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Activity Answer the given problems. Show complete solution and box the final answers. A. A 480-V, 60 Hz, four-pole synchronous motor draws 50 A from the line at unity power factor and full load. Assuming that the motor is lossless, answer the following questions: (a) What is the output torque of this motor? Express the answer both in newton-meters and in pound-feet. (b) What must be done to change the power factor to 0.8 leading? Explain your answer, using phasor diagrams. (c) What will the magnitude of the line current be if the power factor is adjusted to 0.8 leading?
B. A 480-V, 60 Hz, 400-hp 0.8-PF-leading six-pole A-connected synchronous motor has a synchronous reactance of 1.1 and negligible armature resistance. Ignore its friction, windage, and core losses for the purposes of this problem. (a) If this motor is initially supplying 400 hp at 0.8 PF lagging, what are the magnitudes and angles of EA and IA? (b) How much torque is this motor producing? What is the torque angle 6? How near is this value to the maximum possible induced torque of the motor for this field current setting? (c) If EA is increased by 15 percent, what is the new magnitude of the armature current? What is the motor's new power factor? C. A 440-V. three-phase. Y-connected synchronous motor has a synchronous reactance of 1.50 per phase. The field current has been adjusted so that the torque angle 6 is 28° when the power supplied by the generator is 90 kW. (a) What is the magnitude of the internal generated voltage E, in this machine? (b) What are the magnitude and angle of the armature current in the machine? What is the motor's power factor? (c) If the field current remains constant, what is the absolute maximum power this motor could supply? D. The infinite bus in the figure below operates at 480 V. Load 1 is an induction motor consuming 100 kW at 0.78 PF lagging, and load 2 is an induction motor consuming 200 kW at 0.8 PF lagging. Load 3 is a synchronous motor whose real power consumption is 150 kW at 0.9 PF lagging. Determine the power factor the synchronous motor must be adjusted to in order to reduce the transmission power losses by 20%. Ind. motor 100 kW 0.78 PF lagging 200 kW Ind. Infinite bus 0.8 PF Transmission line motor lagging Synchr. 150 kW motor PF = ? Piot Plant ttttt ta