12. Question Bank.docx

Electrical Power System-II (2160908)

QUESTION BANK SEM-VI Electrical Power System-II (2160908)

PREPARED BY: EEDEPARTMENT- 2016-2017 VADODARA INSTITUTE OF ENGINEERING, KOTAMBI-391510

Electrical Power System-II (2160908)

1 Performance of Transmission Line 1 A single phase overhead transmission line delivers 1100Kw at 0.8 p.f. lagging.The total resistance and inductive reactance of the line are 10 ohms and 15 ohm respectively. Determine i) Sending end voltage ii) sending end power factor and iii) transmission efficiency. (Vs = 33,709 V, P.F = 0.7956 lagging , efficiency = 98.44 %) 2 An overhead 3 phase transmission line delivers 5000 kW at 22 kVat 0.8 p.f. lagging. The resistance and reactance of each conductor is 4 ohms and 6 ohms respectively. Determine: i) Sending end voltage ii) percentage regulation iii) transmission efficiency. (Vs = 13820.8, Regulation = 8.825 % , Efficiency = 93.94%) 3 A three phase line delivers 3600Kw at 0.8 lagging to a load. If the sending end voltage is 33 kv , determine i) the receiving end voltage ii) line current iii) transmission efficiency. The resistance and reactance of each conductor are 5.31 ohm and 5.54 ohm respectively. (VR= 31.93 kv, IR = 81.36 A, Efficiency = 97.15%) 4 A short three phase transmission line with an impedance of (6+j8) ohm/phase has sending and receiving end voltages of 120 kv and 110 kv respectively for some receiving end load at a p.f of 0.9 lagging. Determine i) power output and ii) sending end power factor. (P= 1,11,490 kw,p.f = 0.88 lag) 5 A single phase overhead transmission line delivers 4000 KW at 11 kV at 0.8 p.f. lagging. If resistance and reactance per conductor are 0.15 and 0.02 ohm respectively, calculate: i) Percentage regulation ii) Line losses iii) Sending end power factor ( i. 19.83% ii. 620 kW iii. 0.77 lag) 6 A single phase 11 kV line with a length of 15 km is to transmit 500 KVa. The inductive reactance of the line is 0.5 ohm/km and resistance is 0.3 ohm/km. Calculate the efficiency and regulation of the line for 0.8 lagging power factor. (97.74%, 3.34%) 7 A medium length single phase transmission line 100 km long has following constants: Resistance/km/phase =0.185ohm Capacitive reactance/km/phase =0.377ohm Receiving end line voltage =132kV

Electrical Power System-II (2160908) Assuming that the total capacitance of the line is localized at the receiving end alone, determine: i) Sending end current ii) Line value of sending end voltage iii) Regulation iv) Sending end power factor (i. 377.3 A, ii.155.7kV, iii.17.9%, iv.0.774 lag) 8 A 3 phase , 50Hz overhead transmission line has the following constants: Resistance/ phase =9.6 ohm Capacitance/phase =0.765 microfarad Inductance/phase = 0.097 Mh If the line is supplying a balanced load of 24,000 KVa 0.8 p.f. lagging at 66 kV , calculate: i) Sending end current ii) Line value of sending end voltage iii) Sending end power factor (i.204 A , ii. 75kV , iii.0.814 lag iv.13.63 % , v.93.7%) 9 10

i) ii)

For the above example calculate Percentage regulation Transmission efficiency

11 A 3 phase overhead transmission line has a total series impedance per phase of 200 80° ohms and a total shunt admittance of 0.0013 90°siemen per phase. The line delivers a load of 80 MW at 0.8 p.f. lagging and 220 kV between the lines. Determine the sending end line voltage and current by rigorous method. (263.574 kV, 187.5 A) 12 A 3 phase transmission line , 160 km long has the following constants: Resistance/km/phase =0.2ohm Reactance/km/phase =0.3127ohm Shunt admittance / phase /km = 1.875 × 10-6 S. Determine the sending end voltage and current by rigorous method when the line is delivering a load of 25 MVA at 0.8 .f. lagging. The receiving end voltage is kept constant at 110 KV. (116.67kV, 131.1 A) 13 A 3 phase, 50 Hz overhead transmission line 100 km long has the following constants: Resistance/km/phase = 0.1 ohm Inductive reactance/km/phase =0.2 ohm Capacitive susceptance/km/phase = 0.04 × 10-4siemen Determine i) the sending end current ii) sending end voltage iii) sending end power factor and iv). Use nominal T method. ( i) 100 A ii) 69.533 Kv iii) 0.853 lag)

