UFC 3 -520-01
June 10, 2002
Figure B -4. Adjustable Speed Drive Economic Evaluation
Adjustable Speed Drive
Economic Evaluation
Obtain Motor Nameplate Data and
Motor Service Factor Rating
Monitor Motor Performance to
Determine Actual Load Profile
and Existing Energy Usage
Calculate ASD Energy Usage at
Lower Operating Speeds
Determine if Harmonic Distortion
Effects Will Require Additional Filtering
Determine Energy Cost and
Calculate Estimated Savings
Estimate ASD Installation Cost
and Calculate Payback Period
B-7.2
The key to an economic evaluation is to determine whether or not the motor
will be fully loaded under e xpected operating conditions. If the motor is always loaded
at or near 100 percent of rated load, then little if any savings will be realized.
Fortunately, it is common to discover that the actual load current is significantly less
than rated. For example, Figure B -5 shows a typical case in which a 60 horsepower
(44,800 watts) motor normally operates at a load of less than 24 kW. In this case, an
ASD can provide substantial savings.
B-10
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