Tham khảo tài liệu '(mcgraw-hill) (instructors manual) electric machinery fundamentals 4th edition episode 1 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 5-21. Assume that the generator is connected to a 480-V infinite bus and that its field current has been adjusted so that it is supplying rated power and power factor to the bus. You may ignore the armature resistance Ra when answering the following questions. a What would happen to the real and reactive power supplied by this generator if the field flux and therefore EA is reduced by 5 . b Plot the real power supplied by this generator as a function of the flux Ị as the flux is varied from 75 to 100 of the flux at rated conditions. c Plot the reactive power supplied by this generator as a function of the flux Ộ as the flux is varied from 75 to 100 of the flux at rated conditions. d Plot the line current supplied by this generator as a function of the flux Ộ as the flux is varied from 75 to 100 of the flux at rated conditions. Solution a If the field flux in increase by 5 nothing would happen to the real power. The reactive power supplied would increase as shown below. The reactive power 135 b If armature resistance is ignored the power supplied to the bus will not change as flux is varied. Therefore the plot of real power versus flux is c If armature resistance is ignored the internal generated voltage EA will increase as flux increases but the quantity EẤsin 8 will remain constant. Therefore the voltage for any flux can be found from the expression Ea f - i EAr Wr and the angle 8for any Ea can be found from the expression 8 sin-11 sin 8 E V Ea where Ộ is the flux in the machine ộr is the flux at rated conditions EAr is the magnitude of the internal generated voltage at rated conditions and 8r is the angle of the internal generated voltage at rated conditions. From this information we can calculate IA for any given load from equation T E A - V A jXs and the resulting reactive power from the equation Q 3VệIA sin e where e is the impedance angle which is the negative of the current angle. Ignoring Ra the internal generated voltage at rated conditions is E A V jXs IA