Electrical Power System-II (2160908) 14 For the above example find transmission efficiency when supplying a balanced load of 10,000 Kw at 66 kv, 0.8 lagging. 97.34% 15 A transmission line of 210km length has certain values of parameters A, B, C, D. If the length is made 100km, thus parameter is __________. 16 A 60Hz 320km lossless line has sending end voltage 1.0pu. The reciving end voltage on no load is _____________. 17 The sending end voltage of a feeder with reactance 0.2pu is 1.2pu. If the reactive power supplied at the receiving end of the feeder is 0.3pu, the approximate voltage drop in the feeder is _________. 18 A 100km transmission line is designed for a nominal voltage of 132kV and consists of one conductor per phase. The line reactance is 0.726Ω/km. The static transmission capacity of the line, in MW would be __________. 19 The per unit impedance of a circuit element is 0.15. If the base kV and base MVA are halved, then the new value of per unit impedance of the circuit element will be _______________. 20 A short transmission line having its line impedance angle as θ, delivering a given power at the receiving end at a lagging pf angle of Φ. Which of the following conditions gives maximum regulation: a. Φ = θ/2

b. Φ – θ = π/2

c. Φ = θ

d. Φ + θ = π/2

21 In the above question which of the following gives zero regulation? a. Φ – θ = π/2

b. Φ = θ

c. Φ + θ = π/2

d. Φ = θ/2

22 A single phase transmission line of impedance j0.8Ω supplies a resistive load of 500A at 300V. The sending end power factor is _________ 23 When bundle conductors are used in place of single conductors, the effective inductance and capacitance will respectively a. Increase and decrease

b. Decrease and remain unaffected

c. Decrease and increase

d. Remain unaffected and increase

24 The inductance of a three phase transmission line is 1.2mH/phase/km. If the spacing of

Electrical Power System-II (2160908) conductors and the radius of the conductor are doubled, then the inductance of the line will be __________ 25 The self inductance of a long cylindrical conductor due to its internal flux linkages is k H/m. If the diameter of the conductor is doubled, then the self inductance of the conductor due to its internal flux linkages would be a. 0.5k H/m

b. 1K H/m

c. 1.414k H/m

d. 4k H/m

26 Compare ABCD Parameters for short, medium and long transmission line. 27 Compare Voltage regulation for short, medium and long transmission line.(Write detailed equations). 28 Derive power transfer equation for short transmission line. 29 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Draw and explain vector diagram for short transmission line. Draw and explain vector diagrams for amedium transmission line. Draw and explain vector diagrams for long transmission line. Derive ABCD parameters for long transmission line using rigorous solution method. Derive equivalent circuit of long transmission line for PI model. Derive equivalent circuit of long transmission line for T model. List necessary assumptions to be made while finding voltage regulation and efficiency of short transmission line. Derive equation of voltage regulation and efficiency for short transmission line. Derive equation of voltage regulation and efficiency for medium transmission line. Derive equation of voltage regulation and efficiency for long transmission line. Explain different methods of evaluation of A, B, C, D constant for long transmission line. Derive equation of sending end power and receiving end power through a transmission line. Derive equation of maximum receiving end active power and reactive power through a transmission line. List the important conclusion that can be derived from equations of power transfer through a transmission line. Draw and explain receiving end power circle diagram. Explain the relationship between voltage and reactive power with use of necessary equations. What is reactive power compensation? Explain in brief. What is the need of voltage control in power system? Explain in brief. List different methods of voltage control. Explain reactive power injection method in detail. Write brief explanation about static VAR generator and its application as voltage controller.

