Possible interconnection of the European Network of Transmission System Operator for Electricity (ENTSO-E) and joint power system of the former USSR (IPS/UPS) will cause the necessity to evaluate the security state of large transmission systems. One important problem for a large interconnection is the frequency control. This paper considers distinctions of frequency control in interconnected power systems during emergency situations with a deep frequency drop. To restore the system to its normal operating frequency, automatic underfrequency load shedding (UFLS) serves as a last-resort tool to prevent the system from collapse. This paper presents results of analysis of frequency behavior for different algorithms of UFLS and possible solutions of frequency control problem. The frequency behavior is analyzed for different active power deficiencies in different sides of interconnection. Due to the difference in the UFLS structure in both systems either overfrequency or low frequency situations can take place during operation of load shedding. For more reliable frequency restoration process smart uniform philosophy of the load shedding system should be preferable.