In ring distribution scheme, of a transformer form a loop.

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SSC JE Electrical 05 Jun 2024 Shift 3 Official Paper - 1

Answer 1

Ring main system:

In this system, the primaries of distribution transformers form a loop.
The loop circuit starts from the substation bus bars, makes a loop through the area to be served, and returns to the substation.
Fig. shows the single-line diagram of the ring main system for a.c. distribution where the substation supplies to the closed feeder LMNOPQRS.

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The distributors are tapped from different points M, O and Q of the feeder through distribution transformers.

The ring main system has the following advantages:

There are less voltage fluctuations at consumers’ terminals.
The system is very reliable as each distributor is fed via two feeders. In the event of fault on any section of the feeder, the continuity of supply is maintained.
For example, suppose that fault occurs at any point F of section SLM of the feeder. Then section SLM of the feeder can be isolated for repairs and at the same time continuity of supply is maintained to all the consumers via the feeder SRQPONM.