Papaers Solution OF Power System Analysis & Simulation

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Quastion asked in paperspaper ofchepter no.page no.bookQ 1 (A)What is importance of receiving end power circle diagram? Explain the steps of constructing it.Jan-131 (B)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 and 0.9 respectively. The line charging admittance is 0.310-6 /km/phase. Compute the voltage regulation and transmission efficiency by applying nominal method. Jan-131Q 2 (A)A four bus sample power system is shown in fig 1.Calculate the fault current 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 pre fault current be zero. G1:11.2 KV,100 MVA, xg1=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, xg2=0.08 pu T1:11/110KV,100MVA, XT1=0.06 pu T2: 11/110KV,100MVA, XT2=0.06 puJan-133 (B)Discuss the effect of change in excitation of synchronous machine.Jan-132 (B)What is importance of one line diagram of a power system? How it is drawn?Jan-132Q 3 (A)Explain the importance of bus impedance matrix in fault calculation.Jan-133 (B)A 100 MVA, 33 KV three phase generator has a reactance of 15%. The generator is connected to the motors through transmission line and a transformer as shown in fig 2. Motors have rated inputs of 40MVA, 30 MVA, and 20 MVA at 30 KV with 20 % reactance each. Draw the P.U. diagram.Jan-133Q 3 (A)How the circuit breaker is selected for any particular location.Jan-133 (B)Explain steady state, transient and sub transient reactance of a synchronous machine.Jan-133Q 4 (A)Explain the zero sequence impedance of transformer for various connections.Jan-134 (B)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-135Q 4 (A)Explain how fault current can be calculated when L-G fault occur through a fault impedance Zf.Jan-135 (B)A 25 MVA, 13.2 KV alternator with solidly grounded neutral has a sub transient reactance of 0.25 p.u.. the negative and zero sequence reactances are 0.35 and 0.1 p.u. respectively. Find the fault current when (1) a single line to ground fault occurs at the terminals of an unloaded alternator (2) a L-L fault occurs.Jan-135Q 5 (A)Explain how corona affects the electrical design of transmission line. State the factors on which corona loss depends.Jan-136 (B)The three phase 220KV, 50 Hz line is 250 Km long consisting of 22.26mm diameter conductor spaced in a 6 mt delta configuration. The following 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 Peeks formula.Jan-136Q 5 (A)What are the various methods of neutral grounding? Explain any two.Jan-137 (B)Explain single and double frequency transient.Jan-138

Q 1 (A)Give reasons for following: 1. The analysis of unsymmetrical faults can be more easily done with the help of symmetrical components than by a direct solution of the unbalanced circuit. 2. A travelling wave suffers reflection when it reaches discontinuity. 3. The disruptive critical voltage is less than visual critical voltage.May-135,3,6 (B)Figure 1 shows the single line diagram of a simple system. The transformer ratings, generator rating, line impedance and load impedance are shown. Draw impedance diagram. Find actual value of generator current, line current, load current, load voltage and load power. Carry out the calculation in p. u. neglecting phase shift in transformer.May-133Q 2 (A)What is an equivalent and equivalent T circuit of a long transmission line? Derive expression of parameters of these circuits in terms of line parameters.May-131 (B)A 300 km 132 kV 3-phase overhead line has a total series impedance of 52+j200 /phase and a total shunt admittance of j1.5 X 10-3 siemens 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-131 (B)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-136Q 3 (A)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-134 (B)A 50 MVA, 11 kV, 3-phase alternator was subjected to different types of faults. The fault currents were: 3- fault 1870A, line to line fault 2590 A, single line to ground fault 4130 A. The alternator neutral is solidly grounded. Find pu values of the three sequences reactance of the alternator.May-135Q 3 (A)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 (i) delta-star transformer with star point grounded. (ii) delta-delta transformer. (iii) star-star transformer with star point grounded.May-134 (B)A 33 KV line has a resistance of 4 ohm and reactance of 16 ohm respectively. 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-133Q 4 (A)Derive an expression for the fault current for a single line-to ground fault asan unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. 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.May-135Q 4 (A)Derive an expression for the fault current for a double-line fault as an unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. The generator is operating 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 for line to line fault).May-135Q 5 (A)Discuss the phenomenon of wave reflection and wave refraction. Derive expression for refraction and reflection coefficients.May-138 (B)Why it is necessary to earth neutral? Explain the difference between resistance and reactance grounding.May-137Q 5 (A)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-138 (B)With help of circuit & phasor diagram explain resonant grounding method.May-137

Q 1 (A)Draw the equivalent network of uniform long line and derive its model.Jun-121 (B)Using the nominal method, find the sending end voltage and voltage regulation of a 250 km,3-phase, 50 Hz transmission line delivering 25 MVA at 0.8 powerfactor (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. Jun-121Q 2 (A)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-124 (B)Write a brief note on phase shift of symmetrical components in Y- transformer banks.Jun-124 (B)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 Jun-124Q 3 (A)Derive the double line to ground fault in a 3 phase alternator.Jun-125 (B)An unloaded star connected solidly grounded 10 MVA, 11KV generator has positive, negative and zero sequence impedances are j1.3 , j0.8 , and j0.4 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).Jun-125Q 3 (A)Write a brief note on selection of circuit breaker.Jun-123 (B)A synchronous generator and a synchronous motor each rated 25MVA, 11KV having 15% subtransient reactance are connected through transformer and a line as shown in fig.(B). The transformer s are rated 25 MVA, 11/66KV 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 powerfactor leading and a terminal voltage of 10.6 KV when a symmetrical three- phase fault occurs at the motor terminals. Find the subtransient current in the generator, motor and fault.Jun-123Q 4 (A)Discuss the advantages of per unit computations.Jun-122 (B)A generator is rated 1000 MVA, 33 KV. Its star connected winding has a reactance of 0.9 p.u. Find (1) Ohmic value of reactance of the winding if the generator is working in a circuit for which the bases are specified as 250MVA, 22KV (2) The p.u. value of reactance of generator winding on the specified base.Jun-123Q 4 (A)Explain travelling waves of a transmission line when the receiving end is shortcircuited.Jun-128 (B)Write a note on zero sequence networks in brief.Jun-124Q 5 (A)Explain need of neutral grounding using phasor diagrams. Explain any one method of neutral grounding.Jun-127 (B)Starting from the first principles, show that surges behaves as travelling waves. Find expression for surge impedance and wave velocity.Jun-128Q 5 (A)Discuss factors affecting corona.Jun-126 (B)Find the critical disruptive voltage and corona loss for a 3 phase line which is operating at 220 KV, 50 Hz frequency. The line has conductor of 1.5 cm diameter arranged in a 3 meter delta connection. Assume air density factor of 1.05 and dielectric strength of air to be 21.1 KV/cm.Jun-126

