The electricity is the interaction of particles charged under the action of the electromagnetic Force . This phenomenon Physique is present in many contexts: electricity constitutes the Nerve impulse as well living beings as the flash S of a storm. It is largely used by the developed companies to transport great quantities of energy easily usable.
The properties of electricity started to be included/understood during the 19th century, in particular thanks to work of Nikola Tesla. The control of the Electric current allowed the advent of the second Industrial revolution. Today electrical energy is omnipresent in the developed countries: starting from different energy sources (mainly hydraulic, thermal and nuclear), electricity is nowadays a energy Vecteur employed with very many uses Domestique S or Industriel S.
Nature of electricityIt is the movement of the electric charges in the Matière which is at the origin of electricity.
Like the Mass, the electric Charge is a property of the matter, which makes it possible to explain the origin of certain phenomena. That wants to say that anybody observed an electric charge directly forever, but that the scientists noticed similarities of behavior by studying some Particule S. They postulated that these particles had a joint characteristic, whose properties coincided with their observations.
Contrary to the mass, there exist two types of electric charges, which behave as if they were “opposite” one with the other; one thus calls them by Convention positive and negative.
Loads of opposite nature are cancelled. That means that particle which has as many positive loads than negative comprises as if it did not have any of it. It is said that it is electrically Neutre.
See also: Electrostatic
In nature the electron S are negative charge carriers and the Proton S of the positive charge carriers. The Atome S which compose the ordinary matter are made of electron S which moves around a core made up of Proton S and neutrons which are electrically neutral. The number of electrons being equal to the number of protons, the unit is electrically neutral.
When one rubs certain materials between them, the surface electrons of the atoms of the one are torn off and recovered by the atoms of the other. For example a stem of Verre rubbed on a fabric of Soie takes care positively, because its atoms lose electrons for the benefit of silk; if one rubs a balloon of goldbeater's skin on Cheveu X dry, one charges it negatively, because it collects electrons with the hair.
A plastic rule in rubbed on clothing has a negative charge. It can then attract small pieces of Papier. The rule modifies, by electrostatic Induction, the burden-sharing in paper: the negative charges of the rule push back the negative charges at the other end of the piece of paper and attract the positive loads of the paper atoms.
One speaks about static electricity, because the electric charges cannot circulate: they are trapped in materials Isolant S: the plastic , the Verre, the Papier… which resists the circulation of the loads.
The electric current
See also: Electric current
There exist also conducting materials, like the metals, the Eau salted, the human body or the Graphite for example, which make it possible the electric charges to move easily.
When one walks on a Moquette, the friction of the feet on the ground tears off electrons and the body takes care of static electricity. When one touches a metal Poignée of door, one feels then small a Electric shock accompanied by a spark, caused by the brutal displacement of the electric charges running out towards the ground through conducting materials of the door.
This flow is due to the fact that there were more loads in the body than in the ground: as two loads of comparable nature tend to be pushed back, in a driver they will seek to move towards the point charged. This difference in loads between the body and the ground is called a potential difference.
To create a Electric current, one thus needs a circuit of conducting materials which will make it possible the electric charges to move and, a system able to create a potential difference between the two ends of the circuit. This system is called a generating : it can be for example a pile or a Dynamo.
The direction of the currentIn an electrical circuit one says that the electric current, noted I , circulates between the electrode S since the positive pole towards the negative pole of the generator. This direction is purely conventional since the current can as well be caused by positive loads which will be attracted by the negative pole of the generator, that by negative charges which will move in opposite direction, towards the positive pole. Thus in an electric wire, the positive loads (cores of the atoms) remain fixed in the structure of metal and cannot constitute any electric current; the electric current in a metal is created only by the displacement of the negative charges (free electrons) towards the positive pole of the generator: it is a current electronics , however one always uses the conventional direction I of the current, instituted before this discovery.
One speaks about D.C. current when the direction remains constant and, of Alternative course when it changes periodically. The Fréquence of an alternative course is the number of periods by second. It is expressed in Hertz (Hz), for example in Europe the current distributed in electrical installations is at a frequency of 50 Hz and in America 60 Hz .
Hydraulic analogyTo include/understand certain properties of the electric current, it is interesting to compare it with water running out in a circuit of Tuyau X. The generator can then be seen like a Pompe charged to put in pressure this liquid in the pipes.
The potential difference, or tension, resembles the difference in pressure then between two points of the water circuit. It is noted U , and is expressed in Volt S (V).
