The situation of synchronous operation of the Baltic power systems in case of disconnection from the BRELL association (Belarus, Russia, Estonia, Latvia, Lithuania) and the transition to parallel operation with the power systems of continental Europe (ENTSO-E association) is considered. Based on the proposed equivalent scheme of the Baltic power system model, computer modeling of 75 possible modes of their operation was carried out both in emergency situations and under the influence of other factors. These factors may be: an excessive share of unpredictable distributed generation from renewable energy sources (RES) in power systems, the introduction of new electricity generation technologies based on the use of RES, the complication of power supply network schemes, an increase in the length of power lines, the introduction of consumer-side management, etc. The general model of the ENTSO-E synchronously operating extended power connection network allows TSO operators to monitor each possible state of the electric power system (EPS) for the admissibility of the electrical regime in their area of responsibility. The simulation results allow us to assess the reliability of the EPS operation taking into account all network limitations and, first of all, the capacity of Baltic States' intersystem connections with continental Europe.