12:26
TillBIIUVAW UNIVEksrt'Y
INSTinn"E OF ENGINEERING
Examination Control Division
1077 Chaltra
Eum.
BE
Lnel
l'ro&,.mmc BEi
Yar/Part
I F.UMarkl I 10
I Pus Marki I 32
I Tim,
I /II
-.
l 3 hn.
Subj«t: • Electric Circuits and Machine (EE 460)
✓ Candidates are required to give their answers in their own words u far u practicable.
✓
✓
✓
Attempt&!, qua/ions,
dJL qw.,tlons carry ,quo/ .-lu.
, . _ n,ltablt dala /f M«ssary.
1. Explain the phenomena of resonance in parallel circuit and also derive thc expression for
resonance frequency and thc impedance 11 resonance.
2. Find currents and voltages across each clements 11 t • 0--. Also find dV..'dl and dlJ dt for
t•O+.
+
.
.
4.5V • ,
.
•,
10
20
4H
.
2F
'--~-·---
t•
,
~
•
60V ~
. .
3. Find the expression of cuncnl and voltage across inductor for t > 0 using direct solution
method.
11v·
IF
4. In the nelWOfk lhown, the switch it cl.-! 11 t • O. widl Ibo ;..i.,.ork previously
w,enerslled. For the element value pven on diagnm, find Ibo expression for mesh
cumnta i1(I) and i,(t), by Laplace Tnufonnation ,ndbod.
·➔~~
5. Find Z parameters of the two port network shown and c:heclc its reciprocity.
2
I
211
111
2n
I'
f 4V 1
I~
10
2'
1/2
6. A wrought iron bar 40cm long and 3cm in
diameter is bent into a circular shape as in
following figure. It is then woun d with 800 turns
of wire. Clllcul11tc the cum:nt requi red to
produce a flux of0.35m Wb in the magnetic circuit
in the following cases.
a) No air gap
b) With an air gap of 1mm; asswnc the follow
ing data for the magneti:mion iron
Hin AT/m 2500 3000 3500 4000
Bin T
1.55 1.59 1.6
1.615
7. A IO KVA , 200/400 V, 50 Hz single phase
transf
OC test (hv winding open)
SC test (Iv winding shoit ~ircu itcd)
onner iave the following test result s:
: 220V,
: 22V,
Find param eters ofequivalent circuit as referred
1.3A
30A
120W
200W
to Iv windi ng.
8. Derive the emf equation and torque equation
of de machine, defining comspaDdin& tams
involved.
9. Describe the torque speed characteristic of three
phase
torque, maximum torque and operating region. Also induction motor show ing starting
show the effect of rolOr resislancc in
the T-S characieristics with a conclusion.
10. What are initial conditions? Explain the proce
dure to evaluate the initial condition .
•••
2/ 2
DUlli rT"Uf t"\1,t,f rRl'\1 ,
,....
, , . __
ll
HI
i.-..c.: w-..
, ..., , , _
1, 11
u•h11t1N ( 0111m l 1,..-,,.....
f..
• l .> 4,,,.,. ... ~ e J • f••• , ......... . .ci
✓ Atttmpl A11 q11estlons.
✓
✓
fi\ t.:lr IA' w--C,. .IJ
hr U ~
l ~&
TMjig11res /11 1he marg/11 mdicat~ £1111 M«rks
Assume suilahlc dau, if nr-cessary
I. What do you mean by resonance in electric circuit? Derive the
condi lion for series
resonance. Also determine lix expression ofb:md \\idth.
(2+2+4)
2. For the circuit shown bclO\\, find cum:n15 and vollagcs across
each clemc111s at l " o+.
Also find the value of chari;c .ii I O
18)
0
,
3 An cxponcnti3l source V(l} = 20c·11 is suddcnl) applied 01 lime
I • 0 to a series RLC
circuit compris ing R = 4 ohms, L ~ I II lllld C = I 3 F. Ob1oin
the expression for the
current i(t) in Lhc circuit u.sing Laplooe Transform method.