Electrical Power System-II (2160908) 48 49 50 2 51

List important observations derived from equation of static VAR generators. Write a note on rotating VAR generator and its application. Explain voltage control with use of transformer. Symmetrical Three Phase Faults A 25 MVA, 11KVgenerator with Xd’’ = 20% is connected through a transformers and line to a bus that supplies three identical motor as shown in fig. Each motor has Xd’’ = 25% and Xd’ = 30% on a base of 5 MVA, 6.6 KV. Three phase rating of step up transformer is 25 MVA, 11/66KV with leakage reactance of 10 % and that of step down transformer is 25 MVA, 66/6.6 kV with leakage reactance of 10% . The bus voltage at the motors is 6.6 kV when three phase fault occurs at the point F. For the specified fault calculate, Line reactance is 15%. a) The subtransient current in the fault b) The subtransient current in breaker B c) The momentary current in breaker B. (Isc = 9229 A, Isc(B) = 7479.5 A, Im(B) = 11967 A)

52 For the system in fig. the ratings of the various components are: Generator: 25 MVA, 12.4 kV, 10% subtransient reactance Motor: 20 MVA, 3.8 kV, 15% subtransient reactance Transformer T1: 25 MVA, 11/33 kV, 8% reactance Transformer T2: 20 MVA, 33/3.3 kV, 10% reactance Line: 20 ohms reactance

Gen

T1

T2

Motor

(8.87 kA, 4.93kA) [Hint: Assume a suitable voltage base for the generator. The voltage base for transformers, line and motor would then be given by the transformation ratios.] 53 A synchronous generator and synchronous motor each rated 25 MVA, 11 kV having 15% subtransient reactance are connected through a transformer and a line as shown in fig. The transformers are rated 25 MVA, 11/66 kV and 66/11 kV with leakage reactances of 10% each. The line has reactance of 10% on a base of 25 MVA, 66 kV. The motor is drawing 15 MW at 0.8 power factor leading and a terminal voltage of 10.6

Electrical Power System-II (2160908) kV when a symmetrical three phase fault occurs at the motor terminals. Find the subtransient current in the generator, motor and fault. (i) 9816.4 - j2197.4 A ii) (-816.2 – j9041.8) A iii) (-j11239) A) Line Gen

motor

54 A three-phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3 s. What is symmetrical breaking Current? 55 For the power system shown in the figure below, the specifications of thecomponents are the following :

G1: 25 kV, 100 MVA, X =9% G2: 25 kV, 100 MVA, X =9% T1: 25 kV/220 kV, 90 MVA, X =12% T2: 220 kV/25 kV, 90 MVA, X =12%Line 1: 200 kV, X= 150 ohms Choose 25 kV as the base voltage at the generator G1, and 200 MVA as the MVA base. Draw impedance diagram. 56 Two synchronous generators are connected in parallel at the low voltage side of a threephase -Y transformer as shown in Fig. 3.2. Machine 1 is rated 50 MVA, 13.8 kV. Machine 2 is rated 25 MVA, 13.8 kV. Each generator has subtransient reactance, transient reactance and direct axis synchronous reactance of 25%, 40% and 100% respectively. The transformer is rated 75 MVA, 13.8 /69Y with a reactance of 10%. Before the fault occurs, the voltage on high voltage side of the transformer is 66 kV. The transformer is unloaded and there is no circulating current between the generators. Find the current supplied by the generators. Select a base of 75 MVA and 69 kV in the high tension circuit. 57 For the above network a three-phase short circuit occurs at P. Determine the subtransient, transient and steady state short circuit current in each generator. 58 For the above network a three-phase short circuit occurs at Q. Determine the subtransient, transient and steady state short circuit current in each generator 59

