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The basics of electrical energy supply

Electrical energy is a flexible, adaptable form of energy, but it is difficult to store, and consumption by customers and coincidental demand are constantly varying.

Production, transmission, control and protection of electrical energy
Production, transmission, control and protection of electrical energy guide by Legrand

These requirements necessitate permanent transmission and provision of energy via a distribution system:

  1. High voltage for high powers and long distances
  2. Low voltage for medium and low powers and short distances

Although the term “network” is often used in the singular to describe the whole infrastructure required to carry energy from the production centres to users, it would be more accurate to use the plural to cover all the different systems which make up each level of the overall system.

The system is regulated by means of requirements placed on producers, in particular the requirement to keep the current frequency at 50 Hz (or 60 Hz). Too much power results in an unwanted increase in frequency, while insufficient power causes a drop in frequency.

Automated systems disconnect producers that do not comply with the standards, but for the regulators of the system this automation results in random events that are not controlled and may cause damage.

Block diagram - From production to use of energy
Block diagram – From production to use of energy

In many countries throughout the world the system is not interconnected, either because it is not sufficiently advanced, or because the country is too large.

The creation of a network of systems in Europe contributes considerably to the reliability and availability of those systems by enabling exchanges of energy.

New energy sources such as wind or solar power involve new problems, due to their considerable variability and above all the difficulty of accurately forecasting their production several hours in advance. The question therefore arises of the balance between potential consumption and the available power of the new sources.

Electricity transport network

Voltages of 225 and 400 kV, in the VHV (Very High Voltage) range, have historically been used in France, but other voltages (see table 5 in standard IEC 60038) are used throughout the world. These very high voltages limit energy loss over long distances.

Production centres are connected to one another via interconnection stations which are used for distribution across the whole area and also, if required, for exchanging energy with bordering countries, as in Western Europe, by the use of a single voltage of 400 kV.

Title:Electrical energy supply – 3rd Power book by Legrand
Size:6.1 MB
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Guide to production, transmission, control and protection of electricity
Guide to production, transmission, control and protection of electricity by Legrand

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  1. D.Sabari Eswaran
    Jun 28, 2018


    Thanks for the super document. It is good to read and can be understood by all irrespecive of their domain.

  2. Dejan
    Nov 10, 2016

    Hello. Data for Voltage tolerance for Slovenia is unfortunatelly not correct. Iz should be +/- 10%.

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