Solution:

•

a}The reluctance 0/ the circuit

b) Theflux and flux density inside the core

2. Consider the toroid shown in the ftgu~ (2), which Is wound with a coil of100 tums. Assume thot the current Is 40A and that the core isnonmagnetic. It is requ;~ to calculate:

Solution:

3. Consider the magnetic structure shown. Find the current in the SO-turnwinding to set up a flux density of O.8T in the airgap. Assume that therelative permeability of the core material Is 1800. Use the concept ofreluctance in your solution.

Solutionj

4. Forthe magnetic structure of problem 3, find the flux density in the airgap for a current of 45A.

Solution:

5. Consider th~ magnetic structure shown In the following figure. Draw anequivalent magnetic circuit for rtJ~system. Assume that the nlatlvepermeability of the core is 2500. Calculate the flux in the right-hand airgap for an MMF In th~coil 0/800 At.

Solution:

1"'", . ! ,,. 71-'II....... .""' ••~ -! - I

~ 'DCI

oz~.. r----i)<,.,'1-----~L· .). ':'~,'" .....,' tc. .......1- --T 'j-

r- -_. "'C'" .•

6. Findthe flux density In the air gap tor on MMF 01180 At. The softferromagnetic moterial 01 the structure shown in F1g. (3) has a relativepermeability 0110,000. The thickness 01the core Is2 em. find the flUX inthe core given that N = 400, It= lA, 12 = 1.2A.

I

Solution:

B. Define the following terms In a magnetic structure: core losses, coerciveforce, and types of materials.

,.

Solution:

7. Slvte the adllQntages and disadvantages of steam power stations.

Solution:

- "r''"f''t i 'II-·r,...· .....:..../,,-~'101

I I I~II

- '- - .. _ - . ,_ • =1•.~r'_. __ .J L_._ _J

"~~.-

1>1--:, 1II I

I L_':..!....- .• ---

i: Sketch Ihe 19uivaJeni electrical circuit.

ii. Findout the flux flowing In the sectors ab and be

9. The magnetic circuit shown in figure has the following data: Number ofturns of ~ field coil = 5000, field call current. = 6 amp. The data of themagnetic core is: Ab = 80 em, at=80 em, fe = 60 em, air gap length = 2 em,the cross sectional area = 10cml, relative permeabillry = 1000find:

Solution:

"

lO.Forthe magnetic structure shown Infigure, find the current requi1'f?dto setup a /lux density o/l.S in the air gop. Assume that the relativepermeability 0/ the core material is 1800

So/ut{on:

11.Polnt out tile parameters upon which the fo/{owing losses depend, givingthe corresponding relation:I. Copper lossn. Core lass

1?

Solution:

r-;-i-'" F ' ---- -::;l 5It; 1--......., r--"-l.__J-I.-. I ~ .;»

:' ' ! Ie·,. • I . _ ...: ~ I' : , ~-:::;I '; Ir: ,J • I,._..__~I ~'.'.' --1 '--..__ '" .:__. ,,_ .. s.:__ .__ ..~::_

12. Themagnetic circuit shown infigure has the following data: number aftums 01the field cail =1000, excitation current =5 amp.Themean length 01 the magnetic path is:Ab = 2Ocm, of = 30cm, Ie = 40 em, the cross sectional area =ScmI, relativepermeability = 1000.Required:i. Sketch the equiva{ent electrical circuit.ii. Findout the /fuJ(flowing In the sectors ab and Ie.

Solution:

/{- Colculate the flUx.density in the gap

reluctances.

13.Forthe magnetic circui: shown In the figure:

• Part A has amean length of 60 em, and a of 3500,

• Part B has a mean length 0/80 em, and a of 2200,

• The air gap has a mean length of 2mm, and

• All parts have a cross-section of 2S cm2•

• ForN =300 turn, and I =4A. Then,

i- Draw tbe; equivalent circuit showing the values of 01/

Solution:

....,.1

JD(',w

!

1 J,,,,It

14.The magnetic circuit shown In fig has the following data:

• number of turns =750 turn• excitation current = 4 A• relative permeability =2000 ,then answer the following:

i) For x= 2mm find the flux density In air gap11)If II increased to 4 mm find the flux density In air gapiii) For II= 4 mm find the new value of current I to have the same value of

fluxdensity as in part i

Solution;

JS.Draw a single Nne diagram that shows the main components of a typicalelectricpower system. Explain the function of each component of thesptem.

,.

