Operating European-Made Motors on U.S. Current

      A discussion of the effect of United States alternating current voltage and cycle frequency on shop machinery wired for European electric power supplies. December 6, 2009

Question
I'm looking into a couple of European machines (used) that are 380v 50hertz. I understand they will run a little faster on 400v, 60 hertz. Is there a way to get them to run in my shop at 220v 3 phase, which I assume is 60 hertz?

Forum Responses
(Solid Wood Machining Forum)
From contributor J:
The easiest way would be to use a transformer. You could either get a single large unit that could handle the amp draw from multiple machines, or go with smaller units, one per machine. One benefit from running a transformer near the main panel is that you can run smaller wire out to the machine due to the higher voltage/lower amp draw. In my shop, we use a disconnect between the transformers and main panel to turn them off every night and weekend to save a bit on energy.



From contributor O:
They can be transformered as contributor J suggests. The 50HZ makes them run 15% faster. Depending on type of machine, this may not be a problem. I have been told this also shortens the motor life a little.


From contributor C:
The motors will run slower.
60 cycle = 3600 RPM
100 cycles = 6000 RPM
120 cycles = 7200 RPM
So less than 60 = less than 3600.


From contributor M:
I think contributor J is right. Think of it this way - if in Europe, the machine is running 3600 rpm at 50 cycles, then here at 60 cycles it should be faster.


From contributor C:
You are correct - I was thinking exactly backwards because I have so often had the opposite question put to me.

A 480 volt 60 hertz will run slower on the European or SA power (380/50). And it is obvious that a 380/50 motor will run at a higher RPM on 480/60, as my own example illustrated. What I would question is whether the 380/50 is really running at 3600 RPM.
I will not deal in non US equipment, so I really don't know.



From contributor E:
Of course there's one other option... Since they're used anyway, you could replace the motors. Assuming they have a standard frame, 3 phase motors are relatively cheap, especially on the used market.


From contributor T:
Calculating Synchronous Speed: AC motors are considered constant speed motors. This is because the synchronous speed of an induction motor is based on the supply frequency and the number of poles in the motor winding. Motors designed for 60 hz use have synchronous speeds of 3600, 1800, 1200, 900, 720, 600, 514, and 450 rpm.

To calculate synchronous speed of an induction motor, apply this formula:
rpmsyn = 120 x f / Np
rpmsyn = synchronous speed (in rpm)
f = supply frequency in (cycles/sec)
Np = number of motor poles

Example: What is the synchronous speed of a four pole motor operating at 50 hz?
rpmsyn = 120 x f / Np
rpmsyn = 120 x 50 / 4
rpmsyn = 6000 / 4
rpmsyn = 1500 rpm
or 1800 rpm for 60 hz
Actual speed is slightly slower due to rotor slip.



From contributor B:
I don't know if you have done anything yet about the 380v/50hz machine or not. We have a machine from Italy with the same specs. It was simple to convert to 220/60 3ph. You only have to change the wiring in the box on top of the motor.

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