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Explain energy conservation technique “by improving power quality” for induction motor.

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Energy Conservation by Improving power quality for Induction Motor: 1) Voltage 2) Frequency 3) Closeness of the supply to sine waveform, which also is a means for knowing the harmonic content of the supply.

1) Voltage: Maintaining the voltage at the rated value for motors results in the properly expected torque speed characteristics available to drive the load. Lower voltage leads to excessive current drawn due to which the line losses increase, machine copper losses increase, line voltage drops increase. Even if voltage is above required value higher flux density results in motors that leads to higher iron losses. These lead to decrease in efficiency. Hence proper voltage has to be maintained.

2) Frequency: It governs the speed related losses and iron losses. If its value is more than rated these losses increase as speed is directly proportional to the frequency the speed dependent friction & windage losses increase that will decrease the efficiency. Lower value of frequency leads to lower speed that affects the output power. Hence frequency has to be maintained at rated value.

3) When the supply waveform is purely sinusoidal the harmonics are absent which means no iron & copper losses due to harmonic voltage & currents. Also the harmonics even if very small lead to production of unwanted harmonic torques in motors which need to be overcome & this requires energy which is wasteful. Hence the supply voltage must be as near as possible to sine wave in case of AC motors.

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Energy conservation method in induction motor by improving power quality: Electrical energy can be conserved by improving the power quality. It can be achieved by avoiding voltage unbalance, maintaining voltage & frequency value and avoiding harmonic distortion.

i) Voltage unbalance: Three phase induction motors are designed to operate on a balanced three phase A.C. Supply. In unbalanced condition the voltages in three phases are unequal which may cause a significant problem to motor such as excessive heating and vibrations. This condition leads to increase in the I2R loss in motor.

ii) Maintaining voltage & frequency value: Maintaining the frequency and the required form factor of 1.11 (sine wave) minimizes the harmonics, and iron / mechanical losses as the speed is maintained at specified value.

iii) Harmonic distortion : Increased use of the power electronics devices in the system leads to add the harmonics in a supply frequency. Undesirable effect of these higher frequencies related to the harmonic voltage distortion causes increase in iron and copper losses in motor. These losses can be minimized by using harmonic filter thus reducing the harmonics in the system.

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