Solution:

16.Oiscuss with the aid of sketches the construction and operation of a typicaltt.~1 power station.

Solution:

17.What are the main types of power stations? Discuss with the aid ofsketches the construction and operation of an example of a typical powerstat/on.

23

lB.Compore between the different materials used in a magnetic core.

Solution:

Solution:

19.£xpJainth~ following terms in 0 magnetIc structure:- Coreloss. - Coercilleforce. - Air gap effects-Nonmagnetic mat~rials - Air gap effects.

'15

].A

..~ ...~CI".~

il H~UCl. i.2-.... ~-,lKl'i ...m=~

,..•

zo..",~ iron con $/town has a cross ~ctionoJ are« of 2 cm1and a ~vepBmeGbiHty =1000. 1/ the air gap length is 1mm and N1= SOOturns,B!9UImJ:i. Draw th~equival~t magn~tic drcult.H. Calcul~ the- Reluctances 0/ e-adr part 0/ the Iron CO~and the air

gop.iii. Wltot Is themagnitude 0/ the current In coif 1 required to prodUCt! a

flux density of 0.8 T In the air fJOp.{Take 1'0 = 4 IT x lO·"}

Solution:

19.D#!/fne the following terms and give theIr units and their definIngmathematical expression:- Magnetic flux density.-Magnetic field intensity .. The reluctance.- CoreLosses-Residual /lux'density.

1- ---I---~

~-"{I~~m r=.::.. 3UiJUII1'.> IHiicm-r--t=:-- ---

"'"m-+-

lOA ferromagnetic core with a relative permeability of 2000 ls shawn In the

Figure. The dimensions are as shown in the diagram, and the depth of the

core is 7em. The air gaps on the left and right sides of the core Ore0.050

and 0.070 cm, respectively. Because 0/fringing effects, the effective area

of the air gaps'is 5percent Jarger than their phYSicalsize. If there are 300

turns In the coil wrapped around the center leg of the core and 1/the

currentin the coif Is 1.0,A, what Is the flUX in each oj the left; center, and

right legs of the core? What /5 the /lUI( density in each air gap? Hmo := 4 fJ 'X

10.7,..

30

I"

-,

- - -u c..........P :/

N-5(l N-·W

IJ []- -.....

I ,

2l.Consider tM magnetic structure shown In Fig. (Dimensions in mm).Assume relative permeability oj the material is 2000 and thickness =5mm. Determine the magnetic flUX established In the gap for l.r=5ampereand Iz=4 ampere.

I"- I,)

ILl - -...._I

22.Findthe current necessary to establish a./lux of 3X10-rlWb in the seriesmagnetic circuit of Fig.(Dimensions in mm] with relative permeability Ofcast iron and sheet steel 2500 and 4500 respectillely and the thickness :::10mm.

, , j ,-.

p". j-'-D-I-

r """.r"" IrL'!! \ll,,':"l ~'.~l

~ .

Depth in paper = 5 em

4!)cm

emem

~iii) find the flux dens;ty In the right leg

Required

i) Sketch the equivalent electrical circuit

;iIfind the flux density In the ai, gap

23.Themagnetic circuit shown infig has the following dattJ:• number of turns =500 turn• excitation current =4A• relative permeability =2000

30cm

33

Solution:

24.Mentlon the different reasons a/using high voltages inpowertransmission netwarlcs.

,.

Solution:

oiL'

I __.i P ~\=---"'W

~

..

- ~

- .,

!

2S.Considerthe magnetic structure shown in the figure (Dimens;on inmmJ.Assume relative permeobmty of tile materia/Is 2500 and thidmcss=50mm. Determine the magnetic flUX establishlffi In the gap for 1=4ampere.

35

26. ThemagDeticc:ircuit shown iD fig has thefDJlowing data

aumber of turns -7S0 tum

excitation current - 4 AreJat.ive permeability -2000

i) For x-2 mm find the flux density in air gap

it) I£x increased to 4 arm find tbe fl~ density inair gap

iii) For x =- 4 DUD find the Dew value ot cu.m::a.t I to

have the same value of flux deosity as inpart i

Solution:

I_ ..

1. Forthe small toroidal call as shown in the following figure. Assume thatthe relative permeability of the core material is 1500 and that the outsideradius of the toroid Is0.2 cm. The area of cross sections drcular withdiameter O.OScm.And the magnetomotive force required to set up a fluxdensity of 1milH~teslaIn the core. Find the flux In the core.

Sheet(2)