A 100 kW, 60 Hz, 1175 r/min motor is coupled to a flywheel by means of a gearbox. The kinetic energy of all the revolving parts is 300 kJ when the motor runs at rated speed. The motor is plugged to a stop and allowed to run up to 1175 r/min in the reverse direction

Question

A 100 kW, 60 Hz, 1175 r/min motor is coupled to a flywheel by means of a gearbox. The kinetic energy of all the revolving parts is 300 kJ when the motor runs at rated speed. The motor is plugged to a stop and allowed to run up to 1175 r/min in the reverse direction. Calculate the energy dissipated in the rotor if the flywheel is the only load.

Accepted Answer

During the plugging period, the motor speed drops from 1175 r/min to zero. The heat dissipated in the rotor is 3 × 300 kJ = 900 kJ. The motor then accelerates to nominal speed in the reverse direction. The energy dissipated in the rotor during this period is 300 kJ. By reversing the speed this way, the total heat dissipated in the rotor from start to finish is therefore 900 + 300 = 1200 kJ.

Question 14.4: A 100 kW, 60 Hz, 1175 r/min motor is coupled to a flywheel b...

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