Object-oriented methods drive protective relay system

China is a developing country, and shortages in electrical power supply exist in most provincial power systems. Stability margins are always very limited, which requires operators to run the system carefully. With each change in either the power system configuration or operating conditions, a series of actions must be taken to guarantee the safety of the power system. The actions adopted for the protective relays include arranging protective devices appropriately and setting relays at their appropriate values for all elements involved. In addition, as power systems are developing very fast in China, the number of skilled operators available is far less than required. Expert systems are urgently needed. This article describes the use of object-oriented (OO) methods to develop expert systems and, in particular, features the object-oriented expert system for the power system protective relay operation and management (OOPRES). The article covers knowledge acquisition and representation, knowledge management, and inference engine.