The Commutation Process in Armature Coils

The commutation process in an armature coil refers to the reversal of current as it crosses the commutator segments known as the MNA (Mid-Neutral Axis). This process is crucial for the proper operation of DC motors and generators. Let's explore this process in more detail.

What is Commutation?
Commutation is a process that ensures the continuous and smooth flow of current in the armature coil of a DC machine. It involves the reversal of current in the coil as it moves from one commutator segment to another. This reversal is necessary to maintain the desired direction of current flow in the external circuit, which in turn determines the rotation direction of the motor or generator.

The Role of MNA
The Mid-Neutral Axis (MNA) is an imaginary line located in the middle of the armature coil. It divides the coil into two equal halves. As the coil rotates, it passes through the MNA, and at this point, the current needs to reverse to maintain the desired direction.

The Process of Commutation
When the coil is in the position where it crosses the MNA, the current is flowing in a specific direction. To reverse the current, the commutator segments play a crucial role. The commutator segments are connected to the ends of the coil windings and are in contact with the stationary brushes.

Reversal of Current
When the coil is aligned with the MNA, the brushes make contact with the commutator segments. At this point, the current flows through the coil in a specific direction. As the coil moves further, the brushes start to lose contact with the current segment and simultaneously make contact with the next segment. This transition causes a momentary short circuit between the segments.

Spark Formation
During the transition, a spark is formed due to the short circuit. This spark is known as the commutation spark. The spark occurs because the current tries to maintain its previous direction even as the brushes move from one commutator segment to another. The spark is undesirable as it causes arcing, heating, and reduced efficiency.

Importance of Proper Commutation
Proper commutation is essential for the smooth operation of DC machines. It ensures that the current in the armature coil maintains the desired direction, resulting in the desired rotation of the motor or generator. Proper commutation also minimizes sparking and reduces the wear and tear of the brushes and commutator.

In conclusion, the commutation process involves the reversal of current in the armature coil as it crosses the MNA. This process is crucial for the proper functioning of DC motors and generators, ensuring continuous and smooth current flow and minimizing sparking and arcing.