Page 185 - Electrician - TT (Volume 2)

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B phase starts from 1+4 = 5th slot and
C phase starts from 1+4+4 = 9th slot.
6 Arrangement of coils
As in the example 12 coils with pitches as 7 & 5 slots.
1-8,2-7; 5-12, 6-11; 9-16, 10-15; 13-20, 14-19; 17-24, 18-23; 21-4, 22-3.
Grouping of coils

The coil should start from every alternate 2 slots (i.e.) 2 slots for top sides and two slots for bottom sides. As per
the example, coils start from 1 & 2, 5 & 6, 9 & 10, 13 & 14, 17 & 18, 21 & 22.
As the connection is half-coil type, with the help of one group of coils, 2 poles need to be created. Hence grouping
is as follows:
A B C
1-8, 2-7 5-12, 6-11 9-16, 10-15

13-20, 14-19 17-24, 18-23 21-4, 22-3
In whole coil connection, the starting end connection is from the alternative groups (i.e.) if ‘A’ starts
from the first group, ‘B’ starts from third group and ‘C’ starts from fifth group. Whereas in half-coil
connection, the starting ends will be from continous group, if ‘A’ starts from the first group, ‘B’
starts from second group and ‘C’ starts from the third group. Refer to the developed diagram.

7 End connections (Fig 1): Half coil connection.(End to start and start to end)
Coil connections : Half coil connection. (Fig 2)
In half coil connection, the connection of the coil group shall be from the finish end to the start end and then from
the start end to the finish end of the group coils as shown in Fig 2.

Fig 1 Fig 2

Development diagram : Draw the development diagram showing the coil group and end connection. As an
example a development diagram is shown in Fig 3.
Ring diagram
Cross check the end connection with the help of the ring diagram as explained below. Write the end connection
table and mark the direction of current using the clock rule. Note that when a three-phase supply is given to
the windings at an instant, and if two phases carry current in one direction, the third phase carries current in the
opposite direction as shown in Fig 4.

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