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Thread: Inverter Transformer Wiring

  1. #1
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    Inverter Transformer Wiring

    Inside the larger 3phase inverters are transformers that change the voltage from a 200-220 volt delta to a 208 wye or 480 volt wye for connection to the buildings utility supplied power to feed back to the grid. So at the inverters transformer they don't solidly ground the mid point of the wye side on the output to create a grounded conductor and it is not used to connect to the utility's power system. They just run the 3 phase without the grounded conductor. It is not used or needed. That how it was explained today at Solectria inverter presentation.

  2. #2
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    Quote Originally Posted by shortcircuit2 View Post
    Inside the larger 3phase inverters are transformers that change the voltage from a 200-220 volt delta to a 208 wye or 480 volt wye for connection to the buildings utility supplied power to feed back to the grid. So at the inverters transformer they don't solidly ground the mid point of the wye side on the output to create a grounded conductor and it is not used to connect to the utility's power system. They just run the 3 phase without the grounded conductor. It is not used or needed. That how it was explained today at Solectria inverter presentation.
    That is consistent with what I have seen with the larger inverters I have dealt with. When connected to the grid their output is inherently balanced over the three phases so that if there were a neutral conductor it would carry little or no current.

  3. #3
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    Thanx for the reply! So when the inverter backfeeds a building in this configuration that is served with a 480/277volt wye utility supply that has 277volt lighting on a day when the building is using only the power from the solar PV system because the demand is low enough...does the unbalanced power travel back to the inverter on the equipment grounding conductor between the inverter and the building service?

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    Quote Originally Posted by shortcircuit2 View Post
    Thanx for the reply! So when the inverter backfeeds a building in this configuration that is served with a 480/277volt wye utility supply that has 277volt lighting on a day when the building is using only the power from the solar PV system because the demand is low enough...does the unbalanced power travel back to the inverter on the equipment grounding conductor between the inverter and the building service?
    I don't think so. You don't ever want to intentionally put current on the EGC.

    I believe that the power from the inverter remains balanced and the imbalance is handled by the grid just the same as if there were no PV. It is highly unlikely that your loads will ever exactly match the output from the inverter, so there will always be some exchange with grid. In the case of unbalanced loading, the exchange will be different on the different phases and the difference in current will be on the service neutral. I'm pretty sure that's how it works.
    Last edited by ggunn; 04-26-12 at 12:41 PM.

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    Quote Originally Posted by shortcircuit2 View Post
    Thanx for the reply! So when the inverter backfeeds a building in this configuration that is served with a 480/277volt wye utility supply that has 277volt lighting on a day when the building is using only the power from the solar PV system because the demand is low enough...does the unbalanced power travel back to the inverter on the equipment grounding conductor between the inverter and the building service?
    No, the inverter just supplies the 3 phase back to the utility transformer, that transformer takes care of creating the neutral just as it does normally.

    Weird huh?

    I asked these same questions the first time I hooked one up.

  6. #6
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    yea wierd...how do those electrons from the inverter know to take a left turn to the utility transformer before they go back into the building to the loads that want them?

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    Quote Originally Posted by shortcircuit2 View Post
    yea wierd...how do those electrons from the inverter know to take a left turn to the utility transformer before they go back into the building to the loads that want them?
    They know enough to flow were they are needed.

    It does mess with your mind when you start back-feeding into a source ....... at least it does with me.

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    But, how do the corresponding holes know anything?

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    Quote Originally Posted by BillK-AZ View Post
    But, how do the corresponding holes know anything?
    Who you callin' a hole?

  10. #10
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    yea man

    I had this exact same discussion / 3week interrogation by my boss. It went so far as I was required to show a grounding of the neutral connection to the isolation transformer in the inverter despite what was shown in the inverter installation manual. And just like you guys said, the whole discussion is where does the unbalanced current go?

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