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Frequency of motor power supply 60 Hz versus 50 Hz

  1. Apr 2, 2013 #1

    rollingstein

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    If a 60 Hz equipment needs to be run off a 50 Hz power supply (3 phase, AC) what are typical options?

    One brute force approach is to simply change motors. But I was wondering if a VFD / thyristor or some such might work?

    This is medium sized equipment with rating of ~5 kW.

    As an aside, were someone to accidentally cross connect a 60 Hz rated motor to a 50 Hz supply would the results be disastrous? Is the risk symmetric? i.e. A 50 Hz motor connected to a 60 Hz supply?
     
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  3. Apr 2, 2013 #2

    russ_watters

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    Welcome to PF!

    If you check the specs of the device, odds are it says it will run just fine on a 50hz supply, just at reduced performance.
     
  4. Apr 2, 2013 #3

    gerbi

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    Motor designed to 60 Hz will run on 50 Hz, but (as russ said, at reduced efficiency):
    - reduced RPM (by 20%),
    - reduced output power (by 20%, as it is function of RPM),
    - reduced cooling (may be critical),
    - inceased flux in core (increased losses, may be critical) -> can deal with it by reducing voltage.

    It would be much safer to run 50 Hz motor on 60 Hz.

    All in all.. it may be dangerous to motor. Some VFD is a good idea I think.
     
  5. Apr 2, 2013 #4

    rollingstein

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    Thanks! 20% rpm drop we can probably tolerate. It goes into an industrial spin dryer.
     
  6. Apr 2, 2013 #5

    jim hardy

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    I assume we're talking about an old fashioned induction motor, not one of these newfangled appliance motors that's driven by a microcomputer generating three phase..... (Woe is me -- I can no longer fix wife's washing machine!)

    Check nameplate of motor and see if it gives two different voltages for 50hz and 60 hz.
    A 50 hz motor needs more iron laminations for same voltage than does a 60 hz motor. A high quality motor could be designed to run on either by simply including the extra iron. But one might want to adjust pulley diameter to restore drum speed.

    If the motor is not suitable for reduced frequency it will hum and get very hot. As an old engineer from Tennessee put it, "If it'll fry spit it's in trouble". So give it the feel test after a few minutes of operation.

    If it's "one of those newfangled ones" the computer is already a VFD that's probably oblivious to line frequency. But that's a guess from afar. I'm sure you can tell by looking at it.

    "One experiment is worth a thousand expert opinions".
     
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