Electricity is the interaction of particles charged under the action of the force electromagnetic. This physical phenomenon is present in many contexts: the power is both the nerve impulses of living things , that the lightning of a thunderstorm. It is widely used in developed societies to carry large amounts of energy usable.

The properties of electricity were discovered during the ^eighteenth century. The control of electrical current has the advent of the second industrial revolution. Today, power is ubiquitous in the industrialized countries from different energy sources , mainly hydro , thermal and nuclear power , electricity is an energy carrier used in very many uses domestic or industrial.

Power line near a railway line in Poland.

The Lightning was the first visible manifestation of electricity for humans.

Electrical cables high voltage near a power transformer for distribution.

It is the movement of electrical charges of the matter is the source of electricity.

As the mass , the electric charge is an intrinsic property of matter, which helps explain the origin of certain phenomena. Nobody has ever directly observed an electrical charge, but scientists have noticed similarities in the behavior of certain particles , so they have postulated that these particles had characteristics in common, whose properties coincide with their observations.

Unlike the mass , there are two types of electric charges, which behave as if they were "opposed" to each other: they are called so by convention positive and negative.

two charges of opposite nature attract	two charges of similar nature, for example, two positive charges repel

Charges of opposite nature vanish: this means that a particle has both positive and negative charge behaves as if it had none. They say it is electrically neutral.

Static electricity

In nature, the electrons are carriers of negative charges and protons positive charge carriers. The atoms that make up ordinary matter include electrons moving around a nucleus composed of protons and neutrons , the latter being electrically neutral. The number of electrons equals the number of protons, the whole is electrically neutral.

When certain materials are rubbed together, electrons of surface atoms of one are extracted and recovered by the other atoms. For example, a rod of glass rubbed on a piece of silk becomes positively charged because its atoms lose electrons to the benefit of silk if you rub a balloon on hair dried, it is negatively charged, because it captures electrons hair.

A rule in plastic rubbed on the fabric of a garment has a negative charge, so it can attract small pieces of paper. Rule changes by electrostatic induction , the distribution of charges in the paper: the negative charges of the negative charges repel rule at the other end of the piece of paper and draw the positive charges of the atoms of paper.

We are talking about static electricity when there is no movement of electric charges. Experimentally this is usually achieved by using materials in which the charges are "trapped", materials insulation as plastic , the glass , the paper ... resistant to traffic loads ^{Electric current}

There are also conductive materials such as metals , the water salt, the human body or graphite , which allow electrical charges to move easily.

When walking on a carpet , the friction of the feet on the ground tears electrons and the body static charge. When you touch a doorknob metal so it feels a little electric shock accompanied by a spark caused by the sudden displacement of electric charges flowing to the ground through the conductive materials of the door.

This flow is due to the fact that there were more charges in the body in the ground: as two charges of similar nature tend to repel, in a conductor they will seek to move the point of minimum charge. This difference in costs between the body and the ground is called a potential difference.

To create an electric current , so you have a circuit of electrically conductive materials that allow electrical charges to move, and a system capable of creating a potential difference between the two ends of the circuit. This system is called a generator : it can be for example a battery or a dynamo.

The current direction

In an electrical circuit is said that the electric current, I, flowing between the electrodes from to the of the generator. This meaning is purely conventional, since the current may well be caused by positive charges that are attracted to the negative pole of the generator, by negative charges that move in the opposite direction, toward the positive pole.

In some cases, positive and negative charges move at the same time and this double movement is responsible for the overall electrical current. This is the case in ionic solutions, where the cations and anions move in opposite directions, and the semiconductor as a diode, where electrons and " holes "are the same. The charges can not all move under the action of electric field and thus in a wire, the positive charges (the nuclei of atoms) remain fixed in the metal structure and can be no electricity; the electric current in a metal is created solely by the movement of negative charges (free electrons) to the positive pole of the generator: it is an electronic current, however, is used in all cases the conventional sense I of the current, established before the discovery of the negative charge of the electron.

We talk about DC when the direction remains constant and, ac when it changes periodically. The frequency of an alternating current is the number of times per second. It is expressed in hertz (Hz), for example the power supplied to the electrical installations is at a frequency from 50 Hz in Europe and 60 Hz in the United States.

