This set of Design of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Turns Compensation”.

1. What is the use of the turns compensation in current transformer?

a) to increases the ratio error

b) to reduce the ratio error

c) to increase the phase angle error

d) to reduce the phase angle error

View Answer

Explanation: There are 2 types of errors in the current transformer. The turns compensation is used to reduce the ratio error.

2.What is the formula of the actual ratio?

a) actual ratio = turns ratio + load current * secondary current

b) actual ratio = turns ratio * load current * secondary current

c) actual ratio = turns ratio + load current / secondary current

d) actual ratio = turns ratio / load current * secondary current

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Explanation: The turns ratio is first calculated. Next the load current and secondary current is calculated and on substitution gives the actual ratio.

3. What happens if the number of secondary turns is reduced?

a) the primary turns is reduced

b) the output is reduced

c) the efficiency is reduced

d) the transformation ratio is reduced

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Explanation: The reduction of the number of secondary turns reduces the transformation ratio. If the number of secondary turns reduces by 1 percent the actual transformation ratio reduces by equal percentage.

4.What is the best number of secondary turns of the current transformer?

a) 1

b) 2

c) 1 or 2 less than the number such that the turns ratio is equal to the nominal current ratio

d) 1 or 2 more than the number such that the turns ratio is equal to the nominal current ratio

View Answer

Explanation: The best number of secondary turns of the current transformer is 1 or 2 less than the number such that the turns ratio is equal to the nominal current ratio. For example in a 1000/5 current transformer, the secondary turns number would be 198 or 199 rather than 200.

5. The phase angle error is significantly affected by the small change in secondary turns?

a) true

b) false

View Answer

Explanation: There are 2 types of errors which is the ratio error and phase angle error. The phase angle error is not significantly effected by a small change in secondary turns.

6. What is the dimension of the round copper wire made use of in the windings of current transformer?

a) 3 cm^{2}

b) 3 mm^{2}

c) 3 m^{2}

d) 3 cm

View Answer

Explanation: Copper strip is used for primary windings. The dimension of the round copper wire made use of in the windings of current transformer is 3 mm

^{2}.

7. What is the range of current density in the windings of the current transformer?

a) 1-3 A per mm^{2}

b) 2-3 A per mm^{2}

c) 1-2 A per mm^{2}

d) 0.5-2 A per mm^{2}

View Answer

Explanation: The minimum value of the current density in the windings I A per mm2. The maximum value of the current density is 2 A per mm

^{2}.

8. How many factors are present in the behavior of transformer under short circuit conditions?

a) 2

b) 3

c) 4

d) 5

View Answer

Explanation: There are 3 factors present in the behavior of the transformer under short circuit conditions. They are temperature rise, current density, mechanical forces.

**Sanfoundry Global Education & Learning Series – Design of Electrical Machines.**

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