Friday, 17 January 2020

AC Distribution System- Radial System, Ring main System, Interconnected System

AC Distribution System

         AC distribution system is defined as the part of power system which distribute electric power for local use.

AC Distribution System
AC Distribution System 

In distribution system it consist of 3 main components.

1. Feeder 
2. Distributor
3. Service mains


  • A feeder is a conductor which connect the substation to the area where power is to be distributed i.e. distributor conductor. 
  • No tapping are take from the feeder therefore current in it remains same  through out. 
  • A feeder is design from the point of view of its current  carrying capacity.


  • A distributor is a conductor from which tapping are taken for supply to the customer. 
  • The current flowing through distributor is not constant 
  • While designing distributor conductor voltage drop is main consideration.

 Service Main

It is a generally a small cable which connect the distributor to the consumer end.

Classification of AC distribution system 

According to the nature of current 
1. AC (Alternating Current)
2. DC (Direct Current)

According to construction 
1. Overhead 
2. Underground 

According to scheme of connection 
1. Radial system 
2. Ring main system 
3. Interconnected system 

1. Radial System 

Radial System
Radial System

  • In this system separate  feeders are taken from  single a substation and feed the distributor at one end only.
  • This system is employed only when power is generated at low voltage and substation is located at the center of load.

1) The end of the distributor nearest to the feeder will be heavily loaded.

2) The customer at the distant end of the distributor would be subjected to serious voltage fluctuation when the load on system changes. 

3) The consumer are dependent on single feeder and distributor and also single substations. Therefore any fault is occur supply will be cut off. No continuity of supply is maintained. 

2. Ring Main System 
Interconnected System
Ring main System 

  • In this system primary of all distribution transformer is connected to each other to form a loop. 
  • The main advantage of ring main system is the system is very reliable because each distribution via two feeder so less voltage fluctuation.

3. Interconnected system

Interconnected System
Interconnected System 

  • When the feeder ring or loop is energized by two or more than two substations or generating plant is called the interconnected system.
  • It increases service reliability. 
  • Substation and generating plant can share increasing demand on power system that is why only one plant or substation will not be under burden for supplying the maximum demand power. 

Requirement of Ideal Distribution System 

1. Proper Voltage 

  • One important requirement of distribution system is that voltage variation at customer terminal should be as low as possible 
  • Therefore a good distribution system should ensure that the voltage variation at a customer terminal are within permissible limit that is + - 6% 

2. Availability of power on demand 

  • Power must be available to the customer in any amount that they may require from time to time that means the distribution system must be capable of supplying load of customer.

 3. Reliability 

  • Modern industry is almost the dependent on electrical power for its operation therefore distribution system must be reliable which should maintain continuity of power supply.


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