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Unformatted text preview: 235 R F = 200 Ω n m = 1200 r/min R adj = 0 to 300 Ω , currently set to 120 Ω This motor has compensating windings and interpoles. The magnetization curve for this motor at 1200 r/min is shown in Figure P96. Note: An electronic version of this magnetization curve can be found in file p96_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. 916. The motor described above is connected in shunt . (a) What is the noload speed of this motor when R adj = 120 Ω ? (b) What is its fullload speed? (c) Under noload conditions, what range of possible speeds can be achieved by adjusting R adj ? S OLUTION Note that this magnetization curve has been stored in a file called p96_mag.dat . The first column of the file is an array of ia_values , and the second column is an array of ea_values . These values are valid at a speed o n = 1200 r/min. These values can be used with the MATLAB interp1 function to look up an internal generated voltage as follows: load p96_mag.dat; 236 if_values = p96_mag(:,1); ea_values = p96_mag(:,2); ... Ea = interp1(if_values,ea_values,if,'spline') (a) If adj R = 120 Ω , the total field resistance is 320 Ω , and the resulting field current is adj 240 V 0.75 A 200 120 T F F V I R R = = = + Ω + Ω This field current would produce a voltage Ao E of 256 V at a speed of o n = 1200 r/min. The actual A E is 240 V, so the actual speed will be ( ) 240 V 1200 r/min 1125 r/min 256 V A o Ao E n n E = = = (b) At full load, 100 A 0.75 A 99.25 A A L F I I I = = = , and ( )( ) 240 V 99.25 A 0.14 226.1 V A T A A E V I R = = Ω = Therefore, the speed at full load will be ( ) 226.1 V 1200 r/min 1060 r/min 256 V A o Ao E n n E = = = (c) If adj R is maximum at noload conditions, the total resistance is 500 Ω , and adj 240 V 0.48 A 200 300 T F F V I R R = = = + Ω + Ω This field current would produce a voltage Ao E of 200 V at a speed of o n = 1200 r/min. The actual A E is 240 V, so the actual speed will be ( ) 240 V 1200 r/min 1440 r/min 200 V A o Ao E n n E = = = If R adj is minimum at noload conditions, the total resistance is 200 Ω , and adj 240 V 1.2 A 200 0 T F F V I R R = = = + Ω + Ω This field current would produce a voltage Ao E of 287 V at a speed of o n = 1200 r/min. The actual A E is 240 V, so the actual speed will be ( ) 240 V 1200 r/min 1004 r/min 287 V A o Ao E n n E = = = 917. This machine is now connected as a cumulatively compounded dc motor with adj R = 120 Ω . (a) What is the fullload speed of this motor? (b) Plot the torquespeed characteristic for this motor. (c) What is its speed regulation? S OLUTION 237 (a) At full load, 100 A 0.75 A 99.25 A A L F I I I = = = , and ( ) ( )( ) 240 V 99.25 A 0.14 0.05 221.1 V A T A A S E V I R R = + = Ω + Ω = The actual field current will be adj 240 V 0.75 A 200 120 T F F V I R R = = = + Ω + Ω and the effective field current will be ( ) * SE 12 turns 0.75 A 99.25 A 1.54 A1....
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 Spring '05
 Shaban
 Electric motor, Brushed DC electric motor, Radj, r/min

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