Electrical Power System-II (2160908) Given that: Vs1=Vs2= 1 +j0 p.u; The positive sequence impedance are Zs1= Zs2=0.001+ j0.01 p.u and ZL=0.006+ j0.06 p.u 3-phase Base MVA = 100 voltage base = 400 kV(Line to Line) Nominal system frequency= 50 Hz. The reference voltage for phase ‘a’ is defined as V (t) =Vmcos(ωt). A symmetrical three phase fault occurs at centre of the line, i.e. point ‘F’ at time ‘t0’. The positive sequence impedance from source S1 to point ‘F’ equals 0.004 +j0.04 p.u. The wave form corresponding to phase ‘a’ fault current from bus X reveals that decaying d.c. offset current is negative and in magnitude at its maximum initial value, Assume that the negative sequence impedances are equal to positive sequence impedance and the zero sequence impedances are three times positive sequence impedances. The instant (t0) of the fault will be________. 60 Calculate rms value of the component of fault current (If ) for above data. 61 Instead of the three phase fault, if a single line to ground fault occurs on phase ‘a’ at point ‘F’ with zero fault impedance, then find the rms of the ac component of fault current (Ix) for phase ‘a’ for above data. 62 A generator is connected through a 20 MVA, 13.8/138 kV step downtransformer, to a transmission line. At the receiving end of the line a load is supplied through a step down transformer of 10 MVA, 138/69 kV rating. A 0.72 pu. load, evaluated on load side transformer ratings as base values , is supplied from the above system. For system base values of 10 MVA and 69 kV in load circuit, what will be the value of the load (in per unit) in generator ? 63 The bus admittance matrix of a three-bus three-line system is

76 77 78 79 80 81 82

If each transmission line between the two buses is represented by an equivalent πnetwork, the magnitude of the shunt susceptance of the line connecting bus 1 and 2 is __________. Give the formula to calculate base current, Ib and base impedance of a three-phase system. Give the equation for load impedance and load admittance per phase of a balanced star connected load. Give the equation for load impedance and load admittance per phase of a balanced delta connected load. What is the advantage of per unit method over percent method? Define base impedance and base kilovoltamperes. Define per unit value of any electrical quantity. What are the quantities whose base values are required to represent the power system by reactance diagram?

Electrical Power System-II (2160908) 83 What is the need for base values? 84 Write the equation for converting the per unit impedance expressed in one base to another 85 List the advantages of per unit computations 86 What is meant by short circuit fault? 87 Give the equation for base current and base impedance of a balanced three phase circuit. 88 Why the line value of voltage directly used for per unit calculation in three phase systems? 89 Why the three phase kVA directly used for per unit calculation in three phase systems? 90 Write a note on Selection of circuit breaker. 91 Derive equation of short circuit current through transmission line during transient condition 92 Explain type-2 modification of Z bus building algorithm. 93 Draw and explain wave form of short circuit current of synchronous machine under transient condition. 94 “Modern circuit breakers are design to interrupt the current in the first few cycle.” Justify the statement. 95 Explain Type-3 modification of Z–bus algorithm. 96 Explain Type-4 modification of Z–bus algorithm. 97 Derive equation for sub transient, transient and steady state short circuit current for a synchronous machine (loaded) under fault condition. 98 Explain transient in R-L Circuit with waveform. (Doubling Effect). 99 Explain the terms making current and breaking current in context of circuit breaker. 100 What is maximum momentary current?? Explain its significance in circuit breaker sizing. 3 Symmetrical Components 101 Draw positive and negative sequence network for the network shown in fig.

102 The currents in three phase unbalanced system are Ia= (12 + j6), Ib = (12 – j12), 103 104 105 106 107

Ic=(-15 + j10) A. The phase sequence is abc. Calculate negative sequence components of current. The currents in three phase unbalanced system are Ia= (12 + j6), Ib = (12 – j12), Ic=(-15 + j10) A. The phase sequence is abc. Calculate zero sequence components of current. The currents in three phase unbalanced system are Ia= (12 + j6), Ib = (12 – j12), Ic=(-15 + j10) A. The phase sequence is abc. Calculate positive sequence components of current. The currents in three phase unbalanced system are Ia= (10 + j5), Ib = (6 – j6), Ic=(-15 + j10) A. The phase sequence is abc. Calculate positive sequence components of current. The currents in three phase unbalanced system are Ia=10 + j5), Ib = (6 – j6),), Ic=(-15 + j10) A. The phase sequence is abc. Calculate negative sequence components of current. The currents in three phase unbalanced system are Ia= (10 + j5), Ib = (6 – j6), Ic=(-15 + j10) A. The phase sequence is abc. Calculate zero sequence components of

Electrical Power System-II (2160908) current.

