The Iberian blackout demonstrated the importance of voltage control and reactive power, and how a weak grid, with poor controls, was brought down by a single faulty solar inverter. In this second part of my analysis of the Iberian blackout, I examine the specific technical causes of the incident. Where technical concepts such as frequency, voltage, and oscillation dynamics are not explained here, they are covered in Part 1, which outlines the physical principles and control challenges in modern grids.

This blog is based on a concise but informative report produced by Red Eléctrica de España (“REE”), the Spanish Transmission System Operator (“TSO”), which is more accessible than the much longer government report (available only in Spanish – rough English translation here).

The key messages from the REE report are:

The Iberian blackout demonstrated the importance of voltage control and reactive power, and how a weak grid, with poor controls, was brought down by a single faulty solar inverter. In this second part of my analysis of the Iberian blackout, I examine the specific technical causes of the incident. Where technical concepts such as frequency, voltage, and oscillation dynamics are not explained here, they are covered in Part 1, which outlines the physical principles and control challenges in modern grids.
This blog is based on a concise but informative report produced by Red Eléctrica de España (“REE”), the Spanish Transmission System Operator (“TSO”), which is more accessible than the much longer government report (available only in Spanish – rough English translation here).

The key messages from the REE report are:

 The blackout was triggered by a PV inverter–induced voltage oscillation
 Inappropriate disconnections of wind and solar generation, and widespread failure of reactive power support, escalated the disturbance
 REE relied on static controls and failed to deploy dynamic response assets
 Grid code non-compliance was widespread among renewables, conventional generators, and even REE itself (via non-compliant transformers)
 The collapse exposes systemic risks in low-inertia grids with high levels of inverter-based resources (“IBRs”) and inadequate voltage control

It is notable that, despite confident denials from some renewables advocates in the immediate aftermath, it was in fact a malfunctioning solar installation that triggered the voltage oscillation initiating the collapse. Wind and solar generators failed to meet fault ride-through obligations, and both inverter-based and conventional generators failed to provide the required reactive power support. Crucially, conventional generators did not trip prematurely – they remained online until system conditions breached their design tolerances...

...1. Forced oscillation at 0.6 Hz, possibly originating in a photovoltaic power plant in the province of Badajoz, triggers system-altering protocolized actions. Shunt reactors are operated, lines are coupled due to oscillations, and schedules are modified. (N-1)
2. Natural oscillation at 0.2 Hz triggers further system-altering protocolised actions. Shunt reactors are operated, lines are coupled due to oscillations, and schedules are adjusted. (N-2)
3. Generation under P.O. 7.4 does not absorb the required reactive power. (N-3)
4. Variations in RCW generation during active power regulation affect voltage control and many of them don´t fulfil their obligations. (N-4)
5. The conventional generation requested after the oscillations was not connected
6. Generation loss in distribution: P < 1 MW and self-consumption of 435 MW before 12:32:57 (N-5)
7. Inappropriate tripping of a generation transformer in Granada (N-6)
8. Inappropriate tripping of solar thermal generation (Badajoz) and tripping of photovoltaic (Badajoz) without point-of-interconnection data from transmission network (N-7)
9. Inappropriate tripping of a photovoltaic power plant connected also in the province of Badajoz but in a different transmission substation (N-8)
10. Tripping of three wind farms (Segovia) without point-of-interconnection data from transmission network
11. Tripping of one wind farm and a PV plant located at the province of Huelva, without point-of-interconnection data from transmission network
12. Inappropriate tripping of photovoltaic power plant in Seville (N-9)...