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Power factor

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A single phase electric motor has an output power of 10 kW and an efficiency of 90% at full load. The motor is fed from a 240 V supply via a cable that has a resistance of 10 milli ohms per metre length. If the terminal voltage to the motor must not fall below 90% of the supply voltage, calculate the maximum return length of the cable for a motor power factor of:

A. unity

B. 0.8 (sketch a circuit diagram and phasor diagram, the motor and line voltages are no longer in phase)

C. The power dissipated in the cable for each of the above two cases.

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Three-Phase Induction Motor

A three phase Y-connected 480 V (line to line) 30 hp 60 Hz four pole induction motor has the following equivalent circuit constants in Ohms-per-phase referred to the stator:

R1=0.21 R2= 0.20 X1=1.2 X2=1.1 Xp=39

The total friction windage and core losses may be assumed constant at 1340 Watts. The motor is connected directly to a 480 V source. Compute speed, shaft output torque in Nm, power in horsepower, efficiency, and terminal power factor for slips of 1, 2, and 3 %.

If need be, please scan your handwritten solution and submit that so I can get an idea of the direction I need to go. Thanks,

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