# TRANSFORMER PART TWO

**Instructions:** Click the answer button to see the correct answer.

- Which of the following statements is/are correct statements?
- For ideal transformer efficiency is 100%
- both
- For ideal transformer voltage regulation is 100%
- none of these

Answera

- Scott connections are used for
- single phase to three phase transformation
- three phase to two phase transformation
- any of the above
- three phase to single phase transformation

Answerb

- In which transformer, the tertiary winding is used?
- Star – star
- Delta – star
- Delta – delta
- Star – delta

Answera

- For successful parallel operation of two single phase transformers, the most essential condition is that their
- polarities are properly connected
- percentage impedance are equal
- turn- ratios are exactly equal
- KVA ratings are equal

Answera

- A delta/star transformer is connected in parallel to a star/delta transformer. The turn ratio former is x times latter, the x is
- √3
- 3
- 1/3
- 1/√3

Answerb

- Two transformers operating in parallel will share the load depending on their
- per unit impedance
- ratings
- efficiency
- leakage reactance

Answera

- A 100/10, 50 VA double winding transformer is converted to 100/110 V auto transformer. The rating of auto transformer is
- 550 VA
- 100 VA
- 110 VA
- 500 VA

Answera

- Tappings of a transformer are provided
- at the middle of hv side
- at the phase end of hv side
- at the neutral side end of hv side
- at the phase end of lv side

Answera

- In an auto-transformer, power is transferred through
- None of these
- Both
- Induction process only
- Conduction process only

Answerb

- It is an advisable to use auto transformer if the transformation ratio is
- 0.5
- Greater than 1
- 0.25
- near to 1

Answerd

- In auto transformer if the turn ratio is K, What is the power transferred inductively
- (1-K) × input power
- none of these
- both
- K × input power

Answera

- A 10KVA auto transformer, turn ratio is 0.4. Find the power transferred inductively?
- 4 KVA
- 10 KVA
- 6 KVA
- 0 KVA

Answerc

- A 20KVA auto transformer, turn ratio is 0.8. Find the power transferred conductively?
- 4KVA
- 16KVA
- 20KVA
- 0KVA

Answerb

- In an auto transformer, for what value of turn ratio, power transferred by inductively and conductively are same?
- any of the
- 0
- 0.5
- 1

Answerc

- The

total core loss of a 400 V, 50 Hz transformer is 2400W, when it is

supplied by 200 V, 25 Hz loss is 800W. Calculate eddy current loss and

hysteresis loss?- 1600W, 800W
- 800W, 1600W
- 1400W, 1000W
- 1000W , 1400W

Answera

- In a transformer which of the following losses are zero ?
- rotational loss
- iron loss
- copper loss
- all of these

Answera

- When maximum flux density is constant, the eddy current losses are proportional to
- f²
- V
- f
- V²

Answera

- When flux density is constant in a transformer, hysteresis loss varies as
- V²
- f
- f²
- V

Answerb

- In a transformer maximum flux density is not constant, the eddy current loss varies as
- V²
- f
- f²
- V

Answera

- The working principle of transformer depends on
- Coulombs law.
- Amperes law.
- Newtons law.
- Faradays law of electromagnetic induction.

Answerd

- Addition of 0.3 % to 4.5 % silicon to iron
- increases the hysteresis loss.
- increases the electrical resistivity of iron.
- reduces the saturation magnetization.
- none of these

Answerb

- A laminated iron core has reduced eddy current losses because
- more wire can be used with less dc resistance in coil.
- the magnetic flux is concentrated i
- the lamination are insulated from each other.
- the lamination are stacked vertically.

Answerc

- The two windings of a transformer have an inductor of 2 H each. If mutual inductor between them is also 2 H, then
- none of these.
- transformer is an ideal transformer.
- it is a perfect transformer.
- turns ratio of the transformer is also two.

Answerc

- Lamination of core are generally made of
- silicon steel.
- stainless steel.
- case iron.
- carbon.

Answera

- A single-phase transformer has its maximum efficiency at 60 percent of full load. At full load copper loss will be
- more than core loss.
- equal to core loss.
- zero.
- less than core loss.

Answera

- In a core type transformer
- LV winding is placed nearer to the core limb.
- HV and LV windings are placed in different core limbs.
- HV winding is placed nearer to the core limb.
- any of the LV or HV can be placed nearer to the core limb.

Answera

- The primary and secondary windings of a transformer are
- electrically linked.
- mechanically linked.
- conductively linked.
- inductively linked.

