LAXMI INSTITUTE OF TECHNOLOGYkV with 100% power factor. Find the volateg , current and power at the sending end and voltage regulation of the lie. Given z= 0.5239∟79.02° Ώ/ km

LAXMI INSTITUTE OF TECHNOLOGY SARIGAM

COURSE FILE

Faculty Name : RAHUL JADAV

Subject Name : ELECTRICAL POWER SYSTEMS -II

Subject Code : 2160908

Course Name : B.E (Electrical Engineering)

Semester : VI

Session : Dec - April 2019

DEPARTMENT OF ELECTRICAL ENGINEERING

SCHEME

SYLLABUS

Unit Topics Teaching Hours

Module % Weightage

I Current and Voltage Relations on a Transmission Line:

Representation of line, The short transmission line, The medium-

length line, The long transmission line: Solution of the differential equations, The long transmission line: Interpretation

of the equations, The long transmission line: Hyperbolic form of

the differential equations, The equivalent circuit of a long line, Power flow through a transmission line (circle diagrams),

Reactive compensation of transmission lines

8 15

2 Symmetrical Three-Phase Faults: Transients in RL Series

circuits, Short-Circuit currents and the reactances of Synchronous machines, Internal voltages of loaded machines under transient

conditions, The bus impedance matrix in fault calculations, A bus

impedance matrix equivalent network, The selection of circuit breakers.

8 20

3 Symmetrical Components: Synthesis of Unsymmetrical phasors

from their symmetrical components, The symmetrical

components of unsymmetrical phasors, Phase shift of symmetrical components in StarDelta Transformer Banks [2],

Power in terms of symmetrical components, Sequence circuits of

Y and Δ impedances, Sequence circuits of a symmetrical transmission line, Sequence circuits of the synchronous machine,

Sequence circuits of a Y- Δ transformer, Unsymmetrical series

impedances, Sequence networks

8 15

4 Unsymmetrical Faults: Single line to ground fault on an unloaded generator, Line to Line fault on an unloaded generator, Double

Line to Ground fault on an unloaded generator, Unsymmetrical

faults on power systems, Single line to Ground fault on a power system, Line to Line fault on a power system, Double Line to

Ground fault on a power system, Interpretation of the

interconnected sequence networks, Analysis of unsymmetrical

faults using the bus impedance matrix, Faults through impedance, Computer calculations of fault currents

8 20

5 Transients in Power Systems: Transients in Simple Circuits, 3-

phase Sudden Short Circuit of an Alternator, The Restriking Voltage after Removal of Short Circuit, Travelling Waves on

Transmission Lines, Attenuation of Travelling Waves,

Capacitance Switching, Overvoltage due to Arcing Ground.

6 15

6 Corona: Critical Disruptive Voltage, Corona Loss, Line Design based on Corona, Disadvantages of Corona, Radio Interference,

Inductive interference between Power and Communicationlines.

6 15

Semester Course Title Course Code

Theory Paper L T P

6th

EPS-2 2160908 4 0 2 70

List of Reference Books

S.No Book Title Author Publication

1 Power System Analysis John J. Grainger, William

D. Stevenson Jr

Tata McGraw Hill

[1,2,3]

2 Elements of Power Systems Analysis W. D. Stevenson Jr. McGraw Hill

3 Electrical Power systems C. L .Wadhwa New Age

International

Publishers.

4 Modern Power system Analysis I J Nagrath, D P Kothari Tata McGraw Hill

5 Power System Analysis Hadi Saadat Tata McGraw Hill.


Department of Electrical Engineering Academic Year : 2018 -2019

ASSIGNMENT – I

Name of the Subject: EPS-II Date: 04.02.2019


S. No Question Remarks

1. Derive long transmission equivalent π model.

2. Determine the voltage, current and power factor at the sending

end of a 3 phase, 50 Hz, overhead transmission line 160 km

long delivering a load of 100 MVA at 0.8 pf lagging and 132

KV to a balanced load. Resistance per km is 0.16Ω, inductance

per km is 1.2 mH and capacitance per km conductor is

0.0082µF. Use nominal π method.

3. Draw & explain receiving end power circle diagram

4. Derive the ABCD constants for medium transmission line using

Nominal Π representation. Also write the expressions for

voltage regulation and efficiency for the same line.

