This paper describes a new transient stability control system named the TSC system developed for application to the trunk power system of Chubu Electric Power Co. (CEPCO). The TSC system prevents wide-area power system blackout by shedding optimal generators when a serious fault occurs. This system has the following features: (1) the TSC system performs detailed stability calculations based on online information telemetered from the actual network, and it periodically evaluates the stability of the power system against contingencies with a high degree of accuracy. The system selects the optimum generators to be shed; (2) if a contingency actually occurs, the generators to be shed that were determined in advance are shed about 150 ms after fault occurrence to maintain the stability of the power system; and (3) the system can be applied to any power system configuration of CEPCO, such as a loop network, radial network, etc. The TSC system will be put into regular service in June 1995. It will be the world's first real-time stability control system that performs detailed transient stability calculations on a large power system online.