I09/1 I
2008

ELECTRICAL ENGINEERING
Paper 1
Tillie.' 3 Hours jrMaximum Alarhs 300

INSTRUCTIONS
Candidates should attempt all the questions in Parts B However, they have to choose only three questions in Part D. C.
Answers must Kannada). be written in the medium opted (I.e. English or
This paper has four parts
A B C D 20 marks 100 marks 90 marks 90 marks Marks allotted to each question are indicated in each parl.


09/1 (2I PART A 4x5=20
Answer all questions. Each question carries 5 marks.
1. What are the different types of voltage and current sources Identify the type of source shown in the circuit.

(bl What is the equivalent resistance between A and D III the circuit shown below


What is meant by an underexcited synchronous motor If a synchronous motor is overexcited, does its mechanical power output increase?


The Maxwell bridge is shown below. Draw the phasor diagram under balanced condition.


12 R2

L2
•
1
3
L4H3
R414

V
V
21

V
09/1
PARTB 1OxllJ=lOO
Answer all questions. Each question carries 10 marks.
2. Calculate below. the currents through VI and V2 m the circuit 8hO'wn

VI 2A ..- V2
2 3 4

4A 5A
i i

5f! 10 lOfl 5Q

3.
Find the trigonometric Fourier senes for the square shown in the figure and plot the line spectrum that shows the amplitude of each harmonic.

4.
State and explain Gauss's law as applied to the electrostatic field.


With reasons state the electric field strength and potential at all within an isolated metal sphere of radius r. Assume the charge on the sphere to be Q.
5 State Biot -Savart's law as applied to steady magnetic field. Formulate an expression [or the magnetic flux density at a point P due to thl' current in a differential element of a current carrying conductor.
6. Sketch the deflection system for a Cflthode Ray Tube. Discuss briefl.v the function of each component.
i Turn over
09/1 (4
7.
Two resistors R1 and R2 are connected In senes. If the values of R1 and R2 are respectively (100 ± 0·1) Q and (50 ± 0·03) calculate the uncertainty in the combined resistance.

8.
An npn transistor with 50 is used in a common emitter circuit with VCC 10Vand RC 2 K. The hias is ohtained by connecting a 100 K resistance from collector to base. Assume VBE O. Find the quiescent point and the stability factor.

9.
Show that a high pass RC circuit functions as a differentiator. Also sketch the output voltage if the input to the differentiator is a triangular wave shown below,


v.,

10. If the conductor carnes a current of 800 A m the direction shown. calculate

the force on the conductor and


the force on the moving N pole.


......,,........_-Conductor in the slot

•

5 I 09/1

1L The autotransformer shov-m below has an 80 percent tap and the supply voltage is 800 V. If a 3·6 kV, upf load is connected across the secondary, calculate
[ill tlll: secondary voltage and current the currents that flow in the winding the relative amount of copper required for portions Be and CA.

A

09/1 161
PARTe 6x15=90
Answer ull questions. Each question carries 15 marks.
12. Determine which of the circuits shown 18 planner and redraw it with no crossing branches.
8(1
2Q
5Q 4Q
1Q

3Q
10V
L...
4Q
Ii) Iii)
IL) Determine the current through 2 .Q resistor.
12 Q 4Q 4Q



13. A charged particle moves 'lith a uniform velocity of 4ftx mis m a
region where E 20ay Vim and B Boaz such that the velocity of the particle remains tesIa, Determine Bo constant. Derive the
• expression used for solving the problem. A Vl,ry large solenoid with 2 x 2 em cross-section has an iron core of permeability 1000 and 4000 turns/metre. If it carries a current of 500 rnA, find
its self inductance/metre the energy/metre stored in its field.
14. the equivalent circuit for the CE and CC configurations subject to the restriction that R L O. Show that the input impedances of the two circuits are identicaL Approximate conversion formulas for transistor parameters shown in the table can be used.
Turn over

(7I
Draw the equivalent circuit for the CE configurations subject to the restriction that the input is open-circuited. Show that the output impedance.s of the two circuit.'3 are identical. Approximate conversion formulas for transistor parameters shown in the table can be used.
Table -Approximate conversion formulas for transistor parametE'l's
CC
Symbol
CE
CB
h
hi"
hIe
w

1-h
hbh I
I OJ_ h

l+hfl) I'll

h/11
hi'p
hrh h
hill'
hoe
ob

h

h

"
h
fe
hh
Ie
lIfe
T


+..

hk
h

h
OP
e,D


h· h. h.
hib
Ihrc 1 11 1I

1
hi, -hfC hfll

h

h fb
09/1 18)
15. What is creeping in energy meters Is it advantageous to consumers? If the answer is no, how is it prevented
In the measurement of a resistance by the voltmeter-ammeter method, connections as in and were used. In case the curnmt measured was 2 A and the voltage 180 V. Find the percentage error in calculating R as the quotient of the readings; the true value of and the reading of the voltmeter in case if the current indicated by the ammeter is 2 A.
A 001 Q A 0·01 Q

V 2000 Q
R
R
Ii) Iii)
16.
HPerfectly synchronized synchronous machines have an inherent tendency to remain in step on account of the changes produced in their arrnaturl' currents by a divergence of phase." Substantiate the statement.

