Frequency Problem

Your speed will be less. If your motor is an 1800 rpm type at 60Hz, it will become 1500 rpm at 50Hz. If it's a 3600 rpm motor at 60Hz, it will be 3000 rpm at 50Hz. Current-wise, it will consume a little less current and consequently, a little less power.

Is this good or bad? 'Depends on your application. If your load requires a speed of, say, 1800 rpm, then don't change your motor to a 50Hz type. If your load can operate at a lower speed, then it should be okay.

The motor will run hotter as the inductive reactance will be less = higher current = more DC heating on the coils.

http://en.wikipedia.org/wiki/Reactance

This may cause problems. so you might want to derate it accordingly after you speak with the maker.

I was thinking in terms of what I've observed from running motors on variable frequency drives or VFDs. At 50Hz, the current is a little less than running it at 60Hz. When you use a VFD, you also need to use a motor with higher insulation rating but since the OPs problem doesn't involve VFDs, it shouldn't matter.

As for heat, running a motor at less than its nominal speed means the motor runs a little hotter than usual due to the reduced cooling action of the cooling fan. However, the difference between 50 and 60Hz is not that big.

Still, if you want to consult with the manufacturer, that would be a good idea. They know their product best (except when they have other interests in mind ).

Quote:

"I was thinking in terms of what I've observed from running motors on variable frequency drives or VFDs. "

In VFDs [Variable Freq Drives] are actually VFVVDs [Variable- Freq- Variable- Voltage] as the output varies [increase V with increase in F to keepcurrent almost constant] linearly or any-set slope [V/F Slope] as on low freq Motors will draw very high current ifyou keep V constant.

In reply:

"europium Guru #8 In reply to #5

The inrush current is independent of the line frequency, as the inrush itself is a transient condition that exists independently of what follows it - whether 50 Hz, 60 Hz, or DC. "

Remember that in AC 50 or 60Hz current will be limited by freq [back-emf], but in DC there will be no end piont & on saturation of core will occur where back-EMF will be zero & current infinite.

HMM...

Interesting, the motor will turn little slower, consequently current will be lower. (that is what you have said,). Thinking along this line, at a blocked rotor situation, with Zero RPM, the current will be Zero as well?

Truth is :

1. Motor will run slower.
2. Motor power or HP, (at plate RPM) is de-rated at the same ratio as the speed.
3. motor will run hotter.
4. FLA (plate Amp.) must be de-rated as well.

Think about recalculating your motor protection device, whatever it is, as starting inrush current will also be somewhat higher due to lower inductive resistance.

Wangito.

The inrush current is independent of the line frequency, as the inrush itself is a transient condition that exists independently of what follows it - whether 50 Hz, 60 Hz, or DC.

-e

Not really.

"Spool-up" time is longer for 60 Hz motors operating on 50Hz line. inrush current will be little higher and a lot longer. This should be taken into account when selecting the protection device, Curve and current should be adjusted accordingly.

But aren't we getting little too picky?

Wangito

Picky? No. But I do think we're talking about two different things.

Cheers!

-e

I'm not professing to understand everything and I've had to limit what I've explained to avoid prolonged typing.

The relationship is not linear. The current will drop with the frequency up to a certain point. I don't remember what frequency that is but I've observed it. At even lower frequencies, the current will shoot up (alarmingly). For this reason, I've set the low frequency limits on my frequency drives to 15 Hz and I've made sure that, if it does go down to that level, it won't stay long there or else I shut down the drive.

I didn't do calculations because I don't need to. I'm speaking from observation.

In any case, the question doesn't involve varying the frequency, just using a 60 Hz motor on a 50 Hz source. Since we won't have to deal with lower frequencies then it shouldn't matter.

If the reverse is happened

i.e the motor 50hz but the supply 60 hz ?

what is happen ?

The motor runs faster in proportion, draws less current and produces less horsepower.

So if the motor at 50 Hz was closely matched to the load it may not be capable of full speed/load operation at 60Hz

Your under voltage (UV) protection for the motor will probably trip the motor off line. Also, the motor will run hotter and thus reduce the life expectancy of the motors insulation. (Especially if operated in the high service factor range SF - say up to 1.15) Motors are designed to run at nameplate frequence, for optimal performance and longevity. You should not deviate from nameplate data operating parameters.

Regards: cgl.

Guest writes: "You should not deviate from nameplate data operating parameters."

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I disagree - for small motors. Experimentation is instructional provided safety is observed. I've used small motors at frequencies and voltages at considerable deviations from nameplate data with some success. If the O.P. is speaking of a large, multihorsepower device, that's a different story.

My 0.02 worth.

-e

He is right if proffesional instal do not dev. but if your messing around cool. Bottom line is that it can be done but you really need to take in acount tourque. It is entierly possible that running a 50hz motor on 60 hz might be better than same motor at 50. If you where to look up product data sheet ultimeatly it will show you a rating for both 50 and 60 hz.

I will look it up but you can find torque in foot pounds off of rpm and pully size.

Thank you. Please see post #9.

-e

Your motor will run at 50/60 of its rated RPM. Depending on the motor, it may run hotter or it may be perfectly happy at the lower line frequency. If it runs hotter, you can scale-back the input voltage to compensate while sacrificing output torque. If it is a fractional-HP motor, it may be possible to reduce the motor's input voltage with a variac, except that a variac will typically cost a bit more than the motor itself.

These are a few, general suggestions. Can you tell us what kind of electric motor you have? Induction motor, capacitive-start, synchronous, etc?

-e

You are all assuming the voltage stays the same as the frequency drops. In many cases the voltage is lower as well. Motors work on a V/Hz ratio and as long as that ratio remains the same, the torque remains the same. So if you have a 460V 60Hz motor and you take it to a country where they have 50Hz, chances are good that it is 380V 50Hz. 460 / 60 = 7.67V/Hz. 380/50 = 7.6V/hz. The difference is negligible, so you will attain the same output torque at 50Hz in that scenario. As to overheating, if this is the case the motor will only overheat if the load is higher than the power rating. At 20% slower speed, the HP will go down because HP = Tq. x RPM/5250. Although the Tq remains the same, the RPM is lower, so the HP is lower as well. However if the motor was designed with a 20% overhead as many are, the net effect on the application remains speed only.

Bottom line, you need to consider all factors.

Now, connect this motor to a water pump, for example. Although torque capability remains the same, Q (flow) is less by approximately 15%, due to slower speed, and that is what the user is worried about. (I guess).

Wangito.

If motor voltage is same, then your speed will be 20% lower,that's all!

It all depends on the type of motor and how you use it. That is is it a brush motor or an induction motor? Will it be at full load or partial load. Do you wish to use a variable speed device or constant speed application? More info is rquired to give a good answer.