Electricity

Nature of electricity

It 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.

Static electricity

The electric current

The direction of the current

In 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 analogy

To 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

Electrical production

Transport and distribution

Conversion transformation

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.

Storage

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.

the storage of electrical energy in coils or inductance coils offers interest only with superconductive materials , which is yet only experimental field as regards storage.

Trades of electricity

Electrical 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 consumption

Today 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.

Industrial applications

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 ( $U/R < 30~ {\ rm my}$ ).
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 context

In 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.

Standardization

There 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.

In addition, an approved standard can be returned of obligatory application by decree, but this procedure until now only little was used in electricity. ( NF C 15-100 , NF C 13-200 )

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 nature

The 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.

The lightning

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.

Electric fish

Nerve impulse

All 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.

Random links:

Orthez | National bank of the old-age insurance of the employed persons | Amand of Bordeaux | Masha | Acta Eruditorum