575 vs 480 v motor rating

[softground]

We are currently preparing a piece of underground equipment for a current project. The electrical and other components were refurbished several years ago by an outside shop which has since disolved. Part of the rebuild was to rewind the motors (3 @ 15 hp) for 480 v (the plate still indicates 575 v). A new attachment has increased torque requirements which has caused excessive current draw. However, the increase appears to be greater than anticipated. We now believe that the motors may still be rated at 575 v. Time is critical... is there a relatively simple means of testing the motors to determine optimum (+/-) voltage. Adding a transformer is simple and fast, disassembling and rewinding will take time we don't have.

 

[mike_kilroy]

... is there a relatively simple means of testing the motors to determine optimum (+/-) voltage.

with a dyno test stand, sure. without, no.

about the only thing you could look at without a vfd drive on it is plug it in, run it UNLOADED at 575v and see use clamp on ammeter to measure the current into it; compare to the 575v nametag on the motor; if more than 1/2 the old 575 nametag current no load, then it was likely NOT rewound to 460v. a motor running no load at its rated voltage will pull typically 1/3 to no more than 1/2 the nameplate current. That is about all you got to go on. If you run it at 460v, this is less than the old 575, so no matter if rewound or not, it will draw less than 1/2 nameplate current so that tells you nothing.

 

[mike_kilroy]

with a dyno test stand, sure. without, no.

about the only thing you could look at without a vfd drive on it is plug it in, run it UNLOADED at 575v and use clamp on ammeter to measure the current into it; compare to the 575v nametag on the motor; if more than 1/2 the old 575 nametag current no load, then it was likely rewound to 460v. a motor running no load at its rated voltage will pull typically 1/3 to no more than 1/2 the nameplate current. That is about all you got to go on. If you run it at 460v, this is less than the old 575, so no matter if rewound or not, it will draw less than 1/2 nameplate current so that tells you nothing.

typo; could not remove 'NOT' typo above.... this cc is corrected.

 

[softground]

Thanks.. ordering a transformer as I type..