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Extra High Voltage AC and DC Transmission System
Questions
1. Explain the technical and economical reasons for adopting EHV transmission system for
transfer of bulk power over long distance.
2. What are the problem associates with EHV transmission system?
3. What are the special factors and technical considerations for EHV lines?
4. what is meant by power handling capacity of a transmission line? Write is the equation
from power handling capacity and percentage transfer loss in the line and explain how the
higher transmission voltages are important for bulk power transmission.
5. Explain what is meant by bundled conductor? What the properties of the bundled
conductor and why they are used?
6. Explain the concept of geometrical mean radius of bundled conductors. Why it is
calculated?
7. What is difference between bundle radius and equivalent radius of bundle?
8. Derive a general formula to find GMR of a bundle conductor having N sub-conductor.
9. Derive a general equation for the inductance of a bundled conductor consisting of N sub-
conductors and show that the inductance of a bundled conductor reduced to 1/N times of
that of a one conductor.
10. What are the causes of generation of corona, audible noise and radio interference?
Discuss the factors affecting corona loss.
11. Explain the estimation of conductor surface voltage gradients for EHV lines. OR
12. Derive the expression for surface voltage gradient for two bundle conductor for EHV
lines.
13. What are the maximum, minimum and overvoltage value of surfaces voltage gradients.
Explain cosine low of variation (distribution) of surface voltage gradients.
14. What is the effect of high electrostatic field on human being under an EHV lines? Why
does a normal human being not experience a shock when walking under beneath a line?
15. Describe difference between primary and secondary shock current. What is meant by “let-
go” current?
16. Write short note on compensation provided in transmission line and advantage and
disadvantage of the system.
17. Briefly describe the series compensation provided in transmission line and advantage and
disadvantage of the system.
18. What are the main problems created by series compensation? Discus the sub-
synchronous reactance problem in series capacitor compensated line and counter measure
taken to deal with the problem?
19. What are the technical and economical advantages of HVDC transmission over EHV AC
transmission?
20. What are the different types of HVDC link (DC link)? Briefly describe each of them.
21. Briefly discuss the method of connecting DC link into AC system.
22. Write short note on i) ground return in HVDC transmission and ii) Multi terminal DC
link.
23. Derive the expression for power at sending end and receiving end of an HVDC system in
terms of at sending end and receiving end voltage and line resistance.
24. A bipolar two terminal HVDC link is delivering 1000MW at ±500kv at the receiving
end. Total losses in DC circuit are 60MW. Calculate the following: sending end power,
power in the middle of line, sending end voltage, voltage at middle of line and total
resistance of the DC circuit.
25. A bipolar two terminal HVDC transmission HVDC transmission system has a 12 pulse
converter per pole each terminal. The system has following data :
Rated DC voltage = ±500kv
Rated bipolar power = 1500MW
Line resistance per pole = 5 ohms
DC voltage at rectifiered = ±500kv
Rectifier terminal feeds rated power in DC line. Calculated the following: DC current,
DC line loss, inverter and DC voltage, DC power delivered to inverter end, DC voltage
of 6 pulse converter at rectifier end, DC voltage of 6 pulse converter at inverter end,
bipolar DC voltage rectifier and bipolar DC voltage of inverter.
26. Sketch and explain the configuration of 6 pulse bridge converter.
27. Explain the commutation and overlap angle for a 6 pulse rectifier bridge.