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Connect 3phase generator to purely resistive load

  1. Jan 30, 2013 #1
    Hi. Most grateful for your suggestions on the following. My generator is a Stamford/Newage 125 kva, 1500 r.p.m., 174 Amps, 415/240 Volts rating and power factor is 0.8. The load comprises 36 heating elements, each element rated at 6Amps/ 240 Volts (1500 Watts). I have divided the elements into 3 groups , each group thus has 12 elements. What would be the most efficient way to wire this? Is a phase wire and a neutral per group the way to go?
    Thanks in advance.
  2. jcsd
  3. Jan 31, 2013 #2
    Hello JD - Welcome to PF.

    It sounds like you have this right. Wire up the 12 elements in parallel, and then one of the leads to one of the phases and the other to the neutral. Repeat for each phase, when you are done the neutral should have three leads going to it.
    Note: Each "leg" of the heater wiring will have 72A current - all told this is not really an amateur's project, I would at a minimum have a professional (like an electrician) review your work.
  4. Jan 31, 2013 #3

    jim hardy

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    You haven't said whether there's a breaker panel.

    You might find it easier to wire your generator 240 volt delta and use 3 phase breakers, each breaker feeding several heaters also delta.

    That saves a neutral wire and keeps voltage between phases lower.
    BUT- probably needs larger conductors.

    We don't know your installation or local electrical code.
    Talk it over with your electricians ...

    old jim
  5. Feb 4, 2013 #4
    That option isn't available to jdominic. A 415/240V rating doesn't mean the generator has switchable output voltages; it's the standard way of specifying 3 phase supply in the UK and compatible countries. It means that the output has 415V phase to phase (delta connected) and 240V phase to neutral (wye or star connected). As jdominic has 240V heaters they have to be connected phase to neutral and hence the installation does need phase and neutral connections to each heater (along with the appropriate earth mat, conductors and cross-bonding).
    A neutral conductor is still required but keeping the load balanced (i.e. the same) across the 3 phases will allow its size to be reduced. If it's going to be possible to switch subsets of the heaters on, jdominic should keep equal numbers of heaters on each phase in each subset. (3-phase breakers or contactors can be used for this.) The generator will also be happier running into a balanced load.
  6. Feb 5, 2013 #5

    jim hardy

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    Graham are you sure about that?

    Since 415 is 240√3, i'd assume that his generator has three 240 volt windings which,
    when connected delta,
    give 240 volts phase to phase with no neutral

    and when connected wye,
    give 415 volts phase to phase and 240 phase to neutral.

    image (courtesy of anaheim automation, via google images ) for a 220/380 machine,
    .... same √3 relation as 240/415 to nearest volt.


    this website claims his brand of generator has twelve wire connections
    which suggests that each winding is actually two half voltage windings , allowing 120/208 voltage too.

    perhaps op can post a photo of nameplate or page from his manual...?
    Last edited: Feb 5, 2013
  7. Feb 5, 2013 #6
    Ah yes. I was considering the load point of view but, yes, if the generator wiring gives that flexibility your proposal is good too. Thanks for the extra information.

    The ratings book here gives more details of the wiring options:

    The op needs to check the data sheets for the specific model number of his generator to check which wiring options are possible on his generator - I got the impression that you can't have every option on every generator but it's tricky to check without a generator to look at.

    And again the op needs to check with his electrician that 240V phase to phase operation is acceptable for his local installation code.
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