LAN-Based Control for Load Shedding Bin Qiu,Yilu Liu,Eng Kiat Chan,Lawrence L.J.Cao oad shedding takes place as an emergency measure used for generation units to avoid malfunction due to in cases of falling frequency conditions or loss of surges.This time delay may result in fast frequency drop power generation.Particularly in isolated (island) under severe overload conditions and cause under-fre- systems,due to lower inertia and limited reserves,the quency relay tripping in the generation unit.The load- rate of frequency decay due to loss of generation can be shedding strategy may,therefore,fail.Modern SCADA more pronounced.Therefore,a more carefully designed systems are designed as open and distributed systems. load-shedding scheme is required in an island system Industry-standard hardware and software,configured in than in a large interconnected system. local area networks (LAN),have become the basic sys- To restore the system operating frequency after seri- tem building blocks in SCADA systems.The intense com- ous disturbances,one of the main protection strategies petition among different SCADA vendors requires the is the under-frequency load-shedding scheme.It is sim- distributed computer systems to be low-cost,fast- ple and inexpensive;however,sometimes it has poor response,and high reliability.Low cost demands the use performance in coordination due to tedious steps and is of simple,standardized,open systems and easy installa- apt to result in over or under shedding.In addition, tion,configuration,and extension.Real-time is character- under-frequency relays with time delay are generally ized by high bandwidth,low latency,fast,and continuous update of the system status.Achievement of B.Oiu and Y.Liu are with Virginia Polytechnic Institute and State Uni- reliability is by means of structural redundancy and a versity,Blacksburg.Virginia,USA.E.K.Chan is with Power Automation fault-tolerant computer control system. Pte.Ltd.,Singapore.LL.J.Cao is with Foxboro Australia Pty.Ltd., Advances in network and communication technolo- Alexandria,NSW,Australia. gies open the door for fast load-shedding controller 38 IEEE Computer Applications in Power ISSN0895-0156/01/10.00©2001IEEE38 IEEE Computer Applications in Power ISSN 0895-0156/01/$10.00©2001 IEEE L oad shedding takes place as an emergency measure in cases of falling frequency conditions or loss of power generation. Particularly in isolated (island) systems, due to lower inertia and limited reserves, the rate of frequency decay due to loss of generation can be more pronounced. Therefore, a more carefully designed load-shedding scheme is required in an island system than in a large interconnected system. To restore the system operating frequency after seri￾ous disturbances, one of the main protection strategies is the under-frequency load-shedding scheme. It is sim￾ple 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-fre￾quency 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 sys￾tem building blocks in SCADA systems. The intense com￾petition 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 installa￾tion, configuration, and extension. Real-time is character￾ized 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 technolo￾gies open the door for fast load-shedding controller Bin Qiu, Yilu Liu, Eng Kiat Chan, Lawrence L.J. Cao B. Qiu and Y. Liu are with Virginia Polytechnic Institute and State Uni￾versity, Blacksburg, Virginia, USA. E.K. Chan is with Power Automation Pte. Ltd., Singapore. L.L.J. Cao is with Foxboro Australia Pty. Ltd., Alexandria, NSW, Australia. ©2000 Image 100 Ltd