Grid voltage shuts down inverter with no record

dale · May 2009

After going online last May my Xantrex GT3.3 was shutting down due to a high grid voltage. The installer contacted the utility company which verified they were providing 255 volts (out of range) to my house. The situation appeared resolved, but could be happening under the radar on a daily basis.

The production and hours online had been going down for the last two weeks. This weekend the inverter shut down for four hours each day with the "AC Voltage Faults" error displayed. The Grid Reading voltage was 258.5. This morning the voltage was 255 when I called my utility company, but dropped to 249.2 before they inspected it. They did see that the inverter was getting the same voltage reading measured at the electric meter.

An hour after they left the inverter shutdown again. This time I documented it by taking photos of my watch next to the inverter display panel. The Grid Readings ranged from 255-285.7 volts and the inverter was offline till 4 pm.

The Xantrex manual shows the default 'Phase-to-Neutral (rms) High Threshold Voltage" as 131.50 and the "Phase-to-Neutral (rms) Reconnect Voltage" as 126.96. This indicates if one phase of the Grid voltage exceeds 131.5 volts the inverter will shutdown and not go online till the Grid voltage drops below 126.96.

This results in the system shutting down during the most productive period. I doubt utility companies would intentionally cause systems to under perform, but fixing problems might be a low priority since localized renewable energy systems are a potential threat to their profitability.

People who don't check they output frequently would never notice this. I check daily, but the inverter doesn't 'record' outages. I'd like to correct this by recording the time of day when this happens and the duration. Does anyone have any suggestions on how to do this? I'd also like to know if anyone else has seen this before.

BB. · May 2009

Re: Grid voltage shuts down inverter with no record

Solar Guppy wrote and supports GT Inverter logging software here (runs on a PC).

Your line voltage is way out of specification (PDF from our utility PG&E--Northern California). Your utility should fix this.

[FONT=Fixedsys]             aim  true
Service min  max  max   
 [/FONT][FONT=Fixedsys] 120   114  120  126  
  208   197  208  218
  240   228  240  252 
  277   263  277  291  
  480   456  480  504 [/FONT]

The maximum voltage is around 132/264 VAC (that is what I had my AC power supplies designed for)... Australia was known (in times past) for extremely high AC line voltages (to push power to remote regions).

If your "240v" measurements where fine--and only your 120v measurements where out of specifications... Then you probably have a failed or failing neutral (i.e., L1 to neutral reads high, and L2 to neutral reads low).

If your utility is not being responsive--then you might have to contact your state PUC for help.

My 240 VAC runs from 240 to 247 volts or so (Xantrex GT inverter readings)... Matches what my utility meter reads too (my GE digital utility meter has a mode I can enter by holding a magnet next to the face -- and it scrolls through a dozen or more parameters it can monitor).

I would, at first, focus on getting them to address the >264 VAC readings--those are not kosher.

-Bill

niel · May 2009

Re: Grid voltage shuts down inverter with no record

they are not kosher not only for your ability of the selling of power standpoint, but also one of your appliances and lights being dealt a shorter lifespan from the excess voltages. here where i am i too had a problem with excess voltage and they are not allowed beyond 126vac per leg and 252vac total here in pa. i found that my washing machine dryer combo didn't last long and my florescent lights where burning out yearly. the few incandescents i had were going several times a year. so far my frig hasn't gone, but i suspect it won't be long.
sometimes they may switch in another generator to handle higher anticipated loads that never come to be and sometimes they are just padding your bill as i believe most are doing. this happens because of wattage and resistance relationships. p=i x v and p=i^2 r. take a simple 60w light bulb and figure the current it draws for 120vac for which it was made for. 60w/120v=.5a. the resistance set by that light bulb is figured from r in ohms= v/a. 120v/.5a=240 ohms. now raise the voltage to 126vac. the resistance is constant and will stay the same so 126v/240 ohms=.525a. for the total power 126v x .525a = 66.15w and is an increase of about 10% more power and so your bill for everything running at this higher voltage will also be 10% higher than it should be. this is legally allowed here in pa, but not anything higher than that 126vac is allowed here and sometimes they get too greedy and bump it to 128vac or even more for short time periods that most would not notice.
if your voltage is high and has been verified to be legally too high, put them on notice that they must stop such practices immediately or be held responsible for any and all premature appliance failures in addition to theft as they give themselves an undue raise in revenue by this practice. you should also tell them that you would notify your state utility commission should they not resolve the problem they created for you and many other customers. just think about that legal 10% hike they are allowed to do here and multiply that out by every customer and they hit the jackpot. taking it further and illegally out of bounds and you get the picture as it can be in the millions in unwarranted income for them depending on just how far the voltage is upped and for how long.

