course planner subject electrical power system...

ELECTRICAL ENGINEERING DEPARTMENT

COURSE PLANNER

SUBJECT: ELECTRICAL POWER SYSTEM – II

[2160908] B.E. – Third Year

Class–Electrical 2014

Term: 16/2 (DEC-16 to APR-17)

Faculty: PROF. J. I. JARIWALA PROF. T. M. PANCHAL

PROF. A. S. SHAH PROF. N. B. KANTHARIA

Contents: 1. Course Outcomes 2. Course Contents[Syllabus] 3. List of Reference Books 4. List of Experiments

5. Major Equipments required for Experiments 6. List of Open source software and learning websites required for

experiments 7. Active Learning Assignments and Tutorial.

Instructions for Assignment/Tutorial:

[1] This set of Assignment-Tutorial consist the collection of questions of past GTU

Question papers.

[2] Attend those questions which are bold marked and/or frequently asked in GTU

exam.

[3] Students should make a separate Chapter wise Files[write on File Pages] to solve

these Questions.

[4] Students must solve these given set of Assignments by themselves only.

[5] Assessment of given assignment should be done regularly after completion of each

chapter by Students from the respective faculty members.


[1] Course Outcomes:

After the completion of this course, the student shall able to do

1. Analyze the performance of Short, Medium and Long transmission line.

2. Describe the symmetrical components and its applications.

3. Analyze Symmetrical faults in power systems.

4. Analyze Unsymmetrical faults in power systems.

5. Describe transients in power systems.

6. Describe corona effect.


[2] Course Contents:

CHAPTER

NO. SYLLABUS TOTAL

HRS %WEIGHTAGE

1

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 transmission line (circle diagrams), and Reactive compensation of transmission lines.

8 15

2

Symmetrical Three-Phase Faults: Transients in RL Series circuits, Short-Circuit currents and the reactance 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 Star-Delta 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 Communication

lines

6 15


[3] List of Reference Books:

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., 4th Edition, McGraw Hill International. [4]

3) Electrical Power systems: C. L .Wadhwa, 5th Edition, New Age International Publishers.[5, 6]

4) Modern Power system Analysis by I J Nagrath, D P Kothari,4th Edition Tata McGraw Hill.

5) Power System Analysis by HadiSaadat, Tata McGraw Hill.


[4] List of Experiments:

SR.

NO. LIST OF EXPERIMENTS

1 TO SIMULATE SERIES RL CIRCUIT.

2 TO SIMULATE SERIES RC CIRCUIT.

3 TO SIMULATE SERIES RLC CIRCUIT.

4 TO ANALYZE PERFORMANCE OF SHORT TRANSMISSION LINE AND TO REALIZE

FERRANTI EFFECT BY USING TRANSMISSION LINE PANEL.

5 TO ANALYZE PERFORMANCE OF SHORT TRANSMISSION LINE BY USING MATLAB.

6 TO ANALYZE PERFORMANCE OF MEDIUM TRANSMISSION LINE BY USING

TRANSMISSION LINE PANEL (“PI-MODEL”).

7 TO ANALYZE PERFORMANCE OF MEDIUM TRANSMISSION LINE BY USING

TRANSMISSION LINE PANEL (“T-MODEL”).

8 TO SIMULATE BALANCED 3-PHASE 3-WIRE SYSTEM.

9 TO SIMULATE UN-BALANCED 3-PHASE 3-WIRE SYSTEM.

10 TO STUDY TRANSIENT ANALYSIS OF TRANSMISSION LINE.


[5] Major Equipments required for Experiments:

1. Transmission line panel

2. Digital Multimeter

3. Resistive load trolley 1-Phase, 3kW Make: Satya

4. connecting wires

5. Rheostats 50 OHM/5 AMP (MAKE:STEAD)

6. 1Ø continuously variable voltage auto transformer

7. Inductive coil 8. COMPUTER SYSTEM (20 No.)

1) CPU INTEL P4 5) CABINET U MAX

2) MB 41WV 6) MONITER 15.6'' LCD LG

3) HARD DISK 500 GB 7) KEY BOARD 104 LOGITECH

4) RAM 2GB DDR-3 8) MOUSE OPTICAL LOGITECH 9. MATLAB software

[6]List of Open source software and learning websites required for experiments:

http://nptel.iitm.ac.in/coursecontents_elec.php


[7]Learning Assignments:

Chapter-1 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), and Reactive compensation of transmission

lines.

