ITC InfraMation - = August 2003

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August=20 2003

Volume 4, Issue=20 8

In This=20 Issue:=20

Welcome

IR in the News

Infrared Thermography Finds Overheating=20 Motors

Brainteaser of the Month

Last Month's Brainteaser

Past Issues

Upcoming Classes

About the ITC

View the=20
Conference Video

Paper=20 Titles being presented in 2003

Hello=20 {{user("firstname")}},

I hope your=20 are enjoying your summer. Many of you take a vacation at this time = of year=20 to rest up for the new school year just around the corner; I know = I need=20 to, can't believe we are already nearing the end of = summer.

In this issue=20 we have a great article for you on using IR=20 to find overheated motors by Forest Wilcox. Remember to click = on any=20 image for a higher resolution view.

Check out the=20 paper = titles for=20 the InfraMation Conference coming up in October. We have over 50 = papers=20 this year!

And=20 be sure to check out our new Brainteaser of the Month.

If you want to=20 save this newsletter for viewing off line in your computer, just = go to the=20 web page using=20 your browser and select File....Save As or save this email = page as html in=20 your email software.

Have a great=20 rest of the summer,

Gary=20 Orlove,
Editor and = Publisher

IR in the=20 News [top]

JOBS AT THE TIMES
Berkeley=20 Voice, CA - Jul 25, 2003
... = ongoing. A=20 500-square-foot exhibit that offers a variety of = hands-on
activities=20 as well as displays on thermography, x-ray and hearing.=20 ...
Helicopters scrambled to combat rail=20 nuisance
Bucks = Free=20 Press, UK - Jul 24, 2003
... = hurt.". The=20 helicopter, which uses a 360-degree thermal = imaging=20 zoom
camera to monitor the route, was first launched in the = spring.=20 ...
CITY HOMES ARE HOT = STUFF
Aberdeen Evening=20 Express, UK - Jul 11, 2003
... = The=20 detailed thermal image of the entire city - = pinpointing=20 individual homes
and business premises - has been produced by = the=20 council in a bid to spark ...
Joann Loviglio (Associated = Press)
Hindustan=20 Times, India - Jul 9, 2003
... = Other=20 scientists are looking at "thermal imaging" = (training a=20 heat-sensitive camera
on people's faces that would register = increased=20 blood flow around the eyes ...=20

Infrared Thermography Finds = Overheating=20 Motors = [top]

By Forrest Wilcox
Level I=20 Thermographer
J.R. Simplot Co.

Are you replacing electric motors = after one to=20 five years that should last ten years? In the past this was not = unusual in=20 the plant where I work. Furthermore, how much power is being = wasted while=20 these motors are running at less than nameplate = efficiency?

The J.R. Simplot = Co. plant at=20 Pocatello, Idaho produces sulfuric and phosphoric acid and various = grades=20 of liquid and granular fertilizer. With the intense competition in = this=20 industry, we must do everything possible to insure that we produce = our=20 products at the lowest possible cost. Establishing an infrared = inspection=20 program on the motors has been a key factor in achieving our goals = in this=20 area. Most large chemical plants have hundreds of electric motors = and=20 maintaining proper motor temperature is very important if motor=20 maintenance costs are to be kept to a minimum.

Generally = speaking, each 10 C=20 degree rise above the rated temperature cuts motor life by half. = An=20 increase of 20 C degrees above rated temperature would reduce = motor life=20 to about one-fourth of normal. Regularly scheduled infrared = inspections of=20 electric motors identify motors, which are starting to overheat.=20 Additional inspections can identify small problems before they = become=20 major problems.

A common problem = we find is=20 restricted cooling airflow caused by build up of process residue = on the=20 fan end of the motor. Some of our big process mixer motors are = mounted=20 high above floor level where the fan end is not visible. A quick = infrared=20 inspection from floor level allows inspection without climbing up = to=20 inspect the air intake grill. If a brief shutdown is possible = without=20 affecting the plant process, the motor is shut off long enough to = perform=20 minor cleaning on the air intake grills, and a thorough motor = cleaning is=20 scheduled for the next plant down day.

Since starting our = regular=20 infrared inspections on the motors, we have had no motor failures = due to=20 lack of cooling airflow.

3D"Fig 3D"Fig

Figure 1 on the = left was taken=20 November 14 shows the motor running at 244.9 degrees F. Figure 2 = taken the=20 next day after minor cleaning was performed on the air intake = grill shows=20 the temperature has came down 53.8 degrees F. Considering there = was a 6.1=20 degree F difference in ambient temperature there was a net = improvement of=20 47.7 degrees. It was still operating over recommended temperature, = but we=20 were able to continue running it until a regularly scheduled down = day when=20 a thorough cleaning could be performed.

3D"Fig Figure 3 shows the dirt buildup on the cooling air grill, = partially=20 restricting the cooling air to the motor. Before we started our = infrared=20 inspections it was not unusual to find intake ports completely = plugged=20 with this material.

Very Small = Resistive=20 Imbalances Can Cause Very Significant Increases In Motor=20 Temperature

From time to time = we find=20 motors that are overheated, are not dirty, have good cooling = airflow, and=20 are not overloaded. It takes a little more detective work, but = often the=20 problem can be identified with an infrared inspection.