108 The voltage in three phase unbalanced system are Ia= (12 + j6), Ib = (12 – j12), 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 5 201

Ic=(-15 + j10) A. The phase sequence is abc. Calculate positive sequence components of current. The voltage in three phase unbalanced system are Ia= (12 + j6), Ib = (12 – j12), Ic=(-15 + j10) A. The phase sequence is abc. Calculate negative sequence components of current. The voltage in three phase unbalanced system are Ia= (12 + j6), Ib = (12 – j12), Ic=(-15 + j10) A. The phase sequence is abc. Calculate zero sequence components of current. Derive expression of power in terms of symmetrical components. Draw positive network for synchronous machine. Mention necessary equations. Derive expression for positive, negative and zero sequence voltage components in terms of given set of unbalance voltage phasorsVa, Vb, Vc.. Draw negative network for synchronous machine. Mention necessary equations. Draw zero network for synchronous machine. Mention necessary equations.

Draw sequence network for transmission line. Draw sequence network for star delta transformer with neutral grounded. Draw sequence network for star delta transformer with neutral ungrounded. Draw sequence network for delta star transformer with neutral grounded. Draw sequence network for delta star transformer with neutral ungrounded. Draw sequence network for star star transformer with neutral grounded. Draw sequence network for delta delta transformer . Write a note on phase shift in star-delta transformers

Transients in power system

Find the voltage, Vc(t), over the capacitor for all time t>0 (3e^(-t/3ms)) 202 A 12-V power supply is connected to a 1K ohm resistor and a 3mF capacitor which are in series. The power supply has an internal source resistance of approximately 50 ohms. (a) Draw a diagram to model this circuit (b) How long will it take the circuit to reach steady-state from the time the power supply is switched on? (c) Sketch the current through the 1K ohm resistor as a function of time.

203 Given a course voltage of 10V, a source resistance of 10 ohms, a 10mH inductor, and a 5nF capacitor, choose a load resistance and draw a circuit that will have an underdamped (decaying sine wave) second order transient response.

Electrical Power System-II (2160908) 204 The voltage source Vs in the circuit shown below is nominally 5V. A power surge at time t=0 causes it to instantaneously jump to 10V, and then at time t=5ms, it instantaneously drops back to 5V. Express the current flowing down through the 30 ohm resistor (as a function of time). a) What is the 30 ohm resistor current at t=0+? b) What would the final 30 ohm resistor current be if Vs stayed at 10V? c) What is the 30 ohm resistor current at t=5ms+? d) What is the final 30 ohm resistor current? e ) Write the full expression(s) for the 30 ohm resistor current as a function of time.

205

In the circuit shown above, the switch is controlled by the voltage Vx: Vx> 2V, the switch opens Vx< 0.1V, the switch closes A sketch of the voltage Vx over time is shown below (the scale of each axis is not shown). Give a mathematical expression to describe Vx during the first period. You will need to describe it in two different portions of time: as Vx rises and as Vx falls, so be sure to note the time range during which your formula is valid.

Electrical Power System-II (2160908)

206 In lab you try to charge up a large capacitor (50 mF) using the circuit shown below. However, when you turn on the supply, the 10 ohm resistor makes a loud pop, turns black, and smoke rises! The other students in the lab give you a dirty look as a bad smell permeates the room.   

What went wrong? Quantify. What resistor value should you have used? How long will it take the capacitor to charge up using the new resistor?

207 You and your lab partner wire the circuit shown below on a protoboard. However, the voltage source is poorly connected to the board and when your partner jiggles the cable, it becomes disconnected momentarily from the circuit at time 0 and then reconnected after 100ms. a) Use transient analysis to describe the current i(t) flowing right through the 8 Kohm resistor by providing the mathematical formula(s) for t>0 (split into multiple intervals if needed, but clearly label the time range of each interval). b) Sketch a graph of i(t) for t>0. c) What is the current at time 50ms and at time 150ms?