ATTEMPT ALL BOLDED QUESTIONS

SR

NO. QUESTION YEAR MARKS

1 From first principles, derive the A, B, C and D constants of a long

transmission line.

DEC-10

NOV-13 07

2

Prove that the active and reactive powers transmitted to load over a

long line are

DEC-10 07

3

Starting from the first principles, show that surges behave as

travelling waves. Find expressions for surge impedance and wave

velocity.

DEC-10 07

4

Using A, B, C and D constants of transmission line, VR as reference

Phasor and with other usual notations, derive expressions of active

powers and reactive powers at both ends. Write expression of

maximum power that can be transmitted at the receiving end.

JUN-11 07

5

Derive expressions of voltage Phasor and current Phasor at any point

of a long transmission line as function of distance x from receiving

end in terms of distributed parameters of the line, voltage Phasor VR

(voltage at receiving end) and current Phasor IR (current at

receiving end). State difference between characteristic impedance

and surge impedance of the line.

JUN-11

DEC-15

08

07

6 Derive equivalent- π circuit of a long transmission line using the

expressions derived in above question. JUN-11 06

7

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.

DEC-11

MAY-16 08

8

Derive the expression for real power PR and reactive power QR at

receiving end of a medium transmission line in terms of

transmission line constants (ABCD Constants)

DEC-11 06


ATTEMPT ALL BOLDED EXAMPLES

SR


1

A long line with A = D = 0.9∠1.5° and B = 150∠65° has at the load

end, transformer having a series impedance ZT= 100∠67°. The load

voltage and current are VLandIL. Obtain expressions for VSandISin

the for

and evaluate these constants.

DEC-10 07

9

What is characteristic impedance? Derive the expressions of VR

and IR at any point of line as a function of distance X from the

receiving end using distributed parameters.

DEC-11 07

10 Draw the equivalent network of uniform long line and derive its π

model. JUNE-12 07

11

What is an equivalent π and equivalent T circuit of a long

transmission line?Derive expression of parameters of these

circuits in terms of line parameters.

JAN-13 07

12 Describe one line diagrams of power systems. Explain how they are drawn and state its applications.

NOV-13 07

13

Derive expressions of voltage phasor and current phasor at any point of a long transmission line as function of distance x from receiving end in terms of distributed parameters of the line, voltage phasor VR (voltage at receiving end) and current phasor IR (current at receiving end).

NOV-13 07

14 Explain how receiving end power circle diagram and sending end power circle diagram are drawn? State applications of them.

NOV-13 07

15 Derive expressions of active power and reactive power at the receiving end of a lossless line.

NOV-13 DEC-15

07

16 Using rigorous solution method obtain the value of A,B,C,D constant for long transmission Line

JUNE-14 07

17 Derive the equation for attenuation of a travelling wave. JUNE-14 07

18

Derive the equations of ABCD parameters for nominal π (pi) configuration of a transmission line from first principles with usual notations Derive A,B,C and D constants of a medium transmission line for nominal π configuration

NOV-14 DEC-15

07

19

Deriving the expression of voltage and current of the long transmission line considering the fact that line parameters are distributed uniformly through the line, explain SIL and wavelength of the transmission line

MAY-15 07


2

Consider a 230 mile long 60 Hz transmission line. Its series

impedance z is 0.1603 + j8277 Ω/mile and shunt admittance y 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 and power at the

sending end and the voltage regulation of the line. Also find the

wavelength and velocity of propagation in miles and miles/s

respectively. Please consider the line as a long line.

