COURSE PLANNER SUBJECT: ELECTRICAL POWER SYSTEM II

Transcription

1 COURSE PLANNER SUBJECT: ELECTRICAL POWER SYSTEM II [260908] B.E. Third Year Class Electrical 204 Term: 6/2 (DEC-6 to APR-7) Faculty: PROF. J. I. JARIWALA PROF. A. S. SHAH PROF. T. M. PANCHAL PROF. N. B. KANTHARIA Contents:. 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: [] 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.

2 [] Course Outcomes: After the completion of this course, the student shall able to do. 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.

3 [2] Course Contents: CHAPTER SYLLABUS 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. 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. 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. 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 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. TOTAL HRS %WEIGHTAGE

4 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 5

5 [3] List of Reference Books: ) Power System Analysis : John J. Grainger, William D. Stevenson Jr., Tata McGraw Hill [,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,4 th Edition Tata McGraw Hill. 5) Power System Analysis by HadiSaadat, Tata McGraw Hill.

6 [4] List of Experiments: SR. LIST OF EXPERIMENTS 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 7 TO ANALYZE PERFORMANCE OF MEDIUM TRANSMISSION LINE BY USING TRANSMISSION LINE PANEL ( PI-MODEL ). 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. 0 TO STUDY TRANSIENT ANALYSIS OF TRANSMISSION LINE.

7 [5] Major Equipments required for Experiments:. Transmission line panel 2. Digital Multimeter 3. Resistive load trolley -Phase, 3kW Make: Satya 4. connecting wires 5. Rheostats 50 OHM/5 AMP (MAKE:STEAD) 6. Ø continuously variable voltage auto transformer 7. Inductive coil 8. COMPUTER SYSTEM (20 No.) ) CPU INTEL P4 5) CABINET U MAX 2) MB 4WV 6) MONITER 5.6'' LCD LG 3) HARD DISK 500 GB 7) KEY BOARD 04 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:

8 [7]Learning Assignments: Chapter- 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 QUESTION YEAR MARKS From first principles, derive the A, B, C and D constants of a long transmission line. Prove that the active and reactive powers transmitted to load over a long line are DEC-0 NOV-3 2 DEC Starting from the first principles, show that surges behave as travelling waves. Find expressions for surge impedance and wave velocity. 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. 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. Derive equivalent- π circuit of a long transmission line using the expressions derived in above question. 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. 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-0 JUN- JUN- DEC-5 08 JUN- 06 DEC- MAY-6 08 DEC- 06

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. Draw the equivalent network of uniform long line and derive its π model. 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. Describe one line diagrams of power systems. Explain how they are drawn and state its applications. 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). Explain how receiving end power circle diagram and sending end power circle diagram are drawn? State applications of them. Derive expressions of active power and reactive power at the receiving end of a lossless line. Using rigorous solution method obtain the value of A,B,C,D constant for long transmission Line DEC- JUNE-2 JAN-3 NOV-3 NOV-3 NOV-3 NOV-3 DEC-5 JUNE-4 7 Derive the equation for attenuation of a travelling wave. JUNE-4 Derive the equations of ABCD parameters for nominal π (pi) 8 configuration of a transmission line from first principles with usual NOV-4 notations DEC-5 Derive A,B,C and D constants of a medium transmission line for nominal π configuration 9 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-5 ATTEMPT ALL BOLDED EXAMPLES SR QUESTION YEAR MARKS A long line with A = D = and B = has at the load end, transformer having a series impedance ZT= The load voltage and current are VLandIL. Obtain expressions for VSandISin the for DEC-0 and evaluate these constants.

