CONCENTRICCONCENTRIC WINDINGWINDING Three-phase concentric winding consists of coil groups laid in

the slots so that all the coils of each group are concentric. That is, the coil with the smallest slot pitch is surrounding by

the coil with the next larger slot pitch and so on to make up a coil group.

Each coil consists of several turns and the cross-over from one coil to the next is indicated by a short slanted line (jumper).

In order to construct the diagram for a winding, the following

data must be known:S - The number of slots in the stator

P – The number of poles

m – The number of phases

YS – The pitch of the winding

a – The number of parallel circuits in the windings

The pitch of the winding is determined by the formula

The pitch is the distance between two sides of a coil expressed as the difference between the numbers of the slots in which the sides lie.

Another important value of the winding of ac machines is the number of slot per phase per pole denoted by the letter q. It can be determined by the formula

Sometimes q is called a pole-phase group is defined as a group of coils of a phase under one pole.

The number of slots per pole per phase in concentric winding can be seen directly from the diagram. It is equal to the number of coils in a coil group.

P

SYS

Pole-pitch

Coil-sides

mP

Sq

q

Start (S)

Finish(F)

Jumper

A coil-group with 3-coils

Y3

Y1

Y2

1

2

310

12

11

CONNECTTNG COIL GROUPS INTO PHASES

As soon as all the coils have been laid in the slots, the coil groups are connected in to phases.

Each group is provided with two leads for the start and finish of the group.

The total number of leads is therefore twice the number of coil groups.

A stator winding must have six leads brought out to the terminal panel these leads being the beginnings and ends of the three phases.

All the reaming leads must be interconnected in the respective phases with in the winding.

It is now necessary to decide in order to determine the beginnings and ends of each phase.

IN GENERAL TWO MAINS RULES ARE IN GENERAL TWO MAINS RULES ARE FOLLOWEDFOLLOWED

The distance between the beginning of the phase and the distance between the ends of the phase must be equal to 120 electrical degrees.

Any slot can be chosen as the beginning of the first phase.

The coil groups in each phase should be interconnected by joining there unlike leads, i.e. start to finish, or finish to start.

Example#1: on concentric winding Given data

S=24; p=4;m=3; a=1; type=Concentric• Solution

a) The number of coil groups, K

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

c) Coil pitch

The shorter coil pitch = YS-1=6-1=5 The larger coil pitch = YS+1=6+1=7

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 C is slot 1+2=1+8=9

64

24

p

SYS

243

24

pm

Sq

Full-Pitch ( average pitch)

i.e. there are two coils in a group

62

43

23K P

i.e. there is two coil groups per phase

7204180180 P

3024

720

S

slots430

120120

B

B’

A’

A

C

C’600

Phase sequence

A A C’ C’ B B A’ A’ C C B’ B’ A A C’ C’ B B A’ A’ C C B’ B’

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

connection Diagrams

A

A’

Phase A

1 8

2 7

13 20

14 19

I

IV

+7

+5

+7

+5

B

B’

Phase B

5 12

6 11

17 24

18 23

II

V

C’

C

Phase C

9 16

10 15

21 4

22 3VI

III

PROCEDURE FOR CONSTRUCTING OF CONCENTRIC WINDINGS

Data: S= 24, P = 4, a = 1, q = 2, K = 6

1

2 8

7

6

5

4

3 9

10

19

18

11 17

1614

1513

12

23

22

21

20 24

Coil Groups of Phase A2. The first and second slots will be occupied by left-hand

sides of the first coil group of phase A.

3. Leave four, or 2q slots free for other two phases occupy slots 7 & 8 with the right hand side of the first coil group.

4. Next to it will lie a second coil group of the same size which occupies slots 9,10,15,16.

Coil Groups of Phase B In order to find, where the second phase (B) should begin, it is

necessary to know the angle between slots in electrical degrees.

=180.P = 180.4 = 7200 – Electrical degree The angle between adjacent slots,

The distance between phase beginnings will have

1

2 8

7

6

5

4

3 9

10

19

18

11 17

1614

1513

12

23

22

21

20 24

slots430

120120

3024

720

S

Coil Groups of Phase C

1

2 8

7

6

5

4

3 9

10

19

18

11 17

1614

1513

12

23

22

21

20 24

3

4

3

4

22

21

21

22

1

2 8

7

6

5

4

3 9

10

19

18

11 17

1614

1513

12

23

22

21

20 24

21

22 3

4

22

21

3

4

NSNS

Current direction

N

1-6

N

13-18

S

7-12

S

19-24

1

2 8

7

6

5

4

3 9

10

19

18

11 17

1614

1513

12

23

22

21

20 24

21

22 3

4

22

21

3

4

NSNS

Phase A – Coil groups interconnection

1

2 8

7

6

5

4

3 9

10

19

18

11 17

1614

1513

12

23

22

21

20 24

21

22 3

4

22

21

3

4

NSNS

Phase B – Coil groups interconnection

1

2 8

7

6

5

4

3 9

10

19

18

11 17

1614

1513

12

23

22

21

20 24

21

22 3

4

22

21

3

4

NSNS

Phase C – Coil groups interconnection

1

2 8

7

6

5

4

3 9

10

19

18

11 17

1614

1513

12

23

22

21

20 24

21

22 3

4

22

21

3

4

NSNS

A B’A’C’ CB

Terminals

1

2 8

7

6

5

4

3 9

10

19

18

11 17

1614

1513

12

23

22

21

20 24

21

22 3

4

22

21

3

4

NSNS

A B’A’C’ CB