Objective Questions or MCQs on Transformer                               

01) Eddy current loss will depends on

Frequency

Flux density

Thickness

All of the above

. So eddy current loss will depend upon frequency, flux density and the area of the eddy current loop.

02) Hysteresis loss will depends on

f

f²

f³

f^1.6

. So, hysteresis loss will depends on frequency.

03) Thin laminations are used in a machine in order to reduce

Eddy current losses

Hysteresis losses

Both 1 and 2

Copper losses

Thin laminations are used in order to reduce the eddy current losses only. Due to laminations the area of the eddy currents loops are minimized and the losses due to eddy current losses are minimized.

04) Hysteresis loop represents the area of

copper loss

eddy current loss

Hysteresis loss

total iron losses

Hysteresis loop will represents only hysteresis losses. It is found out by area of B-H loop curve of a magnetic material.

05) Total core loss is also called as -------------?

Eddy current loss

Hysteresis loss

Magnetic loss

Copper loss

As iron loss is proportional to flux density or flux, these are also called as magnetic loss. The total core loss or magnetic loss consists of eddy current loss and hysteresis loss.

06) Which of the following are variable losses?

eddy current loss

hysteresis loss

shunt field copper loss

armature copper loss

Armature copper loss is directly proportional to square of armature current. Therefore as the load varies these will also vary.

07) Maximum efficiency will occur, when copper loss is_______to iron loss?

greater than

less than

equals to

any of the above

Condition for maximum efficiency is, copper loss = iron loss or variable losses is equals to fixed losses.

08) The noise resulting from vibrations of lamination set by magnetic forces, is termed as

magnetostriction.

boo.

 hum.

zoom.

The hum is generated by the magnetic field that happens due to the continuous reversing of the frequency of the supply or it is due to magnetostriction. The magnetic field in the AC machine or transformers has coils which are still able to move slightly due to the vibration. The laminations of the armature are treated in a similar way but also vibrate at the line frequency and it is almost impossible to stop. We can only reduce it by good design.

09) Auto transformer makes effective saving on copper and copper losses, when its transformation ratio is equal to

 very low

 less than one.

 greater than one.

approx to one.

To quantify the saving the total quantity of copper used in an auto transformer is expressed as a fraction of that used in a two winding transformer as,This means that an auto transformer requires the use of lesser quantity of copper given by the ratio of turns. Hence, if the transformation ratio is approximately equal to one, then the copper saving is good and the copper loss is less.

10) Which of the following statements is/are correct?

High frequency power supplies are light weight

Transformer size get reduced at high frequency

Both 1 and 2

None of the above

From the induced emf equation of transformer E ∝ φf For same emf, φf = constant φ₁f₁ = φ₂f₂ B₁A₁f₁ = B₂A₂f₂ For constant flux density B₁ = B₂ A₁f₁ = A₂f₂ For high frequency f₂ > f₁ A₂ < A₁ Therefore at high frequencies transformer size get reduced and also light weight.