JUN-11 07

3

A single circuit 60 Hz transmission line is 370 km long. The load on

the line is 125 MW at 215 kv with 100% power factor. Find the

voltage, current and power at sending end and voltage regulation of

the line. (Given z=0.5239 79.020 Ω⁄km and y=3.17 Χ 10-6

900mho⁄km

DEC-11 07

4

Using the nominal π method, find the sending end voltage and

voltage regulation of a 250km,3-phase, 50 Hz transmission line

delivering 25 MVA at 0.8 power factor (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.

JUNE-

12 07

5

A 300 km 132 kV 3-phase overhead line has a total series

impedance of 52+j200 Ω/phase and a total shunt admittance of

j1.5 X 10-3siemens per phase to neutral. The line is supplying 40

MVA at 0.8 p.f. lagging at 132 kV. Using long line equations find

sending end voltage, current, power factor and power.

MAY-13 02

6

A three phase 50 Hz transmission line is 150 Km long and delivers

25 MW at 110KV at 0.85 p.f. lagging. The resistance and reactance of

the line per conductor per kilometer are 0.3 Ω and 0.9 Ω respectively.

The line charging admittance is 0.3×10-6 ʊ /km/phase. Compute the

voltage regulation and transmission efficiency by applying nominal π

method.

JAN-13 07

7

A three phase, 60 Hz, completely transposed 345 kV, 200 km line has z= 0.032 + j0.35 _/km and y= j4.2 x 10-6 S/km. Full load at the receiving end is 700 MW at 0.99 p.f leading and at 95% of rated voltage. Assuming a medium length line, determine the following: ABCD parameters of the nominal _ circuit, sending end voltage and current and real power delivered by sending end.

NOV-13 07


8

A 3-phase overhead transmission line delivers a load of 80 MW at 0.8 pf lagging and 220 kV between the lines. Its total series impedance per phase and shunt admittance per phase is 200800 ohms and 0.0013900 mhos per phase respectively. Using nominal T method determine (i) A,B,C,D constants of the line (ii) Sending end voltage (iii) Sending end current (iv) Sending end power factor (v) Transmission efficiency of the line

JUNE-14

07

9

A 275 kV transmission line has the following line constants: A = 0.85 50, 200750 (i) 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 (b) What type of compensation equipment would be required if the load is 150 MW at unity pf with the same voltage profile as in part (i)

JUNE-14

07

10

A three phase 50 Hz transmission line is 150 Km long and delivers 25 MW at 220KV at 0.8 p.f. lagging. The resistance and reactance of the line per conductor per km are 0.3 Ω and 0.9 Ω respectively. The line charging admittance is 0.3×10-6 ʊ/km/phase. Compute the voltage regulation and transmission efficiency by applying nominal π (pi) method

NOV-14 07

11

A 50 Hz transmission line 300 km 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 220 kV with 0.8 lagging power factor. Find the sending end voltage and current using exact method.

DEC-15 07

12

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

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.

MAY-16 07


Chapter-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.


SR

NO.

QUESTION YEAR MARKS

1

Draw the waveforms for fault current for a 3-phase fault

on alternator terminals. Explain the sub-transient,

transient and steady state reactance. What is their

significance in fault calculations?

DEC-10 07

2

Justify the following statement:

“For a fault at alternator terminals, a single line to ground

fault is generally more severe than a 3-ph fault whereas for

faults on transmission lines, a 3-ph fault is more severe than

other faults.”

DEC-10 07

4

Explain the phenomena of sudden three phase short circuit

at the generator terminal on no load condition and define sub

transient, transient and steady state reactances of

synchronous generator.

DEC-11 07

5

Write a brief note on selection of circuit breaker.

With suitable example explain how the symmetrical fault

analysis is useful for selection of circuit breakers.

Explain in detail how fault analysis is helpful in selection of

circuit breaker

JUN-11

JUN-12

JUNE_14

NOV-14

MAY-15

NOV-13

DEC-15

07

6

Explain the importance of bus impedance matrix in fault

calculation

What is bus impedance matrix? How it is useful in

symmetrical fault analysis?

JAN-13

NOV-14 07

7

Derive 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.