10 Consider a 230 mile long 60 Hz transmission line. Its series impedance z is j8277 Ω/mile and shunt admittance y is j5.05 X 0-6 mho/mile. The load on the line is 25 MW at 25 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. A single circuit 60 Hz transmission line is 370 km long. The load on the line is 25 MW at 25 kv with 00% power factor. Find the voltage, current and power at sending end and voltage regulation of the line. (Given z= Ω km and y=3.7 Χ mho km 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 32 kv. The line conductors are spaced equilaterally 3 m apart. The conductor resistance is 0. ohm/km and its effective diameter is.6 cm. Neglect leakages. A 300 km 32 kv 3-phase overhead line has a total series impedance of 52+j200 Ω/phase and a total shunt admittance of j.5 X 0-3 siemens per phase to neutral. The line is supplying 40 MVA at 0.8 p.f. lagging at 32 kv. Using long line equations find sending end voltage, current, power factor and power. A three phase 50 Hz transmission line is 50 Km long and delivers 25 MW at 0KV 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 ʊ /km/phase. Compute the voltage regulation and transmission efficiency by applying nominal π method. JUN- DEC- JUNE- 2 MAY JAN-3 7 A three phase, 60 Hz, completely transposed 345 kv, 200 km line has z= j0.35 _/km and y= j4.2 x 0-6 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-3

11 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 JUNE ohms and mhos per phase respectively. 4 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 A 275 kv transmission line has the following line constants: A = , (i) Determine the power at unity power factor that can be received, if the voltage profile at each end is to be maintained JUNEat 275 kv (b) What type of compensation equipment would be 4 required if the load is 50 MW at unity pf with the same voltage profile as in part (i) A three phase 50 Hz transmission line is 50 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 ʊ/km/phase. Compute the NOV-4 voltage regulation and transmission efficiency by applying nominal π (pi) method A 50 Hz transmission line 300 km long has a total series impedance of (40 + j 25) ohms and a total shunt admittance of 0-3 mho. The receiving end load is 50 MW at 220 kv with 0.8 lagging power factor. DEC-5 Find the sending end voltage and current using exact method. A 3-phase. 50-Hz overhead transmission line 00 km long has the following constants. Resistance/km/phase = 0. Ώ Inductive reactance/km/phase = 0.2 Ώ Capacitive susceptance/km/phase = siemen MAY-6 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 0,000 kw at 66 kv p.f 0.8 lagging. Use nominal T method.

12 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. ATTEMPT ALL BOLDED QUESTIONS SR QUESTION YEAR MARKS 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? 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. 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. 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 Explain the importance of bus impedance matrix in fault calculation What is bus impedance matrix? How it is useful in symmetrical fault analysis? 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. DEC-0 DEC-0 DEC- JUN- JUN-2 JUNE_4 NOV-4 MAY-5 NOV-3 DEC-5 JAN-3 NOV-4 NOV-3 0 Explain the sub-transient, transient and steady state reactance of a synchronous machine in relation to fault current NOV-4 Deriving proper equations explain doubling effect MAY-5 2 Explain type 2 modification of Zbus building algorithm MAY-5 3 Explain type 3 modification of Zbus building algorithm. MAY-5

13 4 Explain sub-transient, transient and steady state reactances of synchronous machine and draw the machine circuit models using them DEC-5 ATTEMPT ALL BOLDED EXAMPLES SR QUESTION YEAR MARKS Figure shows a single-line diagram of power system network. The breaking capacity of breakers A is 00 MVA. Find out the per unit value of reactor R. Also find out the breaking capacity of breakers B. DEC-0 2 A 25 MVA 3.8 KV generator with Xd = 5% 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 3.8/6.9 KV with a leakage reactance of 0%. 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-

14 A 33 KV line has a resistance of 4 ohm and reactance of 6 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 0,000 KVA with 0% 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) 3 MAY A four bus sample power system is shown in fig.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.0 pu and prefault current be zero.g:.2 KV,00 MVA, x g=0.08 pu,line from to 2=0.20 pu, Line from to 3 =0.20 pu, Line from to 4=0.0 pu, Line from 2 to 3=0.0 pu, Line from 2 to 4=0.0 pu, G2:.2 KV,00 MVA, x g2=0.08 pu T:/0KV,00MVA, XT=0.06 pu T2: /0KV,00MVA, XT2=0.06 pu A synchronous generator and a synchronous motor each rated 25 MVA, kv having 5% sub-transient reactance are connected through transformer and a line as shown in Fig. 2. The transformers are rated 25 MVA, /66 kv and 66/ kv with leakage reactance of 0% each. The line has a reactance of 0% on a base of 25 MVA, 66 kv. The motor is drawing 5 MW at 0.8 power factor leading and a terminal voltage of 0.6 kv when a symmetrical three-phase fault occurs at the motor terminals. Find the sub-transient current in the motor, generator and fault JAN-3 DEC-5

