In lap winding, the number of brushes is always

A. 2

B. 4

C. 2P

D. P

Answer: D. P
Explanation: 
  • The brushes in Dc machines are used for collecting the current from the commutator segment. 
  • The brushes are made from carbon. 
  • In Dc machines Number of brushes are equal to the number of parallel paths or the number of poles. 
  • For wave winding, a number of parallel paths are equal to 2 and the number of brushes is required also 2.  
  • For lap winding, the number of parallel paths(A) is equal to the number of poles(P) and a number of brushes required in lap winding are equal to the number of poles. 
  • In lap winding, there are equalizer rings are required for good commutation. The equalizer rings are used in lap winding because there are more parallel paths in lap winding than in wave winding. 
  • The equalizer rings are used in lap winding to reduce the unequal current distribution at brushes and reduce the sparking between the carbon brushes and commutator. 
  • In wave winding, there are dummy coils are used. 
  • The dummy coil provides the mechanical balance to the rotor only and dummy coils are physically connected but electrically not connected. 
  • The lap winding is used in low voltage and high current applications. 
  • The wave winding is used in high voltage and low current applications. 
  • The efficiency of the lap winding is less and the efficiency of the wave winding is more. 
  • In simplex lap winding number of parallel paths is equal to the number of poles. 
  • In duplex lap winding, the number of parallel paths is equal to twice the number of poles. 
  • In triplex lap winding, the number of parallel paths is equal to the thrice the number of poles.
  • The wave winding is called incomplete winding and some slots remain empty. these empty slots are filled with dummy coils. 
  • There is more emf induced in the wave winding and less emf induce in lap winding. 
  • The other name for lap winding is parallel winding or multiple winding. 
  • The other name for wave winding is two circuits or series winding.
  • For simplex lap winding range of the winding pitch of (2,-2). For progressive winding pitch = Forward pitch - Backward pitch. 
  • For simplex lap winding, commutator pitch is equal to 1 and -1. 
  • The resultant pitch in lap winding is equal to the difference between the back and front pitches. 
  • The resultant pitch in wave winding equals the sum of the back pitch and front pitch. 





Electrical Interesting Questions | All Posts
Previous Post Next Post