Motor drawing higher current

[Clayton79]

I have a motor, lincoln 30 hp, 1.25sf wired for 460v nominal. fla 39 its hooked to an hydraulic pump on a test bench. when it is in use system pressure at 7200psi, it draws 39-40 amps. the exact same motor and pump on another bench draws 10 amps less. The motor has just been rewound and new bearings the pump also has a fresh rebuild on it, no change in amperage. on thermal image camera it showed a hotter phase on one leg, but that was before rebuild havent had a chance to retake more images probably this week.

we are out of ideas, so im throwing it out there to see what you guys think.

clayton
:?

 

[hurk27]

Have you taken voltage readings while the motor was running under load?, and what is the current on the other two phases?, my arm chair guess is you might have a voltage imbalance, but without the voltage readings its a wild guess. if you do find a voltage imbalance then check with your IR all connections and contacts back to supply panel.

 

[Clayton79]

i will retake voltage readings, (i cant remember what they were) amp readings were if looking at contactor, t1 40, t2 39, t3 38. ill post back within the hour. all test benches fed from a 480v buss bar with individual 60amp buss plugs. no other problems on any other of the 7 benches (only 1 of which is a twin of the problem bench).

 

[hurk27]

i will retake voltage readings, (i cant remember what they were) amp readings were if looking at contactor, t1 40, t2 39, t3 38. ill post back within the hour. all test benches fed from a 480v buss bar with individual 60amp buss plugs. no other problems on any other of the 7 benches (only 1 of which is a twin of the problem bench).

With those amp reading being within one amp, then I would say maybe a pump problem, try swapping the pump with the motor that is reading lower and see if the problem follows it? unless the voltage is lower then its supposed to be (460) which I suspect your on a 480 system, it doesn't seem to be a voltage problem?

 

[GeorgeB]

30 hp 460v nominal. fla 39 its hooked to an hydraulic pump on a test bench. when it is in use system pressure at 7200psi, it draws 39-40 amps.

OK, that suggests 6.5 to 7.5 gpm. What's the chance the pumps are different displacements?

With rated FLA on this one vs. 75% FLA on the other, the load is likely 50% to 60% on the other ... exactly what I'd expect if the pump were maybe half to 2/3 displacement ...

What is no-load current; I'd expect something in the 16-21A depending on the motor optimizations.

Hydraulic pump loads, as you likely know, are very good "brakes" to create and measure load. Do you have a system relief valve that you can use to vary the load pressure and compare between the 2 units?

I wonder if a gauge is off on one vs the other; I always TRY to use the same gauge when I compare systems like this ... diagnostic gauge ports are wonderful to have.

 

[Clayton79]

voltage readings show 470v all three phases whithin one volt. 270 to ground all withing one volt

amp readings were at this time all 38.8 with fluctuation of an amp

clate

 

[hurk27]

Also when taking comparison measurements, always use the same test equipment, you never know when a low battery or something will throw off one meter from another.

 

[Clayton79]

Yes george B, we used the relief/pressure valve to dial in both loads to the same pressure these tests are of a high press. cycling nature with a solenoid valved opening and closing to basically pound the device under test. which is why we see a little fluctuation in current and voltage as we read, however to answer your concern we used the same calibrated pressure transducer to get our pressure readings vs. using the in system ones installed on the benches themselves.

i like the swap pumps idea, hmm, the MM might not though. (sooo glad im a sparkky sometimes)

 

[hurk27]

Yes george B, we used the relief/pressure valve to dial in both loads to the same pressure these tests are of a high press. cycling nature with a solenoid valved opening and closing to basically pound the device under test. which is why we see a little fluctuation in current and voltage as we read, however to answer your concern we used the same calibrated pressure transducer to get our pressure readings vs. using the in system ones installed on the benches themselves.

i like the swap pumps idea, hmm, the MM might not though. (sooo glad im a sparkky sometimes)

Now that you said how your dialing in the pressure measurement, if you do swap out the pump, I would just put the motor on the other bench with the other pump and controls and regulator, this will rule out the pump and or the pressure transducer/regulator problem, then if the readings stay high you know its the motor, if they go back to normal then you have to swap the regulator and pressure transducer to see if its the pump or the loading caused by a bad pressure transducer? I still like having a mechanical oil filled gage in line as a back up, playing around with that high of pressure can get ugly if it were to go wrong.

 

[Besoeker]

I have a motor, lincoln 30 hp, 1.25sf wired for 460v nominal. fla 39 its hooked to an hydraulic pump on a test bench. when it is in use system pressure at 7200psi, it draws 39-40 amps. the exact same motor and pump on another bench draws 10 amps less.

Stating the obvious, I know, but they can't be exactly the same.
You say the motor has been rewound. I have been told that each time a motor is rewound, it loses a little in efficiency. Maybe the new bearings are tight.
Can you run both motors uncoupled and measure the no-load current of each? That would maybe shed some light on where the differences are.