what is isolator , feeder and what is the purpose of a transformer?
Are you talking about power transmission line?
If so an isolator is also know as a insulator.
Feeders are the smaller electrical lines feeding or leading out of the main power bus.
A transformer reduces the voltage from the higher levels used in the transmission lines to the levels where it can be used.
For more information on the electrical grid and its components go to the Wikipedia link below.
Niel Leon
engineering.com