Date of Submission: 08.02.2019

Name & Sign of Subject In-charge: Mr. Rahul Jadav



ASSIGNMENT – II

Name of the Subject: EPS-II Date:



1. Draw the waveform for fault current for a 3 phase fault on

alternator terminals. Explain the subtransient, transient and

steady state reactance. What is their significance in fault

calculation?

2. Write a brief note on selection of circuit breaker.

3. Derive an expression of current when there is a sudden three

phase short circuit at the other end of unloaded transmission

line. Assume a constant voltage source is connected at sending

end and neglect line capacitance.

4. Discuss the principle of symmetrical components. Derive the

necessary equations to convert:

a) Phase quantities into symmetrical components

b) Symmetrical components into phase quantities.

Also prove that the transformation used is power invariant.

Date of Submission:




ASSIGNMENT – III




1. Draw a general circuit which can be used to determine zero

sequence network of a two winding transformer. Using this circuit,

draw the zero sequence networks for

a) Delta-star transformer with star point grounded.

b) Delta –delta transformer

Star –star transformer with star point grounded.

2. Explain Single line to ground fault on an unloaded generator using

symmetrical components. Draw connection of sequence networks.

3. A 25 MVA, 13.2 kV alternators with solidly grounded neutral has

a subtransient reactance of 0.25 pu. The negative and zero

sequence reactances are 0.35 and 0.1 pu. Find the fault current

when ,

a) LG fault occurs at terminals of an unloaded alternator

b) LL fault occurs at terminals of an unloaded alternator

4. Derive the double line to ground fault in 3 phase alternator

Date of Submission:




ASSIGNMENT – IV




1. Starting from the first principle show that surges behave as

travelling waves. Find the expression for surge impedance and

wave velocity.

2. Derive equation for attenuation of a travelling wave.

3. Find the critical disruptive voltage and the critical voltages for

local and general corona on a three phase overhead transmission

line, consisting of three stranded copper conductors spaced 2.5 m

apart at the corners of an equilateral triangle. Air temperature and

pressure are 21 ˚C and 73.6 cm Hg respectively. The conductor

diameter, irregularity factor and surface factor are 10.4 mm, 0.85,

0.7 and 0.8 respectively

4. Explain the phenomena of corona. Give reasons for following: The

disruptive critical voltage is less than visual critical voltage.

Date of Submission:


Laxmi Institute of Technology, Sarigam Approved by AICTE, New Delhi; Affiliated to Gujarat Technological University, Ahmadabad

QUESTION BANK CHAPTER -1

Q.1 Derive the ABCD constants for medium transmission line using Nominal Π representation.

Also write the expressions for voltage regulation and efficiency for the same line.

Q.2 Determine the voltage, current and power factor at the sending end of a 3 phase, 50 Hz,

overhead transmission line 160 km long delivering a load of 100 MVA at 0.8 pf lagging and 132

KV to a balanced load. Resistance per km is 0.16Ω, inductance per km is 1.2 mH and

capacitance per km conductor is 0.0082µF. Use nominal π method.

Q.3 A 3-phase. 50-Hz overhead transmission line 100 km long has the following constants.

Resistance/km/phase = 0.1 Ώ

Inductive reactance/km/phase = 0.2 Ώ

Capacitive susceptance/km/phase = 0.04 × 10 -4 siemen

Q.4 Determine (i) the sending end current (ii) sending end voltage (iii) sending end power factor

and (iv) transmission efficiency when supplying a balance load of 10,000 kW at 66 kV p.f 0.8

lagging. Use nominal T method

Q.5 Consider a 230 mile long 60Hz transmission line. Its series impedance is 0.1603+j8277

Ώ/mile and shunt admittance is j5.105 x 10-6 mho/mile.The load on the line is 125 MW at 215

kV with unity power factor. Find the voltage, current an dthe power at the sending end and the

voltage regulation of the line. Also find the wavelength & velocity of propogation in miles and

miles/s respectively. Consider the line as long line.

Q.6 A single ciruit 60Hz transmission line is 370km long. The load on the line is 125MW at 215

kV with 100% power factor. Find the volateg , current and power at the sending end and voltage

regulation of the lie. Given z= 0.5239∟79.02° Ώ/ km and y = 3.17 x 10-6 ∟90 ° mho/km.