NOV-13 07

10

Explain the sub-transient, transient and steady state reactance of a synchronous machine in relation to fault current

NOV-14 07

11 Deriving proper equations explain doubling effect MAY-15 07 12 Explain ‘type 2 modification’ of Zbus building algorithm MAY-15 07 13 Explain ‘type 3 modification’ of Zbus building algorithm. MAY-15 07


14 Explain sub-transient, transient and steady state reactances of synchronous machine and draw the machine circuit models using them

DEC-15 07


SR


1

Figure 1 shows a single-line diagram of power system network. The

breaking capacity of breakers A is 100 MVA. Find out the per unit

value of reactor R. Also find out the breaking capacity of breakers B.

DEC-10 07

2

A 25 MVA 13.8 KV generator with Xd ’’ = 15% is connected

through a transformer to a bus which supplies four identical

motors as shown in Fig. The sub transient reactance Xd ’’ of

each motor is 20% on a base of 5MVA, 6.9 KV. The three phase

rating of the transformer is 25 MVA 13.8/6.9 KV with a leakage

reactance of 10%. The bus voltage at the motors is 6.9 kv when

a three phase fault occurs at the point P. for the fault specified,

Determine (a) the sub transient current in the fault, (b) the sub

transient current in breaker A.

DEC-11 07


3

A 33 KV line has a resistance of 4 ohm and reactance of 16

ohmrespectively. The line is connected to generating station bus

bars through a 6000 KVA step up transformer which has a reactance

of 6%. The station has two generators rated 10,000 KVA with 10%

reactance and 5000 KVA with 5% reactance. Calculate the fault

current and short circuit KVA when a 3-phase fault occurs at the h.v.

terminals of the transformers and at the load end of the line. (See

figure 2)

MAY-13 08

4

A four bus sample power system is shown in fig 1.Calculate the

faultcurrent at bus no 4 for three phase solid fault occurring at that

bus.Various data are given below. Assume pre fault voltage as 1.0 pu

and prefault current be zero.G1:11.2 KV,100 MVA, x’g1=0.08 pu,Line

from 1 to 2=0.20 pu, Line from 1 to 3 =0.20 pu,

Line from 1 to 4=0.10 pu, Line from 2 to 3=0.10 pu,

Line from 2 to 4=0.10 pu,

G2:11.2 KV,100 MVA, x’g2=0.08 pu

T1:11/110KV,100MVA, XT1=0.06 pu

T2: 11/110KV,100MVA, XT2=0.06 pu

JAN-13 07

5

A synchronous generator and a synchronous motor each rated 25 MVA, 11 kV having 15% sub-transient reactance are connected through transformer and a line as shown in Fig. 2. The transformers are rated 25 MVA, 11/66 kV and 66/11 kV with leakage reactance of 10% each. The line has a reactance of 10% on a base of 25 MVA, 66 kV. The motor is drawing 15 MW at 0.8 power factor leading and a terminal voltage of 10.6 kV when a symmetrical three-phase fault occurs at the motor terminals. Find the sub-transient current in the motor, generator and fault

DEC-15 07


Chapter-3

Symmetrical Components:

Synthesis of Unsymmetrical phasors from their symmetrical components, The

symmetrical components of unsymmetrical phasors, Phase shift of symmetrical

components in Star-Delta 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.


SR


1 Write a brief note on phase shift of symmetrical components in

Y-Δ transformer banks.

JUN-11

JUN-12 07

2 Write a note on zero sequence networks in brief.

JUN-11

JUN-12

DEC-15

07

3

Derive the expressions of positive, negative and zero

sequence voltage components in terms of given set of

unbalance voltage phasorsVa, Vb and Vc. Also prove that

the transformation used is power invariant.

DEC-11

MAY-16 08

4

Discuss principle of symmetrical components. Derive the

necessary equations to convert: (i) phase quantities into

symmetrical components (ii) symmetrical components in to

phase quantities.

MAY-13 06

5 How the circuit breaker is selected for any particular location. JAN-13 07

6

Describe how zero sequence impedances of generator, transmission line and transformers are obtained. Draw zero sequence diagrams of transformer with different connections of primary and secondary.

