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Thread: 3 phase 220V generator

  1. #1
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    Default 3 phase 220V generator

    HI Forum

    Back from holidays and already hit my first impasse! oh well, work is work.

    We have a client that wants to substitute his 3 phase 220V generator with a 2kW PV system. Fine, but he wants to be able to switch between the generator and PV. The trouble is that the circuits are mixed up between the phases of 220V. So he has one circuit L1-L2, one L2-L3 and another L1-L3.

    Is there any way we can keep the circuits as they are, yet switch between PV single phase and then to the 3-phase motor if the batteries are low?

  2. #2

    Default Re: 3 phase 220V generator

    This may be a dumb question: can you not simply install a 3-phase inverter system? I know Outbacks can be wired this way.
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  3. #3

    Default Re: 3 phase 220V generator

    Quote Originally Posted by Cariboocoot View Post
    This may be a dumb question: can you not simply install a 3-phase inverter system? I know Outbacks can be wired this way.
    I'll second that. SMA, Studer and Victron will also do 3-phase.
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  4. #4
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    Default Re: 3 phase 220V generator

    Nope, 3 phase is a no can do- just one 5kVA inverter single phase, already bought. And anyway, they would give 380V 3 phase and the generator is 220V 3 phase

  5. #5
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    Default Re: 3 phase 220V generator

    Quote Originally Posted by lazza View Post
    Nope, 3 phase is a no can do- just one 5kVA inverter single phase, already bought. And anyway, they would give 380V 3 phase and the generator is 220V 3 phase
    The motor could be handled either with a VFD which would generate the 3 phase required or with a rotary converter. The latter would probably only be about 50% efficient and would have to be run up to speed before the motor is started. Probably more reasonable to start the generator when the 3 phase motor has to be run.

    But before going deeper into this, I would like to know for sure just what the generator is providing!

    In the US, the POCO would supply 208 volts line to line and 120 volts line to neutral. Since your system is based on 220 volts with no neutral, the generator probably actually is configured to deliver 220 volts Line to Line. As such, there is no way that you can substitute a single phase 220 volt source from the inverter without making the transfer switch do a lot more reconnecting to maintain the single phase 220 volt loads, and the 3-phase motor would have to be completely disabled or else transferred to a separate 3-phase supply as I first mentioned.

    Assuming that you can do the required load shedding to not overload the inverter, and calling the two Inverter outputs A and B (220 volt w/o neutral), the transfer switch would have to connect L1 to A and L2 to B to provide power just to that one leg (L1 to L2) of the loads, and then disconnect the second leg (L2 to L3) L3 connection and transfer it to A. The third leg (L3 to L1) could then have its L1 side connected to A and its L3 side connected to B.

    The only other alternative that I can see would be to use a single-phase to three-phase converter running off the inverter output to power everything. This could NOT be a rotary converter, since they are not designed to handle separate single phase loads.
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  6. #6
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    Default Re: 3 phase 220V generator

    Thanks for your replies, yes it will require some form of complex switching, which may or may not be practical. The problem is he wants to switch between the two forms of power and this is difficult... without changing the generator setup..

  7. #7

    Default Re: 3 phase 220V generator

    Quote Originally Posted by lazza View Post
    Thanks for your replies, yes it will require some form of complex switching, which may or may not be practical.
    More than impractical, I think it'll be a costly nightmare, especially since you won't be able to switch between gen and inverter without dropping the loads.
    3 x single phase off-grid inverters will solve all this and provide a nice clean install, where the generator can be switched in without losing any power to the loads. You can configure them to be 230V 3 phase or 380V 3 phase.
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  8. #8
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    Default Re: 3 phase 220V generator

    .. am I right in supposing that the generator has a Delta 3-phase wiring, which would give it 220V between phases without a neutral... if it were a Wye 3-phase wiring would it then give 380V ??

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    Default Re: 3 phase 220V generator

    Quote Originally Posted by lazza View Post
    .. am I right in supposing that the generator has a Delta 3-phase wiring, which would give it 220V between phases without a neutral... if it were a Wye 3-phase wiring would it then give 380V ??
    From the description of the load connections (phase-to-phase), it would have to be a delta application with 220 volts phase-to-phase regardless of how the generator is actually built and whether or not it has a neutral also.

    If it were a wye with 220 from phase to neutral, then yes, the phase-to-phase would be 380. But we do not know how the generator is actually wired. We just know how it is intended to be used.

    It will be far easier to change or supplement the inverter to make 3 phase power available than to reconfigure all of the loads and the generator itself!

    Regardless of how the failover occurs in terms of switching and reconnection, either there will be a short drop as the relay contacts transfer or there will have to be a full-time UPS in the process somewhere. Doing the complex connection rearrangement with contactors and relays will not leave the loads disconnected for much (if at all) longer than just transferring 3 line connections via simple relays.

    One critical requirement for safety though is that all three phase wires have to be interrupted in one operation and that operation must complete before any of the phase wires are reconnected to a power source. The consequences of one phase hanging on the generator while the others transfer to the inverter or vice-versa could be really bad.
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  10. #10
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    Default Re: 3 phase 220V generator

    Quote Originally Posted by stephendv View Post
    More than impractical, I think it'll be a costly nightmare, especially since you won't be able to switch between gen and inverter without dropping the loads.
    3 x single phase off-grid inverters will solve all this and provide a nice clean install, where the generator can be switched in without losing any power to the loads. You can configure them to be 230V 3 phase or 380V 3 phase.
    Not all single phase off-grid inverters have synchronizing capabilities which would allow them to work together to generate three proper phases. Not all of the loads are single phase, there is also a motor involved. Even if there were not, the delta connection of the loads demands that the three inverters be synchronized.
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