Radial, Parallel, Ring main and Interconnected Distribution Systems

An electric power distribution system can be classified according to its feeder connection schemes or topologies as follows -

• Radial distribution system
• Parallel feeders distribution
• Ring main distribution system
• Interconnected distribution

There are few other variations of distribution feeder systems, but we'll stick to these four basic and commonly used systems.

[Also read: Classification of distribution systems according to number of phases and wires involved.]

Radial distribution system

This system is used only when substation or generating station is located at the center of the consumers. In this system, different feeders radiate from a substation or a generating station and feed the distributors at one end. Thus, the main characteristic of a radial distribution system is that the power flow is in only one direction. Single line diagram of a typical radial distribution system is as shown in the figure below. It is the simplest system and has the lowest initial cost.

Image credit: Wikimedia commons

Although this system is simplest and least expensive, it is not highly reliable. A major drawback of a radial distribution system is, a fault in the feeder will result in supply failure to associated consumers as there won't be any alternative feeder to feed distributors.

Parallel feeders distribution system

The above-mentioned disadvantage of a radial system can be minimized by introducing parallel feeders. The initial cost of this system is much more as the number of feeders is doubled. Such system may be used where reliability of the supply is important or for load sharing where the load is higher. (Reference: EEP - Distribution Feeder Systems)

Ring main distribution system

A similar level of system reliability to that of the parallel feeders can be achieved by using ring distribution system. Here, each distribution transformer is fed with two feeders but in different paths. The feeders in this system form a loop which starts from the substation bus-bars, runs through the load area feeding distribution transformers and returns to the substation bus-bars. The following figure shows a typical single line diagram of a ring main distribution system.

Ring main distribution system is the most preferred due to its following advantages.

Advantages of ring main distribution system

• There are fewer voltage fluctuations at consumer's terminal.
• The system is very reliable as each distribution transformer is fed with two feeders. That means, in the event of a fault in any section of the feeder, the continuity of the supply is ensured from the alternative path.

Interconnected distribution system

When a ring main feeder is energized by two or more substations or generating stations, it is called as an interconnected distribution system. This system ensures reliability in an event of transmission failure. Also, any area fed from one generating stations during peak load hours can be fed from the other generating station or substation for meeting power requirements from increased load.