Jawaharlal Nehru Technological University Hyderabad 2008-1st Sem M.Tech Electrical Power System Code No: 52102/MT, –Supplementary s, tember, - ANALYSIS OF POWER ELECTRONIC CONVERTERS - Question

Here i am submitting M.Tech. – I Semester Supplementary Examinations, September, 2008- ANALYSIS OF POWER ELECTRONIC CONVERTERS in the provided beneath attachment.

Code No: 52102/MT

M.Tech. - I Semester Supplementary Examinations,

September, 2008

ANALYSIS OF POWER ELECTRONIC CONVERTERS ( Common to Power Electronics & Electric Drives/

Power & Industrial Drives/ Power Electronics/

Power Engineering & Energy Systems)

Time: 3hours    Max. Marks:60

Answer any FIVE questions All questions carry equal marks

1.a)    What is Synchronous tap changer? Discuss the application of ac voltage controller as tap changer.

b) An ac voltage controller feeding a resistance of 50 is fed from a 220V, 50Hz supply. Determine the form factor of the current as a function of firing angle a . Determine the power factor, displacement factor and distortion factor as function of a .

2.    a) A three phase star connected balanced resistances are supplied

from a three phase ac voltage controller. Derive the expression for rms value of load current in the complete range of firing angles. Draw the waveforms of load current. b) A three phase ac voltage controller feeds a balanced star connected R-L load. The value of resistance is 50 and inductance is 7.5mH. The controller is fed from a 3-phase supply of 400V, 50Hz. Determine for a firing angle of 90⁰, the values of

i) rms load current ii) rms load voltage iii) Power factor.

3.    a) Explain and compare the circulating and non-circulating current

modes of operation of cycloconverters. b) A six pulse cycloconverter is fed from 380V, 3-phase supply. Source has a reactance of 0.40/phase. If the load current is 50A, determine the output load voltage for firing angles of 30⁰ and 60⁰.

4.a)    Explain the following terms:

i) Input power factor    ii) Displacement factor

iii) Harmonic factor    iv) Total harmonic distortion and derive the relation between input p.f. and displacement factor.

Code No: 52102/MT

b) What are the various power factor improvement methods in converters? Discuss any two of them with relative merits and demerits.

5.a)    Describe the operation of a six pulse bridge converter with a resistive load and draw the input and output current & voltage waveforms for a firing angle of 30.

b) Show that the average value of dc voltage is 3'\[2

V_d =-Vcosa, for 0 < a < n/3

n

V_d = v[l + cos(a + n/3)l, for n/3 <a <2n /3 n

Determine also expressions for displacement factor and power factor as a function of a .

6.    a) Explain the principle and operation of Buck and Boost regulator

with neat waveforms. What are advantages and applications of this regulator?

b) A dc chopper operating from a 220V dc supply feeds a load of resistance of 50 in series with an inductance of 30MH. The chopper frequency is 200Hz and ON time of the chopper is 1.2ms. Determine the limits of variation of load current.

7.    Explain briefly the following modulation techniques with relative advantages and disadvantages.

a) Multiple PWM b) Sinusoidal PWM c) Delta modulation.

8.a)    Compare the 180⁰ and 120⁰ conduction modes of operation of a three-phase inverter.

b) Explain the space vector PWM technique as applicable to 3-phase inverter control with neat schematic diagrams.

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Attachment: jawaharlal-nehru-technological-university-hyderabad-2008-m-tech-electrical-power-system-47187-1.pdf

Earning:   Approval pending.