DC Motor and MCC Motor: Principles and Operation
Constitution of an MCC Motor
It is based on the principles of electromagnetic force and induced electromotive force. To carry out these principles, it consists of inductive motors and induced components:
- Inductor: Its mission is to create the electric field. It is located in the fixed part or stator of the motor. It is formed by a copper wire coil placed around a ferromagnetic material with polar exhibition. The coil carries an electric current, whose direction will depend on the sign of the magnetic field created.
- Induced (Armature): Its mission is to create opposing magnetic fields in the motor. It is shaped by copper conductors arranged in a coil. The coils are located in grooves in a cylindrical package of ferromagnetic sheets, which is subject to the axis of rotation of the engine, and the rotor is the machine.
The beginning and end of the various coils are electrically connected to a collector, a piece of thin copper that rotates with the shaft. The segments are the parts into which the manifold is divided and are isolated from each other. To introduce the current in the armature conductors, brushes are used. These are pieces of graphite that are in contact with the slip rings, connecting the external circuit to the inside of the machine.
Constitution of a DC Motor
- Fixed Stator: Formed by isolated magnetic sheets, grooved internally. A three-phase winding is introduced into these slots.
- Rotor (Moving Part): Formed by isolated magnetic sheets, slotted externally. There are two choices for the motor winding:
- Copper or aluminum bars injected into these slots, shorted at both ends, leading to a squirrel-cage asynchronous motor.
- A three-phase short-circuit winding similar to the stator, giving rise to a wound-rotor asynchronous motor.
The air gap between the stator and the rotor is called the operating air gap. Its operation is based on the rotating magnetic field created by a three-phase current.
Speed Regulation
The intention is to maintain the speed at a preset value. The regime rate is conditioned by equal torque and resistance, as defined by the intersection of the respective mechanical characteristics. The problem of speed regulation is to act on the following parameters:
- If we want to regulate the speed, we act on the applied voltage or the flux.
- We can act on the voltage with one of these methods:
- Inserting a resistance in series with the armature.
- Varying the supply voltage.
- If we act on the flow, we will regulate the flow of excitation through the connection of a resistor that, depending on the type of engine, will be connected one way or another.
Inversion of the Direction of Rotation
Electric motors can work in both directions of rotation, simply by changing the wiring of the armature with respect to the inductor. The motor torque direction depends on the magnetic field and the direction of current in the armature conductors. Therefore, it is sufficient to reverse the connections on the inductor and the armature. If the change is made when the machine is stopped, it is indistinct to change the connections of the inductor or the armature. If done while running, it is necessary to change the connections of the armature and not the inductor, so that the engine is not left without excitation.
Braking of DC Motors
Based on the principle of reversibility that such a machine has. That is, at the time of stopping the engine, it goes on to function as a generator, reversing the torque. This type of braking is known as electric braking, and can be done in two ways:
- Dynamic Braking: It consists of dissipating the energy that is generated by acting as a generator through braking resistors. These are often the same ones used for starting.
- Regenerative Braking: The energy generated is returned to the feeding line.