Answer: In radial distribution system, the feeder radiate from the secondary substations and branches into sub-feeders and lateral which extends into all parts of the area served. Radial feeder is the simplest most economical and the most commonly used feeder. It has the drawback of poor reliability and greater voltage drop.
In ring main feeder, distributor makes a closed loop or ring and fed at or more than one points. Such an arrangement has an advantages of greater reliability and better flexibility.
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.
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.