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Power supply

The term power supply designates a set of systems capable of supplying electricity to devices operating with this energy.

An electric power supply is, in particular, a more or less complex apparatus or apparatus, intended to supply electricity, from an electric network to another apparatus. This device providing one or more functions thanks to electricity, but the latter must have specific current, voltage and frequency characteristics, on pain of malfunction or worse of destruction.

Production distribution


The production of electricity in mass is done in power stations by transformation of energy or:

  • Fossil fuels: gas, coal, oil,
  • Nuclear energy by fission or fusion,
  • Solar energy,
  • Cogeneration energy, geothermal,

go through a transformation of the base material into thermal energy, then into mechanical energy on the other hand,

  • Wind energy,
  • Hydraulic energy,
  • Tidal energy,

are simply channeled to provide mechanical energy;

Groupe : moteur thermique, alternateur.

Then alternators or generators transform this mechanical energy into electricity.

The thermal / mechanical energy transformation is carried out almost exclusively: by a steam cycle (see steam engine) which gives an efficiency close to 30 to 40%.

The power of these plants is expressed in kilowatts (kW), megawatts (MW) or gigawatts (GW) and, the energy they produce given in kilowatt-hours (kWh), MWh, GWh. Power stations are often close to places of high consumption, as well as cold sources, for thermal (river, sea, ocean, wind corridor) and, of course, to the energy source when possible (mine coal, gas storage, large water flow, high waterfall …). They are interconnected by an electricity transmission network.

Electricity transmission network

The electricity produced in the power stations is transported to the transformer stations by lines where the electricity circulates under high voltage (approximately 400kVolts) in order to reduce losses. These lines are most often overhead (cables stretched between pylons along the countryside) but tend, when technically possible and economically bearable, to be buried for political, aesthetic, ecological and security reasons. The electricity is then transformed into 225kVolts is distributed to the large company (SNCF, Iron and steel industry, …) or retransformed into 20kVolts for companies then by a last transformer in 400 Volts in homes.

Electricity market

The electric energy market is based on: production, transport and distribution networks as well as of course on the consumption of electricity.


Electricity pricing does not only follow traditional commercial policies, changing the price according to the volume consumed. Electrical energy is a particular good, difficult to store, start, slow down, or stop a production unit is much more delicate than flipping a switch on the consumer side. This is why one can find tariff options encouraging to make consumption more homogeneous and varying according to the periods of the day or the year. The best-known example: the off-peak and peak-hour tariff. Order of magnitude in 2005 and in France: 0.10 € / kW.h during the day and 0.07 € / kW.h at night. This forced the suppliers to equip their metering systems with a device allowing the modification of the tariff remotely, the producer sends a time signal on the lines indicating the current period, This signal is relayed by a dry contact, with the aim of to enslave the operation of certain large consumer device at the most advantageous price. Example the electric water heater: It is equipped with a water reserve which is generally only heated at night, to be consumed throughout the day. A dedicated relay, located in the electrical panel of the home, is responsible for cutting or establishing the device circuit according to the tariff signal received.



For the power supply of industrial sites, which are very large consumers, electricity arrives at high voltage. It is transformed into low voltage only as close as possible to energy-intensive installations, all of these installations are generally assembled and maintained by the manufacturer.

Transformer station (electrical transformer)

Poste de transformation
Electric transformer

In order to be able to ensure distribution under acceptable safety conditions, the electricity from the transmission lines passes through transformer stations where its voltage is lowered.


From transformer stations to consumers in apartments, villas, offices, stores, power lines carry low voltage current.


Tableau électrique domestique

At the entrance to the consumer’s room, the electricity supplier installs a meter which allows the latter to bill the consumer for the exact quantity of electricity known by the latter.

  1. Electrical safety standards and regulations have long required that protection systems be integrated into the premises where electricity is consumed.
  2. These personal protection and power line protection systems (fire prevention) are grouped together on a panel quickly accessible to the occupants of the room in the event of need, electrocution of a person or the fire of a device.

Industrial equipment

  • TGBT
  • Machines: electric motor, oven, electrolysis, heating, refrigeration.

Domestic appliances

Integrated power supply

In most household and office appliances, certain circuits require a power supply of different characteristics than that distributed from individual electric meters. At the input of the devices, before or integrated into the power supply, there is a filter intended to suppress incoming interference, but above all those generated by the power supply itself and those of the device that could disturb the network.

Alimentation de PC.
Integrated power supply

We can distinguish two main types of food:

  • Those of low power which only serve to power a small part of the appliance: The majority of household appliances, a minimum sophisticated, can be broken down into two distinct electrical parts, the control circuit and the power circuit.
    – The control circuit, since it serves as an interface with humans, is at very low voltage, a power supply transforms the 230 V into a voltage (less than 50V, generally 12V) compatible with the control circuit.
    – The power circuit is supplied by the mains voltage through a switching device controlled by the control circuit.
  • And those through which pass all the electricity consumed by the device, this often provides several separate voltages, assigned to different tasks.

Separate power supply

Alimentations basse tension externe
Separate power supply

Technological advances favoring an increasingly reduced consumption of appliances, small household and office appliances: radio receiver, telephone, desk lamp, printer, are supplied for safety reasons and, sometimes for aesthetics, very low. voltage using an external power supply unit. Frequently this block is only a simple step-down transformer, sometimes associated with a rectifier delivering a direct voltage, sometimes a voltage regulator supplements these supplies.

Laboratory food

Alimentation de laboratoire.
Laboratory food

In workshops and laboratories where electrical and electronic equipment is designed, tested or repaired, much more sophisticated power supplies allow the parts of the devices under examination or test to be supplied with maximum safety. All the parameters of the currents and voltages to be delivered can be adjusted separately and very precisely to avoid any damage to equipment and personnel.

Protection system

  • Lightning rod.
  • Grounding.
  • shielding
  • Circuit breaker.
  • Fuse.

Standard names

  • VHV = very high voltage
  • HV = high voltage
  • LV = low voltage
  • VBV = very low voltage

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