P1346
Instructions to candidates :
1) Answer Q.1 or Q.2, Q.3 or Q.4, Q.5 & Q.6 questions from Section I and Q.7
or Q.8, Q.9 or Q.10, Q11 or Q12 questions from Section II.
2) Answers to the two sections should be written in separate books.
3) Neat diagrams must be drawn wherever necessary.
4) Figures to the right indicate full marks.
5) Use of logarithmic tables, slide rule, Mollier charts, electronic pocket
calculator and steam tables is allowed.
6) Assume suitable data, if necessary.
Q1) a)
Draw the circuit diagram of three - phase fully controlled converter
feeding a resistive load and the following:
Waveforms for = 30º.
[10]
i) Supply phase voltages.
ii)
Supply line voltages.
iii) Output voltage.
iv) Supply Current (any one phase).
b)
Q2) a)
b)
v) Current through SCR (any one).
Explain the effect of source inductance on the performance of a single
phase full converter with waveforms. Derive expression for its output
voltage interms of maximum voltage (vm), filing angle , and overlap
angle .
[8]
OR
Explain with a neat circuit diagram and relevant waveforms, the operation
of a three-phase circulating current type dual converter. Derive an
expression for the peak circulating current in terms of the filing angle.[10]
With the help of a neat circuit diagram, explain the technique for achieving
equal voltage sharing of two series connected diodes. Derive the
relationship between the current sharing resistors in terms of the diode
parameters.
[8]
P.T.O.
Q3) a)
With the help of a neat circuit diagram, relevant waveforms and mode
equivalent circuits, explain the operation of a three phase, 120º mode,
voltage source inverter feeding a balanced, star - connected resistive
load. Also derive an expression for R.M.S. phase output voltage. [10]
b)
Briefly explain any one technique for output voltage control and harmonic
reduction in inverters.
[6]
OR
Q4) a)
With the help of circuit diagram explain the circuit of Boost inverter
circuit with analysis.
[8]
b)
A three-phase bridge inverter is fed from a d.c. source of Edc volts. The
inverter is operated in 180º conduction mode and it is supplying a purly
resistive star connected load with R / phase. Determine the ratings of
thyristors.
[8]
Q5) a)
With the help of a neat circuit diagram, relevant waveforms including
capacitor (switch) voltage and inductor (load) current and mode
equivalent circuits, explain the operation of a class E resonant converter.
[10]
b)
What are the advantages of resonant, converters over switched mode
converter.
[6]
OR
Q6) a)
b)
With the help of neat circuit diagram and relevant waveforms, explain
the Symmetrical Angle Control (SAC) technique for power factor
improvement in AC-DC converters.
[8]
How will you measure.
i)
Sinusoidal voltage and current.
ii)
Nonsinusoidal voltage and current.
[8]
Q7) a)
With the help of a neat circuit diagram and relevant waveforms, explain
the operation of a bipolar voltage chopper drive for P. M and hybrid
stepper motor.
[10]
b)
What are the effects of discontinuous armature current for dc motor drive.
[4]
c)
Explain ‘Field failure and under voltage protections for D.C. motor.[4]
OR
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2
Q8) 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 continuous armature current mode.
[8]
b)
A 210 V, 1200 rpm, 10A separately excited motor is controlled by a
single phase fully controlled converter with an a.c. source ‘voltage of
230 V, 50Hz. Assume that sufficient inductance is present in the armature
circuit to make the motor current continuous and ripple free for any
torque greater than 25 percent of rated torque Ra = 1.5 .
i)
What should be the value of the filing angle to get the rated torque
at 800 rpm?
ii) Compute the filing angle for the rated braking torque at - 1200
rpm.
iii) Calculate the motor - speed at the rated torque and = 165º for the
regenerative braking in the second quadrant.
[10]
Q9) a)
b)
c)
Q10)a)
b)
With the help of a circuit diagram and the motor torque - speed
characteristic, explain stator voltage speed control of induction motors.[8]
What do you understand by soft start? State and explain the soft start
methods employed for motors.
[4]
Justify “The speed range of an induction motor is restricted to above
30% of full range while operating with slip power regulation system. [4]
OR
Draw and explain the operation of three - phase brushless d.c. motor
drive. Also explain the related waveforms.
[8]
Explain the induction motor operation, when the V/f ratio is held constant.
Also derive the expression for maximum torque.
[8]
Q11)a)
What is energy audit? Explain the required procedure of energy audit.[8]
b)
Define the term Voltage Sag? Explain different sources of Sags and
interruptions.
[8]
Q12)a)
b)
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OR
What is power quality? Why it is required? Explain different types of
power line disturbance.
[8]
Explain probable preventive solutions to control the factors contributing
the power quality distartions.
[8]
3