Follow up to The Importance of Correlating Predictive
Technologies in Electric Motor Diagnostics [top]

by Gary Orlove

I received a letter from O.J. Utter, a thermographer from Northwest Electric, Inc. in Lincoln NE, with comments about Juan Hidalgo's article last month. I contacted Juan and he sent me a response. I am sure many of you had the same questions so I have reprinted it below:

1. Readings on the external housing of the motor is not a true indication of the actual motor winding temperature. In many of the motors that I have run across in the field (not comparing with thermal couples) there is a minimum temperature rise between the outer housing and the windings of 40ºF (again this is minimum).

I totally agree with you, readings on the external part of an electrical motor with infrared are not true indication of the real temperature of the windings. But based on my experience I should say between the casing and the windings there would be a minimum difference of 15-20 C and this will depend on the ambient temperature. Many articles probe this, you can refer to an excellent article published by Jack Nicholas on P/PM issue of October 1997.

Perhaps I did not say it explicitly in the article, but if you add 99 C + 20 of temperature difference between the casing and the windings you end up with a temperature of 119 C well below of 155 C for an Insulation Class F Motor.

2. The next point that was not discussed is the environmental conditions that this motor was operating in. What was the atmospheric and Tambient temperatures both times the motor was checked. 3. Plus a host of other information like operating load, cooling fan restriction, etc.

Continuing with the explanation in the previous paragraph, the heat transfer in a motor will not only depend on the actual ambient temperature but on the frame size, mass and if the frame is ribbed or not, also will depend if the motor is totally enclosed or not and other cooling factor not explained in my brief article.

For the particular case the motor was running under the same condition, load, ambient temperature, etc.

I think the key issue here was the trend on temperature indicating something was wrong with the motor. Using a good judgment and always being on the safe side, I did recommend doing further testing. And it turned out to be accurate.

The best part that was noted in the article was that ALL infrared mechanical is the 1st Line of Defense for fault identification but needs to be followed up with another condition monitoring technology. Many of the customers that we perform Mechanical IR Inspections on also have us perform Vibration Analysis and Emax Testing as well. In some instances Ultrasonic has even been used to determine a lubrication issue.

Mr. Utter mentioned another key issue on this brief article: for mechanical problems IR can not be alone since it needs another CM technology to back it up and to detail the failure mechanism.

Thanks very much for your comments on my article and contributing to this fascinating field...If I can be of further assistance do not hesitate to contact me. - JC

Home Fire Safety Using IR  [top]

By Joe DeMonte
ASNT/PdM-TIR Level III
ITC Senior Thermography Course Instructor

We have seen, in the past few years, articles on the benefits of infrared in our own homes.  Heat loss is on everyone’s mind with the rising cost of fuel and electricity.  IR can trace these losses and increase the efficiency of our homes reducing money out of our pockets.

This article is one of those home discussions, but from another vantage point: FIRE SAFETY.

I had just gotten back from a long trip teaching a course, and was ready to get to bed on a Thursday night.  My wife asked me a peculiar question at a very tired point in my day:

“Honey, your Mom and I smell a burning smell in her basement.  Can you check it out with the camera tomorrow morning?”

 “Sure thing sweetheart (adding a smile and a wink)”, I replied.

When I got up for work the next morning, I called my Mom and asked her to turn on as many lights and electric appliances that she could.  You see, the smell was not only in the basement, but strongest above the TV according to my wife, Mom, and Dad.  That is where the house’s main breaker is kept inside a wooden cabinet and surrounded by… you guessed it… more decorative wood on the walls (see fig. 1). 

I waited about an hour to let everything become steady state.  After load is added to an electric circuit, the heat generated by the product of the I² (current squared) times the R (resistance) takes some time to increase the temperature of the components to its final value depending on the surrounding environment.

When I got to Mom’s house that morning, I powered up the IR camera, and opened up the wooden door to the breaker cabinet.  I almost didn’t expect to find anything, but since I took the time to write this article, you probably guessed that I did find something.  Check out fig. 2.

At this point in time, I do not care what temperature I see with the radiometric imager. I am looking at the breaker casing and ANY unnecessary heat is a problem when talking about a residence (especially my Mom’s residence). My next step is to remove the outside metal panel from the breaker box, and trace out where the heat is being generated. Fig. 3 shows the image in grayscale with the cover removed.

Instead of moving spots around, or adding line profiles, isotherms, or area functions, I chose another method of analysis. I changed the color palette to IR Rainbow. This choice of color keeps my 256 bands of color, but separates the scale in a set of 8 color bands to distinguish the different radiances the camera perceives from the bottom to the top of the scale/span. I can therefore trace the conductive patterns on the breaker casing and cable to see if it is going from the breaker to the outside, or vice versa. Fig. 4 shows that resultant color change.

The heat was being generated from the breaker and conducting up the incoming cable. My next step was to call an electrician and inform him/her of our repair needs. Just to show the electrician the path of heat, we also took an image of the outside meter area above the incoming line (Fig. 5).

The electrician arrived an hour later and de-energized the circuit. I showed him the IR images and he proceeded to perform the necessary work. I then returned to my home office to finish paperwork for my last class. A little bit later, the electrician called me and said that he had found no “burning” or “damaged” components visually. That was not a concern to me, and I just politely asked him to clean and retighten the breaker connection and contacts for us.

When electric circuits have an increased resistance and begin building up excess heat, the problem snowballs and becomes progressively worse. Added heat can mean higher temperatures in those components, and that can increase the corrosion rate and will increase the electric resistance of copper and aluminum. I knew from past Utility and substation experience that just because we can’t visually see the problem doesn’t mean that it isn’t a problem. The electrician performed the work and then re-energized the circuit.

That evening, Mom had placed load on the circuit again as I had instructed. I returned to the scene with the camera and performed another inspection. Fig. 6 shows the result of the EXCELLENT work by our electrician.

Fire safety in the home starts with many often overlooked plans and equipment such as fire extinguishers and smoke detectors.  Even residences can benefit from an IR scan when pinpointing problems by traditional methods prove inadequate.

According to the University of Nebraska Cooperative Extension in Lincoln, Nebraska, nearly all home fires can be prevented.  Families are urged to reduce the risks of fire by following a few rules.

• Matches and lighters: Keep all matches and lighters out of children’s sight and reach.

• Smoking: Never smoke when you are sleepy or in bed.

• Wiring: Don’t overload outlets or run wires or extension cords under rugs, behind radiators, through door jams or across walkways.

• Combustible liquids: Combustible liquids should be stored outdoors in a cool place out of reach of children.

• Heating equipment: Many home fires can be traced to defective or improperly operated or installed heating equipment.

• Trash: A quick check of the attic, basement and storage areas in and around the home will reveal any excess trash that should be removed.

• Cooking equipment: Most fire hazards in the kitchen are associated with either cooking or careless use of the kitchen range.

Excerpt taken from Lorene Bartos, Extension Educator at the University of Nebraska

Meet the Staff - Paul Frisk [top]

Paul Frisk, P. Eng
Instructor - ITC Level III

Paul is a Professional Engineer with a bachelor’s degree in Applied Science from the University of Toronto, Canada. Paul has been in the infrared business since 1979 and with FLIR Systems for the past 16 years. Paul is a Level III Thermographer (ITC) and has 2 duties within FLIR. As the Automation Product Champion, Paul has extensive experience in Automation (Process Monitoring and Control) processes. His duties ranged from Software System Design, Manufacturing and System Installation as well as sales. Paul’s second “calling” is as ITC Instructor and provides enthusiastic training sessions that are well received by his students.

Past Issues  [top]

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