Electrical distribution system


In this article we are discuss about the electrical  distribution system which means how to Electrical power distribute. In this system we will also  describe about the type of electrical distribution system .

Electrical distribution system

The conductor system, by means of which electrical energy is conveyed from bulk power source or sources to the consumers, is known as distribution system may be divided into two systems known as high voltage (primary) distribution and low voltage (secondary) distribution.
Primary electrical distribution system

Electrical distribution system, ac distribution system, radial fider , dc distribution system

From generating stations the electrical energy is usually transmitted to various substations through extra high tension transmission lines at voltage from 33 to 220 Kv . At these substations this voltage is stepped down to 11 or 6.6 or 3.3kv and power at this voltage is conveyed to different substations for distribution and to the bulk supply consumers.
Secondary electrical distribution system
At distribution substations, the voltage is stepped down to 400 to volts. From these substation various low voltage (400 volts between phase and neutral) distributors radiate out and feed the consumers.
Classification of distribution system
Distribution systems may be classified in various ways.
According to current the distribution system may be classified as

1. AC distribution

2. DC distribution


A.C Distribution system


  1.  Primary distribution system


                 It is the main type of  A.C distribution system

·       It is that part of AC distribution system which operate at voltage such as 3.3KV,6.6KV and 11kv . which is higher than that of general utility 230/440v and handle large blocks of power from the generating station located in or near the city.
At these substation which is known as secondary substation ,the voltage is step down to 11,6.6,3.3kv with the help of power transformer for primary distribution .the feeder may be radial ,parallel , interconnected or ring type .

A.    Radial feeder

Electrical distribution system, ac distribution system, radial fider , dc distribution system
 the feeder radiates from  the secondary substation and branches into sub feeders and laterals which extend the distribution transformer are connected to the primary feeders,sub-feeders and laterals usually through the fuse cut out ,it is the simplest,most economical and most commonly used.it is advantages for supplying the power to heavy industrial load and near the
secondary substation ,isolated load such as villages. But there are some draw-back also-

·       Poor reliability

When a foult occurs at any point on the feeder,supply to all consumers beyond that foult point towords the tell end get interrupted.

·       In case of increase in load demand ,the length of the feeder has to be extended and may result in a greater voltage drop.

B.    Parallel feeders:
Electrical distribution system, ac distribution system, radial fider , dc distribution system


  • In a parallel feeders system ,two radial feeders feed from the same or different secondary substation are run in parallel each feeder,though capable of supplying the entire load,shares the total load equally in normal condition. This system is expensive but reliability is increased as in case of fault on one feeder the total load can be supply by the healthy feeder . interruption of supply is only for the time duration that is taken in transferring the load from the faulty feeder to healthy one either by manual or automatic cities.Such a system is employed where ever the continuity of supplying is of greater importance

Loop feeder:


In a loop feeder system two or more radial feeder connected from the same or different secondary substations are setup on different roots of load areas.
Electrical distribution system, ac distribution system, radial fider , dc distribution system
THE arrangement having the end of two feeder tied together through the normally open switching device is known as open loop system.while the arrangement having the ends of two feeders tied together through the normally closed switching device known as ring man feeder  the use of  this system is restricted due to the very large investment . it is used where continuity of supply is first priority feeders end loop component must have sufficient reserve capacity to handle the load that may be transferred lender abnormal condition .

Interconnected N/W system

Electrical distribution system, ac distribution system, radial fider , dc distribution system

In interconnected N/W system is very useful for AC distribution system .
When the feeder ring main is energized from two or more generating stations or substations,such systems known as interconnected n/w system. Because of interconnected feeder,power can be supplied to all the distributor transformer even though a part of network may be out of service. Such a system provides better reliability metro pollution cities where continuity of supply is the most important.

2.  Secondary distribution system


It is the second type of AC distribution system .
A.    Three phase 4 wire distribution system
B.    Single phase ,2 wire distribution system


The secondary distribution system may be  radial,open loop or N/W distributor. 
hence these are main type of C distribution syste





According to the character of service, the distribution systems may be classified as

1. General light and power

2. Industrial power

3. Railway

4. Street lighting etc.

According to the type of construction, the distribution system may be classified as

1. Overhead electrical distribution system

2. Underground distribution system

According to number of wires the distribution system may be classified as


1. Two wire

2. Three wire

3. Four wire distribution systems
In case of dc supply three wire distribution system in usually employed owing to its advantages over two wire distribution system. In case of a.c. supply three phase 3 wire is employed for balanced loads such power use, 3 phase 4 wire system employed for unbalanced loads such as light and power loads combined. Single phase two wire system is used for lighting and small power appliances.

According to scheme of connections, the distribution systems an classified as

1. Radial
2. Ring
3. Inter-connected

1. Radial system

In this system of distribution, the distributors are fed at one end only.

2. Ring main system

In this system, each consumer is supplied via two feeders. The arrangement is similar to two feeders in parallel on different routes.

3. Interconnected system

When two or more generating stations are connected together, the system is known as interconnected system. Reliability of the system increased in this case.
Bundled conductors
A bundle conductor is a conductor made up of two or more sub-conductors and is used as one phase conductor .it is found that the increase in transmission capacity justifies economically the use of two conductor bundles on 220kv lines. The following are the advantages in using bundle conductors.

1. Reduced reactance

2. Reduced voltage gradient

3. Reduced corona loss

4. Reduced radio interference

5. Reduced surge impedance

The reactance of the bundle conductors is reduced because the self GMD of the conductors increased and as we know reactance = kln GMD/GMR and as GMR is increased the reactance is reduced.

There is an optimum sub-conductor spacing for bundle conductors that will give minimum gradient on the surface of a sub-conductor and hence highest disruptive voltage. Since the voltage gradient is reduced by using bundled conductors the radio interference is also reduced.

Surge impedance = root of L/C


Since by bundling. The self GMD is increased, the inductance is reduced and capacitance increased as a result the surge impedance is reduced.

Hence these are electrical distribution system. if you will find any incorrect in above article you must comment below in comment box.

If you want to know more about the electrical distribution system. you must watch this video.


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