HCS Optional Paper: Electrical Engineering Optional Paper 2014
Baljit Dhaka
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HCS Optional Paper: Electrical Engineering Optional Paper 2014

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HCS Mains Electrical Engineering Optional Paper 2014

Time : 3 Hours                                                                                                                                M.M.: 150
Note i) Attempt five questions in all. All questions carry equal marks. Question number 1 is compulsory. Answer any two questions from Part I and two questions from Part II. Parts of the same question must be answered together and must not be interposed between answers to other questions. 

Q1. Write critical notes on any four: 
a. Memory interfacing in Microprocessor 
b. Swing curve and equal area criterion 
c. Wind Energy Conversion System 
d. Wave propagation in bounded media 
e. Sample and hold circuits 
f. Superhetrodyne receivers                                                                           (4x7.5 = 30) 

                                                                    Part - I

Q2. In free space, the magnetic flux density is given by as follows
         B = y2ax+z2ay+x2az   Wb / m2

(i) Show that B is a magnetic field.
(ii) Find the magnetic flux through x=l, 0 < y < 1 and 1 < z < 4.
(iii) calculate current density (J)                                                                          (15)

(b) Define intrinsic impedance. A uniform plane wave in free space is given as follows

      Es=200∠30° e-j250z.ax  V/m.


(i) Phase Constant (ß)
(ii) Angular frequency (ω)
(iii) Wavelength (λ)
(iv) Intrinsic impedance (η)
(v) Magnetic field (Hs)                                                                                              (15)

Q3. (a) Explain briefly the early effect phenomenon in BJT.                                          (10)

For the circuit shown in Figure =hfe=100,

(i) Verify if the transistor is in the cut-off, saturation, or in the active region 
(ii) Find V0                                                                                                           (10)

(c) What is the effect of the gate capacitance of MOSFET in driving circuit when it is used in high-frequency power switching applications like sine wave inverter or DC-DC converter?   (10)

Q4. Using -Y substitution, determine the resistance between a and d, in below figure:

(b) Determine the current I in below figure using the ladder method:


(c) Specify power supply voltage range, output logic 1 level voltage and output logic 0 level voltages for standard TTL gates.      (10)

                                                                    Part II

Q5. Draw the signal flow graph corresponding to the block diagram of the system below. Evaluate the closed-loop transfer function of the system using Mason's formula. 

(b) A unity negative feedback control system has open loop transfer function
                    G(s) = K (s + 1)s3+as2+2s+1

Using Routh's criterion. determine the value of 'K' and 'a'. so that system oscillates at a frequency of 2 rad. / sec.                                                                                           (10)

(c) Explain the phenomenon of superconductivity. Estimate the critical magnetic field for the superconductivity of Niobium at 5° K.                                                                        (10)

Q6. (a) The time-current characteristics of an induction type overcurrent relay is:

It is desired to determine the time of operation of 5-ampere relay having a current setting of 125% and TMS of 0.6 connected to a supply circuit through a C.T. ratio 400/5 ampere when the circuit carries a fault current of 4000 amperes.  (10)

(b) Describe the various addressing modes in the microprocessor 8085. Give suitable examples for each addresing modes.  (10)

(c) What are different types of electrical resistance strain gauges? Strain gauge with gauge factor of 2 is fastened to a metallic member subjected to a stress of 1000 kg/cm2. The modules of elasticity of metal is 2 X 106kg/cm2. Calculate percentage change in resistance of the strain gauge. What is the value of poisson's ratio? (10)

 Q7. (a) For a 2-bus system shown below, derive expressions for real pow-er and reactive power at receiving end and sending end.  (20)

(b) What are the main causes of low power factor? Discuss measures by which low power factor can be avoide (10)