Design of protective scheme for tie line tripping of an industrial power system

This paper presents the design of tie line tripping and load shedding for a large customer system with multiple cogeneration units. The mathematical models with the corresponding parameters of cogenerators, governors, exciters and the equivalent generation unit to represent the external utility power system have been identified. The critical clearing time has been solved by performing the transient stability analysis for the tie line tripping of the industrial power system under various contingencies of the utility network. To enhance the system stability, the protective scheme by including the directional over current relay, under voltage relay and under frequency relay with proper settings has been applied. By this manner, the industrial power system is able to be isolated from the utility system in time to prevent the collapse of the industrial power system and the cogeneration units. To restore the system frequency to the normal operation condition, the load shedding is considered by both frequency deviation and frequency change rate for each load shedding step. The computer simulation of the industrial power system has verified the effectiveness of the proposed protective strategy