Q.7Use nominal Π method find sending end voltage and voltage regulation of a 250km 3 phase

50 Hz transmission line delivering 25 MVA at 0.8 pf lagging to a balanced load at 132 kV. The

line conductors are spaced equilaterally 3 m apart. The conductor resistance is 0.11 ohm/km and

its effective diameter is 1.6 cm. Neglect leakages.

Q.8 three phase 60Hz completely transposed 345 kV 200km line has z= 0.032+j0.35 Ώ/km and

y= j4.2 x 10-6 S/km.Full load at the receiving end is 700MW at 0.99 pf leading and at 95% of

rated voltage. Assuming a medium length of line, determine ABCD parameters of a nominal Π

circuit , sending end voltage and current and real power delivered by sending end.

Q.9A 275 kV transmission line has the following line constants A = 0.85∟5°, B = 200∟ 75°.

Determine the power at unity power factor that can be received if the voltage profile at each end

is to be maintained at 275 kV.What type of compensation equipment would be required if the

load is 150 MW at unity pf with same voltage profile.

Q.10 A 50 Hz transmission line 300km long has a total series impedance of 40+j 125 ohms and a

total shunt admittance of 10-3 mho. The receiving end load is 50 MW at 220kV with 0.8 lagging

power factor. Find the sending end voltage and current using exact method

.

CHAPTER 2

Q.1 Draw the waveform for fault current for a 3 phase fault on alternator terminals. Explain the

subtransient, transient and steady state reactance. What is their significance in fault calculation?

Q.2 Write a brief note on selection of circuit breaker.

Q.3 Derive an expression of current when there is a sudden three phase short circuit at the other

end of unloaded transmission line. Assume a constant voltage source is connected at sending end

and neglect line capacitance.

Q.4 What is bus impedance matrix? How it is useful in symmetrical fault analysis.

Q.5 Derive equations to explain doubling effect.

CHAPTER 3 & 4

Q.1 Discuss the principle of symmetrical components. Derive the necessary equations to convert:

a) Phase quantities into symmetrical components

b) Symmetrical components into phase quantities.

Also prove that the transformation used is power invariant.

Q.2 Draw a general circuit which can be used to determine zero sequence network of a two

winding transformer. Using this circuit, draw the zero sequence networks for

a) Delta-star transformer with star point grounded.

b) Delta –delta transformer

c) Star –star transformer with star point grounded.

Q.3 Discuss phase shifting in a single phase transformer and star-delta transformations.

Q.4 Prove that for a fully transposed line, the zero sequence impedance is much higher than

positive or negative sequence impedance.

Q.5Prove that positive and negative sequence impedances of fully transposed transmission lines

are always equal.

Q.6Explain Single line to ground fault on an unloaded generator using symmetrical components.

Draw connection of sequence networks.

Q.7 Derive the double line to ground fault in 3 phase alternator.

Q.8 A 25 MVA, 11 kV generator with Xd˶ = 20 % is connected through a transformers , line and

a transformers to a bus that supplies three identical motor as shown in fig. . Each motor has Xd˶

= 25 % and Xd = 30 % on a base of 5 MVA , 6.6 kV . Three phase rating of the step up

transformers is 25 MVA , 11/66 kV with leakage reactance of 10 % and that of the step down

transformer is 25 MVA , 66/6.6 kV with a leakage reactance of 10 %. The bus voltage at the

motors is 6.6 kV when a three – phase fault occurs at the point F. For the specified fault,

calculate. (a) The subtransient current in the fault , (b) The subtransient current in breaker B, (c)

The momentary current in breaker B.

Q.9 A 3 phase , 11kV, 25 MVA generator with Xo = 0.05 p.u, X1 = 0.2 p.u and X2 = 0.2 p.u is

grounded through a reactance of 0.3 Ώ .Calculate fault current for a single line to ground fault.

Q.10 One conductor of a 3 phase line is open as shown in fig. The current flowing to the Δ

connected load through the line R is 10 A. With the current in line R as reference and assuming that

line B is open , find the symmetrical components of the line currants.

