EE356: Power Transmission,
Distribution and Utilization
Farhan Mahmood, PhD
Department of Electrical Engineering
UET, Lahore
October 10, 2020
Outline
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Power systems
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Structure of a power system
Page 2
Power Systems
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Purpose of a power system is to transport and distribute the electrical energy
generated in the power plants to the consumers in a safe and reliable way.
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An electrical power system can be classified into:
–
Generation system → creates electrical power with specified voltage and
frequency
–
Transmission system → transports electrical power from generation to load
–
Distribution (and Utilization) system → distributes and consume electrical power
Generator
T.L
Load
Transmission Line
(a) Typical power system configuration
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Power Systems
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Generation, transmission & distribution of
electrical power is accomplished by means of
three-phase circuit.
˗
Voltages are equal in amplitude and
displaced in phase by angle of 120°.
˗
Such a system is called as a balanced
(b) Three-phase sinusoidal voltages
system.
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Structure of a Power System
Page 5
Structure of a Power System
G.S
Power Plant Substation
Transmission substation
Zone substation
Distribution substation
Page 6
Structure of a Power System
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The generating station converts the energy of gas, oil, coal or nuclear fuel to electric
energy. The output voltage of the generator voltage is around 15-25 kV (12.5 kV at
Mangla Dam).
•
The main transformer increases the voltage to 230-765 kV (220-500 kV in Pakistan).
This reduces the current and losses.
•
The high voltage transmission line transports the energy from the generating station
to the large loads, like towns.
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The high voltage substation reduces the voltage to 120-69/(132-66) kV. The
substation serves as a node point for several lines.
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The sub-transmission lines (69 kV-120 kV) / (66 kV–132 kV) connect the high
voltage substation to the local distribution station.
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Structure of a Power System
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The distribution lines (11-33 kV) distribute the energy along streets or underground.
•
Each line supplies several step-down transformers distributed along the line.
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The distribution transformer reduces the voltage to 230/115V/(400/220V), which
supplies the houses, shopping centers, etc.
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Transmission and distribution lines are three-phase (excluding HVDC)
˗
Most industrial consumers use three-phase power
˗
Most residential consumers use single-phase power
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Structure of a Power System
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THANK YOU FOR YOUR ATTENTION