This set of Electrical Measurements Questions and Answers for Experienced people focuses on “Electronic Energy Meter, Adjustments in Single Phase Energy meters”.
1. An electronic energy meter makes use of ___________
a) IC
b) Transformer
c) CRO
d) Multimeter
View Answer
Explanation: Basically, integrated circuits also known as IC’s are used for the operation of an electronic energy meter.
2. Measurement of energy involves _________
a) inductance and capacitance measurement
b) power consumption and time duration
c) resistance measurement and voltage drop
d) current consumption and voltage drop
View Answer
Explanation: An electronic energy meter is used in two stages. Energy measurement basically involves the measurement of power and the time duration. In the first stage, it is used as a wattmeter while in the second stage it is used monitoring the power consumed in a time interval.
3. Average power is _________
a) product of voltage and current
b) product of average current and voltage
c) product of instantaneous voltage and current
d) product of absolute voltage and current
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Explanation: The average power is computed as the product of the instantaneous voltage across the load and the instantaneous current flowing through the load. A scaling device is used to bring the supply voltage to a proper level.
4. What is the role of a multiplier?
a) it multiplies the voltage and current
b) divides the alternating voltage and current
c) supplies instantaneous voltage and current
d) multiplies alternating voltage and current
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Explanation: A multiplier basically performs the multiplication of the alternating voltage and the current. Multiplier also provides the current in the form of instantaneous power to a voltage controlled oscillator.
5. Frequency of oscillation in an electronic energy meter depends on __________
a) output current of multiplier
b) output voltage of multiplier
c) output power of multiplier
d) input resistance of multiplier
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Explanation: Oscillator used in an energy meter generates a square wave. The frequency of the this depends on the output current flowing through the multiplier.
6. Analog signal is converted _________
a) into oscillations
b) into digital
c) into pulses
d) into current
View Answer
Explanation: The analog signal obtained in an electronic energy meter is converted into digital by making use of a digital circuit. By making use of a seven-segment display, energy is mentioned in watt-hours.
7. An electronic energy meter is advantageous compared to conventional ones.
a) True
b) False
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Explanation: An electronic energy meter does not have frictional losses, creeping is not needed irrespective of the nature of the load such as low load, full load power factor, etc and the accuracy in the reading is of the order of ±1%.
8. Energy meter can be directly used in measurement.
a) True
b) False
View Answer
Explanation: Adjustments need to be made in an energy meter before it is used for the measurement of energy. This is done in order to keep the errors due to measurement within allowable limits of ±5 %.
9. Creeping in an energy meter can be found using _________
a) creep adjustment
b) preliminary light load adjustment
c) full load u.p.f adjustment
d) light load adjustment
View Answer
Explanation: Energy meter can be tested for creeping using preliminary light load adjustment. Disc holes are so positioned that they aren’t under the poles of a series magnet.
10. Preliminary light load adjustment involves _________
a) applying rated voltage across current coil
b) making use of a light load
c) applying rated voltage across pressure coil
d) adjusting the light load
View Answer
Explanation: Rated voltage is applied across the pressure coil. No current flows through the current coil. Till the disc stops rotating, light load device or equipment is adjusted continuously.
11. Creep adjustment involves _________
a) adjusting the creep
b) exciting the current coil
c) adjusting the turns ratio
d) exciting the pressure coil
View Answer
Explanation: The pressure coil is excited by 110% with respect to the rated voltage. Load current is zero. The meter will not creep provided the light load is adjusted correctly.
12. Light load adjustment involves _________
a) applying rated voltage across the pressure coil
b) adjusting a light load
c) applying rated current across the transformer
d) applying rated voltage across the current coil
View Answer
Explanation: Disc rotation is adjusted in such a way that correct speed is maintained. The pressure coil is supplied with the rated voltage and the current coil is provided with only about 5 % of the full load at u.p.f.
13. Low power factor adjustment involves _________
a) adjusting the power factor at lower loads
b) applying rated voltage to pressure coil and a p.f. of 0.5 for current coil
c) only applying rated voltage to pressure coil
d) only a p.f. of 0.5 for the current coil
View Answer
Explanation: Rated voltage is applied to the pressure coil. The current coil is provided with a current at 0.5 p.f. lagging. Till the disc rotates at correct speed, lag device is adjusted.
14. Full load u.p.f adjustment involves _________
a) adjusting the loads at unity power factor
b) applying rated voltage to pressure coil and a p.f. of unity for current coil
c) only applying rated voltage to pressure coil
d) only a p.f. of unity for the current coil
View Answer
Explanation: Rated voltage is applied to the pressure coil. The current coil is provided with a current at unity p.f. Errors are kept minimum and the position of the brake magnet is so adjusted that disc rotates at the correct speed.
Sanfoundry Global Education & Learning Series – Electrical Measurements.
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