Q.11 Two generators G1 and G2 are rated 15 MVA, 11KV and 10MVA, 11KV respectively. The

generators are connected to a transformer shown in fig.. Calculate the subtransient current in each

generator where a three phase fault occurs on the high voltage side of the transformer. Choose a base

15 MVA.

Q.12 A generating station consists of two 100 MVA generators with 6% reactance each and one 150

MVA generator with 8% reactance as shown in fig. 2. These generators are connected to a common

busbar from which loads are taken through a number of circuit breaker on (i) low voltage side and

(ii) on high voltage side. Take base power 150 MVA

Q.13 A 50 MVA, 11 KV, synchronous generator has a subtransient reactance of 20%. The generator

supplies two motors over a transmission line with transformers at both ends as shown in fig. 4. The

motors have rated inputs of 30 and 15 MVA, both 10 KV, with 25% subtransient reactance. The

three-phase transformers are both rated 60 MVA, 10.8/121 KV, with leakage reactance of 10% each.

Assume zero-sequence reactance for the generator and motors of 6% each. Current limiting reactors

of 2.5 ohms each are connected in the neutral of the generator and motor no 2. The zero sequence

reactance of the transmission line is 300 ohms. The series reactance of the line is 100 Ω. Draw the

positive, negative and zero sequence networks. Assume that the negative sequence reactance of each

machine is equal to its subtransient reactance. Assume base power 50 MVA and base voltage 11KV

Q.14 Draw the positive, negative and zero sequence networks of the power system network as shown

in Fig.

CHAPTER 5

Q.1 Derive equation for attenuation of a travelling wave.

Q.2 A 25 MVA, 13.2 kV alternators with solidly grounded neutral has a subtransient reactance

of 0.25 pu. The negative and zero sequence reactances are 0.35 and 0.1 pu. Find the fault current

when ,

a) LG fault occurs at terminals of an unloaded alternator

b) LL fault occurs at terminals of an unloaded alternator

Q.3 Explain travelling waves of a transmission line when the receiving end is short circuited.

Q.4 Starting from the first principle show that surges behave as travelling waves. Find the

expression for surge impedance and wave velocity.

CHAPTER 6

Q.1 Explain the phenomena of corona. Give reasons for following: The disruptive critical

voltage is less than visual critical voltage.

Q.2 A 3 phase 220 Kv, 50 Hz transmission line consists of 1.5 cm radius conductor spaced 2

meters apart in equilateral triangular formation. If the temperature is 40o C and atmospheric

pressure is 76 cm, calculate the corona loss per km of the line. Take mo = 0.85.

Q.3 Find the critical disruptive voltage and the critical voltages for local and general corona on a

three phase overhead transmission line, consisting of three stranded copper conductors spaced

2.5 m apart at the corners of an equilateral triangle. Air temperature and pressure are 21 ˚C and

73.6 cm Hg respectively. The conductor diameter, irregularity factor and surface factor are 10.4

mm, 0.85, 0.7 and 0.8 respectively

Q.4 Explain methods of reducing corona.

Laxmi Institute of Technology , Sarigam Approved by AICTE, New Delhi; Affiliated to Gujarat Technological University, Ahmedabad

Academic Year 2018-19

Centre Code: 086 Examination : Mid Semester Examination-1 Branch: Electrical Semester: 6th Sub Code: 2160908 Sub: EPS-II Date:01.02.19 Time:- 9 am -10 am Marks: 20 Note: Internal options are given.

Q.1 Obtain the Equivalent circuit for nominal representation for long transmission line. 5

OR

Q.1 Explain methods of reducing corona. 5

Q.2 A three phase 50 Hz transmission line is 100 Km long and delivers 20 MW at 220KV

at 0.9p.f. Lagging and at 110V. The resistance and reactance of the line per conductor

per km are 0.2 Ω and 0.4 Ω respectively. While capacitance admittance is 2.5×10-6

ʊ/km/phase. Calculate (i) the current and voltage at sending end (ii) Efficiency of

transmission line. Use nominal T method.

