Instrument Transformers MCQ

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Instrument Transformers MCQ

Instrument Transformers MCQ, Multiple Choice Questions on Instrument Transformers, Engineering MCQ, Instrumentation MCQ, Measurement MCQ, Instrument Transformers MCQ

Objective Type Questions

Q.1. The advantages of Instrument transformers are

  • The readings of instruments used in conjunction with them do not depend upon their resistance, inductance etc.
  • The ratings of instrument transformers have been standardized and the rating of instruments used in conjunction used with them also get standardized. Therefore, there is reduction of cost and ease in replacements.
  • The metering circuit is electrically isolated from the power circuit thereby providing safety to operating personnel.
  • all of the above.

Answer: all of the above

Q.2. The disadvantages of shunts for use at high currents are

  • it is difficult to achieve good accuracy with shunts
  • power consumption of the shunts is large
  • the metering circuit is not electrically isolated from the power circuit
  • all of the above

Answer: all of the above

Q.3. The disadvantages of using multipliers with voltmeters at high voltages are:

  • The power consumption of multipliers becomes large at large voltages.
  • The multipliers at high voltages have to be shielded in order to prevent capacitive currents.
  • The metering circuit is not electrically from the power circuit.
  • all of the above

Answer: all of the above

Q.4. The nominal ratio of a current transformer is:

  • primary winding current/secondary winding current
  • rated primary winding current/rated secondary winding current
  • number of secondary winding turns/number of primary winding turns
  • all of the above

Answer: rated primary winding current/rated secondary winding current

Q.5. The transformation ratio in the case of a potential transformer is defined as ratio of:

  • primary winding voltage/secondary winding voltage
  • rated primary winding voltage/rated secondary winding voltage
  • number of turns of primary winding/number of turns of secondary winding
  • all of the above

Answer: primary winding voltage/secondary winding voltage

Q.6. The burden of current transformers is expressed in terms of:

  • secondary winding current
  • VA rating of transformer
  • voltage, current and power factor of secondary winding circuit
  • none of the above

Answer: VA rating of transformer

Cathode Ray Oscilloscope (CRO) MCQ

Q.7. A current transformer has a rating of 100/5 A. Its magnetizing and loss components of the exciting current are 1 A and 0.6 A respectively and secondary winding burden is purely resistive, its transformation ratio at rated current is:

  • 20.12
  • 20.2
  • 200.2
  • none of the above

Answer: 20.12

Q.8. A current transformer has a rating of 1000/5 A. Its magnetizing current and loss component of exciting current are 10 A and 6 A respectively. The phase angle between secondary winding induced voltage and current is 30°. The phase angle error of the transformer at rated current is:

  • 0.65°
  • 0.305°
  • 0.496°
  • none of the these

Answer: 0.305°

Q.9. The errors in current transformers can be reduced by designing them with:

  • high permeability and low loss core materials, avoiding any joints in the core and also keeping the flux density to a low value
  • using primary and secondary windings as close to each other as possible
  • using large cross-sections for both primary and secondary winding conductors
  • all of the above

Answer: high permeability and low loss core materials, avoiding any joints in the core  ….

Q.10. The current in the primary winding of a current transformer depends upon:

  • burden of the secondary winding of transformer
  • load connected to the system in which the C.T. is installed
  • both burden of the transformer secondary winding and load connected to the system
  • none of the above

Answer: load connected to the system in which the C.T. is installed

Q.11. Turns compensation is used in current transformers primarily for reduction of:

  • Phase angle error
  • both ratio and phase angle errors
  • ratio error, reduction in phase angle error is incidental
  • none of the above

Answer: ratio error, reduction in phase angle error is incidental

Q.12. A short-circuiting link is provided on the secondary side of a current transformer because:

  • when the secondary winding of the C.T. is short-circuited by the link with the primary winding energized, a very high current flows on the primary side
  • when the secondary winding of the C.T. is short circuited by the link with the primary winding energized, it is possible to make any adjustments in the secondary winding circuit like replacing a faulty ammeter.
  • when the short-circuiting link is opened with the secondary winding open-circuited, the current on the primary side falls to almost zero.
  • all of the above

Answer: when the secondary winding of the C.T. is short circuited by the link with the primary winding energized, it is possible to make any adjustments in the secondary winding circuit like replacing a faulty ammeter.

Q.13. When the secondary winding of a current transformer is open-circuited with the primary winding energized

  • the whole of the primary current produces large value of flux in the core (limited only saturation) thereby producing a large voltage in the secondary winding.
  • the large voltage may act as safety hazard for the operators and may even rupture the insulation
  • when the large magnetizing force is taken off it leaves a large value of residual magnetism.
  • all of the above

Answer: all of the above

Q.14. Clamp on meters are used because

  • with their use it is possible to measure to current flowing a line without breaking the circuit.
  • their accuracy is high
  • it is not possible to measure voltage without them
  • all of the above

Answer: with their use, it is possible to measure the current flowing a line without breaking the circuit.

Q.15. When the secondary winding of a potential transformer is suddenly open-circuited with primary winding excited:

  • large voltages are produced in the secondary winding may be a safety hazard to operating personnel.
  • the large voltages so produced may rupture the insulation.
  • the primary winding draws only the no load current
  • none of the above

Answer: the primary winding draws only the no-load current

Q.16. The ratio and phase angle errors in potential transformers may be reduced by

  • increasing the exciting current
  • increasing the resistance and leakage reactance in the transformer
  • by not employing turns compensation
  • none of the above

Answer: none of the above

Q.17. Capacitive potential transformers are used

  • for primary winding phase voltages above 100 kV
  • for keeping the value of transformation ratio constant irrespective of the burden by Making certain adjustment
  • because they are cheaper than the electromagnetic transformers above a certain voltage range
  • all of the above

Answer: all of the above

Q.18. The size of potential transformers:

  • is the same as that of power transformers of the same VA rating
  • is much greater than that of power transformers of the same VA rating because they are designed for low ratio and phase angle errors which require large sized cores and winding conductors
  • is smaller that that of power transformers of the same VA rating
  • none of the above

Answer: is much greater than that of power transformers of the same VA rating because ……

Q.19. The ratio of transformation In the case of potential transformers:

  •  increases with increase in power factor of secondary burden
  • remains constant irrespective of the power factor of secondary burden
  • decreases with increase in power factor of secondary burden
  • none of the above

Answer: decreases with increase in power factor of secondary burden

Q.20. In the case of potential transformers

  • the phase angle error is always positive
  • the phase angle error is always negative
  • the phase angle error is usually zero
  • the phase angle error is positive when the secondary winding voltage reversed leads the primary winding voltage and is negative when the secondary winding voltage reversed lags behind the primary winding voltage.

Answer: the phase angle error is positive when the secondary winding ……

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