If it's terrorism, they're going to want to have an effect that is large. That is the nature of terrorism. Small events that are insignificant are not the goal of terrorism.
If a person wanted to cause harm and damage the electrical infrastructure. They would have spent time planning and figuring out how to cause the most damage, with the least detection, with having the most PR and effect. Shooting a bunch of neighborhood transformers isn't the way. In their research they would have found so many other high-reward low-risk targets.
OR this was a "vulnerability scanning", and not the actual attack. Perhaps they were a group of friends that wanted to shoot and see if sparks will fly (literally), like we see in the movies.
OR assuming it is a group of sleepers/terrorists doing a pen-test (not the actual penetration/assault). They now (back then) answered the following critical questions: How long does it take to incapacitate such an installation? Will readily available guns do to work? How many people/guns/bullets do we need to pull this through? What monetary value damage can we do? Who/where is the back of this place? What do we need to shoot in there to make more damage (time, money, both)?
So know "they" know that smaller boxes were replaced in a few minutes and larger boxes cost more and take 6 months (so large boxes it is!!!)
Exactly like a vulnerability scanning/penetration test. "They" now so much more on the target, it's vulnerability, it's protection, how to disable.
This said, they know that taking down one of these things is but a scratch. How about 3? 5? 10? Can a group of 50, broken down in teams.of 4, with 1 rifle and 20 bullets each, take down a station like that and be our of there in 5 minutes?
These are questions that anyone with security, military, project background will be asking (and I am not CIA, KGB, etc)(so imagine how these 'departments'(?)) must have thought of it further...
Unless.. this post was all about trying to identify criminal minds.. in which case.. guys.. I am in the good side on this!! The good hat!! (no more white-black hats)
If a person wanted to cause harm and damage the electrical infrastructure. They would have spent time planning and figuring out how to cause the most damage, with the least detection, with having the most PR and effect. Shooting a bunch of neighborhood transformers isn't the way. In their research they would have found so many other high-reward low-risk targets.