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CONTENTS
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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
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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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The designations "National Electrical Code” and “NEC” refer to the
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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?
- 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.
- 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.
- 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:
- 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.
- 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.
- 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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