Inverter for solar and harmonics don't play well together.

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11bgrunt

Pragmatist
Location
TEXAS
Occupation
Electric Utility Reliability Coordinator
Worked a complaint yesterday where the new solar system is not getting to work at full potential because the inverter is shutting down before the peak can be reached.
The inverter log alarms are coming back as PQ distortion. There are two different PV systems on the property fed by the POCO on a single phase primary tap with two overhead transformers and independent metering. The one system at the barn is older and has no problem but the current distortion was seen, the new one is at the house and is only a couple months old. The Solar company keeps pushing homeowner back to the POCO.
Test with Fluke 345 PQ show 1% THDv and 8% THDi with his normal load. The current wave was ugly. This was the first time I have seen the current wave pulse wave form like a heartbeat.
I want to blame settings on the inverter for kicking it off line and customer load for the crappy current (technical term). I considered removing the customer load and connect a 10kW resistive load to see if current stayed choppy.
We deal with harmonics in the oilfield caused by VFDs but this POCO circuit is mostly rural residential and far from the oilfield.
What have you guys seen?
I am just getting started on this complaint.
PQ recorders have been installed and will be pulled in a week.
 

coop3339

Senior Member
Location
NJ
Any chance it is disconnecting from high voltage? This can be caused by grid impedance. I had a case where inverters were shutting down supposedly on a over frequency fault during peak production. It turned out it was actually over voltage from high grid impedance.
 

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
IMO the 8% current THD distortion seem quite high that the inverter is not liking and causing shutdown. I had a weird situation on my simple PV system on my house where I had an external cooling fan hooked up to a Digi time clock to cool the inverter.
After I installed it the clock was constantly loosing the program to turn it on and off.
I thought the ebay clock I bought was bad till I hooked it up at another outlet at my house away from the inverter and it worked fine. It appears the inverter was causing some kind of interference with the electronics in the clock.
Can you provide us snapshots of the voltage and current waveforms?
Also the inverter specs.
I use a Fluke 43B (single phase) meter to look at my system to make sure that the waveforms are not doing any damage to my house appliances.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
IMO the 8% current THD distortion seem quite high that the inverter is not liking and causing shutdown. I had a weird situation on my simple PV system on my house where I had an external cooling fan hooked up to a Digi time clock to cool the inverter.
After I installed it the clock was constantly loosing the program to turn it on and off.
I thought the ebay clock I bought was bad till I hooked it up at another outlet at my house away from the inverter and it worked fine. It appears the inverter was causing some kind of interference with the electronics in the clock.
Can you provide us snapshots of the voltage and current waveforms?
Also the inverter specs.
I use a Fluke 43B (single phase) meter to look at my system to make sure that the waveforms are not doing any damage to my house appliances.

The inverter has no way to sense the current distortion as the grid supplies local loads. It can only respond to the voltage distortion that the harmonic current causes across some resistance in the path. Or voltage distortion (e.g flat topping) from POCO.
 
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