15 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. ATTEMPT ALL BOLDED QUESTIONS SR QUESTION YEAR MARKS Write a brief note on phase shift of symmetrical components in Y-Δ transformer banks. 2 Write a note on zero sequence networks in brief. 3 4 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. Discuss principle of symmetrical components. Derive the necessary equations to convert: (i) phase quantities into symmetrical components (ii) symmetrical components in to phase quantities. JUN- JUN-2 JUN- JUN-2 DEC-5 DEC- MAY-6 08 MAY How the circuit breaker is selected for any particular location. JAN-3 Describe how zero sequence impedances of generator, 6 transmission line and transformers are obtained. Draw zero sequence diagrams of transformer with different connections of primary and secondary. NOV-3 Describe analysis of single line to ground fault at a point of 7 power system using symmetrical components and sequence networks. NOV-3 8 Discuss phase shifting in a single phase transformer and Y-_ transformers. NOV-3 9 Draw the zero sequence networks for different types of transformer connections JUNE-4 0 Derive the equation of three phase power in terms of NOV-4 symmetrical components of voltages and currents MAY-6 Prove that positive and negative sequence impedances of fully transposed transmission lines are always equal MAY-5 2 Derive the relationship between symmetrical components of line and delta currents. MAY-5 3 Prove that for a fully transposed line, the zero sequence impedance is much higher than positive or negative sequence impedance JUNE-4

16 4 Introduce symmetrical components and state their applications. Derive symmetrical components of a given set of three unbalanced current phasors. NOV-3 DEC-5 ATTEMPT ALL BOLDED EXAMPLES SR QUESTION YEAR MARKS Two 25 MVA, kv generators are connected to a common busbarwhich supplies a feeder. The star-point of one of the generators is grounded through resistance of 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 Feeder (Ω/ph.) (p.u.) j 0.4 X j 0.2 DEC-0 X 2 j 0.5 j 0.4 X 3 j 0.08 j 0.8 Assume fault impedance to be zero The voltage across a 3-phase unbalanced load are Va=200/400, Vb = 320/900,Vc=480/3400. Determine the symmetrical components of voltages. Phase sequence is abc. The currents in three phase unbalanced system are IR = (2 + j6) A, IY = (2 - j2) A, IB = (-5 + j0) A. The phase sequence is RYB. Calculate, positive, negative and zero sequence components of currents. The currents in three phase unbalance system are IR=(2+j6) A,IY=(2-j2) A, IB = (-5+j0) A. The phase sequence is RYB. Calculate, positive, negative and zero sequence component of current. 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 3.2 KV are represented by just two equivalent motors. The neutral of one motor M is grounded through reactance. The neutral of the second motor M2 is not grounded. Rated inputs to the motors JUN-2 NOV-4 MAY-6 JAN-3 DEC- 08

17 are 200 MVA and 00MVA for M and M2 respectively. For both motors X = 20%. The three phase transformer T us rated 350MVA, 230/20 KV with leakage reactance of 0%. Transformer T2 is composed of three single phase transformers each rated 27/3.2kv, 00 MVA with leakage reactance of 0%. 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. Figure shows a power system network. Draw positive, negative and zero sequence networks. The system data is as under: 6 DEC-0 7 A delta connected balanced resistive load is connected across an unbalanced three-phase supply. The currents in lines A and B are 0 30 o and 5-60 o respectively. Find current in line C. Find symmetrical components of phase currents flowing in the individual resistances of the delta connected load. JUN-

