Punjab University 2003 B.Tech Electronics and Communications Engineering Industrial Electronics - Question Paper

EC
Industrial Electronics
(B.Tech fifth Semester, 2063)
Time : three Hours Maximum Marks : 60
NOTE:- This paper consist of 3 parts. part A is compulsory. Do any 4 ques. from
part B and any 2 ques. from part C

Section-A Marks : 20

1 (a) Differentiate ranging from core kind and core less induction furnace.
(b) define briefly different sources of generating high frequency for induction heating.
(c) Elucidate UJT triggering circuit for SCR.
(d) Draw switching characteristics of the power MOSFET and describe various time intervals.
(e) explain the suitability of the polyphase rectifier compared to the single-phase rectifier in relation to
rectifier voltage and ripple factor.
(f) explain the force-commutated inverter in brief.
(g) discuss John's chopper with necessary waveform.
(h) indicate with a neat sketch, a closed loop control scheme for controlling the speed of a DC motor.
(i) Briefly discuss the control scheme of commulator less DC motor.
(j) Compare the features of buck, boost and buck boost regulator.

Section-B Marks:5 every

2. The power input to the charge in a half-ton, 960 Hz induction furnace having a 20 turns on the primary
winding is 325 kW. The cylindrical crucible has an internal diameter of 45 cm and the depth of the charge
in it is 50 cm. Determine the equivalent resistance of charge and the current in the primary winding whiuch is
needed to counter balance the mmf due to secondary current.
3. discuss the operation of Cuk converter with neat circuit diagram. Also mark the direction of various current
and polarity.
4. A 3-phase full convertor charges a battery from a 3-phase supply of 230 V, 50 Hz. The battery emf is 200 V
and its internal resistance os 0.5 ohm. On account of inductance connected in series with the battery, charging
current is constant at 20 A. calculate the firing angle delay and the supply power factor.
5. A 440 V, 50 Hz, 6-pole, Y-connected wound rotor motor has the subsequent parameters:
Rs=0.5 ohm, R'r = 0.4 ohm, Xs = X'r = 1.2 ohm. Stator to rotor resistance is 3.5. Motor is controlled by static
rotor resistance control. External resistance is chosen such that the breakdown torque is produced at standstill
for a duty ratio of zero. compute the value of external resistance. How duty ratio should be varied with speed so
that the motor accelerates at maximum torque.
6. Elucidate the operation of class E commutation by drawing neat schematic diagram. Also draw the needed
waveform.

Section-C Marks : 10 every

7. The single-phase half bridge thyristorized invertor has a resistive load of R = 2.4 ohm and the dc input total voltage
(total) is 48 V. Determine :
(a) The rms output value at the fundamental frequency V1
(b) The output power Po
(c) The avg. and peak current of every thyristor
(d) The peak reverse voltage of every thyristor
(e) The total harmonic distortion THD
(f) the distortion factor
(g) The harmonic factor and distortion of the least order harmonic.
8.(a) Elucidate various modulation techniques used for inverter control.
(b) define any 1 method to decrease harmonic content in the output of inverter with mathematical support.
9.(a) Enumerate different advantages of cycloconvertor. Draw the schematic diagrams of 3-phase to 1-phase using six thyristors and 3-phase to 3-phase.
(b) Derive the general output voltage formula of cycloconvertor.

Earning:   Approval pending.