The armature winding is very important element of a machine, as it directly takes part in the conversion of energy from one form into another. The requirements which a winding must meet are diverse and often of a conflicting nature. Among these requirements the following are of major importance.
- The winding must be designed with the most advantageous utilisation of the material in respect to weight and efficiency.
- The winding should provide the necessary mechanical, thermal and electrical strength of the machine to ensure the usual service life of 16-20 years.
- For D.C. machines proper current collection at the commutator (i.e., absence of detrimental sparking) must be ensured.
- According to the degree of closure produced by winding, armature windings are of the following two types:
- Open coil winding
- Closed coil winding:
The closed armature windings are of two types:
(i) Ring winding
(ii) Drum winding
In general there are two types of drum armature windings:
(i) Lap winding
(ii) Wave winding.
“Lap winding” is suitable for comparatively low voltage but high current generators
whereas “wave of winding” is used for high voltage, low current machines.
- In ‘lap winding’ the finish of each coil is connected to the start of the next coil so that winding or commutator pitch is unity.
- In ‘wave winding’ the finish of coil is connected to the start of another coil well away from the fixed coil.