Jawaharlal Nehru Technological University Kakinada 2008 B.Tech Electronics and Communications Engineering electrical technology - Question Paper

Engineering and Instrumentation & Control Engineering)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
? ? ? ? ?
1. (a) De?ne the terms ‘critical resistance’ and ‘critical speed’ and bring out their
role in the process of self excitation of a dc machine.
(b) Distinguish ranging from external and internal characteristics of dc generator. How
internal characteristics are derived from external characteristics of shunt gen-
erator? [8+8]
2. (a) discuss the di?erent protective devices used in three - point starters.
(b) discuss the method of armature voltage speed control using neat diagram.
[ 8+8]
3. (a) discuss the principle of operation of a transformer.
(b) The maximum ?ux density in the core of 240/2400V, 50Hz, 1- f transformer
is 1.0Wb/sq.m. If the EMF per turn is 16 volts, determine:
i. the primary & secondary turns and
ii. area of the core. [8+8]
4. (a) A 20 kVA transformer has its maximum e?ciency of 0.98 at 15 kVA at upf.
The iron loss is 350W. compute the e?ciency at full load, for 0.8 p.f lag and
upf.
(b) With neat circuit diagrams, discuss the procedure for conducting OC & SC
tests on a provided 1- f transformer to predetermine its regulation & e?ciency.
[8+8]
5. (a) Draw the diagram of connections of a plain auto transformer starter for an
induction motor and discuss its action.
(b) A 25hp, 3-phase, 50 Hz, six pole slip ring induction motor has a full load speed of
960rpm. The stator loss is 5% of the input and mechanical losses are 4% of the
output. The current in every rotor phase is 30 A. obtain the resistance per phase
of the rotor and the e?ciency of the motor. If the rotor standstill resistance
is ?ve times the rotor reactance, ?nd the speed at which the maximum torque
occurs. [8+8]
6. (a) discuss the alternator armature winding kinds with neat sketches.
1 of 2Code No: 07A3EC13 Set No. 3
(b) An alternator on open circuit generates 360V at 60Hz when the ?eld current
is 3.6A. Neglecting saturation, determine the open circuit e.m.f. When the
frequency is 40Hz and the ?eld current is 2.4A. [8+8]
7. (a) elaborate the di?erent kinds of capacitor begin motors? discuss in detail any

Earning:   Approval pending.