5

OR

Q.2 A 200 km long three phase overhead line has a resistance of 48.7 ohms per phase,

inductive reactance of 80.2 ohms per phase and capacitance (line to neutral) 8.42 nF

per km. It supplies a load of 13.5 MW at a voltage of 88 kV at 0.9 lagging power

factor. Using nominal T circuit, find sending end voltage, sending end current, voltage

regulation and power angle of given line

5

Q.3 Find the critical disruptive voltage and the critical voltages for local and general

corona on a three phase overhead transmission line, consisting of three stranded

copper conductors spaced 2.5 m apart at the corners of an equilateral triangle. Air

temperature and pressure are 21 ˚C and 73.6 cm Hg respectively. The conductor

diameter, irregularity factor and surface factor are 10.4 mm, 0.85, 0.7 and 0.8

respectively

5

OR

Q.3 A 3 phase 220 Kv, 50 Hz transmission line consists of 1.5 cm radius conductor spaced

2 meters apart in equilateral triangular formation. If the temperature is 40o C and

atmospheric pressure is 76 cm, calculate the corona loss per km of the line. Take mo =

0.85.

5

Q.4 Explain the phenomena of corona. Give reasons for following: The disruptive critical

voltage is less than visual critical voltage.

5

OR

Q.4 Explain how transmission lines are classified into short , medium and long lines and

Explain their characteristics briefly

5

1

Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) - EXAMINATION – SUMMER 2017

Subject Code: 2160908 Date: 01/05/2017 Subject Name: Electrical Power system – II Time: 10:30 AM to 01:00 PM Total Marks: 70 Instructions:

1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.

Q.1 ATTEMT THE FOLLOWING QUESTIONS 14

1 Differentiate symmetrical faults and unsymmetrical faults.

2 How circuit breaker S.C current ratings are decided?

3 Define negative and positive sequence components.

4 What is the effect of negative and zero sequence currents in 3 phase

system?

5 Define Visual disruptive voltage with its expression.

6 State disadvantages of corona.

7 Define reactive power. State methods of reactive power compensation

8 Define Restriking Voltage.

9 Justify that series capacitor and shunt reactor works as line

compensators.

10 Write equation which shows relationship between Receiving end

active power and load angle, Receiving reactive power and voltage

drop.

11 Define Surge impedance loading of transmission line.

12 Define Arcing ground

13 State causes of transient surges on power line.

14 Define the term voltage regulation related to transmission line. Also

write its expression.

Q.2 (a) What u meant by symmetrical faults? Explain briefly its necessity in

fault analysis. 03

(b) Prove that in case of transients in RL series circuits, short circuit

current contains symmetrical short circuit components and D.C offset

components.

04

(c) For the radial network shown in fig no -1, a three phase fault occurs

at F. Determine the fault current and line voltage at 11 Kv bus under

fault conditions.

07

OR

(c) A synchronous generator and a synchronous motor each rated 25

MVA, 11 Kv having 15% sub transient reactance are connected

through transformers and a line as shown in following fig -2 , when

symmetrical three phase fault occurs at the motor terminals. Find sub

transient current in the generator, motor and fault.

07

2

Q.3 (a) Discuss possible faults on overhead lines. 03

(b) Prove that positive and negative sequence impedances of fully

transposed transmission lines are always equal. 04

(c)

Draw positive sequence network and negative sequence network for

system shown in fig no -3 .Assume that negative sequence reactance

of each machine is equal to its subtrasient reactance. Omit resistances.

07

OR

Q.3 (a) Explain Types of Transmission Line. 03

(b) Obtain the Equivalent circuit for nominal representation for long

transmission line.

04

(c) A three phase 50 Hz transmission line is 100 Km long and delivers 20

MW at 220KV at 0.9p.f. Lagging and at 110V. The resistance and

reactance of the line per conductor per km are 0.2 Ω and 0.4 Ω

respectively. While capacitance admittance is 2.5×10-6 ʊ/km/phase.

Calculate (i) the current and voltage at sending end (ii) Efficiency of

transmission line. Use nominal T method.

07

Q.4 (a) What is 3 phase unsymmetrical fault? Discuss the different types of

unsymmetrical in brief. 03

(b) Derive an expression for fault current for line-to-line fault by

symmetrical components method. 04

(c) The currents in a 3-phase unbalanced system are : IR = (12 + j 6) A ;

I Y = (12 − j 12) A; IB = (−15 + j 10) A The phase sequence in RYB.

Calculate the zero, positive and negative sequence components of the

currents.

07

OR

Q.4 (a) Why is 3-φ symmetrical fault more severe than a 3-φ unsymmetrical

fault?

