How transmission lines are classified? Discuss the terms voltage regulation and transmission efficiency for transmission line.
[3 marks]Derive ABCD constant for medium transmission line using nominal T representation
[4 marks]Find the following for a single circuit transmission line delivering a load of 50 M VA at 110 kV and p.f. 0·8 lagging: (i) sending end voltage (ii) sending end current (iii) sending end power (iv) efficiency of transmission. Given A = D = 0·98 ∠3º; B = 110 ∠75º ohm; C = 0·0005 ∠80º siemen.
[7 marks]How the faults on a power system are classified? What is the difference between steady state reactance X , transient reactance X ’ and sub- d d transient reactance X ’’. d
[3 marks]A 3-phase alternator can supply a maximum load of 5000 kVA at 6600 V. The machine has internal reactance of 6%. Find the reactance per phase of the limiting reactor if the steady apparent power (kVA) on short-circuit is not be exceed 5 times the full-load value.
[4 marks]Write note on Selection of a circuit breaker.
[7 marks]Explain the importance of bus impedance matrix in fault calculation.
[7 marks]What is operator ‘a’? Show that:
[3 marks]a2 = − 0·5 − j 0·866 (ii) a3 = 1 (iii) 1 + a + a 2 = 0
[ marks]Prove that positive sequence impedance and negative sequence impedance of fully transposed transmission line are always equal.
[4 marks]In a 3-phase, 4-wire system, the currents in R, Yand Blines under abnormal conditions of loading are as under: I = 100 ∠30º A; I = 50 ∠300º A; I = 30 ∠180º A. R Y B Calculate the positive, negative and zero sequence currents in the R-line and return current in the neutral wire.
[7 marks]What do you understand by positive, negative and zero sequence impedances?
[3 marks]Show that for a fully transposed line, the zero-sequence impedance is much higher than positive or negative sequence impedance.
[4 marks]The sequence voltages in the red phase are as under: E = 100 V; E = (200 − j 100) V; E = − 100 V. R0 R1 R2 Find the phase voltages E Eand E . R, Y B1
Why is 3-φ symmetrical fault more severe than a 3-φ unsymmetrical fault?
[3 marks]Which sequence current flows through ground and ground wires and why?
[4 marks]Describe analysis of line to ground fault at a point of power system using symmetrical components and sequence network.
[7 marks]What is 3 phase unsymmetrical fault? Discuss the different types of unsymmetrical in brief.
[3 marks]Give reason: for a fault at alternator terminals, a single line to ground fault is generally more severe than a three-phase fault.
[4 marks]A 50 MVA, 11 kV three-phase alternator was subjected to different types of faults. The fault currents are as under: 3-phase fault = 2000 A; Line-to-Line fault = 2600 A; Line-to-ground fault = 4200 A. The generator neutral is solidly grounded. Find the values of the three sequence reactances of the alternator. Ignore resistances.
[7 marks]A 3-phase line has conductors 2 cm in diameter spaced equilaterally 1 m apart. If the dielectric strength of air is 30 kV (max) per cm, find the disruptive critical voltage for the line. Take air density factor δ = 0·952 and irregularity factor m = 0·9. o
[3 marks]Explain the following terms with reference to corona:
[4 marks]Critical disruptive voltage (ii) Visual critical voltage
[ marks]Derive the equation for attenuation of travelling waves
[7 marks]What is corona? What are the factors which affect corona?
[3 marks]Discuss the advantages and disadvantages of corona.
[4 marks]Explain travelling waves of transmission line when receiving end is short circuited briefly
[7 marks]