Commutation in universal motors refers to the process of reversing the direction of current flow in the armature winding of the motor to ensure continuous rotation of the rotor. Universal motors are a type of electric motor that can operate on both alternating current (AC) and direct current (DC) power sources. They are commonly used in applications where high speed and variable speed control are required, such as in power tools, vacuum cleaners, and kitchen appliances.
The basic components of a universal motor include the armature (rotor), the field windings (stator), and a commutator. The armature is the rotating part of the motor that interacts with the magnetic field produced by the field windings to generate mechanical motion. The commutator is a segmented cylindrical component attached to the armature shaft, and it plays a crucial role in the operation of the motor.
Here's how commutation works in a universal motor:
Current Flow: When power is supplied to the motor, current flows through the field windings, creating a magnetic field. Simultaneously, current is also sent through the armature windings, which are wound around the armature core. The interaction between the magnetic field and the armature current generates a torque that causes the armature to rotate.
Commutator Design: The commutator consists of a series of insulated metal segments (usually copper) that are attached to the armature shaft. These segments are arranged in a circular pattern and are separated by gaps.
Reversing Current Direction: As the armature rotates, the commutator segments come into contact with stationary carbon brushes. These brushes maintain electrical contact with the commutator. The critical aspect here is that the direction of current in the armature windings needs to be reversed every half-turn to ensure continuous rotation in the same direction. This reversal of current direction is achieved through the commutator's design.
Commutation Process: When a segment of the commutator passes under a brush, the electrical connection to that segment is established. As the armature continues to rotate, the segment moves away from the brush, breaking the connection. At this point, the commutator is in a neutral state where neither current nor voltage is applied to the armature winding. As the armature rotates further, the next commutator segment comes into contact with the brush, but the polarity of the current reverses due to the mechanical arrangement of the winding. This reversal of current direction ensures that the torque generated by the interaction between the magnetic field and the armature current always acts in the same rotational direction.
By alternating the current direction in the armature winding through the commutator, the universal motor is able to continuously rotate in one direction, regardless of whether it is powered by AC or DC. However, this commutation process can also introduce sparking and wear on the commutator and brushes, which can lead to maintenance requirements over time.