Ring Networks Coordination

[burntcoil]

Hi everyone,

We have multiple Ring Main Units connected together forming a loop as shown in the attachment. Its a 13.8kV Network. The Ring Loops are fed from a 13.8kV Switchgear, Bus-A is feeding one side of the loop while Bus-B is feeding the other side of the loop. Under normal condition, one of the breaker in the middle of the loop will be open (N.O) thus each breaker in the 13.8kV Switch-gear will feed half of each loop.
How Over-current coordination can be carried out for this loop to work both ways i.e. Breaker on Bus-A shall feed the whole loop, Breaker on Bus-B shall feed the whole loop. What are the practices when doing over-current coordination for such networks.

Thanks

 

[davidbeach]

Directional overcurrent and communications.

 

[mgtrp]

Or, if that's not possible, by compromising on the coordination when feeding the whole loop from one source, which presumably doesn't happen very often. It depends on how important it is to you that coordination is maintained in all circumstances.

 

[ppedUK]

This configuration is very common in small installations in the U.K., however for most of the installations of this type, there is no protection fitted to the ring in/out breakers on the Ring Main Units. More often than not, the ring in/out devices are just fault making switches fitted with an earth fault passage indicator which identifies the location of the fault after the ring feeder breaker has tripped. Protection of the ring cabling and RMUs is provided only by the breakers at the main feeding end, and it is then a simple matter of co-ordinating each transformer relay(s) with the ring feeder relay(s). For open ring configurations such as this, there is also normally mechanical key interlocking to ensure that there is always an open point on the ring, so that the main switchboard buses cannot be inadvertently paralleled through the ring.

With the amount of TX load that you have, you may also have to load shed when the whole ring is fed from one end only.