Electricity is the potency of a physicochemical system.

Electricity is the potency of a physicochemical system.

Electricity has several advantages compared with other forms of energy, namely:

- Electricity production in power plants occurs in favorable economic conditions;
- Electricity can be transmitted long distances through the electromagnetic field, either directly by the environment, be routed through power lines;
- At the place of consumption, electricity can be transformed into economic conditions in other forms of energy;
- Electricity can be divided and used in parts no matter how small, as needed;
The disadvantage they present electricity compared to other forms of energy remains that can not be stored. The electricity must be produced when it is required by consumers.
Electricity production is done by converting other forms of energy:

- Converting chemical energy of fuels in air turbines, gas internal combustion engine;
- Converting potential energy or kinetic water;
- Conversion of nuclear energy;
- Transforming other forms of energy: tidal, solar, wind;

Produce electricity by converting the chemical energy of fuels takes place in power plants or power plants.
Produce electricity by converting kinetic energy or water potential is realized in hydroelectric plants that produce electricity about hidrautica. This is economic duration energy source and inexhaustible.
Electrical energy is transported away through a system of electrical networks at different voltages: 110 kV, 220 kV, 400 kV and 800 kV even over. Electricity transmission is done either by airlines or by underground cables.
Voltage 110 kV, the pillars are over 25 meters high, placed at intervals of about 300 m; 220 kV her height of 35 m, the interval is approximately 350m; 400 kV, the height can reach 50 m, distance between them is over 350 m. In certain situations, such as for example water crossings, they can reach greater heights.

Underground cables are used in urban areas and where the additional cost is justified by other considerations such as aesthetics for example. A high voltage underground cable requires additional cooling installations and installations to avoid losses in the ground. For this reason it is much more expensive than an airline.

Airlines are made of conductive copper, aluminum core steel and copper cadmium. Copper conductors are used in all voltages; For wider using the cadmium copper that have a high mechanical strength. Aluminium conductors steel core is used especially for high voltages. There is a tendency to replace copper aluminum, because of the cost or lower.

Electric conductivity varies with temperature for most materials. In general it decreases the conductor temperature rise. Exceptions are coal and electrolytes, which, as with most non-metals, the conductivity increases to raise the temperature.
If underground cables are required layers of insulation and protection. Notice of insulating materials: paper impregnated with oil, natural rubber and synthetic plastics such as polyvinyl chloride or polyethylene (usually used instead of rubber). Paper insulated cables can be used up to 400 kV, while the insulated cables with rubber or plastics, only up to 11 kV.

Protection of impregnated paper cable insulation is first made with a layer of lead or aluminum to avoid moisture and then a layer of reinforced bitumen or without metal reinforcement to avoid corrosion and mechanical damage. Cables insulated with rubber or plastics protection is determined by the needs of service.

Typically, we need to know if the insulator chosen corresponds to the temperature that will work. For this purpose are defined in the following classes of isolation:
- Class Y insulation, good up to 90 degrees C. The paper, cotton, and silk untreated part of this class;
- Class of insulation used up to 105 degrees C. This includes paper, cotton, and silk impregnated;
- Class E insulation corresponds to temperatures up to 120 degrees C. Paper and fabrics impregnated part of it;
- Class B insulation, used up to 130 degrees C. It corresponds materials used in transformers and electric motors and part of it asbestos, mica and porcelain;
           - Class F insulation corresponds to temperatures up to 155 degrees C, class H of up to 180 degrees C and Class C temperatures above 180 degrees C. In all these classes includes various varieties of glass, mica and porcelain.
A semiconductor differs from other electrically conductive materials by additional factors that can influence current passing through it. Its electrical conductivity is between that of a conductor and an insulator and increases the temperature raising.

Its electrical properties are the result of a crystalline structure and the presence of impurities. Most semiconductors, pure, are insulators, but the introduction of impurities creates a surplus of electrons or a lack of electron, each of these states allowing passage of electric current. Commonly used semiconductors are germanium, silicon, selenium, copper oxide, lead sulfide, gallium arsenide, gallium phosphide and silicon carbide.