12 steps toward better Electrical Inspection

7/28/2019 12 steps toward better Electrical Inspection

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Thermal Imaging: 12 Steps Toward BetterElectrical Inspection

Written byJohn Snell and Dave Sirmans

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Electrophysics Resource Center

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Thermal Imaging: 12 Steps TowardBetter Electrical Inspection

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Electrophysics Resource Center:Infrared Inspection

© 2010 Electrophysics Corp and The Snell Group. All rights reserved.

Infrared Inspection A SOFRADIR ECCOMPANY

I you’re having unscheduled electrical outages or any reason, thechances are good that you need to look at how to improve your in-

rared inspection program. Thermal imaging is much less about whatkind o in rared camera you use than it is about using the in raredcamera you have well.

Here are twelve steps, some simple and others less so, that will helpimprove the results you are getting rom this remarkable technology.

Clearly the frst step in any success ul thermography inspection is toensure all work is done as sa ely as possible. While most are amiliar

with NFPA 70E, we fnd there are still gaps in both a practical under-standing o the document as well as, importantly, the implementationo the guidance it provides.

Among other things, NFPA70E (as well as common sense) suggestthermographers should:

• be working with written work procedures• be qualifed to do the work• ollow the guidance in the new version relating specifcally to

thermography• have conducted an arc- ash analysis and kept it updated• wherever possible, reduce risk by improving the system ault

protection and coordination• wear appropriate personal protective equipment

(PPE) and observe required working distances

Thermal Imaging: 12 Steps Toward BetterElectrical Inspection

Introduction

1. Safety

Figure 1: Sa ety, which includes wearing all proper PPE,should be a program’s frst priority.




3Electrophysics is an ISO 9001 Certifed Company.



Realistically, there may be some equipment that cannot be inspect-ed live. The appropriate use o IR windows and viewports should beconsidered in many instances as a means o improving inspectionaccess and requency. These devices should not be used, however,

without care ul planning and orethought. The sa ety goal is alwaysZERO accidents and injuries!

Too o ten we fnd otherwise intelligent people using their in raredimaging systems as i they are “answering machines!” They are not!They are tools which, when properly used, will give remarkable data

or our interpretation. Simply relying on “auto adjust” or “tempera-ture alarm” unctions is not only insu fcient, it is dangerous becauseit means you will miss problems, probably serious ones. A qualifedthermographer knows how to use the in rared imaging systems ully—

ocus, adjust the image manually, capture data with care, use mea-surement tools appropriately, correct or emissivity, background and

transmission, etc—and, importantly, also understands the limitationso the system and technology. I you don’t know how to use a toolproperly and ully, you will not obtain consistent, high-quality results.

In the past, thermographers o ten simply opened a number o enclo-sures and then came back and “inspected” them. This proved notonly unsa e, but also a bad practice as it allowed or signifcant cool-ing o the enclosure’s interior prior to inspection. Best practices nowsuggest a preliminary look at the enclosures prior to opening anyo them; i one is abnormally warm, additional precautions may bewarranted to gain access. At best, there may be some indication ointernal heating; at worst, there will not be a detectable signature.

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Please note, there are still some who insist, or various reasons, thatthey can ully inspect electrical equipment without opening the enclo-sures. These cameras aren’t x-ray machines, they measure sur acetemperature only. The notion o being able to “sur ace scan” is not

true, regardless o the type o imaging system or the skill o the ther-mographer! At best, there may be some indication o internal heating;at worse, there will not be a detectable signature. Gaining sa e accessto the enclosure is essential, either by opening it while it is under load,de-energizing it and then opening it and inspecting immediately there-a ter, or by use o IR windows or viewports (discussed below).

At that point, as is appropriate, enclosures can be opened—againbest practices suggests this be done not by the thermographer butby a qualifed assistant who can also act as a sa ety backup and takeload readings, and who understand the local system i their thermog-rapher does not.

The inspection should be conducted systematically, using imagersettings su fcient to detect any abnormal temperature increases.While the inspection can be conducted quite rapidly, thoroughnessshould not be sacrifced in the interest o speed.

Many components will have bare metal (low-emissivity) sur aces thatcan make detection o problems, as well as the measurement o theirtrue temperature, di fcult or impossible. Recognize that some mayappear normally warm (contactors, overloads) or cool (surge protec-tion). Similarly, some equipment may not be in operation or under ullload at the time and this should be noted or later ollow-up.

