Anti-Islanding sutuations (Xantrex)

Hi!
Ever since I installed solar panels (for 3 years now), I occasionally observe AI errors on my Xantrex 4548 (configuration in my signature). I read about the reasons why AI exists, etc. but there are certain things I am still not very clear of:

1) I thought the whole issue of anti-islanding exists to protect electricians from solar/wind streaming to a grid when there is not grid power. Why then AI errors appear when Sell-to-Grid is not turned on? Whom does it protect then?

2) How long does it take for a Xantrex XW to notice that AC1 power changed below/above interactive limits? I have a stabilizer sitting before my invertor and it is supposed to solve the problem of voltage fluctuations inside the grid. In my case, however, it seems not to always work and I suspect because stabilizer gets too slow. I happened to catch one of those (it seems) situations on video. See https://dl.dropboxusercontent.com/u/17122938/20140629_133446.mp4 for this. However, it is rather confusing because this video shows that the inverter starts two suck to much current from the grid. How can this be explained? I am not even sure this video is related to my question but my local Schneider guy says it is.

Can anyone clarify? Thanks.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Anti-Islanding sutuations (Xantrex)

    Have you measured the voltage at the AC1 terminals and see if the inverter is reporting the correct voltages?

    That is a lot of voltage swing. What does it look like prior to the voltage stabilizer?

    It looks almost like you have too much resistance from the utility transformer to your inverter (very long wire runs, too small of diameter in your AC wiring, some heavy loads on the local transformer, etc.).

    210 volts is getting very close to low voltage cutoff--And the inverter should go "off grid" and supply power locally (is that what happens, or what does happen to the inverter's operation?).

    What do you expect nominal voltage operation for your area? 230 VAC @ 50 Hz? It almost looks like a Wye ("Y") power system with ~208 VAC or so nominal utility voltage--And then I would wonder if the inverter is setup correctly (i.e., 208 VAC line voltage instead of 230 VAC or so)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vomus
    vomus Solar Expert Posts: 32 ✭✭
    Re: Anti-Islanding sutuations (Xantrex)
    BB. wrote: »
    Have you measured the voltage at the AC1 terminals and see if the inverter is reporting the correct voltages?

    That is a lot of voltage swing. What does it look like prior to the voltage stabilizer?

    It looks almost like you have too much resistance from the utility transformer to your inverter (very long wire runs, too small of diameter in your AC wiring, some heavy loads on the local transformer, etc.).

    210 volts is getting very close to low voltage cutoff--And the inverter should go "off grid" and supply power locally (is that what happens, or what does happen to the inverter's operation?).

    What do you expect nominal voltage operation for your area? 230 VAC @ 50 Hz? It almost looks like a Wye ("Y") power system with ~208 VAC or so nominal utility voltage--And then I would wonder if the inverter is setup correctly (i.e., 208 VAC line voltage instead of 230 VAC or so)?

    -Bill

    The "true" AC (the one before stabilizer) really drops. In my area these things happen although normal operation is 220V/50Hz. Two heavy load on my local transformer looks very much like the reason. Besides, my area is rural and there are a lot of hanging wires (no ground based). When wind starts to blow it might actually shorten the transmission which I suspect would lead to increased load to the utility transformer.

    Actually, this was the reason I added a stabilizer. When I asked Schneider about this they told me it might very well be that stabilizer does not have time to swallow those fluctuations and Xantrex inverter senses them. So it was my question about how long it takes for XW to figure out that AC1 fell below the threshold.

    There is a second question though whether I can change threshold of an interactive mode in XW to lowe it a bit. I was told by someone that XW Config Tool can do this but I did not find this among its menus.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Anti-Islanding sutuations (Xantrex)
    vomus wrote: »
    Why then AI errors appear when Sell-to-Grid is not turned on? Whom does it protect then?
    Can anyone clarify? Thanks.

    The Anti-islanding system is a UL requirement for any grid interactive inverter, and it has to be enabled whether the sell-to feature is enabled or not.
    It would be theoretically possible to program the unit so that the AI detection and shutdown function is not enabled unless sell-to is enabled too. But the regulatory and testing conditions are such that this would create a single point of failure that could let the inverter feed power back into the grid when grid power is lost.

