The amount of converter connected production is steadily continuing to increase in the Finnish power system. Most of the new production is wind power which is concentrating on the 400 km long area in the western coast of Finland. This area currently has more than 5 GW of wind power and very little load or synchronous generators, creating issues with converter driven stability.

The Finnish transmission system operator (Fingrid) has managed these converter driven stability issues in short term by curtailing the production and adjusting the control modes of the wind farms. Now also utilization of a system protection schemes has been studied. In longer term, the stability will be managed by Fingrid’s own investments in grid stabilizing equipment such as synchronous condensers and STATCOMs. For customers, new grid code requirements have been introduced such as the fast voltage control requirement for power park modules and grid forming requirements for BESSs. All these above – the curtailments, the investments planned and requirements set - are based on the results of wide area EMT simulations, highlighting the importance of accurate models.

In order to verify and improve the accuracy of the wide area EMT simulation models, Fingrid has conducted a real life grid test where converter driven instability was intentionally evoked by reducing the network strength in a limited area. By opening two 400 kV lines, an area including around 1600 MW of wind power production capacity was left connected to very weak grid. The switchings were made during low wind, and after an increase in wind production the sub-synchronous oscillation in voltage was observed, and the 400 kV lines were connected effectively stopping the oscillations.

This paper presents the grid test which was conducted and what are the findings on the observed converter driven stability phenomena. Also, this paper shows the accuracy of the wide area EMT simulation model and how it could be improved using the grid test data. In addition, the ability of RMS dynamic simulation model to replicate the observed phenomena is discussed.