All abnormalities should be noted or later prioritization. Best prac-tices generally suggest documentation only o anomalies but, whenaccess is challenging or any reason, ull documentation may bewarranted to acilitate possible later analysis. Doing so also assistsin trending o anomalies where applicable. Documentation shouldinclude thermal images, pre erably with two or three o the phases orcomparison, as well as a comparable visual image and, as needed,voice or written annotation. Any anomalies judged to be o an emer-gency nature should be dealt with immediately.

More and more o ten, sa ety concerns suggest we should minimizethe opening o electrical enclosures while they are under load, andyet, not doing so can severely limit our ability to get good data.

One solution that is now being widely used is the installation o IR-transmissive windows or view ports. These devices enable a trainedthermographer to look inside the enclosure without opening it. NFPA 70E allows theses devices to be considered as “barriers” thus poten-tially reducing the level o PPE and the approach distances used.

4. Where Appropriate,Consider Using

IR Windows or Viewports







The use o such devices, however, is not as simple as may be as-sumed. Care must be given to proper sighting o the device in theenclosure to optimize viewing and to using the device e ectively andsa ely. Because IR windows attenuate the thermal signal, both simple

detection o an anomaly as well as measurement o the temperaturesinvolved can be problematic. While a ull discussion is beyond thescope o this article, it should be noted that without a care ully devel-oped written procedure or using IR windows and viewports, resultscan be poor or misleading. Enough o these devices have now beeninstalled, however, that good precedents can be established to en-sure good results.

Basic electrical relationships, I 2R=P, clearly tell us heat output (P)increases as the square o the load. Heat output will increase expo-nentially as the load increases. The relationship being between thesquare o the current and heat, when you double the current, youincrease the heat output 4 times. Increase load by 3 times, heat out-put increases by 9 times. Since heat is the “enemy” thermographersmust, there ore, be particularly care ul when inspecting equipmentwhile it is under a light load where those loads will increase at some

Figure 2: Installing and properly using in rared windows can increase sa ety andspeed inspection time or your program.

Read More About Periodic InfraredInspection Best Practices

In rared thermographic inspection is an established PdM inspectionmodality. Recent advances in in rared camera plat orms have created anew class o in rared imaging instrument which incorporates pen-based

computing and application-specifc so tware into a power ul thermalinspection data logger with many traits similar to mature vibrationdata collection systems. The potential impact o this integration onproductivity, thermography program ROI, training and integration othermal inspection data with CMMS systems is described and presented.

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5. What is the Load?

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point in the uture. The NFPA-70B recommendation or loading is40% as a minimum, unless loads are normally below that level andnot expected to increase.

Likewise, and much less well recognized, is the relationship betweenthe temperature o a material and its electrical resistance. Some willsco at this notion, and in rebuttal, I would like to o er an experimentto prove this out. I you have access to a low-resistance ohm meter,measure the resistance in a sample o copper bus at room tempera-ture. Then, cold soak the sample in a reezer or 8 hours or so and re-peat your measurement. Then, or good measure (pun intended) heatthe sample (sa ely!) to 200°F and measure again. You’ll be surprisedat what you fnd. The vicious cycle o increased loads and heating re-sulting in increased resistance and more heating is one o the reasonsanomalies can remain relatively stable or long periods o time be orecoming rapidly to a point o ailure. The near impossibility o predict-ing exactly when that ailure will actually occur has caused many

good thermographers a sleepless night or two and should never beunderestimated.

Some suggest that the di erent loads a thermographer invariablyencounters can all, somehow, be miraculously “re erenced” backto a 50% norm. While this may be possible in a specifc instancewith considerable engineering modeling, to think that it can be donewholesale is a mistake no reasonable person should make. Only twothings are certain about inspections per ormed when loads are lightand will increase: (1) some anomalies may go undetected and (2)those that are detected may be underestimated because they willgenerally appear cooler than when loads increase.

We are limited, or the most part, to seeing radiation coming roma sur ace. As the sur ace warms it gives o more radiation that canprovide an alarm o a change. The driver o that changing tempera-ture, however, is almost always internal to the sur ace we see; that is,the point o electrical contact and high resistance heating.

6. What is the Thermal Gradient?

Marginal heatgeneration

% of Maximum Load

0% 20% 40% 60% 80% 100%

Sufficient heatgenerated

Inadequate heatgeneration

Figure 3: According to NFPA-70B, a 40% load is the minimum re-quired or accurate thermography readings.







While it is important to view components as directly as possible, orsome, such as a bus stab or a use block or a trans ormer bushing,this may be di fcult or impossible. Even when viewing componentsdirectly, respect that there can be a signifcant “thermal gradient”

between the sur ace being viewed and the internal source o heating.This can be seen, or example, when a bolted connection becomeswelded together at the threads or when a plate connector shows pit-ting on the contact sur aces. For very large gradients, like an internal

ault on a trans ormer bushing, the indication o a severely degradedproblem may be only a ew degrees rise in temperature over normal.

