ELECTRIC MACHINES

An electrical machine is a device capable of transforming any form of energy into electrical energy or vice versa, and machines that transform electricity into the same form of energy but with a different presentation more convenient for transport or use are also included in this definition. . They are classified into three large groups: generators, motors and transformers.

Generators transform mechanical energy into electrical energy, while motors transform electrical energy into mechanical energy by turning a shaft. The motor can be classified as DC motor or AC motor. Transformers and converters preserve the form of the energy but transform its characteristics. An electrical machine has a magnetic circuit and two electrical circuits; Normally, one of the electrical circuits is called excitation, because when it is crossed by an electric current, it produces the necessary ampere-turns to create the flux established in the whole of the machine.

From a mechanical vision, electrical machines can be classified as rotating and static. Rotating machines are provided with rotating parts, such as dynamos, alternators, motors. Static machines do not have moving parts, like transformers.

Power of electrical machines The power of an electric machine is the energy developed in unit time. The power of a motor is that supplied by its shaft. A dynamo absorbs mechanical energy and supplies electrical energy, and a motor absorbs electrical energy and supplies mechanical energy. 

The power that a machine gives at a certain moment depends on the external conditions to it; in a dynamo of the external circuit of use and in a motor of the mechanical resistance of the mechanisms that it moves. Among all the possible power values, there is one that gives the characteristics of the machine, it is the nominal power, which is defined as the power it can supply without the temperature reaching the limits allowed by the insulating materials used. 

When the machine works at this power, it is said to be at full load. When a machine works for brief moments at a power higher than the nominal, it is said to be working overloaded. They are classified into three large groups: generators, motors and transformers.

Classification according to the service It is important to know the kind of service to which a machine will be subjected: Continuous service: Corresponds to a constant load for a time long enough for the temperature to stabilize. 

Continuous variable service: It occurs in machines that work constantly but in which the load regime varies from one moment to another. Intermittent service: Work times are separated by rest times. Duty cycle is the ratio between the work time and the total duration of the work cycle. 

One-hour service: The machine is running for one hour at a constant rate higher than continuous, but it does not reach the temperature that endangers the insulating materials. The temperature does not stabilize.