1 (a)
Explain constant torque and constant power drive methods with relevant diagrams and waveforms.

5 M

1 (b)
A single phase full converter is made to deliver a constant load cutrrent. For zero degree firing angle the overlap angel is 15

_{o}. Calculate the overlap angel when firing angel is 45_{o}.
5 M

1 (c)
Introducing motor speed control with constant supply voltage and reduced suppy frequency is rarely used in practice. Justify the stateent.

5 M

1 (d)
List the merits and demerits of online UPS and offline UPS

5 M

2 (a)
With neat circuit diagram explain the working of a load commutated chopper with relevant voltage and current waveforms. Show voltage variation across each pair of SCR?s as a function of time.

10 M

2 (b)
Describe modified Mc-Murray Bedford method of half bridge inverter circuit with related voltage and current waveforms.

10 M

3 (a)
Explain the neat diagram the working of parallel inverter employing feedback diodes. Draw the voltage and current waveforms. What care should be taken to avoid commutations failure?

10 M

3 (b)
A 220V, 1500 RPM, 10A separately excited D.C motor has an armature resistance of 0.1 ? if it is fed from a single phase fully controlled bridge rectifier with an A.C source voltage of 230V, 50 Hz. Assuming continuous load current compute:

(i) firing angel for rated motor torque at 600 rmp.

(ii) firing angel for rated motor torque at (-500) rmp

(iii) motor speed for ? =150

(i) firing angel for rated motor torque at 600 rmp.

(ii) firing angel for rated motor torque at (-500) rmp

(iii) motor speed for ? =150

_{o}and half rated torque
10 M

4 (a)
Draw and explain the power circuit of semiconverter feeding a separately excited D.C motor. Explain with typical voltage and current waveforms the operation in both continuous and discontinuous armature current modes.

10 M

4 (b)
Draw the circuit diagram and explain the rotor resistance control method of using chopper for the speed control of 3 phase induction motor.

10 M

5 (a)
Explain with relevant circuit diagrams the static scherbius drives for obtaining speeds below as well as above the synchronous speeds.

10 M

5 (b)
Explain with diagram the operation of series inverter. State the limitations. How these limitations are overcome?

10 M

6 (a)
With the help of circuit diagram and waveforms, explain the operation of isolated flyback converter in discontinuous mode. Also state the advantages and disadvantages.

10 M

6 (b)
Describe the principle of step- up chopper. Derive an expression for the average output voltage. State the assumptions made.

10 M

Write short notes on :-

7 (a)
Dual converter

7 M

7 (b)
PWM inverter

7 M

7 (c)
Step up chopper

7 M

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