Electrical Drives and Controls (EDC) MCQs | Page - 2

 derating refers to the operation of equipment at reduced capacity/power or speed. derating in motors can be caused due to the following reasons- frequency, voltage, ambient temperature, altitude.

 the armature shaft must be able to withstand any unbalanced magnetic pull on the armature core, bending moment due to weight of the armature and commutator, twisting stains due to transmission of torque, for a good and long run application of motor.

 in a dc machine residual magnetism is present and it plays very important role in starting of any dc machine. it’s present because of the previous application on the same motor, it also provides some no-load voltage.

 sparking at brushes and commutator segments lead to damage of commutators, which is the main distinguishable component in a dc machine. so, it is advisable to fasten the commutation speed and avoid sparking.

 there are 5 steps in the construction of the single phase induction motor. they are stator, stator windings, rotor, starting switches, electrolytic capacitor.

 the stator is made up of a block of laminations. the block of laminations are made up of cast iron or die cast aluminium alloy frame.

 the slots house the starting and running windings. the single phase induction motors are generally wound with concentric coils.

 there are basically 3 kinds of single phase windings. they are concentric, progressive and skein.

 the concentric windings have a single pole for a common centre. they have different pitches for each individual coil.

 the progressive windings is one kind of the stator windings. they are in the form of the single layer diamond coil windings.