03

(b) Derive an expression for fault current for double line-to-ground fault

by symmetrical components method. 04

(c) In a 3-phase, 4-wire system, the currents in R, Y and B lines under

abnormal conditions of loading are as under : IR = 100 ∠30º A ; I Y =

50 ∠300º A ; IB = 30 ∠180º A Calculate the positive, negative and

zero sequence currents in the R-line and return current in the neutral

wire.

07

Q.5 (a) Explain methods of reducing corona. 03

(b) Explain travelling waves of transmission line when receiving end is

short circuited briefly. 04

(c) Prove that the synchronous machine offers time varying reactance on

no load condition. 07

OR

Q.5 (a) Explain any two causes which are producing Transient on line. 03

(b) Explain switching of capacitor phenomenon on transmission line. 04

(c) A 3 phase 220 Kv, 50 Hz transmission line consists of 1.5 cm radius

conductor spaced 2 meters apart in equilateral triangular formation. If

the temperature is 40o C and atmospheric pressure is 76 cm, calculate

the corona loss per km of the line. Take mo = 0.85.

07

3

4

1


GUJARAT TECHNOLOGICAL UNIVERSITY BE – SEMESTER – VI (NEW).EXAMINATION – WINTER 2016

Subject Code: 2160908 Date: 24/10/2016

Subject Name: Electrical Power system – II

Time: 10:30 AM to 01:00 PM Total Marks: 70 Instructions:

1. Attempt all questions.

2. Make suitable assumptions wherever necessary.

3. Figures to the right indicate full marks.

Q.1 (a) Derive long transmission equivalent π model. 07

(b) Determine the voltage, current and power factor at the sending end of a 3 phase,

50 Hz, overhead transmission line 160 km long delivering a load of 100 MVA

at 0.8 pf lagging and 132 KV to a balanced load. Resistance per km is 0.16Ω,

inductance per km is 1.2 mH and capacitance per km conductor is 0.0082µF.

Use nominal π method.

07

Q.2 (a) Draw & explain receiving end power circle diagram. 07

(b) Two generators G1 and G2 are rated 15 MVA, 11KV and 10MVA, 11KV

respectively. The generators are connected to a transformer shown in fig.1.

Calculate the subtransient current in each generator where a three phase fault

occurs on the high voltage side of the transformer. Choose a base 15 MVA.

07

OR

(b) A generating station consists of two 100 MVA generators with 6% reactance

each and one 150 MVA generator with 8% reactance as shown in fig. 2. These

generators are connected to a common busbar from which loads are taken

through a number of circuit breaker on (i) low voltage side and (ii) on high

voltage side. Take base power 150 MVA.

07

Q.3 (a) Write note on Selection of a circuit breaker. 07

(b) Explain the importance of bus impedance matrix in fault calculation. 07

OR

Q.3 (a) Explain Type-2 modification of Zbus building algorithm. 07

(b) Discuss principle of symmetrical components. Derive the necessary equations to

convert: (i) phase quantities into symmetrical components (ii) symmetrical

components in to phase quantities.

07

Q.4 (a) Draw the positive, negative and zero sequence networks of the power system

network as shown in Fig. 3.

07

(b) A 50 MVA, 11 KV, synchronous generator has a subtransient reactance of 20%.

The generator supplies two motors over a transmission line with transformers at

both ends as shown in fig. 4. The motors have rated inputs of 30 and 15 MVA,

both 10 KV, with 25% subtransient reactance. The three-phase transformers are

both rated 60 MVA, 10.8/121 KV, with leakage reactance of 10% each. Assume

zero-sequence reactance for the generator and motors of 6% each. Current

limiting reactors of 2.5 ohms each are connected in the neutral of the generator

and motor no 2. The zero sequence reactance of the transmission line is 300

ohms. The series reactance of the line is 100 Ω. Draw the positive, negative and

zero sequence networks. Assume that the negative sequence reactance of each

machine is equal to its subtransient reactance. Assume base power 50 MVA and

base voltage 11KV.

07

OR

2

Q.4 (a) Prove that for a fully transposed line, the zero sequence impedance is much

higher than positive or negative sequence impedance.

07

(b) Fig. 5 shows a three phase generator in which phases b and c are short circuited

and connected through an impedance Zf to phase a. Draw equivalent sequence

network.

07

Q.5 (a) List and Describe factors affecting corona. Outline different methods to reduce

corona.