Q 1 (A)Derive the ABCD constants for medium transmission line using Nominal representation. Also write the expressions for voltage regulation and efficiency for the same line.Nov-111 (B)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) Nov-111Q 2 (A)Explain the Equivalent Circuit model of Synchronous machine. From the first principal, derive Vt = Ef Ia (Ra+ jXs) Where Xs = Xar + Xl. Also draw the equivalent circuit diagram.Nov-112 (B)With the help of neat phasor diagram, explain the operation of synchronous generator for different field excitation. Nov-112 (B)The three phase ratings of a three winding transformer are: Primary Y Connected, 66 KV, 15 MVA, Secondary Y Connected, 13.2 KV, 10 MVA, Tertiary Connected, 2.3 KV, 5 MVA, Neglecting resistance, the leakage impedances are Zps= 7% on 15 MVA 66 KV Base, Zpt= 9% on 15 MVA 66 KV Base, Zst= 10% on 10 MVA 13.2 KV Base Find the per unit impedances of the star connected equivalent circuit for a base of 15 MVA, 66 KV in the primary circuit. Also derive the expressions you use.Nov-112Q 3 (A)What is P. U. system? Explain the advantages of P. U. System.Nov-112 (B)A 300 MVA 20 KV 3 generator has a subtransient 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 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 km Draw the reactance diagram with all the reactances marked in per unit. Select the generator rating as base in the generator circuit. Nov-113Q 3 (A)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.Nov-111 (B)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 km and y=3.17 10-6 900 mhokmNov-111Q 4 (A)Derive the expressions of positive, negative and zero sequence voltage components in terms of given set of unbalance voltage phasors Va, Vb and Vc. Also prove that the transformation used is power invariant. Nov-114 (B)One conductor of a three phase line is open. The current flowing to the 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. Nov-114Q 4 (A)Explain traveling and reflecting waves on transmission line with open end at the receiving .Nov-118 (B)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 subtransient 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 subtransient current in the fault, (b) the subtransient current in breaker A. Nov-113Q 5 (A)Enlist the methods of neutral grounding. Explain any one of the method in detail.Nov-117 (B)Explain the phenomena of arcing grounds. How does neutral grounding eliminate the arcing ground? Also enlist the advantages of neutral grounding.Nov-117Q 5 (A)Explain the phenomena of corona. Also discuss the measures taken to control corona in EHVAC transmission lines. Nov-116 (B)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.Nov-113

ch-1PSAs : Questions from Ch-1Current and Voltage Relations on a Transmission Line

Quastion asked in paperspaper ofchepter no.page no.bookQ 1 (A)What is importance of receiving end power circle diagram? Explain the steps of constructing it.Jan-131 (B)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 and 0.9 respectively. The line charging admittance is 0.310-6 /km/phase. Compute the voltage regulation and transmission efficiency by applying nominal method. Jan-131Q 2 (A)A four bus sample power system is shown in fig 1.Calculate the fault current 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 pre fault current be zero. G1:11.2 KV,100 MVA, xg1=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, xg2=0.08 pu T1:11/110KV,100MVA, XT1=0.06 pu T2: 11/110KV,100MVA, XT2=0.06 puJan-133 (B)Discuss the effect of change in excitation of synchronous machine.Jan-132 (B)What is importance of one line diagram of a power system? How it is drawn?Jan-132Q 3 (A)Explain the importance of bus impedance matrix in fault calculation.Jan-133 (B)A 100 MVA, 33 KV three phase generator has a reactance of 15%. The generator is connected to the motors through transmission line and a transformer as shown in fig 2. Motors have rated inputs of 40MVA, 30 MVA, and 20 MVA at 30 KV with 20 % reactance each. Draw the P.U. diagram.Jan-133Q 3 (A)How the circuit breaker is selected for any particular location.Jan-133 (B)Explain steady state, transient and sub transient reactance of a synchronous machine.Jan-133Q 4 (A)Explain the zero sequence impedance of transformer for various connections.Jan-134 (B)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-135Q 4 (A)Explain how fault current can be calculated when L-G fault occur through a fault impedance Zf.Jan-135 (B)A 25 MVA, 13.2 KV alternator with solidly grounded neutral has a sub transient reactance of 0.25 p.u.. the negative and zero sequence reactances are 0.35 and 0.1 p.u. respectively. Find the fault current when (1) a single line to ground fault occurs at the terminals of an unloaded alternator (2) a L-L fault occurs.Jan-135Q 5 (A)Explain how corona affects the electrical design of transmission line. State the factors on which corona loss depends.Jan-136 (B)The three phase 220KV, 50 Hz line is 250 Km long consisting of 22.26mm diameter conductor spaced in a 6 mt delta configuration. The following 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 Peeks formula.Jan-136Q 5 (A)What are the various methods of neutral grounding? Explain any two.Jan-137 (B)Explain single and double frequency transient.Jan-138

Q 1 (A)Give reasons for following: 1. The analysis of unsymmetrical faults can be more easily done with the help of symmetrical components than by a direct solution of the unbalanced circuit. 2. A travelling wave suffers reflection when it reaches discontinuity. 3. The disruptive critical voltage is less than visual critical voltage.May-135,3,6 (B)Figure 1 shows the single line diagram of a simple system. The transformer ratings, generator rating, line impedance and load impedance are shown. Draw impedance diagram. Find actual value of generator current, line current, load current, load voltage and load power. Carry out the calculation in p. u. neglecting phase shift in transformer.May-133Q 2 (A)What is an equivalent and equivalent T circuit of a long transmission line? Derive expression of parameters of these circuits in terms of line parameters.May-131 (B)A 300 km 132 kV 3-phase overhead line has a total series impedance of 52+j200 /phase and a total shunt admittance of j1.5 X 10-3 siemens 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-131 (B)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-136Q 3 (A)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-134 (B)A 50 MVA, 11 kV, 3-phase alternator was subjected to different types of faults. The fault currents were: 3- fault 1870A, line to line fault 2590 A, single line to ground fault 4130 A. The alternator neutral is solidly grounded. Find pu values of the three sequences reactance of the alternator.May-135Q 3 (A)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 (i) delta-star transformer with star point grounded. (ii) delta-delta transformer. (iii) star-star transformer with star point grounded.May-134 (B)A 33 KV line has a resistance of 4 ohm and reactance of 16 ohm respectively. 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-133Q 4 (A)Derive an expression for the fault current for a single line-to ground fault asan unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. 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.May-135Q 4 (A)Derive an expression for the fault current for a double-line fault as an unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. The generator is operating 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 for line to line fault).May-135Q 5 (A)Discuss the phenomenon of wave reflection and wave refraction. Derive expression for refraction and reflection coefficients.May-138 (B)Why it is necessary to earth neutral? Explain the difference between resistance and reactance grounding.May-137Q 5 (A)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-138 (B)With help of circuit & phasor diagram explain resonant grounding method.May-137

