2016-ban már történt hasonló eset, akkor az alábbi összefoglaló készült, azzal, hogy 2026-ig megépítenek egy nagy kapacitású HVDC interconnect-et a Spanyol-Francia határon és közösen kezelik az kicsi (és ezért nagy impedanciájú) interconnect problémáját. Azt hiszem, ez most jobban előtérbe fog kerülni.
The small signal stability of a power system is defined as the ability of the system to maintain synchronism during small disturbances arising from variations in demand, generation, opening of lines, etc. Electromechanical oscillation phenomena are intrinsic to the very nature of power systems. Inter-area oscillations, in which groups of generators oscillate coherently with other areas of the system, are particularly relevant in large electricity systems. This is the case of the European continental synchronous system, with the current situation of the interconnection of the Iberian system with France with high impedances between their ends and the centre. These oscillations, with a typical frequency between 0.1 Hz and 0.5 Hz, are not a problem for the system if they are correctly damped. However, weak damping can cause the usual oscillation modes of the generators to become excited “spontaneously” (in the event of small, normal variations in system variables). Also, in the event of a disturbance and increasing oscillations in the operating parameters of the system –frequency, power flows, voltages– appear. If these “fluctuations” are not properly corrected, an incident can occur at the global level of the interconnected synchronous system. Technical literature [1] as well as operating procedure 13.1 [2], establish a minimum damping threshold of 5% for oscillatory phenomena in the electricity system to guarantee its safety. There are many factors that affect the oscillation mode of electricity systems and their ability to damp them correctly (structural characteristics of the system – level of meshing and “extension”– generation mix, load level on the lines, power flows between the ends of the system and the centre, etc.). Very simplistically, it can be said that oscillations are more likely to occur in situations where the systems are electrically further apart –the impedance between their ends being greater– and with higher power flows from the ends. If we apply these premises to our system, it can be concluded that the reduced interconnection capacity of the Iberian Peninsula with France is a determining factor in the appearance of these oscillations, and that the greater the export from the Spanish mainland to France, the greater the risk of poor damping. On the other hand, due to the very physical nature of the phenomenon, it is at the extremes of the electricity systems where oscillations of greater frequency amplitude are recorded, and where corrective measures tend to be more efficient.
At the level of the European continental electricity system, there are several oscillation modes, although the Spanish mainland is mainly affected by two of them:
• East-West mode: the generators at the western and eastern ends of the synchronous system oscillate against each other in counter-phase (Spanish mainland against Turkey). The usual frequency of this mode is in the range of 0.12-0.16 Hz. It can be claimed that, generally speaking, this mode is correctly damped.
• East-Centre-West mode: the generators at the western and eastern ends of the system (Spanish mainland and southern Balkan Peninsula and Turkey) oscillate almost in counter-phase with the generators in the centre of the European continent (Denmark, Germany, Poland, Switzerland, Czech Republic, and Italy). This mode usually manifests itself at oscillation frequencies in the range of 0.22-0.28 Hz and is generally worse damped than the East-West mode.
This latter oscillation mode, at a frequency different from the usual one, manifested itself on 1 December 2016 [3] in an undamped manner, Figure 1, which highlighted the need to improve the damping capacity of the system.