Page 83 - Electric Machinery Fundamentals

11'1 1 KUUUL I l UI'! I U lVI }\l...I-,lI I'lbJ<.r l ' I<'LI'IL1VLb') ;)7

x x x x x x x

x x x x x

x x x x x
xv= IOmls
X X X X
1= 0.25 III
X X X X X X
') A wire moving in a
X X X X X X FIGURE Pl-7
magnetic field (Problem
B = 0.2 T, into the page 1- 10).

! V= lmJ,
(
I B =O.S T

1=0.5 m

FIGURE PI- 8
A wire moving in a magnetic field
(Problem 1- 11 ).

in Problem 1- 7 that the relative permeability was equal to 1200 a good assumption
for these conditions? Is it a good assumption in general?
1- 13. A core with three legs is shown in Figure Pl-lO. Its depth is 5 em, and there are 400
turns on the center leg. The remaining dimensions are shown in the figure. The core
is composed of a steel havi ng the magnetization curve shown in Figure I- lOc. An-
swer the following questions about this core:
(a) What current is required to produce a flux density of 0.5 T in the central leg of
the core?
(b) What current is required to produce a flux density of 1.0 T in the central leg of
the core? [s it twice the current in part (a)?
(c) What are the reluctances of the central and right legs of the core under the con-
ditions in palt (a)?
(d) What are the reluctances of the central and right legs of the core under the con-
ditions in part (b)?
(e) What conclusion can you make about reluctances in real magnetic cores?
1-14. A two-legged magnetic core with an air gap is shown in Figure Pl-l 1. The depth of
the core is 5 em, the length of the air gap in the core is 0.05 em, and the number of
turns on the coil is 1000. The magnetization curve of the core material is shown in