# Problem when feeding a motor with high frequency source



## GustavoSilvano (Oct 3, 2016)

Hello there!I'm in a project that we're designing a rolling table to transport a bundle of steel rod. To improve the productivity, I want to increase the speed of the gearmotor with an inverter.The plate info of the gearmotor shows that the nominal rotation is 1780 rpm. But in contact with the manufacturer, it shows that it can run safety with 2800 rpm.My question is. What a high frequency feeding source can cause to my motor? It will reduce it lifespan?

Some more info.

The duty cicle is about 10 seconds in every 5 minutes. So it only run for 10 seconds, then it stays down for 5 minutes, then run again for 10 seconds.

The gearmotor is of 1,5 HP, and if fed with 440 V.
The normal currently of work, with load, is about 1,6 A.

Thanks


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## knight1fox3 (Oct 3, 2016)

I don't quite understand your question. What are the specifications for the high-frequency source you referenced?


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## GustavoSilvano (Oct 4, 2016)

Sorry. I'm feeding it with an inverter.


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## knight1fox3 (Oct 4, 2016)

So I guess I don't consider that to be a high-frequency source assuming you are utilizing some type of utility power at 60Hz. Now if you're talking about the carrier frequency of the VFD, then yes, that is typically high depending on the design of the drive. If the existing motor you have is of the squirrel cage design but NOT rated for inverter-duty, then yes it will likely decrease the lifespan of the motor. As small as the motor is and with it not drawing much current, I would anticipate the decrease in lifespan to be minimal.


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## GustavoSilvano (Oct 4, 2016)

Thanks for your reply. Here are some considerations:

When I say that I'm feeding it with high frequency, is because I'm increasing the frequency from 60 Hz to 90Hz, so that my motor run on a higher speed.

Sorry or my question, but how can I know that the motor is rated for inverter-duty?


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## knight1fox3 (Oct 4, 2016)

GustavoSilvano said:


> Thanks for your reply. Here are some considerations:
> 
> When I say that I'm feeding it with high frequency, is because I'm increasing the frequency from 60 Hz to 90Hz, so that my motor run on a higher speed.
> 
> Sorry or my question, but how can I know that the motor is rated for inverter-duty?


Oh I see, that makes more sense. You're now referring to the drive output to the motor. One thing to verify first is the rated RPM of the motor. If it only has one rating, then that rating is not to be exceeded under any circumstances. Some motors are designed to withstand higher RPMs and are therefore dual-rated (e.g. 1750/2300 RPM). This should be evident on the nameplate of the motor in question.

Depending on the age of this motor, sometimes it will be indicated on the nameplate if the motor is inverter-duty or not (see example nameplate below, upper right-hand corner in black box). If it is not indicated, then the next best thing would be to look up the technical specs of the motor based on the corresponding part number. Or try contacting someone in sales/applications from the motor manufacturer.


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## GustavoSilvano (Oct 5, 2016)

Ok. But can't I increase the speed using my inverter? I mean, isn't it the reason for using inverter, to make the speed variable, even if it is for more?

Is just that the torque isn't important in my application. What is more important is the speed.

And in contact with the manufacturer, they said that it can run safety with 2800 rpm.

Is just that I'm concerned with what can happen with the bearing and shaft. And how can I prevent it.


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## knight1fox3 (Oct 5, 2016)

GustavoSilvano said:


> Ok. But can't I increase the speed using my inverter? I mean, isn't it the reason for using inverter, to make the speed variable, even if it is for more?


Of course you can. However, most industrial applications are typically designed around a maximum of 60Hz on the output of a drive. For instance, the example nameplate I provided would not be able to be operated at 90Hz. The drive could still be set to output 90Hz regardless, but would likely have unintended detrimental consequences to the motor.

Even the default drive output parameter is typically set for 60Hz and one would need to manually change that to 90Hz. As mentioned above, if the motor is rated to handle the RPMs at 90Hz (per the nameplate data), then the motor and its corresponding mechanical assembly (i.e. rotor, shaft, bearings, etc.) should be fine.


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## GustavoSilvano (Oct 5, 2016)

Ok then. Thank you for your reply!

Best regards!


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