Page 88 - Electric Machinery Fundamentals

64 ELECTRIC MACHINERY FUNDAMENTALS

1-22. A linear machine has the fonowing characteristics:
B = 0.5 T into page R ~ 0.25 n
l~ 0.5m VB ~ 120V
(a) If this bar has a load of 20 N attached to it opposite to the direction of motion,
what is the steady-state speed of the bar?
(b) If the bar runs off into a region where the flux density falls to 0.45 T, what hap-
pens to the bar? What is its final steady-state speed?
(c) Suppose VB is now decreased to 100 V with everything else remaining as in
part (b). What is the new steady-state speed of the bar?
(d) From the results for parts (b) and (c), what are two methods of controlling the
speed of a linear machine (or a real de motor)?
1-23. For the linear machine of Problem 1-22:
(a) When this machine is operating as a motor, calculate the speed of the bar for
loads of 0 N to 30 N in 5 N steps. Plot the speed of the bar as a function of load.
(b) Assume that the motor is operation with a 30 N load, and calculate and plot the
speed of the bar for magnetic flux densities of 0.3 T to 0.5 Tin 0.05 T steps.
(c) Assume that the motor is running at no-load conditions with a flux density of
0.5 T. What is the speed of the bar? Now apply a 30 N load to the bar. What is
the new speed of the bar? What fLux density would be required to restore the
loaded bar to the same speed that it had under no-load conditions?

REFERENCES

1. Alexander, Charles K., and Matthew N. O. Sadiiku: Fwu/amellfa/s of Electric Circuits, 4th ed.,
McGraw-Hill, New York, 2008.
2. Beer, F, and E. Johnston, Jf. : Vector Mechanics Jor Engineers: Dynamics, 7th ed., McGraw-Hill,
New York, 2004.
3. Hayt, William H.: Engineering Electromagnetics, 5th ed., McGraw-Hill, New York, 1989.
4. Mulligan, J. E: Introductory College Physics, 2nd ed., McGraw-HilI, New York, 1991 .
5. Sears, Francis W., Mark W. Zemansky, and Hugh D. Young: University Physics, Addison-Wesley,
Reading, Mass., 1982.