50HZ motor connected to 60HZ system

[clsarmiento]

A laminator vacuum pump rated at 50HZ, 3-phase, 15KW max is connected to a 60HZ, 480V panel with a 30A/3P feeder breaker. Contractor didn't install a frequency converter on the equipment, and the breaker keeeps tripping. Is the 50HZ something to do with this current surge?

 

[stew]

breaker is way too small. At 15 kw you are talking almost 25 hp. hence an 80 amp breaker should do the trick nicley. thats roughly 31 amps x250 = 77 amps. The fact that the motor is rated at 50 cycle isnt a problem. No converter is needed. Anyhow the small breaker wont allow this load to start.

 

[hurk27]

50hz motors can be a problem on 60hz.

a 50hz motor on 60hz will run faster, and when used for blowers or centrifugal pumps, will also draw more current, if the motor was sized close to the rated HP needed for the given blower, it can be over its rated load if it is spinning at a higher RPM.

 

[hurk27]

breaker is way too small. At 15 kw you are talking almost 25 hp. hence an 80 amp breaker should do the trick nicley. thats roughly 31 amps x250 = 77 amps. The fact that the motor is rated at 50 cycle isnt a problem. No converter is needed. Anyhow the small breaker wont allow this load to start.

not sure where you got your math from, but 15,000 watts at 480 volts is 18 amps 3 phase?

15,000/480/1.732=18.0 amps?

15,000/746= 20 hp.

 

[hurk27]

I would look at the voltage rating of the motor, most 50hz equipment I have run into was 380 volts or 400 volts both which would need a buck/boost type transformer setup, running a 400 volt motor at 480 would be very damaging to the motor.

 

[stew]

oops my head didnt catch up with my math. yup 20 hp 18 amps x 2.5 makes it 45 amps. breaker still too small in my opinion. You are correct when you say that a 50 hz motor rated 380 volts would have a problem if it were run on 480. This would be true if it were run on 480 50 cycle. In my opinion however if you run it on 480 volts 60 cycle all that would happen is that the synchronous speed would increase from 1550 to 1750 or thereabouts. Motors rated at 480 60 hz will normally run just fine on 380/50 as well. That being said the service factor on a driproof motor at 1.15 will drop to 1.0 with the resultant drop in speed .It would be interesting to know in this case if the motor ever does get up to speed what the amperage reading is . If the reading is at or less than nameplate amps then you are good to go.

 

[Besoeker]

I would look at the voltage rating of the motor, most 50hz equipment I have run into was 380 volts or 400 volts both which would need a buck/boost type transformer setup, running a 400 volt motor at 480 would be very damaging to the motor.

The 480V 60Hz is the same V/f ratio as 400V 50Hz so that in itself shouldn't be a problem.
The 20% increase in rotational speed might be.

 

[clsarmiento]

Thank you all for the enlightening responses. What's interesting is that on another site, that same motor was connected or fed by a GE breaker type SELA36AT0030 and I was told that no problem there. I don't know what type breaker they are using on this one, but it's the same 30amp size. It's puzzling!

 

[buldogg]

not sure where you got your math from, but 15,000 watts at 480 volts is 18 amps 3 phase?

15,000/480/1.732=18.0 amps?

15,000/746= 20 hp.

18 amps, it's a 15 HP motor