17.
An induction motor has an efficiency of o·g when the load is 50 hp. At this load, the stator copper and rotor copper loss each equals the iron loss. The mechanical losses are one-third of the no load loss. Calculate tht, slip.


•
I 09/1 PARTD

Answer any three of the following questions. Each question carries
30 marks.

V
o
I For the circuit shown, find



what value of a will produce
Vo I 10





R3
Rz
R4
V

a

ala
50t• t
ib) For the circuit shown below, v 120 e-50t and i 30 O.
R

•
Find Land R.

•
Det£'rmine the time constant.

•
Calculate the initial energy In the inductor.

•
\That fraction of the initial energy is dissipated in 10 ms


2
sis lOJ
If Zls) . 0 talll the Second Foster form network. +4)ls2 161
1!J. List the MuX",cll's equations for the static electromagnetic fields in the point and integral forms. Also mention the law Of postulate governing the individual equation of Maxwell's.
(bOi Derive an expression for th£' power flow associated with arl electromagnetic wave.

Prove that v. r where r IS the position vector of any point In space.
Turn over
09/1 I 10)
20. Based on the input impedance, the output impedance voltage or current gain, compare the voltage, transconductance and transresistance amplifiers. and the current,
Determine the final output waveform X for the circuit shown below with the input waveforms Band C.
A.J! A X
21. A salient pole synchronous generator with damper winding IS supplying power to an infinite bus. Explain what would happen if its field circuit gets open circuited accidentally.
The maximum efficiency of a 500 kVA, 3300/500 50 Hz, single· phase transformer is 97l and occurs at 75% full load, unity power factor. If the impedance is lOW, calculate the regulation at full load, power factor 0-8 lagging.
22. Detennine the equations of balance for Wien's bridge the value of unknown frequency. to determine
Three voltmeters are uRed to measure the power input to an inductive load In series with a non-inductive resistance. Tho voltages across the resistor, the load, and the combination respectively are 75 80 V and 140 V. The current is 4 A. Find the power absorbed by the load and by the non-inductive resistor.



09/2 (2
PART A

Answer all questions. Each question carries 5 marks.
1. What are the three types of d.c. drives based on input supply? Also list the further classification of anyone type.

A wound rotor induction motor is excited by a 3-phase, 50 Hz SDurce. State the mode of operation of the machine and calculate the frequency of the rotor current under the following conditions


Motor turning at 500 rpm In the opposite direction of the revolving field.


Motor turning at 1500 rpm In the same direction as the reva}ving field.




The currents in a system are In 12 j6


Iy 12-j12 A and IE -15 jl0 A. Find the zero sequence
component.
I A modulated carner wave has maXImum and minimum amplitudes of Hi V and 4 V. Calculate the value of percentage modulation.
I 09/2
PARTB Answer all questions. Each question carries 10 marks. lOx 10=100
For the positive feedback system shown, determine loop transfer function, control ratio, Ie) error ratio and system characteristic equation.

Els)

I"


C(s
His)
s(s

""
60

s
3. A single phase full bridge inverter is shovm below. Draw thE' wavpfllrJ1l for the output voltage and briefly explain the operation of the inverter.
Q I
T
2
I



-.L
s
T
2
I

D I D3 Q:J
a I ILuad} b1




4. A 10 kW, 4-20 4-polp, 50 IIz, delta connected squirrel cage induction motor gave the following data fi)f blocked rotor test:
210 V, 20A, 5kW.
Stator core loss at rated voltage and frequency is 300 ,Y. The d.c. rpsistance mea.sured between any two stator terminals is 0·6 Q. Determine the starting torque at rated voltage and frequency. Assume the a.c. resistance to be 1·2 times the d.c.
lTurn over
09/2
5.
Discuss the methods of starting a synchronous motor.

6.
A 3-phase line is supported by a suspension string having 3 units. The voltage across the nearest to the line is 20 kV and that across the adjacent unit is 15 kV. Find


the ratio of capacitance of joint to capacitance of the disc,


the system line voltage, and


the string efficiency.



7.
Describe with the aid of a diagram of connection, the Merz pnce circulating current system for the protection of transformers.

8.
An electric motor has load variation as given


Torque in Nm 240 140 300 200
Duration in minutes: 20 10 10 20

If the speed of the motor is 720 rpm, find the power rating of motor.
9.
Define the channel in communication. List separately the various sources of noise.

