Jawaharlal Nehru Technological University Kakinada 2010-1st Sem B.E Electrical and Electronics Engineering Code No: V3112/R07 III B.TechSupplementary s, POWER ELECTRONICS (Electrical

Code No: V3112/R07 Set No. 2
III B.Tech I Semester Supplementary Examinations, May 2010
POWER ELECTRONICS
(Electrical & Electronic Engineering)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks

1. The specifications of a Thyristor operating from a peak supply of 400V is as follows :
Repetitive Peak current Ipk = 200A
(di/dt)max = 15A/us , (dv/dt)max = 108V/us.
Choosing a factor of safety of two for Ipk, (di/dt)max and (dv/dt)max, design a suitable snubber circuit, if the minimum loads (RLmin) be 10 ohms resistive. [8+8]

2. discuss the operation of a single phase full wave mid-point converter with R-load with the help of circuit and output waveforms with respect to supply voltages. Derive the output voltage for alpha= 45degrees. [6+6+4]

3. A 3 phase semi conductor is operated from a 3 phase star connected 220V, 60Hz supply. The load current is continuous and has negligible ripple. The avg. load current is Idc = 150A and commutating inductance per phase is Lc = 0.5mH.
Determine the overlap angle if
(a) alpha= Pi/6
(b) aplha= Pi/3 [8+8]

4. A single phase load of resistance of 12 ohms is fed from 240V (rms), 50 Hz supply by a pair of inverse parallel thyristors. obtain the mean power in the load at firing angle of
(a) 0 degrees
(b) 90 degrees and
(c) 120 degrees. Ignore source inductance and device voltage drops. [6+5+5]

5. explain the working of a single phase mid point cyclo converter with R-L loads and for discontinuous operation with neat circuit diagram and output rms voltage and current waveforms for f0=1/3 fs. [4+7+5]

6. discuss the time ratio control and current limit control strategies used for choppers, with necessary waveforms and circuit. [8+8]

7. Single phase half bridge inverter has a resistive load of R = three ohms and dc input voltage Edc = 50V. compute
(a) rms output voltage at fundamental frequency E1
(b) the output power
(c) avg. and peak current of every thyristor [6+4+6]

8. discuss the voltage control in case of single phase bridge inverter circuit, in order to get variable voltage and variable frequency output. [16]

Earning:   Approval pending.