Selected news about electricity.
For a year 1799, in which volta, based on Galvani's experience, built a battery of electrochemical cells as the first source of electricity, the period of dynamic encroachment of electrical engineering into everyday human life begins, as well as in all areas of economic life.
Electrical engineering is a science dealing with electrical and electromagnetic phenomena and their practical use.
In order to present the full characteristics of electrotechnical products, basic information about electricity is needed, presented in physics lessons.
The phenomenon of electricity can be explained, based on information about the structure of matter. Matter is made up of atoms, and each atom consists of electrons circulating in the shells, so-called. electron layers, and from protons and neutrons, included in the nucleus.
As you know electron, is an elementary particle of matter endowed with a negative charge. Under certain conditions, the electrons of some atoms (for example. metals), weakly attached to the nucleus, they can pass from one atom to another. Such electrons are called free electrons. The body, in which free electrons can be generated, they are called guides, while the body, in which no free electrons are formed, they are called dielectrics (non-conductors). An intermediate place is taken by semiconductors, such as e.g.. german (Give), silicon (And), which are used in electronics.
Physical phenomenon, consisting in arranging electric charges that move or change over time, called electric current (I, i).
The direction of movement of positive charges has been assumed as the current direction; the unit of electric current is the ampere (1A). It is distinguished depending on the current waveform over time:
• direct current (about the graphic symbol - ), i.e.. such, in which equal electric charges flow in a constant direction at arbitrarily short intervals;
• AC (about the symbol ~), i.e.. periodically changing its direction.
The electric current cannot be directly observed, but other phenomena can be seen, accompanying its flow, for example. glowing, thermal effects.
Movement of particles, and with them negative electric charges, it causes rise in their space electromagnetic field (two component fields). One of the basic quantities characterizing this field is the electromagnetic field strength E, the unit is volts per meter (V/m).
It takes a certain amount of work to move loads along a certain path. The ratio of the work performed to a given charge is called the electrical voltage and denotes the letter U. The unit of electrical voltage is volt (IV). Measuring devices are used to measure electric current and voltage, such as: ammeter, voltmeter or universal meter.
In addition to the basic parameters of electric current already mentioned, in the case of the characteristics of electrotechnical products, it is also necessary to mention: frequency of electrical vibrations, measured in hertz (Hz), and power. Ratio of work performed (Energy) by electric current the time is called power and denotes the letter P.. The unit of power is the watt (IW), however, in practice we use the kilowatt (1kW = 1000W).
Energy can come in many forms, for example. mechanical, thermal, chemical, luminous, nuclear and electricity, which can be transformed into one another, in various types of transducers. The SI unit of electricity is the kilowatt hour (1kWh = 3,6 •106 J ).
In the work of a seller of electrotechnical products, it is very important to know the meaning of symbols appearing on the goods sold.
Rated voltage UN - this is the voltage, on which device was built. Similarly, the rated current and rated power of the device are defined.
Graphic symbols used on electronic devices, which you can meet most often, this:
- direct current -
- alternating current ~
- attention danger ϟ
| To the basics physical quantities, which the seller must know include: | ||||||||||||||||||
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Electrotechnical instruments should be so designed and constructed, that they operate safely during normal use and do not pose a threat to people or the environment. There must be absolutely adequate protection against accidental touching of parts, energized. The insulation must be in accordance with the requirements for the relevant protection class. Covers of electrical equipment should not have other openings, than necessary for use, resulting from the technical design. The instruments should not overheat under normal operating conditions. All live devices should be protected against moisture. Accidental change of the setting of the thermostatic regulator or other control device may not reduce the safe use of the electrotechnical product.