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B.E.2(sem4)(MECH)
ELECTRICALTECHNOLOGY
SECTIONII
Time:3Hours TotalMarks:100
INSTRUCTIONS:
1)Attemptallquestion.
2)Figuretotherightindicatesfullmarks.
3)Assumesuitabledatawhereverrequiredanddrawfigureswhenevernecessary
4)Scientific
calculator
up
to
Casio
Superfx100D,
100W,
100MS
series
and
equivalent
are
permitted.
4 (a) Fillintheblanks: 10
(1) In a synchronous generator, the __________is always a
stationarymemberandthe___________movingmember.
(2) The speed of 3phase induction motor operation in its
stable
region_______withincreaseinloadtorque.
(3) An4 pole,3phase,50Hz inductionmotoronfull loadrunsat
1440rpm,
the
slip
speed
is_______.
(4) For a given load the armature current of a synchronous
motor
willbeminimumfor___________powerfactor.
(5) Slipofinductionmotorduringblockedrotortestis_______
(6) The distribution factor for a 36 slot stator with three
phase, 8
polewinding,having120degreephasespreadis______.
(7) The maximum torque that a synchronous motor can develop
withoutlossofsynchronismisknownas________torque.
(8) If a squirrel cage rotor is r replaced by a solid cylinder
in an
inductionmotor
its
no
load
slip
will
__________.
(9) Theefficiencyofsynchronousmotoris________thanthatofan
inductionmotorofsamesizeandoutputrating.
(10) Synchronousreactancecanbedefinedassumof________and
____________reactance.
(b) Explain the construction of 3 phase alternator with neat
5
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sketches.
(c) Explainwiththeneatsketch,constructionsandworkingofstar
deltastarterusefor3 phaseinductionmotor.
5
5 (a) Discuss Effect of variation in field excitation of
synchronous
motorwithconstantload.
3
(b) A 400V, 3 phase, 50 Hz, starconnected induction motor
has
thefollowingtestresults:
NoloadTest:400V 8.5A 1100W
BlockedrotorTest:180V 45A 5799W
Calculate the linecurrentand power factorwhenoperatingat
4%slip.Thestatorresistanceperpahseis0.5ohm.
12
OR
5 (a) What is armature reaction? Explain the effect of
armature
reaction on the terminal voltage of an alternator at (i)
unity
power factor load (ii)zero leadingpower factor load.Draw the
relevantphasordiagrams.
7
(b) A 3phase, star connected, 1000 KVA, 11000 V alternator
has
rated current of 52.5 A. The ac resistance of the winding
per
phase
is
0.45
ohm.
The
test
results
are
given
below:
OCTest:Fieldcurrent=12.5A,Voltagebetweenlines=422V
SCTest:Fieldcurrent=12.5A,linecurrent=52.5A
Determinethefull loadvoltageregulationofthealternator (a)
0.8pflaggingand(b)0.8pfleading.
8
6 Attemptanythree. 15
(1) Universalmotor.
(2)
ZPFmethod
to
find
out
regulation
of
alternator.
(3) Derive condition for maximum torque in 3 phase induction
motor.
(4) Speedcontrolof3phasesquirrelcageinductionmotor.
(5) Principleofoperationofsynchronousmotor.
