60Hz into a 50Hz Motor

We are shop testing a system that is being shipped to a location with 380V @50Hz. All of the motors are rated 190/380V (jumpered for high voltage), 50Hz, 2860rpm. In the shop we are supplying 380V to the motors but can't provide anything other than 60Hz. Didn't think it would make a big difference but all of the motors are drawing more than 4 x their FLA unloaded. This is happening on 3 different sized drives from 3 different manufacturers. Does 10Hz really make that much of a difference? It's not uncommon to over-freq a motor with a VFD without any problems but does that fact that the motors are directly connected to the lines make a difference?

Without being there to see exactly what is going on, I am going to answer in a general sort of way so don't take it as the correct answer. Having said that, normally when you get 4x amps like you said, somehow the motors are wired incorrectly. It could be that they should be wired in Wye and they are in fact wired in delta. Generally speaking, the physical characteristics are about the same and the real difference is that the motor rpm on the 60 hz source turns approximately 16% faster or about 3500 rpm in your case. Also, generally speaking, the current sometimes increases as the power frequency is lowered and decreases at higher frequencies due to the inductive nature of windings and iron in motors. You also stated that the drives were unloaded. I'm wondering if they are fans or pumps. Overspeed of the rpm due to the higher frequency could be a serious problem as pumps and fan loads are different than conveyor motors or some other similar load. I'm certain that there are motor experts on the forum that can provide you a better answer. Someone else may jump in Monday or sooner.

Motor available torque and current draw are a function of the volts per hz ratio. Therefore, on a motor designed for full output at 380V/50hz = 7.6 you are connecting 380V/60hz = 6.33. This is equivalent to severe undervoltaging the motor and the current could be expected to go way up.

But, under no load conditions, I think 4 times FLA is too much. I agree that you probably have the motor jumpers connected wrong.

I agree it sounds like a motor wiring problem
with a voltage of 190/380 3ph 50hz I would guess it's a European motor.
They generally have a 6 post terminal block with jumpers to make the connections. Sometimes they can be confusing if you don't work with them a lot.
With 4 motors acting the same I would venture that you have them wired wrong.
a 50hz motor will work fine on 60hz in some cases even better, better cooling.

Could you be more precise about your initial statement "jumpered for high voltage" by photo or just more detail.

spaderkung said:

Could you be more precise about your initial statement "jumpered for high voltage" by photo or just more detail.

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Could you post the wiring diagram on the motor, and tell us which (if there's more than one) that you used when you wired it up?

"Drives"? Are those VFD's or are you running the motors across the line? If using drives, you should be able to perfectly simulate 380V/50Hz.

As mentioned already, they will be wired incorrectly. Swap for delta if in star or vice versa.

Mistyped. Meant to type motors not drives.

We ran HDM injection machines (with their 50hz motors) for ages with no problems with the motor (the magnesium coupling that was designed for 50hz was a different matter).

I would have to agree with the others that there is a wiring problem.

380/190 is not a valid voltage combination, so something is wrong here. The sq. rt. of 380 is 220. Id say it's more likely that you are using a NEMA design motor made for 230/460V and is intended to be connected Y/YY or D/DD, because that makes your statement of it being 380/190 correct. You can run a NEMA 460V 60Hz designed motor at 380V 50Hz because the ratio of voltage and frequency is roughly the same. But you may have connected it as it it were an IEC motor where the higher voltage is connected Star and the lower is connected Delta. If this is the case, you didn't need the transformer, you could have just connected it at 460V in Star or Delta, whichever way it is designed.

The other possibility is that you have an IEC motor that is wound for 690/400V, which would work fine for 380V supplies. That is a standard motor design now. In that design, the 400V connection would be Delta, not Star.

Please provide photos of name plate and terminal box.