Nowadays modern overhead transmission lines (OHL) constructions having several significant differences from conventional ones are being used in power grids more and more widely. Implementation of compact overhead lines equipped with FACTS devices, including phase angle regulator settings (compact controlled OHL), appears to be one of the most effective ways of power grid development. Compact controlled AC HV OHL represent a new generation of power transmission lines embodying recent advanced achievements in design solutions, including towers and insulation, together with interconnection schemes and control systems. The main features of compact controlled OHL are as follows [1, 2]: - phase-to-phase distances (both on towers and within the spans) are extremely reduced to minimal required values subject to regulatory restrictions on the dielectric strength of “phase to phase” gaps, taking into account the maximum operating voltages and switching and lightning overvoltages; - split phases have an optimal design subject to existing maximum conductor surface electric field strength requirements adopted for corona discharge elimination; - tower phases are so configured as to have the grounded tower parts (poles, crossarms, suspension components) placed outside the space between approached phases; - if necessary, insulating elements (insulating spacers or ties) are installed in spans between approached phases of OHL to maintain the selected distance between phases and damp conductor’s vibrations or galloping under severe weather conditions, thus ensures a high level of mechanical stability and operating reliability for approached phases in spans; - angular shifts are created between voltage vectors applied to approached phases of compact controlled lines: in the case of three-phase single-circuit compact OHL, an angle of 120 electrical degrees between three approached phases of OHL and, in the case of double-circuit compact controlled self-compensating overhead lines (CSOHL) between approached phases of different circuits, an angle controlled within 0–120 (0-180) electrical degrees or fixed at 120 or 180 electrical degrees, while maintaining an angle of 120 electrical degrees between voltage vectors of each single circuit; - high-speed phase control and adjustable compensation systems are used (such as FACTS devices); - special algorithms are used for controlling the OHL mode parameters in accordance with the preset requirements and adaptable to changing conditions in the normal and emergency operation modes; The above mentioned technical solutions can be used together or separately. Compared to conventional OHL, compact-design OHL equipped with FACTS devices provide the following: – 1.2-1.6-fold increase in OHL capacity without raising their voltage class; – 1.5–2-fold reduction in the area of land allocated for OHL with equal capacity; – electromagnetic field reduction in the external space thus environment and people impact decrease; – 15–30% decrease of total costs per power transfer unit; – provide power flow value and direction control in power systems; – operating efficiency of reactive power control improvement; – total energy losses reduce in the power system; – increase OHL mechanical strength under severe weather conditions Compact controlled OHL can be used as intersystem and intrasystem high-voltage connections and for power distribution, ensuring that issues of power transmission and distribution are addressed at a qualitatively new level. Results of comprehensive research and development in relation to 110–500 kV compact controlled power transmission lines together with theoretical basis, substantiation, and methodological approaches to their practical application are given in the present paper.