On January 28 IENE sent to its members a special “News Analysis” following the incident of January 8, 2021 whereby the CET synchronous area of Continental Europe was separated into two parts due to outages of several transmission network elements in a very short time. ENTSO-E had already published initial information on the event on 8 January 2021, followed by an update with geographical view and time sequence on 15 January 2021.
Since then, ENTSO-E has analysed a large portion of relevant data aiming to reconstruct the event in detail. The event was also reported in IENE’s Newsletter "SEE Electricity Market Analysis”, No111 (Week 1: 4 – 10 January 2021).
According to the most recent update published by ENTSOE on 26 January, the analysed sequence of events concludes that the initial event was the tripping of a 400 kV busbar coupler [1] in the substation Ernestinovo (Croatia) by overcurrent protection at 14:04:25.9. This resulted in a decoupling of the two busbars in the Ernestinovo substation, which in turn separated North-West and south-east electric power flows in this substation. As shown in Figure 1 below, North-West bound lines which remained connected to one busbar, connect Ernestinovo to Zerjavinec (Croatia) and Pecs (Hungary), while South-East bound lines which remained connected to another busbar, connect Ernestinovo to Ugljevik (Bosnia-Herzegovina) and Sremska Mitrovica (Serbia).
Figure 1 - Decoupling of two busbars in Ernestinovo
The separation of flows in the Ernestinovo substation, lead to the shifting of electric power flows to neighbouring lines which were subsequently overloaded. At 14:04:48.9, the line Subotica – Novi Sad (Serbia) tripped due to overcurrent protection. This was followed by the further tripping of lines due to distance protection, as shown in Figure 2, below, leading eventually to separation of the systems into two parts at 14:05:08.6.
The full text of this latest IENE News Analysis can be seen here.
Figure 2 - Tripping of additional transmission network elements after the decoupling
of two busbars in Ernestinovo
[1] A busbar is an electrical junction in a substation, which connects overhead lines, cables and transformers through electrical switches. Usually, there are several busbars in a substation, which can be connected by a busbar coupler.
