1. a) Describe the construction and operating modes of SCR. 7 b) Explain the two transistor analogy of SCR. 7 OR 2. a) Illustrate various layers of TRIAC and also explain its operation

NKT/KS/17/7269/7274 1 P.T.O

B.E.Fourth Semester (Electronics Engineering / Electronics Telecommunication /

Electronics Communication Engineering) (C.B.S.) Power Devices & Machines

P. Pages : 2 NKT/KS/17/7269/7274

Time : Three Hours Max. Marks : 80

_____________________________________________________________________

Notes : 1. All questions carry marks as indicated. 2. Solve Question 1 OR Questions No. 2.

3. Solve Question 3 OR Questions No. 4.





8. Due credit will be given to neatness and adequate dimensions.

9. Assume suitable data whenever necessary.

1. a) Explain the operation of SCR using two transistor analogy and derive the expression for

anode current.

7

b) Draw & explain Dynamic characteristic of SCR. Define Turn ON time.

6

OR

2. a) Explain four mode of operation of Triac.

7

b) Write short notes on application of Traic as phase control circuit.

6

3. a) Give constructional details of IGBT, Explain how IGBT works. Draw V-I characteristic.

7

b) Give comparison between the SCR, power MOSFET & IGBT.

7

OR

4. a) Explain basic structure, symbol & operation of power MOSFET? Explain formation of

depletion region & creation of Inversion layer & show V-I characteristic.

8

b) Write short notes on GTO.

6

5. a) Explain the operation of single phase fully controlled full wave converter with resistive

load.

6

b) With the help of a neat circuit diagram & waveform explain single phase fully controlled

half wave controlled rectifier with R-L load & freewheeling diode.

7

OR

6. a) Describe the operation of 3 phase half wave controlled rectifier (HWCR) with resistive

load.

7

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NKT/KS/17/7269/7274 2

b) Draw & explain midpoint single phase cycloconverter with Resistive load. Give

advantage & application of cycloconverter.

6

7. a) Classify choppers based on quadrant of operation & output voltage. Explain class C

chopper.

7

b) What are the different control techniques used in chopper. Explain in short.

6

OR

8. a) Explain operation of simple series inverter. Draw all relevant waveform.

6

b) Explain the operation of 3 phase bridge Inverter in 120º mode. Draw waveform.

7

9. a) What is an open-delta (V-V) connection? What are the applications of this system.

7

b) What are the distinguishing features of &Y,Y,YY connections. Give

advantages.

6

OR

10. a) Why starters are necessary for starting of Induction motor? Explain Star-Delta starter.

7

b) Discuss the various methods of speed control of 3 phase I.M. Explain any one method.

6

11. a) Explain speed control of DC shunt motor.

i) Flux control method.

ii) Voltage control method.

7

b) A 250 volt dc shunt motor has armature resistance of 0.25, on load it takes an armature

current of 50A and runs at 750 rpm. If the flux of motor is reduced by 10% without

changing the load torque. Find the new speed of the motor.

7

OR

12. a) Write short notes on speed control of DC series motor.

1) Flux control.

2) Rheostatic control.

8

b) Explain with neat diagram construction & principle of operation of universal motor.

6

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KNT/KW/16/7269/7274 1 P.T.O

B.E. Fourth Semester (Electronics Engineering / Electronics Communication Engineering /

Electronics Telecommunication Engineering) (C.B.S.) Power Devices and Machines Paper - II

P. Pages : 2 KNT/KW/16/7269/7274

Time : Three Hours Max. Marks : 80

_____________________________________________________________________

Notes : 1. All questions carry marks as indicated. 2. Solve Question 1 OR Questions No. 2.






8. Due credit will be given to neatness and adequate dimensions.

9. Assume suitable data whenever necessary.

10. Illustrate your answers whenever necessary with the help of neat sketches.

1. a) Describe the construction and operating modes of SCR.

7

b) Explain the two transistor analogy of SCR.

7

OR

2. a) Illustrate various layers of TRIAC and also explain its operation in 4 modes.

7

b) Write short note on AC regulator employing TRIAC-DIAC arrangement.

7

3. a) What are different types of POWER MOSFET ? Explain any one in detail.

6

b) Draw the layer diagram of IGBT. Also state its advantages and applications.

7

OR

4. a) Draw and explain the output characteristics of power MOSFET.

7

b) Explain the construction and operation of GTO.

6

5. a) Explain with waveform single phase half wave rectifier with R-L load also give the

significance of free wheeling diode.

6

b) A single phase fully controlled bridge rectifier with R L load is used for obtaining a

regulated dc output voltage. The RMS value of ac input voltage is 230V and firing angle is

maintained at 3

, with load current 4A. (1) calculate the dc output voltage (2) Assuming

load resistance remains some. Calculate the dc output voltage if a free wheeling diode is

used at a same firing angle. (3) If 3SCR is damaged and gets open circuited calculate

average DC output with free wheeling diode.

7

OR

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6. a) Explain with waveform 3-phase half wave controlled rectifier with resistive load.

8

b) Explain single phase AC voltage controller with resistive load.

5

7. a) Give the classificator of chopper and Explain class 'B' chopper in detail.

7

b) State and explain control strategies of chopper.

6

OR

8. a) Explain single phase half bridge inverter with R-L load.

6

b) Explain 3 bridge inverter 180º Mode conduction with wave forms.

7

9. a) Draw and explain in detail (1) star-star connection (2) star-Delta connection of 3 phase

transformer.

6

b) A 3 , 50Hz transformer has a delta corrected primary and star corrected secondary the line

voltages bring 22000V & 400V respectively. The secondary has a star connected balanced

load at 0.8 power factor lagging. The line current on the primary side is 5A. Determine the

current in each coil of primary and secondary line. What is the output of the transformer in

KW?

8

OR

10. a) Explain working principle of 3 induction motor.

6

b) State different speed control technique in induction motor and explain speed control by

charging rotor circuit resistance

8

11. a) State different types of DC motors. Explain armature controlled method of speed control in

dc series motor.

7

b) A dc series motor operates at 800rpm with a line current of 100A from 230V mains. Its

armature circuit resistance is 15.0 & its field resistance is 0.1. Find the speed at which

motor runs at a line current of 25A. assuming flux at this current is 45% of flux at 100A.

6

OR

12. a) Explain working principle of universal motor & its application.

7

b) Write applications of DC series motors, DC shunt motors & DC compound motors.

6

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Documents

1. a) Describe the construction and operating modes of SCR. 7 b) Explain the two transistor analogy of SCR. 7 OR 2. a) Illustrate various layers of TRIAC and also explain its operation