BB. · May 2009

Re: Grid voltage shuts down inverter with no record

Actually, a filament lamp is not a linear "ohmic" resistor. Its resistance changes with temperature (as the tungsten filament gets hotter, its resistance increases)--and to a fair degree, acts like a constant current source/sink when presented with a time varying voltage.

So, for a filament lamp instead of:

60 watts * 126^2 / 120^2 = 66.15 watts increase

Instead, with current fixed we get (approximately):

60 watts * 126 / 120 = 63 watts

Or, a 5% increase in energy usage with a 5% increase in voltage.

Also, many other devices are, more or less, constant power devices... Electric Induction Motors, many electronic devices, lamps with ballasts, etc. will draw a fixed power--so if voltage increases, current decreases.

The inverse of this property was "discovered" in the old USSR (at least, that is what I heard many decades ago)--The USSR needed to reduce energy usage in an area--so they cranked down the voltage--Instead of reducing energy usage--they only succeeded in destroying electric motors.

That is why brownouts are so problematic--the utilities (at least in the US) will cut power rather than letting the system "brownout" (I remember brownouts in the 1960's--we would have to go around and unplug the fridge and freezer).

Dropping Grid Voltage was again "discovered" by Dr. Wattenburg when he suggested a 2.5% drop in line voltage (120 to 117 volts) would decrease power usage by 2.5% as a partial solution to California's 2000-2001 "Enron" electrical blackouts.

It took a couple of weeks before the engineers could convince the powers that be that this was not going to save any power:

The concept of lowering power line voltages in an attempt to save energy has been applied by utilities in several other states, but it remains controversial.

Michael O'Hare, an engineer and professor of public policy at the University of California at Berkeley, insists that energy economies from voltage reductions "are precisely zero" when they are applied to refrigerators, air conditioners or "anything else controlled by a thermostat" because they would merely run a little longer than they do with full voltage.

"In sum," O'Hare said in a recent comment to The Chronicle, "the promised efficiencies from voltage reduction are either imaginary or subject to being nibbled away by human compensating behavior" -- in other words, by people using electric bulbs with higher wattages or by setting thermostats lower on their air conditioners.

And since many devices are "constant power" -- their current draw would actually go up and system wide I^2 * R losses would be increased--I would guess, potentially zeroing out any energy savings by non-constant power devices (heating elements, filament bulbs, etc.).

-Bill

niel · May 2009

Re: Grid voltage shuts down inverter with no record

ok so some items aren't as bad as i initially indicated by example and some not at all, but far too many items will present a higher wattage load. they raise it often for this extra income that is not approved or legal. why do you suppose it went from the 110vac standard and kept going up to today's standard of 125vac? it's because the utility commissions eventually cave to the whims of the greedy electric companies as this gives them an artificial raise in revenue, there is only one real reason the voltages are always on the high side (besides overcoming resistive losses of the wires they fail to maintain) as many are going over the legal voltage for that reason.
lowering to 117vac would save some power, but not in enough quantity that they needed. so why be the utility advocate as increases in voltage beyond that which is legal destroys the lifespans of many of the items it's going to and often does up the cost of the electric, not to mention lessen your ability to "sell" to the grid?

dale · May 2009

Re: Grid voltage shuts down inverter with no record

Neil, Bill,
I hadn't realized that providing a high line voltage would result in an increase electric bill. With the exception of my televisions and dvd players, I hadn't noticed any damage to my major appliances.

My utility company hasn't responded at all. The voltage is almost always 249.2 volts in the morning, but higher at night. When I got home it was 258.5. It probably didn't go to 262 since there was 11 hours of online time. They've denied any problems, but my watch shows the date and time, so the photos should remove any doubt.

They said they going to turn it over to their engineers, but I've not heard anything. I'm going to contact them tomorrow to see how they plan to fix this. The tech's mentioned a meter that tracks the voltage, so this could be an ongoing problem.

It's difficult for me to monitor the voltage during the day, so I'm hoping the program Solar Guppy wrote will catch this.

Thanks again for your help. I'll let you know how it pans out.

Solar Guppy · May 2009

Re: Grid voltage shuts down inverter with no record

SG-View can log as fast as one second interval and will likely be an eye opener how far off the utility is ...

All you need is a pc and comm cable ... then you will have some good data to give the electric company ...

Grid voltage shuts down inverter with no record

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