The National Transmission System Operator Transelectrica SA, in collaboration with hydropower company Hidroelectrica SA and the Bulgarian Transmission and System Operator ESO - EAD conducted on Saturday the most complex National Electricity System restoration exercise, which implied the black start-up of the Lotru and Vidraru hydroelectric power plants, Transelectrica and Hidroelectrica informed in a release.

The activities were carried out at the Vidraru and Lotru hydroelectric power plants and the adjacent network sections, and at the transformer stations Arefu, Sibiu Sud, Bradu, Targoviste, and Sotanga.

The exercise was aimed to test and validate the capacity to restore the National Electricity System in the scenario of a major failure through the 'bottom-up' method, i.e. by restarting the system from local stand-alone energy sources and gradually expand the supply to the entire network.

Two independent energy islands were created, which were synchronized in the 400/220/110/20 kV Arefu power transformer station, and the synchronization with the Bulgarian power system was subsequently achieved along a specially configured technical route.

The exercise, which was carried out under completely safe conditions with the operational teams of Transelectrica, Hidroelectrica, Romanian energy distributor DEER and Nova Power & Gas, followed a planned scenario that did not affect the normal functioning of the national grid. The following aspects were tested: the independent and simultaneous black start-up of the Lotru and Vidraru hydroelectric power plants; the creation of two energy islands capable of supplying local areas and consumers, such as pump stations, storage facilities, national power grid lines, the usage of storage facilities within National Power System in the restoration processes; the synchronization of the two islands at the 400/220/110/20 kV Arefu substation, followed by synchronization with the Bulgarian energy system.

The main goals of the exercise were: validating the capacity of the Lotru and Vidraru hydropower plants to operate autonomously and supply consumers in an islanded regime; the technical verification of the equipment and routes involved in the restoration process; training and preparation of the operational and technical personnel of the entities involved in the operation of the National Power System.

According to the cited source, the defense and restoration of the National Power System are key activities that allow the management of emergency situations and the return of the system to normal operating conditions. In a regional context where energy security is becoming increasingly important, this type of exercises contribute to strengthening the rapid response capacity, improve cross-border cooperation in South-Eastern Europe, and help increase the resilience of the national energy system. AGERPRES (RO - writing by: George Banciulea; EN - writing by: Simona Klodnischi)