Hyderabad | Delhi | Bhopal | Pune | Bhubaneswar ... - 2019 Prelims... · previous questions from 1992 onwards. The style, quality and content of the Solutions for previous ESE Questions

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Electrical Engineering(Volume - II)

(Analog and Digital Electronics, Systems and Signal Processing, Control Sytems,Electrical Machines, Power Systems and Power Electronics and Drives )

Previous years Objective Questions with Solutions, Subjectwise & Chapterwise (1992 - 2018)

ACEEngineering Publications

(A Sister Concern of ACE Engineering Academy, Hyderabad)

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ForewordUPSC Engineering Services in Electrical EngineeringVolume - II Objective Questions: From 1992– 2018

The Stage-I (Prelims) of ESE – 2018 consists of two objective papers. Paper-I is of General

Studies & Engineering Aptitude. Paper-II is of Electrical Engineering of 300 Marks and 3 hours

duration. In stage-II (Mains), the technical syllabus is divided into two papers. The subjects

included in this volume are:

1. Analog and Digital Electronics 2. Systems and Signal Processing

3. Control Systems 4. Electrical Machines

5. Power Systems 6. Power Electronics and Drives

Keeping in view of the above topics, the present Volume-II for prelims of new pattern is redesigned using the

previous questions from 1992 onwards.

The style, quality and content of the Solutions for previous ESE Questions of Electrical Engineering, will encourage

the reader, especially the student whether above average, average or below average to learn the concept and

answer the question in the subject without any tension. However it is the reader who should confi rm this and any

comments and suggestions would be pleasantly received by the Academy.

It is observed that majority of ESE objective Questions are being asked as it is in many PSUs, state service

commission, state electricity boards and even in GATE exam. Hence we strongly recommend all students who are

competing for various competitive exams to use this book according to the syllabus of the exam concerned. This

book can also be used by fresh Teachers in engineering colleges to improve their Concepts.

We proudly say that questions and solutions right from 1992 onwards are given in this book. The questions which

appeared early 90’s are most conceptual oriented and these are being repeated in the recent exams in a different

way. Hence we advise the students to practice these questions compulsorily. The student is also advised to analyze

why only a particular option is correct and why not others. Evaluate yourself, in which case, these other options

are correct. With this approach you yourself can develop four questions out of one question.

The student is advised to solve the problems without referring to the solutions. The student has to analyze the given

question carefully, identify the concept on which the question is framed, recall the relevant equations, fi nd out the

desired answer, verify the answer with the fi nal key such as (a), (b), (c), (d), then go through the hints to clarify his

answer. The student is advised to have a standard text book ready for reference to strengthen the related concepts,

if necessary. The student is advised not to write the solution steps in the space around the question. By doing so,

he loses an opportunity of effective revision.

With best wishes to all those who wish to go through the following pages.

Y.V. Gopala Krishna Murthy,M Tech. MIE,

Chairman & Managing Director,ACE Engineering Academy,

ACE Engineering Publications.

1. Analog and Digital Electronics: Operational ampli iers – characteristics and applications, combinational and sequential logic circuits, multiplexers, multi-vibrators, sample and hold circuits, A/D and D/A converters, basics of ilter circuits and applications, simple active ilters; Microprocessor basics- interfaces and applications, basics of linear integrated circuits; Analog communication basics, Modulation and demodulation, noise and bandwidth, transmitters and receivers, signal to noise ratio, digital communication basics, sampling, quantizing, coding, frequency and time domain multiplexing, power line carrier communication systems.

2. Systems and Signal Processing: Representation of continuous and discrete-time signals, shifting and scaling operations, linear, time-invariant and causal systems, Fourier series representation of continuous periodic signals, sampling theorem, Fourier and Laplace transforms, Z transforms, Discrete Fourier transform, FFT, linear convolution, discrete cosine transform, FIR ilter, IIR ilter, bilinear transformation.

