Page 80 - Electric Machinery Fundamentals

56 ELECl'RIC MACHINERY FUNDAMENTALS

1-4. A motor is supplying 50 N • m of torque to its load. If the motor s shaft is turning
at 1500 rlmin, what is the mechanical power supplied to the load in watts? In
horsepower?
1- 5. A ferromagnetic core is shown in Figure Pl-2. The depth of the core is 5 cm. The
other dimensions of the core are as shown in the figure. Find the value of the current
that will produce a flux of 0.005 Wb. With this current, what is the flux density at
the top of the core? What is the flux density at the right side of the core? Assume
that the relative permeability of the core is 800.
5em
f--lO em 20em -j l
T

15 em
I¢
i
+ t (
-------
-------
( ------- 500 turns 15 em
1
-------

I¢ 1
15 em
1

Core depth = 5 em
FIGUREPl -2
The core of Problems 1- 5 and 1-16.
1-6. A ferromagnetic core with a relative permeability of 1500 is shown in Figure Pl-3.
The dimensions are as shown in the diagram, and the depth of the core is 5 cm. The
air gaps on the left and right sides of the core are 0.050 and 0.070 cm, respectively.
Because of fringing effects, the effective area of the air gaps is 5 percent larger than
their physical size. If there are 300 turns in the coil wrapped around the center leg
of the core and if the current in the coil is 1.0 A, what are the flux values for the left,
center, and right legs of the core? What is the flux density in each air gap?
1-7. A two-legged core is shown in Figure Pl-4. The winding on the left leg of the core
(N] ) has 600 turns, and the winding on the right (N ) has 200 tums. The coils are
2
wound in the directions shown in the figure. If the dimensions are as shown, then
what flux would be produced by currents i 1 = 0.5 A and i2 ::: 1.00 A? Assume f-Lr =
1200 and constant.
1-8. A core with three legs is shown in Figure PJ- 5. Its depth is 5 cm, and there are 100
turns on the leftmost leg. The relative permeability of the core can be assumed to be
2000 and constant. What flux exists in each of the three legs of the core? \Vhat is the
flux density in each of the legs? Assume a 5 percent increase in the effective area of
the air gap due to hinging effects.