motor temp ?

[mickeyrench]

what determines the maximun operating temperture of a 3 phase motor ?
thanks for any input.

 

[bphgravity]

Design, load, age, any perhaps a dozen other variables. Do you have a more specific question?

 

[mickeyrench]

when doing pm on motors the company whats the motors temp. at the time of testing and if it is within spec. I though we use the insulations temp. rating. If not what would I use ? thanks again

 

[cadpoint]

Can I guess there's more to this question ?

Heat to the wire or its efficiency, Maybe is your answer ?

A simple answer is the type of Wire being used againest the type of motor your using. And they have many types.

It could be as simple as its own effienicy but alot of drops down to typical math forumla's of basic motor concepts.
This in not all the available forumal's...

It could be E(induced) = B x l x v

where
B= magnetic flux density
l = length of conductor (remeber that motor can be wired in series-ac)
v = velocity of motion

or Faraday's Law:

E(inducded) = -N d ? / dt

where N is the number of coils
d? / dt expresses the number of lines of force that the conductor cuts across each second. This effect is sometimes called the generator effect.

formula's
"Electromechnical Devices
Theroy, Applications, and Troubleshooting"
Richard A. Honeycutt

The thoughts are on me

 

[mickeyrench]

and i though motors had temperture rating . thanks

 

[mxslick]

and i though motors had temperture rating . thanks

They do..but the wording of your question is open to a lot of interpretation.

Look on the nameplate, you will see a space marked "Rise" or "Temp." , the number found there is MAXIMUM ALLOWABLE TEMPERATURE ADDED TO AMBIENT (ROOM) TEMPERATURE. (I think I said that right.)

Example:

Motor Nameplate gives "Rise" of 40 deg C (most common rating)
Room temperature at the motor is 25 deg C

Maximum safe temperature for the motor would be 65 deg C.

Simple math really.

 

[ohm]

Per the American Electrician's Handbook:
General purpose open-type motors are rated for continuous operation in a 40 deg C ambient temperature under normal service conditions. These conditions include 40 deg C ambient temp., operation at an altitude no greater than 3300 ft., voltage within 10%, freq. within 5%, unobstructed ventilation, proper mounting & coupling to load.

Depending on the insulation class of the motor or generator the max winding temps (deg C) are:

A: 105 to 115
B: 130 to 140
F: 155 to 160
H: 180

 

[mickeyrench]

got it, thanks again for all the help and explanatios.

 

[mxslick]

You're welcome..

ohm: Thank you for that information..it appears to explain the "other" part of my post (since I only gave example of "Rise" ratings.)

Always great to learn more on here..

 

[ohm]

You're welcome..

ohm: Thank you for that information..it appears to explain the "other" part of my post (since I only gave example of "Rise" ratings.)

Always great to learn more on here..

Glad to help, that stuff fades out of memory pretty quick.

 

[winnie]

Ohm's post pretty much nailed a reasonable answer to your question. The motor has a maximum winding temperature rating; if you can measure the temperature of the 'hot spot' in the motor, during operation, and it is below that maximum winding temperature, then the temperature is 'in spec'.

Of course, unless you are lucky enough to have a temperature sensor installed deep in the winding, getting that 'hot spot' temperature will be difficult.

There are various tricks that you can use, for example getting at an accessible part of the winding and measuring its temperature, and then adding a fudge factor for the difference between the exposed winding and the hot spot. I'm sure that there are specs for this, but I don't know what they are. You can measure winding resistance both hot and cold, and use this to calculate the _average_ winding temperature; again with the 'hot-spot' issue.

Finally, as cadpoint was leading up to, there is an entirely different way of looking at motor temperature: trying to answer the question "What _should_ the motor temperature be, given the operating conditions?" The same motor will run at vastly different temperature depending upon mechanical load, cooling, operating voltage, frequency, etc. If the temperature is different from what you expect, this could be diagnostic of a problem somewhere in the entire system. It is possible to calculate what the temperature should be...but I think such temperature information is only useful if you have trend data on a particular motor.

