Reliability considerations of multifunction protection

In this paper, the authors identify many of the application and maintenance questions that may have an impact on perceived versus actual reliability, such as the following. (1) Does the application of a single multifunction system for primary and backup protection of a given zone create potential reliability problems? What engineering, operating, and economic factors must be considered?; (2) Should the same manufacturer or different manufacturers be used when independent multifunction systems are applied for primary and backup protection? What engineering, operating, training, and economic factors must be considered?; (3) Is the overall reliability of numeric protection systems more likely to be influenced by hardware or software related issues? What factors should be considered before upgrading existing hardware and software?; (4) What type of maintenance is actually being performed on multifunction systems? What factors should be considered before changing established maintenance guidelines? The challenge of today's protection engineer is to make sure that protection reliability is maintained at or above the technologies being replaced. Understanding the application issues and potential problem areas is critical to that success. This paper provides insight and guidance toward that end.