Device and principle of operation of an alternating current electric motor

Electric engines produce synchronous, asynchronous, collector, each has its own characteristics of work. Minus big: the Internet gives scant ideas about the differences in work, the principle of action. We can read reviews about synchronous motors, do not understand as a result of the main thing: the nuances! Why are such generators used at hydroelectric power plants, in the life of the mirror motors it is not visible( the AC motor is reversible)?

Electric engines:

variants At once, we didn’t set a goal to bring comprehensive information on this topic to our readers. It is impossible to grasp the immensity. Cases omitted by literature will be considered. Information like laid out, systematize publishers too busy. We will help you to understand how types of electric motors function. Let's start by simple listing.

Collector engines

Often confused with synchronous. Carbon brushes are detected. The similarity is limited to this, the frequency of rotation of the collector engines varies widely, everyone can see the example of a washing machine. Speed ​​control is performed by switching the windings, adjusting the value of the current voltage( changing the cut-off angle of the voltage of industrial frequency).

The main difference between devices is the presence of a collector. The original sectional design, mounted on the shaft. Composed of many coils, evenly going around. The collector provides serial switching so that the field gradually moves around the shaft. Clinging to the stator, the rotor starts moving.

Fragility( for industry) is considered a disadvantage of collector engines. In everyday life, the type of devices dominant. Speed ​​adjustment is carried out in a simple way( by cutting off a part of the sinusoid period).Collector engines see other disadvantages / pros, mentioned earlier, now we will study the features. The presence on the shaft sectioned drum.

Can you put a magnet instead, rotate the stator field? Yes, we get a synchronous motor( a typical example is washing machine pumps).Can I feed the winding with direct current, rotate the stator field? Yes, there will be a synchronous motor. You see, the collector clearly makes it clear the type of device.

Asynchronous motors

Mostly used by industry. We get the simplicity of the design, a bunch of buns. Shock resistance, vibration strength: no carbon brushes. Instead, it turns out a pile of designs. The family is the most numerous.

First, the rotor. May be short-circuited, phased. The first means: a construction is mounted on the shaft( to reduce the weight of silumin), where copper streaks are inserted. Shorted perimeter with two rings. It turns out the drum, sometimes called the squirrel cage.

A field arises under the action of a rotating stator emf, in contrast to the collector, asynchronous motors do not start DC.Secondary difference. The primary one was called: contacts( excluding the starting rheostat) are not suitable for the rotor, the shaft is surmounted by a squirrel cage, the conclusion about the belonging is unequivocal. As for the phase asynchronous machines, the power supply of the rotor coils is made through slip rings. Shaft picks up, gradually gaining momentum.

Synchronous motors

The type of devices, to comprehend which, according to the notes of the network, is simply impossible. The difference is simple: the field is so strong that it is captured without problems, does not slip, as in the case of asynchronous or( to a lesser extent) collector motors. It is provided with a permanent magnet more often, or the excitation winding is located on the rotor. The stator is supplied with alternating voltage of the desired frequency.

The speed of rotation depends on the frequency of the power supply. There are only two poles, therefore it is 25 Hz( 1500 rpm).The line on which we can assume: we see a synchronous motor - a multiple, an integer. The key is the coincidence of the speed of rotation of the shaft and the frequency of the supply voltage. Much depends on the number of poles. For example, at hydroelectric power stations, generators operate at a shaft frequency of 1-2 Hz, industrial 50 Hz are obtained by winding numerous stator coils connected in parallel.

How electric motors work

Asynchronous motors

Briefly described the external differences of electric motors, now a couple of words about the device and operation. Asynchronous motors using a stator create an axis of rotation of the magnetic field. The squirrel cage drum is rarely made of ferromagnetic materials( if there is any at all).Otherwise, the heat would come out significant. In fact, an induction furnace is obtained.

The Silumin drum along the magnetic field lines contains copper conductors. The difference in conductivity is such that no insulation is carried out: the current is carried by red-brown wires. The field induced by the stator EMF is weak. Apply special measures to help disperse the shaft. The magnetic field of the rotor badly clings, the asynchronous motor is a pillar. An effective measure to counter the problem is limited to the creation of a double squirrel cage: the second row of copper veins passes along the drum at a certain depth. United by the ends of a single network.

