0195136047.pdf

498 MAGNETIC CIRCUITS AND TRANSFORMERS

50 cm

50 cm 50 cm

1000 turns

1000 turns

5 A 5 A

0.5 cm

Figure P11.2.6

*11.2.7Consider the magnetic circuit shown in Figure
P11.2.7. Assume the relative permeability of the
magnetic material to be 1000 and the cross-sec-
tional area to be the same throughout. Determine
the current needed in the coil to produce a flux
density of 1 T in the center limb, if the excitation
coil has 500 turns.
11.2.8In the magnetic circuit shown in Figure P11.2.8
the center leg has the same cross-sectional area
as each of the outer legs. The coil has 400 turns.
The permeability of iron may be assumed to be
infinite. If the air-gap flux density in the left leg
is 1.2 T, find:
(a) The flux density in the air gap of the right
leg.
(b) The flux density in the center leg.
(c) The current needed in the coil.
11.2.9Figure P11.2.9 shows the cross section of a rect-
angular iron core with two air gapsg 1 andg 2.
The ferromagnetic iron can be assumed to have
infinite permeability. The coil has 500 turns.
(a) Gapsg 1 andg 2 are each equal to 0.1 cm,
and a current of 1.83 A flows through the

winding. Compute the flux densities in the

two air gaps,Bg 1 in the center gapg 1 , and

Bg 2 in the end gapg 2.

(b) Let gapg 2 now be closed by inserting an

iron piece of the correct size and infinite

permeability so that only the center gapg 1 =

0 .1 cm remains. If a flux density of 1.25 T

is needed in gapg 1 , find the current that is

needed in the winding.

11.2.10Consider the magnetic circuit in Figure P11.2.10,

in which all parts have the same cross section.

The coil has 200 turns and carries a current of 5

A. The air gaps areg 1 = 0 .4 cm andg 2 = 0. 5

cm. Assuming the core has infinite permeability,

compute the flux density in tesla in (a) gapg 1 ,

(b) gapg 2 , and (c) the left limb.

11.2.11The magnetic circuit shown in Figure P11.2.11

has an iron core which can be considered to be

infinitely permeable. The core dimensions are

AC =20 cm^2 ,g= 2 mm, andlC = 100

cm. The coil has 500 turns and draws a current

of 4 A from the source. Magnetic leakage and

fringing may be neglected. Calculate the follow-

ing:

30

cm

25 cm 25 cm

Figure P11.2.7

0.75

cm

0.50

cm cm^30

25 cm 25 cm

Figure P11.2.8