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Electric Machinery Fundamentals (Solutions Manual) Part 8

Tham khảo tài liệu 'electric machinery fundamentals (solutions manual) part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | The resulting plot is shown below 6-3. A 2300-V 1000-hp 0.8-PF leading 60-Hz two-pole Y-connected synchronous motor has a synchronous reactance of 2.8 and an armature resistance of 0.4 . At 60 Hz its friction and windage losses are 24 kW and its core losses are 18 kW. The field circuit has a dc voltage of 200 V and the maximum I F is 10 A. The open-circuit characteristic of this motor is shown in Figure P6-1. Answer the following questions about the motor assuming that it is being supplied by an infinite bus. a How much field current would be required to make this machine operate at unity power factor when supplying full load b What is the motor s efficiency at full load and unity power factor c If the field current were increased by 5 percent what would the new value of the armature current be What would the new power factor be How much reactive power is being consumed or supplied by the motor d What is the maximum torque this machine is theoretically capable of supplying at unity power factor At 0.8 PF leading Note An electronic version of this open circuit characteristic can be found in fil p61_occ.dat which can be used with MATLAB programs. Column contains field current in amps and column 2 contains open-circuit termina __voltage in volts._ 152 Solution a At full load the input power to the motor is P pT P ech P re Cp We can t know the copper losses until the armature current is known so we will find the input power and armature current ignoring that term and then correct the input power after we know it. P 1 000 hp 7 6 W hp 24 kW 18 kW 7 8 kW Therefore the line and phase current at unity power factor is 1 788 kW 19 A A L V3 Ỵ PF V3 2300 V 1.0 The copper losses due to a current of 198 A are 2 2 CU 3 M P 8 A 0.4 47.0 kW Therefore a better estimate of the input power at full load is P 1000 hp 7 6 W hp 24kW 8 kW 4 kW 8 and a better estimate of the line and phase current at unity power .