Travelling Waves Interview Questions and Answers:
1. What are the values of natural impedances for overhead lines and cables ?
Ans. The value of natural impedance for an overhead line is between 400 Ω and 600 Ω while for a cable it is between 40 Ω and 60 Ω.
2. Why velocity of propagation over all overhead lines is same ?
Ans. Velocity of propagation over all overhead lines is same because product of L and C is same for all overhead lines.
3. What is meant by crest of a wave ?
Ans. Crest of a wave is the maximum amplitude and is usually expressed in kV or kA.
4. What is meant by front of a wave ?
Ans. Front of a wave is the portion of the wave before crest and is expressed in time from the beginning of the wave to the crest value in ms or μs.
5. A transmission line of surge impedance ZC is terminated through a resistance R. Give the coefficients of refraction and reflection.
Ans. Coefficients of refraction = 2R/R+ZC and coefficient of reflection = R-ZC/R+ZC.
6. While connecting station equipment to an overhead line through a cable it is important that length of the cable should not be very small. Why ?
Ans. In connecting station equipment to an overhead line through a cable it is important that the length of cable should not be shorter than the expected length of the wave otherwise successive reflections at the junction may cause piling up of voltage and the voltage at the junction may attain the value of incident voltage.
7. What is the effect of shunt capacitance at the terminal of a transmission line ?
Ans. The effect of shunt capacitance at the terminal of a transmission line is to cause the voltage at the terminal to rise to full-value gradually instead of abruptly i.e.. to cause flattening of the wave front, which reduces the stress on the line-end windings of a transformer connected to the line.
8. What is the application of Bewley’s lattice diagram ?
Ans. With the use of Bewley’s lattice diagram one can know at a glance the position and direction of motion of every incident, reflected and transmitted wave on the system at every instant of time.