Specifications

43
Pole pitch
12
4
3
56
8
7
910
12
11
R YB
R YB
Pole pitch
in such a manner that their emfs add. The windings of the other phases are also similarly
completed. The current directions marked in Fig. 4.9, is an arbitrary direction at any instant.
Problem 2 : Develop a 3 phase, single layer concentric type of winding for a 4 pole ac machine
having 24 slots.
Solution : Slots per pole per phase = = 2 , From equation 3.5, slots per pole =
24
4
= 6
From equation 3.8, angle between consecutive slots, â = = = 30
0
.
The allotment of slots to the three phases for a pole pair is given in Fig. 4.10, and this
allotment repeats itself for other pole pairs.
Fig.4.10 - Slots per pole per phase
Half coil winding
If the first phase, say R or A phase starts at slot no.1, the Y or B phase should start at 120
0
/30
0
= 4 slots away ie., in slot (1 + 4 = ) 5, and the B or C phase should start at (5 + 4 =) 9.
The winding should be connected between alternate North and South poles. First, R or A
phase winding is started. If one side of the coil is placed in slot no. 1, the other side of the coil
should be placed in slot no. 8, ie., the last coil side of phase R or A phase under the next pole.
The coil side in slot no. 2 should be connected to the last but one coil side of the same phase
under the next pole, ie., slot no. 7, in this case. Now, the coils formed by coil sides placed in the
slots 1 and 8, and 2 and 7 belong to the same phase, and are concentric with each other.
Fig. 4.11 - Coil group connections for half coil winding
24
3x4
180
slots per pole
180
6