1. Given the bars per pole is 6 and the current per bar is 20 A, what is the value of the maximum current in the end rings?
a) 60 A
b) 80 A
c) 90 A
d) 70 A
Explanation: maximum current in the end ring= bars per pole / 2 * current per bar
Maximum current in the end ring = (6/2)*20 = 3 * 20 = 60 A.
2. What is the formula for the maximum value of current through end ring, when the current is not maximum in all the bars under one pole at the same time?
a) maximum current in end ring= (2*3.14) / (bars per pole/2*no of poles) * current per bar
b) maximum current in end ring= (2/3.14) * (bars per pole/2*no of poles) / current per bar
c) maximum current in end ring= (2*3.14) * (bars per pole/2*no of poles) * current per bar
d) maximum current in end ring= (2*3.14) / (bars per pole/2*no of poles) / current per bar
Explanation: The bars per pole is first obtained. Then the no of poles is calculated along with the current per bar. On substituting in the formula the maximum current in the end ring with the current through all the bars under one pole is not maximum.
3. What is the formula for the maximum current through each bar?
a) maximum value of the current through each bar = 2 * current through each bar
b) maximum value of the current through each bar = (2 * current through each bar)1/2
c) maximum value of the current through each bar = (2 * current through each bar)2
d) maximum value of the current through each bar = (2 * current through each bar)1/3
Explanation: Firstly, the current through each bar is calculated. Then it is multiplied by 2 and its square root provides the maximum value of current through each bar is obtained.
4. What is the formula for the rms value of the end ring current?
a) rms value of end ring current = (bars per pole * current per bar) / (3.14*no of poles)
b) rms value of end ring current = (bars per pole * current per bar) * (3.14*no of poles)
c) rms value of end ring current = (bars per pole * current per bar) / (no of poles)
d) rms value of end ring current = (bars per pole * current per bar) / (3.14+no of poles)
Explanation: First the bars per pole is obtained. Then the current per bar is calculated and the no of poles is calculated. Substituting in the above formula, the rms value of the end ring current is obtained.
5. The value of the current density is chosen for the end rings such that the desired value of rotor resistance is obtained.
a) true
b) false
Explanation: The value of current density is chosen for the end rings should be chosen such that the desired value of the rotor resistance is obtained. If not it can lead to the starting problems in the machine.
6. How is the current density of the rotor bars chosen with respect to the end rings?
a) current density of rotor bars < current density of end rings
b) current density of rotor bars > current density of end rings
c) current density of rotor bars = current density of end rings
d) current density of rotor bars <= current density of end rings
Explanation: The ventilation is generally better for the end rings. Thus, the current density of the end rings should be greater than that of the rotor bars.
7. What is the formula for the area of the ring?
a) area of the ring = depth of the end ring + thickness of the end ring
b) area of the ring = depth of the end ring – thickness of the end ring
c) area of the ring = depth of the end ring / thickness of the end ring
d) area of the ring = depth of the end ring * thickness of the end ring
Explanation: For calculation of the area of end rings, first the depth of end rings is calculated. Next, the thickness of the end ring is calculated and substituting in the above formula gives the area of the ring.
8. What is the rotor windings for wound rotor motors?
a) single phase windings
b) double phase windings
c) three phase windings
d) concentrated phase windings
Explanation: The rotor windings for wound rotor motors are 3 phase windings. The number of rotor slots should be such that a balanced winding is obtained.
9. How should the number of slots be in the case of fractional slot windings?
a) multiples of slots
b) multiple of phases
c) multiple of phases and pair of poles
d) multiples of pair of poles
Explanation: Fractional slot windings can be used in the wound rotor design. It is preferable to use a number of slots which are a multiple of phases and pair of poles in the case of fractional slot windings.
10. How many types of design of wound rotors are available?
a) 2
b) 3
c) 4
d) 5
Explanation: They are 4 types of design of wound rotors. They are Number of Rotor Slots, Number of Rotor Turns, Area of Rotor Conductors, Rotor Windings.