Monday, February 15, 2010



DC Machine Armature Winding

The Dc armature windings are always of the closed continuous type of double layer lap or wave winding. For small machines, the coils are directly wound in the armature slots using automatic winders.In large machines, the coils are performed and then inserted into the armature slots. Each coil consists of a number of turns of wire, each turn taped and insulated from the other turns and form the rotor slots. Each side of the turn is called the conductor. The number of the conductors on a machine's armature is given by

Z= 2CN

where : Z= numbers of conductors on rotor
C= numbers of coils on rotor
N= number of turns per coil

Since the voltage generated in conductor under the south pole opposite the voltage generated in the conductor under the North pole, the coil span is equal to 180 electrical degrees, one pole pitch. In a 2 pole machine 180 electrical degrees is equal to 180 mechanical degrees, whereas in a 4-pole machine 180 electrical degrees is equal to 90 mechanical degrees. In general, the relationship between the electrical angle and mechanical angle is

electrical angle = (P/2) mechanical angle

where P is the number of poles.


In one type known as Simplex Lap Winding the end of one coil is connected to the beginning of the next coil with two ends of each coil coming out at adjacent commutator segment. For a progressive lap winding the commutator pitch y = 1. A typical coil of N turns for a simplex lap winding is shown in figure below:

In the simplex lap winding the number of parallel path between brushes is equal to the number of poles. This type of winding is used for low-voltage, high current application.

Let us consider a f4-pole, 2-layer simplex lap winding with 8 slots. I f the number of turns per coil N = 1, the total number of conductors is Z = (2)(1)(8) = 16. The coil pitch is

y = 8/4 = 2 slots


In the wave winding, the two ends of a coil are connected to a commutator segments that are approximately 360 degrees apart. This way all the coils carrying current in the same direction are connected in series. Therefore, there are only two parallel paths between the brushes, a=2 independent of the number of poles. This type of winding is used low-current, high voltage application.


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