NOV-13 07

7 Describe analysis of single line to ground fault at a point of power system using symmetrical components and sequence networks.

NOV-13 07

8 Discuss phase shifting in a single phase transformer and Y-_ transformers.

NOV-13 07

9 Draw the zero sequence networks for different types of transformer connections

JUNE-14 07

10 Derive the equation of three phase power in terms of symmetrical components of voltages and currents

NOV-14 MAY-16

07

11 Prove that positive and negative sequence impedances of fully transposed transmission lines are always equal

MAY-15 07

12 Derive the relationship between symmetrical components of line and delta currents.

MAY-15 07

13 Prove that for a fully transposed line, the zero sequence impedance is much higher than positive or negative sequence impedance

JUNE-14 07


14 Introduce symmetrical components and state their applications. Derive symmetrical components of a given set of three unbalanced current phasors.

NOV-13 DEC-15

07


SR


1

Two 25 MVA, 11 kV generators are connected to a common

busbarwhich supplies a feeder. The star-point of one of the

generators is grounded through resistance of 1 4, while that of

the other generator is isolated. A line-to-ground fault occurs at

the far end of the feeder. Determine:(i) the fault current and

(ii) the voltage to ground of healthy phases of the feeder at the

fault point. The sequence impedances of each generator are

and feeder are

given below:

Each Generator

(p.u.)

Feeder (Ω/ph.)

X 1 j 0.2 j 0.4

X 2 j 0.15 j 0.4

X 3 j 0.08 j 0.8

Assume fault impedance to be zero.

DEC-10 07

2

The voltage across a 3-phase unbalanced load are

Va=200/400, Vb = 320/1900,Vc=480/3400. Determine the

symmetrical components of voltages. Phase sequence is abc.

JUN-12 07

3

The currents in three phase unbalanced system are IR = (12 + j6) A, IY = (12 - j12) A, IB = (-15 + j10) A. The phase sequence is RYB. Calculate, positive, negative and zero sequence components of currents.

NOV-14 MAY-16

07

4

The currents in three phase unbalance system are IR=(12+j6)

A,IY=(12-j12) A, IB = (-15+j10) A. The phase sequence is RYB.

Calculate, positive, negative and zero sequence component of

current.

JAN-13 07

5

A 300 MVA 20 KV 3 Φ generator has a sub transient reactance

of 20 %. The generator supplies a number of synchronous

motors over a 64 km transmission line having transformers at

both ends, as shown in fig. The motors, all rated 13.2 KV are

represented by just two equivalent motors. The neutral of one

motor M1 is grounded through reactance. The neutral of the

second motor M2 is not grounded. Rated inputs to the motors

DEC-11 08


are 200 MVA and 100MVA for M1 and M2 respectively. For

both motors X’’ = 20%. The three phase transformer T1 us

rated 350MVA, 230/20 KV with leakage reactance of 10%.

Transformer T2 is composed of three single phase

transformers each rated 127/13.2kv, 100 MVA with leakage

reactance of 10%. Series reactance of the transmission line is

0.5 Ω⁄km Draw the reactance diagram with all the

reactancesmarked in per unit. Select the generator rating as

base in the generator circuit.

6

Figure shows a power system network. Draw positive,

negative and zero sequence networks. The system data is as

under:

DEC-10 07

7

A delta connected balanced resistive load is connected across an unbalanced three-phase supply. The currents in lines A and B are 1030o and 15-60o respectively. Find current in line C. Find symmetrical components of phase currents flowing in the individual resistances of the delta connected load.

JUN-11 07


8

An unbalanced delta connected load is connected across a balanced three phase supply of 400 V as shown in fig. Find the symmetrical components of line currents and delta currents

JUN-14 07

9

Consider the three bus system shown in fig. The generators are 100 MVA, with a transient reactance of 10% each. Both the transformers are 100 MVA with a leakage reactance of 5%. The reactance of each of the lines to a base of 100 MVA, 110 kV is 10%. Obtain the value of fault current for a three phase solid short circuit on bus 3. Assume prefault voltages to be 1.0 p.u. and prefualt currents to be zero

JUNE-14 07

10

Fig.(A) shows a power system network. Draw zero

sequence networks for this system. The

system data is as under.

