Use of 277V, 60Hz Motor in 208V, 50Hz System 1

[eetag]

Recently my company purchased equipment that used 115V, 1P, 60 Hz motors. However, the equipment application was for a 115V, 50 Hz power system. To address the reduced frequency, the supplier provided 277V, 1P, 50 Hz motors. Again, the available power is 120/208, 50 Hz.

Questions:
1. For the 277V motor, the volts to hertz ratio is as follows:
@ 60 Hz: 4.62
@ 50 Hz: 4.16 (i.e. ~10% decrease)
Everything I've read indicates the key is to maintain the volts per hertz ratio. Would this decrease be acceptable? What is an acceptable range for volts per hertz deviation?

 

[aolalde]

An acceptable voltage drop is 10%.

277/60x50x0.9= 207.75 Volts

however I have some doubts:
1- 1P means single phase? If so check that the starting winding is not operated by a centrifugal switch, it could not open operating at 50 HZ speed.
2- If your line voltage drops below the nominal 208 Volts the motor will be operating under marginal condition.

 

[Skogsgurra]

It would work fine - if you do not expect full torque from the motor. But if you need full torque, it will have too much slip and heat the rotor. Possibly with heat hitting bearing and cause premature bearing failure.

Standard acceptable deviation is +/-5 %.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[dpc]

faq237-1224

 

[waross]

By my calculations, a 277 volt motor will rerate to 277x5/6=230.8 volts.
230 volt motors have been run happily on 208 volt systems at 60 Hz.
It is pushing the limit though.
HOWEVER, I understand that your new motors are rated 277 V 50 Hz.
What ever, I would first clarify the frequency of the new motors. Then, if they are 60Hz. rerate the voltage with the formula 277x50/60=230.8
If they are 277 V 50Hz motors use 277 volts.
Now buy an autotransformer to boost your available voltage to either 230 volts or 277 volts.
By the way, clarify your voltage. You state that it is a 115 V system and then that it is a 120/208 volt system. When you are trying to resolve a voltage within 5%, you don't want to start with an error of over 4%.
Oh, by the way, if these are capacitor start motors, you may have to increase the value of the capacitors if changing from 60Hz to 50Hz. Probably not though.
respectfully

 

[eetag]

Thanks for the responses! Just to provide some clarifications:
1. The existing motor is rated for 277V @ 60 Hz.
2. The existing power system is 208/120 @ 50 Hz.
3. For the record, the motor has been installed and is currently operating.

The question is "How will the rated 277V @ 60 Hz motor perform operating at 208V @ 50 hz?". More importantly, will the motor be subject to premature failure in the 208V @ 50 Hz environment?

For the record, the motor
As I see it, the V/Hz ratio actually decreases from 4.62 (277/60) to 4.16 (208/50) so it would seem that the current would likely decrease and overheating will not be an issue. However, I would expect the HP to decrease by ~ 16% (10/60). Accounting for the reduced frequency, the acceptable voltage range for the motor would be 277 x (5/6) x .90 = 208V.

Any comment would be appreciated!

 

[waross]

The torque stays the same. Rated amps are the same. Speed drops in the ratio of 5/6, so the same torque times less rpm means less horsepower in the ratio of 5/6. If the load is light and the current is equal to or less than rated current, you should have no problems. If the running current is over the rated current, consider an autotransformer to boost the voltage to 230 volts.
respectfully