HT Motor Winding Temperature

Dear Srinivas ji, is the running current of all phase is equal .kindly mention or check same time. check also the loosing of connection side first.

Inspect the connections with an infra red or thermal scanner to see if a layer of oxidation on part of the connection has caused some ohmic heating.

Some sort of phase imbalance can also cause this. Can you monitor phase current?

Check your voltage balance and current balance between phases. A small voltage imbalance will create a much larger current imbalance, which causes negative sequence currents that then can cause heating in the windings.

But also what is the winding insulation temperature class rating of this motor? Are the values you state absolute or are they the rise OVER ambient? If those values are the absolute temperature, they are not likely in the dangerous area yet if the insulation temperature class is any of the more modern varieties. You may be needlessly shutting down. Even if it is Class B (IEC class 130), the maximum hot spot temperature is 130C.

I don't have much of a professional opinion myself (or better said, not one I would risk mentioning!), but I did like your post personally, you appear to have the right questions and ideas.....

Let us see what happens!!

How are the winding temperatures being measured and is the motor windings rated to be operated at that tempurature to begin with as in being wound with honest rated Class B, F or H insulation?

NEMA Winding Class temperature limitations

Motor winding temperature rating Vs ambient temperature and motor frame type.

If your motor winding insulation was only rated for 110 - 130 C peak (Class A or cheap class B rating) it's 20,000-hour service life is already up and it's starting to break down causing small shorts between windings that are driving the temperature up even higher.

Good question about temperature measuring. Can the 3 stator phases be located physically so individual temperatures can be measured? Seems unlikely to me but I'm ready to be corrected. OP says it's been done but as you ask, how?

Good comments above ,

I think seven degrees of difference between phases is not much, and it may be that the position of PTC resistors for it is in a zone that has a poorer ventilation .

Efforts should be made to the motor work to as lower operating temperature because the rule is that every 10 degrees higher temperature life expectancy of the motor insulation decreases by half.

Good hunting

I would run a megger test on the windings to determine the direction to go first....then either redip the windings if out if spec, or concentrate on incoming electrical feed for proper phase alignment and voltage, or loose or corroded electrical connections, any motor starter or contactor that could be failing using an ir gun or imager to check operating temperatures at any contact points leading to the motor, including breakers supplying power to the motor....

Yea but how many questions do we get here that are something like,

"Dear CR4 members, we have a 2 MVA generator (or motor) running a 3 MVA load and it keeps tripping the over temp cutouts.

What should we adjust to correct the problem? We have no money so we can't get a larger generator/motor or reduce the load either."

Signed, The guy who is tired of standing there spraying it with a garden hose to keep it running. (We can't afford the water either.)

PS. (We can't afford the water either and the neighbor wants his garden hose back tomorrow.)

LOL!

How true - sadly!

Sadly, in India and similar areas money is usually diverted to friends and cronies, and overmanning (a relic of socialist India), as if a non productive job had any value at all.

So in universities there is no cash for equipment, in industry there is no cash for maintenance. It runs and breaks and the government is forced to, at long last, do something.

So the poor guys have no money to get the original installer to fix it, so here they are asking questions here.

Um first thing ask them to count the number of Jelly Beans in the Jar.

This history website gives rules and the time lapse trailer to the size of the problem VS time (its all I can find now but a few jpg's) Jellybean_outline

Ask them to download the 10 Videos, I did.

Task: Separate all the frames as eg 12345678.jpg of all the videos with unique sequential incrementing or decrementing numbers if there really cheeky say do it with random numbers (LOL) (DOS 8.3 format). Then write a program that converts certain images of the blue conveyor belt with jellybeans on it so you can copy the n th frame to a separate folder. Then once you have the conveyor ribs synced in the output directory you can make a guesstimate (deposit money) saves time.

Free Hint "FOR i = 101795 TO 110006 STEP 43.1912" The Video Frame Rate to conveyor calculator..

They may then understand the slip ratio of an induction motor geared down to the load and number of jellybeans on a conveyor belt.

Signed: Smokingwheels

If you are really stuck for an answer there is SUSI at SUSI App Prototype part of the Loklak.org a Free program on Github Source Code Will run on Windows see Wiki

If you understand the code and the rules you may build you own custom one.

It is from the creator of the Yacy Search Engine all about freedom.

In my opinion, the European standard does not consider a service factor more than 1 but the duty=the statement of the load(s) to which the machine is subjected, including, if applicable, starting, electric braking, no-load and rest and de-energized periods, and including their durations and sequence in time [IEC 60034-1]. The maximum permissible temperature is more-or-less the same as per NEMA MG.

Usually the rated insulation temperature class is F [155oC allowable] but the calculated and tested temperature is for class B [130oC].

The measured temperature rise is limited according the measuring system.

If the ambient temperature is 40oC , if a resistance is employed then 80 but for an E.T.D it could be 90.

[ETD = Embedded temperature detector].

Since the conductor temperature rise is direct proportional with the square of current then a factor of (2400/2200)^2=1.19 has to be employed for the actual temperature rise.[80/1.19=67oC-total 107oC].

[for 113oC -rise of 113-40=73 the power has to be sqrt(73/80)*2400=2293 kW.]

These are theoretical speculations, only. Actually, in my opinion, if the currents are equilibrate the unbalance of conductor temperature is not dangerous.

An error of 10 oC of the measuring system it is also possible.

Briefly, check the currents and check the temperature and power measuring systems. Also check the duty[rated and actual].

If you are still worried you may stop the motor and test it as the standard requires.