University Of Pune Question Paper
S.E. (Electrical) (Semester – I) Examination, 2011
ELECTRICAL MEASUREMENTS
(2003 Course)
Time : 3 Hours Max. Marks : 100
Instructions: 1) Answers to the two Sections should be written in separate
books.
2) Neat diagrams must be drawn wherever necessary.
3) Black figures to the right indicate full marks.
4) Use of logarithmic tables, slide rule, Mollier Charts, electronic
pocket calculator and steam tables is allowed.
5) Assume suitable data, if necessary.
6) Attempt Que. No. 1 or 2, Que. No. 3 or 4, Que. No. 5 or 6.
Que. No. 7 or 8, Que. No. 9 or 10, Que. No. 11 or 12.
SECTION – I
1. a) With a neat sketch explain the method of absolute measurement of current by
Rayleigh’s current balance. 8
b) Explain the terms : 8
i) Hysteresis. ii) Threshold.
iii) Dead band. iv) Accuracy.
OR
2. a) In a survey of 15 owners of a certain model of a car, the following figures are
for average petrol consumption where reported : 25.5, 30.3, 31.1, 29.6, 32.4,
39.4, 28.9, 30.0, 33.3, 31.4, 29.5, 30.5, 31.7, 33.0, 29.2.
Calculate :
i) Mean value ii) Median value
iii) Standard deviation iv) Average deviation
v) Variance vi) Probable error. 10
b) Explain parallax error and error due to inherent shortcomings of the instruments.
How to minimise them ? 6
3. a) Discuss briefly the following methods for measurement of medium resistance :
i) Ammeter - voltmeter method
ii) Substitution method
iii) Wheatstone bridge method. 8
b) A length of cable is used for testing its insulation resistance by loss of charge
method. An electrostatic voltmeter of infinite resistance is connected between
the cable conductor and earth, forming a joint capacitance of 600 pf. It is
observed that after charging the voltage falls from 250 V to 92 V in 1 min.
Calculate insulation resistance of the cable. 4
c) Classify the resistances from measurement point of view and give 2 examples
of each. 4
OR
4. a) Explain the effect of voltage, frequency and form factor of waveform on iron
losses. 6
b) What are the difficulties in magnetic testing of bar specimen in comparison
with ring specimen ? What is permeameter ? With a neat diagram describe
Hopkinson permeameter. 10
5. a) Write a short note on various sources and null detectors used for AC bridges. 6
b) With a neat diagram explain the working of vibrating reed type frequency
meter. 6
c) Write short note on Dynamometer type single phase power factor meter. 6
OR
6. a) With a neat diagram explain the use of Maxwell’s inductance -capacitance
bridge for measurement of unknown inductance. Derive an expression for
unknown inductance. Why is this bridge not suitable for large Q coils ? 9
b) The four impedances of an ac bridge are :
Z1 = 400 ∠50 ° Ω , Z2 = 200 ∠40° Ω, Z3 = 800 ∠ − 50 Ω , Z4 = 400 ∠20°Ω .
Find out whether the bridge is balanced under these conditions. 6
c) Explain the term sliding balance for achieving balance point quickly in AC
bridges. 3
SECTION – II
7. a) Derive the torque equation for D’ Arsonal galvanometer with usual notations.
Explain the intrinsic constants involved and write the equation of motion to
examine dynamic behaviour of galvanometer. 10
b) State and explain methods of producing damping torque in indicating type
instruments. What are the effect of over damping and under damping ? 8
OR
8. a) With neat sketch explain the construction and working of attraction type moving
iron instrument. State its advantages and disadvantages. 8
b) The coil of moving coil voltmeter is 40 mm× 30 mm wide and has 100 turns
wound on it. The control spring exerts a torque of 0.25×10–3 Nm when the
deflection is 50 divisions on scale. If the flux density of magnetic field in the
airgap is 1 Wb/m2, estimate the resistance that must be put in series with coil
to give 1 volt/div. Resistance of voltmeter is 10,000 ohm. 6
c) Explain the type of suspensions provided to the galvanometer. How is damping
torque produced in the galvanometer ? 4
9. a) Derive the torque equation of single phase dynamometer type wattmeter with
usual notations. 6
b) Compare dynanometer type wattmeter and induction type wattmeter. 4
c) With a neat circuit diagram and phasor diagram explain two wattmeter method
for measuring active power in three phase star connected (R+L) balanced
load. 6
OR
10. a) With neat diagram explain construction of low power factor type wattmeter.
State its application. 6
b) A wattmeter reads 5 kW when current coil is connected in R phase and pressure
coil is connected between R and N for a balanced symmetrical three phase
system suppling three phase inductive load of 25 Amp at 400 volts. What will
be the reading of wattmeter if connections of current coil are unchanged and
pressure coil is now connected between B and Y phases ? Find total reactive
power for this case. 4
c) With a neat circuit diagram and phasor diagram explain one wattmeter method
for measurement of reactive power in three phase star connected load. 6
11. a) What are different systems in induction type energymeter ? Describe each in
brief. 6
b) Derive the expression for ratio error for CT with usual notations. 6
c) What is difference in CT and ordinary transformer ? 4
OR
12. a) With a neat circuit diagram explain CT, PT operated energy meter. 6
b) What are the methods of reducing errors in case of PT. 4
c) What is phase angle error and creeping error in induction type energy meter ?
