Keywords: computer relays, fault tree analysis, FTA, Markov models, reliability estimation, safety critical systems, software reliability, transmission line protection, digital signal processing, DSP, reliability estimation
Software reliability estimation of computer relaying for transmission line protection using user-oriented software reliability model
Advancement in signal processing techniques and VLSI technology has rapidly substituted conventional electromechanical relays with novel alternatives like digital relays, also termed as computer relays in power system parlance. A computer relay is considered as a digital signal processor which continuously processes the values of line currents and voltages. Hence, the heart of the computer relay is the algorithm that implements the relaying scheme. Therefore, any computer relay software, before implementation in the real-time power system, has to be thoroughly tested for performance under various conditions. This paper presents a reliability estimation method of computer relay software based on modular structure of its components and the overall reliability requirement of its modules that involves the probabilistic inter-modular transitions to be formulated from the program flow based on a Markov model. The case study in this paper validates the efficacy of the proposed software reliability estimation for computer relaying of transmission line protection.