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26 February 2019

Electric system: lasting lesson of balancing by Transmission System Operators


Last January 10th, RTE, the French TSO, called on flexibility of industrial customers, through the interruptible load programme, in order to maintain the network frequency at 50Hz, a value on which all the electrical appliances are calibrated. However, there was no “black-out risk” on that day – a fear often transmitted but usually exaggerated… Let us try to have a clearer understanding!

On January 10th, the European electricity system experienced variations, under the form of a drop in the frequency, measured at 49.81 Hz at 21:00. This frequency drop was explained by several factors:

  • The modification of cross-border exchange schedules between European countries;
  • The mismeasurement of exchanges between Germany and Austria;
  • The constant frequency deviation in Europe due to the situation between Kosovo and Serbia.

Let us underline that this frequency drop of 0.19Hz does not itself constitute a black-out risk. However, it was necessary to call on various means at the disposal of TSOs to bring the frequency back to its normal level. In this case, on January 10th, the mobilisation of the frequency containment reserve in each European country, and in France, of the interruptible load programme, made it possible to get the situation under control.

The transmission system operators have several tools to restore frequency

In order to compensate for possible situations of frequency imbalance of the electricity system, TSOs can now count on several tools, such as the so-called “balancing” reserves, provided by European law and usable within the gate-closure time. TSOs activate these reserves when the situation requires it: thus, we distinguish the primary reserve, activated in less than 30 seconds to react to a frequency deviation, the secondary reserve which makes it possible to bring back the frequency to its normal level, and the tertiary reserve that complements (or little by little replaces) the two first reserves to stabilize the frequency at 50Hz. Beyond this existing cooperation, the different reserves are currently subject of mutual projects between TSOs in order to increase their efficiency and reduce their costs by an in-depth coordination.

TSOs can thus rely on numerous tools to restore frequency, based on a set of rules and proven practices, and on a cooperation of every moment at the EU level, thereby balancing the electricity system!

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