Buddy out in Arizona has put together a series of videos explaining transformer theory in easy to digest way. He’s got you covered in most everything you will need to keep your crew off your ass. His library grows monthly. He teaches/explains open banks, vectoring and how to apply it, ferro-resonance in easy to follow way.
His YouTube channel is Hiline Academy (https://youtube.com/channel/UCKZy5BYtGX70HBAcrI0h5Dw)
Cody is a solid lineman and excellent teacher. Give his channel a look.