4. For the tW<' ron n1:1wor\. sho,m below, find h•p.iram
ctcr nnd T' parameter. Also d,cck
for reciproc ity of network .
181
(81
0.3 \ '1
5. a) Dcri\·c the equivale nt Y-rar:imeters of two numbrr of
I\\O pon network when
connected in parnlld.
b) Find the cxp1ession of inductor c1•rrcn1 fort .., (I u, ing clJ,~,r~I
method.
20A
t
s~ II
son
[4)
141
6. An iron ring has me!an leng th
of" 2m and cro ss-s ectional are a of
0.01 ni2. It has a radial air
gap of 4 mm . The ring is wou nd
wit h 250 turn s. Wh at de cur ren t wou
ld be needed in coil
to pro duc e a flux den sit)' of 0.5 Tes
la in the co~e? (~ -= 400 0)
7. Fol low ing resu lts wer e obt aine
d from test on a tran sfor mer of rati
ng 8 kV A, 400/120V,
50H z.
Ope n circ uit Tes t (LV side ): I 20
V, 4A, 75 W
Sho rt circ uit Tes t (Irv side): 9.5
V, 20A, l l 0 W
Cal cula te equ ival ent circ uit par ame
ters referred to LV and HY side
and dra w equivalent
circ uit of sam e.
[ 8]
8. Exp lain how rota ting mag neti
c field is pro duc ed in cen tral spa ce
of thre e pha se indu~tion
mo tor. Sho w that mag nitu de of
rota ting m:1gneti c fiel d is 1.5 tim
es maximum flux
density.
[SJ
9. A shu nt gen erat or del ive rs
SOKW at 250 V anlt 400 rpm. The
ann atur c resistance is
0.0 20 and field resistan ce i~ 50Q
. Cal cula te the ind uce d emf by ann
atur e nnd clec1ricnl
efficiency.
f8)
l O. Derive the exp ress ion of torq
ue dev eloped
shu nt mot ors can be rev erse d?
[8]
in
arm atur e of De motor. How the dire
ction of
14+4]
·"iui i~
TRIBH UVAN UNIVERSITY
JNSTITIJTE OF ENGINEERING
lkcul ar
I F■IJ Marks 110
BE
Level
32
Progr am me BEL. BEX. BCT PH1 Marks 1
J hrs
'
Time
Year / Part , II / I
Exam inati on Con trol Division
2079 Bbad ra
1)
Subject: • Elec1ric Circu it 'Iltco ry (EF. 50
✓
✓
✓
✓
own
Candidates arc required to give their answers in their
ons.
questi
dJ!.
Auempt
T~jig ures in the ,nargin indicate f ull Marlts.
Assume suitable data ifnecessary
words as far as practicable.
circuit? Define half power frequencies
I . a) What do you mean by resonance in RLC series
ssion for them.
expre
obtain
and
t
and bandwidth in RLC series circui
2
. .rz, -d:!i_ , -di-, and d i., at t - 0'.
. .t sho wn .rn t I1c Ii1gure bet ow, Iirnd 11,
2dt
b) For the crrcur
dt
dt
f4+4 )
18)
100
2 mH
ton ~
voltage across cap3Citor for
2. a) U~ing classical method, find current and
circuit shown below.
1 >
O i.n the
(81
1•0
100
20 0
100 V
: )
200
IOµF
ssion of current through inductor for
b) tr the switch is closed at t • 0, find the expre
IO ms using classical method.
after
or
induct
I > 0. Also calculate the voltage across
l- _J::-71,s11'n
~
><IV
IOV-
200
, -u
T__ ... _____ __r
expression of current and voltage across
3. a) ~sing ~plac e T~s~ orm method find the
O.
