Alternator: device, principle of operation, purpose

Electric current is the main type of energy, doing useful work in all spheres of human life. It sets in motion different mechanisms, gives light, heats the houses and animates a whole host of devices that provide our comfortable existence on the planet. Truly, this kind of energy is universal. From it you can get anything you like, and even great destruction with mismanagement.

But there was a time when the electrical effects were still present in nature, but did not help the person. What has changed since then? People began to study physical phenomena and invented interesting machines - converters, which, in general, made a revolutionary leap of our civilization, allowing a person to get one energy from another.

So people have learned to produce electricity from ordinary metals, magnets and mechanical motion - that's all. Generators were built, capable of delivering enormous energy fluxes, calculated in megawatts. But it is interesting that the principle of the operation of these machines is not so complicated and it may even be understandable even for a teenager. What is an electric current generator? Let's try to understand this question.

The effect of electromagnetic induction

The basis for the appearance in the conductor of an electric current is the electromotive force - EMF. It is able to make charged particles move, which are many in any metal. This force appears only if the conductor undergoes a change in the intensity of the magnetic field. The effect itself was called electromagnetic induction. The higher the emf, the greater the rate of change in the flux of magnetic waves. That is, you can move a conductor near a permanent magnet , or influence the field of an electromagnet by a fixed wire, changing its strength, the effect will be the same - an electric current will appear in the conductor.

On this issue in the first half of the XIX century, scientists worked Oersted and Faraday. They also discovered this physical phenomenon. Later, on the basis of electromagnetic induction, current generators and electric motors were created. Interestingly, these machines can easily be converted into each other.

How DC and AC generators work

It is clear that the electric current generator is an electromechanical machine that generates a current. But in fact it is a converter of energy: wind, water, heat, anything in EMF, which already causes a current in the conductor. The device of any generator basically does not differ in any way from a closed conducting circuit that rotates between the poles of a magnet, as in the first experiments of scientists. Only much more is the magnitude of the magnetic flux produced by powerful permanent or more often electric magnets. The closed contour has the form of a multi-turn winding, which in the modern generator is not one, but at least three. All this is done in order to get as much EMF as possible.

The standard electric alternator (or permanent) generator consists of:

• Shells . Performs the function of the frame, inside which the stator is fastened with the poles of the electromagnet. In it are established bearings of rolling of a rotor shaft. It is made of metal, it also protects the entire internal stuffing of the machine.
• Stator with magnetic poles. On it is fixed the winding of excitation of the magnetic flux. It is made of ferromagnetic steel.
• Rotor or anchor. It is a movable part of the generator, the shaft of which generates an extraneous force into the rotational motion. The self-excitation winding is placed on the armature core, where an electric current is formed.
• Nodes of commutation. This element of the design serves to divert electricity from the rotary shaft of the rotor. It includes conductive rings that are movably connected to graphite current collectors.

Creating a direct current

In a generator producing a direct current, the conducting circuit rotates in a space of magnetic saturation. And for a certain moment of rotation, each half of the contour is close to one or another pole. The charge in the conductor for this half-turn moves in one direction.

To obtain the removal of particles, a mechanism is made for the removal of energy. Its feature is that each half of the winding (frame) is connected to a conductive half-ring. Semirings are not closed with each other, but are fixed on a dielectric material. During the period when one part of the winding begins to pass a certain pole, the semicircle is closed in the electrical circuit by brush contact groups. It turns out, on each terminal comes only one kind of potential.

It is more correct to call the energy not constant, but pulsating, with constant polarity. The pulsation is caused by the fact that the magnetic flux on the conductor during rotation has both a maximum and a minimum effect. In order to align this ripple, several windings on the rotor and powerful capacitors at the input of the circuit are used. To reduce the loss of magnetic flux, the gap between the armature and the stator is minimized.

Alternator circuit

When the moving part of the current generating device rotates, the EMF is also induced in the conductors of the frame, as in the DC generator. But a small feature - the alternator of the collector node device has another. In it, each pin is connected to its conductive ring.

The principle of the alternator is as follows: when half the winding passes near one pole (the other, respectively, near the opposite pole), the current flows in the circuit in one direction from the minimum to its highest value and again to zero. As soon as the windings change their position relative to the poles, the current starts its movement in the opposite direction with the same regularity.

At the input of the circuit, a waveform is obtained in the form of a sinusoid with a half-wave frequency corresponding to the period of rotation of the rotor shaft. In order to obtain a stable signal at the output, where the frequency of the alternator is constant, the period of rotation of the mechanical part must be unchanged.

Magnetic generators of gas type

Constructions of current generators, where a conductive plasma, liquid or gas is used instead of a metal frame as a charge carrier, are called MHD generators. Substances under pressure are driven in a field of magnetic tension. Under the influence of the same EMF induction, charged particles acquire directional motion, creating an electric current. The magnitude of the current is directly proportional to the velocity of passage through the magnetic flux, and also its power.

