Download Unit 4 Assignment

E. (Mech., Mech. Sandwich & Auto) Examination, May 2014
Electronics and Electrical Engineering (203152) (2012 Pattern)
Marking Scheme and Model Answers
Q.1. (a)
Explain following instructions of 8051 microcontroller quoting suitable examples.
(i) ORL A, #data (ii) RRC A (iii) RET
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Solution:
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Explain the sphere gap method used for measurement of peak value of voltage.
Q1. (a)
Solution: Sphere Gap used for measurement of peak value of voltage
Sphere Gap: This is one of the oldest technique adopted for the measurement of all the types
(dc =, ac ~ and impulse) high voltages of either polarity. It remained the most widely
used method for decades. The field between two identical spheres is a classical example
of "weakly nonuniform” field. The breakdown characteristic of such a gap is linear for
the gap distances not greater than the radius of the spheres. Measurement voltage is made
as a function of minimum distance at which it can flash over or sparkover.
The breakdown voltage of the gap does not depend upon the duration of application of voltage
and also not upon its variation with time.
(1 mark)
Construction of the Sphere Gap: A sphere gap consists of two adjacent metal spheres of equal
diameters whose separation gap distance is variable. The ability to respond to peak
values of impulse voltages, if the time to peak is not too short ( 1-3 µsec), is governed by
a short statistical time lag or the delay in time required for the availability of an electron
to initiate an electron avalanche and hence the breakdown.
•
Within the limited gap distance between the spheres, a weakly nonuniform field exists,
hence no PB or corona appears before the complete breakdown or flashover.
•
For a given dimension of the diameter/radius of the spheres and a gap distance between
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them, the magnitude of the voltage at which the breakdown occured is read from the
standard calibrated tables available for different types of voltages and for both their
polarities.
•
The inaccuracy of measurement of voltage by this method is about 3%.
Disadvantages:
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For the measurement, breakdown in the gap has to take place.
•
Continuous measurement of the voltage is not possible.
•
This method is not very accurate.
(3marks)
Fig. Vertical Sphere Gap: 1. Insulating support. 2. Sphere shank. 3. Opening gear, showing
maximum dimensions. 4. High-voltage connection with series resistor. 5. Stress distributor,
showing maximum dimensions. P. Sparking point of .v. sphere. A. Height of P above ground
plane. B. Radius of space free from external structures. X. Item 4 not to pass through this plane
within a distance B from P. (Diagram: 3 marks)
Two-wattmeter method is used for measurement of input power of a three phase induction
motor. If two wattmeter readings are 1700 watts and 1100 watts; determine i) input power to
motor ii) power factor of the motor iii) input current drawn from 440 V, 3 phase AC supply.
input power to motor=2800W
(2 marks)
Solution:
Q.7. (b)
power factor of the motor=0.9375lag
(2 marks)
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input current drawn from 440 V, 3 phase AC supply=3.9189 A
(2 marks)
What is Wien’s Bridge? Derive expression for frequency of Wien’s Bridge.
Q.8. (a)
Solution: Wien’s Bridge
Diagram: (3 marks)
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Wien Bridge has a series RC combination in one and a parallel combination in the adjoining
arm. Its basic form is designed to measure frequency.
(1 mark)
The bridge balance equation is: Z1Z4= Z2Z3
( 3 marks)
Explain one wattmeter method used for measuring reactive power of a three phase balanced load
Q.8. (b)
with the help of connection diagram and phasor diagram.
Connection diagram
(2 marks)
Solution: One wattmeter method:
Phasor diagram
(2 marks)
Reactive power measurement
(2 marks)
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