Well, not being psychic I may well be wrong. Yes OP was possibly not serious, but did ask a question. As I said, your answer did seem to answer it up to a point, Hevans answer was interesting and informative about why someone might want to measure the output, and how they would process that data when they had it. My point was that he seemed to skip the bit about HOW you measure these things. Just changing the words used to describe the process dodges the issue. Measuring something and acquiring data about something are just different names for the same process. All I psyched about the original question (or in my words "guessed") was that he would have wanted to know how it was done. Otherwise, why ask the question?
Your answer I accept is correct, as I have no knowledge of this subject. I said "ïncrement" or up to a point, as I understood the idea of a voltage transformer (though I'm not so clear about a current transformer), but wondered what this would be like? Would they have a special transformer between the output lines, which I guess (again being psychic here) would need some serious insulation, or could they just add another secondary winding to one of the big step up (or down?) transformers that I guess (there I go again) might exist between the generator and the transmission line?
I guess (ditto) that if I really wanted to know, the answer is to go to good old WikiP and start researching power generation and distribution. In fact until I saw this question, I'd never given it a thought. What made me interested was the answer. It seemed to me that although Hevans had given a detailed and interesting description of why people measure generated power and lots of interesting other info, he had done what we all tend to do at times and completely skipped the question. It contrasted markedly with your very brief answer which actually told me something that would help me understand how to measure the voltage.
When you go to the doctor and say, "I have a sore throat?" only to be told, "ÿou have laryngitis" or say, "my knee is sore" and get told, "you have arthritis", etc, which is standard protocol with my doctor at least, you really are not being told anything, other than perhaps that the doctor does not know what is wrong, so is just trying to comfort you.
Many experts use this technique: the standard response from plumbers, builders and garage mechanics when you tell them about a fault is, "<sucks teeth> , you've got a problem!"
Edward DeBono quite seriously categorised this as first level explanation, one up on "I don't know" and a big up at that. But though it suffices for many places in everyday life, I think we need to recognise its limitations and try for more detail - as you did.
Psychic regards. Donchick.