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CONTENTS
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Maintaining Batteries, Part
1
Maintaining for Energy
Savings, Part 2
Electrical Troubleshooting
Quiz
Solving for Motor Heat
NEC in the Facility
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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Maintenance
Maintaining
Batteries, Part 1
Until recently, data centers were about the only places
where you’d find racks of stationary lead acid batteries. A factory
might have a small point-of-use UPS in the accounting office and a few
more for things such as the plant Ethernet and the emergency phone
system.
Special equipment wasn’t needed for maintaining the small VRLA
batteries that backed up this handful of systems. Maintenance was
basically a matter of battery replacement on a regular schedule or when
the UPS began to give off a bad smell.
Today, many facilities have racks of lead acid batteries.
Unfortunately, the maintenance program in many cases is identical to
that for the small systems. Realizing that calendar or failure-based
replacement is insufficient, some users have added hygrometer testing
in
the mistaken belief it tells them the condition of the battery.
This under-maintenance leaves the batteries unable to support the
load
upon power loss, defeating the purpose of having the batteries in the
first place. Furthermore, calendar-based replacements invariably result
in wastefully replacing good batteries. In Part 2, we’ll explain some
basic strategies for keeping reliability up and costs down.
Maintaining
for
Energy Savings, Part 2
Just about every production facility has undergone
extensive modifications, for reasons such as expansion, refurbishment,
or production changes. The building structure modifications
include:
- Addition of wall-mounted equipment.
- External add-ons of rooms as new buildings.
- Relocation of windows or doors.
- Temporary openings (e.g., when installing new equipment).
These modifications create opportunities for leaks in the building
envelope, resulting in energy loss and added load on the HVAC. If
you’re smart, you already do infrared thermography on your power
distribution equipment. Apply this same technology to the entire
envelope of your building(s), especially at corners, seams, and joints.
Begin with a thorough scan of each room that has an outside wall and
plug all the holes. After that, routinely conduct a thermographic scan
after any penetration of the building envelope. You may want to check
the performance of doors and windows annually.
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Repair
Electrical
Troubleshooting Quiz
A critical motor has failed. Based on discoloration of
the rotor and bearings, you determined that overheating killed the
motor. But what caused the overheating?
- The MCC has inputs to your central power monitor. The power logs
showed no evidence of voltage imbalance.
- The motor is properly ventilated, lubricated, and aligned.
- The motor was balanced at the motor shop and inspected before
installation.
- The motor is the correct size, type, and heat rating for the
application.
- The motor drives a gearbox, which operates freely and shows no
signs
of overheating.
Because this is the second motor failure in two months, you’re under
pressure to find what caused this motor to overheat. The previous motor
lasted 17 years, and there have been no configuration changes in the
last four years. What is your next troubleshooting step?
Solving for Motor
Heat
Overheating is the main cause of motor failure. Just
replacing a failed motor with a new one doesn’t solve the overheating
problem and thus is not a complete repair. Fortunately, a dead motor
provides clues as to what killed it.
Discolored paint is an obvious sign of overheating. Nevertheless,
its
absence doesn’t mean heat wasn’t the culprit. Look inside the motor
for burns or scorch marks on the rotor, windings, and bearings. Also,
see if the bearing grease has “coked” into a hard substance.
The most common cause of motor overheating is voltage
imbalance. The source of this could be anywhere between the service
distribution panels and the motor. To complete the repair, locate and
correct the underlying cause of the overheating.
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Operation
NEC in the
Facility
Don’t be intimidated by Hazardous Location Classes
and
Divisions, as covered in NEC Chapter 5. They are much simpler than they
seem.
If an area contains:
- Flammable gases or vapors, it’s Class I.
- Combustible dust, it’s Class II.
- Combustible fibers, it’s Class III.
Do you see the pattern? The larger the particle, the higher the Class.
But what about Divisions? Just remember normal and abnormal. If the
area meets a Class designation during normal operations, it’s
Division
1. If it meets that designation during abnormal operations, it’s
Division 2.
Safety
Jewelry and electrical work are mutually exclusive. The
most obvious reason is that jewelry helps form a conductive path, but
jewelry can be deadly even without direct contact to energized
components. One reason is it increases the risk of flashover. Another
reason is that dangling jewelry can get caught in rotating parts.
Piercings and metallic implants are increasingly common among
younger
workers. Although they may seem like part of the body, it doesn’t
make
them any less dangerous. They are still jewelry and are still too
dangerous to wear when doing electrical work.
Quiz Answer
Answer to
Electrical Troubleshooting Quiz
The fact that this motor failed so soon after
installation indicates a problem with the installation.
We know that overheating killed this motor. We also know that
voltage
imbalance is the No.1 cause of overheating. The power monitor
doesn’t show imbalance, but the input to the power monitor is back at
the MCC and not at the motor itself.
Before you disconnect the motor leads, use an insulation resistance
tester (not a 9V DMM) to measure across each wire joint at the motor.
You probably have one high-resistance wire joint, and this is how you
will find it.
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