Generators MHD have a simpler design solution - they do not have a mechanism for rotating the rotor. Such power supplies are capable of delivering large amounts of power in short periods of time. They are used as backup devices and in emergency situations. The coefficient determining the useful effect (efficiency) of these machines is higher than that of an electric alternator.

Alternating Current Synchronous Generator

There are such types of alternators:

• Machines are synchronous.
• Machines asynchronous.

The synchronous alternator has a strict physical relationship between the rotational motion of the rotor and the generated frequency of electricity. In such systems, the rotor is an electromagnet assembled from cores, poles and exciting windings. The latter are fed from a DC power source through brushes and ring contacts. The stator is a coil of wire, connected by a star principle with a common point - zero. They already induced the EMF and produced a current.

The rotor shaft is driven by an extraneous force, usually turbines, whose frequency of motion is synchronized and constant. The electrical circuit connected to such a generator is a three-phase circuit whose current frequency in a separate line is shifted by a phase of 120 degrees relative to other lines. To obtain the correct sinusoid, the direction of the magnetic flux in the lumen between the stator and rotor parts is regulated by the structure of the latter.

The excitation of the alternator is realized by two methods:

1. Contact.
2. Non-contact.

In the contact excitation circuit, electricity from the other generator is supplied to the coils of the electromagnet through the brush pair. This generator can be combined with the main shaft. It, as a rule, has less power, but enough to create a strong magnetic field.

The non-contact principle provides that the synchronous alternator on the shaft has additional three-phase windings in which the EMF is induced to rotate and electricity is generated. It passes through the rectifying circuit to the excitation coils of the rotor. Structurally, there are no movable contacts in this system, which simplifies the system, making it more reliable.

Asynchronous generator

There is an asynchronous alternator. The device differs from the synchronous one. There is no exact EMF dependence on the frequency with which the rotor shaft rotates. There is such a thing as "slip S", which characterizes this difference of influence. The magnitude of the slip is determined by the calculation, so it is wrong to think that there is no regularity in the electromechanical process in the asynchronous motor.

If the generator, idling, loads, the current flowing in the windings will create a magnetic flux that prevents the rotor from rotating at a specified frequency. This forms a slip, which, naturally, affects the production of EMF.

The modern asynchronous alternator of a moving part has three different designs:

1. Hollow rotor.
2. Short-circuited rotor.
3. Phase rotor.

Such machines can have a self-and independent excitation. The first scheme is realized due to the inclusion of capacitors and semiconductor converters in the winding. Excitation of an independent type is created by an additional source of alternating current.

Schemes of generator switching

All powerful power supplies of power lines produce a three-phase electric current. They contain three windings in which alternating currents are formed with a phase shifted from each other by 1/3 of a period. If we consider each individual winding of such a power source, we get a single-phase alternating current going into line. Voltage of tens of thousands of volts can produce a generator. 220 V the consumer receives from the distribution transformer.

Any alternator, the winding device is standard, but the connection to the load is of two types:

• A star;
• Triangle.

The principle of operation of an alternator powered by a star implies the unification of all the wires (zero) into one, which go from the load back to the generator. This is due to the fact that the signal (electric current) is transmitted mainly through the output winding wire (linear), which is called the phase. In practice, it is very convenient, because you do not need to pull three additional wires to connect the consumer. The voltage between the line wires and the line and neutral wires will be different.

By connecting the winding of the generator with a triangle, they are connected to each other consecutively in one circuit. From the points of their connection, lines are drawn to the consumer. Then there is no need for a zero wire, and the voltage on each line will be the same regardless of the load.

The advantage of the three-phase current before single-phase current is its smaller ripple when straightening. This has a positive effect on power supplies, especially DC motors. Also, the three-phase current generates a rotating flux of magnetic field that is capable of driving powerful asynchronous motors.

Where applicable DC and AC generators

DC generators are much smaller in size and weight than AC machines. Having a more complex design than the latter, they are still used in many industries.

The main distribution they received as high-speed drives in machines where speed control is required, for example, in metalworking machinery, mine hoists, rolling mills. In transport, such generators are installed on diesel locomotives, various ships. Many models of wind generators are assembled on the basis of sources of constant voltage.

Direct current generators for special purposes are used in welding, for excitation of windings of generators of synchronous type, as direct current amplifiers, for supplying galvanic and electrolysis plants.

The purpose of the alternator is to generate electricity on an industrial scale. This kind of energy gave mankind Nikola Tesla. Why is it that the polarity-reversing current, not the permanent one, is widely used? This is due to the fact that in the transmission of DC voltage there are large losses in the wires. And the longer the wire, the higher the losses. Variable voltage can be transported over huge distances at much lower costs. Moreover, it is easy to convert an alternating voltage (lowering and raising it), which the generator generates 220 V.

Conclusion

Man did not fully know the nature of magnetism, which permeates everything around. And electric energy is only a small part of the open secrets of the universe. The machines that we call energy generators are essentially very simple, but what they can give us is amazing. Yet the real miracle here is not in technology, but in the thought of a man who could penetrate into the inexhaustible reservoir of ideas spilled in space!