Transient stability enhancement is an important issue for all large power systems in the world, especially in case of widespread blackouts. In order to increase the transient stability level, various technical devices and methods are developed in electrical power systems, such as the wide area control system (WACS). We have proposed a method for assessing the transient stability level on the basis of calculating the equal acceleration/deceleration areas, similarly to D-decomposition in small-signal stability analysis, and used it for finding the optimal settings of excitation (AVR+PSS) and governing control (AGC) with additional signals from wide area measurement system (WAMS) in a 330 kV Kola-Karelian Intertie test model.