Page 182 - Electrician - TT (Volume 2)

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To insulate the coil sides from each other within the slot follow the procedure shown in Fig 17 for both open and
semi-closed slots. A creased separator or insulation paper of proper width, length and thickness (usually 0.25 to
0.375 mm) is used as insulation between the top and bottom coil sides in the slot. Slide an awl over the bottom coil
side as shown in Fig 18a and press it over the bottom coil and slide the separator underneath the awl as shown
in Fig 18b. Let the separator project about 10mm beyond the core on either side.

Method of overlapping : Now insert one coil side in slot number 24 (coil side 47) and the other coil side of the
same coil (coil side 10) in slot number 5 as the top coil over the bottom coil side 9. Likewise insert another coil side
45 of a next coil in slot number 23 and the other coil side 7 of the same coil in slot number 4. Proceed likewise till
you reach slot number 6. During this process as you reach near about the 10th slot or much earlier you will feel
the hindrance of the throw coils which are tied to the stator. At that time untie the cotton tape from the stator and
tie the bunch in the opposite side of the stator as shown in Fig 19 with a leatheroid paper in between the coils
and the core.
While tieing the cotton tape see that the slot number 6 is easily approachable without any difficulty. After inserting
the bottom coil side 11 in slot 6 insert the corresponding other coil side 22 in slot 11 as the top coil side. After
inserting the top coil side fold the slot liners one side over the other, insert the separator and the wedge.
Now untie the throw coil bunch and release the free end of the coil in slot 5 and insert the same as top coil side in
slot 10. Proceed likewise to insert the coils from slots 4,3,2 and 1 in the corresponding slots.
Overhang Insulation : Now cut and prepare the leatheroid paper to the shape of half moon as in the original
which is to be used as phase insulation between the overhanging coils. According to the developed diagram coil
sides 1 and 3 form the first phase, 5 and 7 the second phase and 9 and 11 form the 3rd phase. Identify these coils
and start inserting the leatheroid paper between 3 and 5 as well as between 7 and 9.

Thus proceed to insert this phase insulation for the entire winding as shown in Fig 20. If you find the space
between these coils is less, you may use a fibre wedge to prime the coils to facilitate insertion of the leatheroid
paper. Do not use too much force which may crack the slot liner insulation and result in grounding the coils with
the stator core.
End connections : There are three types of connections to be made - first the coil connection for coil grouping,
second for connecting the coil groups in one phase, and thirdly connecting the lead wires. Better to proceed
one by one in the above sequence. Any connection to be made in winding the wires should start with proper
identification of the coil ends. For a beginner, it may be necessary to refer to the developed diagram, connection
diagram, as well as the actual winding often to eradicate the confusion.

Fig 19 Fig 20

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