1. What is the relation of closed slots with leakage reactance and overload capacity?
a) closed slots give high leakage reactance, and increases the overload capacity
b) closed slots give high leakage reactance, and decreases the overload capacity
c) closed slots give low leakage reactance, and decreases the overload capacity
d) closed slots give low leakage reactance, and increases the overload capacity
Explanation: The closed slots have the main advantage of giving high leakage reactance. A high leakage reactance gives the advantage that the current at the starting can be limited.
2. What is the relation between surface of rotor and the operation?
a) smooth surface leads to the quiet operation
b) rough surface leads to the quiet operation
c) smooth surface leads to the noisy operation
d) rough surface leads to the noisy operation
Explanation: For the design of the rotor bars of the three phase induction machine, smooth surface is preferred. Smooth surface helps in the silent operation.
3. Rectangular shaped bars and slots are preferred to circular bars and slots.
a) true
b) false
Explanation: Rectangular shaped bars and slots are preferred to circular bars and slots. This is because while using the rectangular shaped bars, rotor resistance increases and this leads to the improvement of starting torque
4. What is the relation between clearances and slots?
a) high clearances are provided for salient slots
b) low clearances are provided for skewed slots
c) low clearances are provided for salient slots
d) high clearances are provided for skewed slots
Explanation: When the skewed slots are being used, higher clearances are provided. High clearances can lead to the smooth and efficient operation of the machine for skewed slots.
5. What is the range of clearance that can be left between rotor bars and the core?
a) 0.1-0.4 mm
b) 0.2-0.4 mm
c) 0.15-0.4 mm
d) 0.4-0.6 mm
Explanation: The range of clearance is chosen based on whether the slots are skewed or not. The range is usually chosen between 0.15-0.4 mm.
6. How does the revolving field produce emf in the bars?
a) revolving field produces emf of fundamental frequency in the bars
b) revolving field produces emf of third frequency in the bars
c) revolving field produces emf of no frequency in the bars
d) revolving field produces emf of sinusoidal frequency in the bars
Explanation: The stator winding is 3 phase distributed winding and thus produces a revolving field. This revolving field produces emfs of fundamental frequency in the bars.
7. What happens if the resistance of the end rings is negligible?
a) resistance coming in each current path is resistance of three bars
b) resistance coming in each current path is resistance of four bars
c) resistance coming in each current path is resistance of two bars
d) resistance coming in each current path is resistance of five bars
Explanation: If the resistance of end rings is negligible then the resistance of combined bars are taken into account. Generally the resistance of two bars are taken into account
8. What factors does the current in the bars depend on?
a) emfs, position of bars in magnetic field
b) instantaneous emfs, position of bars in magnetic field
c) emf
d) instantaneous emf
Explanation: The current that the bars carry are proportional to their instantaneous emfs. The instantaneous emfs are proportional to the position of the bars in the magnetic field.
9. The end resistance, if not negligible, will tend to distort the bar current distribution from being sinusoidal.
a) true
b) false
Explanation: The end resistance is proportional to the current distribution. If it is not negligible then the resistance will distort the bar current distribution.
10. What is the formula for the maximum current in end ring, if the current in all bars are maximum at the same time?
a) maximum current in the end ring= bars per pole * 2 * current per bar
b) maximum current in the end ring= (bars per pole / 2) * current per bar
c) maximum current in the end ring= bars per pole / 2 / current per bar
d) maximum current in the end ring= bars per pole * 2 / current per bar
Explanation: First the bars per pole are obtained. Then the current per bar is calculated. Then substituting in the above formula, the maximum current in the end rings.