Nowadays power system control and management are associated with different kinds of problems, i. e. complexity of existing structures, existence of different management approaches, differences in standards and so on. Protective relaying and emergency automatics is one of the most effective tools of reducing blackouts risks in power systems. For that reason, out-of-step protection was created, which allows to carry out optimal power system division into parts to maintain their operability and functionality. Out-of-step regime is one of the most dangerous regimes. This regime is usually associated with loss of stability between power plants (power systems parts) or separate generators, which may cause damage to power systems elements and long lasting interruptions of customers’ power supply. Generally out-of-step regime causes huge economic losses. In order to reduce the impact and the consequences of such regimes, it is necessary to use advanced out-of-step protection operating principles. In researches main attention was paid to selectivity and modelling accuracy. The key achievements are reflected in the national patents and scientific articles, as well as international editions, for instance, Springer publishing house book „Monitoring, Control and Protection of Interconnected Power Systems” (2014). New out-of-step automatics operating principles are verified using the model of Latvia power system, which was carried out using modern software ETAP 12.5. During modelling blackouts of power system certain data were obtained, which demonstrates absolute operability and functionality of new out-of-step protection. Also settings selection and verification algorithm of power systems protective relaying and emergency automatics is proposed. As a special research direction, new out-of-step protection operation analysis in different regimes of power system is observed for proving proposed blocking and operating algorithms adequacy and functionality.