Specifications

46
Mush winding
In drawing this winding, the slots are numbered from 1 to 24 and the long and short sides
are alternatively drawn, as shown in Fig. 4.15
If the first phase, say R or A phase starts at slot no.2, the Y or B phase should start at 120
0
/
30
0
= 4 slots away ie., slot (2 + 4 = ) 6, and the B or C phase should start at (6 + 4 =) 10.
Slots per pole per phase = = 2. Thus a phase group has 2 slots.
Coil span =
12
2
= 6 slots. This is an even number and hence winding is not possible with
a coil span of 6 slots. So a coil span of 5 slots is used.
Starting R phase in slot no. 2, the coil side in slot no. 2 is connected to the coil side (2 + 5
= ) 7. The coil side 8 is connected to coil side (8 + 5 = ) 13, ie., 1. The coil groups are connected
in such a manner that their emfs add. The windings of the other phases are also similarly
completed.
The current directions marked in Fig. 4.15, is an arbitrary direction at any instant.
Problem 3 : Develop a 3 phase, single layer concentric type of winding for a 2 pole ac machine
having 24 slots.
Solution : Slots per pole per phase = = 4
From equation 3.5, slots per pole =
24
2
= 12
From equation 3.8, angle between consecutive slots, â = = = 15
0
.
The allotment of slots to the three phases for a pole pair is given in Fig. 4.16, and this
allotment repeats itself for other pole pairs.
Fig. 4.14 - 3 phase 4 pole 24 slots single layer winding diagram (whole coil)
24
3x4
24
3x2
180
slots per pole
180
12