Abstract
A digital relay can be conceived as a digital signal processor in which the values of line currents and voltages are continuously monitored and processed. Hence, the heart of the digital relay is the software used for implementing the relaying algorithms in an efficient way. Assessment of software reliability is an area of utmost importance for such software-based systems for safety-critical applications such as digital relaying of power transmission lines. But software testing of safety-critical systems is particularly challenging because of the availability of meager failure data. Therefore, this article presents a methodology for estimating software reliability of digital relaying using statistics of extremes. The unique advantages of using such a methodology are the independence of the evaluation of the test sampling order, the amount of available data, and a priori knowledge about the underlying distribution of any parameter. The case studies demonstrate the efficacy of proposed methodology for evaluating the software reliability for digital relaying of transmission lines.