Reverse Power Relay

[augie47]

The job I inspected has a 2500 amp 480v buss fed by a separate switchboard at each end (no "tie" breaker..no break in the buss). Each Powertran Switchboard is being fed from separate 15kv feeders.
I had immediate concern about the buss not being properly protected and more so concerning the possibility of the 15kv feed to switchboard "A" being turned off and then back-fed from the power supplied to "B", a situation I have seen prevented by the kirk-key set up.
In this case I am advised by the engineer that a "new and improved" method is being used, a Bassler Reverse Power Relay" which prevents such back feeds.
My "old school" mind is not comfortable with the system without the manual control of a tie breaker.
Is anyone here familiar with the BRPR and find my concerns unwarranted.

 

[hillbilly1]

I had never heard of this type of relay before, but it is interesting in what it can do. Would I trust it.......... I don't know, if it failed could be a very dangerous situation. It seems to be used on generators mostly, probably co-generation set ups. Here's a link to the info I found. http://pm.geindustrial.com/FAQ/Documents/ICW/GER-2309A.pdf

 

[david luchini]

I had immediate concern about the buss not being properly protected and more so concerning the possibility of the 15kv feed to switchboard "A" being turned off and then back-fed from the power supplied to "B", a situation I have seen prevented by the kirk-key set up.
In this case I am advised by the engineer that a "new and improved" method is being used, a Bassler Reverse Power Relay" which prevents such back feeds.
My "old school" mind is not comfortable with the system without the manual control of a tie breaker.
Is anyone here familiar with the BRPR and find my concerns unwarranted.

I think you've got a valid concern. If on switchboard A, the main is turned of, AND all of its load breakers were opened such that there would be no load on switchboard A even if it was backfed, then the reverse power relay won't detect any power flowing thru the buss and back to switchboard A, and would not trip. But in this case, voltage would backfeed to switchboard A. (That is to say the voltage would backfeed A, but no current would be flowing to A from the buss. No current, no "reverse" power.)

It might not be a likely situation, but it is possible.

 

[david luchini]

I had never heard of this type of relay before, but it is interesting in what it can do. Would I trust it.......... I don't know, if it failed could be a very dangerous situation. It seems to be used on generators mostly, probably co-generation set ups.

Yes, very common on generators in co-gen setups. Dealt with these quite a few year back working with steam-turbine generators. The relay was really meant to protect the turbine rather than the generator.

If the turbine suddenly lost its prime mover (the steam supply) the generator would basically turn into a motor, with the generator turning the turbine, which could damage the turbine. The reverse power relay would sense that power was flowing to the generator (motoring), instead of from the generator, and trip the generator breaker.

 

[zog]

The job I inspected has a 2500 amp 480v buss fed by a separate switchboard at each end (no "tie" breaker..no break in the buss). Each Powertran Switchboard is being fed from separate 15kv feeders.
I had immediate concern about the buss not being properly protected and more so concerning the possibility of the 15kv feed to switchboard "A" being turned off and then back-fed from the power supplied to "B", a situation I have seen prevented by the kirk-key set up.
In this case I am advised by the engineer that a "new and improved" method is being used, a Bassler Reverse Power Relay" which prevents such back feeds.
My "old school" mind is not comfortable with the system without the manual control of a tie breaker.
Is anyone here familiar with the BRPR and find my concerns unwarranted.

Reverse power is a term generally used for generator protection, the similar scheme of a directional relay would apply more here. Your backfeed concern is valid but can be prevented electronically several different ways, hard to tell without more info on the gear.

Now my much larger concern here would be the availabale fault current of the 2 transformers in paraell exceeding the interuption ratings of the breakers, that is a much more common problem to find in a set up like this. There are special breakers designed for this type of set up but I often find them to be misapplied. I have personally had to repair 3 major explosions (Complete switchgear replacements) this year because this same thing was being done and a fault occured.

 

[Cold Fusion]

...I had immediate concern about the buss not being properly protected and more so concerning the possibility of the 15kv feed to switchboard "A" being turned off and then back-fed from the power supplied to "B", a situation I have seen prevented by the kirk-key set up. ...

Get the one-lines with the protective devices listed on it. Get the coordination curves. Get the protective relay manuals.

The engineer can tell you anything she wants until you go through it and understand it. The only other options are hire your own engineer or believe her.

...My "old school" mind is not comfortable with the system without the manual control of a tie breaker. ...

I didn't know that manual control of a tie breaker, or even requireing a tie breaker was a regulatory issue. What code section is that?

cf

 

[Hameedulla-Ekhlas]

The job I inspected has a 2500 amp 480v buss fed by a separate switchboard at ----

Generally

Distribution systems are radial in nature. This holds true for both utility and plant distribution systems. If there is a fault on the utility's distribution system, it may trip a breaker thereby isolating plant from the grid. This plant may still remain connected with downstream loads as shown in photos. Consequently, power will flow from the plant generator to these loads.
If in the prefault state, power was being fed to the plant, then this reversal of power flow can be used to island the plant generation and load from the remaining system. This approach is useful to detect loss of grid supply whenever the difference between load and available generation is not sufficient to obtain an appreciable rate of change of frequency but the active power continues to flow into the grid to feed the external loads.

Example
In fig 3.4, consider that the plant imports at all times a minimum power of 5 MW. Studies indicate that for various faults in utility side, minimum power export from the plant generator is 0.5 MW. Deduce the setting of reverse power relay. If the plant generator is of 50 MW capacity, what is likelihood of underfrequency or rate of change of frequency relay picking up on such faults?
Ans: Reverse power flow relay can be set to 0.4 MW. Since minimum reverse power flow is 1% of plant capacity, it is quite likely, that utility disconnection may not be noticed by underfrequency or the rate of change of frequency relays.
.
if it is a Basler not bassler see below link type you can download the manual.