Hydraulic Analogy

To understand some properties of the electric current, it is interesting to compare it to water flowing through a circuit of pipes. The generator can then be viewed as a pump responsible for pressurizing the liquid in the pipes.

The potential difference, or voltage, similar to the difference in pressure between two points in the water circuit. It is denoted U, and expressed in volts (V).

The electric current can be equated to the flow of water in the pipe. It reports the number of charges that pass a point each second in the circuit and is often denoted I, measured in amperes (A).

The resistance of an electrical circuit would be analogous to the diameter of the pipe. More pipes are smaller, it takes pressure to get the same flow; similarly, the greater the resistance of a circuit, the higher you need a high potential difference to have the same intensity. The electrical resistance reflects the ability of a material more or less stop the flow of current. It is rated R and is expressed in ohms ( ).

It is possible to push this analogy much further but it is important to bear in mind that it has its limits and that some properties of the electric current differ materially from this model based on fluid, hoses , and pumps.

Electricity in nature

Electrical trade are ubiquitous in nature. In general, there is little visible phenomena, but they are fundamental forces electromagnetic and electroweak form part of the four fundamental interactions that structure throughout the universe.

Lightning

The friction of many natural materials or artificial product of the tribo. Lightning is a huge electric shock due to the accumulation of static electricity in the clouds. In normal times the air is an insulator , which blocks the passage of electricity. When the electric charge in the clouds of storm reaches a certain value, the potential difference, the different accumulated charges is such that it manages to change the structure of the gases in the air, turning them into a local plasma ionized, which leads him perfectly electricity. Electric arcs are formed when giant, two clouds or between a cloud and the earth: the lightning , allowing the rebalancing of electric charges.

The electrification of the air may give rise to other phenomena, such as St. Elmo's fire.

In the heart of matter

The movement of electric charges occurs in many natural phenomena, especially in the chemical reactions oxidation-reduction such as combustion.

The Earth's electromagnetic field is also created by electric currents flowing in the core of our planet.

The electric fish

Pacific torpedo

Electric fish are able to take advantage of electric current to move, to protect themselves or to communicate. There are species capable of producing real electric shocks: 620 V for the electric eel , and this allows him to stun its prey before eating them. They produce such electric shocks through their electric organs , which have an internal structure similar to the muscles of the human body.

The nerve impulse

All living things produce electricity to animate the muscles or to transmit the information by the nerve impulses in the nerves. Thus, doctors use the electrocardiography and electroencephalography to diagnose the functioning of the heart or brain. The science that studies the production of electricity in living things is the electrophysiology.

History

Electricity is a word derived from Greek , elektron, meaning amber yellow. The ancient Greeks had discovered that by rubbing amber, they produced an attraction on other objects, and sometimes sparks. They therefore called this force power.

William Gilbert was the first in his De Magnete (1600), made the distinction between body electric (he coined this term) and magnetic. He likened the Earth to a magnet, rated the laws of attraction and repulsion of magnets with their poles, and the influence of heat on the magnetism of iron. He also established the first notions about electricity, including a list of bodies electrified by friction.

An observation period started in the ^eighteenth century when it became known to create static electricity. In 1733, Mr. Du Fay , "said Charles Francis Cisternay, discovered the positive and negative charges and observed the interactions between these charges. But that Coulomb who first enunciated the laws of physics.

In 1799 , Alessandro Volta invented the electric battery , and in 1868 the Belgian Znobe Gram made the first dynamo. In 1879 , Thomas Edison first introduced his incandescent light bulb. A hydraulic power of 7 kW was built the same year in St. Moritz , then in 1883 , Lucien Gaulard and John Dixon Gibbs created the first power line. In 1889 , a 14 km line was built in the Creuse , between the Cascade Jarrauds , place of production, and the city of Bourganeuf.

The electricity is then developed gradually during the ^twentieth century , first in the industry , the lighting and the railroad before entering the home. Different ways of generating electricity developed: central hydraulic , thermal , wind and nuclear ...