3. Control Systems: Principles of feedback, transfer function, block diagrams and signal low graphs, steady-state errors, transforms and their applications; Routh-hurwitz criterion, Nyquist techniques, Bode plots, root loci, lag, lead and lead-lag compensation, stability analysis, transient and frequency response analysis, state space model, state transition matrix, controllability and observability, linear state variable feedback, PID and industrial controllers.

4. Electrical Machines: Single phase transformers, three phase transformers - connections, parallel operation, auto-transformer, energy conversion principles, DC machines - types, windings, generator characteristics, armature reaction and commutation, starting and speed control of motors, Induction motors - principles, types, performance characteristics, starting and speed control, Synchronous machines - performance, regulation, parallel operation of generators, motor starting, characteristics and applications, servo and stepper motors.

5. Power Systems: Basic power generation concepts, steam, gas and water turbines, transmission line models and performance, cable performance, insulation, corona and radio interference, power factor correction, symmetrical components, fault analysis, principles of protection systems, basics of solid state relays and digital protection; Circuit breakers, Radial and ring-main distribution systems, Matrix representation of power systems, load low analysis, voltage control and economic operation, System stability concepts, Swing curves and equal area criterion. HVDC transmission and FACTS concepts, Concepts of power system dynamics, distributed generation, solar and wind power, smart grid concepts, environmental implications, fundamentals of power economics.

6. Power Electronics and Drives: Semiconductor power diodes, transistors, thyristors, triacs, GTOs, MOSFETs and IGBTs - static characteristics and principles of operation, triggering circuits, phase control recti iers, bridge converters - fully controlled and half controlled, principles of choppers and inverters, basis concepts of adjustable speed dc and ac drives, DC-DC switched mode converters, DC-AC switched mode converters, resonant converters, high frequency inductors and transformers, power supplies.

Syllabus for Electrical Engineering (EE)

I. Analog and Digital Electronics

01.Operational Amplifi ers.............................................................................. 02 - 24

02. Number system and Coding Conversion ................................................. 25 - 29

03. Boolean Algebra ...................................................................................... 30 - 36

04. Logic Gates .............................................................................................. 37 - 45

05. Combinational Circuits............................................................................. 46 - 49

06. Sequential Circuits .................................................................................. 50 - 63

07. Logic Gate Families ................................................................................. 64 - 70

08. AD and DA Conversion ........................................................................... 71 - 72

09. Semiconductor Memories ........................................................................ 73 - 78

10. Architecture of 8085 ................................................................................ 79 - 83

11. Pin Details and Interrupt of 8085 ............................................................. 84 - 94

12. Interfacing with 8085 ............................................................................... 95 - 106

13. Instruction set of 8085 ............................................................................. 107 - 128

14. Programing with 8085 ............................................................................. 129 - 139

15. 8086 Microprocessor ............................................................................... 140 - 146

16. Amplitude Modulation ............................................................................ 147 - 161

17. Angle Modulation .................................................................................... 162 - 178

18. Digital Communication ........................................................................... 179 - 192

19. Channel Capacity and Information Theory ............................................. 193 - 199

20. Receivers ................................................................................................. 200 - 205

21. Noise ........................................................................................................ 206 - 209

CONTENTSSNNOCONTENTS

22. Radar Communication ............................................................................. 210 - 211

23. Sattellite and Television Communication ................................................ 212 - 214

24. Miscellaneous .......................................................................................... 215 - 220

II. Systems and Signal Processing

01. Classifi cation & Modeling ....................................................................... 221 - 261

02. Fourier Series & Application .................................................................... 262 - 275

03. Fourier Transforms & Application ........................................................... 276 - 301

04. Laplace Transforms & Application .......................................................... 302 - 321

05. Z-Transforms & Application .................................................................... 322 - 342

III Control Systems

01. Basics of Control Systems ........................................................................ 344 - 362

02. Block Diagram and Signal Flow Graph ............................................... 363 - 384

03. Time Response Analysis............................................................................ 385 - 418

04. Stability ..................................................................................................... 419 - 437

