ehvacdc tutorial (1)

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Maulana Azad National Institute of Technology, Bhopal

Tutorial Sheet

EHV AC & DC TRANSMISSION (E-403)

UNIT-I

1. Draw a schematic of bipolar HVDC system identifying its main components. Explain about each

component.2. Explain parallel operation of DC link with an AC network.

3. What are the problems involved in transmission of power using, EHV A. C. System? Discuss in detail.

4. Compare EHV A. C. And HVDC transmission on economic & technical basis & power handling capacity

5. What are the problems associated with the operation of d. C. System when connected to a weak a. C.

System.

6. Discuss the various kinds of DC links & applications of HVDC Transmission.

7. List the Limitations of AC interconnection & advantages of HVDC Transmission.

8. Discuss planning for HVDC transmission.

UNIT-II

1. What is load compensation? Discuss its objectives in power systems.2. Explain reasons for variation of voltage in a power system & suggest methods to improve voltage profile.

3. Comment on the statement,” it is not possible to achieve simultaneously both the UPF & zero voltage

regulation”.

4. Explain what you mean by loadability of overhead lines & discuss loadability characteristic of these lines.

5. Explain & differentiate between steady state, transient state & dynamic stability limits of power system.

6. Discuss briefly some of the disadvantages of operating the system under voltage & overvoltage. Explain:

Infinite Line, Flat Line.

7. Discuss the problem associated with charging long uncompensated line & suggest the method to overcome

this problem.

8. Explain series & shunt compensation of lines & discuss their effect on the surge impedance loading of

lines.

9. Show mathematically that under certain operating condition, the power angle characteristic could be astraight line characteristic.

10. Explain the phenomenon of sub synchronous resonance in power system operations & suggest remedies toovercome this problem.

11. Why compensation is required in extra long transmission line ? Explain why 100% series compensation is

not desirable.

12. Write notes on: Ground electrodes, Power handling capacity cf A. C. and D.C. lines, Ferranti effect, Tuned

power lines.UNIT-III

1. What is travelling wave? Explain the development of ' such a wave on overhead transmission line.

2. Explain the mechanism of lighting stroke.

3.What are the various causes of over-voltages in transmission line ? Transmission lines are generally

terminated by cables at substation. Explain its reasons.

4.

A surge of 100 kV travelling in a line of natural impedance 600 ohms arrives with two lines of

impedances 800 ohms and 200 ohms respectively. Find the surge voltages and currents transmitted intoeach branch line.

5. What are the causes of over voltages on EHV AC transmission lines? Give their order of magnitude

6. Derive an expression for the surge impedance of a transmission lines.

7.

A 300 km long overhead transmission line having inductance of 1.25 mH/kM and capacitance of 5nF/km

terminates at a load impedance of 2 kilo-ohms. When a surge voltage of 100 kV is applied to the

transmission line, obtain the voltage reflected back from the load.

8.Explain the term attenuation & distortion in travelling waves propagating on O.H. Lines. What is the

effect of corona on the transmission lines

9. Derive an expression for reflection coefficient of travelling waves at a junction.

10.

A surge of 20 kV magnitude travels along a cable towards its junction with an overhead transmission line.

Inductance & capacitance the cable and O.H. line are 0.3mH, 0.4µF & 1.5mH, 0.012µF respectively. Find

the voltage transmitted in the O.H. line. Derive the relation used.

11.A transmission line has inductance of 1mH/kM & capacitance of 11.11nF/kM. The conductor plus groundresistance amounts to 0.4 ohm/kM. taking only a single phase representation calculate: (i) the velocity of

propogation (ii) surge impedance (iii) the attenuation factor for 400kM length.



p p g ( ) g p ( ) g

UNIT-IV

1. Explain the operation of Graetz circuit and derive for output voltage

2.A bridge connected rectifier is fed from 220 kV/110 kV transformer with primary connected to 220 kV.

Determine the d.c. output voltage when the commutation angle is 15o and the delay angle is 45o.

3.Explain the working of a 3-phase bridge converter with current and voltage waveform and deduce

relationship for output voltage and current considering the commutation angle.

4. Discuss Reactive power requirements of HV D. C. converter. & Converter control characteristics of H.VD. C. system.

5. What are the causes of harmonics in HVDC systems? Discuss the characteristic and non-characteristic.

6. Explain D.C. filters, mentioning the criteria by which the effectiveness of the D. C. filters can be judged.

7. Explain the principle of resonance in a shunt filter.

8.What are the main objectives in designing the size and branches of AC harmonic filters & DC harmonicfilters in a HVDC substation?

9.

Calculate equivalent frequency deviation in the detuning condition of tuned filter with the following data:

deviation in supply frequency of 50 Hz: ±1%; failure of capacitor units:0-0.25% ; capacitance variation due

to temperature:±1% ; initial detuning error:±0.25% .

UNIT-V

1. Explain HVDC converter firing control system

2. Write a short note on Causes of Harmonics in HVDC converters.

3. Explain: multi-terminal D.C. systems, Firing-angle control, Functions of smoothing reactors.

4. Describe the principle of terminal DC link control.

5. Discuss the converter control characteristics of both stations

6. Write a short note on current & extinction angle control.

ehvacdc tutorial (1)

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