Fast valving scheme using parallel valves for transient stability improvement

A new fast valving scheme of steam turbines using two parallel valves for improving the transient stability of a power system is proposed. The influence of the actuation time parameters of a conventional fast valving scheme using a single valve is first studied in detail to justify the need for a parallel valve scheme. A systematic procedure for selecting suitable valve actuation times, the sequence and the conditions to be monitored for implementing a coordinated parallel valve actuation scheme is presented. The proposed scheme is applied to a typical nuclear power plant connected to an infinite busbar system. A four stroke valve operation mode of the scheme is found to improve the second and subsequent swing stability significantly. A multiple stroke operation mode of the scheme for improving the rotor angle damping over a longer period of transient is also presented