3 phase, 380V, 50Hz motors need to operate at 3 phase, 480V, 50Hz

J

jking1991

Member
Location
Bristol, TN
Occupation
Electrical Engineer
I have quantity 4, 3 phase induction motors with the following nameplate specs:
50Hz
380V
4.80A
3 HP
2.2kW
S.F.: 1.0
Nom. Efficiency: 87.5
Min. Efficiency: 85.5

The issue is that the power supply at the site is 3 phase 480V, 50Hz.

Would a 3 phase transformer 480V/50Hz primary and 380V/50Hz secondary be our best solution?

Another potential issue is that the 3 phase 480V, 50Hz power supply is only capable of 15A, so approx. 12.5kVA. The 4 motors together will need 12.7kVA which allows for no safety margin. Is the only solution a larger power supply?

Thank you!
 
JoeStillman

JoeStillman

Senior Member
Location
West Chester, PA
petersonra said:
Or maybe get some vfds and run off 480 v 60 hz.

This is a very odd duck if it is really 480 v 50 hz.
Click to expand...
OP says 380V 50Hz. The mismatch for me was a HP rating instead of a kW rating. Is 2.2 kW a standard size? If motors are replaced, it might be a problem running at higher nominal RPM. Typically, 1500 rpm vs 1800.
 
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P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
JoeStillman said:
OP says 380V 50Hz. The mismatch for me was a HP rating instead of a kW rating. Is 2.2 kW a standard size? If motors are replaced, it might be a problem running at higher nominal RPM. Typically, 1500 rpm vs 1800.
Click to expand...
You can run the drives at 480 v 60 hz input and the output at 380 v 50 hz.

But something seems like it is off here
 
J

jking1991

Member
Location
Bristol, TN
Occupation
Electrical Engineer
JoeStillman said:
Might be cheaper to buy American motors than to buy all that conversion stuff.
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We did buy American motors just had our supplier make a poor assumption on the actual voltage. They didn't believe the 480V and designed for 380V and didn't ask us even though our PO clearly stated 480V. Frustrating
 
synchro

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
petersonra said:
Or maybe get some vfds and run off 480 v 60 hz.

This is a very odd duck if it is really 480 v 50 hz.
Click to expand...

Motor starting currents could be a significant issue with the very limited power supply kVA. VFDs could be also be used to reduce the starting currents as well as accommodating the desired voltage for the motors, as you mentioned.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Your two viable options are to just get a transformer to step down the 480V 50Hz to 380V 50Hz. Simple, but I doubt anyone makes that transformer off the shelf, so you will likely need to have it made. Makes your power supply issue worse though because there will be losses in that transformer. Option 2 is to buy VFDs for the motors and just program them to put out 380V 50Hz. It will actually help a little bit with the power source issue because the VFDs can mitigate the starting current problems you will have.

All that said, no country on record uses 480V 50Hz, so it’s far more likely that something is wrong with this assessment. I believe someone is TELLING you this, but it’s likely they don’t know what they are talking about. For this to be true, someone would have had to go out of their way to fabricate a custom generator that produces something that is then incompatible with ANY standard anywhere in the world. Makes no sense.
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Jraef said:
Your two viable options are to just get a transformer to step down the 480V 50Hz to 380V 50Hz. Simple, but I doubt anyone makes that transformer off the shelf, so you will likely need to have it made.
Click to expand...
Jraef do you think the autotransfromer in post# 10 would not work?
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I'd be comfortable using this transformer for 480V:380V 50Hz operation.

The transformer is _rated_ for 600V:480V at 60Hz, and has an 'alternate' rating for 480V:380V.

The spec sheet in post 15 mentions 50Hz operation. The 'technical drawing' doesn't mention 50Hz, but operating at at the same V/Hz ratio as 600V 60Hz will be pretty much fine.


I'm still very surprised that the OP has a 480V 50Hz source, unless it is some sort of inverter based device or a modified generator. Thus I'd want very detailed specifications for the source before proceeding in any case.

One of the other questions that the OP had was about using 12.7kVA of motors on a 12.5kVA source. To answer this we'd really need to know how strict that 12.5kVA limit is...thus more details about the power supply.

-Jon
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
15 amps at 480 volts is about 12.5 kva.

Might be a 15 amp cb involved. In that case who knows how much current is actually available.

I agree something is screwy with this deal and that needs to be dealt with first before buying a bunch of stuff.
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
That is kinda weird voltage, I’ve been installing a lot of Italian equipment lately, they’re 400 volts, and the manufacturer has been supplying a multi tap transformer that works with 480, though it’s labeled 460. Their setup crew says it’s within their specs.
 
T

topgone

Senior Member
hillbilly1 said:
That is kinda weird voltage, I’ve been installing a lot of Italian equipment lately, they’re 400 volts, and the manufacturer has been supplying a multi tap transformer that works with 480, though it’s labeled 460. Their setup crew says it’s within their specs.
Click to expand...
Right. I have done the same. In my case, the motor was an old 415V motor that I had installed on a 460V utilization voltage. It worked, just a 10% higher supply voltage to the motor and the motor was not even overheating.
 
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