The intensity of the electric current can be close to the water flow in the pipe. It measures the number of loads which spend each second at a point of the circuit; it is often noted I , and is measured in amps (A).
The resistance of an electrical circuit would be then similar to the Diamètre pipes. The smaller the pipes are, the more one needs pressure to have the same flow; in a similar way, plus the resistance of a circuit is high, more one needs a potential difference raised to have the same intensity. Electrical resistance thus measures faculty to slow down more or less the passage of the current. It is noted R and, it is expressed in Ohm S (Ω).
It is possible to push this analogy much further but it is important to keep in mind which it has its limits and which certain properties of the electric current appreciably deviate from this model containing fluid, pipes and, of pumps.
History of electricity
See also: History of electricity
Electricity is a word coming from the Greek êlektron meaning yellow Ambre. The former Greeks had discovered that by rubbing the yellow amber, this one produced an attraction on other objects and, sometimes of the sparks. They thus called this force electricity .
One period of observation starts at the 17th century when one learns how to create static electricity. Mister Of Fay says Charles-François de Cisternay, in 1733 discovers the loads positive and negative, observes the interactions between these loads. But it is Coulomb which states the first physical laws.
In 1799, Alessandro Volta invents the Battery and in 1868 the Belgian Zénobe Gram carries out the first Dynamo. In 1879, Thomas Edison presents his first electric bulb to incandescence. A central hydraulics of 7 kw is built the same year with Saint-Moritz, then, in 1883, Lucien Gaulard and John Dixon Gibbs create the first electric line. In 1889, a line of 14 kilometers is built in the Creuse, between the Cascade of Jarrauds, place of production, and the town of Bourganeuf.
Electricity develops then gradually during the 20th century, initially in the Industrie, the public lighting and the Railroad before entering the hearths. Various means of production of electricity develop: Central hydraulic, thermal, wind, then nuclear…
See also: Electrical production
Electricity represents approximately a third of the power consumption in the world. The electrotechnical is the science of the domestic and industrial applications (production, transformation, transport, distribution and use) of electricity.
The most current method to produce great quantities of electricity is to use a generating , converting a mechanical energy into a alternating voltage. Generally the source is not inevitably mechanical, one can think of the piles or the solar panels for example.
This energy of mechanical origin is obtained most of the time starting from a source of Chaleur, exit itself of a primary energy, the such fossil energies, Pétrole, nuclear or an renewable energy, the solar energy. One can also directly use a mechanical energy, the hydraulic power or the wind energy.
Transport and distribution
See also: Electrical communication
The current which circulates on electrical communication is generally alternate and three-phase current because it is most economic to produce and transport. Whereas the ultimate consumer with need for current with low tension, less dangerous to use, it is more economic to very transport a current to high voltage on long distances.
Indeed, at constant power, if the tension is increased, then one reduces the intensity of the current ( in single-phase current) and thus, also the losses by Joule effect or losses thermal (), but also the effect “skin of orange” which limits the circulation of the strong currents to surface external of the drivers what would oblige the use of copper cables of larger section. One thus uses transformer lifting of tension so as to reduce the intensity of the current to transport it and, transformer step-down transformers for the distribution (in low tension) with the users.
The electric tensions can be transformed and converted.
In general for the large powers, the tensions are alternate and pass by transformers to convert the current into magnetic flux itself converted again into running thanks to reels. This principle makes it possible to change the level of tension while preserving the frequency and a galvanic insulation between the primary and secondary distributers of the transformer. For the powers allowing it technologically, one uses converters with semiconductors (transistors, thyristors):
of the rectifiers to convert an alternating voltage into continuous tension;
- of the inverters to convert the continuous tensions into alternatives;
- of the converters allows the direct conversion of continuous tension into continuous tension by high frequency cutting.
See also: Storage of énergie#Stockage of electricity, Storage of electricity
For the electricity transported and distributed by means of conducting, it is necessary to constantly balance the production and the consumption. The thermo plants with gas, oil or coal, are generally used to answer peaks of request. One uses also stations of Pumping-treatment by turbine action between two water reserves: during the off-peak hours, water is pumped towards the upstream reservoir and during the rush hours, water passes in a Turbine which produces a supplement of electricity on the network.
