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Power factor

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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