This set of Design of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Overall Dimensions – 1”.

1. What is the formula for the diameter of the single phase core type transformer?

a) D = diameter of circumscribing circle + Width of window

b) D = diameter of circumscribing circle – Width of window

c) D = diameter of circumscribing circle * Width of window

d) D = diameter of circumscribing circle / Width of window

View Answer

Explanation: First the diameter of the circumscribing circle is obtained. Next, the width of the window is calculated, and the sum of both the data provides the diameter of the single phase core transformer.

2. What is the formula for height of the single phase core type transformer?

a) height = height of the window – height of the yoke

b) height = height of the window + height of the yoke

c) height = height of the window – (2*height of the yoke)

d) height = height of the window + (2*height of the yoke)

View Answer

Explanation: The height of the window is first obtained. Next, the height of the yoke is calculated and it is multiplied by 2. Addition of both the values gives the height of the single phase core type transformer.

3. What is the formula for width of the single phase core type transformer?

a) width = Width of largest stamping / Diameter of the transformer

b) width = Width of largest stamping + Diameter of the transformer

c) width = Width of largest stamping – Diameter of the transformer

d) width = Width of largest stamping * Diameter of the transformer

View Answer

Explanation: Firstly, the width of the largest stamping is calculated. Next, the diameter of the transformer is calculated and the sum of both the values gives the width of the transformer.

4. What is the formula for the width over 2 limbs?

a) width = Width of largest stamping + Diameter of the transformer

b) width = Diameter + outer diameter of hv windings

c) width = Diameter – outer diameter of hv windings

d) width = outer diameter of hv windings

View Answer

Explanation: width = outer diameter of hv windings is the width over one limb. width = Width of largest stamping + Diameter of the transformer is the formula for width of the transformer.

5. The formula for single phase core type and three phase core type diameter and height are same.

a) true

b) false

View Answer

Explanation: D = diameter of circumscribing circle + Width of window is the diameter of single phase and 3 phase core type transformers. height = height of the window + (2*height of the yoke) is the height of the single and three phase core type transformers.

6. What is the formula for the width over one limb?

a) width over one limb = outer diameter of hv winding

b) width over one limb = 2*Diameter – outer diameter of hv winding

c) width over one limb = 2*Diameter + outer diameter of hv winding

d) width over one limb = Diameter + outer diameter of hv winding

View Answer

Explanation: Width over one limb = 2*Diameter + outer diameter of hv winding is the formula for the width over 3 limbs. For one limb the width is equal to the outer diameter of hv winding.

7. What is the formula for the width of the single phase shell type transformer?

a) width = 2*Width of the window + width of the largest stamping

b) width = Width of the window + 4*width of the largest stamping

c) width = Width of the window + width of the largest stamping

d) width = 2*Width of the window + 4*width of the largest stamping

View Answer

Explanation: First the width of the window is obtained. Next the width of the largest stamping is obtained. Substituting in the above formula provides the width of the single-phase shell type transformer.

8. What is the height of the single phase shell type transformer?

a) height = height of window + width of the largest stamping

b) height = 2*height of window + width of the largest stamping

c) height = height of window + 2* width of the largest stamping

d) height = height of window – width of the largest stamping

View Answer

Explanation: First the height of the window is obtained. Then the width of the largest stamping is calculated and substituting in the above formula provides the height of the single phase shell type transformer.

9. What is the formula to calculate the voltage per turn of the transformer?

a) voltage per turn = space factor * square root of output power

b) voltage per turn = space factor / square root of output power

c) voltage per turn = space factor / square root of output power

d) voltage per turn = space factor * 2*square root of output power

View Answer

Explanation: The corresponding space factor is obtained using the formula. Then the output power is obtained and square root of the output power is taken and substituted in the above formula to obtain the voltage per turn.

10. What is the formula for the net cross sectional area of the core of the transformer?

a) cross sectional area = voltage per turn * 4.44 * frequency * magnetic field

b) cross sectional area = voltage per turn / 4.44 * frequency * magnetic field

c) cross sectional area = voltage per turn * 4.44 / frequency * magnetic field

d) cross sectional area = voltage per turn * 4.44 * frequency / magnetic field

View Answer

Explanation: For obtaining the cross sectional area, the voltage per turn is obtained. The frequency is always 50 Hz. Then the magnetic field is obtained and substituted in the above formula.

11. What is the formula for the diameter of the circumscribing circle of the transformer?

a) diameter of the circumscribing circle = 2*square root of ratio of cross sectional area of the core to the space factor

b) diameter of the circumscribing circle = 3*square root of ratio of cross sectional area of the core to the space factor

c) diameter of the circumscribing circle = square root of ratio of cross sectional area of the core to the space factor

d) diameter of the circumscribing circle = 4*square root of ratio of cross sectional area of the core to the space factor

View Answer

Explanation: First the cross sectional area of the core is obtained by the formula cross sectional area = voltage per turn / 4.44 * frequency * magnetic field. Next the space factor is obtained. Substituting in the formula provides the diameter of the circumscribing circle.

12. What is the formula for the width of the window of the transformer?

a) width of the window = distance between core centers + diameter of the circumscribing circle

b) width of the window = distance between core centers – diameter of the circumscribing circle

c) width of the window = distance between core centers * diameter of the circumscribing circle

d) width of the window = distance between core centers / diameter of the circumscribing circle

View Answer

Explanation: The diameter of the circumscribing circle is obtained from the formula, diameter of the circumscribing circle = square root of ratio of cross sectional area of the core to the space factor. After obtaining the distance between core centers, the width of the window is obtained.

13. What is the formula for window area of the transformer?

a) window area = output power * 2.22 * frequency * magnetic field * window space factor * current density * area of cross section of the core *10^{3}

b) window area = output power / 2.22 * frequency * magnetic field * window space factor * current density * area of cross section of the core *10^{3}

c) window area = output power / 3.33 * frequency * magnetic field * window space factor * current density * area of cross section of the core *10^{3}

d) window area = output power * 3.33 * frequency * magnetic field * window space factor * current density * area of cross section of the core*10^{3}

View Answer

Explanation: The window space factor, the current density and the core cross sectional area are obtained by their respective formula. The frequency is 50Hz and then the magnetic field and the output power is calculated to obtain the window space factor.

14. What is the formula for the height of the window?

a) height of window = area of window * width of the window

b) height of window = area of window + width of the window

c) height of window = area of window – width of the window

d) height of window = area of window / width of the window

View Answer

Explanation: First the area of the window is obtained. Next the window width is obtained. The ratio of both gives the height of the window.

15. The range of the ratio of the height of the window to the width of the window is 2-4.

a) true

b) false

View Answer

Explanation: The ratio of the height of the window to the width of the window should be adjusted such that it is above 2. The ratio of the height of the window to the width of the window should be adjusted such that it is below 4.

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