C.S.(MAIN) EXAM, 2009

ELECTRICAL ENGINEERING
Paper-II

Time Allowed: Three Hours Maximum Marks 300

INSTRUCTIONS

Each question is printed both in Hindi and in English.

Answers must be written in the medium specified in the Admission Certificate issued to you, which must be stated clearly on the cover of the answer-book in the space provided for the purpose. No marks will be given for the answers written in a medium other than that specified in the Admission Certificate.

Candidates should attempt Questions 1 and 5 which are compulsory, and any three of the remaining questions selecting at least one question from each Section.

Assume suitable data if considered necessary and indicate the same clearly. Symbols/notations carry usual meaning, unless otherwise indicated.

All questions carry equal marks. Marks assigned to each part of the question are indicated at the end of the respective part.
SECTION-A

I. Determine the transfer function of the network shown in Fig. <img src='./qimages/22-1a.jpg'> 20
A 50-Hz, three-phase transmission line is 250 km long. It has a total series impedance of (35 j 140) Q and a shunt admittance of 930 X 1 o-6 L90° a. It delivers 40 MW at 220 kV with 0·9 power factor lagging. Find the voltage at the sending end by the nominal-n approximation. 20
The instruction OUT FFH of 8085 is stored from memory location 4 048 H. The opcode for OUT instruction is D3H. Draw and explain the timing diagram for the execution of this instruction giving timings for signals like ALE, Address lines, data lines and memory. 20

2. By giving suitable example explain clearly the difference between accuracy and precision.

A power transformer was tested to determine losses and efficiency. The input power was measured as 3650 Wand the delivered output power was 3385 with each reading in doubt by ± IO W. Calculate the percentage uncertainty in the losses of the transformer and the percentage uncertainty in the efficiency of the transformer, as determined by the difference in input and output power readings. 12=20

List the merits and demerits of outdoor SF 6 circuit breakers.
Draw a simple one line diagram of a generator breaker using SF 6 breaker connecting the generator to EHV bus through a main transformer. 15+5=20

A 50 Hz turbogenerator is rated 500 MVA, 22 kV. It is Y-connected and solidly grounded and is operating at rated voltage at no load. It is • disconnected from rest of the system. Its reactances are X" X2= 0· 15 and X0= 0·05 per unit . Find the ratio of the subtransient line current for a single line-to-ground fault to the subtransient line current for a symmetrical three-phase fault, and inductive reactance in ohms to be inserted in the neutral connection of the generator to limit the subtransient line current for a single line-to-ground fault to that for a 3-phase fault. 10+10=20

Determine the stability of the closed-loop system whose transfer function is given as <img src='./qimages/22-3a.jpg'>

Explain briefly what is the swing equation and use dynamics of angular motion with time to formulate the equation for a synchronous generator of inertia constant H in seconds run by a mechanical turbine with input power P in p.u. to deliver electrical power Pe in p. u. to the electrical network at f Hz in terms of power angle o in radians measured from rotating reference of generator q-axis. Indicate briefly how the solution of the swing equation can be obtained by point by point steps of time) method of calculation. 20

Draw the Mho and Offset Mho characteristics of a distance relay for the protection of transmission lines and give the main applications of offset Mho relay.

A 3 phase, 2 pole, 11 kV, 10,000 kVA alternator has neutral earthed through a resistance of 7 ohms. The machine has current balance protection which operates upon out of balance current that exceed 20% of full load. Determine of winding protected against earth fault. Exclude the% reactance of generator winding for calculation. 10+10=20

4. Explain how the following adjustments are made in a single phase induction type energy meter Lag adjustment Adjustment for friction compensation Creep Overload compensation (v)Temperature compensation. 20

With a neat sketch, show the block diagram of a PCM transmitter and receiver, clearly indicating the various parts. What are the different types of quantizers Give a sketch of the two types of uniform quantizers. How will you reduce quantization error

Bandwidth of an input signal to the PCM is restricted to 4 kHz. Input signal varies in amplitude from -3·8 V to +3·8 V. It has an average power of 30 mW. Required signal to noise ratio is 20 dB. The PCM modulator produces binary output. Assuming uniform quantizatio?? find number of bits required per sample. 12+8=20

Sixteen bytes of data are stored in memory locations 7000 H to 700F H. Copy the data to locations AOOF to AOOO H such that the byte at 7000 H is copied at AOOF the byte at 7001 H is copied at AOOE H and so on.