Q 1 (A)Draw the equivalent network of uniform long line and derive its model.Jun-121 (B)Using the nominal method, find the sending end voltage and voltage regulation of a 250 km,3-phase, 50 Hz transmission line delivering 25 MVA at 0.8 powerfactor (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. Jun-121Q 2 (A)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-124 (B)Write a brief note on phase shift of symmetrical components in Y- transformer banks.Jun-124 (B)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 Jun-124Q 3 (A)Derive the double line to ground fault in a 3 phase alternator.Jun-125 (B)An unloaded star connected solidly grounded 10 MVA, 11KV generator has positive, negative and zero sequence impedances are j1.3 , j0.8 , and j0.4 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).Jun-125Q 3 (A)Write a brief note on selection of circuit breaker.Jun-123 (B)A synchronous generator and a synchronous motor each rated 25MVA, 11KV having 15% subtransient reactance are connected through transformer and a line as shown in fig.(B). The transformer s are rated 25 MVA, 11/66KV 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 powerfactor leading and a terminal voltage of 10.6 KV when a symmetrical three- phase fault occurs at the motor terminals. Find the subtransient current in the generator, motor and fault.Jun-123Q 4 (A)Discuss the advantages of per unit computations.Jun-122 (B)A generator is rated 1000 MVA, 33 KV. Its star connected winding has a reactance of 0.9 p.u. Find (1) Ohmic value of reactance of the winding if the generator is working in a circuit for which the bases are specified as 250MVA, 22KV (2) The p.u. value of reactance of generator winding on the specified base.Jun-123Q 4 (A)Explain travelling waves of a transmission line when the receiving end is shortcircuited.Jun-128 (B)Write a note on zero sequence networks in brief.Jun-124Q 5 (A)Explain need of neutral grounding using phasor diagrams. Explain any one method of neutral grounding.Jun-127 (B)Starting from the first principles, show that surges behaves as travelling waves. Find expression for surge impedance and wave velocity.Jun-128Q 5 (A)Discuss factors affecting corona.Jun-126 (B)Find the critical disruptive voltage and corona loss for a 3 phase line which is operating at 220 KV, 50 Hz frequency. The line has conductor of 1.5 cm diameter arranged in a 3 meter delta connection. Assume air density factor of 1.05 and dielectric strength of air to be 21.1 KV/cm.Jun-126

Q 1 (A)Derive the ABCD constants for medium transmission line using Nominal representation. Also write the expressions for voltage regulation and efficiency for the same line.Nov-111 (B)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) Nov-111Q 2 (A)Explain the Equivalent Circuit model of Synchronous machine. From the first principal, derive Vt = Ef Ia (Ra+ jXs) Where Xs = Xar + Xl. Also draw the equivalent circuit diagram.Nov-112 (B)With the help of neat phasor diagram, explain the operation of synchronous generator for different field excitation. Nov-112 (B)The three phase ratings of a three winding transformer are: Primary Y Connected, 66 KV, 15 MVA, Secondary Y Connected, 13.2 KV, 10 MVA, Tertiary Connected, 2.3 KV, 5 MVA, Neglecting resistance, the leakage impedances are Zps= 7% on 15 MVA 66 KV Base, Zpt= 9% on 15 MVA 66 KV Base, Zst= 10% on 10 MVA 13.2 KV Base Find the per unit impedances of the star connected equivalent circuit for a base of 15 MVA, 66 KV in the primary circuit. Also derive the expressions you use.Nov-112Q 3 (A)What is P. U. system? Explain the advantages of P. U. System.Nov-112 (B)A 300 MVA 20 KV 3 generator has a subtransient 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 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 km Draw the reactance diagram with all the reactances marked in per unit. Select the generator rating as base in the generator circuit. Nov-113Q 3 (A)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.Nov-111 (B)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 km and y=3.17 10-6 900 mhokmNov-111Q 4 (A)Derive the expressions of positive, negative and zero sequence voltage components in terms of given set of unbalance voltage phasors Va, Vb and Vc. Also prove that the transformation used is power invariant. Nov-114 (B)One conductor of a three phase line is open. The current flowing to the 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. Nov-114Q 4 (A)Explain traveling and reflecting waves on transmission line with open end at the receiving .Nov-118 (B)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 subtransient 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 subtransient current in the fault, (b) the subtransient current in breaker A. Nov-113Q 5 (A)Enlist the methods of neutral grounding. Explain any one of the method in detail.Nov-117 (B)Explain the phenomena of arcing grounds. How does neutral grounding eliminate the arcing ground? Also enlist the advantages of neutral grounding.Nov-117Q 5 (A)Explain the phenomena of corona. Also discuss the measures taken to control corona in EHVAC transmission lines. Nov-116 (B)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.Nov-113

ch-2PSAs : Questions from Ch-2System Modeling

Quastion asked in paperspaper ofchepter no.page no.bookQ 1 (A)What is importance of receiving end power circle diagram? Explain the steps of constructing it.Jan-131 (B)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 and 0.9 respectively. The line charging admittance is 0.310-6 /km/phase. Compute the voltage regulation and transmission efficiency by applying nominal method. Jan-131Q 2 (A)A four bus sample power system is shown in fig 1.Calculate the fault current 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 pre fault current be zero. G1:11.2 KV,100 MVA, xg1=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, xg2=0.08 pu T1:11/110KV,100MVA, XT1=0.06 pu T2: 11/110KV,100MVA, XT2=0.06 puJan-133 (B)Discuss the effect of change in excitation of synchronous machine.Jan-132 (B)What is importance of one line diagram of a power system? How it is drawn?Jan-132Q 3 (A)Explain the importance of bus impedance matrix in fault calculation.Jan-133 (B)A 100 MVA, 33 KV three phase generator has a reactance of 15%. The generator is connected to the motors through transmission line and a transformer as shown in fig 2. Motors have rated inputs of 40MVA, 30 MVA, and 20 MVA at 30 KV with 20 % reactance each. Draw the P.U. diagram.Jan-133Q 3 (A)How the circuit breaker is selected for any particular location.Jan-133 (B)Explain steady state, transient and sub transient reactance of a synchronous machine.Jan-133Q 4 (A)Explain the zero sequence impedance of transformer for various connections.Jan-134 (B)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-135Q 4 (A)Explain how fault current can be calculated when L-G fault occur through a fault impedance Zf.Jan-135 (B)A 25 MVA, 13.2 KV alternator with solidly grounded neutral has a sub transient reactance of 0.25 p.u.. the negative and zero sequence reactances are 0.35 and 0.1 p.u. respectively. Find the fault current when (1) a single line to ground fault occurs at the terminals of an unloaded alternator (2) a L-L fault occurs.Jan-135Q 5 (A)Explain how corona affects the electrical design of transmission line. State the factors on which corona loss depends.Jan-136 (B)The three phase 220KV, 50 Hz line is 250 Km long consisting of 22.26mm diameter conductor spaced in a 6 mt delta configuration. The following 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 Peeks formula.Jan-136Q 5 (A)What are the various methods of neutral grounding? Explain any two.Jan-137 (B)Explain single and double frequency transient.Jan-138