I conditions are poor or an inspection, a lightly loaded system orwind, or example, a relatively insignifcant indication exhibited by alarge gradient component may go undetected. To better understandthe signifcance o fndings, it may be use ul to categorize gradientsas either small (connectors viewed directly), moderate (breakers orlarge connectors) or large (oil-flled devices and bus ducts).

One o the most poorly understood issues thermographers mustcontend with is the low emissivity (and high re ectivity) o bare met-als. The result o this inherent physical property is that bare metalsnot only don’t reveal their true temperature easily but they also tendto mask over it with untruths!

While it is possible to make corrections or emissivity, the reality isthat errors are unacceptably high when doing so or any bare metal.In many cases, the real danger is not just an inaccurate measure-ment, but a ailure to detect the anomaly because the mix o emittedand re ected radiation is so con using. As a practical guide, andmany will fnd this shocking, it is virtually impossible to accuratelyand repeatably measure the temperature o a bare metal sur ace that

is as “bright” as any o the coins in your pocket. This is true regard-less o your procedure or the brand o in rared system you are using.It is also nearly as di fcult to measure phase to phase di erenceswhen they are bare metals.

7. Bare Metals Are Dif cult toUnderstand

Figure 4: Understand that there can be a signifcant “thermal gradient” be-tween the sur ace being viewed and the internal source o heating.




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In the end, it is always advisable to increase the emissivity o baremetal sur aces using an appropriate high-emissivity “target” materialsuch as electrical tape or Glyptol paint. I this is not possible, look ora nearby high-emissivity sur ace, such as the conductor’s insulation

or a cavity radiator, make your measurement there and acknowledgethe probably large size o the resulting thermal gradient.

It is vital to structure inspection routes to optimize the reliability oessential equipment. The process begins by defning what is es-sential, a task that has o ten already been done by someone in anorganization. While the “high” end o a system (switchgear andtrans ormers, or example) is typically considered vital, downstreamequipment must also be considered care ully. The HVAC system orthe electrical room, or example, is o ten critical or reliable opera-tion, and the loss o something as seemingly insignifcant as a usein a control system can have dire consequences. Routes are best

designed with input rom all relevant stakeholders.

The task o assigning a requency o inspection is one that is all tooo ten either over simplifed (“annually”) or made ar too complex.Initially the driver or requency will be based on the resources avail-able or inspection. Those should be distributed in such a way as toprovide the greatest returns on the investment a ter considering such

actors as the age o the equipment, its duty cycle, whether or not itis housed in a cooled area, the history o ailures, etc.

A ter several inspection cycles, the eedback provided by the in-spection results will serve to help refne the requency. I or no otherreason (and there are many others) it is crucial to note all anomalies,

even i they are not all immediately repaired. Anything less than thatwill only result in a misplacement o resources.Mechanical Room

Scan Equip ID Name Locator Preparation Inspect Date Time Load (A) Problem TG# Photo #E1 EL360 Electrical Panel System 01 NO; OP Y 02/ 04/20 10:30 20 NE2 EL352 Electrical Panel System 02 NO; OP Y 02/04/20 10:40 90 NE3 EL344 Electrical Panel System 03 NO; OP Y 02/04/20 10:50 15 NE4 EL333 Electrical Panel System 12 NO; OP Y 02/04/20 11:05 15 NE5 EL329 Electrical Panel System 06 NO; OP Y 02/04/20 11:17 45;40;40 Y 1,2 1E6 EL321 Electrical Panel System 10 NO; OP NL 02/04/20 11:30 0 UE7 EL317 Electrical Panel System 07 NO; OP Y 02/04/20 11:35 88 NE8 EL325 Electrical Panel System 03 NO; OP Y 02/04/20 11:45 23 NE9 EL336 Electrical Panel System 11 NO; OP Y 02/04/20 11:55 60 NE10 EL340 Electrical Panel System 09 NO; OP NL 02/04/20 12:00 2 UE11 EL348 Electrical Panel System 05 NO; OP Y 02/04/20 12:15 17 NE12 EL356 Electrical Panel System 04 NO; OP Y 02/04/20 12:30 44 NE13 EL367 Pump 1 Disconnect West Wall NO; OP Y 02/04/20 12:46 18;21;18 Y 3 2E14 EL368 Pump 2 Disconnect West Wall NO; OP NF 02/04/20 12:58 UE15 EL369 Fire Pump 1 Disconnect East Wall NNO; LU Y 02/04/20 12:59 NE16 EL370 Fire Pump 2 Disconnect East Wall NNO; LU NR 02/04/20 13:05 UE17 AC003 Exhaust Fan Disconnect East Wall NO; OP Y 02/04/20 13:06 N

