Electric Motors: Construction, Operation, and Types

Electric Motors: Construction and Operation

Current Motors: Establishment and Operation

Constitution

The constitution of these motors is determined by the need to establish a magnetic field and to have a series of coils traversed by electric current, and located within the field. They consist of two main elements: the stator and the rotor.

• The stator is the fixed part of the motor, responsible for establishing the magnetic field. It has a number of coils, called spools, placed around the poles of an electromagnet. These poles are attached to the housing.
• The rotor is the moving part of the motor. It consists of another set of coils, called induced coils, which are wound on the slots of an iron core that is called induced. The ends of the coils are welded to a series of copper plates, named delgas, which form the collector. The set is formed about an axis. The motor has brushes mounted on holders. These devices are in constant contact with the collector and supply electric current to the induced coils.

Operation

When connecting the motor to the power supply, electric current flows through the inductive coils, creating an electromagnet that generates the necessary magnetic field. This current also flows through the induced coils via the brushes and commutator. Once the magnetic field is established, pairs of forces act on the induced coils, causing them to spin and, with them, the rotor to rotate. Thus, the supplied electrical energy is converted into mechanical energy of rotation.

Starting of Current Motors

In the motor starting, the current drawn can be up to three times the rated current. It is therefore necessary to limit the heat generated by this current. To achieve this, simply place a rheostat in series with the armature.

Inversion of Direction

To reverse the direction of rotation, it is necessary to change the connections of the inductor with respect to the armature when the machine is stopped, changing either the inductor or induced connections. However, if the armature connections are changed, it must be done in a way that prevents the annulment of the existing magnetic field in the inductor.

Three-Phase Asynchronous Motor

Constitution

• Stator: A cast iron casing inside which a group of steel plates are arranged, forming grooves that house the stator windings. If the motor is three-phase, the windings are connected in a star or triangle configuration.
• Rotor: Depending on the type of equipment, there are two types:

a) Rotor Winding

Similar to a DC motor. Formed by electrical sheet pressure mounted on an axis and forming slots where the rotor winding is housed. Consisting of three phases whose ends are connected to each other and whose beginnings can be connected to three-ring connectors on the three brushes that rub, allowing power input to the rotor. The brushes are connected to three terminals (K, L, M) that must be united for the rotor to turn.

b) Squirrel Cage Rotor

It does not have a winding but instead has copper bars welded at the ends of two copper rings, and the whole assembly is mounted on a shaft. The copper bars are shorted in the rotor; hence, this is called a short-circuit rotor.