Training Manual on Energy Efficiency - APO Asian Productivity ...

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<strong>Training</strong> <strong>Manual</strong> on Energy Efficiency for Small and Medium Enterprises Motor efficiency versus load Figure 6-3 Load and power Output Input−Losses 746×HP Output Efficiency = ×100 = ×100 = ×100 Input Input Watts Input Electric motors are electromagnetic energy converters whose function is based on the force exerted between electrical currents and magnetic fields, which are usually electrically excited as well. Due to their principle of functioning, electric motors have a relatively high efficiency. A typical efficiency value for an 11 kW standard motor is around 90%, for 100 kW, up to 94%. The efficiency levels of large motors are higher than those of smaller motors. It should be noted that peak efficiency occurs at about 75% loading and drops significantly when loading is below about 30%. Core losses: Stator and rotor resistance losses: 6.3 THE TYPES OF MOTOR LOSS Core loss is around 22% of total loss at full load. Core losses represent the energy required to magnetize the core material (hysteresis) and are expended by small electric currents that flow in the core (eddy currents). Core loss of a motor is constant and is independent of the motor load current, and thus it accounts for a much higher percentage of the losses at low motor loads. Loss due to stator and rotor resistance is about 56% of total loss at full load. It occers due to the current flow (I) through the motor conductors of resistance (R). Loss is proportional to the square of the stator and rotor current and is also called I2R loss; it is influenced largely by loading on motor. - 58 -
Friction and windage losses: Loss due to friction and wind represents about 11% of total loss at full load. This loss results from friction within the shaft bearings and from the resistance to air being circulated through the motor by cooling fans. It depends on bearing quality and condition to a great extent. - 59 - Energy Efficiency in Electric Motors Stray load losses: Stray load loss is about 11% of total loss at full load. Stray load loss results from leakage of magnetic flux, and depends on the rotor slot design. Like I2R losses, it is dependent on the square of the load current and tends to increase with motor load. 6.4 ENERGY EFFICIENCY OPPORTUNITIES IN MOTORS Two approaches, namely a systems approach and operational measures, can be adopted for energy efficiency improvements in motors. 6.4.1 Systems approach The key to systematic or large energy savings in motors involves several fundamental procedures: • Switching off equipment when not needed. • Providing energy-efficient capacity controls (variable frequency drives or VFDs) instead of throttling. • Process re-engineering for reducing work done. 6.4.2 Operational measures Operational measures for energy efficiency include the following: Maintain voltage close to rating: Although motors are designed to operate within 10% of nameplate voltage, large variations significantly reduce efficiency, power factor, and service life. When operating at less than 95% of design voltage, motors typically lose 2 to 4 points of efficiency, and service temperatures increase up to 20 º F, greatly reducing insulation life. Running a motor above its design voltage also reduces power factor and efficiency.
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The opinions expressed in this publ
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2.5 Boiler water treatment 14 2.6 E
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7. ENERGY EFFICIENCY IN PUMPS 64 7.
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LIST OF TABLES 1-1 Gross calorific
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6-1 Induction motor 56 6-2 Boosting
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FOREWORD With the rising costs of e
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Annex S. No. Enconomic Opportunity
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