Describe the flags of 8085 microprocessor.10+10=20

SECTION-B

5. With the help of a block diagram explain the principle of working of a digital storage oscilloscope. Discuss advantages of this oscilloscope over analog oscilloscope. 20

Give two reasons for using c.t.s. for overcurrent protection in ac medium voltage distribution and subtransmission of power systems. Explain the term 'Plug Setting' define lug Setting Multiplier' (P.S.M.) and draw a typical time of operation t (in seconds) versus P.S.M. characteristic of an Inverse Definite Minimum Time Lag (IDMTL) overcurrent relay showing its speciality.

Draw the c.t.s., phase and ground fault overcurrent relay connection diagram at a substation for the minimum number of relays to cater for all types of fault on a 3-phase overhead line. What modification is necessary to extract information about the type of fault

For a radial 3 phase 1 1 kV, 50 Hz line ABCD fed at A only, a relay at- substation C clears the 3-phase 200 MVA fault close to C in section CD of very short length in 0· 1 sec. Find the P.S., P.S??M. and the Time Setting Multiplier (T.S.M.) of the IDMTL overcurrent relay at substation B connected via 400/5 amp c.t.s. to provide a discrimination time of O· 5 seconds. The nomograph of the relay for TSM 1 ·O is as follows
<img src='./qimages/22-5b.jpg'>
Justify the discrimination time of 0·5 seconds based on a 5 cycle breaker. For choosing P.S., P.S.M. should be as close to 20 as possible. 7=20

What are the advantages and disadvantages of delta modulation compared to PCM With the help of sketch, mention the various noises associated with delta modulation. How will you overcome these noises

A sine wave of frequency f and amplitude A is applied to a delta modulator of step size m Show that the slope overload distortion will occur if <img src='./qimages/22-5c2.jpg'> where T5 is sampling period. What is the maximum power that may be transmitted without slope overload distortion 10+10=20


6. Consider the system shown in Fig. where the damping ratio 0·6 and the natural frequency ro 5 rad/sec. Obtain the values of rise time t p;ak time t maximum overshoot M and settling time t for Pthe criterion when fue system is subjected to a unit-step input.<br><br> <img src='./qimages/22-6a.jpg'>
Write a segment of 8085 Assembly language program to execute the instruction NOP 1000 times.
In UO mapped UO mode of 8085, how many maximwn input devices and maximum output devices can be connected What will be their addresses
Which flags are set or reset by the following instructions INX B CALL address MOY B



Give the block diagram to recover baseband signal from a BPSK signal. Also plot the power spectral density of BPSK signal. From that plot, show that minimum bandwidth of BPSK signal is equal to twice of the highest frequency contained in baseband signal. Mention one major drawback of BPSK receiver. 20
7. How is the differential output taken from an l inductive transducer Explain the advantages when inductive transducers are used in pushpull configuration.
A LVDT has an output of 6 V rms when the displacement is 0·4 x 1 0-3 m. Determine the sensitivity of this instrument in volt/mm. A 1 0 V voltmeter with 1 00 scale divisions is used to read the output. Two tenths of a division can be estimated with ease. Determine the resolution of the voltmeter. The above arrangement is used in a pressure transducer for measuring the deflection of a diaphragm. The diaphragm is deflected by O· 5 x l O 3 by a pressure of 1 000 N/m2 . Determine the sensitivity and resolution of this instrument. 12=20

An 8085 processor based interrupt system requires handling of 11 interrupting devices, excluding TRAP interrupt. Show schematically how this can be achieved. Indicate any one interrupt vector address. 20
A linear block code have the fo llowing parity -check matrix H <img src='./qimages/22-7c1.jpg'> Determine generator matrix G and code word for the data bit 101.
Give a basic sketch illustrating a convolutional encoder with k k 1 and n 2. What are its advantages and disadvantages over block codes 12+8=20
8. Consider the state equation <img src='./qimages/22-8a.jpg'> Find the state vector fo r t 0 when the input is a unit step input. 20

A 50-Hz generator is rated 500 MVA, 20 kV, with 0·20 per unit. It supplies a purely resistive load of 400 MW at 20 kV. The load is connected directly across the terminals of the generator. If all three phases of the load are short-circuited simultaneously, find the initial symmetrical current in the generator (RMS value) in per unit on a base of 500 MVA, 20 kV. 20
Draw the block diagram of a microprocessor based distance relay for protection of transmission line. 20

Note English version of the In structions is printed on the fr ont cover of this question paper.