6. a) Write the problems of telephonic interference of HVDC transmission system and also write the

steps for reducing the telephonic interference. (5 marks) b) Write short notes on HVDC lightning

arresters with parallel branches

b)

for high energy. (4 marks)

Part C

A 3 phase overhead transmission linc has equivalent spacing of 5.5m between
conductors and conductor diameter is 3 cm. Atmospheric temperature is 10 °C and
barometric pressure is 740 mm of Hg. Surface irregularity factor for stranded
conductors is 0.9. Calculate the following.

i) Critical surface stress peak value, for fair weather and visual corona, for both

centre conductor and side conductor.

ii) Critical disruptive phase voltage and phase to phase voltage for

visual corona under fair weather condition ( 12 marks)

Explain the significance of creepage distance for AC insulators and DC (12 marks)

insulators in insulation coordination.

a) Explain the corona phenomenon in HVDC transmission system. (6 marks)

Explain the process of overvoltage on the ac side ofHVDC substation. (6 marks)