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

5. 2 short-shunt compound generators A and B running in parallel supply a load
current of 140A at a terminal voltage 100 V. An equalizig bar connects the two
machines. The data regarding the machines are:
Generator A: Ra=0.02 ohm; Rsh=80ohm; Rse=0.02 ohm.
Generator B: Ra=0.05 ohm; Rsh=100 ohm; Rse=0.05 ohm; e.m.f generator B, 105
V.
Calculate:
(a) current in series windings
(b) armature currents
(c) current in equalizer
(d) e.m.f generated by generator A. [4+4+4+4]
1 of 2Code No: 07A30201 Set No. 2
6. (a) discuss the basic performance equations for a dc motor.
(b) A 4-pole, 250 V series motor has a wave-connected armature with 1254 con-
ductors. The ?ux per pole is 22 mWb when the motor is taking 50 A. Iron
and friction losses amount to 1.0 Kw. Armature resistance is 0.2 ohm and
series ?eld resistance is 0.2 ohm. Calculate:
i. the speed
ii. the BHP
iii. the shaft torque and
iv. the e?ciency at this load. [8+8]
7. (a) Draw and discuss the speed-torque characteristics and torque charectristics of
dc shunt motor.
(b) A 240V, 50A,800 rpm dc shunt motor has armature circuit resistance of 0.2O.
If load torque is decreased to 60% of its full-load value and a resistance of 2O
is inserted in series with armature circuit, ?nd the motor speed. Armature
reaction weakens the ?eld ?ux by 4% at full load and by 2% at 60% of full
load. [8+8]
8. A 10kW 900 rpm, 400V dc shunt motor has armature circuit resistance (including
brushes) of 1O and shunt ?eld resistance of 400O. If e?ciency at rated load is 85%,
then calculate:
(a) The no-laoad armature current,
(b) The speed when motor draws 20A from the mains and
(c) The armature, eurrent, when the total(or internal) torque developed is 98.5
Nm.
presume the ?ux remain constant. [16]
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2 of 2Code No: 07A30201 Set No. 3
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) Prove that energy and coenergy in a linear magnetic system are provided by
identical expressions.
(b) A 10 KW, 1500rpm d.c shunt generator has a time constant Lf/Rf of 0.5 sec

Earning:   Approval pending.