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June 11, 2007 A Penton Media Publication Vol. III No. 11



CONTENTS
Maintenance and Energy Savings

Electrical Troubleshooting Quiz

PF Capacitor Replacement

NEC at the Facility

NFPA 70E

Let's Go Racing! Win a Free Road America Race Weekend for Two.

Don't Miss These FREE Live Sessions Scheduled for June 14th in the EC&M e-Tradeshow

Answer to Electrical Troubleshooting Quiz


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MRO Insider addresses topics such as:

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  • Troubleshooting techniques
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    Maintenance
    Maintenance and Energy Savings
    Feeder maintenance practices can reduce energy waste. You can find several energy-saving opportunities, starting with your distribution transformers.

    Wherever you have liquid-filled transformers, take advantage of the various tests they permit. What about dry-type distribution transformers? Contrary to popular opinion, dry-type distribution transformers can (and should) be maintained. Unfortunately, they typically receive no maintenance. The inevitable results are higher costs and shorter times between failures.

    True, you can't employ all of the predictive maintenance tests with dry-types that you can with liquid-filled transformers. But there's still plenty you can do to reduce energy waste while improving reliability.

    Thermal analysis will reveal defective connections, leaking insulation, and other defects, if conducted by a qualified person who knows what to look for. The investment typically pays for itself several times over.

    One of the easiest tests to perform, especially with the newer test equipment, is the insulation resistance test. This can warn you of potential winding faults and other issues before they result in failure. A catastrophic failure may cause more than just loss of power. It can cause loss of life plus massive property damage.

    An insulation resistance testing program is most effective if you trend results over time. Insulation deterioration is normal, so as you plot the results you will gradually see a gently sloping downward trend. When this trend suddenly "breaks" -- that is, the gentle slope starts to nosedive -- you have evidence of impending failure. Schedule a replacement before failure occurs.

    Vented units accumulate dust, which is a thermal insulator. You can remove most dust with a vacuum cleaner, though more robust cleaning methods may be required. Caution: De-energize transformers before cleaning. For one thing, the static charge on a plastic vacuum cleaner nozzle is a potential fault path. For another, blindly reaching into an energized transformer is likely to prove suicidal.

    Finally, be diligent about maintaining clearances around transformers so they have proper ventilation.


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    Repair
    Electrical Troubleshooting Quiz
    This is an actual case history. Over a period of a few weeks, several loads on the same feeder dropped out inexplicably and the breaker for this feeder tripped several times. The drawings showed only 75% load. What is the first step in solving this problem?

    The answer to this question appears at the end of this newsletter.


    PF Capacitor Replacement
    Power factor (PF) correction at the service allows you to avoid a PF surcharge from the utility. If service PF capacitors fail, you'll probably incur a PF surcharge until they've been replaced.

    However, exact replacements may be incorrect. Existing capacitors may be sized for a different inductive load than what you have now. Since the original installation, it may be true that:

    • Inductive loads have been added, making the capacitors undersized.
    • Inductive loads have been removed, making the capacitors oversized.
    If PF is now "borderline," a minor change can result in a PF surcharge. System inductance may have changed significantly since the original installation, even if you haven't added or removed motors. PF-corrected motor drives replaced with uncorrected drives put motors back into the PF picture. Lighting design changes can also change the total inductive load.

    PF correction at the service lowers your electric bill. But it doesn't address PF-related losses within your facility. To do that, correct PF at individual inductive loads.

    It's more effective and less costly to address PF correction via a planned program, rather than reacting to a failure. The two steps are:

    1. Calculate the PF correction for your largest inductive loads (consult your drive manufacturer for motor PF correction).
    2. Calculate the service PF correction for the remaining inductive component.
    If you've already PF-corrected some loads, ensure your service PF correction capacitors are properly sized for the remaining inductance. Too much PF correction might not trigger a surcharge, but either direction from unity results in more energy consumption.

    Finally, don't buy new PF correction capacitors without taking a close look at lid designs. Choose a unit that will permit replacement of single capacitors with the least amount of hassle.


    Operation
    NEC at the Facility
    Junction boxes and other enclosures often have unused openings. These need to be properly plugged [408.7]. Duct tape doesn't count. Caps made specifically for that purpose are inexpensive and easy to apply, making it a snap (literally) to maintain the integrity of your enclosures.


    NFPA 70E
    The latest revision of this standard strongly discourages "working hot." However, there are some things you just can't do with the power off. Voltage measurements, power analysis, and thermal imaging all require the equipment to be energized. You can probably think of many more tasks that must be done with the power on.

    One impetus for the "don't work hot" slant of the latest NFPA 70E is the persistent assumption that circuit breakers provide personal protection. But a circuit breaker or fuse might never trip on a low-grade fault. A breaker isn't designed to protect people. It's designed to protect conductors from melting due to excessive current.

    If you work around energized equipment, use the correct personal protective equipment (PPE) and follow the relevant procedures for shock and blast protection.


    Show & Events
    Let's Go Racing! Win a Free Road America Race Weekend for Two.
    EC&M magazine and Generac Power Systems have teamed up to offer an expenses-paid weekend (August 10-12, 2007) featuring two of the world's fastest racing series. The third annual Generac Power Weekend is one thrilling day of American LeMans series racing (the Generac 500) and an equally exciting day of Champ Car racing at its finest (the Generac Grand Prix). It's your chance to see both series compete in a single weekend at one of North America's most beautiful tracks. Located in the hilly heart of Wisconsin's scenic Kettle Moraine area, Road America is a four-mile permanent road course that tests drivers with 14 challenging turns.

    Enter by July 10, 2007. Visit the Generac Power Systems virtual booth at the EC&M E-Tradeshow. Full contest rules are available online in the Generac E-Tradeshow booth. For more information about the Generac Power Weekend, go to www.roadamerica.com.



    Don't Miss These FREE Live Sessions
    Scheduled for June 14th in the
    EC&M e-Tradeshow

    • "Major Energy Savings Through Lighting Management" presented by Patrick Kelly, Encelium, at 10:00 a.m. Eastern and Pacific time
    • "Mitigating Harmonics in Industrial Environments" presented by John Houdek, Allied Industrial Marketing, at 10:00 a.m. Eastern and Pacific time
    Before and after the conference sessions, visit the many exhibitors in this virtual tradeshow and take a look at the On-Demand Theater, where you can view past online webcasts 24 hours a day, 7 days a week, 365 days a year.

    Click here to access the EC&M e-Tradeshow and attend one of these FREE live events.


    Quiz Answers
    Answer to Electrical Troubleshooting Quiz
    The first step is to take the drawings in hand and physically walk down this feeder. That's what this engineer did, thinking he'd find the "missing load" that was "left off" of the drawings. This "missing load" wasn't on the drawings, because it was an artificial load.

    The 480V feeder fed a stepdown transformer that supplied 120V to several panels. The transformer and panels were in an unventilated equipment room (roughly 8 feet x 12 feet). When he opened the door, the heat about knocked him over. It was worse for the equipment.

    Cardboard boxes stacked neatly against transformer vent openings blocked airflow across the windings. Boxes stacked on top of the transformer provided significant thermal insulation. The big surprise was that those boxes hadn't yet ignited.

    The engineer decided the transformer was operating at saturation because it hadn't been derated for high-temperature operation. He removed the rogue materials from the room and had upper and lower vents installed in the door. The problems never occurred again.



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