Typical AC Power Supply System
Typical AC Power Supply System
Typical AC Power Supply System
The lines network between Generating Station (Power Station) and consumer of
electric power can be divided into two parts.
Transmission System
Distribution System
We can explore these systems in more categories such as Primary transmission and
secondary transmission. Similarly primary distribution and secondary distribution.
This is shown in the below image (One Line or Single Line diagram of Typical AC
power System Scheme).
It is not necessary that the entire steps which are sown in the above image must be
included in the other power schemes. There may be difference. For example, there
is no secondary transmission in many schemes, in some (small) schemes there is no
transmission, but only distribution.
The following parts of a typical power supply scheme are shown in figure 1.
Generating Station
Primary transmission
Secondary transmission
Primary Distribution
Secondary Distribution
The place where electric power produced by the parallel connected three phase
alternators/generators is called Generating Station (i.e. power plant).
The Ordinary power plant capacity and generating voltage may be 11kV, 11.5 kV
12kV or 13kV. But economically, it is good to step up the produced voltage from
(11kV, 11.5kV Or 12 kV) to 132kV, 220kV or 500kV or greater (in some countries, up
to 1500kV) by Step up transformer (power Transformer).
Primary Transmission:
The electric supply (in 132kV, 220 kV, 500kV or greater) is transmuted to load
center by three phase three wire (3 Phase 3 Wires) overhead transmission system.
Area far from city (outskirts) which have connected with receiving station by line is
called Secondary transmission. At receiving station, the level of voltage reduced by
In other cases, for heavier consumer (at large scale) their demand is about 132 kV
or 33 kV. they take electric supply from secondary transmission or primary
distribution ( in 132 kV, 66kV or 33kV) and then step down the level of voltage by
step-down transformers in their own sub station for utilization ( i.e. for electric
traction etc).
Secondary Distribution:
Electric power is given by (from Primary distribution line i.e.11kV) to distribution sub
station. This sub station is located near by consumers areas where the level of
voltage reduced by step down transformers 440V by Step down transformers.
These transformers called Distribution transformers, three phase four wire system
((3 Phase 4 Wires)). So there is 400 Volts (Three Phase Supply System) between
any two phases and 230 Volts (Single Phase Supply) between a neutral and phase
(live) wires.
Residential load (i.e. Fans, Lights, and TV etc) may be connected between any one
phase and neutral wires, while three phase load may be connected directly to the
three phase lines.
Elements of Distribution System
Feeders
Distributors
Feeders:
Those Electric lines which connect Generating station (power station) or Sub Station
to distributors are called feeders.Remember that current in feeders (in each point) is
constant while the level of voltage may be different; the current flowing in the
feeders depends on the size of conductor. Fig 2.
Distributors:
Those taping which extracted for supply of electric power to the consumers or those
lines, from where consumers get electric supply is called distributors.As shown in fig
2.Current is different in each section of the distributors while voltage may be same.
The selection of distributors depends on voltage drop and may be design according
voltage drop. It is because consumers get the rated voltage according rules.
Good to Know: the main difference between Feeder and Distributor is that Current
in Feeder is same (in each section) in the other hand, Voltage is same in each
section of Distributor
The Normal cable which is connected between Distributors and Consumer load
terminal called Service Line or Service Mains.Here is a a complete Typical AC Power
Supply system scheme, in other words, the above whole story in below image.