Q 1 (A)Give reasons for following: 1. The analysis of unsymmetrical faults can be more easily done with the help of symmetrical components than by a direct solution of the unbalanced circuit. 2. A travelling wave suffers reflection when it reaches discontinuity. 3. The disruptive critical voltage is less than visual critical voltage.May-135,3,6 (B)Figure 1 shows the single line diagram of a simple system. The transformer ratings, generator rating, line impedance and load impedance are shown. Draw impedance diagram. Find actual value of generator current, line current, load current, load voltage and load power. Carry out the calculation in p. u. neglecting phase shift in transformer.May-133Q 2 (A)What is an equivalent and equivalent T circuit of a long transmission line? Derive expression of parameters of these circuits in terms of line parameters.May-131 (B)A 300 km 132 kV 3-phase overhead line has a total series impedance of 52+j200 /phase and a total shunt admittance of j1.5 X 10-3 siemens 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-131 (B)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-136Q 3 (A)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-134 (B)A 50 MVA, 11 kV, 3-phase alternator was subjected to different types of faults. The fault currents were: 3- fault 1870A, line to line fault 2590 A, single line to ground fault 4130 A. The alternator neutral is solidly grounded. Find pu values of the three sequences reactance of the alternator.May-135Q 3 (A)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 (i) delta-star transformer with star point grounded. (ii) delta-delta transformer. (iii) star-star transformer with star point grounded.May-134 (B)A 33 KV line has a resistance of 4 ohm and reactance of 16 ohm respectively. 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-133Q 4 (A)Derive an expression for the fault current for a single line-to ground fault asan unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. 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.May-135Q 4 (A)Derive an expression for the fault current for a double-line fault as an unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. The generator is operating 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 for line to line fault).May-135Q 5 (A)Discuss the phenomenon of wave reflection and wave refraction. Derive expression for refraction and reflection coefficients.May-138 (B)Why it is necessary to earth neutral? Explain the difference between resistance and reactance grounding.May-137Q 5 (A)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-138 (B)With help of circuit & phasor diagram explain resonant grounding method.May-137

Q 1 (A)Draw the equivalent network of uniform long line and derive its model.Jun-121 (B)Using the nominal method, find the sending end voltage and voltage regulation of a 250 km,3-phase, 50 Hz transmission line delivering 25 MVA at 0.8 powerfactor (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. Jun-121Q 2 (A)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-124 (B)Write a brief note on phase shift of symmetrical components in Y- transformer banks.Jun-124 (B)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 Jun-124Q 3 (A)Derive the double line to ground fault in a 3 phase alternator.Jun-125 (B)An unloaded star connected solidly grounded 10 MVA, 11KV generator has positive, negative and zero sequence impedances are j1.3 , j0.8 , and j0.4 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).Jun-125Q 3 (A)Write a brief note on selection of circuit breaker.Jun-123 (B)A synchronous generator and a synchronous motor each rated 25MVA, 11KV having 15% subtransient reactance are connected through transformer and a line as shown in fig.(B). The transformer s are rated 25 MVA, 11/66KV 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 powerfactor leading and a terminal voltage of 10.6 KV when a symmetrical three- phase fault occurs at the motor terminals. Find the subtransient current in the generator, motor and fault.Jun-123Q 4 (A)Discuss the advantages of per unit computations.Jun-122 (B)A generator is rated 1000 MVA, 33 KV. Its star connected winding has a reactance of 0.9 p.u. Find (1) Ohmic value of reactance of the winding if the generator is working in a circuit for which the bases are specified as 250MVA, 22KV (2) The p.u. value of reactance of generator winding on the specified base.Jun-123Q 4 (A)Explain travelling waves of a transmission line when the receiving end is shortcircuited.Jun-128 (B)Write a note on zero sequence networks in brief.Jun-124Q 5 (A)Explain need of neutral grounding using phasor diagrams. Explain any one method of neutral grounding.Jun-127 (B)Starting from the first principles, show that surges behaves as travelling waves. Find expression for surge impedance and wave velocity.Jun-128Q 5 (A)Discuss factors affecting corona.Jun-126 (B)Find the critical disruptive voltage and corona loss for a 3 phase line which is operating at 220 KV, 50 Hz frequency. The line has conductor of 1.5 cm diameter arranged in a 3 meter delta connection. Assume air density factor of 1.05 and dielectric strength of air to be 21.1 KV/cm.Jun-126

Q 1 (A)Derive the ABCD constants for medium transmission line using Nominal representation. Also write the expressions for voltage regulation and efficiency for the same line.Nov-111 (B)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) Nov-111Q 2 (A)Explain the Equivalent Circuit model of Synchronous machine. From the first principal, derive Vt = Ef Ia (Ra+ jXs) Where Xs = Xar + Xl. Also draw the equivalent circuit diagram.Nov-112 (B)With the help of neat phasor diagram, explain the operation of synchronous generator for different field excitation. Nov-112 (B)The three phase ratings of a three winding transformer are: Primary Y Connected, 66 KV, 15 MVA, Secondary Y Connected, 13.2 KV, 10 MVA, Tertiary Connected, 2.3 KV, 5 MVA, Neglecting resistance, the leakage impedances are Zps= 7% on 15 MVA 66 KV Base, Zpt= 9% on 15 MVA 66 KV Base, Zst= 10% on 10 MVA 13.2 KV Base Find the per unit impedances of the star connected equivalent circuit for a base of 15 MVA, 66 KV in the primary circuit. Also derive the expressions you use.Nov-112Q 3 (A)What is P. U. system? Explain the advantages of P. U. System.Nov-112 (B)A 300 MVA 20 KV 3 generator has a subtransient 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 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 km Draw the reactance diagram with all the reactances marked in per unit. Select the generator rating as base in the generator circuit. Nov-113Q 3 (A)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.Nov-111 (B)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 km and y=3.17 10-6 900 mhokmNov-111Q 4 (A)Derive the expressions of positive, negative and zero sequence voltage components in terms of given set of unbalance voltage phasors Va, Vb and Vc. Also prove that the transformation used is power invariant. Nov-114 (B)One conductor of a three phase line is open. The current flowing to the 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. Nov-114Q 4 (A)Explain traveling and reflecting waves on transmission line with open end at the receiving .Nov-118 (B)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 subtransient 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 subtransient current in the fault, (b) the subtransient current in breaker A. Nov-113Q 5 (A)Enlist the methods of neutral grounding. Explain any one of the method in detail.Nov-117 (B)Explain the phenomena of arcing grounds. How does neutral grounding eliminate the arcing ground? Also enlist the advantages of neutral grounding.Nov-117Q 5 (A)Explain the phenomena of corona. Also discuss the measures taken to control corona in EHVAC transmission lines. Nov-116 (B)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.Nov-113

