Feature Report: Power Grids

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Electricity Transmission

Electricity is transmitted from power plants to end consumers via an extensive grid of overhead or underground power lines. Cable is still the only means of electricity transmission.

Electricity is transmitted over extremely long distances using extra-high voltage power lines. Shown here is the Baixas station, located at the France-Spain interconnection. ©EDF / ROUX LIONEL

After leaving the powerIn physics, power is the amount of energy supplied by a system per unit time. In simpler terms, power can be viewed as energy output... plant where it is produced, electricityForm of energy resulting from the movement of charged particles (electrons) through a conductor... first flows through the high and extra-high voltage transmission grid (HV/EHV). Most of the power lines are overhead, which means they are easy to maintain. However, although the solution is more expensive, an increasing number of power lines are being buried underground for greater safety and less energy loss.

The electricity then enters the medium and low voltage distribution grid, which delivers power over shorter distances to end consumers. A number of components ensure a safe and secure flow of electricity at this point. These include:

  • Substations, where incoming high voltage is transformed to a lower voltage for distribution1.
  • Transformers inside the substations, which step down voltage so the electricity can enter the distribution grid.
  • Circuit breakers, which protect the grid against overloading due to lightning, a short circuit caused by a tree branch, etc., by interrupting the power supply to certain sections of the power line.

The WHO launched a study into the potential dangers of high and extra-high voltage power lines in 1996. 

Are High Voltage Power Lines Hazardous?

High and extra-high voltage power lines create powerful electromagnetic fields (EMF)2. Extensive research on the possible effects on the health of people living near power lines and the environment has been carried out through the International EMF Project, launched by the World Health Organization (WHO) in 1996. This research3 has shown that "at a distance of between 50 to 100 meters, the strength of EMF drops off to around the levels measured in areas far away from high voltage power lines." However, the WHO has also identified some "gaps in knowledge" about EMF. Pending further scientific research on the subject, international guidelines for limiting EMF exposure have been drawn up. They take into account the occupation and age of exposed persons and the amount of time they spend close to high voltage power lines.

 

Sources :

(1) RTE - Power substations (in French only)

(2) See RTE study (in French only)

(3) French Senate report (in French only)