Maintenance Technology April 2017 - 28

PREDICTIVE STRATEGIES

Add
Electrical
Motor
Testing to

Your PdM
Toolkit
This predictive approach
offers reliability benefits
that time-based
maintenance can't.

NUMEROUS STUDIES have tried to
establish guidelines for creating plant
reliability and efficiency. Depending
on which research is cited, the bottom
line is that between 65% and 75% of all
motor failures are mechanical in nature.
For that reason, vibration analysis, a
cornerstone of any predictive-maintenance (PdM) program, would appear to
provide the "biggest bang for the buck"
in pinpointing possible problems. Still,
while an aggressive vibration-analysis
program may accurately predict most
mechanical issues, it can't diagnose
the 25% to 35% of motor failures that
are due to electrical weaknesses and
faults. That's why electrical testing
is so important.
To put it simply, the insulation
system within a motor is the unit's
"heart"-and nothing but a series of
electrical tests can fully evaluate the
health and integrity of that heart.
Comprehensive evaluation involves

28 |

MAINTENANCE TECHNOLOGY

the use of static-testing and dynamicmonitoring technologies. To understand the benefits, it's important to
know why and how motors degrade.

Electrical testing of
a site's motors puts
personnel in the
reliability driver's seat.
Motor degradation
Various factors, including the initial
quality of a motor's insulation, affect
the pace at which it degrades. Since
heat is the main enemy of all insulation
materials, maintaining a cool, dry
environment will increase motor life.
Many things contribute to excessive
heat. Typically, the situation is acerbated by a combination of issues that

individually wouldn't create a problem.
High ambient temperature, numerous
restarts, starting under heavy loads,
slight misalignment, some unbalance
with the supply voltage, and contamination, all contribute to the heat a motor
experiences.
Another issue affecting the life of a
motor's insulation system is starting
and stopping. In fact, most plant-floor
personnel have, at some point in their
careers, heard the old saying that "if
you don't want your motor to fail, don't
start it, and if it's running, don't stop it."
Startup and, to some extent,
shutdown of a motor, are generally
the most stressful times in the unit's
life. Contactor and breaker "bounce"
at startup can generate voltage spiking
four or five times greater than the
operating voltage. The initial in-rush
of AC voltage, pushed by as much as
eight or 10 times the nameplate current,
"attacks" the insulation and greatly
APRIL 2017



Table of Contents for the Digital Edition of Maintenance Technology April 2017

Maintenance Technology April 2017 - 1
Maintenance Technology April 2017 - Cover1
Maintenance Technology April 2017 - Cover2
Maintenance Technology April 2017 - 1
Maintenance Technology April 2017 - 2
Maintenance Technology April 2017 - 3
Maintenance Technology April 2017 - 4
Maintenance Technology April 2017 - 5
Maintenance Technology April 2017 - 6
Maintenance Technology April 2017 - 7
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Maintenance Technology April 2017 - Cover3
Maintenance Technology April 2017 - Cover4
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