motor drawing high amps after rewinding. is it acceptable? 2

[chumet1]

motor rating: power=32kW, FLC=63A, Voltage=380V
before rewind: winding resistance=7.9ohms, line current=55A, phase current=31.8A
after rewind: winding resistance=9.1ohms, line current=84A, phase current=45A

after rewinding, the motor is drawing 33% more than the rated current but monitored it for 3days and it is not overheating. general consensus was, its specs will change after rewinding, so as long as its not overheating then its fine. my question is how do you determine the acceptable current and if this scenario can be left to run

 

[chumet1]

*note: motor is running a submersible pump and on average runs for 4mins and is on stop for 30mins.

 

[ozsalty]

Specs shouldn't really change after a rewind.Maybe the rewinder has dropped a wire gauge if the stator had tight slots or maybe the iron core had been damaged by too much heat applied(if used) during stripping of the stator.33 percent is a significant change for current draw.

 

[electricpete]

before rewind: winding resistance=7.9ohms, line current=55A, phase current=31.8A

I gather this is delta wound motor and you are monitoring the individual legs?
ratio 55/31.8 = 1.73.. roughly matches sqrt(3)... expected

after rewind: winding resistance=9.1ohms, line current=84A, phase current=45A

ratio 84/45 = 1.87... a bit higher than expected. Could be measurement error, or could be telling us something is off.

I guess there are more than three leads in the terminal box and they were connected on-site? Then on-site wiring error may be a consideration.

How about measuring magnitudes of all three phase currents and all three line currents?



=====================================
(2B)+(2B)' ?

 

[LionelHutz]

What is the difference between line and phase current, since they should be the same thing?

33% is a lot. The current should really not change that much. Before and after power measurements would be nice to know, specifically kW and power factor.

 

[edison123]

The load current is determined by the load, not by the motor. Did you change the pump?

Having said that, that is not a correct rewind (assuming the failed one was an original winding). The resistance values cannot differ by so much. The motor is not burning up since you have a very low duty cycle. With such a higher resistance and a higher current, it will fail eventually.

Muthu

http://www.edison.co.in

 

[chumet1]

[/code]
the phase and line currents are an average. they were balanced.

the pump is still the same. the other pump on the same line is still showing before-rewind figures

 

[edison123]

Then the pump load was changed? Different head, perhaps?

The motor only dictates the no-load current, not the load current.

Muthu

http://www.edison.co.in

 

[zlatkodo]

Is it about the winding with special wires immersed in water?
Have you asked a rewinder what is the reason for increased resistance?
As ozsalty said: "

Maybe the rewinder has dropped a wire gauge if the stator had tight slots

but it is more likely that number of turns per phase is reduced, because of using a wire with thicker insulation. That could explain a high Amps.
Here you can find two videos on submersible pump repair: [URL unfurl="true"]http://winding.wix.com/design#!links/caa0[/url]

Winding Repair and Design

 

[electricpete]

Again I'm assuming the thing you called phase current was a leg of a delta winding. Can you confirm? If everything is balanced, that current should be 1/sqrt3 times the line current when summing the fundamental. Triplen harmonics have zero sequence and would tend to flow around the delta g (not the line) and so that would lower that ratio. But you have higher ratio so hmmm… doesn't add up to much that I can figure (I was expecting an unbalance).

I agree, if the problem is high current then the driven equipment is always the first place to look. And 90% of the time that's where the problem is. Ideally you have flow, dp and density to compare to estimate fluid power and changes in it.

These resistance readings… do you know the winding temperature at time of measurement? (so we can figure out if there really is a difference). If there is a significant difference in temperature correcteed , that is something very specific you can ask the rewinder about. Of course you can engage him to help analyse the whole situation also, as suggested.

=====================================
(2B)+(2B)' ?

 

[zlatkodo]

In addition
I thought both things: using a reduced wire size of active conductor with very thick insulation and consequently reduced number of t / c.

 

[zlatkodo]

Hi, Pete,
I think you're right with:

I'm assuming the thing you called phase current was a leg of a delta winding.

This is Delta connection.
If the winding previously was connected in 1Delta connection and then redesigned to 2Delta , this could be the cause also (I suppose this is a 2-pole winding).
Sometimes, rewind shop has no necessary wire size and they are forced to make such a redesign . But consequence is highly increased amount of insulation in the slot and there is no enough room for all the turns.
The same problem occurs if the original winding 1Wye is replaced with 1Delta or 2Delta.
In short, the changes in the resistance (if the measure was properly) shows that the error was made and rewindshop.

Winding Repair and Design

 

[electricpete]

Sounds plausible to me fwiw. We don't have much to go on yet.

I just noticed some things in op that don't shed any light on the cause, but are worth responding to:

after rewinding, the motor is drawing 33% more than the rated current

That's probably close to your overload setting. Do you know your overload settings? What happens if the motor trips unexpectedly

but monitored it for 3days and it is not overheating.

Monitored the frame temperature? How hot? Frame temperature doesn’t necessraily tell you a lot about winding and core temperature.

general consensus was, its specs will change after rewinding

No, it is not expected for current to increase significantly after rewind unless the fluid system changes.

, so as long as its not overheating then its fine. my question is how do you determine the acceptable current and if this scenario can be left to run

No, I don't think many people would consider it acceptable at the current levels you have. In addition to the concern for unexpected overload tripping, there is a concern for reduced motor life due to excess current. And there is also a concern because something seems to have changed dramatically and unexpectedly.... and we don't know what it is.


=====================================
(2B)+(2B)' ?

 

[edison123]

Another possibility is that the rewinder connected a wye designed winding in delta.

Muthu

http://www.edison.co.in

 

[waross]

My first thought is an error in the rewind shop.
My second thought is that there may have been an intentional restriction in the system that was removed and not replaced when the pump and motor were pulled from the well or sump. That would put a greater load on the motor. The greater load and current and resulting heat may explain part of the increased resistance.

Bill
--------------------
"Why not the best?"
Jimmy Carter