Cochin University of Science and Techology (CUST) 2009-4th Sem B.Tech Electrical and Electronics Engineering s , 2006 scheme - Question Paper

BTS (C) - IV- 09 - 014 - S

B. Tech Degree IVSemester Examination, April 2009

EE 403 ELECTRICAL MACHINES I

(2006 Scheme)

Time : 3 Hours    Maximum Marks : 100

PART-A

(8x5 = 40)

(a)    Explain the working principle and two essential parts of d.c. generator.

(b)    Derive the e.m.f equation of d.c, generator.

(c)    Explain Resistance Commutation method.

(d)    What are the conditions to be satisfied for running two or more dc. shunt generators in parallel?

(e)    Derive the expression for torque produced in d.c. motor.

(f)    Explain the advantage and disadvantage of Swinburnes test.

(g)    Transformer is a constant flux device. Explain.

(h)    Write a note on scott connection and open delta connection.

PART-B

(4x15-60)

II.    (a) Define the following terms :

(i) Pole pitch    (ii) Coil span

(iii) Winding pitch    (iv) Commutator pitch.    (8)

(b) A 4 pole d.c. generator has 500 armature conductors and useful flex of 0.05 Wb/pole.

What will be the e.m.f. generated if it is lap connected and runs at 1200 rpm ? What must be the speed at which it is to be driven to produce the same e.m.f., if it is wave wound?    (7)

OR

III.    (a) Explain the armature reaction of d.c, generator. Enumerate and explain the methods to

overcome the adverse effects of armature reaction.    (7)

(b) Determine per pole, the number (i) of Cross magnetizing ampere-tums (ii) of De, magnetizing ampere turns and (iii) of series turns to balance the back ampere turns in case of a d.c. generator having the following data :

500 conductors, total current 200 A, 6 poles, 2 circuit wave winding, angle of

lead = 10 (Mech), leakage coefficient =1.3.    (8)

IV.    (a) Explain the external characteristics of d.c. shunt generator.    (5)

(b) The open circuit characteristics of d.c. shunt generator is given below:

Emf(Volts) : 22 44 66 84 99 111 120 125

Field current (A) : 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Determine the load current when the terminal potential difference is 120 V, the field resistance 15 Q at a speed of 600 rpm. Armature resistance is 0.025 O (Use graph). (10)

OR

Explain the advantages of parallel operation of two generators. With a neat circuit diagram, explain procedure for connecting two shunt generators in parallel.    (8)

Two shunt generators each with armature resistance of 0.02 2 and field resistance of 25 Q run parallel and supply a total load of 3900 A. The emfs are respectively 200V and 210 V. Calculate bus bar voltage and output of each machine.    (7)

Draw the electrical and mechanical characteristics of d.c. series motor.    (5)

Explain the necessity of starters in d.c. motor and describe three point starter with

neat sketch.    (10)

OR

With a neat circuit explain the Hopkinsons test on two identical d.c. machines.

What are the advantages of this test over other methods?    (10)

A 200 V d.c. series motor drawn full load current of 38 A at the rated speed of 600 rpm.

The motor has armature resistance of 0.4 and series field resistance is 0.2 Q . The voltage drop irrespective of load is 3 V. Find the speed of motor when the load current drops to 19 A.    (5)

A single phase transformer has 1000 turns on the primary and 200 turns on the

secondary. The no load current is 3 A at a p.f of 0.2 lag. Calculate the primary

current and power factor when secondary current is 280 A at p.f. of 0.8 lag.    (5)

What are the losses in transformer? Derive the condition for maximum efficiency. (10)

OR

Consider a 4 KVA, 200/400 V single phase transformer supply full load current at 0.8 lagging power factor. The O and SC tests are as follows :

OS test : 200 V, 0,8 A, 70 W (onL.Vside)

SC test : 20 V, 10 A, 60 W (on H.V side)

Calculate full load efficiency at unity p.f and draw the equivalent circuit referred

to H.V side.    (10)

What are the conditions under which parallel operation of transformers is permissible? (5)

**#

BTS(C) -1V - 09 - 016 E

B. Tech Degree IV Semester Examination, April 2009

EC/EE 405 ANALOG COMMUNICATION

(2006 Scheme)

Time : 3 Hours    Maximum Marks : 100

PART A

(Answer all questions)

(8x5=40)

I.    (a) What is vestigial side band transmission?

(b)    With the help of a diagram explain envelop detection.

(c)    Define and explain frequency deviation in FM.

(d)    Explain the principle of ratio detector.

(e) Define the terms :

(i) Sensitivity (ii) Selectivity (iii) Double spotting.

(f)    Compare AM and Angle Modulation Schemes.

(g)    Explain the term call routing.