ch-3PSAs : Questions from Ch-3Symmetrical Three-Phase Faults

Quastion asked in paperspaper ofchepter no.page no.bookQ 1 (A)What is importance of receiving end power circle diagram? Explain the steps of constructing it.Jan-131 (B)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 and 0.9 respectively. The line charging admittance is 0.310-6 /km/phase. Compute the voltage regulation and transmission efficiency by applying nominal method. Jan-131Q 2 (A)A four bus sample power system is shown in fig 1.Calculate the fault current 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 pre fault current be zero. G1:11.2 KV,100 MVA, xg1=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, xg2=0.08 pu T1:11/110KV,100MVA, XT1=0.06 pu T2: 11/110KV,100MVA, XT2=0.06 puJan-133 (B)Discuss the effect of change in excitation of synchronous machine.Jan-132 (B)What is importance of one line diagram of a power system? How it is drawn?Jan-132Q 3 (A)Explain the importance of bus impedance matrix in fault calculation.Jan-133 (B)A 100 MVA, 33 KV three phase generator has a reactance of 15%. The generator is connected to the motors through transmission line and a transformer as shown in fig 2. Motors have rated inputs of 40MVA, 30 MVA, and 20 MVA at 30 KV with 20 % reactance each. Draw the P.U. diagram.Jan-133Q 3 (A)How the circuit breaker is selected for any particular location.Jan-133 (B)Explain steady state, transient and sub transient reactance of a synchronous machine.Jan-133Q 4 (A)Explain the zero sequence impedance of transformer for various connections.Jan-134 (B)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-135Q 4 (A)Explain how fault current can be calculated when L-G fault occur through a fault impedance Zf.Jan-135 (B)A 25 MVA, 13.2 KV alternator with solidly grounded neutral has a sub transient reactance of 0.25 p.u.. the negative and zero sequence reactances are 0.35 and 0.1 p.u. respectively. Find the fault current when (1) a single line to ground fault occurs at the terminals of an unloaded alternator (2) a L-L fault occurs.Jan-135Q 5 (A)Explain how corona affects the electrical design of transmission line. State the factors on which corona loss depends.Jan-136 (B)The three phase 220KV, 50 Hz line is 250 Km long consisting of 22.26mm diameter conductor spaced in a 6 mt delta configuration. The following 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 Peeks formula.Jan-136Q 5 (A)What are the various methods of neutral grounding? Explain any two.Jan-137 (B)Explain single and double frequency transient.Jan-138

Q 1 (A)Give reasons for following: 1. The analysis of unsymmetrical faults can be more easily done with the help of symmetrical components than by a direct solution of the unbalanced circuit. 2. A travelling wave suffers reflection when it reaches discontinuity. 3. The disruptive critical voltage is less than visual critical voltage.May-135,3,6 (B)Figure 1 shows the single line diagram of a simple system. The transformer ratings, generator rating, line impedance and load impedance are shown. Draw impedance diagram. Find actual value of generator current, line current, load current, load voltage and load power. Carry out the calculation in p. u. neglecting phase shift in transformer.May-133Q 2 (A)What is an equivalent and equivalent T circuit of a long transmission line? Derive expression of parameters of these circuits in terms of line parameters.May-131 (B)A 300 km 132 kV 3-phase overhead line has a total series impedance of 52+j200 /phase and a total shunt admittance of j1.5 X 10-3 siemens 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-131 (B)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-136Q 3 (A)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-134 (B)A 50 MVA, 11 kV, 3-phase alternator was subjected to different types of faults. The fault currents were: 3- fault 1870A, line to line fault 2590 A, single line to ground fault 4130 A. The alternator neutral is solidly grounded. Find pu values of the three sequences reactance of the alternator.May-135Q 3 (A)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 (i) delta-star transformer with star point grounded. (ii) delta-delta transformer. (iii) star-star transformer with star point grounded.May-134 (B)A 33 KV line has a resistance of 4 ohm and reactance of 16 ohm respectively. 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-133Q 4 (A)Derive an expression for the fault current for a single line-to ground fault asan unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. 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.May-135Q 4 (A)Derive an expression for the fault current for a double-line fault as an unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. The generator is operating 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 for line to line fault).May-135Q 5 (A)Discuss the phenomenon of wave reflection and wave refraction. Derive expression for refraction and reflection coefficients.May-138 (B)Why it is necessary to earth neutral? Explain the difference between resistance and reactance grounding.May-137Q 5 (A)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-138 (B)With help of circuit & phasor diagram explain resonant grounding method.May-137

Q 1 (A)Draw the equivalent network of uniform long line and derive its model.Jun-121 (B)Using the nominal method, find the sending end voltage and voltage regulation of a 250 km,3-phase, 50 Hz transmission line delivering 25 MVA at 0.8 powerfactor (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. Jun-121Q 2 (A)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-124 (B)Write a brief note on phase shift of symmetrical components in Y- transformer banks.Jun-124 (B)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 Jun-124Q 3 (A)Derive the double line to ground fault in a 3 phase alternator.Jun-125 (B)An unloaded star connected solidly grounded 10 MVA, 11KV generator has positive, negative and zero sequence impedances are j1.3 , j0.8 , and j0.4 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).Jun-125Q 3 (A)Write a brief note on selection of circuit breaker.Jun-123 (B)A synchronous generator and a synchronous motor each rated 25MVA, 11KV having 15% subtransient reactance are connected through transformer and a line as shown in fig.(B). The transformer s are rated 25 MVA, 11/66KV 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 powerfactor leading and a terminal voltage of 10.6 KV when a symmetrical three- phase fault occurs at the motor terminals. Find the subtransient current in the generator, motor and fault.Jun-123Q 4 (A)Discuss the advantages of per unit computations.Jun-122 (B)A generator is rated 1000 MVA, 33 KV. Its star connected winding has a reactance of 0.9 p.u. Find (1) Ohmic value of reactance of the winding if the generator is working in a circuit for which the bases are specified as 250MVA, 22KV (2) The p.u. value of reactance of generator winding on the specified base.Jun-123Q 4 (A)Explain travelling waves of a transmission line when the receiving end is shortcircuited.Jun-128 (B)Write a note on zero sequence networks in brief.Jun-124Q 5 (A)Explain need of neutral grounding using phasor diagrams. Explain any one method of neutral grounding.Jun-127 (B)Starting from the first principles, show that surges behaves as travelling waves. Find expression for surge impedance and wave velocity.Jun-128Q 5 (A)Discuss factors affecting corona.Jun-126 (B)Find the critical disruptive voltage and corona loss for a 3 phase line which is operating at 220 KV, 50 Hz frequency. The line has conductor of 1.5 cm diameter arranged in a 3 meter delta connection. Assume air density factor of 1.05 and dielectric strength of air to be 21.1 KV/cm.Jun-126

