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Test: Parallel Operation of Single-Phase Transformers - Electrical Engineering (EE) MCQ


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

Test: Parallel Operation of Single-Phase Transformers for Electrical Engineering (EE) 2024 is part of Electrical Machines preparation. The Test: Parallel Operation of Single-Phase Transformers questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: Parallel Operation of Single-Phase Transformers MCQs are made for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Parallel Operation of Single-Phase Transformers below.
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Test: Parallel Operation of Single-Phase Transformers - Question 1

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

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 1

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

Test: Parallel Operation of Single-Phase Transformers - 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

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 2

Total kVA = 1050+180 = 1230 kVA.

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Test: Parallel Operation of Single-Phase Transformers - Question 3

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

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 3

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

Test: Parallel Operation of Single-Phase 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

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 4

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.

Test: Parallel Operation of Single-Phase Transformers - 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

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 5

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.

Test: Parallel Operation of Single-Phase Transformers - 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

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 6

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

Test: Parallel Operation of Single-Phase Transformers - 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

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 7

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

Test: Parallel Operation of Single-Phase Transformers - Question 8

Operating transformers in parallel gives the advantage of

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 8

All are advantages of having parallel connection of transformers.

Test: Parallel Operation of Single-Phase Transformers - Question 9

In a transformer, the load current is kept constant, while the power factor is varied. Under this situation, zero voltage regulation will be observed

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 9

Voltage regulation is the change in secondary terminal voltage from no load to full load at a specific power factor of load and the change is expressed in percentage.

E2 = no-load secondary voltage

V2 = full load secondary voltage

Voltage regulation for the transformer is given by the ratio of change in secondary terminal voltage from no load to full load to no load secondary voltage.

+ sign is used for lagging loads and

- ve sign is used for leading loads

Hence voltage regulation can be negative only for capacitive loads

In transformer minimum voltage regulation occurs when the power factor of the load is leading.

The voltage regulation of the transformer is zero at a leading power factor load such as a capacitive load.

For zero voltage regulation, E2 = V2

> IR cos φ = IX sin φ (negative sign represents leading power factor loads)

This is the leading power factor at which voltage regulation becomes zero while supplying the load.

Test: Parallel Operation of Single-Phase Transformers - Question 10

What is per unit regulation in a transformer when V20 is the secondary terminal voltage on no-load and V2 is the secondary terminal voltage on given load?

Detailed Solution for Test: Parallel Operation of Single-Phase Transformers - Question 10

Concept:

Voltage regulation is the change in secondary terminal voltage from no load to full load at a specific power factor of load and the change is expressed in percentage.

E2 = no-load secondary voltage = V20 

V2 = given load secondary voltage = V2

Voltage regulation for the transformer is given by the ratio of change in secondary terminal voltage from no load to full load to no load secondary voltage.

Voltage regulation = 

Additional Information

Voltage regulation can be expressed as a fraction or unit-change of the no-load terminal voltage and can be defined in one of two ways,

  1. Voltage regulation-down, (Regdown) and
  2. Voltage regulation-up, (Regup)
  • When the load is connected to the second output terminal, the terminal voltage goes down, or when the load is removed, the secondary terminal voltage goes up.
  • Hence, the regulation of the transformer will depend on which voltage value is used as the reference voltage, load or non-load value.

Transformer Voltage Regulation as a Percentage Change:

Transformer when connected to load:

Transformer under no load:

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