Automatic Load-Shedding Protection at a Coal-Chemical Plant: Examining and Designing Effective Low-Frequency Backup Protection Methods

Abstract

This article examines and studies a coal-chemical plant through a dynamic computer model as well as designs an automatic load-shedding protection. The plant has on-site generation to support partial plant loads. In the past, disconnecting from the utility grid had caused frequency and voltage decays in the plant electrical system to dropout critical loads. A complete system computer model is constructed, including generator dynamics, excitation/automatic voltage regulators (AVRs), and prime mover/governor control characteristics. Transient stability simulations of 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. This was accomplished by analyzing frequency versus time and rate of change of frequency versus time curves. Further, through carefully evaluating plant load priorities as well as load dependencies, a feasible load-shedding control scheme with backup strategies was configured and simulated by computer modeling and study. Simulation results verified that the proposed loadshedding scheme can correctly respond to frequency drop and automatically initiate the shedding of noncritical and independent loads to prevent further system frequency drop, thereby exceeding the allowable deviation. The suggested solution is automatic and feasible and has been successfully implemented at the plant.