An estimated 3.8GW of medium and small scale generation automatically disconnected from the grid in Spain and Portugal during an incident on 24 July last year when parts of the synchronised European grid split briefly, according to a new report from an expert panel set up to investigate the incident. Such self-disconnections increase the effect of grid disturbances, both on the system – where they can become cascading faults – and potentially on customers at risk of blackouts and in GB a longstanding programme has been in place to try to ensure asset owners adjust their set-points to ensure assets ‘ride through’ disturbances instead.
The event – which affected some customers but caused no major damage to the system – saw the Iberian networks split from the pan-continental grid for around a half-hour before operators could stabilise the network and reconnect.
The initial cause was transmission lines in Spain that were hit by local wildfires and went out of service. But as the lines disconnected, power flows in the area changed and that caused voltage and frequency to vary beyond strict limits in large swathes of the region. Smaller plant disconnected automatically in response but the report says, “As precise and reliable voltage measurements are only available at the high voltage transmission level, it is difficult to assess the exact amount of non-conform disconnections”.
The experts recommended that network operators exchange more information about likely disconnection levels and upgrade the monitoring of distributed generation, using more digital relays or other recorders where plants connect to the network. It suggests more consistency on how automatic tripping affect generating units at all voltage levels.
With regard to the start of the event, the expert panel said it was a severe fire that broke out in South France on 24 July in the vicinity of two parallel 400kV transmission lines (Baixas–Gaudière). Network operator RTE “was not informed of the wildfire and, therefore, did not electrically isolate the affected area in a timely manner or consider the dangerous environmental conditions in its N-1 security evaluation”. This was despite the fact that the circuit is a “key corridor for the eastern interconnection between France and Spain”.
The report says, “The loss of the eastern corridor caused the western and central France–Spain interconnection corridors to become overloaded. These overloads caused the tripping of the 400kV Argia (FR)–Cantegrit (FR) line at 16:36:37 due to overload protection. This third tripping represents the point of no return that caused a loss of synchronism between the French and Spanish networks, which subsequently led to the complete loss of interconnection between the two systems.”
The expert panel says a lack of information about the wildfire did not allow its potential impact to be anticipated and it wants better communication between electricity networks and civil authorities such as fire and weather services – not just for wildfires but also icing, extreme wind, cold spells and other events that may affect the network.
It also suggested that new technologies, such as thermal cameras or satellite monitoring, could be used to detect wildfires in the vicinity of transmission corridors: “Specific attention should be paid to areas where the risk of wildfire is relevant, and has a significant impact on the power system (due to grid configuration for instance, such as corridors between electric areas).”
The expert group also recommended additional protection and monitoring of key transmission network assets.
Download the full report here

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