Electrical Power System-II (2160908)

208 In the circuit below, resistor R3 is suddenly removed, leaving a gap (an open circuit). Sketch the current through R2 from this moment on.   

Label the graph scales to show the quantified maximum and quantified minimum current that flows. At what time is the current in R2 slightly more than half way between the maximum and minimum? At what time is the current in R2 at exactly 20.0 mA?

209 The circuit shown below starts out without the 4 Kohm resistor connected. At time t=0, the 4 Kohm resistor is connected in parallel to the 1 nF capacitor. After 10us, the 4 Kohm resistor is removed. Compute the voltage across the capacitor for all time. Give your answer as one or more formulas (clearly indicating the time range for each formula) and a sketch of VC versus time.

210 The voltage supply in the circuit shown below is switched on at time 0. Compute the voltage over the 3K ohm resistor for all time.

Electrical Power System-II (2160908) 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253

Define response. Define steady state response. Define transient response. Define natural response. Define forced response. Why transient occurs in electric circuits? What is transient? Define time constant of RL circuit. Define time constant of RC circuit. Voltage across capacitor cannot change instantaneously. Justify. Current through an inductor cannot change instantaneously. Justify. What is the initial condition of the elements capacitor and inductor that have no initial energy storage? What is the final condition of the elements inductor and capacitor? Write the conditions for response of an RLC series network? What is the time constant of RL circuit with R=10Ω and L=20mH. What is damping ratio? What is critical damping? What is critical resistance? Write the expression for critical resistance and damping ratio of RLC series circuit. What is natural and damped frequency? What is meant by switching transients? List the causes of temporary over voltages. Distinguish the terms reflection and refraction of travelling waves. Explain the mechanism of lighting strokes. Derive the necessary expressions to calculate the overvoltages due to lighting strokes. Explain the various types of power system transients. Discuss the effects of transients on power system. Derive the reflection and refraction coefficients of a travelling wave. Discuss the attenuation and distortion with necessary equations. State the origin of switching surges. What are the specification of travelling waves. Discuss the behavior of travelling waves on transmission lines. Derive the necessary equation. Explain overvoltages due to arcing grounds. Explain transients due to capacitance switching. Explain with necessary diagram physical significance of travelling waves. Derive necessary equation for attenuation of travelling waves. Draw and explain transient characteristics of shunt capacitor switching. Write a note on impact of varying system parameters on transient magnification. State methods to control overvoltages due to transients. Derive reflection coefficient of travelling waves. Corona What is Corona? Explain the advantages and disadvantages of Corona. Explain factors effecting Corona.

Electrical Power System-II (2160908) 254 255 256 257

Explain methods to reduce corona Explain the festures of corona. What is critical voltage?

Which harmonics are generated during the corona, which leads to the increase in corona losses? 258 Which climate does the chances of occurrence of corona is maximum? 259 What is the effect on corona, if the spacing between the conductors is increased?

260 Find the spacing between the conductors a 132 kV 3 phase line with 1.956 cm diameter conductors is built so that corona takes place, if the line voltage exceeds 210 kV (rms). With go = 30 kV/cm

261 262 263 264 265

Explain theory of corona formation. Explain the effect of corona on communication lines What is visual critical voltage? Explain power loss due to corona Corona isA. Partial breakdown of air C. Sparking between lines

B. Complete breakdown of air D. None of these

266 Which of the following statements is true regarding coronaA. Corona takes place at a voltage lower than breakdown voltage B. Corona takes place at a voltage higher than breakdown voltage C. Corona is a current phenomenon D. Corona increases the transmission line efficiency

267 What is a difference between the corona effect and the capacitance effect in a transmission line? 268 Higher the frequency, _____________. a. Lower the corona loss. b. Higher is the corona loss. c. Does not effect. d. Depends on the physical conditions. 269 On which factor is the corona loss dependent on? a. Material of the conductor. b. Diameter of the conductor. c. Height of the conductor. d. None of these. 270 Why are bundled conductors employed? a. Appearance of the transmission line is improved. b. Mechanical stability of the line is improved. c. Improves current carrying capacity. d. Improves the corona performance of the line. 271 The effect of dirt on the surface of the conductor is to _____________ irregularity and thereby ________________ the break down voltage.