Q 1 (A)Derive the ABCD constants for medium transmission line using Nominal representation. Also write the expressions for voltage regulation and efficiency for the same line.Nov-111 (B)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) Nov-111Q 2 (A)Explain the Equivalent Circuit model of Synchronous machine. From the first principal, derive Vt = Ef Ia (Ra+ jXs) Where Xs = Xar + Xl. Also draw the equivalent circuit diagram.Nov-112 (B)With the help of neat phasor diagram, explain the operation of synchronous generator for different field excitation. Nov-112 (B)The three phase ratings of a three winding transformer are: Primary Y Connected, 66 KV, 15 MVA, Secondary Y Connected, 13.2 KV, 10 MVA, Tertiary Connected, 2.3 KV, 5 MVA, Neglecting resistance, the leakage impedances are Zps= 7% on 15 MVA 66 KV Base, Zpt= 9% on 15 MVA 66 KV Base, Zst= 10% on 10 MVA 13.2 KV Base Find the per unit impedances of the star connected equivalent circuit for a base of 15 MVA, 66 KV in the primary circuit. Also derive the expressions you use.Nov-112Q 3 (A)What is P. U. system? Explain the advantages of P. U. System.Nov-112 (B)A 300 MVA 20 KV 3 generator has a subtransient 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 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 km Draw the reactance diagram with all the reactances marked in per unit. Select the generator rating as base in the generator circuit. Nov-113Q 3 (A)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.Nov-111 (B)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 km and y=3.17 10-6 900 mhokmNov-111Q 4 (A)Derive the expressions of positive, negative and zero sequence voltage components in terms of given set of unbalance voltage phasors Va, Vb and Vc. Also prove that the transformation used is power invariant. Nov-114 (B)One conductor of a three phase line is open. The current flowing to the 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. Nov-114Q 4 (A)Explain traveling and reflecting waves on transmission line with open end at the receiving .Nov-118 (B)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 subtransient 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 subtransient current in the fault, (b) the subtransient current in breaker A. Nov-113Q 5 (A)Enlist the methods of neutral grounding. Explain any one of the method in detail.Nov-117 (B)Explain the phenomena of arcing grounds. How does neutral grounding eliminate the arcing ground? Also enlist the advantages of neutral grounding.Nov-117Q 5 (A)Explain the phenomena of corona. Also discuss the measures taken to control corona in EHVAC transmission lines. Nov-116 (B)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.Nov-113

ch-4PSAs : Questions from Ch-4Symmetrical Components

Quastion asked in paperspaper ofchepter no.page no.bookQ 1 (A)What is importance of receiving end power circle diagram? Explain the steps of constructing it.Jan-131 (B)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 and 0.9 respectively. The line charging admittance is 0.310-6 /km/phase. Compute the voltage regulation and transmission efficiency by applying nominal method. Jan-131Q 2 (A)A four bus sample power system is shown in fig 1.Calculate the fault current 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 pre fault current be zero. G1:11.2 KV,100 MVA, xg1=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, xg2=0.08 pu T1:11/110KV,100MVA, XT1=0.06 pu T2: 11/110KV,100MVA, XT2=0.06 puJan-133 (B)Discuss the effect of change in excitation of synchronous machine.Jan-132 (B)What is importance of one line diagram of a power system? How it is drawn?Jan-132Q 3 (A)Explain the importance of bus impedance matrix in fault calculation.Jan-133 (B)A 100 MVA, 33 KV three phase generator has a reactance of 15%. The generator is connected to the motors through transmission line and a transformer as shown in fig 2. Motors have rated inputs of 40MVA, 30 MVA, and 20 MVA at 30 KV with 20 % reactance each. Draw the P.U. diagram.Jan-133Q 3 (A)How the circuit breaker is selected for any particular location.Jan-133 (B)Explain steady state, transient and sub transient reactance of a synchronous machine.Jan-133Q 4 (A)Explain the zero sequence impedance of transformer for various connections.Jan-134 (B)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-135Q 4 (A)Explain how fault current can be calculated when L-G fault occur through a fault impedance Zf.Jan-135 (B)A 25 MVA, 13.2 KV alternator with solidly grounded neutral has a sub transient reactance of 0.25 p.u.. the negative and zero sequence reactances are 0.35 and 0.1 p.u. respectively. Find the fault current when (1) a single line to ground fault occurs at the terminals of an unloaded alternator (2) a L-L fault occurs.Jan-135Q 5 (A)Explain how corona affects the electrical design of transmission line. State the factors on which corona loss depends.Jan-136 (B)The three phase 220KV, 50 Hz line is 250 Km long consisting of 22.26mm diameter conductor spaced in a 6 mt delta configuration. The following 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 Peeks formula.Jan-136Q 5 (A)What are the various methods of neutral grounding? Explain any two.Jan-137 (B)Explain single and double frequency transient.Jan-138

Q 1 (A)Give reasons for following: 1. The analysis of unsymmetrical faults can be more easily done with the help of symmetrical components than by a direct solution of the unbalanced circuit. 2. A travelling wave suffers reflection when it reaches discontinuity. 3. The disruptive critical voltage is less than visual critical voltage.May-135,3,6 (B)Figure 1 shows the single line diagram of a simple system. The transformer ratings, generator rating, line impedance and load impedance are shown. Draw impedance diagram. Find actual value of generator current, line current, load current, load voltage and load power. Carry out the calculation in p. u. neglecting phase shift in transformer.May-133Q 2 (A)What is an equivalent and equivalent T circuit of a long transmission line? Derive expression of parameters of these circuits in terms of line parameters.May-131 (B)A 300 km 132 kV 3-phase overhead line has a total series impedance of 52+j200 /phase and a total shunt admittance of j1.5 X 10-3 siemens 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-131 (B)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-136Q 3 (A)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-134 (B)A 50 MVA, 11 kV, 3-phase alternator was subjected to different types of faults. The fault currents were: 3- fault 1870A, line to line fault 2590 A, single line to ground fault 4130 A. The alternator neutral is solidly grounded. Find pu values of the three sequences reactance of the alternator.May-135Q 3 (A)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 (i) delta-star transformer with star point grounded. (ii) delta-delta transformer. (iii) star-star transformer with star point grounded.May-134 (B)A 33 KV line has a resistance of 4 ohm and reactance of 16 ohm respectively. 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-133Q 4 (A)Derive an expression for the fault current for a single line-to ground fault asan unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. 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.May-135Q 4 (A)Derive an expression for the fault current for a double-line fault as an unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. The generator is operating 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 for line to line fault).May-135Q 5 (A)Discuss the phenomenon of wave reflection and wave refraction. Derive expression for refraction and reflection coefficients.May-138 (B)Why it is necessary to earth neutral? Explain the difference between resistance and reactance grounding.May-137Q 5 (A)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-138 (B)With help of circuit & phasor diagram explain resonant grounding method.May-137

