DOUBLE LAYER Double layer windings differ from single layer winding mainly on the following main points: Each slot is occupied by the side of two coils and each coil is

arranged to form two layer round stator. One layer of the winding lies in the bottom half of the slots

and the other in the top half of slots. Unlike the concentric winding double layer winding consists of

identical coils all of the same shape and pitch. In a double layer winding, the coil pitch is the distance

between the top and the bottom sides of the coil expressed by the number of slots spanned or by the coil sides or by the number of slots occupied by each coil side.

A coil pitch may be full or fractional. Majority stator windings use a fractional pitch because The amount of copper used in the overhang (end winding) reduced

and hence a saving on copper, and The magnitude of certain harmonics in the emf and also mmf is

reduced.

The full pitch is determined by

Usually the full pitch is shortened by one-sixth i.e. for example if the full pitch is 12 a fractional will be 10.

Since the coils are wound with a continuous length of wire there are no connections between turns.

P

SYS

Double Layer Three phase windings The main value characterizing the two layer winding is

the number of slots per pole per phase.

By looking double layer winding externally, it is not possible to determine q.

The total number of coils in two layer winding is equal to the number of slot since each side of a coil occupies one half of a slot which is equivalent to occupying one full slot per coil.

In order to avoid making solder joints between coils, several coils, depending upon slots per pole per phase, are generally wound from a single length of wire in to full coil group.

The number of coil groups per phase is a equal to the number of poles the whole winding. That is

This is, twice that in a single-layer winding.

mP

Sq

Pm

K mPK

Rule for double layer windingsThe coil groups should be connected to each

other by joining the leads of like polarity i.e. the finish of one group to the finish of the next group and the start of one group to the start of the next group.

Example # 4: on double layer winding Given data

S=12; p=2;m=3; a=1; type=Double layer: the pitch shortened by one slot• Solution

a) The number of coil groups, K

b) The number of slots per pole per phase, q

c) Coil pitch

Let us shorten the pitch by one slot and make YS = 5.d) The electrical angle,

e) The angle between adjacent slots,

f) The distance between the beginning of each phase,

g) If the beginning of Phase A is slot 1, then the beginning of phase B is slot 1+=5 and the beginning of phase B is slot 1+2=1+8=9

62

12

p

SYS

223

12

pm

Sq

Full-Pitch

i.e. there are two coils in a group

6233K P i.e. there is two coil groups per phase

3602180180 P

3012

360

S

slots430

120120

B

B’

A’

A

C

C’600

Phase sequence(Top layer Coil-sides)

A A C’ C’ B B A’ A’ C C B’ B’

1 2 3 4 5 6 7 8 9 10

11

12

Connection Diagrams

1 6'

2 7'

7 12'

8 1'

I

IV

+5

+5

+5

+5

5 10'

6 11'

11 4'

12 5'

III

VI

+5

+5

+5

+5

9 2'

10 3'

3 8'

4 9'

II

V+5

+5

+5

+5

Phase A Phase B Phase C

A’

AB C

B’ C’

PROCEDURE FOR CONSTRUCTING OF DOUBLE LAYER WINDINGS

Draw 24 vertical lines to represent the two coil sides lying in each of the 12 slots. For each slot the full line at the left hand side will represent a top a coil side and broken line at the right hand side a bottom coil side.

1 1' 2'2 3'3 4 4' 5'5 6'6 7 7' 8'8 9'9 10 10' 11 11' 12 12'1 1' 2'2 3'3 4 4' 5'5 6'6 7 7' 8'8 9'9 10 10' 11 11' 12 12'

Double layer winding

The top part of slot 1 will be taken as the beginning of the first phase. According to the selected fractional pitch, the conductor from slot 1 is now connected to that in the bottom coil side in slot 1 + 5 = 6’.

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

Since q = 2 i.e. each coil group will consists of two coils. The conductor must therefore leave the bottom of slot 6 to enter the top of slot 2 and from there the bottom of slot 7. The lead emerging from slot 7 will be finish of the first coil group.

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

Phase A : Coil groups

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

1'

8

8

1'

A

A’

Phase A

1 6'

2 7'

7 12'

8 1'

I

IV

+5

+5

+5

+5

Phase B: Coil groups

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

4'

5'

1'

4'

5'

1'

8 12

11

8

12

11

B

B’

Phase B

5 10'

6 11'

11 4'

12 5'

III

IV

+5

+5

+5

+5

Phase C: Coil groups

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

4'2'

3'

5'

1'

2'

3'

4'

5'

1'

8 12

11

10

9

8

12

10

9

11

C’

C

Phase C

9 2'

10 3'

3 8'

4 9'

II

V+5

+5

+5

+5

Current directionN

1-6

S

7-12

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

4'2'

3'

5'

1'

2'

3'

4'

5'

1'

8 12

11

10

9

8

12

10

9

11

N S

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

4'2'

3'

5'

1'

2'

3'

4'

5'

1'

8 12

11

10

9

8

12

10

9

11

N S

Current directionN

1-6

S

7-12

Phase A: Coil groups interconnection

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

4'2'

3'

5'

1'

2'

3'

4'

5'

1'

8 12

11

10

9

8

12

10

9

11

N S

Phase B: Coil groups interconnection

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

4'2'

3'

5'

1'

2'

3'

4'

5'

1'

8 12

11

10

9

8

12

10

9

11

N S

Phase C: Coil groups interconnection

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

4'2'

3'

5'

1'

2'

3'

4'

5'

1'

8 12

11

10

9

8

12

10

9

11

N S

Terminal leads

1 1' 4'43'32'2 5 5' 109'6 98'7' 876' 1211'1110' 12'

4'

A B’A’C’ CB

2'

3'

5'

1'

2'

3'

4'

5'

1'

8

12

11

10

9

8

12

10

9

11