Jawaharlal Nehru Technological University Kakinada 2008 B.Tech Electrical and Electronics Engineering ELECTRICAL MACHINES-I - Question Paper

i. assuming the load torque to have remained constant. [16]
7. The speed of a 50 h.p series motor working on 500V supply is 750 rpm at full load
and at 90 % e?ciency. If the load torque is made 350Nm and a 5O resistance is
connected in series with the machine, compute the speed at which the machine will
run. presume the magnetic circuit to be unsaturated and the armature and ?eld
resistance to be 0.5O. [16]
8. The Hopkinson’s test on 2 similar machines gave the subsequent full load outcomes.
Line current =48A
Line voltage =110V
Motor armature current=230A
The ?eld currents are 3A an 3.5A. Armature resistance of every machine is 0.035
ohms.Calculate the e?ciency of every machine assuming a brush contact drop of 1V
per brush. [16]
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2 of 2Code No: 07A30201 Set No. 2
II B.Tech I Semester Regular Examinations, November 2008
ELECTRICAL MACHINES-I
(Electrical & Electronic Engineering)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
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1. (a) define the principle of energy conversion. From a consideration of the vari-
ous energies involved, develop the model of an electro mechanical conversion
device.
(b) Show that the torque developed in a doubly excited magnetic system is equal
to the rate of increase of ?eld energy with respect to the displacement at
constant currents . [8+8]
2. (a) Distinguish ranging from lap and wave windings.
(b) The armature of a two pole, 200V generator has 400 conductors and runs at 300
rpm. compute the useful ?ux or pole. If the number of turns in every ?eld coil
is 1200, what is the avg. value of the emf induced in every coil on breaking
the ?eld, if the ?ux dies away completely in 0.1s. [8+8]
3. (a) How are demagnetizing and cross magnetizing ampere-turns/pole in a D.C
Machines calculated?
(b) Determine AT/pole for every interpole of a four pole generator with 88 slots every
containing 900 amp - conductors. The interpole air gap is 0.01 m and ?ux
density in the interpole air gap is 0.3 T . The e?ects of iron parts of iron parts
of the circuits and leakage may neglected. [8+8]
4. (a) How are the series and shunt windings organizes on the pole of a dc compound
machine?
(b) How will you distinguish ranging from series and shunt windings of a dc compound
machine? [8+8]

Earning:   Approval pending.