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Electrical Machines Mcqs

Q:

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.

A) wood > aluminium > iron B) aluminium > iron > wood
C) iron > wood > aluminium D) iron > aluminium > wood
 
Answer & Explanation Answer: D) iron > aluminium > wood

Explanation: Hysteresis losses occur maximum in the ferromagnetic material.

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59
Q:

The voltage regulation of a transformer depends on its __________

(A) Equivalent reactance
(B) Equivalent resistance
(C) Load power factor
(D) Transformer size
(E) Load current

A) A, B, C, E B) A, B, C, D, E
C) A, B, D, E D) A, B, C, D
 
Answer & Explanation Answer: A) A, B, C, E

Explanation: Voltage regulation is independent of the size of the transformer.

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151
Q:

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 _____________

A) will be positive B) will be negative
C) may be positive D) may be negative
 
Answer & Explanation Answer: A) will be positive

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

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54
Q:

Which of the above are correct for an auto transformer when compared to the identical rating two winding transformer?

I. KVA rating : 1/(1-k)
II. Losses : (1-k)
III. Impedance drop = 1/(1-k)

A) I, II B) II, III
C) 1, III D) I, II, III, IV
 
Answer & Explanation Answer: A) I, II

Explanation: 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).

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49
Q:

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

A) I, III B) II, III
C) II, IV D) I, II, IV
 
Answer & Explanation Answer: C) II, IV

Explanation: 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.

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49
Q:

The statements which support the points that auto transformers are advantageous?

I. Weight of conductor reduces
II. Direct electrical contacts
III. Leakage reactance reduces
IV. Lower short-circuit current

A) I, III B) II, III
C) I, II, III, IV D) I, IV
 
Answer & Explanation Answer: A) I, III

Explanation: 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.

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116
Q:

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

A) I, II, III B) II, III, IV
C) I, II, III, IV D) I, IV
 
Answer & Explanation Answer: A) I, II, III

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

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71
Q:

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

A) conductively B) inductively
C) both conductively as well as inductively D) electromagnetic induction
 
Answer & Explanation Answer: A) conductively

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

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