Commutation MCQs : This section focuses on the "Commutation" in DC Machines. These Multiple Choice Questions (MCQs) should be practiced to improve the DC Machines skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.
___________ the change that takes place in a winding element during the period of a short circuit by a brush.
Explanation: The term Commutation means the change that takes place in a winding element during the period of a short circuit by a brush.
How many methods to obtain Sparkless commutation?
Explanation: There are 3 methods to obtain Sparkless commutation : Resistive commutation, Voltage commutation, Compensating commutation
The time required to change the current through a coil from Ic to -Ic is called?
A. Commutation Period
B. Commutation Time
C. Commutation Set
D. Commutation Count
Explanation: The time required to change the current through a coil from Ic to -Ic is called Commutation Period (Tc)
Commutation is delayed due to __________
A. Leakage reactance
B. Effect of armature reaction
C. Because of other factors
D. Leakage reactance and armature reaction
Explanation: Commutation is delayed due to Leakage reactance and armature reaction.
For a DC machine, in a commutator ________
A. Copper is harder than mica
B. Mica and copper are equally hard
C. Mica is harder than copper
D. Cannot be determined
Explanation: Due to its mechanical strength and insulating properties mica is a satisfactory material. However, mica is much harder than the copper segments, so during manufacturing it requires to under-cut the mica by sawing slots between the adjacent segments of the commutator.
The insulating material used between the commutator segments is normally _______
D. Air gap
Explanation: Each conducting segment of the commutator is insulated from adjacent segments. Mica is a good electric insulator and good thermal conductor as well. Its applications in electric fields are derived from its unique mechanical properties. Thus, it allows mica to be ductile enough for its appropriate space of application.
If Time taken > Tc, then known as?
A. under commutation
B. delayed commutation
C. Both A and B
D. accelerated commutation
Explanation: If Time taken > Tc, then under or delayed commutation
Which are the methods for getting an ideal commutation?
A. Resistance commutation
B. Voltage commutation
C. Current commutation
D. Both A and B
Explanation: Adding resistance between commutator segments and brushes, thus, reducing L/R and consequently getting faster commutation is one of the method. In voltage commutation we, introduce narrow poles called as interpoles to fasten the process.
If Time taken < Tc , then over or accelerated commutation.
C. Can be true or false
D. Can not say
Explanation: True, If T
If the current reversal is completed by the end of commutation period, it is called ideal commutation.
C. Can be yes or no
D. Can not say
Explanation: Yes, If the current reversal is completed by the end of commutation period, it is called ideal commutation.