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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

    EconomicallyMeasure Resistances withVanguards Family of Test Instruments.

    Measures Contact/Resistor time

    Measures Contact Stroke, Velocity

    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

    Built-in 2.5-inch Thermal Printer

    Store 63 Records

    Download Test Records to PC

    Controlled Rise/Fall of Load Current

    Range from 1 Micro-Ohm to 300 Milliohm

    Prevents Tripping of Bus Differential Relay

    Built-in 2.5-inch Thermal Printer

    Store 63 Test Records Weight: 18 lbs

    Simple to Operate Test Over Current/Voltage Relays

    250A Instantaneous Current

    Test CT Saturation

    Test CT Turns Ratio

    CT-7000 Circuit-Breaker

    Time & Travel Analyzer

    DIGITIMER Circuit Breaker

    Time & Travel Analyzer

    EZCT 2000Automatic CT Test Set

    RFD-200

    Single Phase Relay Tester

    ATO 400P/600PMicro-Ohmmeters

    DMOM 100/200: True100/200Amp DC Micro-OhmMeters

    WRM-40Winding Resistance Meter

    ATRT-01, 01B, 01D

    Transformer Ratio Tester

    ATRT-03, 03A, and 03BThree-phase TransformerTurns-Ratio Meter

    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 determine