Test: Parallel Operation of Single-Phase Transformers


10 Questions MCQ Test Electrical Machines | Test: Parallel Operation of Single-Phase Transformers


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QUESTION: 1

Transformer operating in parallel will share a common load in the best possible manner if

Solution:

For same pu leakage impedance, parallel operation of transformers become feasible.

QUESTION: 2

A 2000/1000/500 three winding transformer is to be used as auto transformer with supply of 3000 V. Two loads of 1050 kVA at 3500V,and other one at 180 kVA at 1000V. The total kVA supplied will be

Solution:

Total kVA = 1050+180 = 1230 kVA.

QUESTION: 3

Which if the conditions is must be fulfilled for a satisfactory parallel operation of transformers?

Solution:

out of all, polarity must be correct for the connected transformers.

QUESTION: 4

A. Positive sequence components – 5th harmonic component
B. Negative sequence components – 7th harmonic component
C. Zero sequence components – 3rd harmonic component
Above are the matching made for the harmonics and the associated harmonic component, then the correct marking is

Solution:

3m-1 phases are displaced 120° in opposite and (3m+1) in the same direction as the fundamental. Here ‘m’ is even integer. So 5th harmonic is in negative sequence and 7th harmonic component in positive sequence.

QUESTION: 5

Two single phase transformers A and B are operating in parallel having same impedance. But the x/r ratio of them are not equal. Then total kVA output of the output will be

Solution:

As the leakage reactances are not same for both the transformers, then Ia < I2 and Ib < I/2.
So the kVA will also be less than sum of individual A and B.

QUESTION: 6

Two single phase transformers A and B are operating in parallel having same impedance. But the x/r ratio of them are not equal and xa > xb. Then

Solution:

As xa > xb, leakage impedance angle of A will be more than that of B, so lesser power factor.

QUESTION: 7

Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Also impedance of A is more than that of B,then A

Solution:

Given that, za is more than zb, so Ia will be lesser than Ib, With Ea = Eb, kVA(A) shared by A will more than kVA(B).

QUESTION: 8

Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Also impedance of A is more than that of B,then

Solution:

Leakage impedance in ‘ohms’ are inverse ratio of their respective kVA ratings.

QUESTION: 9

Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Impedance of A is Za and impedance of B is Zb , both sharing a load of Sl. Then the load shared by transformer B is

Solution:

The load sharing is based on the inverse of the kVA rating.

QUESTION: 10

Operating transformers in parallel gives the advantage of

Solution:

All are advantages of having parallel connection of transformers.

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