How they can be compensated ? 6
——————
S.E. (Electrical) (Semester – I) Examination, 2011
ELECTRICAL MEASUREMENTS
(2003 Course)
Time : 3 Hours Max. Marks : 100
Instructions: 1) Answers to the two Sections should be written in separate
books.
2) Neat diagrams must be drawn wherever necessary.
3) Black figures to the right indicate full marks.
4) Use of logarithmic tables, slide rule, Mollier Charts, electronic
pocket calculator and steam tables is allowed.
5) Assume suitable data, if necessary.
6) Attempt Que. No. 1 or 2, Que. No. 3 or 4, Que. No. 5 or 6.
Que. No. 7 or 8, Que. No. 9 or 10, Que. No. 11 or 12.
SECTION – I
1. a) With a neat sketch explain the method of absolute measurement of current by
Rayleigh’s current balance. 8
b) Explain the terms : 8
i) Hysteresis. ii) Threshold.
iii) Dead band. iv) Accuracy.
OR
2. a) In a survey of 15 owners of a certain model of a car, the following figures are
for average petrol consumption where reported : 25.5, 30.3, 31.1, 29.6, 32.4,
39.4, 28.9, 30.0, 33.3, 31.4, 29.5, 30.5, 31.7, 33.0, 29.2.
Calculate :
i) Mean value ii) Median value
iii) Standard deviation iv) Average deviation
v) Variance vi) Probable error. 10
b) Explain parallax error and error due to inherent shortcomings of the instruments.
How to minimise them ? 6
3. a) Discuss briefly the following methods for measurement of medium resistance :
i) Ammeter - voltmeter method
ii) Substitution method
iii) Wheatstone bridge method. 8
b) A length of cable is used for testing its insulation resistance by loss of charge
method. An electrostatic voltmeter of infinite resistance is connected between
the cable conductor and earth, forming a joint capacitance of 600 pf. It is
observed that after charging the voltage falls from 250 V to 92 V in 1 min.
Calculate insulation resistance of the cable. 4
c) Classify the resistances from measurement point of view and give 2 examples
of each. 4
OR
4. a) Explain the effect of voltage, frequency and form factor of waveform on iron
losses. 6
b) What are the difficulties in magnetic testing of bar specimen in comparison
with ring specimen ? What is permeameter ? With a neat diagram describe
Hopkinson permeameter. 10
5. a) Write a short note on various sources and null detectors used for AC bridges. 6
b) With a neat diagram explain the working of vibrating reed type frequency
meter. 6
c) Write short note on Dynamometer type single phase power factor meter. 6
OR
6. a) With a neat diagram explain the use of Maxwell’s inductance -capacitance
bridge for measurement of unknown inductance. Derive an expression for
unknown inductance. Why is this bridge not suitable for large Q coils ? 9
b) The four impedances of an ac bridge are :
Z1 = 400 ∠50 ° Ω , Z2 = 200 ∠40° Ω, Z3 = 800 ∠ − 50 Ω , Z4 = 400 ∠20°Ω .
Find out whether the bridge is balanced under these conditions. 6
c) Explain the term sliding balance for achieving balance point quickly in AC
bridges. 3
SECTION – II
7. a) Derive the torque equation for D’ Arsonal galvanometer with usual notations.
Explain the intrinsic constants involved and write the equation of motion to
examine dynamic behaviour of galvanometer. 10
b) State and explain methods of producing damping torque in indicating type
instruments. What are the effect of over damping and under damping ? 8
OR
8. a) With neat sketch explain the construction and working of attraction type moving
iron instrument. State its advantages and disadvantages. 8
b) The coil of moving coil voltmeter is 40 mm× 30 mm wide and has 100 turns
wound on it. The control spring exerts a torque of 0.25×10–3 Nm when the
deflection is 50 divisions on scale. If the flux density of magnetic field in the
airgap is 1 Wb/m2, estimate the resistance that must be put in series with coil
to give 1 volt/div. Resistance of voltmeter is 10,000 ohm. 6
c) Explain the type of suspensions provided to the galvanometer. How is damping
torque produced in the galvanometer ? 4
9. a) Derive the torque equation of single phase dynamometer type wattmeter with
usual notations. 6
b) Compare dynanometer type wattmeter and induction type wattmeter. 4
c) With a neat circuit diagram and phasor diagram explain two wattmeter method
for measuring active power in three phase star connected (R+L) balanced
load. 6
OR
10. a) With neat diagram explain construction of low power factor type wattmeter.
State its application. 6
b) A wattmeter reads 5 kW when current coil is connected in R phase and pressure
coil is connected between R and N for a balanced symmetrical three phase
system suppling three phase inductive load of 25 Amp at 400 volts. What will
be the reading of wattmeter if connections of current coil are unchanged and
pressure coil is now connected between B and Y phases ? Find total reactive
power for this case. 4
c) With a neat circuit diagram and phasor diagram explain one wattmeter method
for measurement of reactive power in three phase star connected load. 6
11. a) What are different systems in induction type energymeter ? Describe each in
brief. 6
b) Derive the expression for ratio error for CT with usual notations. 6
c) What is difference in CT and ordinary transformer ? 4
OR
12. a) With a neat circuit diagram explain CT, PT operated energy meter. 6
b) What are the methods of reducing errors in case of PT. 4
c) What is phase angle error and creeping error in induction type energy meter ?
How they can be compensated ? 6
——————
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