Reconnection of electricity lines to the network by REE likely behind April 28 blackout

An internal reconnection of electricity lines to the national grid by Spanish network company REE likely caused the ‘zero point’ high voltage problems that left Portugal and Spain powerless on April 28.

This is according to a report from ENTSO-E – the European network that coordinates electricity transmission operators, including Portugal’s REN and Spain’s REE.

Various theories had been mooted for the cause of the power outage including grid fluctuations, grid infrastructure vulnerabilities, simultaneous disconnection of generators, a rapid increase in renewable energy production, induced atmospheric vibration, and even cyberattacks (the last was quickly ruled out ).

But in its latest report on the event, it seems the internal link of electricity lines provides the smoking gun to the problem.

Now, six weeks after the investigation began, ENTSO-E has revealed that even before the blackout, REE decided to reconnect lines to the grid in southern Spain, the epicenter of the blackout. These connections, according to experts interviewed by the Spanish business daily El Economista, may have caused voltage increases above the expected ranges and triggered a shutdown mechanism to protect renewable production plants from these high voltage surges.

This happened shortly before the collapse of the Iberian electrical system, which may have contributed to aggravating the voltage overload that was already affecting the networks at that time, according to Spanish news sources El Economista on Wednesday.

In Portugal, both E-Redes and REN have already submitted their final reports on the blackout to ERSE, and the conclusions presented by the operators of the electricity distribution and transmission networks are not yet known.

In Spain, the REE has asked its Portuguese counterpart REN not to reveal the information it has, according the the news source Negócios.

ENTSO-E suggests in its report that “preliminary findings indicate that, during the half hour before the blackout, two periods of oscillations (of power and frequency) were observed in the Continental Europe Synchronous Area. The first occurred between 11:03 and 11:07 (Portuguese time), being a “local oscillation, mainly affecting the Spanish and Portuguese electrical systems”.