Protection Coordination of Ring Circuits

[mutimuti]

How is it really done? It seems you have bi-directional relays at the source bussbar and uni-directional relays at all the other busses looking towards the source. You then have two sets of uni-directional relays looking in opposite directions. When setting do you consider the situation as two separate radial circuits?

 

[Grollor33]

Is bus differential protection an option?

 

[DanDel]

Typical overcurrent relays are bi-directional, anyway.

As long as every source proective device is coordinated with every load device (each load device must trip before each source device it can be energized from), you will be OK.

If multiple sources are present, they should have added directional relays which are set significantly lower than the overcurrent relays so that, in the case of a fault upstream on one source line, the other sources feeding that fault will trip quickly.

 

[dpc]

For ring bus applications, we have typically used a series of three-input differential relays with overlapping zones to provide bus differential protection for each segment. If the position feeds a local transformer, you can extend the zone to the other transformer winding.

 

[stevenal]

If it is small enough, yes, consider it as two radial feeds, one looking one way around the ring and the other looking the the other way. With a ring of many buses, you will have difficulty coordinating all the TOC elements, though. Line differential might be in order.

 

[RalphChristie]

mutimuti:

You can use differential or directional protection for this kind of situations, like suggested by previous posters. From a coordination or protective viewpoint differential protection might be best option, but depending on the application, it might be much more expensive than directional protection.

From your initial question it seems as if you are more interested in directional protection. Most protective handbooks cover it, and you'll also find a lot of information regarding it on the web. One excellent resource:

Download: NPAG link
Chapter 9 - overcurrent protection for phase and earth faults.
9.14 - 9.15 deals with directional protection.

In short DanDel and stevenal are correct - read through the information in the link - if you have any specific question I will try my best to answer it. (or anyone else!)

Regards
Ralph

[red]Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon[/red]

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[mutimuti]

DPC, STEVENAL, RalphChristie, I salute you all. You are repositories of good information, dont need consultants! With differential protection, co-ordination and setting are not serious issues (but cost is).

mm

 

[mutimuti]

What is a 3-input Differential Relays dpc?

 

[bacon4life]

Three input relays would have one input from each of the two breakers they are connected to locally, and the third input from the remote end of the line.