Code No: RR420202 Set No. 1

IV B.Tech II Semester Supplimentary Examinations, May 2008HVDC TRANSMISSION

(Electrical & Electronic Engineering)Time: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

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1. (a) What are the different applications of HVDC transmission system? Explainthem in detail.

(b) With neat sketches explain the different kinds of D.C. links available. [8+8]

2. Draw the circuit diagram voltage and current wave form of a 3-φ, 6 pulse uncon-trolled bridge rectifier and derive the expression for:

(a) Average DC Voltage

(b) Total VA rating of valves and transformer. [8+8]

3. Discuss in detail, the control characteristics of a converter. [16]

4. Describe the method of Compensation of reactive power in HVDC substation .Drawsimple single line schematics for each. [16]

5. Obtain the mathematical model of a d.c. network and d.c. converter, includingconverter controller. [16]

6. Write short notes on:

(a) Protection against over voltages

(b) Commutation failure in inverter

(c) Arc through. [5+6+5]

7. Give reasons for selecting star-star and star-delta transformer configuration insteadof two star-star configurations for 12 pulse converter. Derive an equation for pri-mary current. [16]

8. What are the various types of filters that are employed in HVDC converter station?Discuss them in detail. [16]

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Code No: RR420202 Set No. 2

IV B.Tech II Semester Supplimentary Examinations, May 2008HVDC TRANSMISSION

(Electrical & Electronic Engineering)Time: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

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1. What is the need for interconnection of systems? Explain the merits of connectingHVAC systems by HVDC tie-lines? [16]

2. Draw a schematic of a 6 pulse converter circuit and derive from fundamentals, theexpression for voltage and currents for the operation of convertor as a rectifier andinverter with relevant waveforms. [16]

3. Write short notes on the following: [8+8]

(a) Constant Alpha control

(b) Inverse cosine control.

4. With block diagram, discuss the principle of operation of a basic power controller.[16]

5. (a) Derive the mathematical model of d.c. link controllers of a d.c. link.

(b) Write the mathematical model of a d.c. converter. [8+8]

6. (a) Explain the fault clearing process in H.V.D.C. poles. Explain how are theH.V.D.C. equipment protected against prolonged short circuit currents thoughthere is no H.V.D.C. circuit breaker on H.V.D.C. pole side.

(b) Explain the protection provided for DC line. [10+6]

7. Write short notes on the following: [8+8]

(a) Telephone influence factor.

(b) Harmonic distortion.

8. What are the various types of filters that are employed in HVDC converter station?Discuss them in detail. [16]

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Code No: RR420202 Set No. 3

IV B.Tech II Semester Supplimentary Examinations, May 2008HVDC TRANSMISSION

(Electrical & Electronic Engineering)Time: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

⋆ ⋆ ⋆ ⋆ ⋆

1. Draw a schematic diagram of a typical HVDC converter station and explain thefunctions of various components available. [16]

2. (a) Clearly explain how harmonics are produced and obtain the expression forrms value of the fundamental component of the current.

(b) Obtain a relation between firing angle and power factor angle in a 3-φ bridgerectifier. [8+8]

3. Write short notes on the following: [8+8]

(a) Combined characteristics of Rectifier and Inverter

(b) Constant - Minimum - Ignition -Angle Control

4. Write a note on the following sources of reactive power:

(a) Synchronous condensers

(b) Static VAR system. [8+8]

5. Derive and explain the solution of AC/DC load flow problem using simultaneousmethod. [16]

6. (a) State and explain why H.V.D.C. circuit breakers are not necessary in mainpoles of H.V.D.C. system.

(b) Sketch a complete single line diagram of D.C. side of H.V.D.C. substation andindicate various surge arresters. [8+8]

7. How do you estimate the harmonic order based upon pulse number of HVDC con-verter station? Give a detailed harmonic analysis of a 12 pulse converter for char-acteristic harmonics. [16]

8. What are the various types of filters that are employed in HVDC converter station?Discuss them in detail. [16]

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Code No: RR420202 Set No. 4

IV B.Tech II Semester Supplimentary Examinations, May 2008HVDC TRANSMISSION

(Electrical & Electronic Engineering)Time: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

⋆ ⋆ ⋆ ⋆ ⋆

1. (a) What are the different applications of HVDC transmission system? Explainthem in detail.

(b) With neat sketches explain the different kinds of D.C. links available. [8+8]

2. Draw the schematic diagram of a typical HVDC converter station with 2 six pulseconverter units and explain the function of each component. [16]

3. With circuit diagram, explain the principle of operation of firing angle controlscheme. [16]

4. What is meant by reactive power control? Explain in detail. How it is achieved.[16]

5. Obtain the mathematical model of a d.c. network and d.c. converter, includingconverter controller. [16]

6. Explain the difference between A.C. circuit breaker and H.V.D.C. circuit breaker.State the principle of artificial current zero employed in H.V.D.C. circuit breakers.State the events occurring in the entire fault clearing process using such a breaker.

[16]

7. What is the reason for using star-star and star-delta transformer configurations for12 pulse converter. Derive an equation for primary current using fourier analysis.

[16]

8. Derive an equation for harmonic voltage and current for single tuned filter anddiscuss the influence of network admittance on design aspects. [16]

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