Contents:

 Introduction
 One-Line Diagram
 Components of Power System

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Introduction
 An electrical power system consists of generation,
transmission and distribution.
 The transmission systems supply bulk power and the
distribution systems transfer electric power to the
ultimate consumers.
 The generation of the electric energy is nothing but the
conversion of one form energy into electrical energy.
 Electrical energy is generated in hydro, thermal and
nuclear power stations.
 Sometimes, electrical energy is generated from non-
renewable energy sources like wind, waves, fossil fuels,
etc. The generating voltages are usually 6.6kV, 10.5kV,
11kV, 13.8kV, 15.75kV, etc.
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Components of an electric power system:
 Generators: A device used to convert one form of energy into electrical
energy.
 Transformer: Transfer power or energy from one circuit to other without
the change of frequency.(to increase or decrease the voltage level)
 Transmission lines: Transfer power from one location to another
 Control Equipment: Used for protection purpose
 Primary Transmission: 110kV, 132kV or 220kV or 400kV or 765kV, high
voltage transmission, 3 phase 3-wire system.
 Secondary transmission: 3 phase 3-wire system, 33kV or 66kV feeders
are used
 Primary distribution: 3 phase 3-wire system, 11kV or 6.6kV, 3 phase 3-
wire system
 Secondary distribution: 400V for 3φ, 230V for 1φ

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 Generators:
 Generator is a device which converts mechanical
energy into electrical energy. Generating voltages are
normally 6.6 kV,10.5 kV or 11 kV.
 This generating voltage can be step up to 110 kV/132
kV/220kV at the generating(indoor or outdoor) to
reduce the current in transmission line and to reduce
transmission losses.
 Generators produce real power (MV) and reactive
power (MVAR).

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 Transformers:
 It is a static device which transfers power or energy
from one circuit to another circuit without change of
frequency.
 The main function of transformers is step up voltages
from lower generation levels to the higher generation
voltage levels and also step down voltages from
higher transmission voltage levels to lower
distribution levels.
 When we are increasing the transmission voltage,
current flowing through the current flowing through
the grid decreases, thereby transmission losses (I2R)
reduces.

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Control Equipment
 Circuit Breaker (CB): Circuit breakers are used for opening or
closing a circuit normal and abnormal (fault) condition.
 Different types of circuit breaker are oil circuit breaker, air-blast
circuit breaker, vacuum circuit breaker, SF6 circuit breaker.
 During fault conditions relay will give command to the circuit
breaker to operate.
 Isolators: Isolators are placed in substations to isolate the part of
system during maintenance.
 It can operate only during no-load condition. Isolated switches
are provided on each side of the circuit breaker.

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Contd…
 Busbar: Busbars are used to connect number of lines
operating at the same voltage electrically.
 It is made up of copper or aluminium. Different types
of busbar arrangements are –single busbar
arrangement, single bus bar with sectionalisation,
double bus bar arrangements, ring bus bar scheme etc.

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Transmission System
 It supplies only large blocks of power to bulk power station
or very big consumers.
 It interconnects the neighbouring generating stations in to a
power pool i.e, interconnection of two or more generating
stations.
 Tolerance of transmission line voltage is ±5 to ± 10% due to
the variation of loads.
Primary Transmission
 If the generated power is transmitted through transmission
line without stepping up the generated voltage, the line
current and power loss would be very high.
 So the generated voltage is stepped up to higher value by
using the step up transformer located in substations known
as sending end substations near the generating stations.

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Contd…
 The high voltage transmission lines transmit power from
sending end substation to the receiving end substation.
 Primary transmission voltages are 110KV, 132 KV or 220KV
0r 400KV or 760KV.It uses 3phase, and 3wire system.
Secondary Transmission
 At the receiving end substation, the voltage is stepped down to
a value of 66 or 33 or 22 KV using step down transformers.
 The secondary transmission line forms the link between the
receiving end substation and the secondary station. It uses
3phase,3 wire system and the conductors used are called
feeders.

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Distribution System
 The component of an electrical power system connecting all the
consumers in an area to the bulk power sources or transmission line
is called a distribution system.
 A distribution station distributes power to domestic, commercial and
relatively small consumers.
 Distribution transformers are normally installed on poles or on
plinth mounted or near the consumers
Primary Distribution
 At the secondary substations, the voltage is stepped down to 11 KV
or 6.6 KV using step down transformers.
 The primary distributor forms the link between secondary substation
and distribution substation and the power is fed in to the primary
distribution system. It uses 3phase, 3 wire system.

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 Secondary Distribution
 At the distribution substation the voltage is stepped down
to 400V (for 3phase) or 230V (for 1 phase) using step
down transformers.
 The distribution lines are drawn along the roads and
service connections to the consumers are tapped off from
the distributors.
 It uses 3 phase, 4 wire system.
 Single phase loads are connected between one phase wire
and one neutral wire.

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 Conclusion:
The basic structure of power system and its various components ,
their role are discussed.
References:
1. Hadi Saadat, ‘Power System Analysis’, Tata McGraw Hill Education Pvt. Ltd., New Delhi, 21st
reprint, 2010.
2. Kundur P., ‘Power System Stability and Control, Tata McGraw Hill Education Pvt. Ltd., New
Delhi, 10th reprint, 2010.
3. Pai M A, ‘Computer Techniques in Power System Analysis’, Tata Mc Graw-Hill Publishing
Company Ltd., New Delhi, Second Edition, 2007.
4. J. Duncan Glover, Mulukutla S. Sarma, Thomas J. Overbye, ‘ Power System Analysis &
Design’, Cengage Learning, Fifth Edition, 2012.
5. Olle. I. Elgerd, ‘Electric Energy Systems Theory – An Introduction’, Tata McGraw Hill
Publishing Company Limited, New Delhi, Second Edition, 2012.
6. C.A.Gross, “Power System Analysis,” Wiley India, 2011.

7. M.Jeraldin Ahila “Power System Analysis”, Lakshmi Publications, Chennai, Eleventh Edition
2017.
8. Other web documents

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