Specifications
67
From Fig. 5.3, it can be seen that the number of parallel paths in a lap winding, will be equal
to number of poles. A = P 5.1
where A = number of parallel paths; P = number of poles
The current through each armature coil / conductor will be the ratio of the total armature
current by the number of parallel paths, ie.,
5.2
where I = current through each armature conductor/coil; I
A
= total armature current
5.3 DOUBLE LAYER DUPLEX LAP WINDING DIAGRAM
Develop a winding diagram for a 4 pole, 12 slot duplex lap connected dc machine. Indicate
the position of brushes.
Solution : Slots per pole = = 3; Number of coils, C = number of slots = 12
Number of coil sides = 2C = 24; From equation 3.2, the back pitch,
From equation 3.3, the winding Pitch, Y = +2m = +4 for progressive winding (m = 2 for duplex
winding); From equation 3.5, the front pitch, Y
f
= Y
b
– Y = 7 – 4 = 3
Combining two simplex lap windings gives duplex lap windings.
Starting with coil side 1 (back end side), back pitch is added to obtain the bottom layer coil
side, ie., 8 (back end side). To the coil side 8 (front end side), front pitch is subtracted to obtain
the top layer coil side, ie., 5 (front end connection). Proceeding in similar way, all the coil sides
are connected and a winding table, as shown in Table 5.2.
Table 5.2 Winding Table for 4 pole 12 slots duplex lap winding
To draw the main winding diagram, first draw 12 solid vertical lines (equal to no. of coils) of
1 Set of simplex winding
18310
512714
9161118
13 20 15 22
17 24 19 2
21 4 23 6
2 Set of simplex winding
Top coil Side (-Y
f
) Bottom coil Side (+Y
b
) Top coil Side (-Y
f
) Bottom coil Side (+Y
b
)
equal length and equal distance. Next, draw 12 dotted lines nearer to the solid lines of same
length and distance, as shown in Fig. 5.4.
Assign odd numbers to the top layer coil sides of the solid lines and even numbers to the
bottom layer coil sides of the dotted lines.
Give the back end and front end connections with reference to the Table 5.2. Then, draw
solid vertical lines (equal to no. of coils) from the top mid-point of each front end connections, as
shown in Fig. 5.4.
I =
I
A
A
12
4
2 C
P
24
4
+ K= + K=6+ K=7