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 Summary:
Is a Repaired Motor "Less Reliable"
Than a New One? With
trilingual summary
Purchase of the newest premium efficiency motors is
optional. Some technologists feel that their higher price is
justified not only by lower operating cost but also by higher
reliability compared to a repaired motor of lower efficiency.
Although electrical apparatus reliability is seldom precisely
defined, it's generally expressed by 1.0 minus an annual failure
rate.
That isn't especially helpful for electric motors. First, little
information exists on failure rates of large groups of identical
motors operating under identical conditions. Secondly, motor
"failure" can take many forms. Motors may be sent to the repair shop
for cleaning because of blocked ventilation passages (equally likely
for either new or repaired units); for replacement of a noisy
bearing; or for many other reasons other than a burned-out winding.
Some repairs can be completed quickly. Others take much longer. Once
returned to the owner, a repaired motor may go into long-term spare
storage (with consequently misleading service life data). Hence,
failure rate surveys performed in the United States between 1960 and
1990 are of limited value in assessing reliability of new vs.
repaired machines.
More recently, one manufacturer published data based on warranty
claims that indicated no difference between reliability of standard
and higher efficiency motors. Following the 1997 effective date of
the Energy Policy Act (EPACT), that issue became unimportant. Older,
less efficient designs could no longer be sold in the United States.
However, a new standard product line of still higher efficiency
("Premium") motors is now being marketed as a higher-priced option.
That has led to the question of relative reliability of those motors
compared to repaired units of either EPACT or pre-EPACT design.
Too few "Premium" motors are now in service to support a useful
failure rate survey. And no survey has ever been made of repaired
motor reliability. That would have to examine the nature of the
repairs; how they were made; and how often. A comparison would have
to recognize that higher efficiency motors do not necessarily
operate at lower temperatures (and that few motors fail from simple
thermal overload). For the present, then, there is no reason to
suppose that a properly-repaired motor is less reliable than a new
machine.
From
"Is a Repaired Motor "Less Reliable"
Than a New One?"
...by
Richard L. Nailen, EA Engineering Editor -
published in Electrical Apparatus January 2004.
© 2004
Barks Publications, Inc. All Rights Reserved.
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