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

By Juan C. Hidalgo B., BSEE
ITC Level II Instructor, Costa Rica

As an experienced thermographer of seven years and user of other PdM technologies, I have encountered many problems using IR technology. But it is sometimes confusing trying to determine the exact cause of failure on an electric motor with IR thermography only.

Using infrared for motors is the fastest diagnostic tool available, you can collect a lot of information in a matter of seconds, contrary to vibration analysis or electrical motor testing. But the quality of information from an IR image is subject to several parameters that other technologies account for.

For example, the image to the right shows a very hot load side bearing. I am sure any thermographer would say there is a problem with the bearing. This is the effect and not the cause, the probable cause could be an alignment problem, damage to the inner track of the bearing, or an eccentricity problem.

This shows us that even though IR thermography can give us a fast indication of a problem, care should be taken in order to make an accurate diagnosis.

Figure No.2 corresponds to an IR scan of a air compressor motor in a semiconductor company taken in 2001.

Figure No. 2 is an insulation class F motor with some defined hot spots in the frame, but the max. temperature recorded reached 72 ºC. This temperature is far below the maximum allowable temperature for this insulation class, according to IEEE 117-2000. Table 1 shows the maximum temperature for each insulation class.

Based on ambient temperature of 40 ºC (104 ºF)
* Used in European Equipment

Infrared thermographers can use this table as a reference to gauge the severity of a potential problem in a motor.

So I decided to inspect this motor again in one year. This is the IR image I recorded in 2002:

Using the trending tool in ThermaCAM Reporter 2000 professional by FLIR, we graphed  the behavior of the casing temperature in a few seconds. The graph clearly shows a Delta temperature rise of 27 ºC, the maximum temperature recorded was 99 ºC. There is a very clear hot spot on the bottom of the motor frame, indicating a problem in the motor that is deteriorating with time. Using table 1 regarding insulation class solely to reject or accept this motor, we would say the motor is acceptable. Trending the infrared images has showed us something has been happening, perhaps in the stator windings.

Electrical machines are designed for efficient heat exchange. When heat is trapped, electrical and mechanical stresses develop and can cause tolerances to be exceeded or electrical material characteristics to be radically changed.

Thanks to the findings of infrared we recommended that Electrical Motor Testing Analysis be performed.

We used the MCEmax manufactured by PdMA Corporation. This tester allowed us to test 6 fault zones using dynamic and static tests. Infrared indicated something has been happening in the power circuit or the stator.

The results on the static and dynamic test showed an inductive and resistive imbalance which indicates a turn-to-turn short. The Resistance to Ground (RTG) is very high, meaning there is still no leakage to ground, this motor can be saved if repair work is performed at soon.

Using different technologies together helps thermographers to obtain more accurate results and confirm our findings.

IR thermography is a fast, easy to use diagnostic tool. An IR image of a motor can take less than 1 minute, and the associated cost per equipment is low compare to other technologies. In this case IR thermography helped us initially to identify a problem and motor testing determined the exact fault cause.

Motor testing is an excellent tool but it takes more time to analyze a motor completely, from half an hour to one hour depending on the type of tests. Therefore, its associated cost per equipment is higher than IR thermography but the results are more accurate.

Correlating PdM technologies from different sources such as Vibration Analysis, IR Thermography, Motor Testing, etc, will allow thermographers to more accurately confirm the type and severity of the problem in electric motors.

Tech Tips - Calculate Temperature Differences with the FLIR PM-695 [top]

by Jason Gagnon
ITC Technical Support Manager

The FLIR PM-695 camera can be set to calculate the difference between two spots on the IR image. This result can be automatically displayed in a report created with ThermaCAM Reporter 2000 Professional.
                 To configure the Delta 2-1 formula in the camera:

1. Click the enter button on the camera to access the menus.

2. Go to Setup > Analysis and set Difference temp to On.  Note that you must also have Multi Spot/Area set to On and have at least two measurement functions set to spot mode.  Click the enter button to save the settings and return to the live image.

3. Click the enter button on the camera and select Analysis.  Select Spot1 and position it at the cold spot, or reference spot, on the image.  Now select Analysis again and click Spot2.  Position Spot2 on the hot spot.  The result of Spot2 – Spot1 will be shown on the right side of the image next to D2-1.

4. Hold down the S button to save the IR image with the two spots and the D2-1 result.

You can display the D2-1 result using a table or a field in ThermaCAM Reporter 2000.

If you are using a Results table: Right-click anywhere on the table and click Contents.  Click the checkbox next to Camera Delta2-1 value and click OK.

If you are using a Table, Summary table, or Field:  Right-click on the cell and click Connect.  Highlight Camera Delta2-1 value and click OK.

Past Issues  [top]

Click the links below to view past issues of this newsletter:

All past issues from February 2000 through December 2002

May 2003

April 2003

March 2003

February 2003

January 2003

December 2002

November 2002