05. Root Locus Diagram ................................................................................. 438 - 454

06. Frequency Response Analysis .................................................................. 455 - 486

07. Controllers and Compensators .................................................................. 487 - 500

08. State Space Analysis ................................................................................ 501 - 520

09. Mathematical Modeling of Physical Systems ......................................... 521 - 537

10. Descrete Data Control Systems ................................................................ 538 - 546

11. Non-linear Control Systems ..................................................................... 547 - 556

IV Electrical Machines

01. Transformers ............................................................................................. 558 - 612

02. DC Machines.............................................................................................. 613 - 673

03. Synchronous Machines ............................................................................. 674 - 732

04. Induction Machines ................................................................................... 733 - 784

V Power Systems

01. Generating Stations .................................................................................. 786 - 805

02. Performance of Transmission Lines and Cables....................................... 806 - 841

03. Insulators ................................................................................................. 842 - 845

04. Load Frequency Control........................................................................... 846 - 851

05. Fundamentals of Power Economics.......................................................... 852 - 864

06. Load Flow Studies ................................................................................... 865 - 876

07. Faults ....................................................................................................... 877 - 895

08. Stability .................................................................................................... 896 - 910

09. Circuit Breakers ....................................................................................... 911 - 915

10. Protection ................................................................................................. 916 - 931

11. HVDC Transmission ................................................................................ 932 - 938

VI Power Electronics and Drives

01. Basics and Power Semiconductor Devices .............................................. 940 - 965

02. AC-DC Converters .................................................................................. 966 - 987

03. DC-DC Converters .................................................................................. 988 - 998

04. DC-AC Converters .................................................................................. 999 - 1012

05. AC-AC Converters .................................................................................. 1013 - 1022

06. Fundamentals of Drives ........................................................................... 1023 - 1028

Electrical EngineeringPrevious years ESE Objective questions (Prelims)

Weightage (2014 to 2018)

S.No. Name of the Subject 2014 2015 2016 2017 2018

01 Engineering Mathematics – – – 14 10

02 Electrical Materials 18 20 19 26 09

03 Electric Circuits & Fields 38 45 46 31 30

04 Electrical & Electronic Mea-surements 37 27 30 12 06

05 Computer Fundamentals – – – 03 12

06 Basic Electronics Engineering – – – 04 03

07 Analog & Digital Electronics 63 53 53 06 07

08 Systems & Signal Processing – – – 07 03

09 Control Systems 27 28 26 14 21

10 Electrical Machines 27 34 34 11 26

11 Power Systems 12 12 20 12 19

12 Power Electronics & Drives 18 21 13 10 04

Total No.of Questions: 150 150

Hyderabad|Delhi|Bhopal|Pune|Bhubaneswar| Lucknow|Patna|Bengaluru|Chennai|Vijayawada|Vizag |Tirupati | Kukatpally | Kolkata ACE Engineering Publications

01. The desirable properties of transformer core

material are (IES-92) (a) low permeability and low hysteresis

loss (b) high permeability and high hysteresis

loss (c) high permeability and low hysteresis

loss (d) low permeability and high hysteresis

loss 02. The efficiency of two identical transformers

under load conditions can be determined by (IES-92) (a) back to back test (b) open circuit test (c) short circuit test (d) any of the above 03. For an ideal transformer the windings should

have (IES-92) (a) maximum resistance on primary side and

least resistance on secondary side (b) least resistance on primary side and

maximum resistance on secondary side. (c) equal resistance on primary and

secondary side. (d) no ohmic resistance on either side

04. Two single-phase 100 kVA transformers, each having different leakage impedances

are connected in parallel. When a load of 150 kVA at 0.8 power factor lagging is applied (IES-92/13) (a) both transformers will operate at power

factor more than 0.8 lagging (b) both transformers will operate at power

factor less than 0.8 lagging (c) one of the transformers will operate at

power factor more than 0.8 lagging and other will operate at power factor less than 0.8 lagging

(d) both transformers will operate at identical power factors

05. Scott connections are used for (IES-92)

(a) single phase to three phase transformation

(b) three phase to single phase transformation

(c) three phase to two phase transformation (d) any of the above.