07

(b) Derive the equation for attenuation of travelling waves. 07

OR

Q.5 (a) Explain inductive interferences due to corona between Power and

communication line.

07

(b) Explain overvoltage due to arcing ground. 07

Fig. 1

Fig. 2

Fig 5

Fig. 3

Fig. 4

*************

Page 1 of 2


GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) EXAMINATION – WINTER 2018

Subject Code:2160908 Date:20/11/2018 Subject Name:Electrical Power system – II Time: 02:30 PM TO 05:00 PM Total Marks: 70 Instructions:


Q.1 (a) Explain Types of Transmission Line. 03

(b) Obtain the Equivalent circuit for nominal-T representation for long

transmission line.

04

(c) A 3 phase 220 Kv, 50 Hz transmission line consists of 1.5 cm radius

conductor spaced 2 meters apart in equilateral triangular formation. If

the temperature is 40o C and atmospheric pressure is 76 cm, calculate

the corona loss per km of the line. Take mo = 0.85.

07

Q.2 (a) How do the term impedance drop, voltage drop and voltage regulation,

in connection with transmission line differs?

03

(b) Prove that in case of transients in RL series circuits, short circuit

current contains symmetrical short circuit components and DC offset

components.

04

(c) Explain Symmetrical components and state their application. Derive

Symmetrical components of a given set of three unbalanced current

phasors.

07

OR

(c) A 3-phase. 50-Hz overhead transmission line 100 km long has the

following constants.

Resistance/km/phase = 0.1 Ω

Inductive reactance/km/phase = 0.2 Ω

Capacitive susceptance/km/phase = 0.04 × 10 -4 siemen

Determine (i) the sending end current (ii) sending end voltage (iii)

sending end power factor and (iv) transmission efficiency when

supplying a balance load of 10,000 kW at 66 kV p.f 0.8 lagging . Use

nominal T method.

07

Q.3 (a) What is arcing ground? Explain its effect on the performance of a

power system.

03

(b) Write a note on selection of circuit breaker. 04

(c) The currents in a 3-phase unbalanced system are :IR = (12 + j 6) A; IY

= (12 − j 12) A; IB = (−15 + j 10) A. The phase sequence in RYB.

Calculate the zero, positive and negative sequence components of the

currents.

07

OR

Q.3 (a) What is the reason for transient during short circuits? 03

Page 2 of 2

(b) Explain Various factors affecting Corona effect. 04

(c) Describe analysis of single line to ground fault at a point of power

system using symmetrical components and sequence networks.

07

Q.4 (a) Discuss phase shifting in star-delta transformers. 03

(b) What is 3 phase unsymmetrical fault? Discuss any one type of

unsymmetrical in brief.

04

(c) With suitable example explain the single and double frequency

transients in power system.

07

OR

Q.4 (a) Explain Capacitance switching. 03

(b) Differentiate between transient and sub transient reactance. 04

(c) Explain travelling waves of a transmission line when the receiving end

is short circuited.

07

Q.5 (a) Explain the performance of loaded Synchronous Machine. 03

(b) Explain why the control of reactive power is essential for maintaining

a desired voltage profile?

04

(c) An unloaded star connected solidly grounded 10 MVA, 11 kV

generator has positive, negative and zero sequence impedances are

j1.3 Ω, j 0.8 Ω and j 0.4 Ω respectively. A single line to ground fault

occurs at the terminals of the generator.

1) Calculate the fault current.

2) Determine the value of the inductive reactance that must be

inserted at the generator neutral to limit the fault current to 50

% of the value obtained in (1)

07

OR

Q.5 (a) Enlist the various unsymmetrical fault occurring in power system. 03

(b) Explain importance of power circle diagram. 04

(c) A generator rated 100 MVA, 20 kV has X1=X2=20% and X0=5%. Its

neutral is grounded through reactor of 0.32 Ω. The generator is

operating at rated voltage with load and is disconnected from the

system when a single line to ground fault occurs at its terminals. Find

the subtransient current in the faulted phase and line to line voltages.

