Page 183 - Electrician - TT (Volume 2)

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Three-phase induction motor winding (single layer

- concentric type - half coil connection)

Objectives: At the end of this lesson you shall be able to:
• state the general requirements pertaining to the concentric type of winding in 3-phase motors
• state the merits and demerits of concentric type winding
• explain the preparation of a winding table for concentric type winding
• explain how to draw the end and coil connection diagrams
• explain how to draw the developed and ring diagrams.

3-phase concentric winding : In general, concentric winding is found in single phase motors, and occasionally,
this type of winding is also used for 3-phase motors.

This concentric winding has to have two or more coils in a group consisting of different pitches. Further in 3- phase
concentric winding, all the three phases consist of the same number of coils, and produce similar concentric
poles. Stepped formers are used to prepare coils for concentric winding.
Merits and Demerits of concentric winding: This type of winding has some merits and demerits also.
Merits
1 This type of winding has more space for cooling.
2 No need of raising (lifting) the coil sides to interleave them during the winding.

3 It is easy to shape the coils uniformly.
4 Possible to save copper, because in distributed winding all the coils are of the same size; on the other hand in
concentric winding, coil groups only will be uniform, but coils of different pitches in concentric form are used.

5 As there is no interleaving of the coil sides, the winding could be done by machine resulting in faster production.
6 It is easy to make the end connection.
7 Easy to wind, as there is no overlapping of coils.
Demerits

1 Skilled labour is required to insert the coils in the slots.
2 A stepped former is required.
3 Not as efficient as basket winding.
1 Grouping
The example given below will clarify the following:
a whether concentric type of winding is possible for a given stator

b If yes, whether it should be half coil or whole coil connected winding.
Example
3-phase induction motor having 36 slots 12 coils 4 pole stator
We have
Total No. of coils
No. of coils per phase
No. of phases
12
4 coils/phas e
3
For whole coil connection
No. of coils/phas e
No. of coils/phas e/pole
No. of poles
4
1 coils/phas e/pole
4

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