Motor overheating for no clear reason
- Thread starter tengineer
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What have you checked/measured so far?
Current, voltage at motor terminals, motor temperature, winding resistance.
I can measure if you need anything else.
OK. I assume currents, voltages, and winding resistances were balanced and within spec?
Is the 85C winding temperature? That doesn't seem terribly excessive to me. But then I'm used to class F insulation with a class C rise.
Preheater suggests a cement works. If so, is the motor ventillation getting clogged up?
Is it a fixed speed application?
Current 20.8, 21.2, 21.4A
Voltage 404v, 408v, 412v
Insulation class- F
I am using a temperature gun to measure the temperature. It even reached 100deg Celsius when run for 4 hrs.
Star delta starter is used.
An outlet damper to control the output air.
A shaft mounted impeller.
The requirement is to run it continuously for 4-5hrs which was working fine till this week when second motor burnt.
but due to this problem this week we are currently running it for 1-2hrs then letting it cool for an hour or so.
mgookin
Senior Member
- Location
- Fort Myers, FL
- Occupation
- Retired inspector, plans examiner & building official
What's the ambient temperature of the environment it's in?
What changed just prior to the first motor burning up?
The electrical measurements all seem to be comfortably with limits. If you are using a temperature gun then I expect that you are measuring case temperature rather than winding temperature. So 100C is very hot for that.
Are you happy that the ventilation is ok? Has any new kit been installed on the same supply?
dmxtothemax
Senior Member
- Location
- Brisbane, Queensland, Australia
have you checked with the manufacturer of the equipment,
that you have the correct horse power motor
for the load which the impellor represents to the motor ?
Are you sure it is exactly the same type of motor as the original ?
Maybe the older motor just had a better ventilation fan
And the new ones don't.
it's either overloaded
or it's not getting enough ventilation.
that you have the correct horse power motor
for the load which the impellor represents to the motor ?
Are you sure it is exactly the same type of motor as the original ?
Maybe the older motor just had a better ventilation fan
And the new ones don't.
it's either overloaded
or it's not getting enough ventilation.
- Occupation
- Licensed Electrician
Why?
big john
Senior Member
- Location
- Portland, ME
Where are your overloads set and have they ever tripped?
Assuming this is a centrifugal blower is there anything other than the motor speed that regulates airflow? Any dampers or engineered filter walls?
Assuming this is a centrifugal blower is there anything other than the motor speed that regulates airflow? Any dampers or engineered filter walls?
Saturn_Europa
Senior Member
- Location
- Fishing Industry
- Occupation
- Electrician Limited License NC, QMED Electrician
What is the enclosure type of the old motor? How about the new motor?
TEFC? ODP?
When you put your hand on the motor's cooling fins can you feel air flow?
Has the motor always run hot?
Any chance there is an valve or damper that has vibrated closed or out of position.
TEFC? ODP?
When you put your hand on the motor's cooling fins can you feel air flow?
Has the motor always run hot?
Any chance there is an valve or damper that has vibrated closed or out of position.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
That's fairly common in a lot of areas over there (India). Their grid is nowhere near as stiff as ours, they typically are required to use Reduced Voltage starting on anything above 11kW (which is a standard IEC motor size, roughly 7-1/2HP). Star-Delta is the lowest cost RV starter.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
You have less than 1% voltage imbalance, so that's not it. That leaves only physical obstruction of cooling air flow, or the wrong motor type selection, possibly exacerbated by high ambient temperature. Could be bearings, but probably not that fast. When you checked the current and said it was only 20A, were the dampers fully open? If not, do they run more open at other times to where the motor may be getting overloaded?
But are you also absolutely sure it is burning up or is there some other form of winding damage? 100C from a thermal scanner is not that accurate of way to determine winding temperature. Class F is good for a 105C rise over 40C ambient with a 10C hot spot. That is the winding temperature however, and the case temperature for sure is going to be lower. But it IS lower, it's 55C lower than the max allowable winding temperature. There is no accurate way of estimating what the winding temperature is based on case temperature, but I'm fairly sure that the windings are not going to be 55C hotter than the case... unless, as lots of people have said, you have a serious cooling issue.
Have the failed motors been analyzed by a COMPETENT motor shop for what type of damage occurred?
At 100C, I'd disinclined to try thaat.....
How long was it in service before the first failure? Is it possible that it's time had come, and subsequent rewinds were improperly performed?
I second Jraef's comment regarding having a failure analysis performed by a competent shop (preferably not the one doing the repairs).
Cheers,
Dave
Sent from my iPad using Tapatalk
I second Jraef's comment regarding having a failure analysis performed by a competent shop (preferably not the one doing the repairs).
Cheers,
Dave
Sent from my iPad using Tapatalk
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Is wye-delta starter properly operating, all leads properly connected?
junkhound
Senior Member
- Location
- Renton, WA
- Occupation
- EE, power electronics specialty
Others have already identified the problem, but the OP did so also - one of those ironic statements ?
Motor overheating for no clear reason
Key words: overheating for no clear: aka - clean up the air passages or fix the fan?
Reverse: run a 5 HP motor at 8 or 9 HP with a bigger fan ?
Motor overheating for no clear reason
Key words: overheating for no clear: aka - clean up the air passages or fix the fan?
Reverse: run a 5 HP motor at 8 or 9 HP with a bigger fan ?
Attachments
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
whats in that black box upper left on floor?
JFletcher
Senior Member
- Location
- Williamsburg, VA
Looks like a Hennessey liquor box with a carbuerator in it.
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