06. Two single phase transformers with equal turns have impedance of (0.5 + j 0.3) ohms and (0.6 + j 1) ohms with respect to the secondary, If they operate in parallel, how will they share a load of 100 kW at 0.8 p.f. lagging? (IES-92)

(a) 50 kW, 50 kW (b) 62 kW, 38 kW (c) 78.2 kW, 21.8 kW (d) 85.5 kW, 14.5 kW

Chapter

1 Transformers

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07. The losses on a transformer are I. Copper losses II. Eddy current losses III Hysteresis losses The constant power loss of a transformer

loss is given by (IES-92) (a) I only (b) I and II only (c) II and III only (d) I, II and III. 08. Which of the following will improve the

mutual coupling between primary and secondary circuits? (IES-92) (a) Transformer oil of high break down

voltage. (b) High reluctance magnetic core (c) Winding material of high resistivity (d) Low reluctance magnetic core

09. The secondary of a current transformer

under operating conditions is short-circuited to avoid (IES-92) (a) break in primary winding (b) insulation break-down (c) core saturation and high voltage

induction (d) high voltage surge.

10. The inductive reactance of a transformer

depends on (IES-92) (a) electromotive force (b) magneto motive force (c) magnetic flux (d) leakage flux

11. Which of the following connection of transformer will give the highest secondary voltage? (IES-92)

(a) delta primary, delta secondary (b) delta primary, star secondary (c) star primary, star secondary (d) star primary, delta secondary 12. In a transformer, if the iron losses and

copper losses are 40.5 kW and 50 kW respectively, then at what fraction of load will the efficiency be maximum?

(IES-93/14) (a) 0.8 (b) 0.57 (c) 0.70 (d) 0.9 13. Can a 50 Hz transformer be used as 25 Hz,

if the input voltage is maintained constant at the rated value corresponding to 50 Hz?

(IES-93) (a) Yes, since the voltage is constant,current

levels will not change (b) No, flux will be doubled which will

drive the core to excessive saturation (c) No, owing to decreased reactance of

transformer, input current will be doubled at load

(d) Yes, at constant voltage, insulation will not be overstressed.

14. Short-circuit test is performed on a

transformer with a certain impressed voltage at rated frequency. If the short-circuited test is now performed with the same magnitude impressed voltage, but at a frequency higher than the rated frequency, then (IES-93)

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Solutions

IA

IB V2 B

L

A

BAL III

141.a 142.b 143.b 144.c 145. a 146.b 147.c 148.d 149.a 150.a 151.d 152.b 153.c 154.b 155. a 156.c 157. b 158.d 159.c 160.c 161.a 162.c 163.d 164.c 165.a 166.a 167. a 168. 22 169. a 170. b 171. a 172. d 173. c 174. a 175. c 176. b 177. b 178. a 179. b 180. c 181. a

01. Ans: (c) Sol: For a transformer, permeability () of

Transformer core should be high i.e if permeability increases, then magnetizing component of current required to create rated flux in the core decreases. Hysteresis loss in the core should be low to get more efficiency.

02. Ans: (a) Sol: During open circuit and short circuit tests

all the losses do not occur simultaneously, therefore the exact temperature rise can not be determined. In order to get exact temperature rise Sumpners test/ back to back test should be conducted.

Iron loss and copper loss are obtained from wattmeter readings, with these results we can find efficiency of transformers.

03. Ans: (d) Sol: In ideal transformer, resistance of windings

and magnetic leakage flux are zero. 04. Ans: (c)

Sol: The XR

ratios of transformers to be

connected in parallel should be equal to avoid operation of transformers at different power factors.

If , B

B

A

A

RX

RX

,

A > B cos A < cos B Where,

AI = current shared by transformer-A

BI = current shared by transformer-B

Therefore, load current BAL III

05. Ans: (c) Sol: Scott connection is one of the special

connection of the Transformer, which is used to convert 3-phase to 2-phase and vice versa.

