Digital protective relaying algorithms and systems — An overview

Abstract This paper gives an overview of the digital algorithms and systems for protective relaying. First, digital relaying algorithms are discussed. Classification and categorization of the proposed algorithms are given. The major classes are: transmission line protection, transformer protection, bus protection, and generator protection. The categories correspond to the different schemes used for the signal processing. The discussion of algorithms is concluded by giving some basic results related to the comparison and selection of the algorithms. A particular methodology is proposed if one is to investigate and compare digital algorithms using more elaborate quantitative techniques. The second major topic discussed is related to the digital implementations of the protective relays. Major philosophies used in designing digital relaying systems are outlined. These philosophies include the following design approaches: a centralized relaying system using a minicomputer; a decentralized relaying system where each protection function is implemented using a separate microprocessor; an integrated relaying system where a number of dedicated microprocessors are connected together in a protection system; an integrated substation control and protection system. Finally, expected trends in the areas of algorithm developments and system implementations are indicated.