station
2. Primary Transmission
3. Secondary Transmission
4. Primary Distribution
5. Secondary Distribution
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6. 1. Power Station
 The bulk power is generated
at the power station by 3-
phase, 3 wire system
employing several alternators
in parallel. The usual
generation voltage is 11kV.
Due to economic
consideration , the
generation voltage(ie; 11kV )
is step up to 220kV or 132kV
at the power station with the
help of step up transformers.
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7. 2. Primary Transmission
 High voltages of the
order of 66 kV 132 kV
220 kV and 400 kV are
used for transmitting
power by 3 phase 3
wire overhead system.
This is supplied to
substations usually at
the out skirts of major
distribution centre or
city.
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8. 3. Secondary Transmission
 On the outskirt of the city, there are sub-
station which step down the primary
transmission voltage to 66kV or 33kV and
power is transmitted at this voltage. This forms
the secondary transmission system. 3 phase
wire system is used.
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9. 4. Primary Distribution
 The transmission lines
or inner connectors
terminate at large
main substations
from which the
power is distributed
to small secondary
substations scattered
throughout the load
area. The voltage
may range from 11
kV to 132 kV.
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10. 5. Secondary Distribution
 This consists of the low-
voltage network laid along
the streets, localities and
over the rural areas. From
these sources connections
to individual customers are
provided. The circuit used
for this purpose is 3 phase 4
wire, 440 V/220 V from
which either 3 phase 440 V
or single phase 220 V
supply to the consumers
may be provided.
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11. INTRODUCTION OF DISTRIBUTION SYSTEM
Distribution of electric power is an important part of power
system. The important requirement of a distribution system is
that the power should be distributed to various consumers
economically and efficiently .
The electric energy is made available for use in a factory or a
residential building by distribution system which can be
subdivided into three distinct parts.
 Feeders
 Distributors
 Service mains

12. DISTRIBUTION SYSTEM
The arrangement of conveying electric power from bulk
power sources (generating stations or major substations) to
the various consumers is called distribution system.
Distribution is of two types. –
1. High voltage or primary distribution
2. Low voltage or secondary distribution
High voltage distribution is carried out at voltages of the
order of 33kv,66kv or,11kv.
Low voltage distribution which is carried out at 400/230
volts (in three phase 4 wires system)

13. Important terms of distribution system
1. Feeder
2. Distributor
3. Service mains
Feeder- A feeder is a conductor which connects sub-station or generating station
to the are where the power is to be distributed. These are the conductors which carry
large currents to the feeding points. In Fig. 3.1, s is the sub-station and SA and SC are
the feeders. A and C are the feeding points.

14. 2. Distributor : A distributor is a conductor from which tapings are taken for supply to
the consumers or it is the conductor t which carries current to the service main form
the feeding points. The current loading of a distributor varies along its length.
3. Service mains : A services main is generally a small cable which connects the
distributor to the consumer terminals.
CLASSIFICATION OF DISTRIBUTION SYSTEMS
1. According to Nature of Construction :
a. Overhead distribution system
b. Underground distribution system
overhead system is cheaper than underground system. However, underground system is
used in thickly populated areas where overhead system may not be practicable.

15. 2. According to nature of current :
a. D.C distribution system
b. A.C distribution system
A.C distribution is universally adopted due to many advantage of a.c.
power over d.c. power.
3. According to number of wires :
a. 2-wire d.c. system
b. 3-wire d.c. system
c. Single phase, 2-wire a.c. system
d. 3-phase, 3-wire a.c. system
e. 3-phase, 4—wire a.c. system

16. 4. According to the system of connection:
(a) Radial system
(b) Ring main system
(c) Interconnected system
Radial System: when the distributor is fed at one end
only, it is called radial distribution system. A single line diagram
of radial system is shown in fig.

17. Advantages of radial system:
1. its initial cost is minimum.
2. this system is employed when electrical energy is
generated at low voltage and power station is
situated at the center of load.
Disadvantages:
1. the end of the distributor nearest to the supply end
would be heavily loaded.
2. the consumers at the distant end of the distributor
would be subjected to serious voltage variations.
When the load on the distributor changes.

18. Ring main system:
when the distributor is supplied by two feeders, it is called
a ring main distribution system. In this system the feeder
closes on itself, i.e. it forms a complete ring and hence the
name ring mains.
Advantages of ring main system:
1. it offers a great reliability of supply. In the event of fault
on any system of feeder, the continuity of supply can be
maintained.
2. each distributor is supplied via two feeders, for
example,- the distributor connected at a point “D” is fed
via feeder ABC and ADC

19. Inetrconnected system:
In an “interconnected system” the feeder ring is energised by two
or more than two generating stations or substations fig. shows the
single line diagram of an interconnected system. The closed
feeder ring ABCDA is supplied by four stations S1, S2, S3 & S4 at
points D,A, B & C.

20. Introduction of Substations
 A substation is a part of an electrical generation, transmission, and
distribution system. Substations transform voltage from high to low, or the
reverse, or perform any of several other important functions.
 Between the generating station and consumer, electric power may flow
through several substations at different voltage levels.
 A substation may include transformers to change voltage levels between
high transmission voltages and lower distribution voltages, or at the
interconnection of two different transmission voltages.
 Substations may be owned and operated by an electrical utility, or may be
owned by a large industrial or commercial customer. Generally substations
are unattended, relying on SCADA for remote supervision and control.
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22. Types of Substations
1. Transmission substation
A transmission substation connects two or more transmission lines. The
simplest case is where all transmission lines have the same voltage. In
such cases, substation contains huh-voltage switches that allow lines
to be connected or isolated for fault clearance or maintenance. A
transmission station may have transformers to convert between two
transmission voltages, voltage control/power factor correction
devices such as capacitors, reactors or static VAR compensators and
equipment such as phase shifting transformers to control power flow
between two adjacent power systems.
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23. Types of Substations
2. Distribution substation
A distribution substation transfers power from the transmission system to the
distribution system of an area. It is uneconomical to directly connect
electricity consumers to the main transmission network, unless they use
large amounts of power, so the distribution station reduces voltage to a
level suitable for local distribution.
The input for a distribution substation is typically at least two transmission or
sub transmission lines. Input voltage may be, for example, 115 W, or
whatever is common in the area. The output is a number of feeders.
Distribution voltages are typically medium voltage, between 2.4 kV and 33
kV depending on the size of the area served and the practices of the
local utility.
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24. Types of Substations
3. Collector substation
In distributed generation projects such as a wind farm, a collector
substation may be required. It resembles a distribution substation although
power flow is in the opposite direction, from many wind turbines up into
the transmission grid. Usually for economy of construction the collector
system operates around 35 kV and the collector substation steps up
voltage to a transmission voltage for the grid. The collector substation can
also provide power factor correction if it is needed, metering and control
of the wind farm. In some special cases a collector substation can also
contain an HVDC converter station.
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26. Components of Substations
Various components are used at grid transmission substations.
These are as follows:
1. Conductors
2. Current transformers
3. Potential Transformers
4. Power transformers(Auto Transformer)
5. Capacitive voltage Transformers
6. Line Isolators
7. Bus Isolators
8. Lighting Arresters
9. Capacitor Bank
10. Circuit Breaker
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27. Thank You
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Prepared by: Abdul Rahman Al Ghanim
(1621091102)
Submitted to Professor: Shivani Balyan