3 phase motor

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Southern

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Alapaha Georgia United States
I have a three phase 460 volt 125 hp motor pulling 80 amps idling incoming voltage is 495 volts it is 152 Fla on motor nameplate they are three machines side by side if I move the same motor to other machine it draws 46 amps idling I checked all joints and check starter and had power company come out and check transformer joints have found no problems so why does it draw 34 more amps on first machine all feed off same transformer voltage is 1/2 % amps are 3 % ?
 
I'd check it, UNLOADED, not connected, with the fastening bolts loose. The only thing that comes to mind is a distorted frame loading the shaft bearings.
 
At the machine with the higher amperage readings with the motor disconnected, check your voltage on the feed wires phase to phase and phase to ground to see if you've lost a phase somewhere.
 
paul_arc said:
At the machine with the higher amperage readings with the motor disconnected, check your voltage on the feed wires phase to phase and phase to ground to see if you've lost a phase somewhere.
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If the OP checked the current, I assume he would have tested all three phases for balance. If he hasn't already, he should check it.
 
Southern said:
I have a three phase 460 volt 125 hp motor pulling 80 amps idling incoming voltage is 495 volts it is 152 Fla on motor nameplate they are three machines side by side if I move the same motor to other machine it draws 46 amps idling I checked all joints and check starter and had power company come out and check transformer joints have found no problems so why does it draw 34 more amps on first machine all feed off same transformer voltage is 1/2 % amps are 3 % ?
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I cannot imagine a 125 Hp motor drawing only 46 amps idling without some sort of pf correction. Does the 46 amp machine have a set of working
caps on it, and the 80 amp machine have no caps or blown fuses protecting the caps?
 
What exactly do you mean by "idling"? What type of machine? I would check with the motors truly unloaded. Power factor is low at no/low load so current readings are probably not the best measurement to use to evaluate what Is going on.
 
Southern said:
I have a three phase 460 volt 125 hp motor pulling 80 amps idling incoming voltage is 495 volts it is 152 Fla on motor nameplate they are three machines side by side if I move the same motor to other machine it draws 46 amps idling I checked all joints and check starter and had power company come out and check transformer joints have found no problems so why does it draw 34 more amps on first machine all feed off same transformer voltage is 1/2 % amps are 3 % ? Average of all three wires a b c phase
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Southern said:
Southern said:
I have a three phase 460 volt 125 hp motor pulling 80 amps idling incoming voltage is 495 volts it is 152 Fla on motor nameplate they are three machines side by side if I move the same motor to other machine it draws 46 amps idling I checked all joints and check starter and had power company come out and check transformer joints have found no problems so why does it draw 34 more amps on first machine all feed off same transformer voltage is 1/2 % amps are 3 % ? Average of all three wires a b c phase
Click to expand...
I have read this again. Same motor, different machine, much lower current. Difficult to see it being anything other than a mechanical issue.
Are the machines mechanically identical? Clutches, fluid couplings gearboxes, mechanical brakes?

What do the machines do? Can you explain precisely what you mean by idling?
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Southern said:
Unloaded not attached to anything
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If all three motors are giving you these amp readings when they are totally uncoupled to the machines, I’m liking the tweaked motor frame concept. Whatever your motor is bolted to is not as flat on that machine as they are on the others so when you crank down on the mounting bolted, the motor frame twists ever so slightly and binds the bearings. That’s why they make shims. I’ve seen it where the motor is serviced and someone doesn’t pay attention to where the shins were or don’t think they are important so they leave them out and the motor bearings fail shortly thereafter.
 
Jraef said:
If all three motors are giving you these amp readings when they are totally uncoupled to the machines, I’m liking the tweaked motor frame concept. Whatever your motor is bolted to is not as flat on that machine as they are on the others so when you crank down on the mounting bolted, the motor frame twists ever so slightly and binds the bearings. That’s why they make shims. I’ve seen it where the motor is serviced and someone doesn’t pay attention to where the shins were or don’t think they are important so they leave them out and the motor bearings fail shortly thereafter.
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I kind of agree. Except I’ve seen older GE aluminum frame motors crack at the feet when torqued down out of plane. Maybe these can give enough to distort without damage.
 
Besoeker said:
But they are not. In one situation it is 80A, in another it is 46A. With the same motor.
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That’s what I meant by “these readings”. I just wanted to clarify that the motors were all totally uncoupled when the current was measured. The only explanation for the issue following the machine, not the motor itself, is something in the machine or the circuit. He has already eliminated the circuit issues (ostensibly) so that leaves only the machine and if everything in the machine was UNCOUPLED that leaves only the motor mounting.
 
Jraef said:
That’s what I meant by “these readings”. I just wanted to clarify that the motors were all totally uncoupled when the current was measured. The only explanation for the issue following the machine, not the motor itself, is something in the machine or the circuit. He has already eliminated the circuit issues (ostensibly) so that leaves only the machine and if everything in the machine was UNCOUPLED that leaves only the motor mounting.
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Maybe we need to await clarification from the OP.
 
Besoeker said:
Southern said:
I have read this again. Same motor, different machine, much lower current. Difficult to see it being anything other than a mechanical issue.
Are the machines mechanically identical? Clutches, fluid couplings gearboxes, mechanical brakes?

What do the machines do? Can you explain precisely what you mean by idling?
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No load not coupled to anything motor only
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