BE3-32 Reverse Power Relays

Link

 

[SG-1]

Augie, here is a link to Basler device 32 relays ( reverse power ). From this page you can down load the manual which will have typical connection schematics. You could compare these to see if any match the relay. No match would be a cause for concern. There is usually a theory section on the operation of the relay.

http://www.basler.com/html/pcs27-49.htm#32O_U

One is a Reverse & Underpower which may assuage some of the concerns above.


Ham is just too fast for me...

 

[dbuckley]

As David Luchini noted above, this class of protective device is designed to minimise plant damage if something goes awry.

The issue Augie is wrestling with is a safety-of-life issue related to islanding.

The liability querstion here is is this relay certified to protect life, or just protect equipment?

I think Augie is right to be very concerned. I would be.

 

[RB1]

Augie,

What is the rating of of the overcurrent protection at each end of the bus? What is the ampere rating of the horizontal bus connecting the two ends of the switchboard?

 

[augie47]

Augie,

What is the rating of of the overcurrent protection at each end of the bus? What is the ampere rating of the horizontal bus connecting the two ends of the switchboard?

That's Phase II of concern that I need to review with the engineers...
All three are rated 2500 amp.
I can not see how that would not subject the buss to overload.

 

[kingpb]

Would it be possible to sketch out a simplified one-line of the system in question. I am having a hard time with the configuration, including placement of the transformers.

If there is a potential for paralleling the two 15kV feeds, it is likely your SC rating of the bus may not be capable of handling the fault.

 

[augie47]

poor sketch

View attachment 4672

 

[kingpb]

Assumption:
The bus in question is double ended without a tie (from one-line).
Power interruption is not desired during switching, therefore the two LV breakers will need to be momentarily paralleled , i.e. make before break, to keep the bus from going black. That is usually an acceptable risk.
With 480V switchgear breakers this is usally accomplished by using electrically operated breakers. Kirk-key would also work, but it's a slower operation and manual operation.

If the 15kV sources are truly two different feeds, can they be out of sync? I would think there is sync check relaying involved at the 15kV breakers?

From what is shown, I'm not sure what the 32 relays accomplish.

 

[Cold Fusion]

poor sketch

View attachment 4672

It's a good sketch. What are the transformer ratings?

1000kva? 1500kva?

The 15kv feeds - they both come from the same source?

cf

 

[zog]

poor sketch

View attachment 4672

For loop circuits or systems with more than one power source, direction overcurrent relays (67 devices) might be used. With this type of system, fault current can flow in more than one direction. Using these types of relays can make it easier to coordinate with other relays that are on the system because they only operate when current is flowing in the tripping direction.

But I would not be so concerned about the relay, my concern here would be the breaker interuption rating not being high enough for the available fault current in that system. You have the transformer kVA and %Z?

 

[augie47]

It's a good sketch. What are the transformer ratings?

1000kva? 1500kva?cf

Unsure. It is all contained in a SqaureD switchboard (transformer & transformer secondary, buss protection in one unit).
I have not had an opportunity to look closely.

The 15kv feeds - they both come from the same source?

cf

From the entire plant one-line that seems to be the case.

This is new installation, huge plant, and there have been numerous changes including the "emergency-alternate" feed.

My boss has a meeting tentatively scheduled with engineers, etc to review. I',m just trying to arm myself with some knowledge so I can listen with reason.

 

[Cold Fusion]

Unsure. It is all contained in a SqaureD switchboard (transformer & transformer secondary, buss protection in one unit). ...

...From the entire plant one-line that seems to be the case.

This is new installation, huge plant, and there have been numerous changes including the "emergency-alternate" feed.

... I',m just trying to arm myself with some knowledge so I can listen with reason.

So you have the updated one-lines? Most everything you need should be on them. - except maybe an operational plan. I reread the posts and didn't see any mention of the plan. Here are ome of the question I would ask:

Are both transformers to be providing power to the connected bus load at the same time? This is pretty common. Load on each transformer is <50% for normal operation. There really isn't any concern with overloading the bus. The load is not limited the transformer secondary CBs. The load is limited by design.

If only one transformer is connected, is the switching open transition or closed transition? Is the switching automatic?

I have no idea of what these reverse power relays are susposed to do or protect. They don't make any sense. If the concern is that a transformer can be back-fed energized if the 15kv feeder CB is opened, my first comment is, "So what?. Second comment is, " If this is a perceived problem, then interlock the secondary main to open if the primary cb opens. That is pretty common practice."

cf

 

[augie47]

Thanks, cf....

One question. You mentioned load as a deciding factor, but would 368.17 not require the OCP not to exceed the buss rating. If both transformers can feed the buss simultaneously, it would appear to be a violation of 368.17 ..............

 

[steve66]

I have no idea of what these reverse power relays are susposed to do or protect. They don't make any sense. If the concern is that a transformer can be back-fed energized if the 15kv feeder CB is opened, my first comment is, "So what?. Second comment is, " If this is a perceived problem, then interlock the secondary main to open if the primary cb opens. That is pretty common practice."

cf

Just a guess here, but it looks like the reverse relay is in case one transformer or feeder shorts.

The reverse relays would keep power from backfeeding the bad transformer/feeder until one (or both) of the breakers on the shorted side trips. Otherwise, a shorted transformer could take out the secondary breaker on the other transformer.

Steve