Types of Armature Windings

The following terms used in connection with armature winding should be kept in mind:

(A) Conductor: The length of a wire lying in a magnetic field is called a conductor. It may be made of one or two or more parallel strands.

(B) Turn: When the two conductors lying in a magnetic field are connected in series, so that emf induced in them help each other or the resultant induced emf becomes double (assuming full pitch coil) of that due to one conductor, it is knows as a turn.

(C) Coil: When one or more turns are connected in series it is termed as a coil. The group of wires or conductors constituting a coil side of a multi-turn coil is wrapped with a tape as a unit.

(D) Coil span or coil Pitch: It is the distance measured in terms of armature slots or armature conductors between two sides of a coil.

(E) Pole pitch: it is defined as the number of conductors per pole. If there are 24 conductors in a 4 pole generator then pole pitch = 24/4 = 6

(F) Full pitch: if the coil span is equal to the pole pitch then the winding is called full-pitched winding. Full pitched winding have the advantage of giving maximum emf induced because, the coil sides of a coil lie under opposite poles.

If the coil span is less than the pole pitch then the winding is called short-pitched or fractional-pitched. The advantages of fractional pitch winding are that the saving is affected in the copper in end connections and commutation is improved.

If the coil span is more than the pole pitch then the winding is called over pitched windings. There will be under the influence of two similar poles and emf induced in that coil be in opposition (may be equal to zero).

(G) Back pitch (Y_B): It is the distance measured in terms of the armature conductors between the first and last conductors of a coil. It is also called the coil span or coil spread. It is denoted by Y_b.

(H) Front Pitch (Y_F): It is the distance in terms of armature conductors between the second conductor of one coil and the first conductors of the next coil which are connected to the same commutator segment on the front or commutator end. It is denoted by Y_F.

(I) Resultant Pitch (Y_R): It is the distance between the beginning of one coil and beginning of the next coil to which it is connected.

(J) Commutator Pitch (Y_C): It is the distance between the commutator segments to which the two ends of a coil are connected.

(K) Single-layer winding: In this winding one conductor or one coil side is placed in each armature slot.

(L) Double-layer winding: In this winding, there are two conductors or two coil sides are placed in each armature slot.

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