# SET-IV

1. (a) Compare the power transfer capacities of A.C. and D.C. transmission systems when an existing A.C. line is converted into D.C. line, with following conditions:

i. Same current and insulating level.

ii. Same percentage losses and insulation level.

(b) Prove that insulation required for D.C. system is 0.866 times that required for A.C. system. Assume the power transmitted, percentage losses and size of conductors are same for both systems.

2. (a) Draw the connection diagram of two, 3φ converter transformers to a 12 pulse converter bridge.

(b) What is meant by firingle angle delay and commutation delay ? Draw the waveforms for voltage and current in a 6 pulse Gractz circuit with α = 300 and μ = 150.

3. With block diagram, explain the hierarchical control structure for a DC link.

4. With block diagram, discuss the principle of operation of a basic power controller.

5. Obtain the mathematical model of a d.c. network and d.c. converter, including converter controller.

6. (a) What are the basic principles of over current protection.

(b) Discuss the various faults exist in converter station? Explain.

7. What do you understand by characteristic harmonics in HVDC System? Using fourier analysis obtain equation for primary current of transformers connected to 12 pulse converter.

8. What are the various types of filters that are employed in HVDC converter station? Discuss them in detail.