running a 220Vac/50Hz motor at 110Vac/60Hz 1

[rasiga]

At this moment I don't know the motor characteristics; this is an upcoming project. The question is: can we run the motor for a couple of hours without burning it? We need to run the motor just for testing purposes. I tend to believe we can do that with no problems.

Any help is welcomed.

 

[electricpete]

both voltage and frequency are changing in a direction to decrease your torque for a given speed.

You may experience starting problems if your motor does not exceed the load torque at all speed through the start. And you may also overheat during starting even if torque is sufficient at every point). A normal start has two components of heating... #1 - heating required to accelerate the inertia; and #2 - Additional heating as a result of difference between motor torque and non-zero load torque. #1 would remain the same as a normal start but #2 will increase due to the lowered motor torque. If there is any load torque during starting, then your reduced-voltage start will be more severe than a normal start of the same load.

For steady state operation, Motor would need to be derated significantly due to higher expected currents for given power level. I don't know the extent of the derating but possibly on the order of 50%

If your testing doesn't require any load at all (uncoupled), I would susepect the motor will be easily capable of accelerating it's own inertia without overheating during the start.

 

[peebee]

I agree. If you just want to see if it runs unloaded, it's probably OK, even for a few hours.

Run that thing at even partial load for just a few minutes, though, and you'll probably smoke it.

If you can, run it at 208 or 240, though, rather than 110. 208 or 240 is available virtually everywhere that 120 is, and that will give you a better test with less chance of motor damage.

 

[jbartos]

Suggestion to rasiga (Electrical) Jul 25, 2002 marked ///\\At this moment I don't know the motor characteristics; this is an upcoming project. The question is: can we run the motor for a couple of hours without burning it?
///It depends which motor characteristics you do not know. Does the motor have an official nameplate?\\ We need to run the motor just for testing purposes. I tend to believe we can do that with no problems.
///It depends on the known characteristics/parameters. Else, you would have to perform various tests to obtain those.\\

 

[cuky2000]

We know that motors are designed with dielectric strength to operate safe above and below 10% of rated voltage. However, I found different point of view in other site that I would like to share with all of you to keep the dialog open in this issue.

Can I run a 60Hz rated motor on 50Hz?
Induction motors use an iron core and require flux in the iron to operate.

In order to achieve the commercial goals of smasllest size and lowest price at best efficiency, induction motors are designed to operate at a high level of flux in the iron. The flux is determined by the turns, voltage and frequency.

In a modern motor, if the flux is increased by a small amount, the iron losses increase and the iron tends towards saturation. At saturation, the inductance begins to fall and the current increases further. To reduce the flux at a given voltage and frequency, the turns on the stator are increased. This reduces the Iron loss, but a longer length of thinner wire is used and the copper loss increases.

Design becomes a balancing act between copper loss and iron loss and so the design is optimised for a given voltage and frequency.

If the voltage applied to the motor is held constant and the frequency is increased, the inductive reactance increases and so the flux reduces. This effectively reduces the maximum torque capacity of the motor and so the motor power rating at the higher frequency remains the same.

If the voltage applied to the motor is held constant and the frequency is reduced, the current will increase and in theory, the torque will also increase. The motor should be able to deliver the same power also, BUT the flux in the iron is now too high resulting in excessive iron loss, and the motor will fail prematurely.

Above a very low frequency, (5 - 10Hz) the impedance of the magentising circuit of the motor is primarily inductive and so in order to keep the flux within limits, it is important to keep a linear V/F ratio (Voltage to Frequency ratio).

If the frequency is reduced by 10%, the voltage must also be reduced by 10%. Because the flux in the iron remains the same, the torque capacity remains the same and so the power rating of the motor also drops by 10%.

Provided the voltage is dropped by the same proportion as the frequency, it is OK to run a 60Hz motor on 50Hz. The speed will be reduced by the reduction in frequency and the power capacity will also reduce by the reduction in frequency.

60 Hz Volts 50 Hz Volts
480 400
460 383
440 367
230 191

REFERENCE:[/color red]

http://www.lmphotonics.com/faq.htm

 

[electricpete]

cuky

It's an interesting text-clip. I gather the author's main point is that the flux depends on the ratio of volts to hertz. If they both increase or both decrease (in proportion), the effects tend to offset each other (flux remains the same... torque remains the same).

In the case of the current post, both variables are changing in opposite directions (decrease voltage, increase frequency), so the effects of these two changes are additive (they both tend to decrease flux and torque), rather than offsetting.

I guess that on first glance I can't detect what is relevant to this thread. If you have in mind a specific comment about this post or the article in general please elaborate. But it is an interesting article.

 

[redtrumpet]

electricpete - I believe the author of that article is none other than Mark Empson, who regularly posts with the handle MarkE.

 

[jbartos]

Suggestion: Visit

http://www.iprocessmart.com/leeson/leeson_electrical_reference.htm

for comparisons of 50Hz and 60Hz induction motor parameters.

 

[Marke]

As suggested above, the reduction in voltage will result in a reduction of torque capacity proportional to the voltage reduction squared, therefore a quarter of the torque. Increase in frequency will further reduce the flux in the iron and therefore the torque capacity will be further reduced. If you want to run the motor open shaft for a couple hours, that will be fine, however if you have more than 20% of rated shaft torque while you are running the motor, ist will operate at increased slip and possibly stall resulting in excess heating of the motor.
Best regards,
Mark Empson. Mark Empson

http://www.lmphotonics.com