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Thread: 480V vs 208V inverters

  1. #11
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    Quote Originally Posted by Carultch View Post
    That topology is atypical, and is subject to the risk that the installer makes an oversight when ordering, and gets it backwards. So you are looking at a somewhat custom transformer, rather than the run-of-the-mill dry-type transformer used in buildings that have both voltage systems. Usually, the delta is on the 480V side, and the wye is on the 120/208V side. But given inverters that need a neutral, you'll need a wye system on the 480V side in some form or another.
    I hear that stated often, but I don't consider that an uncommon transformer at all. I run into them in the wild (for non solar applications) now and again and it's a standard stock item, ready to ship
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    I think this is the auto we used, third page middle. You would have to check sizing since it's an auto, the nameplate of the unit needed may be different than the kva of your load.

    https://www.hammondpowersolutions.co...-of-HTP-16.pdf
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Thank you, both.

    Yes, I am told I need a neutral.

    The building does have a 208Y/120 3PH 4W system.

    Curious in general with transformer terminology:
    I noticed you specified a "step up transformer" and you also mention "208V to 480V" and not the other way around (480V to 208V)? I just want to be 100% sure these two indicate line and load and it is fixed.
    In other words: solar must be on the load side in general and the utility on the line side?

    Silly me, from a theoretical perspective, I always thought transformers would work in either direction.......of course with opposite effect. But it seems the line and load sides are fixed also?
    Just theory, but good to know.

  5. #15
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    Quote Originally Posted by Zee View Post
    Thank you, both.

    Yes, I am told I need a neutral.

    The building does have a 208Y/120 3PH 4W system.

    Curious in general with transformer terminology:
    I noticed you specified a "step up transformer" and you also mention "208V to 480V" and not the other way around (480V to 208V)? I just want to be 100% sure these two indicate line and load and it is fixed.
    In other words: solar must be on the load side in general and the utility on the line side?

    Silly me, from a theoretical perspective, I always thought transformers would work in either direction.......of course with opposite effect. But it seems the line and load sides are fixed also?
    Just theory, but good to know.
    Generally one should ignore the energy flow direction and just consider the inverter side like any other SDS and load. Transformers do work either direction, but are usually designed to have lower inrush current on the utility side for easier starting.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Quote Originally Posted by Zee View Post
    Thank you, both.

    Yes, I am told I need a neutral.

    The building does have a 208Y/120 3PH 4W system.

    Curious in general with transformer terminology:
    I noticed you specified a "step up transformer" and you also mention "208V to 480V" and not the other way around (480V to 208V)? I just want to be 100% sure these two indicate line and load and it is fixed.
    In other words: solar must be on the load side in general and the utility on the line side?

    Silly me, from a theoretical perspective, I always thought transformers would work in either direction.......of course with opposite effect. But it seems the line and load sides are fixed also?
    Just theory, but good to know.
    Some (most?) transformers are listed for bidirectional operation but some are not; that's a question for the manufacturer. You'll want your transformer to be delta (no neutral) on the utility side and wye (grounded neutral, separately derived) on the inverter side.

  7. #17
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    Quote Originally Posted by ggunn View Post
    Some (most?) transformers are listed for bidirectional operation but some are not; that's a question for the manufacturer. You'll want your transformer to be delta (no neutral) on the utility side and wye (grounded neutral, separately derived) on the inverter side.
    And just to clarify, I believe that a transformer must be listed/marked as suitable for being "reverse fed" and applies to which side supplies the magnetizing current, not which way the energy (usually) flows. In other words a transformer used for a pv system need not be marked as suitable for reverse feed.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    YGyg vs. Dyg

    Issues to consider:
    (1) If the inverter needs to properly sense line-ground voltage to properly implement anti-islanding, you will need to use a YGyg transformer. If you use a Dyg transformer, you lose the ability to properly sense line-ground voltages.
    (2) Transformers can move power in both directions but are often rated for excitation and energization from one side. That would be the utility side. The concern is how close the windings are to the core and the resulting inrush current. Consult the manufacturer.
    (3) A transformer introduces 24x7 no-load loss and operational I2R loss. Both impact the overall PV system performance. Consider those when selecting a transformer.
    (4) It is normal for a 600Vdc system to be used for a 208 or 240V AC connection. At 480V, a 1000Vdc system is used. For a 1500Vdc system, they often operate at 600Vac. Check the voltage rating of the array, if the modules are 600Vdc rated, stick with a 208/240V inverter and skip the transformer.
    (5) An autotransformer is YGyg and has a smaller core so core loss goes down. A good choice if you must use 480V inverters on a 208V service.
    e^(i pi) = -1

  9. #19
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    Quote Originally Posted by beanland View Post
    Issues to consider:
    (1) If the inverter needs to properly sense line-ground voltage to properly implement anti-islanding, you will need to use a YGyg transformer. If you use a Dyg transformer, you lose the ability to properly sense line-ground voltages.
    ...
    I'm no expert on transformer engineering but I don't understand how the utility side configuration has any effect on this.

  10. #20
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    Quote Originally Posted by jaggedben View Post
    I'm no expert on transformer engineering but I don't understand how the utility side configuration has any effect on this.
    Same here. I am open to being schooled in this. Inverter could still detect utility L-G voltages as the utility ground/neutral will be solidly connected to the inverter side neutral thru the egc system, so I am skeptical. Also not sure why "some" inverters would want that and others wouldn't. I do recall Mr Gunn stating that he has ran across inverters that speced a wye-wye, but I assumed that was one of those frequent cases of a manufacturer meddling in things they shouldn't care about.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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