1. How many methods are present to obtain all the machine performance characteristics?
a) 3
b) 2
c) 1
d) 4
Explanation: There are 2 methods in obtaining all the open circuit characteristics. They are no load characteristics and short circuit characteristics.
2. How many components does the no load current characteristics comprise of?
a) 2
b) 3
c) 4
d) 1
Explanation: There are 2 main components under the no load current. They are Magnetizing current and Loss component of current.
3. How is the Magnetizing component with respect to the voltage?
a) the magnetizing component is in phase with the voltage
b) the magnetizing component is 90° leading the voltage
c) the magnetizing component is 90° lagging the voltage
d) the magnetizing component is 90° out of phase with the voltage
Explanation: The magnetizing current component is 90° out of phase with the voltage. The loss component is in phase with the voltage.
4. How many parts does the flux produced by stator mmf passes through?
a) 3
b) 4
c) 5
d) 6
Explanation: The flux produced by stator mmf passes through 5 parts. They are air gap, rotor teeth, rotor core, stator teeth, stator core.
5. The flux is distributed sinusoidally and the mmf varies sinusoidally in a DC Machine.
a) true
b) false
Explanation: In a DC Machine, the flux is assumed to be uniform over any cross section and the same mmf for all the paths. But in an induction machine, the flux is distributed sinusoidally, and the mmf varies sinusoidally.
6. What factors does the value of magnetizing current depend on?
a) flux tube
b) output power
c) mean mmf
d) mean mmf and flux tube
Explanation: If the permeability of iron were constant this would cause no difficulty. The value of magnetizing current would be accurately obtained by considering the mean mmf and the flux tube where this mean occurs.
7. When maximum values of the design factors are considered, what is the relation between flux and the magnetizing current?
a) flux is directly proportional to the magnetizing current
b) flux is indirectly proportional to the magnetizing current
c) flux is directly proportional to square of the magnetizing current
d) flux is indirectly proportional to square of the magnetizing current
Explanation: The flux value is indirectly proportional to the magnetizing current. The flux is too small or rather the magnetizing current becomes high.
8. At what angle with respect to the interpolar axis does the flux tube gives a good approximation?
a) 30°
b) 45°
c) 60°
d) 90°
Explanation: The flux tube crossing the air gap at 60° from the interpolar axis will always give a good approximation. The calculation of the magnetizing mmf should be based upon the value of the flux density at 60° from the interpolar axis.
9. What is the formula for mmf for air gap?
a) mmf for air gap = 800000 * air gap flux density * air gap factor * length of air gap
b) mmf for air gap = 800000 / air gap flux density * air gap factor * length of air gap
c) mmf for air gap = 800000 * air gap flux density / air gap factor * length of air gap
d) mmf for air gap = 800000 * air gap flux density * air gap factor / length of air gap
Explanation: For calculating the mmf for air gap, the air gap flux density is first calculated. Next the air gap factor is calculated along with the length of air gap.
10. What is the formula for the mmf required for stator teeth?
a) mmf required for stator teeth = mmf per metre + depth of stator slots
b) mmf required for stator teeth = mmf per metre * depth of stator slots
c) mmf required for stator teeth = mmf per metre / depth of stator slots
d) mmf required for stator teeth = mmf per metre – depth of stator slots
Explanation: First the mmf per meter is obtained separately from its design equation. Then the depth of the stator slots is obtained and the product of both gives mmf required for stator teeth.