Generator (G1): 50 MVA, 11KV, X0 =0.08 p.u.

Transformer (T1): 50 MVA, 11/220 KV, X0 =0.1 p.u.

Generator (G2) : 30 MVA, 11KV, X0 =0.07 p.u.

Transformer (T2): 30 MVA, 220/11 KV, X0 =0.09 p.u.

Zero sequence reactance of line is 555.6 Ω

JUN-12 07


11

Fig (A) shows a part of a power system. Draw zero sequence network for this system. The system data is given below: Generator (G1): 50 MVA, 11KV, X0=0.08 PU Transformer (T1): 50 MVA, 11/220 kV, X0 =0.1 PU Generator (G2) : 30 MVA, 11KV, X0 =0.07 PU Transformer (T2): 30 MVA, 220/11 KV, X0 =0.09 PU Zero sequence reactance of line is 555.6 Ω Grounding reactance of G2 is 0.1 PU

NOV-14 07

12

Considering system shown in fig. 2 at no load, find out the line current ‘Ia’ at fault point when A-G fault occurs at the terminals of the motor. Let zero sequence reactance of generator and motor is 50 % each. Zero sequence reactance of transformers is 25 % each and zero sequence reactance of line is 20 %. 1 ohm each is connected in the neutral circuit of both the synchronous machines.

MAY-15 07

13

In a three phase four wire system the currents in line a, b and c

under abnormal condition are Ia = 100 30 ے º A ,Ib =50 300 ے º A

, Ic=30 180 ے º A. Calculate the zero positive and negative phase

sequence currents in line a and return current in the neutral

conductor.

MAY-16 07

14

One conductor of a 3 phase line is open as shown in fig. 3. 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.

MAY-16 07


Chapter-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


SR

NO. QUESTION YEAR

MAR

KS

1

Using appropriate interconnection of sequence networks,

derive the equation for a line to line fault in a power system

with a fault impedance of fZ.

Mention the steps to find the fault current with LG fault in a

power system. Draw the interconnection of sequence networks

in this regard.

DEC-10

NOV-14 07

2

Justify the following statement:

“For a fault at alternator terminals, a single line to ground fault

is generally more severe than a 3-ph fault whereas for faults on

transmission lines, a 3-ph fault is more severe than other

faults.”

DEC-10 07

3

Explain single line to ground fault on an unloaded

generator using symmetrical components. Draw

connection of sequence networks.

JUN-11

MAY-16 07

4 Derive the double line to ground fault in a 3 phase alternator JUN-12 07

5

The analysis of unsymmetrical faults can be more easily done

with thehelp of symmetrical components than by a direct

solution of theUnbalancedcircuit. GIVE REASON.

MAY-13 02

6 Derive an expression for the fault current for a single line-to

ground fault as an unloaded generator. MAY-13 07

7 Derive an expression for the fault current for a double-line fault

as unloaded generator. MAY-13 07

8 Explain how fault current can be calculated when L-G fault

occur through a fault impedance Zf. JAN-13 07

9

A three phase synchronous generator is initially operating on load. Suddenly a line to ground fault occurs at one of its terminals. Derive the expression for fault current and phase voltages.

JUNE-14 07

10 Describe analysis of single line to ground fault at a point of power system using symmetrical components and sequence networks

DEC-15 07

11 What is 3 phase unsymmetrical fault? Discuss the different types of

unsymmetrical in brief. MAY-16 07



SR


1

Two 25 MVA, 11 kV generators are connected to a common

busbarwhich supplies a feeder. The star-point of one of the

generators is grounded through a resistance of 1 4, while that

of the other generator is isolated. A line-to-ground fault occurs

at the far end of the feeder. Determine:(i) the fault current and

(ii) the voltage to ground of healthy phases of the feeder at the

fault point. The sequence impedances of each generator are

and feeder are

given below:

Each Generator(p.u.) Feeder (Ω/ph.)

