Electrical Distribution System


Distribution System

The system used to deliver power from substation to the load center is called Distribution System.

  • Distribution system is consist of feeder, service mains and distributors .

Feeder is a wire or conductor which is connected between the substation and area where power is deliver. there is no tapping are taken from the feeder so current rating in feeder remaining same. the design of feeder is mainly depends on current carrying capacity. It is shown in fig as SA, SB and SC.

Service mains:

Service mains is simply small cable which is connected between distributor and consumer terminals .


Distributor is conductor from which tapping are taken for supply to the consumers. Current through distributor is not constant because Tappings are taken at different point along its length. the design of feeder is mainly depends on voltage drop along its length. voltage variation is ± 6% of rated voltage at consumer terminal. its shown in fig as. AD , DC ,CB and AB.

Distribution system

Classification of Distribution system:

  • Nature of current
  1. AC system
  2. DC system
  • Type of construction
  1. Overhead system
  2. Underground system
  • Scheme of connection
  1. Radial system
  2. Interconnected system
  3. Ring main system


AC distribution system:

  • Generated electrical energy is transmitted and distributed in form of Alternating Current. AC system classified as primary distribution and secondary distribution.
Primary distribution system:
  • In these part of ac distribution system which operates at some high voltage  then general utilization . the voltage use for primary distribution is depend on amount of power to be deliver as well as distance between substation to the  require fed. primary distribution voltage are 3.3 kv ,6.6 kv and 11 kv. due to economic consideration is 3 phase 3 wire system.
  • power is supply to different substation distribution or to big consumer i.e industrial area . these form of distribution is known as primary distribution.
Secondary distribution system:
  • These part of AC distribution system is include range of low voltage. Which the ultimate consumer use Electrical power deliver to consumer. Secondary distribution voltage is about 230 v , 440 v and it is 3 phase , 4 wire system.

DC distribution system

  • Two types of DC system.
  1. DC Two wire system: As name suggest, these system is consist of two wire. One is positive wire and other is negative wire. The load are use for these system is lamps, motors etc… They are connected in parallel between the two wires.
  2. DC Three wire system: It consist of three wire. Two outer wire and one is middle wire which is earthed at the substation. The voltage between two outer wire is twice to the voltage between outer or middle wire. It is use where loads requirement is high voltage.

if any query about distribution system

comment below…………………. ?


  1. I would like to be able to identify the electrical problems before hiring someone on. I would also like to be able to understand how to protect my electrical power. I think it would be nice to be able to understand DC power.


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