Typical AC Power Supply system (Generation, Transmission and Distribution) scheme and Elements of Distribution System (a complete note With Diagrams)
Typical AC Power Supply system scheme
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 are shown in
figure 1.
- Generating Station
- Primary transmission
- Secondary transmission
- Primary Distribution
- Secondary Distribution
Following is detail of the above
sections
Generating Station:
The place where electric power
produced by parallel connected three phase alternators/generators is called
Generating Station. The Ordinary 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 transmit to load center by three phase three wire overhead
transmission system.
Secondary transmission:
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 step-down transformers up
to 132kV, 66 or 33 kV, and Electric power is transmit by three phase three wire
overhead system to different sub stations. So this is a Secondary Transmission.
Primary Distribution:
At a sub station, the level of
secondary transmission voltage (132kV, 66 or 33 kV) reduced to 11kV by step
down transforms.
generally, electric supply is given to
those heavy consumer which demands is 11
kV, from these lines which caries 11 kV ( in three phase three wire overhead
system) and they make a separate sub station to control and utilize this power.
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). 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
Secondary distribution may be divided
into three parts
- Feeders
- Distributors
- Service Lines or Service Mains
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.
NOTE: 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
Service Lines or Service Mains:
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.
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