GRID V OUT OF RANGE

[Zee]

What do you do when inverter keeps shutting down due to high AC V?

3 @ 30 kW commercial ABB inverters.
They keep shutting off due to high grid voltage. Not sure how to deal with that outside of catching it when it happens or putting some kind of remote monitoring on it. I find it hard to believe grid would be at 15% over spec V.
But all 3 inverters show some degree of overvoltage.

Minor add'l Q's:
-is it malfunction or genuine high V?
-can V window be set/widened? What are implications of doing so?
-why are there high V events in the first place? I was told that due to hot weather and the heavy A/C loads that result, a utility often bumps up V to add more power to grid, w/o exceeding Ampacity limits.

 

[ggunn]

What do you do when inverter keeps shutting down due to high AC V?

3 @ 30 kW commercial ABB inverters.
They keep shutting off due to high grid voltage. Not sure how to deal with that outside of catching it when it happens or putting some kind of remote monitoring on it. I find it hard to believe grid would be at 15% over spec V.
But all 3 inverters show some degree of overvoltage.

Minor add'l Q's:
-is it malfunction or genuine high V?
-can V window be set/widened? What are implications of doing so?
-why are there high V events in the first place? I was told that due to hot weather and the heavy A/C loads that result, a utility often bumps up V to add more power to grid, w/o exceeding Ampacity limits.

A combination of grid voltage near the top of the legal range and voltage drop in the conductors between the inverter(s) and the point of service can trip them off, certainly; it has happened to me. I don't know about ABB but SMA will allow you to raise the upper voltage operational limit a bit once you sign waivers accepting that the responsibility for whatever happens is yours and yours alone.

Solutions vary; for one system our only option was to install buck/boost to lower the voltage on the conductors to our inverters.

 

[BroverCleveland]

What do you do when inverter keeps shutting down due to high AC V?

3 @ 30 kW commercial ABB inverters.
They keep shutting off due to high grid voltage. Not sure how to deal with that outside of catching it when it happens or putting some kind of remote monitoring on it. I find it hard to believe grid would be at 15% over spec V.
But all 3 inverters show some degree of overvoltage.

Minor add'l Q's:
-is it malfunction or genuine high V?
-can V window be set/widened? What are implications of doing so?
-why are there high V events in the first place? I was told that due to hot weather and the heavy A/C loads that result, a utility often bumps up V to add more power to grid, w/o exceeding Ampacity limits.

I used a HOBO data logger on a residential site once where we logged an entire month's worth of main conductor voltage readings and gave the CSV file to the utility to show them that they were outside of their allowed +/-10% deviation. Ultimately they replaced the transformer. HOBO makes some nice products, and have good tech support docs for installation.

We've had issues with Generac inverters, as they are limited to +/-5% deviation, so we've had to set some of our inverters to the Hawaii grid standard which is 10%.

I know ABB and SMA are similar; do they have a grid guard code equivalent? That's what we've used to adjust parameters on SMA's to account for deviations in utility voltage, instead of setting up a data logger for a month, and then watching the utility drag their feet for an additional month to replace the transformer.

 

[retirede]

I used a HOBO data logger on a residential site once where we logged an entire month's worth of main conductor voltage readings and gave the CSV file to the utility to show them that they were outside of their allowed +/-10% deviation. Ultimately they replaced the transformer. HOBO makes some nice products, and have good tech support docs for installation.

We've had issues with Generac inverters, as they are limited to +/-5% deviation, so we've had to set some of our inverters to the Hawaii grid standard which is 10%.

I know ABB and SMA are similar; do they have a grid guard code equivalent? That's what we've used to adjust parameters on SMA's to account for deviations in utility voltage, instead of setting up a data logger for a month, and then watching the utility drag their feet for an additional month to replace the transformer.

ANSI C84.1 dictates utility voltage tolerances. It can vary by system type and voltage, but none of the tolerances are as high as +-10%.

 

[ggunn]

I used a HOBO data logger on a residential site once where we logged an entire month's worth of main conductor voltage readings and gave the CSV file to the utility to show them that they were outside of their allowed +/-10% deviation.

eGauge can do that as well.

 

[Phil Timmons]

A combination of grid voltage near the top of the legal range and voltage drop in the conductors between the inverter(s) and the point of service can trip them off, certainly; it has happened to me. I don't know about ABB but SMA will allow you to raise the upper voltage operational limit a bit once you sign waivers accepting that the responsibility for whatever happens is yours and yours alone.

Solutions vary; for one system our only option was to install buck/boost to lower the voltage on the conductors to our inverters.

Same fix we use. We see it for end-of-the-line-remote in Rural Texas. During sunny Winter days the local grid loads go lower, and the Solar PV production goes up. Local Grid Voltage start floating upward. Inverters start cycling on and off. When the inverters drop off-line, the local grid comes back in spec, and the inverters detect this and reconnect. 5 minute cycle on-off-on-off.

Fix is a local Buck-Boost if the Grid Operator will not put in Automatic Tap Changers on the local transformers.

 

[kwired]

Same fix we use. We see it for end-of-the-line-remote in Rural Texas. During sunny Winter days the local grid loads go lower, and the Solar PV production goes up. Local Grid Voltage start floating upward. Inverters start cycling on and off. When the inverters drop off-line, the local grid comes back in spec, and the inverters detect this and reconnect. 5 minute cycle on-off-on-off.

Fix is a local Buck-Boost if the Grid Operator will not put in Automatic Tap Changers on the local transformers.

Was going to chime in about how local distribution voltage might be effected if there is enough systems in the immediate area contributing to the grid, apparently it can be a problem. POCO's would possibly be needing more tap changers than before these systems were all in place, those tap changers also can and do fail at times leaving customer voltages outside of desired levels.