(h)    Write short notes on DTMF dialing.

PART B

(4x15=60)

II.    (a) Define AM. Derive the power relations in AM. Plot its Spectrum.    (10) (b) What are the advantages of SSB generation?    (5)

OR

III.    (a) Explain the working of super heterodyne receiver.    (10) (b) What are the advantages of SHD receivers over TRF receivers.    (5)

IV.    (a) Give the block diagram of FM sterio. transmitter and explain.    (10) (b) Compare narrowband and wideband FM. (5)

OR

V.    (a) What is meant by pre-emphasis and de-emphasis? Explain with circuit schematic.    (8) (b) What are the different methods used for detection of FM signal and explain any

one of them.    (7)

VI.    What is meant by noise? Explairi the different types.    (15)

OR

VII.    (a) What is the importance of AGC circuit in the receiver?    (7)

(b) Define and explain signal to noise ratio and noise figure of a receiver. (8)

VIII.    (a) Explain different types of signalling.    (10)

(b) With block diagrams, compare In band (VF) and Outband signalling schemes. (5)

OR

IX.    (a) Explain traffic load and grade of service in telephone systems. __(10)

(b) Write short notes on : routing calls.    (5)

BTS (C) - IV- 09 - 012 - C

B. Tech Degree IV Semester Examination, April 2009

IT/CS/EC/CE/ME/SE/EB/EI/EE/FT 401 ENGINEERING MATHEMATICS IH

(2006 Scheme)

Time : 3 Hours    Maximum Marks : 100

PART - A

(Answer ALL questions)

(8x5 = 40)

I.    (a) Show that the function f{z) sin z is analytic.

(b)    What do you mean by conjugate harmonic function? Verify whether the function e^x sin y is harmonic.

(c)    State and prove Canchys integral formula.

(d)    Define the residue of a function at an isolated singularity and determine the poles

z² -2 z

of--r and the residue at each pole.

(z +1) (z² +1)

(e)    Form the'partial differential equation by eliminating the arbitrary constants in z = (x - a)² + (y - b)² +1.

(f)    Solve p² +q² = x² + y².

(g)    Derive one dimensional heat equation.

(h)    Solve the equation = 4 , u (0, = 8e~^3> by the method of separation of variables.

dxdy

PART-B

(4x15 = 60)

II.    (a) Show that the function f(z) .\j\xy\ is not regular at the origin, eventhough Canchy -

Riemann equations are satisfied at the origin.    (5)

(b)    Find the analytic function w~u + IV, given that v = e^lx (x cos 2y y sin 2). (5)

(c)    Find the equation of the orthogonal trajectories of the family of curves given by

3x2y + 2x2 yl 2y2 = a, where a is an arbitrary constant.    (5)

t OR

III.    (a) What do you mean by conformal mapping? Also discuss about

(i)    Translation

(ii)    Magnification and rotation    (5)

(b)    Discuss the transformation about w = sin z.    (5)

(c)    Show that the image of the hyperbola X² y² =1 under the transformation

1

w = is the lemniscate R = COS 2<j).    (5)

z

IV.    (a) Verify Canchys theorem for the integral of z³ taken over the boundary of the

rectangle with vertices 1,1,1 + /, 1 + f.    (5)

z² 1

(b)    Find the Laments series expansion of r-about z = 0 in the region

z +5z + 6

2 <|z| <3.    (5)

(c)    Using Residue theorem, evaluate f-where C : \z - 2j = 2.    (5)

_c^J(z-l)(z²+9)

OR

} jc2    A    

V.    (a) Evaluate 7--~rr-rrr- using contour integration where a > 0 > 0.    (8)

i(x²+a²) (x²+&²)

fsinmx , ,    .    _

(b) Evaluate I-ax using contour integration where m > 0.    (7)

³ x

VI.    Solve -

(i)    p(l + q) = qz    (4)

(ii)    z2(p2x2+q2) = \    (5)

(iii)    (*2 +y2 + yz)p + {x2 +y2-xz)q = z(x + y)    (6)

OR

VII.    Solve -

(i)    (D*-3D2Dl+4D'3)z = ex+2y *    (4)

(ii)    -3DD1 + Z)'2)z = sin;tcosiy    (5)

(iii)    {tf-lDDt2-6D*) = x2y + sm(x + 7y)    (6)

VIII.    (a) A string is stretched and fastened to two points I apart. Motion is started by displacing

the string in the form y = a sin (/TJC f from which it is released at time t = 0.

