Armature windings

The winding through which a current is passed to produce the main flux is called the field winding .the winding  in which  voltage is induced is called the armature winding.

Some Basic terms related to the armature winding are defined as follows

• A Turn  Consists of two conductors connected to one end by an end conductor.
• A coil is formed by connecting several coils in series.
• A winding is formed by connecting several coils in series. 

The turn , coil and winding are show schematically in fig

the beginning of turn or coil , is identify by the symbol S (start) and end of the turn or coil by symbol F (finish).

The concept of electrical degree is very useful in the study of machine. if 

0md = mechanical degree or angular measure in space.

0ed   =  electrical degree or angular measure in cycles.

For a pole machine , electrical degree is defined as following.

The advantage of this notation is that expressions written in term of electrical angles apply to machines having any number of poles.

The angular distance between the centres of two adjacent  poles on a machine is known as pole pitch or pole span.

Regardless of the number of poles in the machine, a pole-pitch is always 180 electrical degrees.

The two sides of a coil are places in two slots on  stator surface. the distance between the two sides of coil is called the coil-pitch. If the coil-pitch is one pole pitch, it is called the full-pitch coil. If the coil pitch is less than one pole pitch, the coil is called the short-pitch coil or fractional-pitch coil. 

Armature winding in an alternator may be either closed type open type. Closed winding forms star connection in armature winding of alternator. There are some common properties of armature winding.

1. First and most important property of an armature winding is, two sides of any coil should be under two adjacent poles. That means, coil span = pole pitch.
2. The winding can either be single layer or double layer.
3. Winding is so arranged in different armature slots, that it must produce sinusoidal emf.

Types of Armature Winding of Alternator

There are different types of armature winding used in alternator. The windings can be classified as

1. Single phase and poly phase armature winding.
2. Concentrated winding and distributed winding.
3. Half coiled and whole coiled winding.
4. Single layer and double layer winding.
5. Lap, wave and concentric or spiral winding and
6. Full pitched coil winding and fractional pitched coil winding.

In addition to these, armature winding of alternator can also integral slot winding and fractional slot winding