HIGHER HARMONICS

149

and its return, 1', 2', 3', covers another third of the circumference
of two poles, in the lower layer of the armature winding, 180°
away from 1, 2, 3. However, this type of true three-phase wind-
ing is practically never used in induction or synchronous machines,
but the type of winding is used, which is shown as 8, in Fig.
57 C. This is in reality a six-phase winding: each of the three

Q

T &££%&
8 P&?.!

2'

1

1o

2'

1o

A

'i%%&'

2'

2'

3' 2'0

1

8

3'

1o 3'

20

3'o 2'

20

3o 2'

1

1o 3' 2;

N S

1'

1o 3

\'

2'

FIG. 57.—Current distribution at air gap of induction motor, fundamental
and harmonics.
phases, 1, 2, 3, covers only one-sixth of the pitch of a pair of
poles, or ^ or 60°, and between the successive phases is placed
o
the opposite phase, connected in the reverse direction. Thus
the return conductors of phases 1, 2, 3 of the upper layer, are
shown in the lower layer as 1', 2;, 3'; in the upper layer, above
r, 2', 3', is placed again the phase 1, 2,- 3, but connected in the
reverse direction, and indicated as 10, 20, So- As 10 is connected
in the reverse direction to 1, and "I1 is the return of 1, lo is in