Q.1
A coil (which can be modelled as a series RL circuit) has been designed for high Q performance. The voltage is rated at and a specified frequency. If the frequency of operation is increasedtimes and the coil is operated at the same rated voltage. The new value of Q factor and the active power P will be?
  • a) P is doubled and Q is halved
  • b) P is halved and Q is doubled
  • c) P remains constant and Q is doubled
  • d) P decreases 100 times and Q is increased 10 times
Q.2
Two watt-meters, which are connected to measure the total power on a three-phase system supplying a balanced load, read 20.5 kW and -3.5 kW respectively. The total power is?
  • a) 13.0 kW
  • b) 17 kW
  • c) 15 kW
  • d) 19 kW
Q.3
A circuit is used to measure the power consumed by the load. The current coil and the voltage coil of the watt-meter have 0.Ω andΩ resistances respectively. The measured power (as compared to the load power) will be?
  • a) 0.4 % less
  • b) 0.2 % less
  • c) 0.2 % more
  • d) 0.4 % more
Q.4
A sampling watt-meter is used to measure the average power of a load. The peak to peak voltage of the square wave isV and the current is a triangular wave ofp-p. The reading in watt will be?
  • a) Zero
  • b) 25 W
  • c) 50 W
  • d) 100 W
Q.5
The line to line input voltage to the 3-phase,Hz, AC circuit, isV rms. Assuming that the phase sequence is RYB; the watt-meters would read?
  • a) W₁ = 886 W and W₂ = 886 W
  • b) W₁ = 500 W and W₂ = 500 W
  • c) W₁ = 0 W and W₂ = 1000 W
  • d) W₁ = 250 W and W₂ = 750 W
Q.6
The meter constant of a single-phase,V induction watt-meter isrev/kW-h. The speed of the meter disc for a current ofA at 0.8 power factor lagging will be?
  • a) 30.3 rpm
  • b) 16 rpm
  • c) 12 rpm
  • d) 33.1 rpm
Q.7
In the Two wattmeter method of measuring power in a balanced three-phase circuit, one wattmeter shows zero and the other positive maximum. The load power factor is?
  • a) 0
  • b) 0.5
  • c) 0.866
  • d) 1.0
Q.8
Two watt-meters connected to measure the total power on a three-phase system supplying a balanced load reads 10.5 kW and -2.5 kW respectively. Then the total power factor is?
  • a) 0.334
  • b) 0.684
  • c) 0.52
  • d) 0.334
Q.9
A 3-phase,V motor, the load having 0.6 power factor uses two watt-meter to measure the power. If the power measured bekW, then the reading of each instrument will be?
  • a) P₁ = 35 kW, P₂ = 10 kW
  • b) P₁ = 47.25 kW, P₂ = -2.25 kW
  • c) P₁ = 39.82 kW, P₂ = 5.179 kW
  • d) P₁ = 45 kW, P₂ = 0 kW
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