It is also possible to store electricity with small scales by means of, condenser or inductance coil accumulator batteries.
the accumulator batteries are very widespread for the use of the equipment and autonomous systems fixed or mobile.
the Condensateur S are used for a long time in electronic electricity and , but appeared recently the Supercondensateur S making it possible to lay out of more than instantaneous power than with traditional accumulator batteries of larger size, but during very short times. A possible use can find its place in the electric traction Automobile for the transitional stages of acceleration, more especially as the refill of the condensers is almost instantaneous.
Trades of electricityElectrical engineering is a whole of technologies which can be practiced by: a Engineer, a electrotechnologist, a Draftsman - designer…
the Bobineur is a technician who carries out the circuits Magnétique S like those of the engines or the generators;
- the assembler-cabler carries out the electrical power boxs and it carries out connection;
- the electrician S cable the networks low tension and high voltage, in the building, industry, the tertiary sector, the navy, aeronautics and the means of transport terrestrial, (Automobile);
- the maintenance men, maintain and repair the electric machines;
- the control engineers, electronics specialists, electrotechnologists create the automatisms and systems of electric regulation to order the automated machines…
and a multitude of trades related to the industry of electricity (for most current: chemist, calorifugor, heat engineer, robinetier, ironmonger, mechanic…).
Uses and consumptionToday electricity is useful for the lighting, the Chauffage or the Climatisation. It makes turn the electrical motors which advance the Train S or function the domestic apparatuses. It makes function the apparatuses electronic S, the Téléphone, the Radiodiffusion, the Télévision, the Sonorisation. The Data-processing , the Automat S, the Communication S Numérique S (Internet, network X) needs electricity.
In spite of encouragements to the savings of electricity and a notable improvement of the energy efficiency of 1999 to 2004, final consumption continues to increase in Europe (UE-25). An average household of the UE-25 consumed 4.098 kWh in 2004, whereas it could have consumed some that 800 kWh if it were equipped with existing apparatuses with low consumption and by giving up the bulbs with incandescence (and even less with technologies more efficient). According to the Joint Research Center (JRC) of the EU, by 2005 to 2006, consumption increased in the UE-25 in all the sectors; in the residential one, in the tertiary sector (+ 15,8%) and in industry (+ 9,5%), at intervals copied on that of the total GDP (+ 10,8%).
Le report/ratio recommends to encourage the solar-fired heaters and energy saving, by replacement in particular of the incandescent lamps. In November 2006, the European commission engaged an action plan for the energy efficiency which must reduce of 20% the consumption of electricity of the UE-25 in 2020 from here 2020. The apparatuses consume rather less, but they are used (explosion of the use of the computer and the cellphone. The time spent in front of television increased by 13% between 1995 and 2005. The night lighting, which has been in addition one of the factors of the phenomenon known as of luminous Pollution is in continuous increase for 50 years. And in the tertiary sector lighting (of day often) is the first station of electricity consumption, 175 TWh consumed per annum and 26% of total electricity consumption of the tertiary sector.
The domestic network
See also: Electrical communication, Électricité domesticates
Separately the apparatuses with piles or the battery S of Automobile, the majority of the electricity used in the daily life comes from the electrical communication. Each dwelling is connected to the network via a table which contains at least a meter intended for the invoicing as well as a Disjoncteur being used as master switch and, making it possible to protect the installation. This circuit breaker two drivers leave which feed the domestic facility: the phase and the neutral and sometimes two additional drivers of phase, in the installations Triphasé be. One finds a third driver for the put at the ground.
One finds then a table of fusible or circuit breakers, distributing the current in the various circuits of the house. One generally envisages one-way circuits for the apparatuses which need much power (Four, electric cooker, washing machine, Lave-vaisselle, Chauffe-eau…), normally, by part a circuit for the lighting and for the electrical outlets.
One uses Interrupteur S to open or close the electrical circuits. It is possible to use special assemblies like a to and from or a Télérupteur when one wishes to create several points of order, for example with each end of a corridor.
the electrolysis is used to manufacture the Aluminum, with to plate metals…
the electrical motors are used to provide energy of operation of the machines
- the electric arcs are used to weld or to cut out metals
- the food of electronic circuits, of relay, Contacteur S allows automated sequences .
Health and electricity
The electrification is the passage of electric current in the human body. When the current is too strong that can for example involve burns or an cardiac arrest. It is usually considered that a tension of more than 50 V alternate/120 V continuous presents a potentially mortal danger: the electrocution.
