EE 255 - Chapter 9c

EE 255 - Chapter 9c - 235 R F = 200 Ω n m = 1200 r/min R...

This preview shows pages 1–4. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

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 P9-6. 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. 9-16. The motor described above is connected in shunt . (a) What is the no-load speed of this motor when R adj = 120 Ω ? (b) What is its full-load speed? (c) Under no-load 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 no-load 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 no-load 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 = = = 9-17. This machine is now connected as a cumulatively compounded dc motor with adj R = 120 Ω . (a) What is the full-load speed of this motor? (b) Plot the torque-speed 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....
View Full Document

{[ snackBarMessage ]}

Page1 / 10

EE 255 - Chapter 9c - 235 R F = 200 Ω n m = 1200 r/min R...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online