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A ac supply

CT

+

–

I

Load

Primary of the CT

Secondary of the CT

06. Ans: (c) Sol: Z1 = (0.5 + j0.3) = 0.58330.96 Z2 = (0.6+j1.0) = 1.1659.3 Given sharing of 100 kW load at 0.8 power

factor lagging

i.e. 8.0

100 125 kVA at = 36.6O

For Transformer-I

Sharing = 21

2L ZZ

ZS

= 76.4970.1

03.5916.19.36125

= 85.29 kVA at 27.63O lag i.e. 75.56 kW at 0.885 lag For Transformer-II

Sharing = 21

2L ZZ

ZS

= 76.4970.1

96.30583.06.36125

= 42.86 kVA at 55.7o lag = 24.15 kW at 0.563 lag 07. Ans: (c) Sol: Copper loss I2 i.e depends on load current

called variable losses. Iron loss (Wh + We) V2 (applied voltage),

called constant losses. 08. Ans: (d)

Sol: Permeability 1reluc tan ce

If the permeability of the core is increases, the mutual coupling between primary and secondary will be improved.

09. Ans: (c) Sol: A current transformer is connected in a

circuit as shown.

Primary of the CT has few turns. It can simply consist of a metal bar of negligible resistance.

Secondary of the CT is virtually short circuited by a low resistance ammeter coil. Unlike in conventional transformers, the primary current is not decided by the secondary current. It is decided by the load current. If the secondary is open, there is no balancing mmf, the core flux will be very high and a high emf is induced in the secondary. This will cause severe insulation stress in the CT and could be a risk to operating persons.

10. Ans: (d) Sol: As leakage flux is more, coefficient of

coupling of transformer will decrease and also the inductive reactance drop will be increased.

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11. Ans: (b) Sol:

Connections Line Voltages

If xv1 is 100%

Voltage on secondary side

- V1 : xv1 100%

Y – Y V1 : xv1 100%

- Y V1 : 3xv1 173.2%

Y - V1 : x3

V1 57.7%

For same rating and applied voltage, /Y

connection gives 73.3% of more voltage compared to / (or) Y/Y connection.

12. Ans: (d) Sol: Efficiency is maximum at any ‘x’ of full

load = cu

i

WW = 40.5 0.9

50

Maximum Efficiency occurs at 0.9 of Full Load.

13. Ans: (b)

Sol: Bmax f

V

Here V constant, f decreased to half Bmax increased to double, which will

drive the core in to deep saturation and also I is very high to create double the rated flux.

14. Ans: (d) Sol: S.C test is conducted at reduced voltage

(Vsc) and at rated frequency. If Vsc constant and ‘f’ (f > frated) is

increased, the consequences are (i) R01 = constant (ii) X01 f

(iii) 2 201 01 01 01z x R z

(iv) ISC = 01

Vsc cons tan tz

(v) cos sc = 01

01

R cons tan tz

15. Ans: (b) Sol: Open circuit test is convenient to conduct

on LV side by opening H.V winding due to the following reasons: 1. If the test is conducted on LV side, LV

source sufficient to conduct the test to maintain rated flux.

2. If the test is conducted on LV side, low range meters are sufficient to conduct the test.

3. As magnitude of no-load current is more on LV side, this high no-load current can be accurately measured on LV side when compared to HV side.

Equivalent circuit under S.C test

X01

12V 0

ISC

VSC

R01


01. As the operating voltage and consequently

the electric stress on the dielectric of solid type cable is increased from a low value, the dielectric power factor cos remains almost unchanged up to a certain value of the stress beyond which cos increases very rapidly. This is due to increase in the (IES-93) (a) resistivity of the dielectric material

(b) ionization in the voids present in the dielectric

(c) core-to-core capacitance of the cable.

