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Test: Auto-Transformer

10 Questions MCQ Test Electrical Machines | Test: Auto-Transformer

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Attempt Test: Auto-Transformer | 10 questions in 10 minutes | Mock test for Electrical Engineering (EE) preparation | Free important questions MCQ to study Electrical Machines for Electrical Engineering (EE) Exam | Download free PDF with solutions
QUESTION: 1

While comparing potential transformer to an auto transformer, a potential transformer transfers power ________

Solution:

Potential divider is resistance division and it does not take part in induction processes.

QUESTION: 2

The statements which support the points that auto transformers are advantageous I. Weight of conductor reduces II. Ohmic losses reduces III. Leakage reactance reduces IV. Lower short-circuit current

Solution:

Short circuit current of the auto transformer is higher than the corresponding 2-winding transformer

QUESTION: 3

The statements which support the points that auto transformers are disadvantageous as compared to 2-winding transformer I. Weight of conductor reduces II. Direct electrical contacts III. Leakage reactance reduces IV. Lower short-circuit current

Solution:

Direct electrical contacts is a disadvantage to the auto transformer.
Short circuit current of the auto transformer is higher than the corresponding 2-winding transformer.

QUESTION: 4

I. KVA rating : 1/(1-k)
II. Losses : (1-k)
III. Impedance drop = 1/(1-k)
Which of the above are correct for an auto transformer when compared to the identical rating two winding transformer?

Solution:

KVA(auto)/KVA(2-W) = V2*I2/V2*(I2-I1)
= 1/(1-I1/I2)
= 1/(1-k)
Losses(auto)= (1-k) *Losses(2-W)
Impedance drop(auto)= (1-k)*Impedance drop(2-W).

QUESTION: 5

The voltage regulation of a transformer at full-load 0.8 p.f leading is -2%. Its voltage regulation at full load 0.8 p.f lagging

Solution:

The leading p.f. has negative v.r. and lagging p.f. has major portion of positive voltage regulation.

QUESTION: 6

The voltage regulation of a transformer is not dependent on its

Solution:

Voltage regulation is independent of the size of the transformer.

QUESTION: 7

Three transformers having identical dimensions but with core of iron, aluminium and wood are wound with same number of turns and have same supply.Then choose the order for hysteresis losses.

Solution:

Hysteresis losses occur maximum in the ferromagnetic material.

QUESTION: 8

Maximum efficiency of a transformer for a constant load current , occurs at

Solution:

Efficiency = KVA*p.f/(KVA*p.f + Losses); So the efficiency is maximum at unity power factor.

QUESTION: 9

A 1-phase tranformer has a leakage impedance of 1+ j4 Ω for primary and 3+ j11 Ω for secondary windings. This transformer has

Solution:

The side which has lower impedance will have lower number of turns and so the low voltage side.

QUESTION: 10

If a transformer is at no load , then it will act like

Solution:

Transformer is nothing but the arranged windings which are magnetically coupled. The windings will inductive predominantly with very low resistance. Use Code STAYHOME200 and get INR 200 additional OFF Use Coupon Code

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