Thijs Vral

System Operations

The Local Inertia project studies phenomena related to inertia distribution that can have a significant impact on the operation of the power grid. Following the replacement of synchronous rotating machines by renewable energy sources, the total inertia on the grid is decreasing. While this reduction does not yet pose an immediate risk to the grid, it does raise issues in terms of inertia distribution.

In the event of a major incident, and if because of non-optimal inertia distribution nearby synchronous machines cannot offset the disturbance, the delocalisation of this occurrence could result in very large exchange flows. These huge flows can cause connections to trip, triggering a domino effect that could create a local blackout or system split.

The project, led by Elia, is developing modelling tools and expertise to bring to light the effect of inertia distribution on power grids. The main question that needs to be answered is: will the reduction of inertia distribution impact the robustness and stability of the power system and especially the Belgian grid?


The first step for Elia was to gain an understanding of the phenomenon of inertia distribution and familiarise itself with the latest scientific findings on the matter.

Grid instability phenomena caused by a lack of local inertia have been observed in other countries, including the United Kingdom. For this reason, Elia decided to use the UK grid as a starting point to create theoretical and experimental models and thereby broaden its knowledge of the effects of poor inertia distribution in Belgium. Before analysing the phenomena and potential mitigation measures in detail, Elia began by gaining an understanding of the nature of the possible results of decreased inertia distribution. The aim of this first stage is to find out whether a local phenomenon (i.e. in Belgium) or the behaviour of neighbouring grids could have an impact on the stability of Elia’s grid requiring an intervention with regard to local inertia.

If the results of the first stage show that action is required for ensuring a stable and reliable power grid, a more detailed analysis will be launched, followed by a stage where mitigation measures will be identified.

The first stage consists of three steps:


Step 1: Understanding the phenomena observed in the UK

As no case study exists in Belgium due to strong AC interconnectors, and as there is limited information on surrounding grids, the UK transmission system will be used as the starting point of the analysis. A scale model of this transmission system exists and is accessible to the public, and the results of some research projects funded at national level are now available. This step aims to simulate the cases observed by National Grid (the TSO of the UK) to reproduce similar cases and lay the groundwork for a theoretical analysis of the effect of local inertia.


Step 2: From observation to theory

Simplified models allowing for a clearer mathematical and analytical understanding will be generated based on the phenomena observed during step 1 or based on other relevant hypothetical situations. While the models are created, parameters will be defined to describe specific situations (e.g. penetration of renewable energy, load inertia, generation inertia and the number of synchronous generators involved). These models will then serve as a basis for understanding and publicising the physical and theoretical basic principles of inertia reduction affecting the stability of the electricity system.


Step 3: General report for the future grid (up to 2030-2050)

The third step will involve examining Belgium’s electricity system between now and 2030-2050 based on various models devised during the previous step. These models will then be applied to a test grid representing Belgium in continental Europe (or a region of the UK in its synchronous area) with uneven inertia distribution. The models will then gradually be refined based on the simulation results to identify the potential risks of Belgium suffering the effects of a lack of local inertia. Once the theoretical context has been ascertained and the models have been refined, recommendations will be formulated to further analyse the characteristics and specific risks associated with this phenomenon. This last step will not be easy because no issues are expected in the near future and simulations will be carried out on a theoretical grid.

This study is being conducted with the support of the Energy Transition Fund.


What is local inertia?

Inertial Response is a property of large rotating masses, especially large synchronous generators. These rotating masses have as an important property that they resist sudden changes in rotational frequency, they cannot instantly move faster or slower but need a certain time to accelerate or decelerate. Thanks to this property, these rotating masses can overcome the immediate and inevitable imbalance between power supply and demand for electric power systems, and this way help to keep the grid stable and balanced.

Local inertia provides an image of the distribution of these rotating masses over a synchronously interconnected power system. Because power delivered by the inertia of a synchronous generator needs to be transported to the place where the disturbance takes place, it is important that the inertia in the grid is well distributed to keep power flows as local as possible.


The project has been split into 3 main parts and 4 deliverables. Each deliverables are mentioned here under and an associated report can be read.


Brunel University of London

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