(d) core-to-earth capacitance of the cable

02. The L/C ratio for 132 kV and 400 kV lines

are typically 160 103 and 62.5 103 respectively. The natural 3-phase loading for the two lines will be respectively

(IES-93) (a) 108.9 MW and 2560 MW

(b) 44 MW and 2560 MW

(c) 44 MW and 640 MW

(d) 640 MW and 44 MW

03. A quarter wave line will behave as (IES-93) (a) a rectifier

(b) an amplifier (c) a transformer (d) a variable capacitance

04. Different terminal conditions at the receiving end of a loss – less overhead transmission line having surge impedance Z are sketched in List-I. The incident and the reflected current waves are sketched in List-II. Match List-I with List-II and select the correct answer using the codes given below the Lists: (IES-93)

List – I (Line with different terminal conditions)

A. B.

C.

List - II (Incident and reflected current waves)

1.

2.

3. Codes:

A B C A B C (a) 3 2 1 (b) 3 1 2 (c) 1 2 3 (d) 1 3 2

No reflection I

I I

I I

Line Short Circuit

LineOpen Circuit

Line R = Z

Chapter

2 PerformanceofTransmissionLines&Cables

Line R = Z

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Engineering Publications

05. Assertion (A): The electric field intensity E is proportional to X, the distance from the axis of the conductor of radius, r, for x r.

Reason (R): Bundled conductors increase the line capacitance from that of a single conductor of the same cross-sectional area.

(IES-93) (a) Both A and R are true and R is the

correct explanation of A

(b) Both A and R are true but R is NOT a correct explanation of A

(c) A is true but R is false

(d) A is false but R is true

06. Assertion (A): In a high voltage cable, concentric conducting surfaces are provided in an insulating medium of same permittivity throughout the cross-section of the cable to reduce the ratio of maximum to minimum electric stress.

Reason (R): The potential differences between the conducting surfaces redistribute the charge distribution (IES-93)

07. The inductance of single-phase two-wire

power transmission line per kilometer gets doubled when the (IES-93) (a) distance between the wires is doubled (b) distance between the wires is increased

four fold. (c) distance between the wires is increased

as square of original distance (d) radius of the wire is doubled

08. Corona loss can be reduced by the use of hollow conductors, because (IES-94) (a) the current density is reduced (b) the eddy current in the conductor is

eliminated (c) for a given cross section, the radius of

the conductor is increased (d) of better ventilation in the conductor.

09. The insulation of modern EHV lines is

designed based on (IES-94) (a) the lightning (b) corona (c) radio interference (d) switching voltage 10. A 3-phase 50 Hz transmission line has the

following constants (line to neutral) Resistance = 10 ,

Inductive reactance = 20 ,

Capacitive susceptance = 4 × 10–4 ℧ The inductance of the arc suppressor coil to

be used in the system is (IES-94)

(a) 0.06368 H (b) 0.127 H

(c) 1.274 H (d) 2.654 H

11. Consider the following statements: 1. The insulation resistance of cable will

increase if the length of the cable is increased

2. For the same overall diameter of cable, the grading of cable will increase the safe working voltage.

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PowerSystems ACE Engineering Publications

3. The normal operating temperature of PVC cable is 70o C

4. The thermal resistance of coil increases as the moisture content of coil increases.

(IES-95) Of these statements

(a) 1 and 2 are correct (b) 2 and 3 are correct

(c) 3 and 4 are correct (d) 1 and 4 are correct

12. Compared with a solid conductor of the

same radius, corona appears on a stranded conductor at a lower voltage, because stranding

(IES-95)

(a) assists ionization

(b) makes the current flow spirally about the axis of the conductor

(c) produces oblique sections to a plane perpendicular to the axis of the conductor

(d) produces surfaces of smaller radius 13. Transmission lines are transposed to (IES-96)

(a) reduce copper loss

(b) reduce skin effect

(c) prevent interference with neighboring telephone line

(d) prevent short- circuit between any two lines

14. A single-phase transmission line of impedance j0.8 ohm supplies a resistive load of 500A at 300V. The sending-end power factor is

