Motor Temperature

[ptonsparky]

A local Village called to have me look at one of their submersible wells protected by a Franklin SubMonitor. I was asked to check the system because he had couple faults on the SubMonitor that indicated high temperatures. I did not get to see the message nor did I take the time to scroll through the history. There was no visual indication of over heated connections. To make it short, after running the pump for 30 minutes or so I used a thermal camera to scan the starter. Sure enough the left & center phase were hot compared to the right. FOP test confirmed it. Pretty impressed but I do not know how it determined the problem. This unit uses a CT type overload with no physical connection to the starter, other than the control contact. Phase currents were not overly imbalanced & did not change after corrections were made.

 

[Jraef]

...Phase currents were not overly imbalanced ...

Franklin requires MUCH more current balance than even the NEMA motor design specs call for. So what you might consider "not overly" imbalanced based on normal experience may still be unacceptable for Franklin.

 

[GoldDigger]

Franklin requires MUCH more current balance than even the NEMA motor design specs call for. So what you might consider "not overly" imbalanced based on normal experience may still be unacceptable for Franklin.

Does this require strict control of both the supplied phase voltages and the per-phase supply impedances (i.e. VD), or can there be some other compensating mechanism?

 

[ptonsparky]

Franklin requires MUCH more current balance than even the NEMA motor design specs call for. So what you might consider "not overly" imbalanced based on normal experience may still be unacceptable for Franklin.

Less then 2 amps variation, IIRC, is what I measured.

 

[GoldDigger]

Less then 2 amps variation, IIRC, is what I measured.

As compared to what average current? The percentage imbalance is what is important, not just the magnitude, and we have not yet seen what the average phase current is.

 

[ptonsparky]

As compared to what average current? The percentage imbalance is what is important, not just the magnitude, and we have not yet seen what the average phase current is.

Your playing hardball...but that is ok. My formula spreadsheet shows that I should be concerned with current imbalance over 2%. The avg current is the 47.57.
The pump is 40 HP 460v with FLA of 54.9 & max of 61.6 amps. When we did the testing the water tank was almost full so our current would be at its lowest or close to it. No, I did not check voltage.:slaphead: or did not write it down if I did. My FOP tests showed 646 mv, 374mv, and 112mv before, with 54.5, 29.8, and 37 after. Left to right.

Ignore the 0.78. Offhand, I don't remember what it stands for in the formula and it may very well be one of those extra calculations I manage to include just be cause I had spare time.

Amp

48.60

46.70

47.40

47.57

0.78

2.17%

.78 is the standard deviation