Q 1 (A)Draw the equivalent network of uniform long line and derive its model.Jun-121 (B)Using the nominal method, find the sending end voltage and voltage regulation of a 250 km,3-phase, 50 Hz transmission line delivering 25 MVA at 0.8 powerfactor (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. Jun-121Q 2 (A)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-124 (B)Write a brief note on phase shift of symmetrical components in Y- transformer banks.Jun-124 (B)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 Jun-124Q 3 (A)Derive the double line to ground fault in a 3 phase alternator.Jun-125 (B)An unloaded star connected solidly grounded 10 MVA, 11KV generator has positive, negative and zero sequence impedances are j1.3 , j0.8 , and j0.4 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).Jun-125Q 3 (A)Write a brief note on selection of circuit breaker.Jun-123 (B)A synchronous generator and a synchronous motor each rated 25MVA, 11KV having 15% subtransient reactance are connected through transformer and a line as shown in fig.(B). The transformer s are rated 25 MVA, 11/66KV 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 powerfactor leading and a terminal voltage of 10.6 KV when a symmetrical three- phase fault occurs at the motor terminals. Find the subtransient current in the generator, motor and fault.Jun-123Q 4 (A)Discuss the advantages of per unit computations.Jun-122 (B)A generator is rated 1000 MVA, 33 KV. Its star connected winding has a reactance of 0.9 p.u. Find (1) Ohmic value of reactance of the winding if the generator is working in a circuit for which the bases are specified as 250MVA, 22KV (2) The p.u. value of reactance of generator winding on the specified base.Jun-123Q 4 (A)Explain travelling waves of a transmission line when the receiving end is shortcircuited.Jun-128 (B)Write a note on zero sequence networks in brief.Jun-124Q 5 (A)Explain need of neutral grounding using phasor diagrams. Explain any one method of neutral grounding.Jun-127 (B)Starting from the first principles, show that surges behaves as travelling waves. Find expression for surge impedance and wave velocity.Jun-128Q 5 (A)Discuss factors affecting corona.Jun-126 (B)Find the critical disruptive voltage and corona loss for a 3 phase line which is operating at 220 KV, 50 Hz frequency. The line has conductor of 1.5 cm diameter arranged in a 3 meter delta connection. Assume air density factor of 1.05 and dielectric strength of air to be 21.1 KV/cm.Jun-126

Q 1 (A)Derive the ABCD constants for medium transmission line using Nominal representation. Also write the expressions for voltage regulation and efficiency for the same line.Nov-111 (B)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) Nov-111Q 2 (A)Explain the Equivalent Circuit model of Synchronous machine. From the first principal, derive Vt = Ef Ia (Ra+ jXs) Where Xs = Xar + Xl. Also draw the equivalent circuit diagram.Nov-112 (B)With the help of neat phasor diagram, explain the operation of synchronous generator for different field excitation. Nov-112 (B)The three phase ratings of a three winding transformer are: Primary Y Connected, 66 KV, 15 MVA, Secondary Y Connected, 13.2 KV, 10 MVA, Tertiary Connected, 2.3 KV, 5 MVA, Neglecting resistance, the leakage impedances are Zps= 7% on 15 MVA 66 KV Base, Zpt= 9% on 15 MVA 66 KV Base, Zst= 10% on 10 MVA 13.2 KV Base Find the per unit impedances of the star connected equivalent circuit for a base of 15 MVA, 66 KV in the primary circuit. Also derive the expressions you use.Nov-112Q 3 (A)What is P. U. system? Explain the advantages of P. U. System.Nov-112 (B)A 300 MVA 20 KV 3 generator has a subtransient 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 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 km Draw the reactance diagram with all the reactances marked in per unit. Select the generator rating as base in the generator circuit. Nov-113Q 3 (A)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.Nov-111 (B)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 km and y=3.17 10-6 900 mhokmNov-111Q 4 (A)Derive the expressions of positive, negative and zero sequence voltage components in terms of given set of unbalance voltage phasors Va, Vb and Vc. Also prove that the transformation used is power invariant. Nov-114 (B)One conductor of a three phase line is open. The current flowing to the 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. Nov-114Q 4 (A)Explain traveling and reflecting waves on transmission line with open end at the receiving .Nov-118 (B)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 subtransient 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 subtransient current in the fault, (b) the subtransient current in breaker A. Nov-113Q 5 (A)Enlist the methods of neutral grounding. Explain any one of the method in detail.Nov-117 (B)Explain the phenomena of arcing grounds. How does neutral grounding eliminate the arcing ground? Also enlist the advantages of neutral grounding.Nov-117Q 5 (A)Explain the phenomena of corona. Also discuss the measures taken to control corona in EHVAC transmission lines. Nov-116 (B)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.Nov-113

