EE 255 - Chapter 9d

EE 255 - Chapter 9d - n= EA 230 V no = (1800 r/min ) = 1711...

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245 ( ) 230 V 1800 r/min 1711 r/min 242 V A o Ao E n n E = = = 9-22. The magnetization curve for a separately excited dc generator is shown in Figure P9-7. The generator is rated at 6 kW, 120 V, 50 A, and 1800 r/min and is shown in Figure P9-8. Its field circuit is rated at 5A. The following data are known about the machine: Note: An electronic version of this magnetization curve can be found in file p97_mag.dat , which can be used with MATLAB programs. Column 1 contains field current in amps, and column 2 contains the internal generated voltage E A in volts.
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246 0.18 A R = Ω 120 V F V = adj 0 to 30 R = Ω 24 F R = Ω 1000 turns per pole F N = Answer the following questions about this generator, assuming no armature reaction. (a) If this generator is operating at no load, what is the range of voltage adjustments that can be achieved by changing R adj ? (b) If the field rheostat is allowed to vary from 0 to 30 Ω and the generator’s speed is allowed to vary from 1500 to 2000 r/min, what are the maximum and minimum no-load voltages in the generator? S OLUTION (a) If the generator is operating with no load at 1800 r/min, then the terminal voltage will equal the internal generated voltage A E . The maximum possible field current occurs when adj R = 0 Ω . The current is ,max adj 120 V 5 A 24 0 F F F V I R R = = = + Ω + Ω From the magnetization curve, the voltage Ao E at 1800 r/min is 129 V. Since the actual speed is 1800 r/min, the maximum no-load voltage is 129 V. The minimum possible field current occurs when adj R = 30 Ω . The current is ,max adj 120 V 2.22 A 24 30 F F F V I R R = = = + Ω + Ω From the magnetization curve, the voltage Ao E at 1800 r/min is 87.4 V. Since the actual speed is 1800 r/min, the minimum no-load voltage is 87 V. (b) The maximum voltage will occur at the highest current and speed, and the minimum voltage will occur at the lowest current and speed. The maximum possible field current occurs when adj R = 0 Ω . The current is ,max adj 120 V 5 A 24 0 F F F V I R R = = = + Ω + Ω From the magnetization curve, the voltage Ao E at 1800 r/min is 129 V. Since the actual speed is 2000 r/min, the maximum no-load voltage is
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247 A Ao o E n E n = ( ) 2000 r/min 129 V 143 V 1800 r/min A Ao o n E E n = = = The minimum possible field current occurs when adj R = 30 Ω . The current is ,max adj 120 V 2.22 A 24 30 F F F V I R R = = = + Ω + Ω From the magnetization curve, the voltage Ao E at 1800 r/min is 87.4 V. Since the actual speed is 1500 r/min, the maximum no-load voltage is A Ao o E n E n = ( ) 1500 r/min 87.4 V 72.8 V 1800 r/min A Ao o n E E n = = = 9-23. If the armature current of the generator in Problem 9-22 is 50 A, the speed of the generator is 1700 r/min, and the terminal voltage is 106 V, how much field current must be flowing in the generator? S
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This note was uploaded on 10/15/2009 for the course EE 255 taught by Professor Shaban during the Spring '05 term at Cal Poly.

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EE 255 - Chapter 9d - n= EA 230 V no = (1800 r/min ) = 1711...

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