You are seriously understimating how easy it is to burn an electrical substation. It is actually a frequent occurrence in France (as seen on TV these days..) and everywhere else. Almost as frequent as copper thefts. Close to where I live they famously left a silicon foundry powerless for a day (with the consequent astronomical bill to restart it) by setting fire to one specific bridge.

The only novel thing here is coordination, but it doesn't seem like a huge stretch of the imagination to target the 4th most frequent high speed rail crossroads, which is exactly what they did.