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In
most cases, the best opportunity to install a more efficient
motor is when a motor fails and must either be replaced or
repaired. At that time, the decision generally needs to be
made quickly. If an energy-efficient motor is not immediately
available, the motor will either be repaired or replaced with
a standard-efficiency motor. So it's important to move motor
decisions from panic to planning. Motor Decisions Matter
(MDM), a national campaign, was developed to encourage just
such sound planning.
By implementing
a management plan to deal with motor failures, a facility
can determine in advance the best motor decisions. Facility
managers can then work with suppliers to ensure that the products
and services are available when needed, either by purchasing
a spare motor or having the supplier stock a replacement.
If a facility does not already have a motor replacement strategy,
some type of planning should be implemented immediately to
avoid bad decisions and capture opportunities for significant
cost savings.
Several
approaches to developing a motor management plan follow.
- Develop
a set of criteria for all repair/replace decisions
- Make
repair/replace decisions in advance on specific critical
application motors
- Develop
a comprehensive motor inventory, a repair/replace decision
for each motor in the inventory, and a list of all spares
that can be used for different applications.
Rather than
three discrete strategies, these approaches represent points
on a continuum from simple decision rules to a comprehensive
inventory.
Simple
Decision Rules
Each
facility must develop motor decisions that fit its unique
situation based on factors such as electricity price, cost
of motor repair, and new motor discounts. An online reference,
like the MDM
Motor Planning Kit, or a tool, like the MotorMaster+® computer program
(WSU 2003), can provide some guidance into the economics of
different motor choices. Following is an example of a set
of general motor decision rules:
- Replace
all failed motors that operate more than 4,000 hours per
year with new NEMA Premium motors.
- Repair
all other failed standard-efficiency motors greater than
(some size) and replace smaller motors with new EPAct motors.
- Repair
all failed EPAct motors greater than (some
size) and replace smaller motors with new EPAct motors.
- Replace
any motor for which the repair cost exceeds 60 percent
of a new motor cost with a new motor of the same size
and speed.
This
process is illustrated in the following figure:
The size
thresholds above will vary depending principally on local
prices for electricity, new motors, and motor repair services.
The range for the repair/replace threshold can vary from 40
to 75 hp among facilities that use this approach. For failed
energy-efficient motors, the threshold is usually one or two
sizes smaller. In all cases where repair is called for, it
is important to have your motor repair shop evaluate the motor
before repairing it. Some types of failures may significantly
damage the motor such that it cannot be restored to reliable
and efficient operation.
Key
Motor Identification
A somewhat more comprehensive approach is to survey all the
motors in some facilities, or at least the larger and more critical
motors. During the survey, which motors should be repaired and
which should be replaced upon failure should be determined and
recorded. This survey can be conducted by plant staff or an
outside group. In the past, some electric utilities have offered
this service at a nominal change, though this is becoming less
common. Consultants, motor suppliers, and some state government
energy efficiency programs also offer this service.
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"Yellow
Dot" Motor Management
Carolina
Power and Light (CP&L) administered a simple program
in the 1980s where the utility assisted customers in
identifying, through audits, which motors should be
repaired and which replaced with energy-efficient motors
upon failure. Auditors identified motors with high operating
hours for which energy-efficient motors offered good
payback at time of motor replacement. Customers were
then encouraged to mark these motors with a large yellow
dot, and maintenance crews were instructed to install
a new efficient motor when a yellow dot motor failed. |
Motor Inventory
The most comprehensive approach to planning motor decisions
requires developing an inventory of motors at the facility (or
at the very least, the large and critical application motors).
This approach involves recording motor location, application,
size, speed, electrical specifications, date installed, and
estimated load and operating hours. In addition, some facilities
also record measured data such as motor speed, voltage and current
(by phase), and vibration. These data can then be used as part
of a preventive or predictive maintenance program to identify
problem motors before they fail. These motors can be replaced
or removed for repair as part of a routine maintenance schedule.
An overview of how to set up a motor inventory program is available
as part of the
MDM
Motor Planning Kit as well as from many utilities and motor
suppliers. Since most facilities have numerous motors, it is
often attractive to use a computer program to maintain the motor
inventory. A number of inventory tools exist, developed by private
parties, government, and utilities. DOE has made available the
MotorMaster+® computer program,
which includes an excellent inventory database tool.
The effort and cost of developing an inventory, however, can
be quite high. One approach is to build the inventory gradually,
starting with key motors and adding additional motors as repairs
or maintenance are performed in the area where the motors are
located. Alternatively, some consultants and motor suppliers
are beginning to offer this as a service. The service might
take several forms. In one form, a motor supplier may provide
motor inventory and management for a customer. In another, a
contractor may survey all motors in a facility and do routine
checks of key motor performance to attempt to predict failures
and implement preventative actions. Upon failure, the contractor
may replace or repair the motor depending upon economic and
operating conditions. |
