Assessment of Station & System Tests of the Attica - Crete HVDC Interconnection

Voltage Source Converter High Voltage Direct Current (VSC HVDC) interconnection, carried out during the period May–July 2025 prior to trial operation.

Due to the rare characteristics of the Cretan power system that consists of High Voltage

Alternating Current (HVAC) and HVDC connections with the mainland system and the innovative HVDC control strategy, special emphasis was placed on dynamic security, gridforming operation of the converters, and the system response under severe contingencies such as HVDC pole trip and outage of the AC interconnection. All critical tests were initially assessed using detailed power system simulations to ensure secure system operation during field execution.

The paper presents field measurements and Phasor Measurement Unit (PMU) recordings from key tests, including active and reactive power capability, fast power reversal, voltage sensitive mode operation, pole trip, and system response to AC link outages. Unforeseen events that occurred during the testing period, such as protection miscoordination and subsynchronous oscillations, are discussed along with the corresponding mitigation measures.

The presented results herewith provide valuable practical experience and lessons learned for the testing and commissioning of VSC HVDC systems connected to weak AC networks.