WINDING

CONTENT• What is Armature winding?• Terms related to armature winding.• Single layer and double layer windings.• Comparison between closed and open windings.• Types of DC armature winding.• Types of AC armature winding.

What is armature winding?

• Armature winding: Armature winding may be defined as an arrangement of conductors to produce emf by relative motion in a hetropolar magnetic field.

Terms related to armature winding1) Conductor.2) Overhang.3) Turn.4) Coil.5) Coil side.6) Coil span or coil pitch.7) Pole pitch.8) Back pitch .9) Front pitch.10) Winding pitch.11) Commutator pitch.12) Numbering scheme.

Single layer and double layer windings.

• Depending upon the physical arrangement of conductors or coil sides in a slot,

• The armature windings can be classified as:a) Single layer winding.b) Double layer winding.

Single layer winding

Double layer winding

Comparison between closed and open windings.

Closed winding1. In this winding, there is a

closed path around the armature periphery.

2. These winding are always double layer type.

3. Closed winding are used in D.C. machine.

4. Design is not flexible.

Open winding1. In this, winding is not closed

instead the armature may be left open at one or more points forming several sections.

2. These winding can be either single layer or double layer types.

3. Open winding are used in a.c. Machines, induction and synchronous machines.

4. Flexible design.

Types of DC armature winding

• According to the way of connecting the conductors, D.C armature winding are classified as:-

1) Lap winding.2) Wave winding. Lap winding :- The way of connecting armature coil sides to

the commutator, there are two types of lap winding: Progressive lap winding . Retrogressive lap winding.

Lap winding.

a) Progressive lap winding

b) Retrogressive lap winding.

AC armature winding

• In ac machine ,the stator ac armature winding in which the alternating emf is inclued. The winding armature if a dc machines is closed and the closed windings are always double layer type. The winding used for armature of ac machines is open. The open winding can be either single layer or double later type.

Terms related to AC armature windings.

1) Coil span2) Full pitched winding3) Short pitched or chorded winding4) Integral slot winding5) Fractional slot winding

Winding factorsPitch factor or chording factor or coil span

factor.• It is defined as the ratio of vector sum of induced emfs per coil

to the arithmetic sum of the induced emfs/coil and is denoted by kp or kc.

• Kp = vector sum of induced emfs/coil arithmatic sum of the induced emfs/coil E=2 ES cosα/2

It is always less then unity

ES = induced emf in each side of the coil

• If the coil is full-pitched then the total induced emf in coil = 2Es .

• If the coil is short by an angle α, then their resultant emf E will be the vector sum of two voltages

• E =2 Es cos α/2

• Pitch factor kp =

=

=

(ii).Distribution factor or spread factor

Commonly Used AC WindingsThe following type of windings are most

commonly used for the stator of ac machine:

• (i) single layer mush windings• This winding is used for small induction

motors.

(ii) Double layer lap windings

• These windings are commonly used for medium and large size Ac machines like induction motors and synchronous machines.

• (i) Design and development of mush windings• This is a single layer winding and is most

commonly used for mall induction motors.

Conditions for designing a mush windings

a) The coils should have a constant span.b) There should be one coil side per a slot. It means that, the number of coil sides = number

of slots(c) There should be only one coil group per phase

per pole pair.(d) The coil span must be odd integer.