This Portion of Electrical andElectronic Measurements and Measuring instruments contains Measuring of Phase and Frequency MCQs (Multiple Choice Questions and Answers) / Objective Type Questions and Answers.

This Section covers below lists of topics.

  1. Power Factor Meter
  2. Frequency Meter
  3. Synchroscopes
  4. Phase Sequence Indicators

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1. The power factor in a single phase circuit is cosΦ = P / VI, where P is the power read by a wattmeter, V is the voltage read by voltmeter and I is the current read by an ammeter. All the three instruments have a limiting error of ±1%. The power factor of the circuits can be known if only one meter i.e an electrodynamometer type power factor having a limiting error ±1% used. The preferred method is to use single instrument like a power factor rather than using 3 instruments because the error with using wattmeter, voltmeter and ammeter is

  • ±2%
  • ±3%
  • ±1%
  • -1%

2. The controlling torque in single phase power factor meter is provided by :

  • Spring control
  • Gravity control
  • Stiffness of suspension
  • None of the above.

3. There will be serious errors, if power factor of non-sinosoidal waveform is measured by electrodynamometer power factor meters. This is true of :

  • Only single phase meters
  • Only three phase meters
  • Both single and three phase meters
  • None of the above.

4. In a reed type frequency meters all the reeds :

  • Have the same natural frequency
  • Have different natural frequency
  • Have different natural frequency but the difference in natural frequencies of adjacent reeds is ±0.5Hz.
  • None of the above.

5. A 53 Hz reeds type frequency meter is polarized with d.c. the new range of frequency meter is :

  • 106 Hz
  • 26.5 Hz
  • 53 Hz
  • None of the above.

6. For a 3 phase, moving iron synchroscope F2  = frequency of incoming machine F1  = frequency of busbars   At equilibrium Φ = ±2πf’t + ɑ ; where f’ =  F2  - F1. If f’ is positive

  • The incoming machine is faster
  • The incoming machine is slower
  • The incoming machine can be synchronized to the busbars
  • None of the above.

7. An electrodynamometers type of instrument is used in Weston type synchroscope while synchronizing an incoming machine to busbars

  • For checking the power factor of the two circuits
  • For checking the voltages of the two circuits
  • For checking whether incoming machine is fast or slow
  • For checking phase sequence of the two circuits.

8. An alternator is being synchronized to the  busbars whose frequency is 50 Hz. The bulbs of the synchroscope  flickers at a frequency of 10 Hz. The frequency of the alternator is :

  • 60 Hz
  • 40Hz
  • 60Hz or 40 Hz
  • None of the above.

9. A phase sequence indicator rotates clockwise for phase sequence of RYB. If the phase sequence is changed to BRY it will rotate

  • Anticlockwise
  • Clockwise
  • Clockwise or anticlockwise
  • None of the above.

10. In a static type phase sequence indicator which uses two identical lamp of pure resistances in the circuit of phase R and Y and inductor in phase B having inductive reactance = resistance of bulb with circuit being connected in star. The reactance is equal to the bulb resistance. If bulb connected to phase R glows brightly and lamp connected to phase Y glows dimly, the phase sequence is :

  • RBY
  • RYB
  • BRY
  • None of the above.

 
 

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