Answerd

- At what power factor, the voltage regulation of a transformer can be zero ?
- Lagging power factor
- Zero power factor.
- Unity power factor.
- Leading power factor.

Answera

- In a three phase star – delta transformer, what is the angle difference between primary and secondary phase voltages?
- Delta side lags by -30°.
- Delta side leads by 30°.
- Star side leads by 30°.
- Star side lags by -30°.

Answerb

- What will be the eddy current loss if the supply frequency of a transformer becomes double?
- Remains same.
- Doubled.
- Four times.
- Eight times.

Answera

- The efficiency of a transformer is mainly dependent on
- dielectric losses.
- stray losses.
- copper losses.
- core losses.

Answerd

- Transformers operating in parallel will share the load depending upon their
- efficiency.
- leakage reactance.
- rating.
- percentage impedance

Answerc

- No load primary current in a transformer
- lags behind applied voltage somewhat less than 90Ã
- lags behind applied voltage by exactly 90Ã
- leads the applied voltage somewhat less than 90Ã
- leads the applied voltage by exactly 90Ã

Answera

- Which of the following is minimized by laminating the core of a transformer?
- Eddy current loss.
- Hysteresis loss.
- Copper loss.
- Stray loss.

Answera

- Breather is provided in a transformer to
- absorb moisture of air during breathing.
- filter the transformer oil.
- absorb moisture from air entering in transformer.
- provide cold air in transformer.

Answera

- ron loss in a transformer mainly occurs in
- transformer insulating oil.
- steel core in transformer.
- winding of transformer.
- iron made tank of transformer.

Answerb

- Short

circuit test is performed on a transformer with a certain impressed

voltage at rated frequency. If the short circuit test is now performed

with the same magnitude of impressed voltage, but at frequency higher

than the rated frequency then- The magnetude of current will increase, but power factor will decrease.
- The magnitude of current will decrease but the power factor will increase.
- The magnitude will both increase.
- The magnitude of circuit as well as the power factor will decrease.

Answerd

- In a transformer the magnetic coupling between the primary and secondary winding can be increased by
- increasing the number of turns.
- using soft material for winding.
- using the magnetic core of low reluctance.
- using transformer oil of better quality.

Answerc

- The short circuit test on a transformer is conducted to obtain
- hysteresis loss.
- eddy current loss.
- copper losses.
- core loses only.

Answerc

- An

auto transformer having a transformation ratio of 0.8 supplies a load

pf 10 KW. The power transfered inductively from the primary to secondary

is- 8 KW.
- 10 KW.
- 2 KW.
- 0 KW

Answerc

- In one 132 / 33 kV transformer the LV resistance is 0.02 per unit. The resistance referred to HV side is
- 0.02 pu.
- 0.01 pu.
- 0.08 pu.
- 0.16 pu.

Answera

- Air core transformer as compared to iron core transformer, has
- less magnetic core loss.
- more magnetic core loss.
- no magnetic core loss.
- more copper loss.

Answerc

- CRGO steel is used in the core of transformer to reduce
- both eddy current and hysteresis loss.
- hysteresis loss.
- eddy current loss.
- ohmic loss.

Answerb

- If input of a transformer is square wave the output will be
- pulsed wave.
- square wave.
- triangular wave.
- sine wave.

Answera

- Two

transformers with identical rating, are designed with flux densities of

1.2 and 1.4 Wb / m sqr respectively. The weight of first transformer

per kVA is- none of these.
- more than that of second transformer.
- equal to that of second transformer.
- less than that of second transformer.

Answerb

- The flux involved in the emf equation of a transformer has
- rms value.
- average value.
- total value.
- maximum value.

Answerd

- The no load current in a transformer lags the applied voltage by
- about 115°.
- about 75°.
- 90°.
- 0°.

Answerb

- The leakage flux in a transformer depends upon
- the mutual flux.
- the frequency.
- the load current.
- the applied voltage.

Answerc

- Which of the following transformer insulating oil generally used in India?
- Aromatics based insulating oil.
- Naphtha based insulating oil.
- Paraffin based insulating oil.
- Olefin based insulating oil.

Answerc

- Winding conductors of an electrical power transformer are mainly insulated by
- paper insulation.
- wooden insulation.
- rubber insulation.
- cotton insulation.

Answera

- The overall power factor of an on load transformer
- depends on the power factor of the load.
- is always unity.
- is always lagging.
- is always leading

Answera