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Why industrial motors etc need 3 phase power?

  1. Feb 18, 2012 #1
    Why industrial motors etc need 3 phase power and something like a TGV (high-speed train) only needs 1 phase (25 kV AC railway electrification), and yet its capable of such performance?
  2. jcsd
  3. Feb 18, 2012 #2
    I don't know much about the train, but I suspect it has a bucket-load of expensive electronics supporting it's motors. Industrial motors that hard start and go one speed are serving a different function than traction motors, which must vary their speed. In all likelihood, your train has a three phase, variable frequency drive on the traction motors.

    Typical industrial motors are minimalistic. The three phases are oreiented such that a constant rotating magnetic vector spins around at some ratio of the line frequency (i.e 1:1 - 3600RPM, 1:2 - 1800 RPM, 1:4 - 900 RPM).
    Typically, they'll start with some means of limiting the current demand (i.e operating in a Y configuration), and then as they speed up, they switch to a full power configuration (Delta).
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