Reliability analysis of digital relay

Technique to quantitatively analyze the reliability of digital relay is proposed. The technique presents a methodology for mathematical modeling of digital relay. The fail-operation rate and false-operation rate are calculated based on the model. The protection availability and protection economy index are proposed and calculated using space states method. Furthermore, the variable parameter method is used to study the sensitivity in order to find the vital factors of reliability. An example is given to demonstrate the proposed techniques. The result proves that the best method to enforce relay reliability is to improve its self-checking ability.