Winding Terminology

Winding Terminology 

1) Conductor : The part of the wire, which is under the influence of the magnetic field and responsible for the induced e.m.f. is called active length of the conductor. The conductor are placed in the armature slots.

2) Turn : A conductor in one slot, when connected to a conductor in another slot forms a turn. So two conductors constitute a turn. This is shown in the Fig. 1(a).

Fig. 1

3) Coil : As there are number of turns, for simplicity the number of turns are grouped together to form a coil. Such a coil is called multiturn coil. A coil may consists of single turn coil. The Fig. 1(b) shows a multiturn coil.

4) Coil side : Coil consists of many turns. Part of the coil in each slot is called coil side of a coil as shown in the Fig. 1(b).

5) Pole Pitch : It is centre to centre distance between the two adjacent poles. We have seen that for one rotation of the conductors, 2 poles are responsible for 360^oelectrical of e.m.f., 4 poles are responsible for 720^o electrical of e.m.f. and so on. So 1 pole is responsible for 180^o electrical of induced e.m.f.

Note : So 180^o electrical is also called one pole pitch.

       Practically how many slots are under one pole which are responsible for 180^oelectrical, are measured to specify the pole pitch.

       e.g. Consider 2 pole, 18 slots armature of an alternator. Then under 1 pole there are 18/2 i.e. 9 slots. So pole pitch is 9 slots or 180^o electrical. This means 9 slots are responsible to produced a phase difference of 180 between the e.m.f.s induced in different conductors.

       This number of slots/poles is denoted as 'n'.

6) Slot angle (β) : The phase difference contributed by one slot in degrees electrical is called slot angle β.

       As slots per pole contributes 180^o electrical which is denoted as 'n', we can write,

.^..    1 slot angle = 180^o/n

       In the above example,      n = 18/2 = 9,    while    β = 180^o/n  = 20^o

Note : This means that if we consider an induced e.m.f. in the conductors which are placed in the slots which are adjacent to each other, there will exist a phase difference of β^o in between them. While if e.m.f. induced in the conductors which are placed in slots which are 'n' slots distance away, there will exist a phase difference of 180^oin between them.