 

[Hv&Lv]

Same fix we use. We see it for end-of-the-line-remote in Rural Texas. During sunny Winter days the local grid loads go lower, and the Solar PV production goes up. Local Grid Voltage start floating upward. Inverters start cycling on and off. When the inverters drop off-line, the local grid comes back in spec, and the inverters detect this and reconnect. 5 minute cycle on-off-on-off.

Fix is a local Buck-Boost if the Grid Operator will not put in Automatic Tap Changers on the local transformers.

I’d like to see one of those..

 

[kwired]

I’d like to see one of those..

Yes, it probably not happening on most residential or even smaller non residential services. (smaller being like at least 1500 kVA and less).

But I'm guessing in areas with a lot of PV there is maybe more voltage regulation equipment installed than had there not been all the PV installs.

 

[Hv&Lv]

Yes, it probably not happening on most residential or even smaller non residential services. (smaller being like at least 1500 kVA and less).

But I'm guessing in areas with a lot of PV there is maybe more voltage regulation equipment installed than had there not been all the PV installs.

Not on the individual transformers.
That’s my point

 

[Phil Timmons]

Not on the individual transformers.
That’s my point

You make a good point. There are some equipment / costs / trade-offs involved.

Think the smallest wide use I have done are in the 5 to 10 MVA range.

Wonder how the money math works out in smaller range? Probably the small local folks using Buck-Boosts (in Winter high production) with a By-Pass for the rest of the time might work out the cheapest option.

But looking back at what was driving all this to start with (in the case of deep(er) rural Texas, end-of-line) was nothing to do with Solar or High Production in Winter -- it was / is ALL-ABOUT-THE-AIR-CONDITIONING. Same as everything else. The overall local grid was designed about Peak Summer Load Air Conditioning -- so the local voltage is cranked high (all year round) to ensure that things stay up during the Summer -- without ever having to change anything.

 

[kwired]

Not on the individual transformers.
That’s my point

I figured that, I wouldn't expect any POCO to even consider that on any transformer with a low voltage secondary.

 

[Phil Timmons]

Then here becomes the look-ahead on these sites -- say a end-of-line location has a transformer feeding a few customers. Let's say maybe four. One or two have Solar. The Solar comes on full production and there is a slight voltage rise. Not really high, but enough to trip the Over-Voltage Threshold of the Inverters. We are already observing that. That is where this thread started.

If the "fix" becomes for the Solar customers all use individual Buck-Boosts -- to lower the Grid Voltage that the individual Inverter(s) sees . . . then all four customers will actually now have Over-Voltage. A possible fix (on the Utility side) could also be to use a Tap Change back at the substation and lower the entire MV distribution circuit? But then that lowers voltage all along the circuit and not just at the remote location where Over-Voltage is occurring. Another fix could be a shared Buck-Boost (for all 4 customers) -- which would be pretty much the same as a complicated Tap Change for the Local Transformer.

What other or better fixes do you see? Larger wire(s) on the MV Distribution might lessen the Line Voltage Drop (or in this case Voltage Rise)? But that may become more expensive, yet.

 

[Hv&Lv]

Then here becomes the look-ahead on these sites -- say a end-of-line location has a transformer feeding a few customers. Let's say maybe four. One or two have Solar. The Solar comes on full production and there is a slight voltage rise. Not really high, but enough to trip the Over-Voltage Threshold of the Inverters. We are already observing that. That is where this thread started.

If the "fix" becomes for the Solar customers all use individual Buck-Boosts -- to lower the Grid Voltage that the individual Inverter(s) sees . . . then all four customers will actually now have Over-Voltage. A possible fix (on the Utility side) could also be to use a Tap Change back at the substation and lower the entire MV distribution circuit? But then that lowers voltage all along the circuit and not just at the remote location where Over-Voltage is occurring. Another fix could be a shared Buck-Boost (for all 4 customers) -- which would be pretty much the same as a complicated Tap Change for the Local Transformer.

What other or better fixes do you see? Larger wire(s) on the MV Distribution might lessen the Line Voltage Drop (or in this case Voltage Rise)? But that may become more expensive, yet.

Can your inverter be set to import reactive power?
Lower your export voltage..

 

[ggunn]

Can your inverter be set to import reactive power?
Lower your export voltage..

Utility interactive inverters are current sources that match the voltage that they see at their terminals. If the line voltage is lower than the lower bound of the voltage they can match, they shut down.

 

[pv_n00b]

There's always adding a battery to limit export. The utility might be convinced to add better voltage control, but I bet they would require the PV customer to pay for it.

 

[Hv&Lv]

Utility interactive inverters are current sources that match the voltage that they see at their terminals. If the line voltage is lower than the lower bound of the voltage they can match, they shut down.

Every one I’ve looked at exports a few volts above utility voltage.

 

[ggunn]

Every one I’ve looked at exports a few volts above utility voltage.

That's due to voltage drop in the conductors. It's just Ohm's Law except that I is constant instead of V when you are dealing with a current source like a PV inverter.

 

[Phil Timmons]

Can your inverter be set to import reactive power?
Lower your export voltage..

That is a clever approach worth considering. Most inverters are default set for Unity. PF = 1. I think the typical spec sheets allow adjustment towards both Capacitive and Inductive.

But you are thinking that by setting it towards Capacitive or Inductive -- the Voltage would lower, while Amps stay up and keep exporting. Clever.

On the Utility Meter there would some loss but that is tolerable?

 

[jaggedben]

Dynamic power factor and watt output reaction to voltage (and frequency) conditions is a thing you guys. See UL1741SA.

Inverters with these features enabled will throttle power factor and/or real power if voltage is too high, which in theory should keep the voltage from getting quite as high.