range of transmission line?
The velocity of Electro Magnetic waves in a Transmission Line is slightly less than the velocity of light --i.e. 300,000 Km.For a 60Hz system ,one wavelength will be 5000 Km.A quarter wavelength will be 1250 Km.A Transmission Line of this length will behave like a Quarter wave Antenna and radiate a lot of power to space by  radiation .  For transmitting Power over 800 Km ,High Voltage Dc Transmission (HVDC) is therefore preferred.  However , if an AC line needs to be connected in parallel to an HVDC Line , then Flexible AC Transmission System (FACTS) is used. You can get some more details from the internet by searcching for HVDC Transmssion and Facts Transmission.  Also you may look into the brochures of Power Companies like ABB,SIEMENS, GE etc.