18 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 8 JUN-4 9 JUNE-4 0 Consider the three bus system shown in fig. The generators are 00 MVA, with a transient reactance of 0% each. Both the transformers are 00 MVA with a leakage reactance of 5%. The reactance of each of the lines to a base of 00 MVA, 0 kv is 0%. Obtain the value of fault current for a three phase solid short circuit on bus 3. Assume prefault voltages to be.0 p.u. and prefualt currents to be zero Fig.(A) shows a power system network. Draw zero sequence networks for this system. The system data is as under. Generator (G): 50 MVA, KV, X0 =0.08 p.u. Transformer (T): 50 MVA, /220 KV, X0 =0. p.u. Generator (G2) : 30 MVA, KV, X0 =0. p.u. Transformer (T2): 30 MVA, 220/ KV, X0 =0.09 p.u. Zero sequence reactance of line is Ω JUN-2

19 Fig (A) shows a part of a power system. Draw zero sequence network for this system. The system data is given below: Generator (G): 50 MVA, KV, X0=0.08 PU Transformer (T): 50 MVA, /220 kv, X0 =0. PU Generator (G2) : 30 MVA, KV, X0 =0. PU Transformer (T2): 30 MVA, 220/ KV, X0 =0.09 PU Zero sequence reactance of line is Ω Grounding reactance of G2 is 0. PU NOV-4 2 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 %. ohm each is connected in the neutral circuit of both the synchronous machines. MAY-5 3 In a three phase four wire system the currents in line a, b and c under abnormal condition are Ia = 00 ے 30 º A,Ib =50 ے 300 º A, Ic=30 ے 80 º A. Calculate the zero positive and negative phase sequence currents in line a and return current in the neutral conductor. 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 0 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-6 4 MAY-6

20 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 ATTEMPT ALL BOLDED QUESTIONS 2 QUESTION 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. 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. YEAR DEC-0 NOV-4 MAR KS DEC-0 3 Explain single line to ground fault on an unloaded JUN- generator using symmetrical components. Draw MAY-6 connection of sequence networks. 4 Derive the double line to ground fault in a 3 phase alternator JUN-2 The analysis of unsymmetrical faults can be more easily done 5 with thehelp of symmetrical components than by a direct MAY-3 02 solution of theunbalancedcircuit. GIVE REASON. 6 Derive an expression for the fault current for a single line-to ground fault as an unloaded generator. MAY-3 7 Derive an expression for the fault current for a double-line fault as unloaded generator. MAY-3 8 Explain how fault current can be calculated when L-G fault occur through a fault impedance Zf. JAN-3 A three phase synchronous generator is initially operating on 9 load. Suddenly a line to ground fault occurs at one of its terminals. Derive the expression for fault current and phase JUNE-4 voltages. Describe analysis of single line to ground fault at a point of 0 power system using symmetrical components and sequence DEC-5 networks What is 3 phase unsymmetrical fault? Discuss the different types of unsymmetrical in brief. MAY-6

21 ATTEMPT ALL BOLDED EXAMPLES SR QUESTION YEAR MARKS Two 25 MVA, 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 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: DEC-0 Each Generator(p.u.) Feeder (Ω/ph.) X j 0.2 j 0.4 X 2 j 0.5 j X 3 j 0.08 j 0.8 Assume fault impedance to be zero. A 25 MVA, kv generator has ''d X = 0.2 p.u., 2 X = 0.3 p.u. and 0 X = 0. 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. A salient-pole generator without dampers is rated 20 MVA, 3.8 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. pu respectively. The neutral of the generator is solidly grounded. Determine the sub transient currents and the lineto-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. One conductor of a three phase line is open. The current flowing to the Δ Connected load through line a is 0 A. with the current in line a as reference and assuming that line c is open, find the symmetrical components of the line currents. An unloaded star connected solidly grounded 0 MVA, KV generator has positive, negative and zero sequence impedances are j.3 Ω, j0.8 Ω, and j0.4 Ω respectively. A single line to ground fault occurs at the terminals of the generator. () Calculate the fault current. DEC-0 JUN- DEC- JUN-2 02

