[krona]

The proximal cause of the blackout was a single faulty solar inverter in a PV plant. The distal cause, however, was inappropriate disconnection of wind/solar generation and widespread cascading failure of reactive power support across the grid. Add to that a whole bunch of noncompliant transformers which tripped inappropriately, and Spanish grid operators inability to react appropriately.

[merb]

It looks like you know way more than the entso report. Which mostly blamed it on governance. Mostly because a small change in a complex system can lead to cascading failures. They also included data to prevent it in the future. And yes solar and wind power makes these failures more complex but they are certainly not to blame. (Just read the article…)

[cyberax]

The reason is that classical grids are mostly self-correcting. Rotating inertia can stabilize frequency and can produce or absorb reactive power.

"Reactive power" sounds fancy, but it just means that motors can create a drag. The power lines are giant capacitors, and capacitors have the lowest effective resistance when they are discharged. So the current is greatest when the voltage crosses the zero mark. Inductive (rotating) loads are the opposite, their effective resistance is greatest when the current starts to rise or fall. So this limits the initial inrush of the current.

But there's more! When you have a transformer and a long line, you can essentially get a boost converter. The voltage from a transformer travels through a low-resistance wire until it reaches the end, and because the line can be modeled as a series of capacitors, you essentially get a "charge pump" ( https://en.wikipedia.org/wiki/Charge_pump ). From the viewpoint of the generator you have one large capacitor, but from the viewpoint of a consumer in the middle of the line, you have two capacitors in series.

As a result, the voltage in power lines can _spike_ if there's not enough rotating load. This is called Ferranti effect, and in Spain it was the primary reason for the faults.

This is all fixable, but it requires investment and regulation. And Spain (and other countries) have been neglecting that, by incentivizing the cheapest possible generation.

[krona]

I already said REE (the operator) was partly to blame, but they were reacting to something their grid was ill equipped to deal with.

Perhaps you should understand the difference between distal and proximal causes of events? Both are important. Voltage oscillation was the proximal cause. Where did this come from? It's explained in the operators own report:

> During the incident analysis, it was determined that the oscillation was not natural to the system but rather forced. This oscillation is observed with significant amplitude at a Photovoltaic Plant located in province of Badajoz (PV Plant A). At the time of the oscillations, the plant was generating approximately 250 MW. Since the oscillation was forced, it ceased once the plant stabilizes it.