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Seventh Semester B.E. Degree Examination, Dec.201 4lJan.20l5HVDG Transmission

Time: 3 hrs. Max. Marks:100

Note: Answer any FIVE full questions, selecting atleast TWO questions from each part'

PART _ A

a. With relevant figures, explain the constitution of EHV-AC and HVDC links. (12 Marks)

b. With a neat diagra*,."pluitr different kinds of DC links. Explain the necessity of a Back to

Back HVDC link. (08 Marks)

Z a. Summarize the advantages and disadvantages of a HVDC Transmission system. (08 Marks)

b. Compare HVAC and HVDC Transmission for Economics of operation, stability limit,

voltage control and reliability. (12 Marks)

3 a. Briefly explain the assumptions made while studying the properlies of converter circuits.(06 N{arks)r'espect toDraw neat(14 Nlarks)

b. Compare ttnee phase one way rectifier and three phase two way rectifier withpeak Inverse Voltage (PIV) and Volt ampere (VA) rating of Transformer Bank.

sketches and derive thc exprcssion used in boih cases.

4 a. ,.Best converter circuit for the HVDC transmission is 3 phase Bridge". Justify the statement

by explaining the advantages of a 3 phase Graetz bridge co-nfiguration . (10 Marks)

b. Oerivl the eipression for average DC voltage Vao and Peak lnverse Voltage efD and valve

utilization factor for a 'p' pulse converters, 'q' valves in a basic_ commutation group where

's' valves are in series and 'r' valves in parallel. Assume the peak valve of the commutation

voltage is 'E-'. (10 Marks)

PART _ B

a. With relevant figures and waveforms, explain the operation of Graetz Bridge cilcuit. Derive

the expression ior average DC output voltage otihe converter without overlap. Assume

converter firing angle as 'cr'. Also obtain the expression for RMS AC current. (l0_Marks)

b. Explain the t6iee and four valve conduction made of a 3 phase bridge rectif'rer when the

ovellap angle is greater than 600. Show that.

Vo: .'6 V,1o coS (u - 300) - 3Rc Ia. (10 Marks)

a. Enumerate the desired features of control for a HVDC converter station. (08 Marks)

b. With relevant figure, explain combined characteristics of rectifier and inverter permitting

reversal of power flow. Clearly explain the signihcance of positive and negative curtent

nlargin. (12 Marks)

7 a. Briefly explain why Constant minimum Ignition Angle (CIA) control, Constant cuffent

Control (iC) and Constant minimum Extinction Angle (CEA) control are desired in a

HVDG link (08 Marks)

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1088751

b. Explain with neat diagram, how Individual Phase Control (IPC) scheme of firing anglecontrol is implemented using constant 'o,' control and Inverse Cosine control for a HVDCconverter. (12 Marks)

8 a. Determine the value of the inductance of the dc reactor required to prevent conseqilentcommutation failure in the inverter described below : ..

.. Number of bridges per pole - 2

Rated voltage per bridge - 200 kVR{ited curent - 1.8 KA

", I

IS2 * i0 KA j .,,.

Frequency - 50 HzNormal extinction angle y': 160

:

-0Ymin

: 8". , ,, I (10 Marks)b. Explain the current oscillations and applications of anode dampers. Why damper is less

effective if it is Corrnected to the cathode side? Explair. ., ,, (10 Marks)

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