Electrical Power System-II (2160908)

272 273 274 275 276

a. Decreases, reduces. b. Increases, increases. c. Increases, reduces. d. Decreases, increases. Find the spacing between the conductors a 265 kV 3 phase line with 200 cm diameter conductors is built so that corona takes place, if the line voltage exceeds 210 kV (rms). With go = 30 kV/cm Find the maximum distriptive voltage a 265 kV 3 phase line with 200 cm diameter conductors is built so that corona takes place, if the line voltage exceeds 210 kV (rms) and spacing is 3.45 between the conductors. Take air density 0.8 With go = 30 kV/cm Find the spacing between the conductors a 33 kV 3 phase line with 200 cm diameter conductors is built so that corona takes place, if the line voltage exceeds 135 kV (rms). With go = 30 kV/cm Find the maximum distriptive voltage a 135 kV 3 phase line with 200 cm diameter conductors is built so that corona takes place, if the line voltage exceeds 210 kV (rms) and spacing is 2.45 between the conductors. Take air density 0.8 With go = 30 kV/cm Ozone effect can be detected by A. Presence of ozone detected by odour B. Hissing sound C. Faint luminous glow of bluish colour D. All of the above

277 Corona loss can be reduced by the use of hollow conductor because A. The current density is reduced B. The eddy current in the conductor is eliminated C. For a given cross section, the radius of the conductor is increased D. Of better ventilation in the conductor 278 Corona occurs between two transmission conductors when they A. Have high potential difference B. Are closely spaced C. Carry dc power D. Both A and B

279 A 3 phase 220 KV, 50 Hz, with conductor radis of 1.5 cm and spacing 200cm ,the temperature is 40c and atmospheric pressure is 76cm .calculate corona power loss per km 280 A 3 phase 220 KV, 50 Hz, with conductor radis of 1.5 cm and spacing 200cm ,the temperature is 50c and atmospheric pressure is 76cm .calculate corona power loss per km 281 A 3 phase 220 KV, 50 Hz, with conductor radis of 1.5 cm and spacing 200cm ,the temperature is 50c and atmospheric pressure is 76cm .calculate critical distriputive voltage if power loss is 800W 282 A 3 phase 165KV, 50 Hz, with conductor radis of 1.5 cm and spacing 200cm ,the temperature is 50c and atmospheric pressure is 76cm .calculate critical distriputive voltage if power loss is 800W

Electrical Power System-II (2160908) 283 Find the spacing between the conductors a 165 kV 3 phase line with 200 cm diameter conductors is built so that corona takes place, if the line voltage exceeds 310 kV (rms). With go = 30 kV/cm.

284 285 286 287 288 289 290

Explain the difference between corona effect and skin effect. Explain the difference between corona effect and Ferranti effect Why is corona effect more common in higher voltage range? What role does air as dielectric play in formation of corona? How effect will corona have if voltage is increase? How can corona be indentified? Corona occurs between two transmission conductors when they A. Have high potential difference B. Are closely spaced C. Carry dc power D. Both A and B

291 292 293 294 295

Will corona effect take place in DC transmission line? Justify your answer What role does conductor spacing play in corona mitigation? What role does distance between conductor play in corona mitigation? Which transmission line has more corona effect? AC or DC justify your answer. The good effect of corona on overhead lines is to A. Increase the lie carrying capacity due to conducting ionized air envelope around conductor B. Increase the power factor due to corona loss C. Reduce the radio interference from the conductor D. Reduce the steepness of surge fronts

296 297 298 299

Which is more adverse corona effect or switching capacitance of transmission line? Which is more adverse corona effect or skin effect? Which is more adverse corona of Ferranti effect? Which harmonics are generated during the corona, which leads to the increase in corona losses? a. Third harmonics. b. Fifth harmonics. c. Seventh harmonics. d. None of these.

300 Explain the role of hollow conductors in reducing corona effect.