cs(main) EXAM, 2010
ELECTRICAL ENGINEERING
Paper II
ITilne Allolved Hours II,Maxfnllun Marks: 3001
INSTRUCTIONS
Each question is printed both in Hindi and in English.
Answers 111US! be written ill the 111,ediu111 .ipecified in the Adnzission Certificate issued to you, which nU,fst be stated clearly on the cover of the in. the space provided for the pu!pose. No Inarks l-vill be given for the QnSl1lerS written in a }'nediuni other lhan that specified in the Adl1!ission Cerlificate.
Candidates should atteJ11pt Question Nos. 1 and which are conlpu.lsory. Gild any three of the renlainitig questions selecting at least one question fron1 each Section.
Assunle suitable data ifconsidered necessary
and indicate the SaJ11e cler;zrly. " SYllibols/notQtiollS carry usual 111eanulg. unless othenvise indicated.
All questions carry equal 1narks. Marks ass"iglled to each part of the question are indicated at the end of the
part.
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Section

Why is a LVDT excited by .high frequency and low voltage? Derive the LVDT output. eo, in terms of excitation voltage winding resistance and· inductances. A bridge ABCD has resistors in its four anns. R I in ann AB. R2 in arm Be.. dummy gauge .in arm AD, and active gauge in ann CD. If a strain of 1'250 J.l.m/rn is applied, find the bridge offset voltage across-.AC if the bridge is supplied with a voltage of 12 V across BD.
Assume.. RI =R2 dummy gauge 350 ohm
and R active strain gauge 350 ohm-has gauge factor' (GF 2·0). 2+10+8=20

Explain the functions of static VAR systems in EHV AC transmission.
(ii)Discuss different types of static VAR system:ms with the aid .of neat figures. 8+12=20
Write an 8085 assembly level program for designing the following system:
When a coin is inserted and when it is valid, port 1 gives code FFH. If it is valid, check whether the request is for tea or coffee at
C-DTN-K-FFB 2 (Contd.)
port 2. 04H code at port 2 is the request for tea and 40H code at port 2 is the request for coffee. Open the valve for liquid to come out with 04H code for tea and 40H code for coffee at port 3. These codes at port 3"are to be used for valve operation. When port 4 gives code OOH, -valve is to be closed with co.de FFH. Repeat process can start with a new coin. If coin is invalid, 00 indication at port 5 is to be given and the instruction for inserting a new coin can be given. Write comments 1n the selected lines of the program. 20
The loop Transfer function of a system is given by
img src='./qimages/1028-2a.jpg'>
Find the number of roots Jocated on the imaginary axis and also their values using the. Routh table. Is there any root on the right hand side of the s-plane? 5+10+5=20
Differentiate between uRestriking Pheno­menon and uReclosing in a circuit breaker. Which one is harmful and which one is useful and why?
C-DTN-K-FFB 4 (Contd.)
A-simple power system IS "shown operating on NO 'LOAD.
img src='./qimages/1028-2b2.jpg'>
A fault occurs at the far end of the system and the breaker contacts separate. Derive an expression for the _voltage across the breaker contacts. Find the frequency of oscillation of the recovery voltage. What is the highest value of the Restriking Voltage and when does it 6+14=20
A two bus system is shown in the figure below:
img src='./qimages/1028-2c1.jpg'>
If 100 MW power IS transferred from plant 1 to load, a loss of 12 MW is incurred. System incremental cost is Rs. 301MWIz. The" incremental costs of the two plants are given by
C-DTN-K-FFB 6 (Contd.)
dc1/dpg1=0.02pg1+16.0 rs./mwh.
dc2/dpg2=0.04pg2+20.0 rs/mwh.
Determnine Pg1 PG2 and power received by load. Derive the economic dispatch criterion for a power system consisting of thermal plants with transmission losses. 12+8=20 .
3.(a)(i)Explain the "principle of the argument' of the complex-variable theory.
(ii)Explain how this is adopted to determine the stability of control systems.
(iii)he critical point in using the Nyquist criterion is in plane and not the origin (0.. jO). Why?
(iv)For minimum phase transfer function, the' polar plot is sufficient to determine the stabiIity of the system. Explain.
(b)(i)Explain comparatively steady state, dynamic and transient stability of a power system.
