Ehv Ac And Dc Transmission

a) Explain the principle of DC link control and converter control characteristics.

b) For a 12 pulse converter with q = 4, s = 3, r = 1. Calculate the maximum DC power and transformer ratings (valve windings) if PIV rating of the valve is V and the rms current rating in I. Rework the problem if q = 3, s = 4, r = 1.

a) What is meant by power handling capacity of a transmission line? Write the equation from power handling capacity and percentage transfer loss in the line and explain how the higher transmission voltage is important for bulk power transmission?

b) A load has an effective power of P = 50 kW at 400 V and the power factor is to be compensated from cosØ = 0.75 to cosØ = 0.95. Determine the required capacitive power.

a) A power of 2000 MW is to be transmitted from a super thermal power station in central India over 800 Km to Delhi. Use 400 kV and 750 kV alternatives. Suggest the number of circuits required with 50% series capacitor compensation and calculate the total power loss and loss per km.

a) Explain clearly how overvoltage is generated when interrupting (i) low inductive current and (ii) low capacitive current. Draw a figure showing ferro-resonance condition in a network when two poles of a circuit breaker are open, and one pole is closed. Also, explain the methods of reduction of switching surges on EHV systems.

b) Describe the various types of converter faults. What protection is used against over currents in an HVDC system?

a) A transmission line is 300 km long and open at the far end. The attenuation of surge is 0.9 over one length of travel at light velocity. It is energized by:

i) A step of 1000 kV

ii) A sine wave of 325 kV peak when the wave is passing through its peak.

b) Calculate and plot the open end voltage up to 20 m sec.

a) What is the role of reactive power on voltage and voltage regulation? What are the components which are responsible for generation and absorption of reactive power in the system?

b) What do you mean by MTDC system? What are the different types of MTDC system? Explain and compare each type of MTDC system.

a) An existing So, double circuit AC lines is to be converted to three-circuit DC line. Assuming the same insulation level and unity power factor in the AC systems. Show that:

i) The ratio of power transmitted by DC to that by AC is equal to √2

ii) The ratio of % loss by DC to that by AC is equal to

1/√2

b) With a neat schematic diagram state the various apparatus required for HVDC station and explain purpose of each.

a) Write a short notes on (any two):

i) Graetz Circuit

ii) Switching over voltage

iii) Problem of extra long compensated lines

iv) Commutation failure