11 kV ring main unit feeder single line diagram
This feeder distribution single line diagram shows an 11 kV ring main unit serving a commercial transformer. Incoming and outgoing 630 A load-break switches keep the ring path continuous, while a separate vacuum circuit breaker supplies a 1000 kVA 11 kV/415 V transformer. A protection CT and overcurrent relay are included on the transformer branch.
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Scenario
This RMU supplies a local distribution transformer from a through ring while maintaining continuity to the outgoing ring feeder.
Key decisions
- Ring continuity: Incoming and outgoing load-break switches preserve the 11 kV ring path.
- Transformer protection: A VCB and CT-protected relay protect the transformer branch.
- LV transformation: A 1000 kVA transformer steps 11 kV down to 415 V.
- Separate LV feeders: Retail and office loads leave from individual protected feeders.
When to reuse this
Use this for a commercial site supplied from an 11 kV ring network. The utility determines the ring operating policy and protection arrangement.
Frequently asked questions
What is an RMU?
Why is a VCB used for the transformer feeder?
Can the ring remain energized during transformer maintenance?
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