Direct load control using a programmable logic controller

This paper presents a fully automated programmable logic controller (PLC) based direct load control system. Unlike other existing systems, it gives the consumer the privilege to share in the load shedding policy. After receiving the warning alarm from the PC at the utility control center, the consumer 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 scenario decided by the utility. Having the consumer decide his own priorities 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-energization. This is done using 48 built-in timers with an accuracy of less than one cycle (10 ms). The hardware at the customer side may be integrated with a digital energy meter to form a complete energy management system.