The existing methods of isolating the TPP auxiliaries in the event of an emergency frequency and/or voltage transient in the grid are discussed. Requirements to the actions of the underfrequency islanding system in such situations are formulated. Based on the studies conducted by the JSC "Firm ORGRES" at a number of power plants, engineering solutions for the automatic separation of TPP auxiliaries are proposed. Emergencies in electric power systems because of short- age of active andor reactive power may cause shutdown of generation equipment and, as a consequence, disconnection of power plants from the grid. Emergency situations in the power system actuate the emergency control system (ECS) intended to restore the normal conditions. If the imbalance between generation and consumption in the power system is beyond the capabilities of the ECS and the auxiliary busbar frequency or voltage is close to the level at which the opera- tion of the essential equipment is impossible, the power plant should be disconnected from the grid automatically or manu- ally. The reactive power shortage accident in the Mosenergo system in May, 2005 caused stator and rotor overcurrent at and disconnection of 28 turbine-generator sets at the Mos- cow Cogeneration Plants. The cogeneration plants (CGPs) were shut down with loss of auxiliary power (1). In such a situation, heat-and-power equipment is tripped, while the control systems are energized from the direct-cur- rent board. Power is supplied only to the information sub- system of the automated plant control system and to some mechanisms (liquidgas fuel cut-off valves, relief valves in the boiler and steam pipelines, emergency lubrication pumps of the turbine, and oil-hydrogen pressure difference pumps of the generator). The other mechanisms (pumps, smoke exhausters, ventilating fans) are deenergized. Hundreds of valves and controls are in an uncertain position. Such trips are often accompanied by faults of equipment, especially large mechanisms with rotating components (tur- bines, generators, feed pumps, etc.). Before the restart, it is technologically necessary to carefully analyze the post-shut- down condition of all components of the equipment. In some cases, it may be needed to disassemble bearings of turbines and generators, large pumps, to drain and purge vessels and steam pipelines, and to do other check-ups to reveal adverse aftereffects of the emergency shutdown without power sup- ply to auxiliaries. Thus, even in best-case scenarios, start-up of the power plant after shutdown with loss of auxiliary power and connection to the grid are possible only in a long period of time. The power back-up at the majority of TPPs is provided by the power system. Therefore, in the event of blackout, the auxiliary power supply system becomes a weak point, and emergency power sources (EPSs) should be used to perform the following functions: — safe shutdown of TPP equipment;