Civil Engineering Reference
In-Depth Information
Use of premium efficiency motors
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Operation of motors at or near the nameplate rating
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Premium Efficiency Motors
Premium efficiency motors have gained widespread use in recent years. Relative to
standard efficiency motors, they offer motor efficiency gains ranging from 1.0 percent
at 200 hp (150 kW) to 9.0 percent at 1 hp (0.75 kW) at 1,800 rpm. Table 30-4
summarizes efficiencies for premium efficiency (at 100 percent load) motors.
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Figure
30-7 illustrates full-load efficiency of standard and premium efficiency motors.
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Premium efficiency motors cost more than comparable standard efficiency motors.
For new installations, the extra cost of premium efficiency motors can usually be
recovered within a few years or less if the motors are operated more than 50 percent
of the time. In fact, where power costs are above $0.05 / kWh and motors are operated
more than 50 percent of the time, premium efficiency motors offer exceptional value
for new installations. Economics must be evaluated carefully where standard motors
are being retrofitted with premium efficiency motors. A methodology for determining
simple payback for conversion from standard motors to premium efficiency motors is
presented in Figure 30-8.
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Benefits of premium efficiency motors include the following:
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Lower energy costs.
Premium efficiency motors use energy more efficiently, and
their superior design may allow them to provide a higher power factor.
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Durability.
Because of the high-quality design and materials, premium efficiency
motors generally last longer, require less maintenance, and are more reliable—
resulting in less equipment downtime. Consequently, premium efficiency motors
often carry a warranty two to three times longer than that for a standard motor.
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Improved tolerance to overvoltage.
Many premium efficiency models are more
resistant to overvoltage conditions.
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Interchangeability.
Design improvements are internal to the motor and do not
affect the frame size or mounting dimensions.
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Lower noise.
Premium efficiency motors run more quietly than standard motors.
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To increase efficiency, emphasis is given to reducing the five major types of motor
losses:
Magnetic losses
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Windage and friction losses
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Stator losses
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Rotor losses
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Stray load losses
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To accomplish this goal, premium efficiency motors may include some or all of the
following design features:
High-grade electrical steel to reduce magnetic losses
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Longer core to lower flux density
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Increased cooling capacity to reduce magnetic and load losses
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