(IES-96) (a) unity (b) 0.8 lagging

(c) 0.8 leading (d) 0.6 lagging

15. On an infinitely long transmission line, the attenuation co-efficient is expressed in terms of the ratio K of the two voltages one kilometer apart on the line, in bels/km. The value of this co-efficient is given by

(IES-96) (a) Kloge (b) 2K

(c) Klog2 10 (d) None of the above

16. For a transmission line with resistance R,

reactance X, and negligible capacitance, the generation constant A is

(IES-96) (a) 0 (b) 1

(c) R + jX (d) R + X 17. A surge voltage of 1000 kV is applied to an

overhead line with its receiving – end open. If the surge impedance of the line is 500 , then the total surge power in the line is

(IES-96) (a) 2000 MW (b) 500 MW

(c) 2 MW (d) 0.5 MW

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PerformanceofTransmissionLines&CablesACE

Engineering Publications

Solutions 01. Ans: (b) Sol: As the operating voltage increases, the stress

will increase so that the di-electric strength at insulation will fail due to the presence of clouds in the di-electric medium.

02. Ans: (c)

Sol: Surge Impedance or natural loading

CLZwhere,

ZV

CC

2

For 132 kV line,

310160132132SIL

= 43.56 MW

For 400 kV line,

3105.62400400SIL

= 640 MW

03. Ans: (c) Sol: Quarter – wave line will be have as a

transformer for impedance matching. It can transform low impedance into high impedance and vice versa.

04. Ans: (a) Sol: For short circuit, reflection current is

positive. For a open circuit, reflection current is

negative. For a flat line, there is no reflection of

current and voltage.

06. Ans: (a) Sol: The given method of grading is known as

inters heath grading. In this method, instead of using various dielectrics and having composite dielectric to distribute the stress properly extra metallic sheaths between the conductor and the main sheath. This method improves voltage distribution in the dielectric of the cable and consequently uniform potential gradient is obtained.

07. Ans: (c)

Sol: Inductance of a transmission line

mH

rDlnKL1

Where, D = distance between the conductors.

r = radius of the conductor.

K = 2 10-7

If the distance between the conductors is squared, Inductance will be doubled

rDlnKL

2

2

rDlnK2 = 2 L1

08. Ans: (c) Sol: By using hollow conductors the diameter of

the conductor is increased without materially adding to its weight, when the diameter is increased corona loss is reduced.

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PowerSystems ACE Engineering Publications

09. Ans: (d) Sol: Switching surge (OR) voltage is the base for

the design of insulation of modern EHV lines

10. Ans: (d)

Sol: The Inductive reactance of the arc suppressor coil is given as 20

XL = 20

2C = 4 10–4 ℧ C = 1.27 F

622 1027.15023

1C3

1L

= 2.653 H. 11. Ans: (b) Sol: The insulation resistance of cable will

decrease of the length of cable is increased and vice versa

(i.e., in1R

)

By grading of a cable is meant the distribution of dielectric material such that the difference between the maximum gradient and minimum is reduced, there by a cable of the same size could be operated at higher voltages or For same operating voltage, size of the cable could be smaller. The normal operating temperature of PVC cable is 700 C

The thermal resistance of coil decreases as the moisture content of coil increases and vice versa.

12. Ans: (d) Sol: For stranded conductor the cross-section of

conductor is a series of arcs of circles each of much smaller diameter than the conductor as a whole. The potential gradient for such a conductor will be greater than for the equivalent smooth conductor, so that the breakdown voltage for a stranded conductor will be some what less for a smooth conductor.

13. Ans: (c) Sol: Transmission Lines are transposed only to

prevent interference with neighboring telephone lines

14. Ans: (d)

Sol: Vs = Vr + Z Ir

= 300 + j0.8 500

= 300 + j400 = 50053.13.

Is = Ir = 5000

coss = cos (53.13) = 0.6lag 15. Ans: (c)

Sol: Vx = V0 ex

x

0

x eVV

For x = 1 km

kVV

x

0 ek1

e = k

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