E18 TMP01 Enclosed Bus Duct Ceiling NA; SE Y 02/04/20 14:00 U NNO=Normally Operating Y=YesOP=Open Panel N=NoSE=Scan Exterior NIL=No-Insufficient LoadLU=Load Up NF=Not FoundNNO=Not Normally Operating NR=Not RunningNA=No Access U=Unknown

Figure 5: A detailed list o equipment, along with relevant data pertaining to eachpiece o equipment, is essential to defning the best inspection routes.

8. What to Expectand When?







Too many thermographers make an arbitrary decision to only note“hot ones.” This is a mistake or several reasons. First, the only wayto accurately gauge asset health is to document everything. Ocourse, it is not realistic to think that every fnding will be addressed

immediately but there must be room in the maintenance system to atleast note all abnormalities and deal with them appropriately.

Second, serious problems may not appear particularly warm at thetime o the inspection or any number o reasons. For instance, i theload is light, not much heat will be generated but, o course, loadingcan quickly change. As stated be ore, equipment with a large gradi-ent will rarely show up as very warm and some equipment, such assurge protection, is near ailure when it exhibits even a small rise intemperature over normal. So note everything that is not normal andthen fgure out how much o a problem it is and what to do about it.

While it is o ten challenging to make accurate measurements oelectrical components, every e ort should be made to do so whilealso understanding the degree o confdence inherent to a par ticularmeasurement. In act, it is use ul to look at not only the componenttemperature (corrected or emissivity and background i possible),but also the rise over ambient air temperature and the phase-to-phase rise as well. These latter two will help one understand uturechanges in temperature that may occur and to isolate a rise relatedto ailure.

9. Note Everything That is Abnormal,No Matter the

Temperature

10. Measure Temperature, butDo It Well

Figure 6: Many times taking an accurate temperature reading isnot as simple as pointing the camera in the right direction.




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Logic suggests that the hotter an abnormal component, the closer itis to ailure, and this is o ten true. However, it is not always true ANDthere are many instances where we don’t have a good indication oeither how hot it actually is (or could become), or how eminent that

ailure is relative to the heat we see. Best practices suggest prioriti-zation o fndings be based on all relevant actors, including temper-ature, but also including the reliability o the data, the criticality o theequipment, the potential or injury, etc. Trending can be per ormed,but only conservatively and with great care, and with an understand-ing o the thermal dynamics involved.

Far better to dump all fndings into one o three “buckets”:(1) those close to ailure or or which the risk is too great(2) those which can be monitored and managed until appropriate

repairs can be made(3) those which are in good health

This simple, exible approach yields remarkable results without beingparalyzed by a complicated analysis. A methodology can also be de-veloped and used to provide ever increasingly “smart” results as thesystem eeds back into itsel .

Figure 7: While temperature is important, basing your prioritizationo fndings on all relevant actors is a better practice.

11. Prioritize FindingsBased on AllRelevant Factors,Not Just

Temperature







In many companies, and or many di erent reasons, 50% o repairsare not e ective the frst time. There ore, it is crucial to re-inspecta ter repairs have been made. The eedback will help drive improvedquality, both on the inspection side as well as the cra t side. The

payo or re-quali ying work is immense and should not be ignoredor short changed.

There may well be other steps to success or variations o the twelvewe’ve discussed. The bottom line is in rared is a remarkable tool thatwill provide returns ar in excess o nearly any other maintenanceinvestment possible, but it is not magic! To ensure a ull return onthe investment, thermography must be used intelligently by qualifedpeople.

An in rared imaging system is one o the most power ul tools avail-able to anyone involved in maintaining or testing electrical systems.I , however, it is not used properly, this remarkable technology canactually be a dangerous diversion rom or mask over what is reality.

Modern in rared systems are very reliable and very easy to use; thelimiting actor is typically the human being using the in rared sys-tem. Qualifcation is essential to both understanding any problemsthat are ound as well as not missing problems that are there butnot obvious. Qualifcation o thermographers is based on training/ education, quali ying experience and proo o qualifcation (testing).Without that, chances are good there will be quality problems andconsequences.

Summary

12. Re-inspect AfterRepairs

Figure 8: It is important to reinspect components a ter the repair has been made.This leads to higher quality repairs and IR inspections.



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