In recent years there have been nemerous power system disturbances resulting in serious load interruptions. Although there were several causes, in many cases overload in part of the system. The ensuing power swings and frequency decay caused further loss of transmission lines and generating units, leading to a complete system shutdown. One approach to the problem of maintaining the integrity of a power system with an excess of load over available generation is the application of an automatic load shedding program. Automatic load shedding, with new static under frequency relays, can effectively restore load/generation balance, conserve a major portion of sytem load and facilitate rapid restoration of the system to normal. For this reason the load shedding programs have also been called Load conservation programs. The proper application of an automatic load conservation program should be preceded by an exrensive study of the system, considering the dynamic characteristics of the generation and load. The complexity of large systems makes it necessary to use digital computer simulation. This paper analyses the bahavior of power systems under unbalaced conditions and describes two digital computer programs suitable for the dynamic simulation of power systems, with special emphasis on the representation of automatic load conservation programs.