High grid voltage- problem for micro inverters?

[Don B]

I moved to a rural property this year and relocated my small machine shop. The line voltage runs 149 to 150 volts, so I had to use buck/boost transformers to drop the voltage for my CNC machines. I will soon be installing a GTI array with Solarbridge micros; do I need to boost the array's voltage to the level of the grid?

[inetdog]

I moved to a rural property this year and relocated my small machine shop. The line voltage runs 149 to 150 volts, so I had to use buck/boost transformers to drop the voltage for my CNC machines. I will soon be installing a GTI array with Solarbridge micros; do I need to boost the array's voltage to the level of the grid?

A GTI will automatically match the grid voltage as long as it is within the present voltage limits.
I suspect that any US market GTI would cut out if presented with 150V AC. Note also that many GTIs, both string and micro, require connection to 208V or 120V. If all you have is single sided 120 you would need a 120/240 transformer to get the GTI to work.
If possible just connect to the load side of your existing buck transformer setup.

[Don B]

Oops, sorry! Typo. Line voltage is 249-250 volts. Will the micro inverters adjust up to that?

[inetdog]

Oops, sorry! Typo. Line voltage is 249-250 volts. Will the micro inverters adjust up to that?

The standard for power delivery from utilities in the US, where the nominal voltage is 120V, is from 114V to 126V.

http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/voltage_tolerance.pdf

On the 240 line to line voltage that translates to 228 to 252. So your measured voltage is within that expected from POCO and so a GTI for the US market should at a minimum accept voltages in that range.
So, yes, they should adjust.

However, in the exact opposite of the voltage drop from service to load, the current flowing through the circuit wires a GTI will cause the voltage at the operating GTI to be higher then the service voltage.

So if your wiring is small enough to cause even a 2% voltage rise, you would be past the upper edge of the expected GTI input range.
However most GTI manufacturers allow the input range limits to be customized by the installer as needed as long as the voltage is within the safety margin of the equipment.

[solarix]

I've had problems a couple times with grid voltage being too high for the GTI inverter causing them to trip out - and the most we we're ever able to measure was like 248Vac. The manufacturer claimed the AC window was up to 256V so there was probably transients. Anyway, my point is that - ya, grid voltage can be a problem especially when you and maybe some of your neighbors are jacking it up with solar. Lessons I've learned: Keep you're voltage drop between inverters and service panel to a minimum - that is close proximity and big wire. In one case, the manufacturer had a configuration parameter that cold be changed to widen the AC input tolerance, but - we had to go to the utility and get permission (big hassle) to do this as it violates the UL1741 spec.

[Don B]

Thanks guys! I doubt that there are other PV installs anywhere near me. I probably get some medium voltage drops when my machine motors kick in. Is there any chance that motors kicking off will cause spikes above ambient voltage? On the Haas mill the spindle motor ramps up and down every few minutes.

[inetdog]

Thanks guys! I doubt that there are other PV installs anywhere near me. I probably get some medium voltage drops when my machine motors kick in. Is there any chance that motors kicking off will cause spikes above ambient voltage? On the Haas mill the spindle motor ramps up and down every few minutes.

Is the motor being driven by a VFD or other speed control? Some VFDs include a regenerative braking option which pumps power back into the AC line as the motor decelerates. In effect a kinetically driver GTI.

[Don B]

Yes, VFD drive and it does use braking. I could easily put a meter on the lugs while the machine is working, but would it react quick enough to show an accurate peak? Is there a specific type meter that would reliably see the short spikes?

[inetdog]

Yes, VFD drive and it does use braking. I could easily put a meter on the lugs while the machine is working, but would it react quick enough to show an accurate peak? Is there a specific type meter that would reliably see the short spikes?

There are voltmeters for several hundred dollars that have the ability to catch a single peak. Some better than others and will different time constants.
For more money you can get a meter that records multiple samples over time.
If the ramp time on the motor is a second or more you should be able to see the regen effect, if any, on an ordinary meter, especially if analog.

[Don B]

I'll give that a try, thanks.

[JFinch57]

Oops, sorry! Typo. Line voltage is 249-250 volts. Will the micro inverters adjust up to that?

Enphase microinverters are rated at up to 264V. My service, before they fixed the problem, was running at 257V and almost 260V with the solar cranking. 1 out of 45 microinverters was kicking out and Enphase pushed a firmware update that allowed a higher voltage. They didn't tell me what the new limit was, but the problem went away. Shortly after that the power company found a faulty voltage regulator on the line and we came down to 246V.

[Don B]

Thanks! Since posting, I have tested all the panels and all are working properly. Reading the documentation, I found that they have a five minute delay to kick in. I was afraid the voltage was too high so I had immediately disconnected.

[inetdog]

Thanks! Since posting, I have tested all the panels and all are working properly. Reading the documentation, I found that they have a five minute delay to kick in. I was afraid the voltage was too high so I had immediately disconnected.

The five minute period to "qualify" the grid stability before kicking in is required by the UL listing for a GTI. It is one of the reasons that cutting back on GTI output by running the pseudo grid frequency or voltage out of range in an AC coupled hybrid system is not a very precise tool.

[peakbagger]

In most states, there is a public utilities commission and they general require the utilities to supply power within a fairly strict range. Rather than trying to make your equipment fit the utilities poor power quality make them fix it. I have friend in rural area who had similar issues, it took him a bit to talk to the right person at the utility and then a couple of folks showed up and installed a power quality meter and left it for a few days. After some research, they found out that there was a problem with their system and fixed it. My friend no longer has the problem.