X 1 j 0.2 j 0.4

X 2 j 0.15 j 0.4

X 3 j 0.08 j 0.8

Assume fault impedance to be zero.

DEC-10 07

2

A 25 MVA, 11 kV generator has ''d X = 0.2 p.u., 2 X = 0.3 p.u. and

0 X = 0.1 p.u.The neutral of the generator is solidly grounded.

Determine the sub-transient current in the generator and the

line-to-line voltages for sub-transient condition when a Y-B-G

fault occurs at the generator terminals. Assume pre-fault

currents and fault-resistance to be zero.

DEC-10 07

3

A salient-pole generator without dampers is rated 20 MVA,

13.8 kV and has a direct-axis sub transient reactance of 0.25 pu.

The negative- and zero–sequence reactances are 0.35 pu and

0.1 pu respectively. The neutral of the generator is solidly

grounded. Determine the sub transient currents and the line-

to-line voltages at the fault under sub transient conditions

when a line-to-line fault occurs at the b and c terminals of the

generator. Assume that the generator is unloaded and

operating at rated terminal voltage when the fault occurs.

Neglect resistance.

JUN-11 07

4

One conductor of a three phase line is open. The current

flowing to the Δ Connected load through line “a” is 10 A. with

the current in line “a” as reference and assuming that line “c” is

open, find the symmetrical components of the line currents.

DEC-11 07

5

An unloaded star connected solidly grounded 10 MVA, 11KV

generator has positive, negative and zero sequence impedances

are j1.3 Ω, j0.8 Ω, and j0.4 Ω respectively. A single line to

ground fault occurs at the terminals of the generator.

(1) Calculate the fault current.

JUN-12 02


(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)

6

A generator rated 100 MVA, 20kV has X1 = X2 = 20% and

X0 = 5%. ItsNeutral is grounded through a reactor of 0.32

ohms. The generator isOperating at rated voltage with load

and is disconnected from the system when a single line to

ground fault occurs at its terminals. Find the sub transient

current in the faulted phase and line to line voltages.

MAY-13 07

7

A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 =

5%. ItsNeutral is grounded through a reactor of 0.32 ohms. The

generator isOperating at rated voltage with load and is

disconnected from the system when a line to line fault occurs at

its terminals. Find the sub-transient current in the faulted

phase and line to line voltages. (Repetition of example Q-4(b)

for line to line fault).

MAY-13 07

8

A synchronous generator is rated at 25 MVA, 11 kV. It is star connected with neutral point solidly grounded. The generator is operating on no-load at rated voltage. Its reactance are X’’=X2 = 0.2 pu and X0 = 0.08 pu. Calculate the symmetrical subtransient currents for (i)LG fault (ii) LL fault (iii) LLG fault (iv) LLL fault. After calculating the values of fault currents do you find something surprising in the values of fault currents for LG and LLL faults? Why?

JUNE-14 07

9

A synchronous generator and a synchronous motor each rated 25 MVA, having 15% subtransient reactance are connected through transformers and transmission line as shown in fig. 2. The transformers are rated 25 MVA, 11/66 kV with leakage reactance of 10 % each. The line has a reactance of 10 % on the basis of 25 MVA, 66 kV. The generator is delivering 15 MW at 0.8 power factor lagging and the prefault voltage is 10.6 kV when a symmetrical fault occurs at the middle of the line. Find the subtransient current in the generator, motor and fault with the help of Thevenin’s Theorem.

MAY-15 07

10

Considering system shown in fig. 2 at no load, find out the line current ‘Ia’ at fault point when B-C-G fault occurs at the terminals of the motor. Let zero sequence reactance of generator and motor is 50 % each. Zero sequence reactance of transformers is 25 % each and zero sequence reactance of line is 20 %. 1 ohm each is connected in the neutral circuit of both the synchronous machines.

MAY-15 07

11 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. MAY-16 07


Chapter-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.


SR


1 Explain travelling waves of a transmission line when the

receiving end is short circuited.

