Motor Question - European

[SuzukiPhil]

Hello All,

My company received some equipment from France (We are located in the U.S.). One item uses a electric motor rated at 230/400V 50Hz. A electrican changed the voltage to settings to match ours. Now the motors has burned up. Could the 50Hz frequency be the cause of the malfunction?

I told my boss that we should be able to have this motor re-wound locally because it is a custom made motor for the equipment.

Thanks

 

[jraef]

SuzukiPhil,
Running the motor at 60Hz would not necessarilly cause the damage, although the motor would run 20% (6/5) faster than normal and provide less relative torque at that speed. These issues can eventaully cause the motor to overload depending on the circumstances of your machine application, but not absolutley.

Another area to check out is exactly what your electrician meant by "changed the voltage setting to match ours." You didn't specify what "yours" is. If by that you mean he set it up to run on 230V 3 phase and you supplied 230V 3 phase, then the speed /torque issues above are the likely root of the problem. If he thinks that setting it for 400V was close enough for your 480V supply then in all likelyhood that is the cause of the burn out. 480V is 20% high for a 400V motor, well beyond the acceptable limit of motor designs.

"Venditori de oleum-vipera non vigere excordis populi"

 

[aolalde]

I wonder what specific change was made by the electrician.

The bearings and winding design of a motor intended to operate at 50 HZ does not necessarily are satisfactory for 60 HZ. Some lucky people has connected 50HZ motors in 60 HZ systems with satisfactory results when the supply voltage at 60 HZ is increased proportional to the frequencies.
V60=V50*60/50 e.g. 400*5/6= 480 Volts. This voltage change produces the same magnetic strength as that of the original motor.

After that is done, the second consideration is the speed increase of the load, if the original load like a pump or fan is left, the power demand could increase as the cubed ratio of the speed increase (6/5)^3 = 1.728 ; a load requiring 10 HP at 50 HZ becomes 17.28 HP at 60 HZ.

 

[jraef]

Oops, you are right aolalde, I forgot to apply the ratio to the voltage.

"Venditori de oleum-vipera non vigere excordis populi"

 

[RRaghunath]

How about higher eddy current and hysteresis losses in the core laminations due to 20% higher frequency and the consequent damage to the laminations (rather inter-laminar insulation)due to additional heat!

 

[aolalde]

rraghunath:

Core losses are certainly another detrimental problem that some times is ignored. Although the loss increase energy developed probably will not reach destructive levels, but the efficiency is affected and the operating temperature rise, since it depends on the grade of steel and magnetic saturation for each particular design.
As a reference per ASTM the Maximum core losses expected in an electrical steel M-36 0.025” thick at 15kGauss (~96.7 kL/sqin) are:
@ 60HZ --- 2.13 Watts/ Lb and @50HZ ----3.71 Watt/Kg (1.684 W/Lb)

That makes an increase of losses of 26.5% at 60 HZ, slightly higher than the proportional frequency increase.

The cooling fans will increase the power consumption and mechanical stress with the speed increase but will provide more cooling air flow.

In conclusion a depth analysis of each particular case should be made to decide if the frequency change will work as expected. That is why I said that “some lucky people has successfully made that change”

 

[SuzukiPhil]

The U.S. distributor of this equipment does not have any motors available so I am taking it to a motor repair shop for new windings.

Thank you for the responses,

Philip

 

[UKpete]

In case you haven't done so already, bear in mind that rewind shops rarely do anything else except copy the old winding, the shop I worked in anyway weren't up to rewiring to a new voltage/frequency. If they put the same winding back in, there is a chance it will just burn out again.

When you say it is custom made, are you sure it isn't an IEC frame which are of course are different to NEMA but they are available in the US.

 

[UKpete]

Come to think of it, you may have to do something more drastic. As already stated by others the speed is 20% above what was intended by the manufacturer, this may require a higher power motor. One way of checking the motor isn't being overloaded is to measure the current (e.g. with a clip-on ammeter) and compare it with the nameplate rating.

If it is overloaded, it may be simpler to buy a variable frequency drive, connect it to your rewound motor and set the speed to that on the motor nameplate. VFD's aren't that expensive these days.

 

[SuzukiPhil]

I informed the rewind shop of the 60hz requirement and they said it would be no problem to rewind to the correct frequency.

Philip