what is the difference between Grid and Sub-station?
I think you need to read this:
I should not ask any question in this forum???
You are very welcome to ask questions, but only questions that are not schoolwork or homework.
If you have questions like that, you can ask them in the homework section, but only after you have made a reasonable effort to find the answer yourself.
You should take any electrical homework questions to this place:
Separate names with a comma.