3 Phase imbalance

[michaelsmorris]

I have a commercial solar job that has been plagued with power quality issues. My phase volatages are AB - 494 V, BC - 504 V, AC - 512 V, AN - 285 V, BN - 284 V, CN - 314 V. I've checked the torque on all terminations in the inverters, load center, step-up and step-down transformers, and AC disconnect. The switch gear is currently inaccessible. Phase to phase was pretty stable at 494 V and each leg at 285 V prior to the inverters being energized. I've had the utility company verify line-side voltages; all checked good. I'll be able to check the CT cabinet voltages this week. Any thoughts?

 

[electrofelon]

I have a commercial solar job that has been plagued with power quality issues. My phase volatages are AB - 494 V, BC - 504 V, AC - 512 V, AN - 285 V, BN - 284 V, CN - 314 V. I've checked the torque on all terminations in the inverters, load center, step-up and step-down transformers, and AC disconnect. The switch gear is currently inaccessible. Phase to phase was pretty stable at 494 V and each leg at 285 V prior to the inverters being energized. I've had the utility company verify line-side voltages; all checked good. I'll be able to check the CT cabinet voltages this week. Any thoughts?

Are you having any problems? Those voltages should well be within the range of the inverters which is typically +/- 10%

 

[GoldDigger]

Are you having any problems? Those voltages should well be within the range of the inverters which is typically +/- 10%

Yes, but near the edge if the line voltage fluctuates.
My concern is the near zero voltage offset on two lines and ten percent voltage "drop" on the third. Either the inverters are not balanced across the three lines or there is an unacceptably high resistance in that line. Probably on the POCO side somewhere.

 

[electrofelon]

The L-L voltages are in spec, but I didnt notice the C-N voltage the first go around, that is quite high. A call to the POCO wouldn't hurt, and hopefully they will actually look into it.

 

[kwired]

Maybe put a balanced test load on the line without the solar equipment in the circuit - this will give you some idea of whether there is a problem from the utility side.

 

[GoldDigger]

Maybe put a balanced test load on the line without the solar equipment in the circuit - this will give you some idea of whether there is a problem from the utility side.

Or an unbalanced load and measure VD on each line anyway. Just so there is current on C.

 

[ggunn]

I have a commercial solar job that has been plagued with power quality issues. My phase volatages are AB - 494 V, BC - 504 V, AC - 512 V, AN - 285 V, BN - 284 V, CN - 314 V. I've checked the torque on all terminations in the inverters, load center, step-up and step-down transformers, and AC disconnect. The switch gear is currently inaccessible. Phase to phase was pretty stable at 494 V and each leg at 285 V prior to the inverters being energized. I've had the utility company verify line-side voltages; all checked good. I'll be able to check the CT cabinet voltages this week. Any thoughts?

I had a similar problem with a single phase (240VAC) system a month or so ago. It turned out to be a problem with the neutral connection in the AC disco between the PV system and the service. Good luck.