Energy Meter MCQs

31. Consider the following statements associated with an energy meter

1. It is an integrating type instrument.
2. It is an induction type instrument.
3. It uses a permanent magnet for rotation of the aluminium disc.
4. It employs a high control torque.

Which of these statements are correct?

1. 1 and 2 only
2. 1,2, 3 and 4
3. 3 and 4 only
4. 2 and 3 only

32. The speed of the meter disc on full load is kept the lowest possible in order to

1. reduce eddy current loss
2. reduce friction error
3. reduce self-braking torque
4. all of the above

33. The braking torque provided by a permanent magnet in a single-phase induction type energy meter can be varied by

1. changing the position of the magnetic shunt provided for this purpose
2. changing the position of brake magnet with respect to the meter disc
3. none of the above
4. both (a) and (b)

34. Consider the following statements:

A phantom’ load used while testing a high capacity energy meter

1. consists of inductances and capacitances so that there is no energy loss during testing.
2. saves energy during testing because its value changes very rapidly from the highest to the lowest, thus enabling quick measurement.
3. involves supplying the voltage circuit with the required voltage and the current circuit from a separate low voltage supply.

of these statements

1. 1, 2 and 3 are correct
2. 1 and 2 are correct
3. 1 and 3 are correct
4. 2 and 3 are correct

35. A dc A-h meter is rated for 15 A, 250 V. The meter constant is 14.4 A-s/rev. The meter constant at the rated voltage may be expressed as

1. 3750 rev/kWh
2. 3600 rev/kWh
3. 1000 rev/kWh
4. 960 rev/kWh

36. A single-phase energy meter is operating on 230 V, 50 Hz supply with a load of 20 A for 2 hours at unity power factor. The meter makes 1,380 revolutions in that period. The meter constant is

1. 695 rev/kWh
2. 150 rev/kWh
3. 0.15 rev/kWh
4. 1/150 rev/kWh

37. If an energy meter disc makes 10 revolutions in 100 seconds when a load of 450 W is connected to it, the meter constant (in rev/kWh) is

1. 5000
2. 1000
3. 1600
4. 800

38. A 230 V, 10A single-phase energy meter makes 90 revolutions in 3 minutes at half load, rated voltage and unity p.f. If the meter constant is 1,800 revolutions per kWh, then its error at the half load will be

1. 13.04% fast
2. 13.04% slow
3. 15% slow
4. 15% fast

39. An energy meter having a meter constant of 1,200 rev per kWh is found to make 5 revolutions in 75 seconds. The load power is

1. 500 W
2. 100 W
3. 200 W
4. 1,000 W

40. The disc of a house service energy meter of 230 V, 1-phase, 5 A, 2400 rev per kWh creeps at 1 rev per min. The creep error (in percent) of full load unity, pf is

1. $+\frac{60}{2400}\times 100$
2. $-\frac{60}{2400}\times 100$
3. $+\frac{60}{115\times 2400}\times 100$
4. $-\frac{60}{115\times 2400}\times 100$