At the seminar "The Power System Under Conditions of an Increasing Share of Power Electronics Devices", held on 4 December 2025 at the Faculty of Electrical Engineering and Computing (FER) in Zagreb, more than 100 participants gathered. The focus was once again placed on the challenges posed by the growing share of renewable energy sources for the distribution system. The seminar opened with introductory remarks by Anton Marušić, President of HO CIRED and President of the Management Board of HEP ODS, together with Tomislav Capuder from FER, who moderated the event.
The HO CIRED President emphasized that analysing power system protection mechanisms is becoming increasingly important in the context of the rapid growth of renewable energy sources, which significantly change the dynamics and behaviour of the grid. “HEP ODS today has more than 41,000 connected distributed energy sources with a total connection capacity of 1511 MW.

We continue to maintain a strong development pace: each month we connect around 1,100 new plants with a total capacity of 30 to 40 MW. This means that between 80,000 and 90,000 power electronic devices are currently operating in the distribution network, bringing along a wide range of challenges – from flicker to overvoltage and other disturbances.

In parallel, HEP ODS is also working intensively on modernising the metering system – every month we install around 50,000 new meters that become part of the advanced metering system. These devices are essential for high‑quality network analysis and management under conditions involving such a large number of electronic devices,” Marušić noted. He added that the strong turnout at the seminar confirms that the topic is highly relevant and that the professional community is seeking new perspectives and solutions for the future development of the distribution system. Presenters at the seminar highlighted the key changes in distribution networks caused by the increasing number of sources connected via power electronics. Traditionally, the system relied on synchronous generators that provided sufficient inertia and grid stability.

However, inverters used in renewable energy sources do not have the same capability to provide inertia, increasing the system’s sensitivity to disturbances. Consequently, there is a growing need to redefine protection concepts and coordination procedures. The core of the seminar was the discussion on the necessity of redefining protection concepts, strengthening coordination between transmission and distribution system operators, and applying advanced digital technologies. Among the conclusions, it was emphasised that the high share of renewables and the increasing use of power electronics require fast and comprehensive adaptation. It was also highlighted that the analysis of protection mechanisms must include broader aspects of supply security and alignment with regulatory and technical requirements, along with the need for new protection standards.
The presentations of individual experts are provided below.