HVDC IMPORTANT QUESTIONS

HVDC IMPORTANT QUESTIONS

UNIT-1

1. (a ) Explain the sequential method for AC-DC power flow.

(b) Derive the mathematical model of a HVDC converter.

2. a) Draw the converter controller model for a HVDC link and explain the same.

    b) Compare simultaneous and sequential methods for AC-DC power flow.

3. Classify the solution methodology for AC-DC load flow and explain the same.

4. a) Explain the simultaneous method for AC-DC power flow.

     b) Write short notes on DC load flow analysis.

5 .a) Explain Per Unit system for DC Quantities

  b)Draw flow chart for AC/DC Load flow

UNIT-2

1.Discuss in detail about the converter faults

(a) Arc through

(b) Short circuits in converter stations

(c) Current extinction

(d) Commutation failure in inverters

2.(a) Explain the necessity of smoothing reactor in a DC line.

(b) Discuss about the over voltage protection scheme employed in a converter station.

3.(a) What is the role played by dc reactors at the converter stations?

(b) Discuss about the basic principles of over current protection in converter station.

4.(a) What are the sources for overvoltages in HVDC systems? How are they

controlled?

(b) Discuss the need for circuit breakers in HVDC links?

5. a)What is the role played by smoothing reactors at the converter stations?

b) Discuss the operation of surge arrestors for overvoltage protection of HVDC

systems.

6.a) What are the sources for overvoltages in HVDC systems? How are they controlled?

  b) What are the factors that result in commutation failure? Show that DC voltage

       becomes zero during commutation failure.

7.a) Discuss in detail about the faults which occur in converters.

b) Explain the principle of operation of a DC circuit breaker.

UNIT-3

1.a) Discuss about characteristic and non-characteristic harmonics which occur in a d.c

        link.

   b) What are the adverse effects of harmonics on the operation of a d.c link?

2.Show that the lowest current harmonic generated in a 6-pulse Graetz converter

   is of the order 5th and its magnitude is 1/5 th of the fundamental. Mention the

    assumptions made.

3..a) What are the causes for non-characteristic harmonic generation in HVDC

    converters?

   b) Show that the lowest voltage harmonic generated in a 6-pulse converter is of

    the order 6th . Also discuss the effect of pulse number on harmonics.

4.a)What do you understand by characteristic harmonics in HVDC System? Using

     fourier analysis obtain equation for primary current of transformers connected to a

     12 pulse converter

b)Using Fourier analysis show that the lowest order voltage harmonic present in

      Graetz circuit output voltage is six.

UNIT-4

1. a) Discuss about various types of AC filters employed in HVDC systems. Also

       draw the their impedance characteristics.

   b) Write short notes on

      i) Size of filter

      ii) Damped filter

2.a)Explain in detail the design aspects of a single tuned filter.

   b) Discuss the design aspects of high pass filter

3.Write short notes on

(a) AC filters

(b) Characteristic harmonics

(c) Corona effect on DC lines