Punjab University 2007-2nd Sem B.Tech Basic Electrical Engineering (., 1st and ester) 03 - Question Paper

ELE-101
Basic Electrical Engineering
(B.Tech., first and second Semester, 2122)
Time : three Hours Maximum Marks : 60
NOTE:- ques. No. one is compulsory. Attempt other 5 ques. taking at lowest 2 from part A and part B

1 (a) describe avg. value at alternating current. obtain this value for waveform shown in Fig.-1.


(b) A circuit consist of 20 ohm resistance and in series with a capacitance of 200 u Farad, connected across 50 Hz
supply. the current through the circuit is i = 10.8 sin 314 t. amp. determine the voltage across every component
and across the circuit.
(c) 3 similar coils every of resistance 20 ohm and of inductance 0.5 h are connected in star across a 3 phase
supply source of 400 v, 50 Hz. compute line current and power absorbed by circuit.
(d) A five k VA, 240/120 V, single- phase transformer supplies rated curentto a load at 120 V. Determine the magnitude
of load impedance as seen from input terminals of transformer. the load impedence is (5 + j 15) ohm.
(e) A DC shunt motor develop an circuit emf of 250 V at 1500 rpm. obtain the torque developed by machine for an
armature circuit of 20 A.
(f) Synchronous motor is a doubly exited machine. How ? Identify the kinds of sources.
(g) elaborate the advantages and disadvantages of wound rotor over squrrel cage rotor in case of induction motor ?
(h) What is the basic kind of instrument used in energy meter ? What is its use and elaborate the units of measurement ?
(i) What is the basic kind of instrument used in energy meter ? What is its use and what is its and elaborate the units
of measurement?
(j) Draw a single line diagram of the power system shown in Fig.-2.
G = Generator (star connected with neutral ground)
T1, T2 = Transformers (Delta-star connections)
TL = Transmittion line
M = Motor ( Delta connected)
part - A Marks : eight every
2.(a) A six - pole, 12 kW, 240 V DC m/c is ware connected. If the identical machine is now lap connected, all other
things remaining same, compute its voltage, current and power ratings.
(b) How does the commutator help in the development of the emf in DC machine?
(c) provide 2 applications of series motor and shunt motor every.
3.(a) A 100 k VA, 2400/240 V, 50 Hz, single phase transformer has an exiting current of 0.64 A and a core loss
of 700 V, when its high voltage side is energized at rated voltage and frequency. compute 2 components of
no- load current and no-load branch parameters.
(b) How short circuit test is performed on transformer ? Draw its set-up and explain the outcomes found from
the test.
4. For circuit shown in the Fig.-3, compute :
(a) Voltage across every branch A,B,C.
(b) Current through every branch
(c) Total current supplied
(d) Power consumed by circuit
(e) Power factor of circuit
(f) phase diagram of circuit.
5. elaborate various methods of power measurement in three-phase balanced system ? explain it along with proper
diagrams and expression evaluations.
6.(a) elaborate the advantages of providing field winding on rotor and armature winding on stator in case of
synchronous machine ?
(b) Sketch a layout salient pole synchronous machine. Clearly indicate the material used and function for every
part of machine.
7 (a) Show that in inductor motor, the rotor always run in the direction of stator field.
(b) Sketch the Torque-speed characteristics of an induction motor working at normal voltage and frequency.
Indicate starting torque, pull-out torque and normal operating region of induction motor on characteristic itself.
8 (a) Which supply system is used for transmission and why is it advisable to transmit power at high voltage levels ?
(b) State the economical and environmental viability of Nuclear Power Plant in Punjab.
9. explain constructional features, working principle of induction motor used in domestic ceiling fan. Draw
neat diagrams.

Earning:   Approval pending.