Commutator Action in a DC Motor

Commutator Action in a DC Motor Points : Commutator Action in a DC Motor In the case of a dc motor, it is necessary that the current through the coils of the. armature winding be reversed as a particular coil leaves one pole (say, the north pole), crosses the neutral line and comes under the influence of next-pole which is of opposite polarity (i.e. the south pole). The operation of the commutator, that serves the above purpose, is given below:

Consider a single turn coil, whose leads are soldered to commutator segments a and b, each carrying a brush, as illustrate. The positive side of the supply line is connected to left hand brush and negative side to the right hand brush. In position I the line current arrives at the commutator segment a, flows through the bottom side 1 of the coil away from the reader and then through the upper (as shown by dot in the circle), reaches the commutator segment b and flows again into the line through the brush. The coil will tend to rotate in clock-wise direction, as determined by Fleming’s left hand rule. In position lithe coil is on the magnetic neutral line; there in no contact between the commutator segments and brushes, and there is no flow of current through the coil. The coil crosses the neutral line by inertia. In case of a multi-turn coil, the remaining turns of the coil will supply the necessary torque.

In position III, the two sides of the coil, 1 and 2, have changed poles, and the current through them has reversed. The commutator segments, however, have also changed contact with the brushes. Thus the coil will continue to rotate in the same direction as before, i.e. clockwise.