STATISTICAL DECISION THEORETIC APPROACH TO DIGITAL RELAYING.

A digital relay is understood in this paper as an equipment that contains a microcomputer or microprocessor to detect a fault condition in a transmission line, power transformer, busbar, and other electrical apparatus. Digital relaying is logicaly decomposed into three successive processes - sensing, evaluating, and discriminating. The first process transforms the system voltage and current into digital form. The middle process produces the criterion value through a specific measuring algorithm. The last process discriminates a faulted condition based on the criterion value. One of the important strengths of digital systems over analog is the ability of making decisions in the final process, which so far has been neglected in the relaying field. With the probabilistic natures in the fault condition in mind, this paper presents an approach toward this direction through statistical decision theory, and also presents a method of determining the sampling rates for the digital relays.