01․ In a DC generator if field winding attains the critical resistance
In a DC generator if field winding attains the critical resistance, the voltage build-up will not take place and the generated emf will be zero.
02․ In a DC machine, the angle between the stator and rotor fields is
The angle between the stator and rotor fields is zero to generate maximum torque.
03․ The purpose of providing dummy coils in a generator is
In DC machine there are some coils in armature winding called dummy coils which are electrically not connected so there is no any current in these coils, so these coils don't give any contribution in power. These coils are there only to provide mechanical balance.
04․ Lamination of core are generally made of
Because of magnetic losses, rotor is built using armature core which in turn is made with many low-hysteresis silicon steel laminations. These laminations are stacked together to create cylindrical structure. Thus hysteresis and eddy current loss are reduced.
05․ Poles of DC machine are often laminated to
The pulsation losses are rotor surface losses and eddy-current losses in the rotor bars and therefore the poles are laminated to reduce them.
06․ The ventilating ducts in most of DC machine are
Both axial and longitudinal ventilation systems are used in DC machines.
07․ In a commutator
Mica in commutator is stronger than copper to protect cascading failure of commutator and brush assembly.
08․ In DC machine, the armature windings are placed on the rotor because of necessity for
The armature windings are placed on the rotor in order to facilitate the process of commutation.
09․ What are slot wedges in a DC machine made of?
Slot wedges are used to reduce the air gap flux to reduce armature reaction. So they are made up of silicon steel.
10․ The armature of DC machine is made of silicon steel lamination to
Because of magnetic losses, armature core is made with many low-hysteresis silicon steel laminations. These laminations are stacked together to create cylindrical structure. Thus hysteresis and eddy current loss are reduced.