Reverse current relay in service switch

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lzielk

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I have a problem with a service switch in a large building we have a reverse current relay connected to a shunt trip breaker that seems to have gone bad we pulled the fuse on the relay and the service stays on line
My question is what is the purpose of this reverse current relay and how. Necessary is it. As we have many more service switches without this feature also is the replacement just a switch out or does it require special calibration?
Thanks for any comments
 

ATSman

ATSman
Location
San Francisco Bay Area
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Electrical Engineer/ Electrical Testing & Controls
The only reason I see that a reverse power relay would be wired to a service entrance disconnect is to prevent a back up generator from feeding back to the utility. I did a startup once where the main breaker of a hospital fed a new Closed Transition transfer switch. This type of ATS momentarily parallels the generator with the utility when transferring the load to emergency for a seamless (no interruption) transfer. I ended up installing a Basler reverse power relay on the ATS door and the inspector had to witness the testing with a sophisticated relay test set to verify that it works.
We need more info, drawings, pics etc.
 

Jraef

Moderator, OTD
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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
When you typically see a Reverse Current Relay on a service is for when you have on-site generators that may be used not as backup for a power failure, but to supplement a utility service during peak demands. So rather than getting hit with a big demand charge, a user will put their own generator in parallel with the utility service when they need more power than they want to take from the utility. But at the same time, they don't want THEIR generator to give free power back to the utility should their load suddenly drop off. So the relay is looking at the DIRECTION of current flow and if it goes back TOWARD the utility, it shunt trips the service disconnect.

In SOME cases if you have a large connected load of rotating machines that might go into regeneration if there is an issue with the utility, then those motors can become generators and the UTILITY hay have mandated the reverse current relay to protect your NEIGHBORS from having your facility put energy back onto a downed power line.

Bottom line, don't remove or disconnect it until you know WHY it is there, you might end up costing the facility a bunch of money, or worse yet, kill someone.
 

lzielk

Member
I don't know. Do you have any parallel generation? Does the utility require it for any reason?
we have an emergency generator with ats switches generator should not be able to feed back o the service its either on or the other connected to the load.
we have many different buildings in the complex and the other service switches do not have these ....they do have shunt trips for ground fault though
 

david

Senior Member
Location
Pennsylvania
I have a problem with a service switch in a large building we have a reverse current relay connected to a shunt trip breaker that seems to have gone bad we pulled the fuse on the relay and the service stays on line
My question is what is the purpose of this reverse current relay and how. Necessary is it. As we have many more service switches without this feature also is the replacement just a switch out or does it require special calibration?
Thanks for any comments

Does the building have a lot of loads with capacitors, Had a utility ask for protection at an industrial facility once.

Capacitors where introduced on motor loads to adjust power corrections, the utility asked for protection from back feeding their lines
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
When you typically see a Reverse Current Relay on a service is for when you have on-site generators that may be used not as backup for a power failure, but to supplement a utility service during peak demands. So rather than getting hit with a big demand charge, a user will put their own generator in parallel with the utility service when they need more power than they want to take from the utility. But at the same time, they don't want THEIR generator to give free power back to the utility should their load suddenly drop off. So the relay is looking at the DIRECTION of current flow and if it goes back TOWARD the utility, it shunt trips the service disconnect.

In SOME cases if you have a large connected load of rotating machines that might go into regeneration if there is an issue with the utility, then those motors can become generators and the UTILITY hay have mandated the reverse current relay to protect your NEIGHBORS from having your facility put energy back onto a downed power line.

Bottom line, don't remove or disconnect it until you know WHY it is there, you might end up costing the facility a bunch of money, or worse yet, kill someone.

When there is co-generation on site and the utility does not want to accept power back into the grid for some reason, a reverse current relay will detect that situation, but using it to disconnect the service seems a bit drastic. Would it not be better to use it to shut down or throttle the local generation rather than cause an artificial outage? I realize that at the moment of the trip the generators (or regeneration) would have to be capable of meeting the entire site load, but that could be just a transient condition.
Bottom line is that it needs to be part of a well engineered load and generation management scheme, not a casual addition. So, as jraef stated, you need to figure out why it was installed in the first place.

One more additional consideration: If there is a Main-Tie-Main configuration to provide two POCO sources for redundancy or very large load, one or more reverse current relays may be part of that system too.
 

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
When there is co-generation on site and the utility does not want to accept power back into the grid for some reason, a reverse current relay will detect that situation, but using it to disconnect the service seems a bit drastic. Would it not be better to use it to shut down or throttle the local generation rather than cause an artificial outage? I realize that at the moment of the trip the generators (or regeneration) would have to be capable of meeting the entire site load, but that could be just a transient condition.
Bottom line is that it needs to be part of a well engineered load and generation management scheme, not a casual addition. So, as jraef stated, you need to figure out why it was installed in the first place.

One more additional consideration: If there is a Main-Tie-Main configuration to provide two POCO sources for redundancy or very large load, one or more reverse current relays may be part of that system too.
Under the right circumstances, maybe not as drastic as it might seem. I have a client, an MDF plant with co-generation using their waste product, who can get a HUGE penalty for putting power back into the utility at the wrong time of day. So when their production line goes down during that time while their generators are supplying supplemental power, they trip the main connecting them to the utility, using reverse current relays. Their plant is not totally down because their own generators are still on line, they have just disconnected the UTILITY SERVICE main.
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Under the right circumstances, maybe not as drastic as it might seem. I have a client, an MDF plant with co-generation using their waste product, who can get a HUGE penalty for putting power back into the utility at the wrong time of day. So when their production line goes down during that time while their generators are supplying supplemental power, they trip the main connecting them to the utility, using reverse current relays. Their plant is not totally down because their own generators are still on line, they have just disconnected the UTILITY SERVICE main.
That is a credible scenario, but I am also sure that it was not done so casually that nobody knew why the relay was there!

Sent from my XT1585 using Tapatalk
 

Jraef

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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
That is a credible scenario, but I am also sure that it was not done so casually that nobody knew why the relay was there!

Sent from my XT1585 using Tapatalk
True. But in my experience, when something is not used for years and there have been layoffs, tribal knowledge gets lost, especially if documentation was poor. I can't count all the times I have gone to sites where there is equipment that has not been used in years and nobody knows where it is powered from. But when I test the line terminals, it's still hot!

By the way GD, that customer of mine is the Ampine MDF plant in Martel, just down the road on Hwy 49 from where (I assume) you are.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
True. But in my experience, when something is not used for years and there have been layoffs, tribal knowledge gets lost, especially if documentation was poor. I can't count all the times I have gone to sites where there is equipment that has not been used in years and nobody knows where it is powered from. But when I test the line terminals, it's still hot!

By the way GD, that customer of mine is the Ampine MDF plant in Martel, just down the road on Hwy 49 from where (I assume) you are.
Yep. I found it on the map, but at population 282 I had never heard of it before. :)
Jackson I know.
 
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