ch-5PSAs : Questions from Ch-5Unsymmetrical Faults

Quastion asked in paperspaper ofchepter no.page no.bookQ 1 (A)What is importance of receiving end power circle diagram? Explain the steps of constructing it.Jan-131 (B)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 and 0.9 respectively. The line charging admittance is 0.310-6 /km/phase. Compute the voltage regulation and transmission efficiency by applying nominal method. Jan-131Q 2 (A)A four bus sample power system is shown in fig 1.Calculate the fault current 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 pre fault current be zero. G1:11.2 KV,100 MVA, xg1=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, xg2=0.08 pu T1:11/110KV,100MVA, XT1=0.06 pu T2: 11/110KV,100MVA, XT2=0.06 puJan-133 (B)Discuss the effect of change in excitation of synchronous machine.Jan-132 (B)What is importance of one line diagram of a power system? How it is drawn?Jan-132Q 3 (A)Explain the importance of bus impedance matrix in fault calculation.Jan-133 (B)A 100 MVA, 33 KV three phase generator has a reactance of 15%. The generator is connected to the motors through transmission line and a transformer as shown in fig 2. Motors have rated inputs of 40MVA, 30 MVA, and 20 MVA at 30 KV with 20 % reactance each. Draw the P.U. diagram.Jan-133Q 3 (A)How the circuit breaker is selected for any particular location.Jan-133 (B)Explain steady state, transient and sub transient reactance of a synchronous machine.Jan-133Q 4 (A)Explain the zero sequence impedance of transformer for various connections.Jan-134 (B)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-135Q 4 (A)Explain how fault current can be calculated when L-G fault occur through a fault impedance Zf.Jan-135 (B)A 25 MVA, 13.2 KV alternator with solidly grounded neutral has a sub transient reactance of 0.25 p.u.. the negative and zero sequence reactances are 0.35 and 0.1 p.u. respectively. Find the fault current when (1) a single line to ground fault occurs at the terminals of an unloaded alternator (2) a L-L fault occurs.Jan-135Q 5 (A)Explain how corona affects the electrical design of transmission line. State the factors on which corona loss depends.Jan-136 (B)The three phase 220KV, 50 Hz line is 250 Km long consisting of 22.26mm diameter conductor spaced in a 6 mt delta configuration. The following 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 Peeks formula.Jan-136Q 5 (A)What are the various methods of neutral grounding? Explain any two.Jan-137 (B)Explain single and double frequency transient.Jan-138

Q 1 (A)Give reasons for following: 1. The analysis of unsymmetrical faults can be more easily done with the help of symmetrical components than by a direct solution of the unbalanced circuit. 2. A travelling wave suffers reflection when it reaches discontinuity. 3. The disruptive critical voltage is less than visual critical voltage.May-135,3,6 (B)Figure 1 shows the single line diagram of a simple system. The transformer ratings, generator rating, line impedance and load impedance are shown. Draw impedance diagram. Find actual value of generator current, line current, load current, load voltage and load power. Carry out the calculation in p. u. neglecting phase shift in transformer.May-133Q 2 (A)What is an equivalent and equivalent T circuit of a long transmission line? Derive expression of parameters of these circuits in terms of line parameters.May-131 (B)A 300 km 132 kV 3-phase overhead line has a total series impedance of 52+j200 /phase and a total shunt admittance of j1.5 X 10-3 siemens 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-131 (B)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-136Q 3 (A)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-134 (B)A 50 MVA, 11 kV, 3-phase alternator was subjected to different types of faults. The fault currents were: 3- fault 1870A, line to line fault 2590 A, single line to ground fault 4130 A. The alternator neutral is solidly grounded. Find pu values of the three sequences reactance of the alternator.May-135Q 3 (A)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 (i) delta-star transformer with star point grounded. (ii) delta-delta transformer. (iii) star-star transformer with star point grounded.May-134 (B)A 33 KV line has a resistance of 4 ohm and reactance of 16 ohm respectively. 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-133Q 4 (A)Derive an expression for the fault current for a single line-to ground fault asan unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. 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.May-135Q 4 (A)Derive an expression for the fault current for a double-line fault as an unloaded generator.May-135 (B)A generator rated 100 MVA, 20kV has X1 = X2 = 20% and X0 = 5%. Its neutral is grounded through a reactor of 0.32 ohms. The generator is operating 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 for line to line fault).May-135Q 5 (A)Discuss the phenomenon of wave reflection and wave refraction. Derive expression for refraction and reflection coefficients.May-138 (B)Why it is necessary to earth neutral? Explain the difference between resistance and reactance grounding.May-137Q 5 (A)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-138 (B)With help of circuit & phasor diagram explain resonant grounding method.May-137

Q 1 (A)Draw the equivalent network of uniform long line and derive its model.Jun-121 (B)Using the nominal method, find the sending end voltage and voltage regulation of a 250 km,3-phase, 50 Hz transmission line delivering 25 MVA at 0.8 powerfactor (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. Jun-121Q 2 (A)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-124 (B)Write a brief note on phase shift of symmetrical components in Y- transformer banks.Jun-124 (B)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 Jun-124Q 3 (A)Derive the double line to ground fault in a 3 phase alternator.Jun-125 (B)An unloaded star connected solidly grounded 10 MVA, 11KV generator has positive, negative and zero sequence impedances are j1.3 , j0.8 , and j0.4 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).Jun-125Q 3 (A)Write a brief note on selection of circuit breaker.Jun-123 (B)A synchronous generator and a synchronous motor each rated 25MVA, 11KV having 15% subtransient reactance are connected through transformer and a line as shown in fig.(B). The transformer s are rated 25 MVA, 11/66KV 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 powerfactor leading and a terminal voltage of 10.6 KV when a symmetrical three- phase fault occurs at the motor terminals. Find the subtransient current in the generator, motor and fault.Jun-123Q 4 (A)Discuss the advantages of per unit computations.Jun-122 (B)A generator is rated 1000 MVA, 33 KV. Its star connected winding has a reactance of 0.9 p.u. Find (1) Ohmic value of reactance of the winding if the generator is working in a circuit for which the bases are specified as 250MVA, 22KV (2) The p.u. value of reactance of generator winding on the specified base.Jun-123Q 4 (A)Explain travelling waves of a transmission line when the receiving end is shortcircuited.Jun-128 (B)Write a note on zero sequence networks in brief.Jun-124Q 5 (A)Explain need of neutral grounding using phasor diagrams. Explain any one method of neutral grounding.Jun-127 (B)Starting from the first principles, show that surges behaves as travelling waves. Find expression for surge impedance and wave velocity.Jun-128Q 5 (A)Discuss factors affecting corona.Jun-126 (B)Find the critical disruptive voltage and corona loss for a 3 phase line which is operating at 220 KV, 50 Hz frequency. The line has conductor of 1.5 cm diameter arranged in a 3 meter delta connection. Assume air density factor of 1.05 and dielectric strength of air to be 21.1 KV/cm.Jun-126

Q 1 (A)Derive the ABCD constants for medium transmission line using Nominal representation. Also write the expressions for voltage regulation and efficiency for the same line.Nov-111 (B)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) Nov-111Q 2 (A)Explain the Equivalent Circuit model of Synchronous machine. From the first principal, derive Vt = Ef Ia (Ra+ jXs) Where Xs = Xar + Xl. Also draw the equivalent circuit diagram.Nov-112 (B)With the help of neat phasor diagram, explain the operation of synchronous generator for different field excitation. Nov-112 (B)The three phase ratings of a three winding transformer are: Primary Y Connected, 66 KV, 15 MVA, Secondary Y Connected, 13.2 KV, 10 MVA, Tertiary Connected, 2.3 KV, 5 MVA, Neglecting resistance, the leakage impedances are Zps= 7% on 15 MVA 66 KV Base, Zpt= 9% on 15 MVA 66 KV Base, Zst= 10% on 10 MVA 13.2 KV Bas