07

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1


GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) - EXAMINATION – SUMMER 2018

Subject Code:2160908 Date:01/05/2018 Subject Name:Electrical Power system – II Time:10:30 AM to 01:00 PM Total Marks: 70 Instructions:


MARKS

Q.1 (a) Define voltage regulation of a transmission line. List out methods for

line compensation based on value of voltage regulation. 03

(b) What is receiving end power circle diagram? Write down steps to

draw it. 04

(c) A 200 km long three phase overhead line has a resistance of 48.7

ohms per phase, inductive reactance of 80.2 ohms per phase and

capacitance (line to neutral) 8.42 nF per km. It supplies a load of 13.5

MW at a voltage of 88 kV at 0.9 lagging power factor. Using nominal

T circuit, find sending end voltage, sending end current, voltage

regulation and power angle of given line.

07

Q.2 (a) Give classification of faults. What is difference between steady state

reactance Xd, transient reactance Xd’ and sub-transient reactance

Xd’’?

03

(b) Three 20 MVA generators each having a reactance of 0.2 pu are

operating in parallel. A fault occurs at generator bus. Find the fault

MVA if fault is symmetrical.

04

(c) What is circuit breaker? How is its rating decided? 07

OR

(c) A three phase 20 MVA, 10 kV alternator has an internal reactance of

5 % and negligible resistance. Find the external reactance to be

connected in series with each phase so that steady state current in

each phase does not exceed 8 times full load current.

07

Q.3 (a) What are symmetrical components and its need? 03

(b) Show that symmetrical component transformation is power

invariant. 04

(c) The line to neutral voltages in a three phase system are Van = 200 +

j0 V, Vbn = - 43.4 – j 246.2 V and Vcn = - 52.1 + j295.4 V. Find Va1,

Va2 and Va0. Form these values, find values of Vb1, Vb2, Vb0, Vc1, Vc2

and Vc0.

07

OR

Q.3 (a) Why does a generator produce only positive sequence voltage? 03

(b) Write equation of phase voltage in terms of symmetrical

components. 04

(c) Discuss the significance of zero sequence circuit. Why should Zn

appear as 3Zn in zero sequence equivalent circuit? 07

Q.4 (a) How does neutral grounding affect the fault calculation? 03

(b) A 30 MVA, 11 kV generator has Z1 = Z2 = j0.2 pu, Z0 = j0.05 pu. A

line to ground fault occurs on the generator terminals. Find the fault

current. Assume that the generator neutral is solidly grounded and

04

2

that the generator is operating at no load condition and at rated

voltage at the occurrence of fault.

(c) Using appropriate interconnection of sequence networks, derive the

equation for a line to line fault in a power system with fault

impedance of Zf.

07

OR

Q.4 (a) Which sequence current flows through ground and ground wires and

why? 03

(b) Give reason: for a fault at alternator terminals, a single line to ground

fault is generally more severe than a three phase fault. 04

(c) A three phase, 37.5 MVA, 33 kV alternator having X1 = 0.18 pu, X2

= 0.12 pu and X0 = 0.10 pu, based on its ratings, is connected to a 33

kV overhead line having X1 = 6.3 ohms, X2 = 6.3 ohms and X0 =

12.6 ohms per phase. A single line to ground fault occurs at the

remote end of the line. The alternator neutral is solidly grounded.

Calculate fault current.

07

Q.5 (a) Write a brief note on capacitance switching. 03

(b) A surge of 15 kV magnitude travels along a cable towards its

junction with an overhead line. The inductance and capacitance of

the cable and overhead line are respectively 0.3 mH, 0.4 μF and 1.5

mH, 0.012 μF per km. Find the voltage rise at the junction due to the

surge.

04

(c) Derive the equation for attenuation of travelling waves. 07

OR

Q.5 (a) Explain the phenomena of corona. 03

(b) Give reasons for following: The disruptive critical voltage is less

than visual critical voltage. 04

(c) Find the critical disruptive voltage and the critical voltages for local

and general corona on a three phase overhead transmission line,

consisting of three stranded copper conductors spaced 2.5 m apart at

the corners of an equilateral triangle. Air temperature and pressure

are 21 ˚C and 73.6 cm Hg respectively. The conductor diameter,

irregularity factor and surface factor are 10.4 mm, 0.85, 0.7 and 0.8

respectively.

07

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Documents

LAXMI INSTITUTE OF TECHNOLOGYkV with 100% power factor. Find the volateg , current and power at the sending end and voltage regulation of the lie. Given z= 0.5239∟79.02° Ώ/ km