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  • Another electrical question

    I brought machines to China. Part of the electrical system is 240 3 phase 60Htz, The Chinese got transformers to change their electricity to something that would work on my machines. They way I understand american electricity with 3 phase is in simple terms that any 1 of the wires is 120 volts any 2 together is 240. I know about the wild leg. but in basic terms this is correct. Well the Chinese transformer each leg is 240 volts, but any 2 wires together is still only 240. It runs the machine fine. I don't see how this will work, but it does. Anyone know why?

  • #2
    What are the voltages to start with? It sounds like they used Buck/ Boost transformers in Buck mode.
    Bob

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    • #3
      380 volts, 50Htz, How do end up with 240 when you start with 240 and be on different phases? It makes my head hurt!

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      • #4
        I have been retired 17 years and it was about 25 - 30 years ago That I was doing extensive transformer hook ups. Long story, I have miss placed my notes and books.
        Have you measured each phase to each other and also to ground,neutral.
        A - B, B - C, A - C as stated 240 volts, but is each phase to ground also 240 volts. A B C. I suspect that they have grounded one phase. This would be to stop the risk of higher voltages being generated if something went wrong in your equipment. They probably have 380 -120 volt transformers. By using two or three this would give you the 240 volts, but with three phase power this on a star/Y hook up would give you about 139 volts from any phase to neutral.

        If they used a delta hook up complete with stinger leg. You could then have 120 to ground from two of the phases and the other leg would be the stinger.

        So again I believe that one phase is grounded. If it was C then C to ground would read 0 volts. Could be either star or delta out put, but would have one phase grounded.

        If they used Buck/ Boost transformers they would have to remove 140 volts to get what you need. This would be very unlikely.

        Bob

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        • #5
          Thought I would bump this and see if you had checked the voltages.

          Bob

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          • #6
            Pretty much has to be one leg grounded, doesn't it?

            I thought of that too, but it didn't quite match the "letter" of the description.

            But I think "any" leg to ground has got to mean "either of the two non-grounded ones. Nothing else makes sense.
            1601

            Keep eye on ball.
            Hashim Khan

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