Generator + PV greenfield install

[ggunn]

I've seen it happen. Lots of trunk slammers interconnect generators and solar out here like that and then we get called on to fix it.

An engine driven generator can also be a motor and it will drive the engine faster than spec. The engine controls will see the overspeed and go closed throttle but speed just keeps rising. It doesn't rise very high before the sensitive routine in the inverters go off spec and drop.

I can't point to any damage caused but I would like to hear any other scenarios you think may happen as an EE. I would love to have more ammo to point at people who say, it's OK don't worry about it.

If it's a situation where the connected load is less than the PV output, then I cannot predict what the generator will do. It won't be good.

 

[electrofelon]

I've seen it happen. Lots of trunk slammers interconnect generators and solar out here like that and then we get called on to fix it.

An engine driven generator can also be a motor and it will drive the engine faster than spec. The engine controls will see the overspeed and go closed throttle but speed just keeps rising. It doesn't rise very high before the sensitive routine in the inverters go off spec and drop.

I can't point to any damage caused but I would like to hear any other scenarios you think may happen as an EE. I would love to have more ammo to point at people who say, it's OK don't worry about it.

I am skeptical that the inverter would drive the generator faster as the frequency wont get above 60.5 HZ

 

[jaggedben]

If the PV inverter were actually trying to push current into the generator wouldn't that cause the generator to slow down, not speed up? I could be wrong here.

It also seems to me that at least some PV inverters have a ramp-up in their power output and that would cause the generator to speed up and generate the over-frequency trip before actual backfeeding occurs.

I've seen it happen. Lots of trunk slammers interconnect generators and solar out here like that and then we get called on to fix it.

An engine driven generator can also be a motor and it will drive the engine faster than spec. The engine controls will see the overspeed and go closed throttle but speed just keeps rising. It doesn't rise very high before the sensitive routine in the inverters go off spec and drop.

I can't point to any damage caused but I would like to hear any other scenarios you think may happen as an EE. I would love to have more ammo to point at people who say, it's OK don't worry about it.

I don't think anyone doubts you've seen a PV system switch on and off as it causes a generator to shift in and out of frequency and/or voltage range. I think ggunn was just questioning whether you were accurately described the details of how and why it happens.

The actual mechanism and behavior may well vary depending on the equipment involved. Older PV inverters that output full current at unity power factor may cause different things to happen than newer 'grid support' inverters with volt-var, frequency-watt, and volt-watt functions enabled. A single inverter vs. multiple inverters (e.g. micros) may also behave differently. And the generator internal controls will also obviously make a difference as well.

 

[analog8484]

I've seen it happen. Lots of trunk slammers interconnect generators and solar out here like that and then we get called on to fix it.

An engine driven generator can also be a motor and it will drive the engine faster than spec. The engine controls will see the overspeed and go closed throttle but speed just keeps rising. It doesn't rise very high before the sensitive routine in the inverters go off spec and drop.

I can't point to any damage caused but I would like to hear any other scenarios you think may happen as an EE. I would love to have more ammo to point at people who say, it's OK don't worry about it.

I think damage risk is also dependent on the PV power level and how fast any generator protection mechanisms can activate.

Here is an example of damage:

Melted Automatic Transfer Switch - PV Tap on Generator Feed

Hello everyone. I just wanted to share a scenario that I came across yesterday. After a routine failover test of a 22kW Generac generator failed, I popped-off the transfer switch cover and found the recent PV installer tapped the generator feed for the PV system. Unless I'm totally missing...

forums.mikeholt.com

 

[six73]

I am not sure what the problem is unless the PV system is already load side connected through a backfed breaker in the MDP. If it is it must be changed to a line side interconnection on the line side of the ATS, but either way it is a simple decision and there is no reason for unprofessional animosity between the installers. The property owner is ultimately responsible for any incurred expense, since he apparently approved the PV system installation without considering what effect a generator would have on it.

This has been a fascinating thread. But to your point, I think a lot of it is because of the personalities involved, it sounds like there was a lot of unprofessional behavior all the way around. And yes, the PV was done without my client's knowledge, not even a simple heads up from the PO, as he was doing the service/generator/ATS install. As I was told the story, the PO and PV installer immediately attacked my client for not providing a means to connect something he wasn't even aware existed. I think the PV may be a "trunk slammer" (a term I hadn't heard before this thread but I really like), and I also think the PO may have gotten too far in debt to my client and is trying to find an excuse to avoid payment now that most of the work is done.

 

[ggunn]

I think damage risk is also dependent on the PV power level and how fast any generator protection mechanisms can activate.

Here is an example of damage:

Melted Automatic Transfer Switch - PV Tap on Generator Feed

Hello everyone. I just wanted to share a scenario that I came across yesterday. After a routine failover test of a 22kW Generac generator failed, I popped-off the transfer switch cover and found the recent PV installer tapped the generator feed for the PV system. Unless I'm totally missing...

forums.mikeholt.com

The problem happens when the loads are consuming less power than the PV system is producing.

 

[ggunn]

This has been a fascinating thread. But to your point, I think a lot of it is because of the personalities involved, it sounds like there was a lot of unprofessional behavior all the way around. And yes, the PV was done without my client's knowledge, not even a simple heads up from the PO, as he was doing the service/generator/ATS install. As I was told the story, the PO and PV installer immediately attacked my client for not providing a means to connect something he wasn't even aware existed. I think the PV may be a "trunk slammer" (a term I hadn't heard before this thread but I really like), and I also think the PO may have gotten too far in debt to my client and is trying to find an excuse to avoid payment now that most of the work is done.

Is the PV interconnected via a backfed breaker in the MDP? If so, then yes, it's going to involve some work and some expense to convert it to a supply side connection on the line side of the ATS, but if it's already a supply side connection on the load side of the ATS it shouldn't be that big a problem to fix. Someone needs to be the grownup.

 

[six73]

Is the PV interconnected via a backfed breaker in the MDP? If so, then yes, it's going to involve some work and some expense to convert it to a supply side connection on the line side of the ATS, but if it's already a supply side connection on the load side of the ATS it shouldn't be that big a problem to fix. Someone needs to be the grownup.

First off, I just realized I never updated my ID here to my professional info, so that's why it changed midstream. As to the question at hand, I don't know if or how it even got interconnected at all yet. This thread has been immensely informative and I'll certainly keep it in mind if I get pulled back into the situation, but at the moment nobody's even talking to each other. Physical threats have a way of derailing professional cooperation.

 

[ggunn]

Physical threats have a way of derailing professional cooperation.

Check, please.

 

[analog8484]

The problem happens when the loads are consuming less power than the PV system is producing.

Yep. A reverse power relay could have helped prevent the damage.

 

[qcroanoke]

The PV system must interconnect on the line side of the ATS. If it were to be connected on the load side of the ATS the PV system could backfeed the generator, which would be bad news for the generator.

"Now who can argue with that?"
Howard Johnson

From the movie
Blazing Saddles