Electric machine

An electric machine (an electric motor)

An electrical machine is a device capable of transforming any form of energy into electrical energy or vice versa. Also included in this definition are machines that transform electricity into the same form of energy but with a different presentation more convenient for its transport or use. 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 electric 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 perspective, 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.

In rotating machines, there is a fixed part called the stator or stator and a moving part called the rotor. The rotor usually rotates inside the stator. The air space between them is called the air gap. Electric motors and generators are the simplest example of a rotating machine.

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 that which can be supplied 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: It corresponds to a constant load for a long enough time to stabilize the temperature.
• Variable Continuous Service: It is given in machines that work constantly but in which the load regime varies from time to time.
• Intermittent service: Working times are separated by resting times. Progress factor is the relationship between working time and the total duration of the work cycle.
• One-time service: The machine is an hour in motion to a constant regimen superior to the continuum, but does not reach the temperature that endangers insulation materials. The temperature doesn't get to stabilize.

Yields

In general, it is defined as the ratio between useful power and absorbed power expressed in %

MIL MIL =PuPab↓ ↓ 100{displaystyle eta ={frac {P_{u}}{P_{ab}}}}

Types of electrical machines