Ensuring Voltage Stability

While frequency on the grid is influenced by the behaviour of active power, voltage is affected by reactive power. As reactive power is difficult to transmit, voltage has to be managed more locally.

A flexible force (illustrated by the springs in the drawing) supports the web so that it can withstand the tugging to which it is subjected. In the case of Elia’s meshed grid, the springs represent reactive energy. As for the "weights" attached to the web, these symbolise various operations affecting the grid, such as injections, offtakes and electrical flows from outside the national grid.

At all times, Elia must have sufficient regulation capacity across its control area to be able to stabilise the voltage in the event of an incident (e.g. the outage of a large power plant) and, once the voltage in the area has been stabilized, maintain it within limits ensuring grid security

To maintain grid voltages at a suitable and stable level, Elia relies on, among other things, reactive power supplied by grid-connected assets: according to the voltage level measured on the grid, grid-connected assets stabilize the voltage by absorbing or generating reactive energy either via automatic activation or at the specific request of Elia (manual activation).

The services that VSPs supply to Elia and the Belgian electricity system follow a particular design. The design note describes the rules and specifications of the voltage service: technical requirements, remuneration mechanism, activation control and contracting process.

The supply of reactive energy to Elia is governed by a voltage control contract between Elia and the provider concerned. Specifically, Elia procures voltage and reactive power regulation services from VSPs.