The theoretical ground and design realization of alternating current power lines of the new type - Controllable Flexible A.C. Transmission Systems (CFACTS) are considered. Earlier lines of such type had been known as Controlled Self - Compensating High Voltage Transmission Power Lines (CSHVL), as well as Controlled Compact Transmission Power Lines. The CFACTS design principles and the basic CFACTS design directions are presented. The design version, connection diagram and control methods are described. The basic characteristics of CFACTS (10, 35, 110 kV) which already built and maintained long as well as CFACTS (220-1150kV) parameters , obtained on the basic of the design are given. It to shown that the basic characteristics of CFACTS are better than those for the usual power lines. CFACTS provide natural power of the line increase by 20 to 50 per cent, 2-3 times larger total power flow density in a line crosssection, parameters and power flow controllability, ecological effect decrease, economy of capital expenses by 10 to 30 per cent and adduced ones expenditure by 10 to 20 per cent per transmitted power unit.