11kv Ring main

[STONE85]

Hello,
I have a question in regards to 11kv ring main circuits. What is a closed ring? Am I correct with the following

Say we have a switch board with two incoming supplies and a buscoupler splitting this board into two sections. Would this buscoupler be closed for a closed ring ?

Thanks

 

[7anoter4]

See -for instance: Schneider Electric Ring Main Unit

https://www.se.com/uk/en/work/products/product-launch/smart-ring-main-unit/

 

[FacEngrPE]

The link (in the image) has information about other bus arrangements.

 

[Hoxton123]

It is 'normal' practice to operate with the ring open, generally about halfway around.

Any main switchboard bus coupler would be open, so the ‘ring’ operates as two separate radial circuits.

In the event of a fault, the breaker in the 11kV board would trip, isolating that part of the ring. If the bus coupler were closed then either or both breakers could open, depending on protection settings.

A traditional UK Ring Main Unit (RMU) has two switches to connect to the ring and one fuse to connect to the distribution step down transformer. The switches are manually operated.

Following the fault, the site engineer has to decide where the fault (usually a cable fault) is and reconfigure the RMUs to get the faulty cable at the ‘open’ part of the ring. The tripped breaker can then be closed, and power restored. Sometimes this operation has to be performed several times until the faulty cable is located!

Manufacturers like Schneider have modernised and automated the system.

The benefit of an RMU is that it is a lot cheaper and smaller than using 11kV traditional circuit breakers and is often located outside.