Automatic Load Shedding Protection at A Coal-Chemical Plant

This paper reports a dynamic modeling of a coal-chemical plant and studies for automatic load shedding protection. The plant had on-site generation to support partial plant loads. In the past, disconnecting from the grid had caused frequency and voltage decay in the plant electrical system to drop out some critical loads. A complete system computer model is constructed including generator dynamics and excitation and prime mover/governor control characteristics. Transient stability simulations to various loading and generation conditions were carried out to understand and study system frequency and voltage behaviors and patterns of change under a sudden islanding case by analyzing frequency vs. time and frequency change rate vs. time curves. Further, through carefully evaluating plant load priorities as well as load dependencies, several feasible load shedding control strategies were proposed and simulated by computer modeling and study. Simulation results verified that proposed load shedding schemes can correctly predicate the frequency drop thus automatically shed non-critical and independent loads to prevent system frequency drop to exceed the allowable deviation. The solution is automatic and feasible which has been successfully implemented at the plant.