Here is a little info found on power outages/substation vulnerabilities

Some Historical Stuff

1990: Con Ed Fire Knocks Out Power, Disrupting Wall St. and Subways

1997: California Blackout Is Seen as Intentional

2002: Physical Security Considerations for Electric Power Systems

2004: Electric Utility Infrastructure Vulnerabilities: pg21/26 cyber & physical

2005: Analyzing the Vulnerability of CriticalInfrastructure to Attack and Planning Defenses

a lone attacker with a high-powered rifle could gravely damage an entire electric powergrid by targeting highly reliable components at just a few key substations.

>https://www.nytimes.com/1990/08/14/nyregion/con-ed-fire-knocks-out-power-disrupting-wall-st-and-subways.html

>https://www.nytimes.com/1997/10/25/us/california-blackout-is-seen-as-intentional.html

>https://fas.org/sgp/crs/homesec/R42795.pdf

>https://www.nap.edu/read/12050/chapter/5

>https://faculty.nps.edu/gbrown/docs/DefendingCIBrownEtAlTutorialDraft.pdf

Fast Forward to recent times

2013: Military-Style’ Raid on California Power Station Spooks U.S.

>https://foreignpolicy.com/2013/12/27/military-style-raid-on-california-power-station-spooks-u-s/

2016: Substation Attack is New Evidence of Grid Vulnerability

With just a few shots from a high-powered rifle, an unknown gunman knocked out an electric power substation in rural south-central Utah last month, cutting off electricity to 13,000 customers for a day and forcing the utility to wait at least six months until the station's disabled transformer is repaired or replaced.

>https://www.eenews.net/stories/1060043920

2018: The Subtle Art of Making Substations Bulletproof

>https://www.greentechmedia.com/articles/read/the-subtle-art-of-making-substations-bulletproof

2019: Revenge of the Power Grid (NY)

>https://www.theatlantic.com/technology/archive/2019/07/manhattan-blackout-reveals-infrastructure-risk/594025/