22 (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 () A generator rated 00 MVA, 20kV has X = 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. A generator rated 00 MVA, 20kV has X = 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). A synchronous generator is rated at 25 MVA, 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? A synchronous generator and a synchronous motor each rated 25 MVA, having 5% subtransient reactance are connected through transformers and transmission line as shown in fig. 2. The transformers are rated 25 MVA, /66 kv with leakage reactance of 0 % each. The line has a reactance of 0 % on the basis of 25 MVA, 66 kv. The generator is delivering 5 MW at 0.8 power factor lagging and the prefault voltage is 0.6 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. 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 %. ohm each is connected in the neutral circuit of both the synchronous machines. MAY-3 MAY-3 JUNE-4 MAY-5 MAY-5 A 3 phase, kv, 25 MVA generator with Xo = 0.05 p.u, X = 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-6

23 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. ATTEMPT ALL BOLDED QUESTIONS SR QUESTION YEAR MARKS Explain travelling waves of a transmission line when the receiving end is short circuited. 2 Write a brief note on capacitance switching. JUN- DEC-5 MAY-6 JUN- NOV-3 MAY-6 3 Explain traveling and reflecting waves on transmission line with open end at the receiving. DEC- 4 Starting from the first principles, show that surges behaves as travelling waves. Find expression for surge impedance and JUN-2 wave velocity. 5 A travelling wave suffers reflection when it reaches discontinuity.give REASON MAY Discuss the phenomenon of wave reflection and wave refraction. Derive expression for refraction and reflection MAY-3 coefficients. 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-3 8 Explain single and double frequency transient. JAN-3 With suitable example explain the single and double frequency NOV-4 transients in power system. 9 Explain in brief transients in RL series circuits ( Doubling effect ). MAY-6 0 Define transient. Explain in brief restrikting voltage after removal of short circuits. MAY-6 ATTEMPT ALL BOLDED EXAMPLES SR QUESTION YEAR MARKS 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-4

24 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 ATTEMPT ALL BOLDED QUESTIONS SR QUESTION YEAR MARKS What are the factors and conditions affecting corona loss? Explain them briefly. Briefly discuss the factors affecting Corona. DEC-0 JUNE-4 NOV-4 MAY-5 JUN-2 DEC-5 MAY-6 2 Describe the phenomena of corona in brief. State and explain any three factors affecting corona. JUN- 3 Explain the phenomena of corona. Also discuss the measures taken to control corona in EHVAC transmission lines. DEC- 4 The disruptive critical voltage is less than visual critical voltage. Give reason. MAY Explain how corona affects the electrical design of transmission line. State the factors on which corona loss depends JAN-3 6 Write a short note on phenomena of corona NOV-3 7 Derive the equation of critical disruptive voltage in relation to Corona discharge. NOV-4 8 Discuss corona formation phenomenon DEC-5 ATTEMPT ALL BOLDED EXAMPLES SR QUESTION YEAR MARKS Find the disruptive critical voltage for a 3-ph line consisting of 2 mm diameter conductors spaced in a 6 m delta configuration. Take temperature as 25 C, pressure as 73 cm of Hg and surface factor What should be the voltage of transmission? DEC-0 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.5 cm diameter arranged in a 3 JUN-2

25 meter delta connection. Assume air density factor of.05 and dielectric strength of air to be 2.KV/cm Find the disruptive critical voltage and visual corona voltage (local as well as general corona) for a 3-phase 220 kv line consisting of 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 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 Find the total loss in fair weather using Peek s formula. Estimate the corona loss for a three conductors each of 0mm 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 Ionization of air may be assumed to take place at a maximum voltage gradient of 30kV/cm. MAY-3 JAN-3 DEC-5 Note:Any misplacement in question with respect to its chapter will found than it is welcome to you to know us.