10.
Calculate the beam width between nulls of a 2 m paraboloid reflector used at 6 kHz. Also calculate the gain of the antenna.

11.
Discuss the factors tlwt dictate the direct coupling of amplifier stage,; instead of other types of coup1ing.


09/2


PARTe
Answer all questIOns. Each question carries 15 marks.
For the unity negative feedback control system shov,m, calculate

the percentage overshoot for a unit step input,


the settling time for a unit stcp input, and


tel the steady state error for input defined by HlP polynomial rll) 41 6t2, t O.

la. A thl'l,p-phase bridge rectifier has a purely resistive load of R Determine
i the efficiency,
the form factor, and
(CJ the ripple factor.

(al Explain the consequence ""hen the rotor of an induction l1lotor connected to rated voltagE' gets locked.
A 4-pole, 3-phase, 50 Hz, inductum motor runs at 4S; shp at ful: load. Determine
the rotor speed,
(ii the frequency of the rotor currents,
the speed of rotor field with respect to the stator, and the speed of the rotor field with respect to the siator field.
ITurn over
09/2 I6I
15. A 36 MVA, 21 kV, 1800 rpm, 3-phase generator connected to a power grid has synchronous reactance of 9 Q1ph. If the exciting voltage is 12 kV Cline-to-neutral) and the system voltage IS 17·3 kV (line-to-linel, calculate the following:

The active power which the machine delivers when the torque angle is 30° (ele).


The peak power that the generator can deliver before it falls out of step or loses synchronism.


¥hat conditions must be met before a generator can be connected to a 3-phase system
16.
A single-phase 50 km long transmission line consists of two aluminium conductors with a 3 em diameter separated by a spacing of 2 metres. The sending voltage is 8 kV at 50 Hz. If the transmission line is operating with the receiving side of the line open-circuited, how much charging current is flowing in the line? The resistance of the line is 2·0 n.

17.
Assuming a quodrilateral speed -time curve, derive the expressiun for the total distance travelled between two stations and tht' velocity at braking.


(bl State the Sampling theorem as applied to pulse modulation system.
7 I 09/2
PARTD 3x30=90
Answer any three of the following questions. Each question carries
:30 marks,
18. (01 The closed loop transfer function of a control system is
Determine the closed loop steady state

response of this system when a sinusoidal input
5 sin (wi is applied.
(hi For the equation 82 2s 2 k determine thf' breakaway points.
I H. Explain wh.y a D.C. motor will not work on A.C. satisfactorily, despite the fact that the revETsnl of line polarity causes no dlangl' in direction of rotation.
(hi Explain why' does an induction generator alwnys supply a lc,adinp current to the bus.
Ie) Explain the methods of obtaining increased torque' wIth permanently short-circuited (induction motor) rotor.
Vhy does tIll' speed D. synchronous motor remain constan t eveIl under variable land
(bi A HJ.·pole, star connccted alternator runs at 600 rpm. It has 120 stator with 8 conductors/slot and the each phase arc connected 10 series. Determine the phase and Ime electromotiv{.' if the flmJpole is 0-13 mvVb, Vhat harrnonic· due to the slots might occur in the phase and line
Ie) Explain the effect of sudden short-circuit of a sYIlchronouc, generator running fully excited on its mechanical design.
ilurn
09/2 (8I
21. A two bus system is shown below. If 100 MW is transmitted from Plant A to the load, a transmission loss of 10 MV is incurred. Find the required generation for each plant and the power received by load when the system Lagrangian multiplier is Rs. 25fI.1\Th. The incremental fuel costs of the two plants aTe
dC A
0·02 PCA 16 Rs./MWh
dPCA
dCB
0·04 PCB 20 Rs./MWh
dP
cn
Load


Plant A Plant B
(bl In u short-circuit test on a circuit breaker, obtained on a frequency transient: the following data was
Time to reach the peak restriking voltage 55 liS.
Oi) The peak restriking voltage 100 kV.
Determine the natural frequency of the circuit and the average rate of rise of restriking voltage.
is the percentage saving of feeder copper if the line voltage in a 2-wire. direct current system be raised from 220 V to 500 for the same trnnsmilted State any assumptions made.
22. A plywood board 0·5 m x 0·2:i m x 0·02 m is to be heated from 25° C to 125° C in 10 minutes by dielectric heating employing ft frequency of 30 MHz. Determine the power required in this heating process. Assume specific heat of wood 1500 Jlkg/oC, weight of wood 600 kg/m3 and efficiency of process 5Ofie,.
(bl A certain difference amplifier has a differential voltage 2000, and common mode gain of 0·2. Determine the common mode rejl'ctlon and express it in decibels. gain ratio
(el Discuss the propagation of electromagnetic waves in waveguidl't'i and transmission lines and state the merits and demerits.