Intelligent protection coordination system

Abstract

System disturbance may cause system instability. In order to prevent the system to fall into the unstable region, die protection system is employed to detect and isolate system disturbance. Fast and correct protection operations will resume supply swiftly in order to improve me supply reliability and availability. It is sometimes reported that protection mal-operation or mis-coordination may cause system black-out. A power network consists up to thousands of power apparatuses and requires enormous protection relays to protect the system. Various protection relays with different operating principles are employed to tackle different types of faults. Very often two or more relays with different operating principles, depending on the voltage level and importance, may be required to operate to protect the equipment. Each protection relay in the power system needs to be coordinated with the relays protecting the adjacent equipment. The overall protection coordination is thus very complicated. Unfortunately in a practical power network, it is almost impossible to obtain a set of protection settings that can satisfy the coordination between all adjacent relays. This thesis proposes a novel method called "Time Coordination Method" to coordinate all protection relay settings. The protection system is modeled as an objective function and a set of constraint equations that can be optimized by artificial intelligent optimization methods. It is also proved that the Time Coordination Method can handle the protection coordination during the dynamic fault current changing condition. This cannot be achieved by other conventional approaches. Through the use of time coordination method, the optimized protection system can also improve the supply reliability. The reliability algorithm is developed. The supply reliability indices are calculated by simulating all busbar faults, stuck breakers and protection failures. The faulty component will be isolated by a sequence of relay operations. As different fault location will result in different relay operations, the step-by-step simulation method is developed to evaluate die sequence of relay operations. The efficiency of the Time Coordination Method is discussed. The key factor to improve the efficiency in order to put in future practical use is also explored.