Corona Camera Imaging
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Transcript of 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,
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Automate Transformer Turns-Ratio Testing; Rapidly Analyze Circuit Breakers, and
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Measure DC Supply Voltage
Monitor Trip/Close Current Initiate Breaker Operation
Built-in 4.5-inch Thermal Printer orExternal Color Printer
Store up to 200 Timing Tests in EEPROM
Store 45 Breaker Test Plans
Measure Contact/Resistor time Measure Contact stroke/Velocity First Trip Time Capability Monitor DC Supply Voltage Monitor OPEN/CLOSE Coil Current Initiate Breaker Operation Built-in 4.5 inch Thermal Printer Store up to 200 timing records, 45 test plan Stand Alone or Computer Control Lightweight and Compact
Reads Turns Ratios from 0.8 to 15,000
Display Excitation Current
Calculates Turns Ratio and Compareswith Measured Ratio
No Calibration Required AC or Battery Powered
Computer Interface
Reads Ratios from 0.8 to 15,000
Calculates Turns Ratio and Compares
with Measured Ratio
AC/DC Power (ATRT-03A) Built-in 4.5-inch Thermal Printer
Computer interface/Windows Software
Store 200 Transformer Records Store 128 Transformer Test Plans
Perform Sat, Ratio, DC Res Test Automatically
2000 Vac Saturation Test Voltage
Test all X1 to X5 CT Windings
Built-in 4.5 Thermal Printer
Store 140 Test Records
Select Current from 10A to 400A/600A
Range from 1 Micro-Ohm to 300 Milliohm
Store 63 Test Records
Built-in 2.5-inch Thermal Printer
RS-232C/USB Interface
Up to 40A Test Current
Reading Range: 1 Micro-ohm to 500 Ohm
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Vanguard Instruments Company, Inc.
1520 S Hellman Ave Ontario, CA 91761 USA
Phone 909-923-9390 Fax 909-923-9391Visit our Website: vanguard-instruments.com
Reliability Through Instrumentation
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www.netaworld.org Summer 2007 NETA WORLD 23
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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A day at the Pennsylvania Breaker and Pennsylvania
Transformer Technology facilities
Over a dozen useful substation and switchgear
presentations
An SF6 handling, management, and emissions
reduction seminar
A circuit breaker timing and analysis seminar
Supplier exhibits every evening in the hospitality rooms
October 1-5, 2007
Omni William Penn Hotel
Pittsburgh, Pennsylvania
Finepoints 14th Annual Circuit BreakerTest & Maintenance Training Conference
For further information and on-line registration, please visit
www.circuitbreakerconference.com
Join Us In Pittsburgh This October!
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www.netaworld.org Summer 2007 NETA WORLD 25
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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
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www.netaworld.org Summer 2007 NETA WORLD 27
Single Phase TestingThe smallest and lightest in its class, the PTE-100-C Plus can test
virtually any type of protective relay element, from time-dependent
overcurrent to the most sophisticated directional,
frequency and distance protection relays. Its
outstanding power, 1000 VA, makes testing
electromechanical, high burden relays a
snap. High power demanding applications
such as knee point analysis on CTs and
long cycle testing of miniature breakers
are also possible with this easy-to-use,
fully protected test workhorse.
Download complete specifications atwww.noramsmc.com or call (918-622-5725)
Test Solutions by Noram-SMC Inc.Three Phase Testing
The brand new Mentor 12 features leading
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panel. It has an extensive choice of options
in the (6 volt and 6 current) power channel
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ogy.
Primary Current Injection TestingThe LET-1000-RD is designed to perform
most of the primary tests that are nec-
essary in substation commissioning. It
has sufficient power for all the primary
current injections to test the proper
function and wiring of all the elements
that compose the protection and mea-
suring section in a substation. (There are
also other models available.)
Circuit Breaker Analyzer & Microhmeter
Two Sets in One!
The PME-500-TR is a fast, easy-to-use in-
strument for the testing, maintenance and
commissioning of medium to high voltage
breakers. The display, a touch screen panel,
is the control interface of the unit and dis-
plays the results in graphic and numerical
format. A thermal printer has been built-in
so that the test results can be immedi-
ately printed.
Technical Trainingby NETA
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Share knowledge with your colleagues!Review information!
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Power Transformer Testingand Maintenance
Presented by Jim White, Shermco Industries
Critical Maintenance for Circuit BreakersPresented by Jim White, Shermco Industries
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.