Increased = resistance to the=20 flow of electricity causes an increase in temperature. An increase = in=20 resistance on one of the feeders to a three phase motor causes a = resistive=20 imbalance. This not only causes a temperature increase at the = point of=20 high resistance, it also causes voltage and current problems that = result=20 in increased motor temperature. A high resistance connection in = the=20 switchgear, disconnect, or motor connection box can usually be = identified=20 with an infrared inspection. If you have a resistive imbalance and = don=92t=20 find a problem in these areas, the problem may be in the stator = windings=20 or internal motor connections, but more often than not we find the = problem=20 is in the power circuit. Often there is a problem in the motor = connection=20 box with loose connections or improperly installed, mismatched, or = corroded components. A few strands of damaged wire on a motor lead = can=20 cause a significant resistive imbalance.

After we find a = motor is hot,=20 and we suspect a high resistance connection in the power circuit, = we begin=20 our inspection at the motor control center. We report any = temperature=20 differences between phases of ten F degrees or greater. Depending = on the=20 importance of the motor to our operation we may report differences = of five=20 F degrees . If this leads us to the motor connection box we = perform an=20 offline motor test if possible. On most of our critical motors = however, a=20 half hour shut down to perform tests is not an option and an = infrared=20 inspection at the motor connection box can often identify the = problem.=20

You may not have = the equipment=20 to perform the motor tests, and an infrared inspection may be your = next=20 best option anyway. I used this 450 horsepower blower motor for = this=20 article because it so clearly demonstrates the effects of a = resistive=20 imbalance. Obviously you won=92t find very many motors with this = much=20 imbalance that are still operating and most motors won=92t have = two separate=20 conduits feeding them. The box cover will usually need to be=20 removed.

Follow all = safety=20 precautions when working around moving machinery and hazardous = voltage.=20 Damage inside motor connection boxes can expose potentially = hazardous live=20 electrical surfaces. The motor should be shut down long enough to = remove=20 the cover if possible.

The motor in the = following=20 infrared image (Figure 4) had been running somewhat hot for over a = week,=20 but was not overloaded. We had sent an infrared inspection report = to the=20 manufacturer with images taken from the other side of the motor. = The motor=20 representative said that the motor was ok to continue running, and = the=20 elevated temperature was not a major problem. The motor connection = box and=20 conduit were not visible in the inspection, which was taken from = the side=20 opposite the connection box. We went back the next day and took = some=20 infrared images from the connection box side, and learned a good = lesson.=20 Always look at the box, and open it if you must. After = adjusting=20 the span on the camera the source of the heating became very = evident. A=20 loose connection was causing heating on one set of parallel = feeders going=20 to the motor and causing a severe resistive imbalance. The = temperature=20 inside the box was so hot that it was visible with the indirect = image=20 taken on the conduit and box cover. Notice the 24.8 F difference = between=20 the top and bottom conduits.

3D"Fig 3D"Fig

After an orderly = shut down of=20 the plant, the motor connection box cover was removed. One of the=20 connections had a loose bolt that was causing the imbalance. The = motor=20 leads had been so hot that there was residue from soot and carbon = on the=20 interior of the box.

The motor was sent = out for=20 repair and all that was required was a cleanup and new motor = leads. The=20 price of the repair including new bearings was $2,414.00. If we = had=20 continued running the motor with the loose connection very much = longer we=20 would have had to do a complete rewind, which would have cost = about=20 $10,000.00. Replacement price of the motor would have been = $19,296.00.=20 With plant downtime costing hundreds or thousands of dollars per = hour, the=20 price of the motor is not the major expense when some of our = motors=20 fail.

The manufacturer = of our motor=20 tester recommends that resistive imbalances over one percent = between=20 phases need to be corrected. You may not be able to see a = temperature rise=20 on the motor leads until the imbalance is somewhat higher than = this=20 depending on how the motor leads are insulated.

Offline motor = tests performed=20 on the motor from the motor control center before it was = disconnected and=20 sent out for repair verified that we had very high imbalances in = the power=20 circuit. We were surprised that the motor was still able to run, = and it=20 probably would have failed in a short period.

Notice in the = motor test=20 report, how much power would be wasted if the motor could run for = a year=20 with an imbalance this high: $47,074.00

450 Horse = Power=20

1^st = Test

2^nd = Test

Test=20 Date

11/19/2001

12/06/2001

Test=20 Time

10:03:07=20 AM

11:54:25=20 AM

Baseline

Frequency

1200

Mohm Ph 1 to=20 Gnd

Charge=20 Time

Voltage

500

Motor=20 Temp

Measured=20 Mohm

456.0

>=20 2000

Corrected=20 Mohm

> = 2000

OVR=20 (MCE)

pF Ph 1 to=20 Gnd

139250

88250

ohm Ph 1 to=20 2

0.20500

0.00682

ohm Ph 1 to=20 3

0.07250

0.00684

ohm Ph 2 to=20 3

0.22450

0.00683

mH Ph 1 to=20 2

1.215

0.410

mH Ph 1 to=20 3

0.160

0.410

mH Ph 2 to=20 3

1.390

0.410

Avg.=20 Inductance

0.922

0.410

% Res.=20 Imbalance

56.67

0.15

% Ind.=20 Imbalance

82.64

0.00

$ Power=20 Loss

47074.00

6.19

Test=20 Location

Top=20 Starter

Motor=20 Leads

The first test was = performed=20 when the motor was taken out of service. The second test was = performed=20 after clean up and replacement of the motor leads. No rewind was=20 necessary.

Summary

Motor cleanliness = and power=20 circuit problems are only two of the many reasons that motors = overheat.=20 Infrared inspections have helped us find these problems, and = together with=20 motor testing, vibration analysis, and high lubrication standards = we are=20 significantly reducing our motor maintenance costs.=20