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Once
a system is correctly installed, it must be maintained and
operated in an appropriate manner to keep losses from increasing.
Opportunities to maintain or increase energy efficiency exist
in mechanical power-transmission systems, improved equipment
lubrication, and better system maintenance. Better practices
can also take the form of simply minimizing "bad" maintenance.
For example, Southwire Company stopped repainting its motors
after discovering that painting resulted in increased motor
temperature. E Source estimates that optimal operation and
maintenance practices could save 3 to 10 percent of all drive
power (E Source. 1999.
Drivepower Technology Atlas Series, Volume IV. Prepared
by B. Howe, A. Lovins, D. Houghton, M. Shepard, and B. Stickney.
Boulder, Colo.: E Source, Inc.).
Belts
Most
motors are connected to their loads through a transmission
system, most frequently a belt. While V-belts are the most
common type, three other types are available that can offer
greater efficiency. Cogged V-belts can be used with the same
sheaves and pulleys while lasting twice as long and requiring
less frequent adjustments. Efficiencies with cogged V-belts
are greatest when used with the smallest appropriate pulley.
Likewise, flat and synchronous belts can offer improved efficiency
when their unique operating characteristics are taken into consideration (Energy-Efficient Motor Systems Handbook).
While
V-belts are rated at 90 to 98 percent efficiency when properly
installed and maintained, in practice many operate well below
the 90 percent efficiency level. A recent review by E Source
of five studies in which V-belts were replaced with cogged
V-belts reported savings of between 0.4 and 10 percent with
a median savings of 4.1 percent. At the 4.1 percent savings
level, the payback from energy savings alone ranged from 1
to 5 months. Similar savings are reported in a Ford Motor
Company case study. Likewise, the selection of efficient gear
drives can result in similar savings (Energy-Efficient Motor Systems Handbook).
Lubrication
The past
20 years have seen significant advances in lubricants, especially
with the introduction of synthetic-based products. Many of
these products have improved resistance to deterioration and
extended lives. The selection of premium lubricants can also
reduce energy losses in various motor and driven devices.
Energy savings of 3 to 20 percent have been realized in gear
reducers, compressors, and motors. In many cases, the additional
cost can be more than justified, just by longer lubricant
life.
Proper
lubrication maintenance can insure that the benefits of the
investment in better lubricants is realized. Different types
of lubricants should not be mixed, as they may react, causing
a loss of the beneficial properties. For greasing bearings,
it is important to routinely purge the grease, which will
remove the old grease that has lost its lubricating properties.
Ideally, the bearings should be rebuilt. Since this is frequently
impractical, at least fresh grease should be pumped into the
grease fitting while the motor is running until clean grease
is forced out of the drain plug.
Too much
lubrication can be as bad as too little. Over-lubrication
can hasten bearing failure by increasing hydrostatic pressure
in the bearings, blowing out seals, and introducing contamination
into the bearings. One expert reports that 80 percent of lubrication
is over-lubrication. It is important that manufacturer recommendations
be followed (Energy-Efficient
Motor Systems Handbook).
Predictive Maintenance
Beyond
regular lubrication and adjustment of the mechanical transmission
systems, modern sensors and our understanding of motor systems
are beginning to allow us to predict when a failure is likely
to occur. As mentioned in the section Specifying
a Quality Motor Repair, many motor failures occur
when a mechanical component fails leading to overheating,
which produces an electrical failure. Among the tools available
for predicting failures are infrared optical sensors that
can be used to identify overheating wiring and bearings, vibration
sensors that can identify misalignment and bearing problems,
and electrical analyzers that can identify power supply problems
and even many mechanical problems such as bearing failure.
The key
to using all these tools is a good record-keeping system.
A number of commercial preventive maintenance programs allow
you to track motor systems. In addition, some motor inventory
systems, such as MotorMaster+®, that are used to manage
motor selection and repair decisions, can also record the
operating characteristics of the motors. If routine measurements
of current operating characteristics reveal a change, the
motor system can be scheduled for maintenance to correct the
problem before a failure occurs. If a motor can be "caught"
before it fails, it can be reconditioned at a fraction of
the cost of a rewind (Specifying
a Quality Motor Repair).
As noted
earlier, a motor can be reconditioned if it can be identified
before an electrical failure occurs.
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