At the start, the frequency of the current and the depth of penetration of the field are large. Both layers of squirrel cage are included in the work. In process of acceleration the difference is leveled, falls to zero. The amplitude of the field decreases, the outer layer of the squirrel cage remains working. Pay attention, to catch up with the field the rotor is powerless, it slips, it is late. Therefore, the engines are called asynchronous. The British make it easier - they call induction.

If the field is rotated at the speed of the rotor, the EMF ceases to be induced. There will be a slowdown, the cycle will be repeated, starting with acceleration. The rotor will still lag behind the field. This is how a closed loop device works. A phase rotor( thanks to Wikipedia) containing a three-phase winding performs several functions according to the purpose of the device:

• It is supplied with electricity through the current collector ring. Now the rotor receives a phase and induces an emf on the stator. Gradually, the shaft is picked up by the field, the further process is described above.
• Powered by DC.Formed synchronous motor.
• Equipped with rheostats, speed control chokes.
• Implements inverter control( complicated first case).

The principle of operation of asynchronous motors: the induced emf is used, the rotational speed is unable to catch the field( currents are lost).Otherwise, the type of motor varies( synchronous).To regulate the speed is often used the amplitude of the supply voltage. The method is suitable for asynchronous motors with a short-circuited, phase-wound rotor. Here are the techniques:

• . For squirrel cage machines:
  1. . Regulation of the frequency of the supply voltage.
  2. Change the number of stator pole pairs. As a result, the field rotation speed changes, giving the desired effect.
• For machines with a phase-rotor, the following is allowed:
  1. Insert a rheostat in the supply circuit. Slip losses increase, naturally changing the speed.
  2. Use special valves. The slip energy is rectified by the Larionov scheme, supplied in the form of a constant voltage to an auxiliary electric motor, cutting pulses through externally controlled thyristors. The power that would normally be lost returns. Through the shaft of the auxiliary engine, a transformer, the windings of which are partially included in the power supply network. Speed ​​control is performed by the introduction of additional EMF.It is done either directly( through the power supply) or by shifting the thyristor switching angle relative to the power supply. Frequency deviates from nominal.
  3. A dual-feed motor is an option for implementing speed control in a phase-rotor equipment. The type is more often used to implement generator circuits. The rotor floats away with the rotational speed - the motor is still asynchronous. The stator, the rotor is fed separately. Allows for each winding to set the frequency, naturally leads to the desired speed changes.

Asynchronous motors are suitable for varying the amplitude of the power supply. The highest efficiency have valve circuits, the most expensive.

Work of synchronous motors

Passed through the collector motors - told how to design - therefore, we are missing the family today. Powerless otherwise tell things much more interesting: there is a lot of controversy in the forums. We are going to consider not quite synchronous motors - a generator. Like decorating hydroelectric power plants.

Have you ever wondered how the speed of the turbine is regulated when the flow of water falls on the blade? Shutters guide? Not. The generator requires feeding not only with direct current, but also with alternating current. The first is fed to the rotor, and the second to the stator. As a result, the shaft could not even move, but water helps it. But the braking energy of the flow is already converted into the EMF of the stator working coils wound next to the auxiliary.

In fact, we have on hand a device of an AC electric motor, among the windings most of the generating ones, the frequency is 50 Hz. Synchronization is provided by the supply voltage. If the water presses too much, the excitation current rises, the breakdown of speed is prevented. In parallel, the power output of the power station increases. Frequency determines the characteristics of the voltage taken, with respect to the nominal 50 Hz, deviations of more than fractions of a percent( 0.1%) are not allowed.

The shaft rotates at a speed of 1-2 revolutions per second. Numerous generator windings connected in parallel to form the desired shape of the sinusoid. We emphasize that the frequency is supported by the excitation voltage, therefore, heightened requirements are imposed on it. It is required to get more power from the power station, simply the flaps of the guide vane open, the mass of water begins to fall down. The blade does not move faster, the excitation current increases, naturally causes the occurrence of stronger fields.

The principle of operation of an AC motor copies the above, there are no generator windings. You need to get more power - increase the excitation voltage, the amplitude of the supply circuit. Enhanced grip fields, eliminating slippage. It is clear that a large mass of the shaft is unable to gain 50 Hz in an instant( and does not gain), the equipment, made correctly, reaches the mode in a short period. The speed depends on the number of poles.

Not yet had time to consider the technical characteristics of AC motors, they have done it many times before in relation to various kinds of devices. We believe in the future reviews may again turn to the topic of the bowsprit.