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November 26, 2007 A Penton Media Publication Vol. III No. 22


CONTENTS
Optimize Your Predictive Maintenance System, Part 1

Motor Maintenance Tip, Part 1

Electrical Troubleshooting Quiz

Common Repair Mistakes, Part 3

NEC in the Facility

Electrical Safety

Answer to Electrical Troubleshooting Quiz



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About This Newsletter
This twice-a-month
e-newsletter is brought to you from the publisher of EC&M magazine.

MRO Insider addresses topics such as:

  • Working with management and supervision
  • National Electrical Code® on the production floor
  • Safety procedures and programs
  • Troubleshooting techniques
  • Equipment maintenance and testing tips
  • Managing motors and generators
  • Trends in training and education
  • Managing energy use


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    Maintenance
    Optimize Your Predictive Maintenance System, Part 1
    Predictive maintenance (PdM) allows you to detect and correct emerging problems before they bring you down. Planned repair of a problem is far less expensive than an unplanned shutdown caused by that problem. How well do you implement the following three PdM methods?
    1. Infrared thermal analysis. Experience has unveiled uses far beyond finding high-resistance connections. If you aren't aware of the latest uses and methods, schedule some infrared classes for the earliest available time.
    2. Ultrasonic surveys. Plant air is expensive. Use ultrasonic leak detectors to locate and eliminate leaks. Leak elimination extends the life of your plant air system while automatically reducing plant air problems such as water accumulation. Reducing the load on plant air compressor motors, which tend to be large, correspondingly reduces power usage. This alone may get you past that peak load problem.
    3. Visual inspection. Maintenance forms often call for "visual inspection," but seldom with structure. To make visual inspection meaningful, ask for specific, measured quantities. For example, the form shouldn't ask "Temperature normal?" It should ask the tech to record the actual temperature.
    We'll examine more PdM methods in Part 2.


    Motor Maintenance Tip, Part 1
    Identify the top failure causes. One approach is to analyze failure data over some period, perhaps a year, and then apply Pareto analysis.

    This analysis allows you to identify the causes behind 80% of motor failures. These will probably be 20% of the known causes. Rather than spread your maintenance resources across all motor failure causes, focus on that 20%.

    A useful analysis requires accurate failure reports. Develop a list of causes plus an "other" choice. This gives you "check-the-box" recording and standardizes the data. You need "other" so people aren't forced to choose something "close" if it's not the actual cause.

    Plot the number of occurrences per cause on a spreadsheet, create a chart, and sort by number of occurrences. Then, you'll know where to invest motor maintenance resources.


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    Repair
    Electrical Troubleshooting Quiz
    The controls for a 75-hp motor in a key conveyor system pass all of the electrical checks prescribed by your motor repair shop. Yet, the motor overloads trip in mid-shift for no apparent reason, and you have to wait nearly an hour before the motor will restart. How should you begin troubleshooting this?

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


    Common Repair Mistakes, Part 3
    You may have read motor troubleshooting guides that take an exclusively electrical approach to motor repairs. Yes, motors are electrical devices. They are also mechanical devices. When doing motor repairs, you must address mechanical issues and not just electrical ones.

    For example, a motor fails due to a burned winding. So, you send that motor out for a rewind. What caused that winding to fail? In the following list of contributing factors, which ones are electrical?

    • Misaligned coupling.
    • Motor foot bolt overtightened, causing misalignment.
    • Motor air filter clogged.
    • Motor vent clogged.
    • Insufficient airflow around motor.
    • Wrong insulation (heat) rating for the application.
    • Vermin intrusion.
    • Dirt, low oil, or wrong oil in gearbox.
    • Operators perform multiple restarts in rapid succession.
    None of these are electrical. Nevertheless, they all contribute to premature winding insulation failure by causing the motor to draw extra current or overheat. You can take ohmic measurements all day long and never identify these problems.

    Interestingly enough, a test instrument originally meant for electrical troubleshooting can reveal the existence of all but one of these mechanical problems. You probably have that very instrument: a thermal imaging device. This will do the trick, provided you know how to use it. The one problem it probably won't reveal is vermin intrusion. However, you can detect that visually by looking for droppings and stains. Also, be alert for the telltale odors rodents leave behind.

    Yes, take those ohmic measurements and fix the problems you find. But don't overlook the mechanical factors, or uncorrected problems will cause déjà vu.


    Operation
    NEC in the Facility
    Before doing design work involving motors, look closely at the application. For example, if you're installing an HVAC system, you must follow the special requirements for HVAC motors in Article 440. If you're installing fire pumps (Article 695), the very purpose of overload protection is different from that in other applications.

    Fortunately, you don't have to guess what the nearly three-dozen special applications are or comb through the entire NEC for each motor-related job. See Table 430.5 for a complete listing of applications and governing Articles.


    Electrical Safety
    As colder weather moves in, a safety issue invariably arises on multi-building sites. When you come in from the outside, your safety glasses fog up. Naturally, you need to remove those glasses to remove the fog. If you're entering an office, this normally doesn't pose any safety issues. But what if you're entering an area with energized equipment -- for example, a transformer vault or fire pump house?

    Here are three tips:

    1. Ask your safety manager if the company can supply antifogging wipes or sprays to prevent fogging. If not, invest your own $1.98 to protect your eyes.
    2. Have two pairs of safety glasses. Keep one in an inner pocket, where it can stay warm. Switch glasses just before entering the heated room.
    3. Turn away from energized equipment before removing your glasses. Wipe away the fog and put the glasses back on before turning around.

    Quiz Answer
    Answer to Electrical Troubleshooting Quiz Thermal overloads protect the motor from overheating [Article 430 Part III] and should prevent restart of an overheated motor. Heat is definitely an issue, or you could restart much sooner. Mid-shift shutdowns also indicate a thermally related problem.

    Use a thermal imaging camera to inspect the motor body, motor vents, motor caps, couplings, and driven load. If you find excess heat in any of these, you have isolated the problem and can more quickly determine the cause.


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