LAN-based control for load shedding

To restore the system operating frequency after serious disturbances, one of the main protection strategies is the under-frequency load-shedding scheme. It is simple and inexpensive; however, sometimes it has poor performance in coordination due to tedious steps and is apt to result in over or under shedding. In addition, under-frequency relays with time delay are generally used for generation units to avoid malfunction due to surges. This time delay may result in fast frequency drop under severe overload conditions and cause under-frequency relay tripping in the generation unit. The load-shedding strategy may, therefore, fail. Modern SCADA systems are designed as open and distributed systems. Industry-standard hardware and software, configured in local area networks (LAN), have become the basic system building blocks in SCADA systems. The intense competition among different SCADA vendors requires the distributed computer systems to be low-cost, fast-response, and high reliability. Low cost demands the use of simple, standardized, open systems and easy installation, configuration, and extension. Real-time is characterized by high bandwidth, low latency, fast, and continuous update of the system status. Achievement of reliability is by means of structural redundancy and a fault-tolerant computer control system. Advances in network and communication technologies open the door for fast load-shedding controller (LSC) designs with low cost, convenience, scalability, and remote access capability. This article describes a LAN-based LSC that makes use of these technologies for the isolated power system.