Page 154 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

where K = any part of S/P or C/P that is subtracted to make Ys an integer.
Back pitch (YB) : The distance measured in terms of the armature conductors which a coil advances on the back
of the armature is called back pitch and is denoted by YB. This is illustrated in Figs 5 and 6. The back pitch is also
equal to the coil-pitch.

Fig 5 Fig 6

As shown in Fig 7, coil side 1 is connected on the back of armature to coil side 8 (same coil). Hence YB = 8 – 1
= 7 conductors.
Front pitch(YF) : The number of armature conductors or elements spanned by a coil on the front (commutator
end of an armature) is called the front pitch and is designated by YF. This is shown in Figs 5,6 and 7. Coil side
8 is connected to coil side 3 (second coil) through the commutator segment. Hence YF= 8 – 3 = 5 conductors.
Average pitch (YA) : The average of the front pitch YFand the back pitch YB is called average pitch.YA

Y Y
i.e., Y A B F
2

It is expressed in number of conductors.
Resultant pitch (YR) : In general, it may be defined as the distance between the beginning of one coil and the
beginning of the next coil to which it is connected or it is the distance between the beginnings of two consecutive
coil sides as shown in Figs 7 and 8 and denoted by letter YR. As in Fig 9, YR=YB–YF, i.e. YR =7–5 =2 conductors.
The resultant pitch YR depends upon the type of winding like lap or wave, as well as simplex or multiplex.
Commutator pitch(Yc) : It is the distance (measured in commutator bars or segments) between the segments to
which the two ends of a coil are connected. It is denoted by Yc. From the Figs 5,6 and 7, it is clear the commutator
pitch Yc = 1 segment.
The commutator pitch Yc varies with the type of winding, like lap or wave as well as simplex or multiplex.
Types of DC armature windings
Lap and wave winding : The DC armature windings are classified into two main groups, lap and wave windings.
The difference between them is the manner in which, the leads are connected to the commutator segments.
Simplex lap winding : In a simplex lap winding, the end lead of coil 1 is connected to the beginning lead of the
adjacent coil(coil 2) through the commutator segments. The commutator pitch of one segment is maintained.
Fig 8 shows the lead connection of a simplex lap winding.

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