The consequences of an electrification depend on the nature of the tension (alternate or continues), of the resistance of the generally allowed human body as being to 5.000 ohms in TBT (Very Low tension), 1.000 ohms under 220 V alternate and 400 ohms under 500 V (resistance is decreasing according to the tension of exposure), of the amplitude of the current having circulated and the time of passage of this current. It is usually allowed some thresholds on which the safety regulations are based:
Above 20 my, cardiac danger of fibrillation if passage by the heart. Therefore, in lower part of the TBT 50 VAC/120 VDC, little danger to the man ().
- Above 1.000 V, danger even without being in contact with the driver because there is ionization of the air, the minimal distances from approach are evaluated according to the level of tension (from where prohibition to enter the electric transformers, the distance between the drivers of the lines high voltage and the noise which one can hear in lower part of these lines consecutive to microamorçages by breakdown of the air).
It should be noted that the visual absence of burn after an electrification does not exclude from the internal burns on the way of passage of the current in the body which can generate necrose.
But electricity is also used to look after: it can be used such as it is, to manage electric shocks or to make nervous or muscular fabric stimulations or to supply the apparatuses of point used in medicine, allowing techniques of care such as Radiothérapie, electropuncture, Cardiac pacemaker, Prothèse, and of diagnosis such as Radiographie, scanner, magnetic resonance, Endoscopie.
Lawful contextIn France, the decree N° 88-1056 of the milked November 14th, 1988 of the protection of workers in the establishments fixed with the labor regulation delivers 2 title 3 which implement electric currents. It also applies to the foreign companies with the establishment and to which this one entrusts either of work on its clean electrical installations, or of work of some nature that it or in the vicinity of electrical installations.
StandardizationThere exists in France three standardizations in electricity:
- international: the international electrotechnical Commission (CEI)
- European: the European Committee for Standardization in electronics and electrical engineering (CENELEC)
- French: the technical Union of electricity (UTE)
Standardization in France is regulated by the Loi of May 24th, 1941 which created the French Association of standardization (AFNOR) and defines the procedure of homologation of the standards. This law is supplemented by the decree n° 84-74 of May 26th, 1974, modified by the Décret S n° 90-653 and 91-283.
There exist two big families of standards which aim on the one hand the construction of the electrical material and on the other hand the realization of the electrical installations. A new standard has just left in August 2007 for control the existing intallations of more than 15 years for the real diagnosis (obligatory running 1st half of 2008, decree on enforcement of a law awaited at the end of 2007)
The principal standards of realization are:
- NF C 15-100: electrical installations with low tension;
- NF C 13-100: stations of delivery;
- NF C 13-200: electrical installations with high voltage;
- NF C 14-100: installations of connection (low tension).
The principal standards of design are:
- NF C 20-010: classification of the degrees of protection gotten by the envelopes;
- NF C 20-030: safety regulations relating to the shock protection electric;
- NF C 71-008: portable lamps.
The experimental standard of control of the existing installations
- XP C 16-600: State of electrical installations of the buildings with use of dwelling - August 2007;
Electricity in natureThe electric exchanges are omnipresent in nature. In general, they are very visible phenomena neither, nor obvious, but they are fundamental; the electromagnetic forces and électrofaibles belong to the four fundamental interactions which structures all the Univers.
See also: the Lightning
The friction of many natural or artificial materials produces Triboélectricité. The lightning is enormous a electric shock due to the accumulation of static electricity in the clouds. In normal weather the air is insulating which does not let pass electricity. When the clouds of storms accumulate too many electric charges, they manage to modify the structure of the air by locally transforming it into an ionized plasma which conducts electricity. Electric arcs are formed then between the cloud and the ground: flashes.
The electrification of the air can give place to other phenomena, like the Feu of Saint-Elme
In the middle of the matter
Electric circulations of charges intervene in many natural phenomena, and in particular in the chemical reactions of oxydoreduction like the Combustion.
The terrestrial electromagnetic field is him also created by electric currents circulating in the core of our planet.
See also: electric Poisson
The electric fish are able to use the Electric current to be directed, to protect themselves or to communicate. There exist species which are able to produce true electric shocks: 600 V for the electric Eel; that enables him to strike its preys before consuming them. They produce such electric shocks thanks to their electric bodies, which have an internal structure similar to the muscles.
Nerve impulseAll the living beings produce electricity to animate the Muscle S or to transmit Information by the Nerve impulse of the Nerf S for example. Thus the doctors use the electrocardiography and the electroencephalography to check the good performance of the heart or the brain. The science which studies the electrical production by the living beings is the electrophysiology.
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