50 Important Multiple choice Question Of Transformer – 2020

50 Important Multiple choice questions Of Transformer – 2020 | Objective Type Question Of TRANSFORMER

Qus1.  The secondary winding of which of the following transformers is always kept closed?

  1. Current transformer
  2. Voltage transformer
  3. Power transformer
  4. Step down transformer

Answer.1. Current Transformer

Explanation. If the current transformer secondary is not shorted when unused and kept open then it can develop a very high voltage across secondary which may damage transformer insulation.


Qus2.  If the supply frequency of a transformer increases, the secondary output voltage of the transformer

  1. Increase
  2. Decrease
  3. Remain the same
  4. Any of the above

Answer.3. Remain Same

Explanation: The transformer is a static device that changes Voltage from one side of its coil to the other at the constant frequency.
Frequency does not change because of the working principle of the transformer-based on Mutual induction which happens without any change in frequency.


Qus3. Power transformers are designed to have maximum efficiency at

  1. Full load
  2. 50% load
  3. 80% load
  4. no load

Answer.1. Full load

Explanation: Power transformer are used for transmission as a step-up device hence they are not directly connected to consumer therefore, load fluctuation is very less. So the power transformer can operate on full load.


Qus4. The open-circuit test in a transformer is used to measure

  1. Copper loss
  2. Winding loss
  3. Total loss
  4. Core loss

Answer 4. Core loss

Explanation: As the transformer is open-circuited there is no output. So the copper loss is neglected as the no-load current is very less.


Qus5. The leakage flux in a transformer depends upon the value of

  1. Frequency
  2. Mutual Flux
  3. Load current
  4. Applied Voltage

Answer 3. Load Current


  • In a Transformer, Core flux is the difference of primary flux and Secondary flux which are opposite to each other in direction.
  • So, some of the primary flux passes through the core and remaining becomes leakage flux (Because Secondary flux forces it to get out of the core).
  • The same is the case with Secondary flux. Now, flux is directly proportional to Voltage and Current.
  • When Current increases due to increased load (and voltage remains the same).Then both primary and secondary flux increase. Because both of them increases, so their difference remains the same. And all remaining flux is forced out. Hence leakage flux increases with current, but Core flux remains constant.


Qus6. Lamination of the transformer core is made of

  1. Cast Iron
  2. Silicon Steel
  3. Aluminum
  4. Cast Steel

Answer 2. Silicon Steel


Silicon steels are used for electrical transformer cores and cores of other electrical devices for the following reasons:-

  1. Low hysteresis loss.
  2. High permeability.
  3. Virtually eliminated aging.
  4. High resistance.


Qus7.  Breather is provided in a transformer to

  1. Absorb moisture of air during breathing
  2. provide cold air in the transformer
  3. The filter of transformer oil
  4. None of above

Answer 1. Absorb moisture of air during breathing.

Explanation: The primary function of the breather is to absorb air moisture during breathing.


Qus8. Which of the following losses varies with the load in the transformer?

  1. Core loss
  2. Copper loss
  3. Both core & copper loss
  4. None of the above

Answer 2. Copper Loss


  • Copper loss is due to ohmic resistance of the transformer windings.
  • The copper loss for the primary winding is I12 × R1 and for secondary winding is I22 × R2.
  • Where I1 and I2 are current in primary and secondary winding respectively.
  • R1 and R2 are the resistances of primary and secondary winding respectively.
  • It is clear that Cu loss is proportional to the square of the current, and current depends on the load. Hence copper loss in the transformer varies with the load.


Qus9. A transformer transform

  1. Current
  2. Voltage & current
  3. Frequency
  4. Voltage

Answer 2. Voltage  & Current


A transformer is a static device that is used to convert the voltage or current to a higher (step-up) or lower (step down) level.

The Distribution Transformer, Auto Transformer, and Tap changing Transformer basically belong to the family of Power Transformer with respective unique features.

In an Instrument Transformer, voltage or current on one side of the transformer, comparatively high (therefore not suitable for direct measurement), is scaled down to voltage or current to levels that is convenient for measurement with suitable instrumentation. Accordingly, the two types of Instrument Transformers are the Current Transformer and the Potential Transformer. Some applications may call for constant current (as in welding) or constant voltage. Such transformers am called Constant Current and Constant Voltage Transformers.


Qus10.  Transformer core are laminated in order to

  1. reduce hysteresis loss
  2. reduce hysteresis & eddy current loss
  3. minimize eddy current loss
  4. Copper loss

Answer 3. Minimize Eddy current loss


  • In a transformer, the eddy current loss is proportional to the square of the diameter of the core.
  • Larger the diameter, more the eddy current loss.
  • Hence the transformer core is laminated so that the net effective diameter of the transformer core reduces and thus eddy current loss can be minimized.

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