Theory of electric motors. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electric motors. Theory of electric motors. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electric motors

Electric motor is an electrical machine in which the energy of an electromagnetic field is converted into rotational or translational motion.

Integral parts of the electric motor

Energy conversion in modern electric motors is carried out by means of magnetic field. Such motors are called inductive. To obtain the strongest possible magnetic fields, ferromagnetic cores are used, which are an integral part of every electric motor.

With alternating magnetic fields, the cores are made from sheet electrical steel in order to attenuate eddy currents and reduce the energy losses caused by them.

Another integral part of the electric motor are windings of conductive materialsthrough which electric currents flow. For the electrical insulation of windings, various electrical insulating materials are used.

As you know, electric motors have reversibility property: each electric generator can work as a motor and vice versa, and in each transformer and electric machine converter of electrical energy, the direction of energy conversion can be reversed.

However, each rotating machine produced by an electrical engineering plant is usually intended for one specific mode of operation, for example, as a generator or engine. Similarly, in transformers, one of the windings is provided to work as a receiver of electrical energy (primary winding), and the other (secondary winding) - to transfer energy.

In this case, it is possible to best adapt the electric motor to the given operating conditions and achieve the best use of materials, i.e., to obtain the greatest power per unit weight of the electric motor.

Losses in electric motors

The conversion of energy in electric motors is inevitably associated with its lossescaused by several factors:

remagnetization of ferromagnetic cores;
the passage of current through conductors;
friction in bearings and air, etc.

Therefore, the power consumed by the electric motor is always greater than the output, or useful, power, and the efficiency * (COP) is less than 100%. Nevertheless, electric motors, in comparison with thermal and some other types of machines, are very advanced energy converters with relatively high efficiency.

So, in the most powerful electric motors, the efficiency is 98-99,5%, and in electric motors with a power of 10 W, the efficiency is 20-40%. Such efficiency values at such low powers are unattainable in many other types of engines.

The high energy performance of electric motors, the convenience of supplying and removing energy, the ability to perform at a wide variety of powers, rotation speeds, as well as ease of maintenance and ease of control, have led to their widespread widespread use.

Rated voltages of electric motors

The rated voltages of electric motors are agreed in GOST with the standard rated voltages of electrical networks. The rated voltages for electric motors and primary windings of transformers are taken equal to the standard voltages of electrical networks, and for generators and secondary windings of transformers - 5-10% more in order to compensate for voltage drops in the networks.

Most common rated voltages of electric motors following:

for DC motors -110, 220 and 440 V;
for DC generators -115,230 and 460 V;
for AC motors and primary windings of transformers 220,380, 660 V and 3, 6,10 kV;
for generators and secondary windings of transformers 230, 400, 690 V and 3,15; 6,3; 10,5; 21 kV (for secondary windings of transformers also 3,3; 6,6; 11 and 22 kV).

Of more high voltage standard are:

for primary windings of transformers - 35,110,150, 220, 330, 500 and 750 kV;
for secondary windings of transformers - 38,5; 121; 165; 242; 347; 525 and 787 kV.

Author: Koryakin-Chernyak S.L.

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