Winding temperature running cooler than sisters
Winding temperature running cooler than sisters
(OP)
Just a brainstorming question.
If we have a motor that has cooler winding temperature than sister motors for no obvious reason, is there any possible reason to think it would represent some condition that might threaten the motor?
This is 13.2kv vertical motor rewound in 1998 with B-stage / hard coils. Core restack was not done at the time and has never been done to my knowledge. The sister motors are 2 or 3 B-stage (by same rewind vendor during same time frame... should have similar characteristics) and 4 or 5 VPI. 3 of them have been restacked failyr recently.
I have a computer-recorded temperature trend trend since 2002. It has run 20-30F cooler than its 7 sister motors during that time. (The sister motors have a spread of about 10F between them).
We check all 6 RTD's and connect up the hottest one to the plant computer (that's the one we have record of). It is 3 wire RTD setup for 10-ohm copper RTD... I guess high resistance in the compensating lead could cause high resistance.
I don't have handy any records to show whether motor was possibly carrying less load than the others... although when I get a chance I'll go look at our vibration records to check the slip.
I suspect (as I'm sure most readers here would) that the most likely cause is indication error of some kind or another. NEVERTHELESS, the motor just tripped on ground fault. We will be checking insulation resistance to try to establish whether it is a valid trip etc. If it turns out to be a motor, we will certainly tear the motor down for a thorough cause analysis... but I will certainly also be faced with intense questioning before we get all our answers, and I want to be prepared to answer an inevitable question: is there any conceivable REAL problem (not indication error or low-load due to pump factors) that could be tied to a (possible) winding failure that we should have foreseen.
If we have a motor that has cooler winding temperature than sister motors for no obvious reason, is there any possible reason to think it would represent some condition that might threaten the motor?
This is 13.2kv vertical motor rewound in 1998 with B-stage / hard coils. Core restack was not done at the time and has never been done to my knowledge. The sister motors are 2 or 3 B-stage (by same rewind vendor during same time frame... should have similar characteristics) and 4 or 5 VPI. 3 of them have been restacked failyr recently.
I have a computer-recorded temperature trend trend since 2002. It has run 20-30F cooler than its 7 sister motors during that time. (The sister motors have a spread of about 10F between them).
We check all 6 RTD's and connect up the hottest one to the plant computer (that's the one we have record of). It is 3 wire RTD setup for 10-ohm copper RTD... I guess high resistance in the compensating lead could cause high resistance.
I don't have handy any records to show whether motor was possibly carrying less load than the others... although when I get a chance I'll go look at our vibration records to check the slip.
I suspect (as I'm sure most readers here would) that the most likely cause is indication error of some kind or another. NEVERTHELESS, the motor just tripped on ground fault. We will be checking insulation resistance to try to establish whether it is a valid trip etc. If it turns out to be a motor, we will certainly tear the motor down for a thorough cause analysis... but I will certainly also be faced with intense questioning before we get all our answers, and I want to be prepared to answer an inevitable question: is there any conceivable REAL problem (not indication error or low-load due to pump factors) that could be tied to a (possible) winding failure that we should have foreseen.
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RE: Winding temperature running cooler than sisters
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RE: Winding temperature running cooler than sisters
"Can the low temperature indication suggest any conceivable REAL problem (not indication error or low-load due to pump factors) that could be tied to a (possible) winding failure that we should have foreseen."
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RE: Winding temperature running cooler than sisters
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Eng-tips forums: The best place on the web for engineering discussions.
RE: Winding temperature running cooler than sisters
Now, with my feeble attempt at humor past, what are these motors driving and if as I suspect they might be the circulators, I'd like to see the pump conditions (pressure and flow if available) before hazarding a guess at what ails this sole sister.
All pumps are not created equal even when they appear to be.
rmw
RE: Winding temperature running cooler than sisters
Pete:
10 ohm copper RTDs are not very accurate compared with Pt100 RTDs. On the way between motor terminal box and recorder location lots of things can happen (poor contacts of terminals and junctions, unequal cross section of wires, etc.). For proper and accurate determination of temperatures one has to measure the three RTD resistances (3-wire RTDs) nearest to the windings, i.e. at the motor terminal box for comparison.
The winding temperatures are very low. A summer-time figure of 190 degrees F is equivalent to a mere 88 degrees C. What type of cooling is present? Does the low temperature motor have a more efficient cooling system (more cooling water flow)? Check the corresponding cooling air inlet temperatures of all units for comparison and for determination of winding temperature rise figures. In our case temperature rise is more important to know.
Regards
Wolf
www.hydropower-consult.com