REVERSE POWER RELAY that will be installed to prevent back-feed

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inforaj

Member
Location
Chiago
Occupation
Member
Hello,
I received feedback on the interconnection application, and they recommended that the single-line diagram be updated to reflect the REVERSE POWER RELAY that will be installed to prevent back feed. In the past, I never used the Reverse Power Relay.

Could anyone be familiar with this equipment and help with the model numbers or brands for residential/commercial projects? So that I can use it in one of our projects.

I tried to find the lists on the ComEd portal but was unable.

I really appreciate any help you can provide.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
A reverse power relay prevents a solar system from backfeeding the grid, or limits backfeed, or similar functions. I've never had to install a reverse power relay, but I've heard they cost many thousands of dollars. One doesn't find a lot of info about them online because (as best I can tell) it's highly specialized stuff that is mostly used only by utilities.

Is this system supposed to backfeed the grid, or not? How big is your system? If your intention was to backfeed the grid then either they made a mistake in their review, or there might be something special about the utility network in this area that might prevent you from doing the project as sold. Utility reviewers do sometimes make copy/paste errors or get confused about what they're looking at. Did they really just say 'recommended', or are they requiring something?
 
I

inforaj

Member
Location
Chiago
Occupation
Member
jaggedben said:
A reverse power relay prevents a solar system from backfeeding the grid, or limits backfeed, or similar functions. I've never had to install a reverse power relay, but I've heard they cost many thousands of dollars. One doesn't find a lot of info about them online because (as best I can tell) it's highly specialized stuff that is mostly used only by utilities.

Is this system supposed to backfeed the grid, or not? How big is your system? If your intention was to backfeed the grid then either they made a mistake in their review, or there might be something special about the utility network in this area that might prevent you from doing the project as sold. Utility reviewers do sometimes make copy/paste errors or get confused about what they're looking at. Did they really just say 'recommended', or are they requiring something?
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The System is only 37.9 KW DC. Here are the comments we received from them.
 

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don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
it appears with your proposed design, you are not permitted to supply any power to the utility. If there is any possibility that could happen they want you to do a net meter installation, or provide the reverse power relay to prevent you from supplying power to the utility.
Not sure of the cost or design implications for a net meter design verses a reverse power relay.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
It's hard to tell with incomplete sentences and lack of context, but he appears to be asking if you want to net meter or not. The reverse relay is necessary if you do not.
 
A

analog8484

Senior Member
Location
CA
Occupation
Tech
First time to see a POCO asking for reverse power relay related to a PV system. I've only seen them used in paralleling large generators.
 
G

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
analog8484 said:
First time to see a POCO asking for reverse power relay related to a PV system. I've only seen them used in paralleling large generators.
Click to expand...
I've seen a utility require such a thing if you install a PV system connected to their downtown network. We built one such system and vowed never to do it again.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
I admit I have never used a RPR and don't know much about them, but seems like a real impractical solution for a PV system. Seems like it would just trip out, the inverters would shut off for 5 minutes, and it will keep doing that over and over. Unless it's a small PV system relative to the local loads where most of the time there is no back feed and the RPR is just there for rare occasions?
 
C

Carultch

Senior Member
Location
Massachusetts
electrofelon said:
I admit I have never used a RPR and don't know much about them, but seems like a real impractical solution for a PV system. Seems like it would just trip out, the inverters would shut off for 5 minutes, and it will keep doing that over and over. Unless it's a small PV system relative to the local loads where most of the time there is no back feed and the RPR is just there for rare occasions?
Click to expand...

You use the reverse power relay, not because you want to, but because you have to. Yes it is an impractical solution, and the underlying idea is that it will rarely (if ever) shut off. You use it, because it is the only solution the utility will accept.

You would design some other control method to dynamically steer your system's production away from the forbidden point of export, or away from the maximum limit of export. The reverse power relay is a fail-safe in case this power controller doesn't work. You meter the net load of your site's service, or another metering setup that would add up to the net load of your site's service. The net load data is used as feedback for a controller that sends setpoints to the inverters, to dynamically change their maximum output power in response to the load.

It is common on larger systems to be required to use a utility-grade relay anyway, in addition to the standard relays built-in to the inverters. Directional power is simply an element that is already available within the relay, which you can program for this purpose.
 
I

inforaj

Member
Location
Chiago
Occupation
Member
ron said:
These are the two that I've used from Basler for large generator installations that we were connecting in closed transition

BE1-32R, BE1-32O/U, Directional Power Relay - Basler Electric

These relays provide versatility and control in protecting machines against reverse power flow, underpower, and overpower conditions.
www.basler.com
ES-32
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Thank you for the details. The solar system only has a 37 KW AC capacity. What power/voltage output did you utilize from your generator for this? I simply want to know if it is available in any size or not.
 
ron

ron

Senior Member
Location
New York, 40.7514,-73.9925
inforaj said:
Thank you for the details. The solar system only has a 37 KW AC capacity. What power/voltage output did you utilize from your generator for this? I simply want to know if it is available in any size or not.
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Depending on what CTs you provide for the measurements, you can go down to almost any size feeder. We had 4000:5 CTs and were looking to trip at 150kW reverse power.
 
A

AlbertL57

Member
Location
Falls Church, VA
Occupation
Solar maintainer
electrofelon said:
I admit I have never used a RPR and don't know much about them, but seems like a real impractical solution for a PV system. Seems like it would just trip out, the inverters would shut off for 5 minutes, and it will keep doing that over and over. Unless it's a small PV system relative to the local loads where most of the time there is no back feed and the RPR is just there for rare occasions?
Click to expand...
I've installed a relay on a system fed by a spot network, where the utility requires a minimum import of 20kW during daylight hours. We installed a curtailment control system as the first line of defense. It throttles back the solar as needed to maintain import power above the relay setpoint, so the relay only trips when there's a sudden large load drop that the controller can't respond to fast enough. The PV production and customer's load are such that, on weekdays, the relay very rarely trips. But on sunny weekends around this time of the year, without the controller, there are days when the relay would cycle continuously, exactly as you said.
 
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kingpb

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
The IEEE 32 function will be the guarantee to the utility that you can't back feed. regardless if the control system is the first line. If this is 480V or less the Basler is probably the cheapest way. If MV system then the MV gear will have a protective relay anyway, just make sure it has the 32 function. Sometimes it's an option to add.
 
K

Ken70

Member
Location
Hawaii
Occupation
Engineer
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