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

PRACTICE IT NOW TO SHARPEN YOUR CONCEPT AND KNOWLEDGE

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 synchroscopeF2  = frequency of incoming machineF1  = frequency of busbars At equilibriumΦ = ±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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