JUN-11

DEC-15

MAY-16

07

2 Write a brief note on capacitance switching.

JUN-11

NOV-13

MAY-16

07

3 Explain traveling and reflecting waves on transmission line

with open end at the receiving. DEC-11 07

4

Starting from the first principles, show that surges behaves as

travelling waves. Find expression for surge impedance and

wave velocity.

JUN-12 07

5 A travelling wave suffers reflection when it reaches

discontinuity.GIVE REASON MAY-13 02

6

Discuss the phenomenon of wave reflection and wave

refraction. Derive expression for refraction and reflection

coefficients.

MAY-13 07

7

Discuss the behavior of a travelling wave when it reaches the

end of (i) open circuited (ii) short circuited transmission line.

Draw diagrams to show voltage and current on the line before

and after the wave reaches at the end.

MAY-13 07

8

Explain single and double frequency transient.

With suitable example explain the single and double frequency

transients in power system.

JAN-13

NOV-14 07

9 Explain in brief transients in RL series circuits ( Doubling effect ). MAY-16 07

10 Define transient . Explain in brief restrikting voltage after removal

of short circuits. MAY-16 07


SR


1

A 500 kV, 2μS, rectangular surge travels along the line which is terminated by a capacitance of 2500 pF. Determine the voltage across the capacitance and the reflected voltage wave if the surge impedance is 400Ω

JUNE-14 07


Chapter-6

Corona: Critical Disruptive Voltage, Corona Loss, Line Design based on Corona,

Disadvantages of Corona, Radio Interference, Inductive interference between

Power and Communication lines


SR


1

What are the factors and conditions affecting corona loss?

Explain them briefly.

Briefly discuss the factors affecting Corona.

DEC-10

JUNE-14

NOV-14

MAY-15

JUN-12

DEC-15

MAY-16

07

2 Describe the phenomena of corona in brief. State and explain

any three factors affecting corona. JUN-11 07

3 Explain the phenomena of corona. Also discuss the measures

taken to control corona in EHVAC transmission lines. DEC-11 07

4 The disruptive critical voltage is less than visual critical voltage.

Give reason. MAY-13 02

5 Explain how corona affects the electrical design of transmission

line. State the factors on which corona loss depends JAN-13 07

6 Write a short note on phenomena of corona NOV-13 07

7 Derive the equation of critical disruptive voltage in relation to Corona discharge.

NOV-14 07

8 Discuss corona formation phenomenon DEC-15 07


SR


1

Find the disruptive critical voltage for a 3-ph line consisting of

21 mm diameter conductors spaced in a 6 m delta

configuration. Take temperature as 25° C, pressure as 73 cm of

Hg and surface factor 0.85. What should be the voltage of

transmission?

DEC-10 07

2

Find the critical disruptive voltage and corona loss for a 3

phase line which is operating at220 KV, 50 Hz frequency.

The line has conductor of 1.5 cm diameter arranged in a 3

JUN-12 07


meter delta connection. Assume air density factor of 1.05

and dielectric strength of air to be 21.1KV/cm.

3

Find the disruptive critical voltage and visual corona voltage

(local as well as general corona) for a 3-phase 220 kV line

consisting of 22.26 mm diameter conductors spaced in a 6 m

delta configuration. The following data can be assumed:

Temperature 25° C, pressure 73 cm of mercury, surface factor

0.84, irregularity factor for local corona 0.72, and irregularity

factor for general (decided) corona 0.82.

MAY-13 07

4

The three phase 220KV, 50 Hz line is 250 Km long consisting of

22.26mm diameter conductor spaced in a 6 mt delta

configuration. TheFollowing data can be assumed. Temperature

250 C, pressure 73 cm of mercury, surface factor 0.84,

irregularity factor for local corona 0.72, irregularity factor for

general corona 0.82. Find the total loss in fair weather using

Peek’s formula.

JAN-13 07

5

Estimate the corona loss for a three conductors each of 10mm diameter and spaced 2.5m apart in an equilateral triangle formation. The temperature of air is 30°c and the atmospheric pressure is 750mm of mercury. Take the irregularity factor as 0.85. Ionization of air may be assumed to take place at a maximum voltage gradient of 30kV/cm.

DEC-15 07

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