Abstract-Reliability of the power system depends on coordination and coherence of continuous processes of production, transmission, distribution and consumption of electric energy. It is offered to consider a power supply system of Russia as a four-level hierarchical system due to the terms of uninterrupted operation of power supplies. For each hierarchical level, there is a system of indexes, reflecting the role of the backbone, transmission and distribution networks. The authors offer to calculate reliability indexes of power supply -regional's group supply points, district centers of supply, local supply points and end-consumers. Indexes cover structural, object and regime parameters of an electrical network. This approach makes it possible to determine bottlenecks, to select and to justify the ways and means of improving the power system reliability without reducing their efficiency.Keywords-reliability; system; index; indicator; power supply I. SITUATION ANALYSIS AND PROBLEM DEFINITIONIt is known that a combination of reliability and profitability forms efficiency of a power supply system. Therefore, the efficiency index, reflecting usefulness of a power system, can be determined by the known function of Cobb -Douglas: The index of profitability I e raises in case of the reduction of costs of production, transmission and distribution of electricity, and the index of reliability I r increases with the reduction of depth, frequency and duration of switch-offs and the imposed restrictions for a power consumption. The ratio of n and m reflects the value of each of two properties. Their choice defines priorities of development of power supply systems. For example, for Soviet period, m≫n ratio was characteristic, and the searching of the way to change the situation was the purpose of the market reform, undertaken in power industry.Obviously, increasing I r , which demands certain expenses, leads at the same time to reducing I e . However, in Russia a decrease of both profitability and reliability of power supply is observed. Currently, a constant growth of electricity costs takes place and, regarding the reliability; annually over 24 thousand failures occur on power generation facilities, 700 of them are considered as serious, and more than 50 -have severe consequences [1].In market relations, in countries with economic competition of power industry subjects, the level of power supply reliability is strictly watched. It allows deriving system effect, which means a profitability increase without a reliability decrease. Interconnection of separate regional power systems into the United Power System (UPS) is the most common way to gain the system effect. To provide system interconnection in Europe and the USA, trunk lines on a direct current are widely used, while in Russia it was carried out in extra high voltage AC lines.