AFCI/GFCI nuisance tripping

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sketchy

Senior Member
Location
MN
We've recently had several customers report that their AFCI or GFCI breakers are tripping. The timing almost immediately after the solar was turned on. We use SolarEdge and Enphase micro's exclusively and both are causing the problem. In one house they have Homeline both 2 pole and single and every day at sunset the only three 2 pole breakers will trip, not one of the single pole. AFCI's were replaced with brand new breakers but that didn't solve anything. Enphase has in line noise filters that we have yet to try. Anyone else have this problem??
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
We've recently had several customers report that their AFCI or GFCI breakers are tripping. The timing almost immediately after the solar was turned on. We use SolarEdge and Enphase micro's exclusively and both are causing the problem. In one house they have Homeline both 2 pole and single and every day at sunset the only three 2 pole breakers will trip, not one of the single pole. AFCI's were replaced with brand new breakers but that didn't solve anything. Enphase has in line noise filters that we have yet to try. Anyone else have this problem??
Yes. No solution yet.
 

PWDickerson

Senior Member
Location
Clinton, WA
Occupation
Solar Contractor
We are having the same issue at a site. The 2-pole breakers are tripping, but the 1-pole breakers aren't. I doesn't just happen at night though. After a bunch of unsuccessful troubleshooting, the owner removed all the 2-pole AFCI breakers in his panel except one that he left in for testing. There are no line conductors connected to the breaker, only the neutral and ground. I watched it trip the other day when I was there.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
There are no line conductors connected to the breaker, only the neutral and ground. I watched it trip the other day when I was there.
Ground is connected to the breaker?
Or do you mean there's a load neutral wire connected to the breaker and also a wire to the neutral bus (if it's not a plug-on breaker)?
Just trying to clarify what you have.
 

SteveO NE

Member
Location
Northeast
Occupation
Engineer
The other post mentioned is more focused on the power-line carrier comms and AFCIs (and is way off topic most of the time) so I figured I'd add a note here though not sure how much it will help you resolve your issue - mostly because we had some controls available that would likely not be available at a residential level; however, I'm posting anyway to maybe seed some more discussion into the why and what should we be pushing some solutions from inverter manufacturers to address this issue. I've also experienced GFPE (large breakers for protective service gear, not people like a GFCI) tripping on some MW scale systems interconnected behind building load. The inverters did not use power line carrier and the breakers tripping were not AFCI's so we can eliminate all of the discussion in the other post (that is mostly off topic). The first time time this happened, over night the customers main breaker and the PV main breaker tripped for an 800A ground fault - obviously a main tripping was a big pain, especially in this facility which required a lot of manual intervention to start things back up again. The first thing we pointed to was that we have an MV distribution system (especially because it happened over night) to get the power to/from the array which was 1500 ft. away so we thought it had to do with the 4.8kV transformers on-site. Our first temporary solution to keep the main from tripping was to cascade the GFPE settings so the PV breaker would trip first - this worked for that purpose but did not stop the tripping of the PV which was still a problem, just less of a problem. I started putting power quality meters in various locations to try and detect the problem. The weird part is that we never actually detected a large ground fault; however, we did detect a utility disturbance that looked like switching that happened regularly enough and most times that occurred, the trip would occur. We electrically opened up the PV system completely, including the neutral to see if the problem still occurred and it did; however, the problem was for a slightly shorter duration and had a slightly different profile to it. What we believe we realized is that this is an unintentional consequence of the new smart-grid requirements of inverters. Essentially an inverter is a grounded cap-bank providing reactive power to the grid (this was really always true even before the smart-grid compatible inverters) - there is a reason you don't typically ground a cap-bank and this is it. In any case the biggest problem this causes is that is sustains the event slightly longer and enough to trip the breakers and passing it through to the neutral. Though someone more versed in protection and controls could weigh in with alternatives or could tell me that I am wrong, we believe the smart-grid inverters are an issue because they are capable of providing support to grid disturbances including load balancing which could cause neutral currents during these system disturbances.

Our solution was to deal with it and we were able to correct the problem by figuring out different tripping curves that served the needs of the site as well as "ignored" the problem. This has happened more than once and this solution worked both times.

Again I post this mostly to see if someone with more knowledge than me in the area of protection and potentially inverter reactive power functionality and capability to weigh into the discussion. It could be your problem on-site too, even though you are at a much smaller scale of a system. For you it poses a bigger problem in that you don't have the ability to adjust trip curves. On resi systems there isn't much money in the budget to throw solutions outside of the box at a problem but I'd first see if they make a neutral ground reactor or neutral ground resistor small on a residential scale...a whole house surge suppressor installed at your combiner panel may functionally be similar - they typically use MOVs to create a path to ground by reducing resistance when I and/or V increase.
 

SteveO NE

Member
Location
Northeast
Occupation
Engineer
Missed my window to edit...the other thing I thought about that could contribute to the issue is to make sure none of your PV equipment has a neutral bond in it. That may sound obvious, but things like meter sockets and combiner panels may have a bond already in them and need bushing kits to electrically isolate them from the EGC.

The post from PWDickerson (separate issue from OP) seems to indicate neutral currents for some reason (the GFCI breakers are just looking for a difference of 30ma between L and N), though letting a breaker float isn't a very reliable test as other things could cause that too inside an energized panel. Neutral currents could be caused by bonding in two locations.
 
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