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

More documents

Recommendations

Info

6. ENERGY EFFICIENCY IN ELECTRIC MOTORS 6.1 INTRODUCTION Motors convert electrical energy into mechanical energy by the interaction between the magnetic fields set up in the stator and rotor windings. Industrial electric motors can be broadly classified as induction motors, direct current motors, or synchronous motors. All motor types have the same four operating components: stator (stationary windings), rotor (rotating windings), bearings, and frame (enclosure). Squirrel cage induction motors account for over 90% of the population. Motor speed Figure 6-1 Induction motor 6.2 SALIENT ASPECTS OF MOTOR PERFORMANCE The speed of a motor is the number of revolutions in a given time frame, typically revolutions per minute (RPM). The synchronous speed in RPM is given by the following equation, where the frequency is in hertz or cycles per second: 120 x Frequency Synchronous Speed (RPM) = Poles It can also be shown that the speed of an AC motor can be varied infinitely by changing the frequency. The actual speed at which the motor operates will be less than the synchronous speed. The difference between synchronous and full load speed is called slip and is measured in as a percentage. It is calculated using the following equation: - 56 -
Slip (%) = Synchronous Speed-Full Load Speed x 100 Voltage frequency relation Load versus power factor Synchronous Speed Impedance of an inductor is proportional to frequency. At low frequencies, this impedance approaches zero, making the circuit appear to be a short-circuit. To maintain a constant flux in the motor, the voltage to the motor must also be changed. This ratio is constant over most of the entire speed range By keeping the ratio constant, a fixed speed induction motor can be made to run at variable speed offering constant torque. At low speeds, due to the motor having inherent resistance in the windings, the ratio must be altered to provide enough magnetizing flux to spin the motor. The VFD allows this relationship to be altered by changing the voltage boost parameter. Figure 6-2 Boosting voltage As the load on the motor is reduced, the magnitude of the active current declines. However, there is not a corresponding reduction in the magnetizing current, with the result that the motor power factor declines, or gets worse, with a reduction in applied load. - 57 - Energy Efficiency in Electric Motors Application of variable frequency drives and variable speed drives, for capacity control of pumps, fans, compressors, process control, as against other conventional methods, is the most relevant energy conservation opportunity in the electric motor industry.
Page 2 and 3:
The opinions expressed in this publ
Page 4 and 5:
2.5 Boiler water treatment 14 2.6 E
Page 6 and 7:
7. ENERGY EFFICIENCY IN PUMPS 64 7.
Page 8 and 9:
LIST OF TABLES 1-1 Gross calorific
Page 10 and 11:
6-1 Induction motor 56 6-2 Boosting
Page 12 and 13:
FOREWORD With the rising costs of e
Page 14 and 15:
Training M
Page 16 and 17:
Training M
Page 18 and 19: Training M
Page 44 and 45: 4. ENERGY EFFICIENCY IN FURNACES 4.
Page 76 and 77: 7. ENERGY EFFICIENCY IN PUMPS 7.1 P
Page 88 and 89: 8. ENERGY EFFICIENCY IN FANS 8.1 IN
Page 100 and 101: 9. ENERGY EFFICIENCY IN COMPRESSED
Page 110 and 111: 10. ENERGY EFFICIENCY IN REFRIGERAT
Page 118 and 119:
Training M
Page 120 and 121:
Training M
Page 122 and 123:
Training M
Page 124 and 125:
Training M
Page 126 and 127:
Training M
Page 128 and 129:
Training M
Page 130 and 131:
Training M
Page 132 and 133:
12. CLEAN DEVELOPMENT MECHANISM 12.
Page 134 and 135:
Training M
Page 136 and 137:
Annex S. No. Enconomic Opportunity
Page 138 and 139:
Training M
show all

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

Create successful ePaper yourself

Delete template?

Save as template?