Page 187 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS ELECTRICIAN - CITS

Refer to Fig 4 in which at the instant shown in x-x we have phases A and B as positive polarity and C has negative
polarity.

Mark the direction of current in the slot and it shall represent production of the required number of poles as per
the example given below.
Whenever you come across a 3-phase induction motor having a single layer concentric type half coil winding
follow the above mentioned procedure and prepare the winding table. Subsequently draw the end connection,
development and ring diagrams.

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

3 phase squirrel cage induction motor - double layer

distributed type winding

Objectives: At the end of this lesson you shall be able to:
• explain the meaning of double layer winding
• explain the winding terms and calculations pertaining to double layer distributed type winding
• draw the end and coil connection diagrams
• draw the ring and developed diagrams.

There are different types of winding used in 3-phase AC motors. Some of the 3-phase windings are double layer,
that is, there will be as many coils as the number of slots. For example 12 coils in the case of 12 slots, 24 coils in
the case of 24 slots. 36 coils in the case of 36 slots, 48 coils in the case 48 slots. Further in the case of distributed
winding the size of all the coils, pitch and shape will be the same as these coils are normally former wound. By
virtue of the arrangement of these coils in slots, they overlap each other just like in a woven basket. This is also
a type of distributed winding.
In double layer winding each slot contains two coil sides i.e. the bottom half contains the left hand coil side while
the top half contains the right coil side of some other coil.
Calculations for double layer distributed winding : The winding data of the distributed double layer winding
will be within the following limitations. As an example 3-phase double layer distributed winding for an induction
motor having 36 slots 36 coils 4 poles is discussed below.
I Grouping
Total No. of coils
1 No. of coils/phas e = No. of phase
As per the exa mple ,
36

No. of coils/phase = = 12 coils per phase.
3

II Pitch

No . of slots
Pole pitch=
No . of poles
36
As per the example, pole pitch = = 9 slots
4

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CITS : Power - Electrician & Wireman - Lesson 86-92 CITS : Power - Electrician & Wireman - Lesson 86-92