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Electrical Measurements Interview Questions and Answers for freshers on “Induction Type Single Phase Energy Meter”.
1. Induction type instruments are used for ____________
a) A.C. measurements
b) D.C. measurements
c) Resistance measurements
d) Voltage measurements
Answer: a
Clarification: A.C. measurements are made using Induction type instruments. Induction type energy meter is used to measure the energy that is consumed in A.C. circuits only.
2. Driving system in an induction type single phase energy meter consists of _________
a) one magnet
b) two electromagnets
c) five electromagnets
d) ten magnets
Answer: b
Clarification: In an induction type single phase energy meter, the driving system consists of two electromagnets, namely series electromagnet and shunt electromagnet.
3. Series electromagnet consists of _________
a) L shaped laminations
b) T shaped laminations
c) U shaped laminations
d) Y shaped laminations
Answer: c
Clarification: The driving system of an induction type single phase energy meter consists of U shaped laminations made of silicon steel. The laminations are insulated from one another and pressed to form the core.
4. Shunt magnet consists of _________
a) N shaped laminations
b) E shaped laminations
c) S shaped laminations
d) M shaped laminations
Answer: d
Clarification: The driving system of an induction type single phase energy meter consists of M shaped laminations made of silicon steel. The laminations are insulated from one another and pressed to form the core of the shunt magnet.
5. Shunt magnet has _________
a) large turns of wire
b) small turns of wire
c) medium turns of wire
d) no turns or wires
Answer: a
Clarification: The central limb of the shunt magnet has a large number of turns. It connected across the supply and is known as the voltage coil or potential coil. It is excited using a current value that is proportional to the applied voltage.
6. Moving system of the induction type single phase energy meter has _________
a) heavy aluminium disc
b) light aluminium disc
c) medium aluminium disc
d) no aluminium disc
Answer: b
Clarification: Aluminium disc is provided in the air gap between the series and shunt magnets. Jewel bearings support the spindle. Hence the moving system in an induction type single phase energy meter consists of light aluminium disc.
7. Braking system consists of _________
a) bar magnet
b) temporary magnet
c) permanent magnet
d) super magnet
Answer: c
Clarification: In an induction type single phase energy meter, edge of the aluminium disc consists of a permanent magnet also known as a brake magnet. E.m.f is induced in the aluminium disc when it rotates as a result of the magnetic field produced by the brake magnet.
8. What is the effect of eddy currents in the aluminium disc?
a) varies by a factor of twice the disc length
b) independent of the disc speed
c) varies by a factor of four times the disc size
d) proportional to the disc speed
Answer: d
Clarification: The eddy currents induced in an aluminium disc vary in proportion to the speed of the disc. As a result the braking torque exerted on the disc varies in proportion to the speed.
9. An energy meter produces a flux of ∅ when connected to a supply V.
a) True
b) False
Answer: a
Clarification: Flux ∅ is produced in an energy meter when it is connected to a supply voltage of magnitude V volts. Since the potential coil is highly inductive, current and flux lag the voltage by 90°.