Direct load control using a programmable logic controller

This paper presents a fully automated programmable logic controller (PLC) b ased direct load control system. Unlike other existing systems, it gives th e consumer the privilege to share in the load shedding policy. After receiv ing the warning alarm from the PC at the utility control center, the consum er has the chance to switch off any desired load. If he does not act within a predefined period, the PLC will take the required action based on the sc enario decided by the utility. Having the consumer decide his own prioritie s release the utility company from blind decisions. This is one of the most important contributions of the proposed system. Also the load restoration process is scheduled to avoid the creation of a new peak during re-energiza tion. This is done using 48 built-in timers with an accuracy of less than o ne cycle (10 ms). The hardware at the customer side may be integrated with a digital energy meter to form a complete energy management system. (C) 199 9 Elsevier Science S.A. All rights reserved.