-Jon

 

[mickeyrench]

guys,It seems like the company feels there is a simple answer to the questions on the pm sheet .such as, what is motor temperture? and we are expected to use the ir gun and point and shoot the motor temp. record the temp. and the next question is does the motor pass this test? is the motor temp in spec? i did not know how to answer this. thanks again for the input.

 

[ohm]

guys,It seems like the company feels there is a simple answer to the questions on the pm sheet .such as, what is motor temperture? and we are expected to use the ir gun and point and shoot the motor temp. record the temp. and the next question is does the motor pass this test? is the motor temp in spec? i did not know how to answer this. thanks again for the input.

Preventative and now predictive maintenance are and will continue to be the way of the future in plant maintenance.

IR measurements and scans can be some of the best tools available
http://www.newark.com/pdfs/techarticles/fluke/Infrared thermography.pdf
Vibration analysis and a megger program are also very valuable.

 

[weressl]

guys,It seems like the company feels there is a simple answer to the questions on the pm sheet .such as, what is motor temperture? and we are expected to use the ir gun and point and shoot the motor temp. record the temp. and the next question is does the motor pass this test? is the motor temp in spec? i did not know how to answer this. thanks again for the input.

Motor temperature is relative. There are identical motors from different manufacturers that will run at different temperatures and be within they design limits. (Some of the early attempts at high efficiency motors run so hot that they represented a burning hazard and would still be within the manufacturers design limits.)

There is also a question of the origin of the heat, loaded bearings will add temperature rise. IR analysis is better when it is a comparative analysis, eg. you already have a previous baseline reading at full load. IR analysis also requires some training to understand what you "see".

Lastly, winding temperature - where the actual thermal damage occurs - could only determined acurately by winding resistance measurement between cold(ambient) and right after full load thermal stabilization. Of course RTD's in winding will also give you this value, but they are more common on large, MV motors.

 

[weressl]

Ohm's post pretty much nailed a reasonable answer to your question. The motor has a maximum winding temperature rating; if you can measure the temperature of the 'hot spot' in the motor, during operation, and it is below that maximum winding temperature, then the temperature is 'in spec'.

Not exactly the actual full load design temperature will be significantly lower than the thermal rise rating of the insulation and will vary between manufacturers and even between different sizes from the same manufacturer enough that no generic base can be established.

Of course, unless you are lucky enough to have a temperature sensor installed deep in the winding, getting that 'hot spot' temperature will be difficult.

Your RTD, thermistor or thermocouple may not be where your 'hot spot' is on the motor. An IR reading will give you a better IDEA of where your hot spot may be and combined with the base and comparative hot resistance readings would get you at elast to the phase where your problem is. I am presuming TEFC motors where the winding is inaccesible.

There are various tricks that you can use, for example getting at an accessible part of the winding and measuring its temperature, and then adding a fudge factor for the difference between the exposed winding and the hot spot. I'm sure that there are specs for this, but I don't know what they are. You can measure winding resistance both hot and cold, and use this to calculate the _average_ winding temperature; again with the 'hot-spot' issue.

Finally, as cadpoint was leading up to, there is an entirely different way of looking at motor temperature: trying to answer the question "What _should_ the motor temperature be, given the operating conditions?" The same motor will run at vastly different temperature depending upon mechanical load, cooling, operating voltage, frequency, etc. If the temperature is different from what you expect, this could be diagnostic of a problem somewhere in the entire system. It is possible to calculate what the temperature should be...but I think such temperature information is only useful if you have trend data on a particular motor.

-Jon

 

[charlietuna]

"Point and shoot" recorded temps will vary upon how much work the motor is doing-which is directly proportional to the current running thru the motor's windings. If the load on the motor is relatively constant, then the temps should remain fairly constant provided you compensate it for ambient temps!