The commutator is one of the core components of a DC motor, and its performance plays a decisive role in the operation of the motor. Once the commutator malfunctions, it may lead to poor commutation of the motor. In severe cases, it may also cause other accidents, resulting in damage to the DC motor, affecting the operation of the winch, turntable, and mud pump, and delaying the drilling production.
English: commutator, commonly known as the rectifier.
The commutator is composed of brushes and a commutator ring. It is a component in a DC permanent magnet series-excited motor that enables the motor to keep rotating. In some motors, we can see a conductive ring composed of many copper pieces installed in the rotor. This ring is connected to an external power source through a pair of brushes. For a motor, we call it a commutator, and for a generator, we call it a rectifier.
The commutator includes: mechanical commutator, semi-plastic commutator, and fully plastic commutator. The commutators used in automotive starters mainly include mechanical arched commutators and plastic commutators.
In terms of structure, the commutator is composed of several contact pieces arranged in a circular shape, which are respectively connected to each contact on the rotor. The two external electrodes are called brushes, which are in contact with them, and only two of the contact pieces are in contact at the same time.
The principle is that when the coil passes through an electric current, under the action of a permanent magnet, it will rotate through the forces of attraction and repulsion. When it rotates to a position in balance with the magnet, the wire that was originally conducting electricity and corresponds to the contact piece on the commutator will be separated from the brush, and the brush will be connected to the contact piece corresponding to the coil that generates the driving force. By repeating this process continuously, the DC motor will keep rotating.
Without the function of the commutator, the motor can only rotate less than half a turn and then get stuck, and it can only be used as an electric brake. It is a device that uses the centrifugal force generated during the rotation of the motor as the power to control the size of the starting resistance, so as to reduce the starting current of the motor, increase the starting torque, and enable the wound asynchronous motor to operate without brushes and automatically. It is mainly composed of a casing, starting liquid, moving pole plate, spring, terminal post, safety valve, exhaust valve, etc. This liquid resistance starter has the characteristics of small starting current, large starting torque, automatic adaptation to the changes of the power supply and load, and protection of the motor. The commutator is a high-speed rotating device, and its rotor winding will be affected by electromagnetic force and centrifugal force. Although it has always been operating under rated parameters, the welding interface between the rotor winding and the commutator riser is a weak point of the commutator rotor, and the traditional soldering process is used. Combined with the measurement results of the DC resistance between the pieces, it is judged that the welding points between the rotor winding and the commutator riser are loose, resulting in fatigue of the end wires, increasing the contact resistance, generating more heat, accelerating the oxidation of the contact surface, further increasing the contact resistance and the heat generation. This vicious cycle will eventually lead to the insulation of the commutator rotor being damaged by high temperature, causing arc discharge to the ground, and damaging the commutator. The results of the disassembly and inspection of the commutator show that the test data and judgment conclusions of the rotor winding are accurate. When the motor commutator is working, in addition to transmitting longitudinal current, it also has the task of commuting the current in the short-circuited armature coil.
These currents are the reverse current and reactance voltage generated in the main current motor commutator, causing edge sparks and arcs when the brushes slide on the surface of the motor commutator. The influence of the motor commutator on the performance of the motor depends on the process of realizing circuit conduction when it slides at a relatively high speed relative to the brushes under certain conditions. Although the description of this process is complex and the theoretical research is still developing, through the comparative analysis of the operation status of micro-motors at home and abroad, it can be determined that wear is the most crucial factor leading to the change of contact resistance. The commutator mainly has specifications such as hook type, groove type, and plane type. It is refined from imported raw materials, and the performance of the product reaches the international advanced level. It is widely used in the fields of power tools, household appliances, automotive, and motorcycle motors; the collector ring, carbon brush holder, and terminal board have various specifications and models of products, which are applied to the fields of automotive generators, gasoline generators, etc. The commutator plays the role of rectification, and its function is to make the current direction in the armature winding alternating, so as to ensure that the direction of the electromagnetic torque remains unchanged. In a generator, the commutator can change the alternating electromotive force in the components into a DC electromotive force between the brushes; in a motor, it can change the externally applied DC current into an alternating current in the components, generating a torque in a constant direction.
