Ensuring Voltage Stability

Voltage regulation and reactive power management

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.

The grid’s relation to voltage fluctuations is similar to a web

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.

Reactive power capabilities of grid-connected technical units

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 technical units: according to the voltage level measured on the grid, grid-connected technical units stabilize the voltage by absorbing or generating reactive energy either via automatic activation or at the specific request of Elia (manual activation).

Elia enters into contracts with VSPs for these voltage and reactive power regulation services. 

Providing voltage and reactive power regulation services to Elia

The supply of reactive energy to Elia is governed by a contract between Elia and the provider concerned. This voltage and reactive power regulation service contract (or VSP contract) defines the rules and specifications for the provision of the voltage and reactive power regulation service.