Production

Sources of global electricity in 2000
	a: coal 39% b: Hydroelectric 17% c: Nuclear 17% d: Gas 17% e: oil 8% f: wind , geothermal ... 2%

Electricity represents about one third of the energy consumed worldwide. The electrical engineering is the science of domestic and industrial applications (production, processing, transmission, distribution and use) of electricity.

The most common method for producing large quantities of electricity is to use a generator , converting a mechanical energy into an alternating voltage. This mechanical energy from the mostly obtained from a source of heat , resulting itself from a primary energy , as the fossil fuels , oil , nuclear or renewable energy, the solar energy. One can also directly use mechanical energy, such as hydropower or wind energy.

Obviously the source is not necessarily mechanical, such as batteries or solar panels.

Transportation and Distribution

The current flowing on the power grid is most often alternating phase because it is cheaper to produce and transport. While the final consumer needs in low voltage, less dangerous to use, it is more economical to transport the power over long distances, use very high voltage.

Indeed, constant power, if we increase the tension, reduces the current ( single-phase) and therefore the losses by Joule effect and heat loss ( ) And the skin effect which restricts the movement of strong currents on the outer surface of conductors: this would require the use of copper cables larger section. It therefore uses transformers step-up in order to reduce the current for transportation, and transformers step-down voltage for distribution (low voltage) to users.

Conversion processing

The voltages can be transformed and converted.

Typically for large powers, tensions are alternatives, and pass through transformers to convert the current to magnetic flux, itself converted into a current in the coils. This principle allows to change the voltage level while maintaining the frequency and galvanic isolation between primary and secondary network processor. For power to the technologically converters are used in semiconductors (transistors, thyristors):

• rectifiers to convert AC voltage into DC voltage;
• inverter to convert DC voltages into alternatives;
• converters allow the direct conversion of voltage into DC voltage by switching at high frequency.

Storage

For electricity transmitted and distributed by drivers , it is necessary to balance at any time production and consumption. Thermal power plants to gas, oil or coal, are generally placed in service to meet peak demand. It also uses stations pumped- two dams: during peak hours, water is pumped to the upper basin, and during peak hours, water passes through a turbine that produces a top up electricity on the network.

It is also possible to store electricity on a small scale by means of batteries, capacitors, inductors or coils.

• The batteries are widely used for autonomous systems and equipment fixed or mobile.

• The capacitors have long been used in electricity and electronics , but appeared recently ultracapacitors to have more instantaneous power than with conventional batteries of larger size, but for very short times. One possible use may find its place in the electric traction motor for transient phases of acceleration, especially as the recharging of the capacitors is almost instantaneous.

• The storage of electrical energy in coils or coils inductors offers interest only materials superconductors , which is still only the experimental field for storage.

The electrical trades

Electrical engineering is a set of technologies that can be performed by: an engineer , an electrical engineer , a draftsman -designer ...

• The winder is a technician who makes the circuits magnetic such as motors or generators;
• the editor-rigger carries out control panels and it makes the connection;
• the electrical -wire low voltage networks and high voltage, in construction, industry, commercial, marine, aviation and ground transportation ( car );
• service technicians, maintain and troubleshoot electrical machinery;
• control engineers, electronic engineers, electrical engineers create the automation and control systems, electrical control automated machines ...

And a multitude of professions related to electricity industry (for the most common: chemist, insulator, heating engineer, robinetier, boilermaker, mechanic ...).

Uses and consumption

We often distinguish two types of uses :

• uses so-called "specific" (sometimes also called "noble"): These are those that can provide only electricity (telephone, electronic, computer, audiovisual, lighting at night ...). Following a trend in energy savings (cooling more efficient, energy-saving lamps ...), consumption by households and apparatus are divided on the rise with the air supply, the development of computer and audiovisual equipment and various electrical gadgets. Especially plasma screens, large LCD screens, home cinema were multiplied by 5 to 10 the power consumption per device. Some controllers , the communications digital ( internet , networks ) consume more electricity. If laptops consume 5-6 or even 10 times less energy than a desktop computer and screen (up to 15 watts for the notebook against 150 for a desktop), they have multiplied, and often s' simply add to the desktop PC instead of replacing them.
• uses so-called "substitutes": It uses thermal (or that could be filled by other energy sources (engines with fuel, gas, hydrogen ... air conditioning / refrigeration, and heating all fuels. The direct thermal heating is more efficient than electric resistance heating, the latter requires 3.2 kWh to produce 1 kWh upstream end, and finally - on average - more CO ₂ emitter using a heating gas or oil, which prompted the prohibition of direct electric heating in Denmark, replaced - with government assistance - through heat pumps, or other alternatives (solar, Canadian well, etc.).