Show that the displacement of any point at a distance x from one end at time t is given

by >>(;t,r) = asin(;rjc/)cos(;rcf/).    (8)

(b) Obtain DAlemberts solution ofthe wave equation by the method of separation of

variables.    (7)

: OR

IX.    (a) A string is stretched and fastened to two points x = 0 and X = apart. Motion is

started by displacing the string into the form y = k{tx Jt² ) from which it is

released at time t = 0. Find the displacement of any point on the string at a distance of* from one end at time t.    (8)

(b) Obtain solution of Laplaces equation over a rectangular region by the method of

separation of variables.    (7)

BTS(C) - IV 09 017-A

B. Tech. Degree IV Semester Examination, April 2009

EB/EC/EI/EE 406 INDUSTRIAL AND POWER ELECTRONICS

(2006 Scheme)

Time: 3 Hours    Maximum Marks: 100

PART-A (Answer all questions)

(8x5 = 40)

I    a) Explain the turn-off mechanism of an SCR.

b)    Draw and explain half wave RC trigger circuit for an SCR.

c)    Explain the difference between a half controlled bridge and fully controlled bridge.

d)    Explain the function of a freewheeling diode, showing how it is connected in the circuit.

e)    Explain auxiliary commutation scheme for SCR.

f)    Explain various PWM techniques used in inverters.

dv

g)    Explain with circuit, protection for thyristors.

dt

h)    What is dielectric heating? Write applications

PART-B

(4x15 = 60)

II    Draw the V.I characteristics of a TR1AC and explain its working in each of the

four modes using appropriate diagrams,    (15)

OR

III    a) What are the various methods to tum-on an SCR.    (7) b) Explain the working principle of thyristars using two-transistor analogy.

Also device necessary equations.    (8)

IV    Draw and explain the various voltage wave forms of a single phase full wave controlled rectifier (with discontinuous load current) with the armature of a d.c.

Motor as load.    (15)

OR

V    Draw the circuit of a three phase full wave rectifier with R load and explain its working.

With suitable waveforms.    (15)

VI    a) Explain the working of Jones Chopper. *    (10) b) Explain the working of single-phase series inverter. (5)

OR

VII    a) Briefly explain the concept of slip power recovery scheme in the speed control of

Induction Motors.    (10)

b) Describe the principle of d.c. Chopper operation.    (5)

VIII    a) Explain online and offline UPS with the help of block diagram.    (8) b) A Boost regulator has an input vpitage of v_in 15 V. The average output voltage

is =25 V and average load ament l_av 0.5 A. If L 50 juH and C20Q juF determine

i)    Duty cycle

ii)    Ripple current in inductor

iii)    Ripple voltage of filter capacitor

Assume the switching frequency as 25 KHz.    (7)

OR

IX    a) What is induction heajing? Explain its principle. Briefly explain any two applications of induction heating.    (10)

b) What is a static switch? List the merits of static switches over mechanical switches. (5)

***+

BTS (C) - IV- 09 015 - F

B. Tech Degree IV Semester Examination, April 2009

EE 404 LINEAR SYSTEM ANALYSIS

(2006 Scheme)

Maximum Marks : 100

Time: 3 Hours

(a)

(b)

(c)

(d)

PART - A

(Answer ALL questions)

(8x5 = 40)

Briefly explain the following with suitable examples :

(i) Time variant and time invariant systems (ii) Static and dynamic systems. Explain and illustrate masons gain formula.

Draw a simple thermal system and explain it with its associated variables and parameters.

Obtain the transfer function of the given system.

~=9 x    ouJrpui^-

I

M, '

V.

6

/

/J

7777/ 7/

TTT7

Define the time response of a system. Obtain the time response of a first order system to a unit ramp input.

Briefly describe about the different static error constants.

S + 4

Decompose the transfer function    

(e)

(f) (g) (h)

and hence obtain the

u(s) (j + l)( + 5)

state model in pole - zero form.

State and explain Liapunovs main stability theorem.

PART-B

(4x15=60)

C()

Obtain the transfer function

of the-system using block diagram reduction.

II.

(15)

Also draw the signal flow graph representation of the system.

Draw the block diagram representation and signal flow graph representation of v the system shown. Find 1- using signal flow graph.

(15)

R\

_/vwi

m

(Turn Oxer)

L

i

Write the dynamic equations for the mechanical system shown and draw the torque - current analogous electric circuit.

y, k, ' . _ *3

-T*

_ 1....... .

Obtain the step response of a second order system.

OR

The maximum overshoot for a unity feed back linear system having its forward path

K

transfer function as G(s) = --- is to be reduced from 60% to 20%. The

(ST + l)

system input is a unit step function. Determine the factor by which K should be reduced to achieve the above condition.

Determine the steady state error for the system whose open loop transfer function is given by

G(s) H (*s) = 2-for the input /*(/) = 10 + 5/ + .

s 214 -h 40    2

A linear - time invariant system is characterized by the following state equation :

(O'