Saturday, January 30, 2016

Lap winding; Simplex and Duplex Lap Winding

In small DC machines the coils are directly wound in the armature slots. In large DC machines, the coils are performed and then inserted into the armature slots. Each coil consists of a number of turns of wire, each turn taped and insulated from the other turns and form the rotor slots.

Each side of the turn is called the conductor. The number of the conductors on a machine's armature is given by

Z= 2CN
where :
Z= numbers of conductors on rotor
C= numbers of coils on rotor
N= number of turns per coil

There are two types of armature windings in DC motors :-
1.  Lap winding
2.  Wave winding.

Lap Winding:-
In this winding continuous coils overlap each other. In this winding finishing end of one coil is connected to the one commutator segment and starting end of next coil situated under same pole and connected with same commutator segment.

In Lap winding number of parallel paths are equal to number of poles.
In Lap winding also number of brushes equal to number of poles.
When two adjacent commutator bars make contact with a brush, one coil is shorted by the brush in the lap winding.
Its name “Lap” comes from that it doubles or laps back with its succeeding coils. Lap winding is as shown below:-

From above we can see that finishing end of coil - 1 and starting end of coil - 2 are both connected to the commutator segment - 2 and both coils are under the same magnetic pole that is N pole here.

Lap Winding has two types:-
1.   Simplex Lap winding
2.   Duplex Lap winding

1.         Simplex Lap Winding
In one type known as Simplex Lap Winding the end of one coil is connected to the beginning of the next coil with two ends of each coil coming out at adjacent commutator segment. For a progressive lap winding the commutator pitch y = 1.  In this winding number of parallel path between the brushes is equal to the number of poles. Simplex lap winding is as shown below:-

2.           Duplex Lap Winding
In this winding number of parallel path between the brushes is twice the number of poles is called duplex lap winding.
There are few points which must be taken care before designing lap winding:-

If,
Z = the number conductors
P = number of poles
YB = Back pitch
YF = Front pitch
YC = Commutator pitch
YA = Average pole pitch
YP = Pole pitch
YR = Resultant pitch

Then, the back and front pitches are of opposite sign and they cannot be equal.
YB = YF ± 2m
m = multiplicity of the winding.
m = 1 for Simplex Lap winding
m = 2 for Duplex Lap winding
When, YB > YF, it is called progressive winding.

YB < YF , it is called retrogressive winding.

Back pitch and front pitch must be odd.
Resultant pitch (YR) = YB - YF = 2m

YR is even because it is the difference between two odd numbers.

Average Pitch(YA)= YB+ YF
2

Pole Pitch (Yp)= Z/P

Back Pitch (YB)= Z/P

Commutator pitch (YC) = ±m
Number of parallel path in the Lap winding = mP