# Design of Electrical Machines Questions and Answers – Overall Dimensions – 2

This set of Design of Electrical Machines Interview Questions and Answers for freshers focuses on “Overall Dimensions – 2”.

1. What is the formula for the depth and height of the yoke for stepped core?
a) depth = width of largest stamping, height = 2* width of largest stamping
b) depth = 2*width of largest stamping, height = width of largest stamping
c) depth = width of largest stamping, height = width of largest stamping
d) depth = 2*width of largest stamping, height = 2* width of largest stamping

Explanation: The depth of the yoke of stepped core is equal to the width of the largest stamping. The height of the yoke for the stepped core is also equal to the width of the largest stamping.

2.The height and the width of the single phase and three phase core type transformers are equal.
a) true
b) false

Explanation: The height of both the single phase and three phase core type transformers are equal. The width of the single phase and three phase core type are not same.

3. What is the formula for the height and width of the single phase shell transformer?
a) width = 2*width of the window + 4*width of the largest stamping, height = height of the window + 2*width of the largest stamping
b) width = 2*width of the window – 4*width of the largest stamping, height = height of the window + 2*width of the largest stamping
c) width = 2*width of the window + 4*width of the largest stamping, height = height of the window – 2*width of the largest stamping
d) width = 2*width of the window – 4*width of the largest stamping, height = height of the window -2*width of the largest stamping

Explanation: First the width of the window is obtained. Next, the height of the window is obtained. Then, the width of the largest stamping is obtained and substituted in the above formula.

4. What is the formula to calculate the number of turns/phase?
a) number of turns = secondary voltage * voltage per turn
b) number of turns = secondary voltage / voltage per turn
c) number of turns = secondary voltage + voltage per turn
d) number of turns = secondary voltage – voltage per turn

Explanation: First the voltage across the secondary winding of the transformer is obtained. Next, the voltage across each turn is obtained. On substituting we get the number of turns.

5. What is the formula for the cross sectional area of the secondary conductor of the transformer?
a) cross sectional area = secondary current * current density
b) cross sectional area = secondary current + current density
c) cross sectional area = secondary current / current density
d) cross sectional area = secondary current – current density

Explanation: The current flowing through the secondary winding of the transformer is calculated. Next the current density is calculated and the ratio gives the cross sectional area of the secondary conductor.
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6. What is the formula for the conductor dimensions in transformer?
a) conductor dimensions = conductor width * conductor thickness + 0.5 mm
b) conductor dimensions = conductor width / conductor thickness + 0.5 mm
c) conductor dimensions = conductor width + conductor thickness + 0.5 mm
d) conductor dimensions = conductor width – conductor thickness + 0.5 mm

Explanation: The width of the conductor is first calculated. Next, the thickness of the conductor is calculated. On obtaining these data the conductor dimensions can be obtained.

7. What is the formula for axial depth of low voltage winding?
a) axial depth = number of secondary turns / width of the conductor
b) axial depth = number of secondary turns * width of the conductor
c) axial depth = number of secondary turns + width of the conductor
d) axial depth = number of secondary turns – width of the conductor

Explanation: The number of secondary turns is calculated first. Then the width of the conductor is obtained. With the 2 data, the axial depth is obtained.

8. What is the formula for the window clearance of the transformer?
a) window clearance = (height of the window + axial depth)/2
b) window clearance = (height of the window – axial depth)
c) window clearance = (height of the window – axial depth)/2
d) window clearance = (height of the window + axial depth)

Explanation: First the height of the window is obtained. Then the axial depth is calculated using the formula axial depth = number of secondary turns * width of the conductor and substituting in the above formula provides the window clearance.

9. What is the formula to calculate the radial depth of low voltage windings?
a) radial depth of the lv windings = number of layers * radial depth of the conductors * insulation between layers
b) radial depth of the lv windings = number of layers * radial depth of the conductors – insulation between layers
c) radial depth of the lv windings = number of layers / radial depth of the conductors + insulation between layers
d) radial depth of the lv windings = number of layers * radial depth of the conductors + insulation between layers

Explanation: The number of layers is first taken note of. Then the radial depth of the conductors is calculated along with the insulation between layers. On substituting the values in the above formula the radial depth of the low voltage windings is obtained.

10. What is the formula for the inside diameter of the low voltage windings?
a) inside diameter = diameter of the circumscribing circle + pressboard thickness insulation between l.v winding and core
b) inside diameter = diameter of the circumscribing circle – pressboard thickness insulation between l.v winding and core
c) inside diameter = diameter of the circumscribing circle + 2*pressboard thickness insulation between l.v winding and core
d) inside diameter = diameter of the circumscribing circle – 2* pressboard thickness insulation between l.v winding and core

Explanation: For calculating the inner diameter, first the diameter of the circumscribing circle is obtained using the corresponding formula. Then the pressboard thickness insulation is calculated.

11. What is the assumption for width of the largest stamping for the stepped core transformer?
a) 0.9*d
b) 0.71*d
c) 0.85*d
d) 0.8*d

Explanation: If the width of the largest stamping is not provided, then for stepped core a = 0.9*d. For the cruciform it is a = 0.85*d and for the square core it is a = 0.71*d.

12. What is the range for the current density at HT side for a distribution transformer?
a) 2.4-3.5 Amp per mm2
b) 2-2.5 Amp per mm2
c) 1-3.5 Amp per mm2
d) 2-3.5 Amp per mm2

Explanation: 2.4-3.5 Amp per mm2 is the range for the current density at HT side for a power transformer. 2-2.5 Amp per mm2 is the range for the current density at HT side for a distribution transformer.

13. What is the relation of the height of the window with the winding height with respect to the rectangular conductors?
a) winding height = 60% * window height
b) winding height = 50% * window height
c) winding height = 80% * window height
d) winding height = 70% * window height

Explanation: In case of selection of the rectangular conductors, first the window height is obtained. Next the 70% of the window height provides the winding height.

14. What is the formula for number of turns/coil axially?
a) number of turns/coil axially = axial length / diameter of the insulated conductor
b) number of turns/coil axially = axial length * diameter of the insulated conductor
c) number of turns/coil axially = axial length – diameter of the insulated conductor
d) number of turns/coil axially = axial length + diameter of the insulated conductor

Explanation: First the axial length is calculated from its respective formula. Then the diameter of the insulated conductor is calculated, and the ratio gives the number of turns/coil axially.

15. The axial length of 16 coils = axial length of each coil * 16.
a) true
b) false

Explanation: The axial length of each coil is calculated initially from its corresponding formula. Then the value is multiplied by the number of coils present.

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