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CONTENTS
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Maintaining for Energy
Savings, Part 8
Electrical Troubleshooting
Quiz
Bottleneck Motor Repairs, Part
5
NEC in the Facility
Enroll In EC&M
University's
Online Arc Flash Courses
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
Maintaining
for
Energy Savings, Part 8
Power factor (PF) traditionally has been one of those
“set-it-and-forget-it” things. The basic idea is that inductive
loads cause vectors to shift in one direction, so you add capacitors to
shift them in the other direction and consequently operate close to
unity PF. But is that all there is to it?
If your facility never adds, modifies, or removes equipment, then
you
probably can “set it and forget it.” For most facilities, however,
such an approach is not practical and leaves money on the table. Plus,
it
can cost a lot of money.
One solution: Add a power survey to your preventive maintenance
procedures. A tech uses a portable power analyzer to determine PF and
other quantities on each feeder, perhaps annually.
A better solution: Set up your power monitoring system to monitor PF
on each feeder. The power monitoring system essentially does the PdM/PM
for you. Each time you correct PF on a given feeder, update the alarm
setting accordingly. Follow up on the alarms to solve for low PF and
for
PF variations.
Why are we talking about PF at the feeder level? If you correct it
at
the entrance, then you avoid the PF penalties from the electric
utility.
But that’s all you do.
You may have PF of 99% at the service and only 77% at the load. This
means the load has to draw significantly more power to do the same
amount of work. You aren’t paying the higher rate per kWH, but
you’re using far more kW each hour. Correct PF from the load toward
the service — not the other direction and not at just the
service.
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Repair
Electrical
Troubleshooting Quiz
You’ve received a work order to investigate a motor
that has been replaced three times in as many months. The supporting
documentation includes the repair history.
The first motor failure was attributed to overheating due to a
consistently high current draw caused by low PF at the motor. PF
capacitors were added when the second motor was installed.
The second motor failure was attributed to “inadequate
grounding.” The repair record doesn’t indicate how that was
determined or exactly how that was solved. However, it does state that
the grounding errors also caused the drive to fail and “ground less
than 25 Ω, ground added.”
Before you install the third motor, what should you do?
The answer to this question appears at the end of this
newsletter.
Bottleneck Motor
Repairs, Part 5
One key to fast repairs is the ability to quickly
determine what the repair action needs to be and what resources the
repair action requires. When a bottleneck motor is down, every minute
lost is revenue hit — that’s not the time to plan out the repair
job.
To reduce the amount of revenue lost, you should already have a set
of standard repair “templates” on file. Each covers a repair
procedure for a specific problem with that specific motor.
These repair templates are variations of a basic repair procedure
(in
a Web-based maintenance system, these can be linked directly from a
master repair document). Based on your troubleshooting guide for that
motor (also developed ahead of time), you proceed to the repair
procedure to which the troubleshooting guide refers you. The symptoms
indicate the problem is X, so perform repair procedure B (which
lists all of the relevant drawings and other information needed).
Using these documents, a repair crew quickly can determine what went
wrong, what repair actions to perform, and how to perform them. Because
you’re using a standardized methodology, there’s no trial by error
or other guesswork — you’ve done those things “offline” instead
of during downtime.
In our next issue, we’ll look at developing specific
troubleshooting guides and their companion repair procedures.
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Operation
NEC in the
Facility
Article 504 covers the installation of intrinsically
safe apparatus, wiring, and systems in Class I, Class II, and Class III
locations (defined in Art. 500.5) [504.1]. An intrinsically safe
circuit
is one that won't ignite due to spark or thermal effect of (flammable
or
combustible) material in the air, under prescribed test conditions
[504.2].
You’ll find those conditions prescribed in ANSI/UL 913-1997. What
you need to know is that anything that’s “intrinsically safe” is
listed as such. If you’re working on an intrinsically safe system,
replace any “intrinsically safe” apparatus with listed apparatus.
If it is part of an intrinsically safe installation, then you must
install it per the control drawing(s) [504.10(A)]. You need to do any
wiring per 504.20 and grounding per 504.50.
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Show & Events
Enroll In
EC&M
University's Online Arc Flash Courses
Need Arc Flash prevention training and continuing
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live,
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acknowledged expert.
- Clarifying NFPA 70E and IEEE 1584 Requirements (April 9)
- Impact of System and Operating Conditions on Arc Flash Energy
Levels
(April 21)
- High Resistance Grounding and Arc Flash Accident Prevention (May 7)
- Mitigation of Arc Flash Hazards Using Fuses (May 12)
- Arc Flash Testing Updates (June 16)
- Arc Flash Hazard Mitigation Case Studies (June 25)
For more information, go to www.ecmuniversity.com. To
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Quiz Answer
Answer to
Electrical Troubleshooting Quiz
It’s unlikely that the drive manufacturer recommended
installing those PF correction capacitors. External PF correction
generally does not work well with a motor drive. Those capacitors are
probably why the drive and second motor failed. The best solution for
PF
correction at a motor is almost always an upgrade to a PF corrected
drive.
The note “ground less than 25 Ω, ground added” tells us
someone misapplied 250.56. This NEC requirement has nothing to do with
motors. Grounding a motor at all is a waste of time and materials, and
driving a second rod is just more of the same waste. A motor is
properly
grounded when it isn’t grounded (connected to earth, see Art.
100 definition). Make sure the motor system is properly bonded
(Art. 100 definition and Art. 250, Part V).
Consult the drive manufacturer about PF correction. Removing the PF
capacitors and upgrading the existing drive will probably prevent
further failures.
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