Corona Camera Imaging

7/30/2019 Corona Camera Imaging

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www.netaworld.org Summer 2007 NETA WORLD 21

No

Outage

Inspection

Corne

r

by Don A. GenutisGroup CBS

Figure 1 Dangerous corona occurring rom middle o the insula-tor. Te corona rom the top corona ring is harmless.

Figure 2 GSU transormer bushing corona is seen irting withashover.

Corona Imaging

See the Invisible

Tis column ocuses on electrical inspection methods and tech-

nologies that are perormed while the electrical system remains

energized. Although no-outage inspections can be very valuabletools, always remember to comply with proper saely guidelines

when conducting energized, on-line inspections.

It elt like a ne spring morning in eastern Oregon as

my colleague and I rolled up the power plant driveway,

although the date on my Blackberry indicated mid-Feb-

ruary. Ater some riendly greetings and hand-shaking with

maintenance personnel, we signed in at the control room and

viewed the not too lengthy or boring saety video. Ten it was

time to don our hard hats and head toward the substation all

half-million volts of it.

It was dry and sunny as our work boots crunched against thecoarse substation gravel rocks. Te massive bushings and insula-tors did not appear to have much, i any, condensation rom thenight beore as we gazed across an acre o GSU transormers,SF

6dead-tank breakers and other equipment. Ideal conditions

or a corona image survey. Ater powering up our new coronacamera and making a ew minor adjustments, we began doingwhat no other person had ever done beore in this substation we were viewing an invisible phenomenon known as corona.What we and plant personnel saw during the next ew hoursthat morning would better our understanding o high voltageengineering in a manner that no text book possibly could.

We saw corona rom insulators that required cleaning,sharp edges rom hardware connections, poor bus work corona

suppression, and dangerous insulator corona caused by coolingtower residue deposits. As the prevailing wind pued anothercloud rom the cooling tower onto the westernmost insulators,


2/7

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3/7


Vacuum technology hasvastly improved thereliability and lifespan of medium voltagecircuit breakers. Whenfailure occurs you cancount on CBS Maxi-Vacproducts for replacement

assemblies.

Contact CBS forassistance in diagnostics,service or replacement.

A Group CBS Company

Ph: 972-250-2500 Fax: 972-250-2501

www.vacuumbreak ers.com Ema il inf o@cbs powerproducts. com

Figure 3 Electrical feld surrounding an insulator

we could hear the corona crackling intensiy as the camera re-vealed near fashover conditions. When it sounds like this, I tellmy guys to get out o the substation, our customer stated. Not abad idea, I thought. Next, we ollowed our customer to a cornero the substation were we examined a fash-damaged insulatorlaying in the gravel, then observed the additional weather shedsadded recently to the in-service insulators nearest the coolingtower. For the most part, the increased surace creepage o the

modied insulators were doing their job by eliminating most othe corona. However, as can be seen in Figure 1, one insulatorwas clearly showing dangerous corona that consistently occurred

rom a deect located hal way down the insulator. Addition-ally, we ound severe corona activity occurring rom the center

phase GSU transormer bushing as shown in Figure 2. We letthe power plant eeling that the customer greatly appreciatedthe value o our new technology and would use the knowledge

gained that day to reduce uture fashover likelihood.

One o the greatest diculties when working with elec-tricity is that it cannot be seen. Te technician must gener-ally determine its presence based upon meter deection or

simple visual or audible warning signals.Perhaps even more dicult to appreciate is the concept

o electrical elds surrounding conductors or insulators inair. A visual representation o the electrical eld is shownin Figure 3,which illustrates the voltage gradient surround-ing an insulator. Medium- and high-voltage equipment is


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Figure 4 Hand held corona camera in use

careully designed so that electrical elds are contained.I the electrical eld is compromised by oreign materials,poor design, or other actors, corona will occur. Corona isresponsible or the generation o ultraviolet radiation, ozone,acids, heat, mechanical-erosion through ion bombardment,electric power loss, and electromagnetic intererence o radiocommunications. Corona by-products destroy insulation andlead to catastrophic ailure while remaining invisible to theeye.Corona can occur due to: poor component or system design

improper installation or workmanship

temporary contamination by icing, salt sprays near high-ways or oceans, og, agricultural chemicals, and otherchemicals

damage due to storm wind or lightening

damage due to vandalism

cumulative damage due to corona activity caused byweather conditions

cumulative damage due to contamination rom nearbysources

Until recent technology breakthroughs, ultrasonic de-

tection was one o the only methods capable or detectingcorona. Tis technology is limited, especially when scanninghigh voltage equipment rom a distance since only the rela-tive direction o the problem source can be determined.


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NETA WORLD Summer 2007 www.netaworld.org26

ETSpick up pg 63sp 07with

new banner

Figure 6 Unwanted corona rom poor test lead clearance

Figure 5 No corona rom breaker during shop high potential test

oday, a relatively new technology allows invisible corona to be visiblethrough a special imaging device. Te handheld camera seen in Figure 4clearlydisplays the ionized air created by harmul corona activity by indirectly detect-ing the associated ultraviolet radiation. Te camera user can change the coloo the corona activity to provide better contrast against varying backgroundsand the camera records the corona image to allow subsequent transer o theimage to a PC or report generation. Tis highly efective technology is quicklybecoming an indispensable tool or the technician. In addition to the obvioumaintenance applications or all types o medium- and high-voltage equip-

ment, the corona camera can also be used or:

supplementing partial discharge and ultrasonic surveys

acceptance testing o new or modied installations

product quality assurance

design verication


7/7


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eld and shop high potential testing

general research

We can now even have a much greater understandingo equipment insulator and conductor behavior when con-ducting routine high potential testing.Figure 5displays theabsence o corona while perorming an ac high potentialtest o a medium-voltage circuit breaker, indicating good

insulator and conductor condition, while Figure 6 showsunwanted corona generating rom inadequate clearance othe energized test conductor during the same test. It is ap-parent that the breaker was good but our temporary shoptest setup was not.

Te uture use o corona imaging promises to providemany new applications and many associated new surprises,but one thing is certain we will never think o corona inthe same manner, or now we can see it.

Mr. Genutis received his BSEE rom Carnegie Mellon University, hasbeen a NEA Certied echnician or 15 years, and is a Certied Coronaechnician. Dons technical training and education is complemented bynearly twenty-ve years o practical eld and laboratory electrical test-ing experience. He is presently serving as Vice President o the GroupCBS Eastern U.S. Operations and acts as echnical Manager or theirsubsidiary, Circuit Breaker Sales & Service located in Central F lorida.

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Corona Camera Imaging