It can also be categorized according to their uses energy impacts:
Contrary to popular belief, the industry is not the main consumer of electricity. In rich countries, it consumes less than a third. For example, in France since the late 1990s, the industry uses less than a third of the final electricity. These are the residential and tertiary, through heating, appliances, lighting and computer) which in 2009 consumes about 67% of electricity.
Moreover, France has justified its nuclear program by the desire to no longer depend on oil in 2009 held the record for per capita consumption of electricity (one average French consume more electricity than average Californian recalls but also, paradoxically, oil consumption per capita , with high debt and fuel poverty for the poorest.
Since the 2000s, when consumption peaks accompanying cold waves, RTE fears a collapse of part of network. It broadcasts, including Britain and Provence-Alpes-Cote d'Azur , incentives to conserve electricity. For as it is not massively store electricity, it is the "Demand" becomes the factor of sizing the electrical distribution system, that is to say the energy consumed at a given time and not only cumulative consumption over the day, season or year. The spatiotemporal distribution of electrical purposes has a major impact on the economy, but also environmental because resources called as a last resort during peak emit the most CO2. Thus, the electric heating "weighs" 2.5 times more instantaneous power (36% at the peak of consumption in the French network) that accumulated consumption averaged over the year (14%). " . Of Commons seeking to reduce the waste associated with Christmas lights, monuments and street lighting, but the motor or lighted billboards remained in operation. The smart grid would help customers reduce consumption at peak times and allow to draw electricity from the shortest path (least line loss), but without addressing the risk of rebound effect .

In Europe, the energy efficiency has been driven by a Directive on minimum efficiency of electrical appliances after a directive on the label in 1992, followed in 1997 by a directive restricting the consumption of refrigerators, freezers and combined, careful not to exceed the optimum for the consumer in terms of rapid recovery of initial investment by the energy savings. In 8 years, the energy efficiency of refrigerators has been improved by 30%, then nothing has been done for 13 years on the electr omnager in Europe, while fuel efficiency standards are developed in the United States since 1989.
despite a significant improvement in energy efficiency from 1999 to 2004, final consumption continues to rise in Europe (EU-25); An average household in the EU-25 consumed 4098 kWh in 2004, when he could consumes only 800 kWh if it were equipped with existing equipment with low consumption and abandoning incandescent bulbs (and even less with the technology the most efficient ). According to the Joint Research Centre (JRC) of the EU, from 2005 to 2006, consumption increased in the EU-25 in all sectors in the residential, in the tertiary sector (+15.8%) and industry (+9.5%) at a rate based on that overall GDP (10.8%).
The report recommends encouraging solar water heaters and energy savings by replacing incandescent lamps in particular. In November 2006 the European Commission launched an action plan for energy efficiency to - 20% of electricity consumption in the EU-25 by 2020 .

The lighting in Europe in the tertiary sector lighting (often during the day) became the first station power consumption, 175 TWh consumed annually and 26% of total electricity consumption of the tertiary sector . Moreover, the night lighting (the main event, with illuminated advertising, the phenomenon known as light pollution ) has been rising steadily for 50 years.

To help consumers optimize their consumption and expenditure by purpose, NGOs have created a website Topten producing an energy independent analysis of most materials used. However, without energy goal of sobriety, a rebound effect (direct or indirect and external) can make the money saved could be re-spend in other energy uses.

The home network

Besides the battery-powered devices or batteries to automotive , most of the electricity used in daily life comes from the power grid. Each home is connected to the network through a table that contains at least one meter for billing and a circuit breaker used to switch and to protect the installation. This breaker out two wires that feed the domestic installation: the phase and neutral and phase conductors sometimes two additional facilities in three phase. There is a third conductor for grounding.