=
1
at
closed
s
1
mductor 1fthc SWJtch
1- 0
X
[ _....,. J, o- -
'
10e·>• Q
18]
I
IOQ
~
_ __ __ _
1H
'---
1
L
__Jr ooF
[8)
b) Using Laplace transform method, find the loop currents i1 and
shown in the following figwe.
h fort > 0 in the circuit
l8)
G
...:i,; C:
ln
7
4. a) Find the voltage ratio transfer function of given TPN.
·.~-~ -c:
(81
30
--
_:_r___L -
£8)
b) For the transfer function below, draw the asymptotic Bode plot.
G(s) =<
50(s + IO)
s(s +-2O)(s 2 + 2s + 225)
5. a) Obtain trigonometric Fourier series of voltage waveform shown in figure below and
plot the line spectra
[8]
:. . . . . . ....... ··iol·~~~. .:. . . .. ... .. . .. . . . . . . . ..
;
-....L.-.......---->-
- I
I
0
I
3
,__...,__ ......_ _
;__7
.. ......... ..... .. .. ·.:.io.... ....... .......... .... .. .. ................
b) Calculate [Y] and [g] parameters of the given circuit and also check whether the
network reciprocity and symmetry.
('8]
2 v,
">-- -- --02
v,
•••
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, _ .- . . . t ~
2°'9 Ch•nn
V
_ea
_ r_l_P_a_
rt_1"""
tl_/ _11_ ~..J.!l..l!"
31u1·.
- -- - - - - - - - - - - - - - ·-·--· -._l
_ _ _ __S_ub
--'~ect: - Electrical Machines I ( EE 55 J
✓ Candi dates are requir ed to give their answe rs in
their
✓ Attempt &J. questions.
✓ The figures in the margin indicate F111/ Mark
s.
✓
)
- - - -----own words as far as practicable.
Assume suitable data ifnecessa,y.
I. a) Expla in the hysteresis loop of a magnetic mater
ial used in electr ical machi ne. Prove
that the area of the loop is propo rtional to the energ
y loss per cycle per unit volum e.
b) A 8 kVA. 400/1 20 V, 50 Hz single phase transf
onner on test gives the following
results:
O.C. test:
S.C. test:
l20V
9.5V
4A
20A
75W
I !OW
(carried on LV side)
(carried on HV side)
Calculate the equivalent circle parameters referred
to HV side.
2. a) A 2 MV A, Delta- star, 33/6.6 kV. three phase trans
fo rmer has primary and secondary
resistance of 8 Ohm and 0.08 ohm per phase. llle
percentage impedance is 7 percent.
Calcu late the voltag e regula tion at full load at 0.75
pf laggin g.
[8}
[8]
[8]
b) Expla in the opera ting princi ple of a single
phase Lransf ormer and derive the emf
equat ion.
[8)
3. a) What is back emf in de motor ? Expla in the rolea
of back emf in de motor.
[8)
b) A 4 pole shunt gener ators with a lap would
bas armature resistance of 0.1 ohm and
field circuit resist ance of SO ohm. The gener ator
suppl y powe r to six filament lamps
of rated 200 V 600 Watt each. The brush conta ct
drop is 1 V per brush. If generator
terminal voltag e is 220 V after lamps a.re conne cted
then find annat ure CWTC llt and
gener ated emf.
[8]
4. a) A 230 V de series motor draws a line current of
100 A from mains while running at
1000 rpm. Its armat ure resistance is 0.1S Ohms
nnd field resistance is 0.1 Ohms.
When the moto r draws cwten t of25 A. calcul ate the
speed.
[)OJ
b) A de shunt moto r is opera ting at a co~ta nt speed
suppl ied with rated voltage. Due to
an accident, the field termin al of the motor
gets 'disconnected. What will happen on
the motor perfo rmanc e? Discu ss on the implication.
s.
(61
5. a) Deriv e the condi tion for maximl.llD torque
of an induction motor. Draw the
Torqu e-slip chara cteristics of induction motor for
differ ent supply voltag e.
