50hz motor 2

[jag27]

hi i have a 50hz AC induction motor ( single phase 110/220 v)

i want to run it on 60hz


what issues might i be facing ??

 

[grobert]

That would not be a problem. The fact that the nameplate voltage will be matched removes other issues. The difference you will see is that the motor RPM will be greater. Take the motor nameplate RPM at 50hz and divide by .8333333 This will give you your new rpm ie; 3000 @ 50hz becomes 3600 @ 60hz, 1500 becomes 1800 and 1000 becomes 1200. Hope this helps.

 

[jOmega]

Just be careful not to exceed the Torque & HP & FLA ratings of the motor at the higher speed.

Unless motor mfgr. advises differently, design of motor is limited to torque and HP values at N/P 50 Hz operating point.

 

[Skogsgurra]

jag27,

The fact that you do have a single phase motor complicates things a little. Going from 50 Hz to 60 Hz will change the impedance of the start/help winding upwards and reduce the capacitor impedance. That means that the phase-shift in the start/help winding is reduced and can reduce the torque so the motor won't start. Reducing the capacitor value about 20 percent could help (same impedance as before, motor winding impedance still on the high side).

You should also bear in mind that the motor needs 20 percent more voltage at 60 Hz. Running at 220 or 110 V will increase the slip and that means a hotter as well as a weaker motor.

Adding 20 percent (60 Hz is 20 percent more than 50 Hz) to 110 V will give you 132 V and I think that 120 V could work. If you have acess to 277, I think that it would be even better since it is close to 220 + 20 percent, which is 264 V. The latter voltage is a far better match for the 220 V winding than is 120 V for the 110 V winding.

Also, do not expect sychronous speed like 1800 or 3600 RPM, but that you already knew.

 

[Baldor]

Hey Skogs..
Isn't it not advisable to increase a motor beyond it's voltage rating? True, if you want to run a 60 Hz motor at 50 Hz, you'd decrease the volts along with the frequency. Above the rated frequency, don't you want to stop at the rated voltage and run in constant HP (reduced torque, higher speed)?

 

[Skogsgurra]

No, Baldor. Done that. No sweat. Safety margins are more than ample. I wouldn't do it in a standard product, though. I get the impression that jag27 has found just one motor and wants to use it for some project - or just test it. And I presume that jag27 does his earthing and fusing according to local safety rules.

 

[jOmega]

Skogs,

at 264 volts, motor would see the same V/Hz as at 220/50.

Impracticallity is that 264 is not a standard voltage value. So, to keep V/Hz the same, there is a voltage source problem to overcome.

Also, as I said above, you'd have to restrict the load torque and not exceed mtr n/p amps ... else, motor would be overloded. Motor designed for xx HP at 50 Hz will also be rated at the same HP at 60 Hz..

Depending upon load characteristic, load torque may exceed motor design at 60 Hz speed.

Need to be mindful of this.

 

[Skogsgurra]

Hi jO,

Yes, I know that you cannot get 264 volts. That's why I proposed 120 V (undervoltage, with poor torque) or the next standard voltage, which seems to be 277 V in some installations in the USA. At least according to the BMI-Dranetz "World-wide Power Scope thresholds".

A standard motor has +/- 5 percent voltage tolerance (this is a lot narrower than the mains voltage allowable swing, which is +/- 10 percent in most western countries and the reason is that the maximum torque is proportional to voltage squared). The ratio between 277 and the "correct" 264 is 1.049 so the voltage is still within limits.

I agree that we are quite close to the upper tolerance limit, but I never thought that jag27 would be using this motor in any kind of standard product that will go into mass production. A responsible designer would not do anything like that, but someone that is curious and wants to experiment can and should just that. There is a lot to be learned from such excersises.

Regarding HP. Yes, you can get more HPs out of a motor when you run it on 60 Hz rather than 50 Hz. This is regularly done and the reason is that if you keep the V/Hz konstant, then you get a constant torque at rated current and since power is Nm times RPM you can get 20 percent more power out of the motor at 60 Hz.

I have assumed constant torque, a fan or centrifugal pump would have a 44 percent higher torque at 20 percent increased speed, so there would be an obvious risk that the motor is overloaded. I am sure that jag27 will find that out once he has got the motor running.

 

[smms]

If you keep the rating constant, the motor will run with an decreased moment (temperature rise will decrease - about 10% lower losses).
If you keep the torque constant, the losses will increase about 5 to 10%. The rating will increase about 20%.

 

[jag27]

guys

i just ran the motor at regular 60hz without any problems
i used standard 115 v and had a 6 amp fuse on it
the motor was rated for 2850 rpm and it did not get hot or even warm after running cont. for 15 mins

so i guess i am cool

thanks a lot for ur help guys

 

[Skogsgurra]

Cool jag27,

Do you intend to load it? Tell us what happens when you attach the load.

PS Remember thermal protection and the Protective Earth!

 

[jbartos]

Suggestion: The motor at 60Hz will experience higher eddy current losses and remagnetization losses (Steinmetz Law).
If you are a traveller, visit:

http://www.franzus.com/electricity.htm

etc. for more info

 

[Skogsgurra]

Yes, jb. Most of us know that. But that is so insignificant when going from 50 to 60 Hz that I find it ridiculous to mention it at all.

 

[jbartos]

Suggestion: If motors are designed for 50Hz and 60Hz with noticeable design margins, then the mentioned phenomena have relatively small effects. Incidentally, I am posting for the original posting not for you and your personal opinions.

 

[jbartos]

Suggestion to skogsgurra (Electrical) Oct 14, 2003
The fact that you do have a single phase motor complicates things a little.
///It may if not desiged for 50Hz and 60Hz.\\ Going from 50 Hz to 60 Hz will change the impedance of the start/help winding upwards and reduce the capacitor impedance.
///This is very trivial since
Xc=1/(2xpixfxC)
appears even in technicians and electricians textbooks.\\ That means that the phase-shift in the start/help winding is reduced and can reduce the torque so the motor won't start. Reducing the capacitor value about 20 percent could help (same impedance as before, motor winding impedance still on the high side).
///Yes, visit

http://www.wempec.wisc.edu/reports/2000/00-04.PDF

for the single phase permanent-split capacitor motor.\\You should also bear in mind that the motor needs 20 percent more voltage at 60 Hz. Running at 220 or 110 V will increase the slip and that means a hotter as well as a weaker motor.

Adding 20 percent (60 Hz is 20 percent more than 50 Hz) to 110 V will give you 132 V and I think that 120 V could work. If you have acess to 277, I think that it would be even better since it is close to 220 + 20 percent, which is 264 V. The latter voltage is a far better match for the 220 V winding than is 120 V for the 110 V winding.
///If motor is not designed for 60Hz, the higher voltage will have impact on the motor aging.\\Also, do not expect sychronous speed like 1800 or 3600 RPM, but that you already knew.