Why do 3-phase motors operate at a lower voltage at 50Hz then at 60Hz?

For example, a small motor I use has the following on the nameplate:

60Hz - 230/460Vac - 1.4/0.70A 50Hz - 200/400Vac - 1.5/0.75A

The output power is the same as the current increases correspondingly, but why does the voltage change?

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The output power is NOT the same. The motor's horsepower rating will be lower at the lower frequency and voltage.

Why the lower votlage? Because that this the standard European voltage. The voltage does not "change", they are giving you current information at the voltage that the motor will be connected to.

Charles Perry P.E.

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Charles Perry

Lower voltage is necessary because you do not want the magnetic components to saturate. Lower frequency means lower reactance. Even so, it looks like this particular rating allows a bit more applied voltage than mere scaling would indicate. That is why the current drawn increases. Finer detail of the trade-offs eludes me.


-- Ferme le Bush

Reply to
Salmon Egg

hi every body

with the magnetiic devices, they are designed for a rated flux, so you should have the ration volt per hertz constant

Salm> On 6/28/06 8:37 AM, in article

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Reply to
Red Face

Charles Perry has it right.The nameplate is giving you the current requirements at different voltages.The output power is easily calculated by Ohms law. Mark

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-------------------- Ohms Law will not give the output power. Ohms law doesn't work for motors.- even DC motors. In addition, Ohm's Law is not a power relationship and the power factor is not unity.

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Don Kelly

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