INDUCTION__MOTOR

INDUCTION__MOTOR - LECTURE NOTES ON INDUCTION MOTOR Facts...

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Unformatted text preview: LECTURE NOTES ON INDUCTION MOTOR Facts about IM About 65% of the electric energy in the United States is consumed by electric motors. In the industrial sector alone, about 75% is consumed by motors and over 90% of them are induction machines. Why IMs are popular they are rugged reliable easy to maintain relatively inexpensive. Their power-to-density ratios (output power to weight) are higher than some other motors. a b c i i i Rotating Field b a c Time t 1 t 3 t 2 i a i c i b b c a a c b max 2 3 max 2 3 - max 2 3 max 2 3 - max 2 3 - max 2 3 max 2 3 max 2 3 max 2 3 At t 1 At t 2 At t 3 i a i c i b b c a Rotating Field min / rev f 60 sec / rev f n s = = The speed of the airgap flux is one revolution per one ac cycle. The time of one ac cycle The speed of the airgap flux f 1 = Number of Poles i a i c i b i a i b i c Number of Poles If each phase has one coil, it is a two-pole machine The rotor moves 360 degrees for one complete ac cycle. If each phase has two coils, it becomes 4- pole machine The rotor moves 180 mechanical for every one complete ac cycle. Number of Poles min / rev p f 120 pp f 60 n s = = Why IM rotates? i l B F v l B e = = ) n , ( f e = ) i , ( f T = Apply 3-phase to Stator Apply 3-phase to Stator Field rotates in airgap Voltage induced in rotor circuit e = B l n Torque is developed in rotor wdgs f = B l i Motor rotates z e i = e i Apply 3-phase to Stator n = 0 Voltage induced in rotor circuit e = B l n = 0 Torque is developed in rotor wdgs f = B l i = 0 Motor slows down What if motor speed is n s ? z e i = = Apply 3-phase to Stator Load demands certain Torque Motor develops equivalent force f = B l i What is the motor speed?...
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INDUCTION__MOTOR - LECTURE NOTES ON INDUCTION MOTOR Facts...

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