(8)
b) A 40 kW, 3-pha se slip ring induction motor of
negligible stator impedance at a speed
of 0.96 times synch ronous speed at rated torque
. The slip at maxim um torque is
4 times the full-lo ad value. If the rotor resista nce of
the motor is increased by 5-times,
determine.
[8]
i) The speed, powe r outpu t and rotor coppe r loss
at rated torque.
ii) The speed correspondi ng to the maxim um torque
.
·
•••
.....
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INl1TTtJT£ Of ..OrNEDING
lsualaade■ C.arnl DiYiliie•
.,.
Yarl , - .
a•
,St \fat • EJedriml Machin II I
lta.
J
ta"''
✓ Candidates are required to give th~ir answers in their own words as far as practjcable.
✓
Attempt All questioru.
✓ . The figuru In the margin indlcale F.U Marg.
✓ Assume suitable data if~t¥ssary.
I. a)~
lain hysteresis pbeno~coon with ac excitation.
~ )/A'fenomagnetic core with a relative permeability of 4~00 is. shown below, The
~dimensional area as shown and depth of core is 7cm. The air gap 1s o.o.sc~ on left and
0.07cm on right side. The effective area o f gap is 5% larger due t~ fiingmg e~ect If
cum:nt in coil is 1OA, calculate flux in left. right and middle part .a long with Oux
density in each air gap.
1::;10:::::::_ -_
.,--i-"'"""'!_
,_
T
30cm
(8)
[8]
--'1'-----•1- ..,,---t-j'---tl
1
_ ......,,______
_ _~--i
- · o.os-
1
7CIII ,___ _ __ _ ___:.......:.;;_ _ _ _ ___,
..L
2. a)1 A lOOKVA. 2200/220V trmsformer wheo tested gave the following raults:
~ OCtest:
400W lOA 220V
::;7 SC test:
80IW 30A 90V
Co~pute all the parametclS of the equivalent cirouil
to HV sides of the
transformer. Draw the equivalent cirouils also.
6
/
.,..,eel
.
(8]
SO KVA. 440CVl20V transfaaper with •
equ1--va-,...
... impedance of
' (O.OH:j0.02.)obm is &o operate in parallel with a 2SX.VA.4400l'J20V lnmfonner with
an equivalent i.mpe-tePae (0.02~0.04) ohm. The twu II el,aoas are coMected in
parallel and madetD amy a l.oad of 6fKVA
;b) A
(i) Find the lndivldall lrlDSfonner cqm;nts
_ 3.
/
yi) What percent oftbe med capacity 11\used in IIICbJ!lmlf'~ er? .:·
tfExplain the voltage build up process fn.de shun~ erator and d~-f ine the meaning of
~
~·· cal resistance and critical speed.
·
(8)
(8)
.
.·A de compolllM;' generator has to suppl~ a ~nt of 120A to the load at 120V. The
shunt field, senes field and armatwc wmd101 resistances a r e ~ Q._OS ohm and
O.Johm respectively. Calculate the emf generated by the annature in
following
two cases:
the
(8)
(i) Jong shunt connection
(ii) Short shunt-connection
1/ 2
·4 . . a) / . ·
the op era tin g pin cip
le of a DC motor ,_an
d clarify die functions
aeg mc nts an d car bo n
of
brushes in de motot.
l>) A 22 0V de -~
mo tor ha s annatutc
win din g resistance of
wi nd ing rai sta nc e··o
0.O I oh m and field
f· ll0 oh ms . It Nn S at
a spe ed of 14 00 rpm
res ista nce of 30 oh ms
• lal1f load. If •
is
in series with the field
increased by lOo/e, calcul
wi nd ing m l load torque
ate the
is
speed of the motor.
S.
Explain the isolal cd mo
.
de
an d gri d ~ e d
gen era lOr.
mo de or thr ee ph ase
induction
/
•
b), A 400V, 4-p ole , SOHz.
