“I live in the Texas and want to know what size easement is required for an electrical line that connects a substation to a substation. The line voltage is 69,000 or 138,000 . Is the size of the easement determined by the city or who?”

I have no idea what the specific answer to your question is. However, if I were looking for the answer, the first place I would call would be the electric company. If they don’t determine the size of the easement, they should know who does.