    A secondary reason to have the AI active even when sell-to is turned off would be to prevent the grid tie functionality from becoming active when the "grid" source is a generator or battery powered inverter, which could lead to an unstable and even dangerous situation even without backfeed.
    SMA SB 3000, old BP panels.
  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    Re: Anti-Islanding sutuations (Xantrex)

    Look at the AC Setting on the combox for the XW, it can pretty much adjust most all settings.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
  • vomus
    vomus Solar Expert Posts: 32 ✭✭
    Re: Anti-Islanding sutuations (Xantrex)
    BB. wrote: »
    Have you measured the voltage at the AC1 terminals and see if the inverter is reporting the correct voltages?
    210 volts is getting very close to low voltage cutoff--And the inverter should go "off grid" and supply power locally (is that what happens, or what does happen to the inverter's operation?).

    The inverter shuts off MPPT for 5 minutes.
    What do you expect nominal voltage operation for your area? 230 VAC @ 50 Hz? It almost looks like a Wye ("Y") power system with ~208 VAC or so nominal utility voltage--And then I would wonder if the inverter is setup correctly (i.e., 208 VAC line voltage instead of 230 VAC or so)?

    Can you do this is XW? I mean setting a lower line voltage.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Anti-Islanding sutuations (Xantrex)

    Some (few, some, all???) GT inverter and Hybrid inverters can have their Anti-Islanding parameters changed--Generally requires a password that many only be given to a local installer.

    However--In your case, you really want the Inverter to call the incoming power "bad" and go "off grid" so it can supply stable energy to your loads. If you drop the qualification voltage below 210 VAC or so--You could "brown out" your 220 VAC loads.

    The five minute timeout may be adjustable too given you are not in North America (utility may give you an "acceptable number", or they may have you disconnect the Hybrid inverter because they do not allow feeding power back into their utility grid--Don't know).

    If it is "rare" (few times a day)--Then it is probably not worth the trouble to reset the timer to a different value.

    If it happens all the time--It may not matter, because the solar array is going to be supporting the loads and possibly recharging the battery bank anyway--So feeding the grid may not really give you much savings in power costs.

    If you are not going to use the Hybrid function to feed back to the grid and you want a wider 220 VAC programmable input voltage range--You might look at the AC2 input (I think this inverter has AC2). This is intended to be the backup generator input, and they generally let you reprogram the "trip/qualification" points to your heart's content.

    If you want the invert to stay connected down to 180 VAC--It may very well let you program the AC2 input to do that. But probably not feed back power to the "grid".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vomus
    vomus Solar Expert Posts: 32 ✭✭
    Re: Anti-Islanding sutuations (Xantrex)
    BB. wrote: »
    Some (few, some, all???) GT inverter and Hybrid inverters can have their Anti-Islanding parameters changed--Generally requires a password that many only be given to a local installer.

    However--In your case, you really want the Inverter to call the incoming power "bad" and go "off grid" so it can supply stable energy to your loads. If you drop the qualification voltage below 210 VAC or so--You could "brown out" your 220 VAC loads.

    What will happen if there is not enough Sun to support the load? It will obviously not go "off-grid". I wonder that when AC1 quickly drops, XW tries to go "off-grid", finds it can not do this, starts to draw power from the batteries. But in the mean time, AC1 returns to within the limits, XW qualifies it and starts charging from AC1. See, for a while I had only three 200W panels. Another 6 just came in and I am installing this Saturday. Does this scenario looks plausible?

    At the first glance I do not see how AC2 settings are different from AC1 but this is the route I'd have to explore.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Anti-Islanding sutuations (Xantrex)

    Here's a question that hasn't been asked: how large is the battery bank?
  • vomus
    vomus Solar Expert Posts: 32 ✭✭
    Re: Anti-Islanding sutuations (Xantrex)
    Here's a question that hasn't been asked: how large is the battery bank?

    200 Ah, 12V batteries. 4 of them to make it 48 VDC.