Then there is an array of fuses or circuit breakers, distributing the current in the various circuits of the house. It typically provides dedicated circuits for appliances that need a lot of power ( oven , electric cooker, washing machine , dishwasher , water heater ...) normally part by a circuit for lighting and one for electrical outlets.

It uses switches to open or close electrical circuits. It is possible to use a special assembly back and forth or a remote switch when you want to create multiple control points, for example at each end of a corridor.

Industrial applications

• The electrolysis is used to refine the aluminum , producing gas, plated metals ...
• Electric arcs are used for welding or cutting metals;
• The electric motors animate machines, pumps, various automatic systems, directly or via hydraulic circuits;
• The supply of electronic circuits , to relay , of contactors , electromagnets, etc. sequences allows automated.

Health and Electricity

The electrification is the passage of electric current in the human body. When the current is too strong it can for example cause burns or cardiac arrest. It is usually considered a voltage exceeding 50 V ac / 120 V dc has a potentially deadly hazard: the electrocution.

The consequences of an electrification depend on the nature of the voltage (AC or DC), resistance of the human body generally accepted as being 5000 ohms ELV (Extra Low Voltage), 1 000 ohms at 220 V AC and 400 ohms at 500 V (the resistance is decreasing as a function of voltage exposure), the current amplitude has circulated and lap times of the current. It is commonly accepted some thresholds which are based on safety rules:

• Above 20 mA, if danger of cardiac fibrillation passage through the heart. By SBT 50 VAC / 120 VDC maximum, the risk to humans is low ( ).

• Above 1 000 V, there is danger, even without direct contact with a driver because there is an ionization of air, minimum approach distances are measured according to the level of tension. Hence the prohibition to enter the enclosures of electrical transformers. Despite the distance separating the consequent high voltage line conductors, the noise can be heard below these lines is due to micro-priming induced breakdown of air.

The lack of visual burn after electrification does not burns on the internal path of current flow in the body, which can cause necrosis.

But electricity is also used to treat: it can be used as such, to administer electric shocks or stimulate nerve tissue or muscle, or peak power equipment used in medicine, for care techniques such as radiotherapy , electropuncture , pacemaker , prosthesis , and diagnostics such as radiography , CT , MRI , endoscopy.

Regulatory Background

In France, Decree No. 88-1056 of 14 November 1988 addresses the protection of workers in establishments subject to the Labour Code Book 2 Title 3 to implement electric currents. It also applies to foreign companies to establish and which it says is its own work on electrical installations or works of any nature whatsoever in the vicinity of electrical installations. This decree gave rise to requirements UTE C18-510 on the safety of persons approaching the electrical circuits.

Standardization

There are in France three normalizations of electricity:

• International: the International Electrotechnical Commission (IEC)
• Europe: the European Committee for Standardization in electronics and electrical engineering (CENELEC)
• French: the Union Electrical Engineering (UTE)

Standardization in France is governed by the law of 24 May 1941 that created the French Association for Standardization (AFNOR) and sets the standards approval process. This Act is supplemented by Decree No. 84-74 of 26 May 1974 , as amended by Decrees No. 90-653 and 91-283.

In addition, a standard approved may be made mandatory by law, but this procedure has so far been used very little electricity except for safety. ( UTE C18-510 , NF C15-100 , NF C13-200 )

There are two major families of standards aimed on the one hand the construction of electrical equipment and also the realization of electrical installations. A new standard comes out in August 2007 for the control of existing plants over 15 years for the real diagnosis (current mandatory ^H1 2008 implementing decree expected late 2007).

The main standards of achievement are:

• The NF C 15-100 : Low-voltage electrical installations;
• The NF C 13-100 : Delivery Points;
• The NF C 13-200 : Electrical installations in high voltage;
• The NF C 14-100 : Facilities Connection (low voltage).

The main design specifications are:

• The NF C 20-010 : Classification of degrees of protection provided by enclosures;
• The NF C 20-030 : Safety Rules for the protection against electric shock;
• The NF C 71-008 : Handlamps lighting and construction.

The standard experimental control of existing facilities:

• The XP-C 16-600 : Status of electrical installations in buildings for residential use - in August 2007.

References

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