Explain point-by-point method of solving . swing-equ3tion stating clearly the' made. 8+12=20
A certain ring feeder has 6 sections. It is fed at one point only.. Using non directional and directional overcurrent relays with suitable line lag. explain the method of protecting this feeder. Assume a minimum operating time of 60 m.s for the relays. In the diagram to be drawn, the location of all the relays and whether they are directional or non directional are to be shown. Also the time of operation of all the relays is to be shown by the side of the relay.
why the pointer of a single phase dynamometer type power factor meter re_main in the same position even after the excitation source is switched off, that is, it does not cOlne back to zero position. Explain the principle of
_operation of the power factor meter. How would the accuracy of such an instrument be affected by frequency -and wave form variations.
Explain the similarities and differences· between:
(1)JUMP and CALL instructions
STA and STAX instructions 20
Mention the salient points of relation between :the delta :modulation and differential pulse code modulation (DPCM). Draw the block diagram of delta modulator and demodu­lator.. Explain threshold and overloading effects in delta modulation. Hoy can a slope overload noise't which occurs due to threshold and overloading.. be reduced? 20
Section
Y A model of the attitude control of a space booster on take off is represented by an invertedpendul mmounted on a motor driven cart shown in the above figure. The objective of the attitude contro] problem is to J;<eep the pendulum in a vertical position. The pendulum can be assumed to move only in one plane (say the xy plane). The control force is applied to the cart. The centre of gravity of the pendulum is at its centre. The moment of inertia of the pendulum is The mass of the pendulum is and the cart is Obtain mathematical model. 20
What is User insistance switching" as applied to circuit breaker operation? Why is it resorted to Derive an expression for the value of the resistance to be used in terms of system parameters. 10
C-DTN-K-FFB 12
(Contd.)
A transmission line is protected by a three zone plain Impedance. Draw the characteristics of this relay in the R-X diagram. If this relay is provided with a directional what modification is to be made in the characteristics drawn on the R-X diagram. Also draw. the contact diagram of the arrangement assuJning directional feature. 10
Pulse code modulation is the most useful and widely used of all pulse modula­ tions..How does' an analog signal get converted to digital signal by the PCM? By which process non-uniform quanlization is practically achieved? Ora"", a diagram of a does this process. Explain its working. 20
6. Explain the 'working principle of a uHannonic Distortion Meter". State some of its typical technical specifications. . Also how is the resistance measured with an electronic multiIneter. 10+2+8=20 I
The interrupt is a process of data transfer whereby a peripheral can.inform the processor . that it is ready for commnnication. How can interrupt be masked or unmasked using a. progranl control? List the instructions used for control of interrupts. Explain anyone by taking a suitable example. -20
C-DTN-K-FFB 14 (Contd.)
15 (Contd.)
Two important types of error-correcting codes are block codes and convolutional codes. Write the main difference between the. ·block codes and convolutional codes. Explain the which are a subclass of linear block codes. 20
7. Why is a Schering bridge particularly suitable for measurement at high voltage? Draw high voltage Schering bridge line diagram, the high voltage transformer. The Wien bridge is used to measure the frequency of excitation voltage. Derive the frequency relation in tenns of bridge elements.
What are the functions .of DMA (Direct Memory Access)? How are HOLD and HLDA 'lines used in DMA operation? List the data transfer modes of DMA' controller. Describe each mode brief. 20
The network layec of OSI (Open Systems Interconnection) has two· major functions, namely routing of packets through the network and a flow control. Explain each of these two· functions taking suitable examples. Prove that the network layer is the most sophisticated of the layered architecture. 20
C ..OTN..K-FFB 16 (Contd.)
Find its characteristic equation.
Determine the controllability matrix.
the system controllable? 20
With the aid of a neat figure, state the main components of a converter station of HVDe transmession system and explain the function of each component.
Differentiate between two-tenninal point to point de transmission link and back to back de link with an example of these links existing in India. 12+8=20
Why do you need the hannonic restraint in the application of differential protection to power transformers? With the help of levant circuit diagram, explain how this harmonic restraint scheme operates?
URelays -are. comparator. 'Justify this statement. Show that an inherent two input amplitude comparator can work as a phase comparator and vice-versa.
10+10==20