# Design of Electrical Machines Questions and Answers – Design of Rotor – 2

This set of Advanced Design of Electrical Machines Questions and Answers focuses on “Design of Rotor – 2”.

1. What is the range of current density in the damper bars?
a) 3-4 A per mm2
b) 3-5 A per mm2
c) 3-6 A per mm2
d) 4-6 A per mm2

Explanation: The minimum value of the current density in the damper bars is given to be 3 A per mm2. The maximum value of the current density in the damper bars is given to be 4 A per mm2.

2. What is the percentage of the damper windings slot pitch with respect to stator slot pitch?
a) 30%
b) 40%
c) 20%
d) 60%

Explanation: The slot pitch of damper windings is 20% of the stator slot pitch. This is because to reduce the current induced in damper windings by tooth ripples.

3. What is the formula for the pole arc?
a) pole arc = number of bars per pole * stator slot pitch * 0.8
b) pole arc = number of bars per pole / stator slot pitch * 0.8
c) pole arc = number of bars per pole * stator slot pitch / 0.8
d) pole arc = 1 / number of bars per pole * stator slot pitch * 0.8

Explanation: The number of bars per pole is calculated along with the stator slot pitch. Next, all the values are multiplied by 0.8 and the pole arc value is obtained.

4. What is the formula for the length of each damper bar for small machines?
a) length of each damper bar = 1.1 * axial length
b) length of each damper bar = axial length + 0.1
c) length of each damper bar = axial length – 0.1
d) length of each damper bar = 1.1 / axial length

Explanation: Length of each damper bar = 1.1 * axial length is the formula for the length of each damper bar for small machines. length of each damper bar = axial length + 0.1 is the formula for the length of each damper bar for large machines.

5. What is the formula for the area of cross-section of each damper bar?
a) area of cross section of each damper bar = total area of bars per pole – number of damper bars per pole
b) area of cross section of each damper bar = total area of bars per pole + number of damper bars per pole
c) area of cross section of each damper bar = total area of bars per pole / number of damper bars per pole
d) area of cross section of each damper bar = total area of bars per pole * number of damper bars per pole

Explanation: The total area of bars per pole is first obtained. Next the number of damper bars per pole is calculated and the ratio gives the area of cross section of each damper bar.

6. What is the formula of the area of each ring short-circuiting the bars?
a) area of each ring short-circuiting the bars = (0.7-0.9) * area of damper bar
b) area of each ring short-circuiting the bars = (0.8-1) * area of damper bar
c) area of each ring short-circuiting the bars = (0.7-1) * area of damper bar
d) area of each ring short-circuiting the bars = (0.8-0.9) * area of damper bar

Explanation: First the area of damper bars is calculated first. Next the area of damper bars is multiplied by a value between 0.8-1 to obtain the area of each ring short-circuiting the bars.

7. Given : total area = 473 mm2 and Number of bars = 8 for a rotor design, what is the value of area of each damper bar?
a) 59 mm2
b) 455 mm2
c) 475 mm2
d) 3784 mm2

Explanation: Area of each bar = total area / number of bars
Area of each bar = 473/8 = 59 mm2.

8. What is the formula for the height of pole shoe sufficient to accommodate the damper windings?
a) height of pole shoe = diameter of damper bars
b) height of pole shoe = 2 * diameter of damper bars
c) height of pole shoe = diameter of damper bars/2
d) height of pole shoe = 3 * diameter of damper bars/2

Explanation: First the diameter of the damper bars is calculated. It is then multiplied by 2 to get the height of pole shoe.

9. Pole profile drawing helps in obtaining the various dimensions of the pole.
a) true
b) false

Explanation: The pole profile drawing is essential to obtain the design characteristics of the rotor. It helps in the process of obtaining the various dimensions of the pole.

10. The pole shoe drawing is completed by fixing the height of pole shoe.
a) true
b) false

Explanation: The pole shoe surface can be drawn with the armature surface being fixed. The pole shoe drawing is completed by fixing the height of pole shoe.

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