Settings for a busbar differential relay

[unclebob]

Hi all!

Does anybody have references about how to choose settings for this type of protection?

We will be using a SEL487B. I know this relay can do a bunch of things, but I will be using only the differencial protection.

BTW, what is the correct spelling for ''busbar''

Thanx

 

[davidbeach]

I believe the SEL487B manual provides a great deal of information about how to set the relay.

 

[dpc]

The advantage of a bus differential system is that it has a clearly defined zone of protection and does not have to be coordinated with other overcurrent devices.

You can set it as low as practical, generally meaning high enough to avoid nuisance tripping on faults outside the zone. This will depend on the quality of your CTs and the magnitude of the maximum fault current.

 

[slavag]

Dear Unclebob.
I strongly recommend to you order settings calculation and commissioning of BBP from company with experience in this relay or better, directly from SEL.
I worked with several types of BBP, each company have some small "things" and not always you'll found them in manuals.
As DPC saied:
"You can set it as low as practical, generally meaning high enough to avoid nuisance tripping on faults outside the zone. This will depend on the quality of your CTs and the magnitude of the maximum fault current."
But it's only small part of setting.
Best Regards.
Slava

 

[dpc]

Hey, I never said it was easy

 

[slavag]

Dear Dpc, sorry, if my words are not correct.
Regards.
Slava

 

[jghrist]

You should also review ANSI/IEEE C37.97, IEEE Guide for Protective Relay Applications to Power System Buses. I wouldn't try to spell "busbar protection", I'd use the more common (at least in USA) "bus protection". That way you can protect tubular bus or strain bus as well as bus made of bars. B-)

 

[dpc]

Slava,

I agree with you - I was just making fun of myself.

 

[slavag]

Dpc, I know .
Slava

 

[unclebob]

The both the relay instruction manual, the user's guide and the application guide have over 500 pages each. They do explain how the relay works, but not how to find, calculate or determine the settings to implent in it...

 

[dpc]

unclebob,

It will be important to determine the accuracy class of each CT used as well as the fault current. You have to determine if any of the CTs will saturate for a fault just outside the protected zone.

SEL seems to like to keep things fairly complicated - job security for the utility protection engineers, I suppose as well as a lot of flexibility in applications.

I'd suggest calling the SEL field service engineer for your area. They are generally pretty helpful with help on setting the relays. Or call the factory. They will usually give you quite a bit of support. You might also take a look at SEL Application Guide AG2004-06 on their website.

And no, I don't work for SEL.

 

[unclebob]

The problem that I have is that I know enough to know that I know noting, if you know what I mean.

For detection of out-of-zone faults, the relay has a directional element that may be programmed. No problem with that part.

For the differential element, you have to set a Restrain Threshold and two Restrain Slopes. How you set these parameters? It's for station bus protection which should be easier than transformer protection

I'm calling the SEL guy tomorrow...

For those of you who are curious, here is the station config:

Two (2) 25 kV, 1200 A switchgears with 3 incoming lines. First 2 lines enter switchgear 1, the other line switchgear 2.

Tie breaker (vaccuum, 600 A) between the 2 switchgears.
All feeders (6) are vaccuum, 600 A breakers.

At all times, 2 lines feed the switchgears, one is reserve.

3-phase fault current: no less then 4000 A
single phase to ground: no less than 500 A

Differential protection CT's: all 1200:5 accuracy class unknown,

I have 2 SEL487B relays, protecting a total of 9 zones.

 

[jghrist]

Schweitzer application guidelines are available at

http://mail.biz.rr.com/agent/mobmain?mobmain=1.

Applying the SEL-487B to Single Busbars, AG2004-06, looks applicable and has AcSELerator files.

 

[slavag]

Hi Uncelbob.
Why you add BBP or 87B to this station?
BBP are common for HV and EHV stations or probably for MV common generation bus.
I see, according to your data,you need two type of protection : phase diff. protection and sensetive ground fault diff. protection.
I don't know SEL-relay, but I think it have both of options.
Good Luck.
Slava

 

[davidbeach]

slavag, the SEL-487B doesn't do sensitive ground fault, but that really doesn't matter if he will get "no less than 500A" for ground faults. In unclebob's scheme he will be using two relays, one for two phases and the second relay for the third phase, no way of calculating earth fault, just faults on an individual phase basis.

 

[slavag]

O.K.
I read now spec of SEL 487B relay. You are right, it's six 3-ph current ( or 18 single phase)inputs per relay,of course no ground faults options.
I'm thinked about other type of BBP, like to Areva, ABB, Siemens, basics on separated bay units and central unit.
About "not less than 500A", it's also less than load current. In BB protection, I prefer setting less than minimum fault current and more than max. load current.
In case of not solidly grounded system, I prefer use SDiffEF, but it's only my opinion. Actually, we never used BBP for MV application, only in special cases we
used " partial diff protection" or high impedance BBP.
For this reason, important contact to SEL and check with field eng. all this points.
Best Regards.
Slava

 

[slavag]

Just idea for Uncelbob station.
One setting (or slope) for phase to phase fault :
I don't know, maybe about 80-90% of l200A primary.
Another setting ( or slope) will use for ground fault with setting about 20% of 1200A primary ( 240A< 500A of min ground fault), but this slope used together with signal from Zero seq. voltages for increase security and prevent unwanted trips.
Of course used both of slopes with additional blocking from
supervisions and maybe add block of slope ground fault from
slope of phase to phase fault.
Regards.
Slava