, 3 pa -. sli p ring illduc:
tioo mo 1or ba s a ddla coa
winding and a sta r coa
ncc ted rot or winding.
nected sta tor
At standstill the 'VOit.iF
sli p rin gs is 19 0V. Th
llc:twceo the tw o
e s\a lor impedance is (0.
S+j2.S ) olma. The NC
rca cta nce II standstill
lar aai stl Dc e and
axe 0.06 obm and 0.3
ma im um torque of ISO
oh m ~ l y ad
it develops a _
N-m. Calcula&c:
(i) Sli p al wh ich mo tor
de velops the maximum
torque.
(ii) To rqu e, po we r ou q,u
t at full l~ k l
a d sli p is 0JM.
~~tor
(8]
connected
•f
new
(8]
[8)
[8)
I•
2 /2
1'J_,1N N'I UWltU ITY
II)
.....
Nlfn. Tru C. m,.klDG;BJUNO
n
[.ua iaad N Coatrel otvW..
.,.
---=- --=-
~
- £1~
,..;; --Ji n
M.dirle•I~
'!Op._.~• ._ o•
✓
Candidates are ttqUITed
✓
Attempt d!J. queslio,u.
The figures in the margin indicate FuUMork.s.
Assume suitable data ffnecessary.
✓
✓
-_-_-_ __
_ . u Ir a pndlc•N"
emf? On what factors do these
I. a) What is meant by statically and dynamically induced
[8]
each.
depend? Give practi ~ examp le of
is bent into circular shape. It
_p) A wrought iron bar of 30 cm long and 2 cm in diameterrequire
d to produce a flux of
current
the
te
is wound 600 turns of winding. Calcula
no air gap b) with an air gap
with
a)
cases:
two
ng
followi
the
in
core
the
in
mwb
0.05
(8]
of 4mm. Given that µ, = 4000.
[8]
gave the following results:
2. j) A 20 kVA, 250/25 00 V transfonner when tested
O.C. test (L.V. side): 105 W,1.4 A, 250 V.
S.C. test(H.V . side): 320 W, 8 A, 120 V.
referred to the L.V . side and
Compute all the parameters of the equivalent circuit as
side.
H.V.
to
also draw the resultant circuit as referred
load. Derive the conditi on for
b) Explain how the efficiency of a transformer varies with
[8]
maximum efficiency.
or. Also, explain the meanin g of
3. a) Explain the voltage build up process in de generat
(6+2]
ce.
resistan
critical speed and critical
the load at 250V. The armature
_!l., A de short shunt compound generator delivers 6kw to have
resistance of 0.1 Cl, 0.2 Cl
g
windin
winding. series field winding and shunt field
(8]
re.
armatu
by
ed
generat
emf
the
te
and 250 n respectively. Calcula
(8)
torque equatio n of a D. C motor.
4. a) Explain workin g principle of D.C. motor. Derive
resistance of 0.2 ohm and field
b) A 250V d.c shunt motor has annature winding
32 Amp. and runs at a speed of
of
current
a
draws
It
ohm.
125
of
ce
resistan
- winding
with the field and the load
series
in
ted
coMec
is
1500 r.p.m. lfa resistance of75 ohm
[8]
speed of the motor?
new
the
be
will
what
20%,
by
ed
increas
is
torque on the shaft
(8)
e.
Explain T-S characteristic of three phase induction machin
5. a)
1>
has a star connected stator
A 400V, 4 pole, 50 Hz, 3 phase slip ring Induction Motor
voltage betwee n the two
the
ill,
standst
At
g.
windin
rotor
ted
connec
star
a
and
winding
rotor resistance and
The
ohm.
0.8+j3
is
nce
impeda
slip rings is 200V. The stator
ively. The motor produces a
respect
ohm
0.2S
and
ohm
0.08
are
ce
reactan
ill
standst
[4+4)
torque of IO Nm at starting. Calculate:
(i) Maximum torque that can be developed by the motor.
.
(ii) Calculate the torque developed by the rotor at 1430 rpm
•••
1/ 1