Generator and grid-tie PV system

[jmbelectrical]

I will be performing an inspection at a residential property next week. The electrical service is 240/120-volt, single-phase, three-wire, 60Hz. It is equipped with a 60kW, whole-house, standby generator and a 13kW PV system. The PV system connects to a loadcenter/panel via a grid-tie inverter. The loadcenter/panel is on the load side of an automatic transfer switch. The system is arranged such that the generator and PV system can operate in parallel. No interlocks have been installed between the generator and the inverter. The PV system is approximately six years old and the generator is approximately three years old.

The PV system is no longer producing power. (I do not know if the fault lies with the inverter, the PV panels, or some other component.) The property owner has alleged that the generator installation - specifically, that the generator can be paralleled with the PV system - resulted in damage to the inverter. I am aware of the dangers of paralleling generators and PV systems, however, it is my understanding that the damage typically occurs at the generator as a result of the PV system backfeeding it. In this case, with the generator size being nearly five times that of the PV system, could the generator have backfed the inverter? What other failure mechanisms could this be attributed to?

Any input would be greatly appreciated.

 

[itsmoked]

Seems a very sketchy setup. I would expect the solar inverter to be toasted by the generator. The generator is big wires and coils and.. thermal mass. The inverter is semiconductors and zilch thermal mass. I'd expect all sorts of possible ways to blow the inverter.


What I typically see is a LARGE complex inverter in charge of everything. The SArray are connected to it and the generator is connected to it and the PoCo is connected to it and it's the load (house) power master of it all. You then program it to control how it uses the solar/generator/PoCo and any batteries that may exist.

That kind of system allows fine control of the various resources and prevents ill-advised interconnects.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Is the inverter frequency agile? All of the standby generators that I have installed and repaired come on line at 61.8 Hz, (That would be 51.5 Hz on 50 Hz systems).
The only time that a typical standby will run at rated frequency is when it is at 100% load. That almost never happens.
If the inverter does not like slightly high frequencies, it may be working as it was designed and will never come on with the generator at light loads.
If it is a grid tied inverter, it should shut down when the grid fails, and come back on-line when the grid is reestablished.
The only way that a grid tied inverter should be able to tell the difference between the grid and the generator is the slightly higher frequency of the generator.
If you have the skills and knowledge to adjust the frequency of the gen set, try setting the frequency a little lower and see if the inverter comes on line.
Another possibility is an overvoltage transient. The sudden removal of a large load may cause an overvoltage transient until the AVR can respond and the field decay to a strength appropriate to the reduced loading.
Note: There may be a 2:1 ratio between the field voltage under load and the field voltage under no load.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!