Getting alternating current: methods and basic definitions

Alternating current is currently the only way to cheaply transmit electricity over distances. It surpasses direct current in a number of parameters, including the ease of transformation. In this article, we will tell you how to get alternating electric current in everyday life and at work.

Content:

Electromagnetic induction and Faraday's law
Methods for obtaining alternating current
Electronic converters

Electromagnetic induction and Faraday's law

Michael Faraday in 1831 discovered a pattern that was later named after him - Faraday's law. In his experiments, he used 2 installations. The first consisted of a metal core with two coiled and unconnected conductors. When he connected one of them to a power source, the arrow of the galvanometer connected to the second conductor twitched. This was how the influence of a magnetic field on the movement of charged particles in a conductor was proved.

The second setting is the Faraday disk. It is a metal disk to which two sliding conductors are connected, which in turn are connected to a galvanometer. The disk is rotated near the magnet, and when rotating on the galvanometer, the arrow also deflects.

So, the conclusion of these experiments was a formula that connects the passage of a conductor through the lines of force of the magnetic field.

Here: E is the induction EMF, N is the number of turns of the conductor, which is moved in a magnetic field, dF / dt is the rate of change of the magnetic flux relative to the conductor.

In practice, they also use a formula that can be used to determine the EMF through the magnitude of the magnetic induction.

e = B * l * v * sinα

If we recall the formula connecting the magnetic flux and magnetic induction, then we can assume how the formula above was derived.

Ф = B * S * cosα

This is how current generation was born. But let's talk about how getting alternating current is closer to practice.

Methods for obtaining alternating current

Let's say we have a frame made of a conductive material. Let's place it in a magnetic field. According to the formula mentioned above, if the frame starts to rotate, an electric current will flow through it. With uniform rotation at the ends of this frame, an alternating sinusoidal current will be obtained.

This is due to the fact that, depending on the position along the axis of rotation, the frame is penetrated by a different number of lines of force. Accordingly, the EMF value is induced not uniformly, but according to the position of the frame, as well as the sign of this value. What do you see on the graph above. When the frame rotates in a magnetic field, both the frequency of the alternating current and the value of the EMF at the terminals of the frame depend on the rotation speed. To achieve a certain EMF value at a fixed frequency, more turns are made. Thus, it turns out not a frame, but a coil.

You can get alternating current on an industrial scale in the same way as described above. In practice, power plants with alternators are widely used. This uses synchronous generators. Since in this way it is easier to control both the frequency and the magnitude of the AC EMF, and they can withstand short-term current overloads many times.

According to the number of phases, three-phase generators are used in power plants. This is a compromise solution related to the economic feasibility and technical requirement of creating a rotating magnetic field for the operation of electric motors, which make up the lion's share of all electrical equipment in industry.

Depending on the kind of force that drives the rotor, the number of poles can be different. If the rotor rotates at a speed of 3000 rpm, then to obtain an alternating current with an industrial frequency of 50 Hz, a generator with 2 poles is needed, for 1500 rpm - with 4 poles, and so on. In the pictures below, you see a synchronous-type generator device.

There are coils or a field winding on the rotor, the current to it is supplied from the generator-exciter (DC Generator - GPT) or from the semiconductor exciter through the brush apparatus. The brushes are located on the rings, in contrast to the collector machines, as a result of which the magnetic field of the windings the excitation does not change in direction and sign, but changes in magnitude - when regulating the current pathogen. Thus, the optimal conditions are automatically selected to maintain the operating mode of the alternator.

So, it was possible to obtain alternating current on an industrial scale by a method based on the phenomena of electromagnetic induction, namely with the help of three-phase generators. In everyday life, both single-phase and three-phase generators are used. The latter are recommended to be purchased for construction work. The fact is that a large number of electric tools and machine tools can operate on three phases. These are electric motors of various concrete mixers, circular saws, and powerful welding machines are also powered by a three-phase network. Moreover, synchronous generators are suitable for such tasks, asynchronous generators are not suitable - because of their poor performance with devices that have large starting currents. Asynchronous household power plants are more suitable for backup power supply of private houses and summer cottages.

Electronic converters

However, it is not always rational or convenient to use gasoline or diesel household power plants. There is a way out - to get a single-phase or three-phase alternating electric current from direct. To do this, use converters or, as they are also called inverters.

An inverter is a device that converts the amount and type of electric current. In stores you can find inverters 12-220 or 24-220 Volts. Accordingly, these devices are converted to constant 12 or 24 volts into 220V alternating current with a frequency of 50Hz. The diagram of the simplest similar converter based on the driver for the IR2153 half-bridge converter is shown below.

Such a circuit produces a modified sine wave at the output. It is not quite suitable for powering inductive loads such as motors and drills. But if not on an ongoing basis, then it is quite possible to use such a simple inverter.

DC-to-AC converters with a pure sinusoidal output are significantly more expensive and their circuits are much more complex.

Important! When purchasing cheap board-modules from aliexpress, do not rely on either pure sine or 50Hz frequency. Most of these devices provide high-frequency current with a voltage of 220V. It can be used to power various heaters and incandescent lamps.

We have briefly discussed the principles of obtaining alternating current at home and on an industrial scale. The physics of this process has been known for almost 200 years, nevertheless, Nikola Tesla was the main popularizer of this method to obtain electrical energy in the late 19th - first half of the 20th century. Most modern home and industrial equipment is focused on the use of named alternating current for power supply.

Finally, we recommend watching a video that clearly shows how the alternator works:

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