Then versus now: A comparison of total scheme complexity

Today\´s protection engineer is not at a loss for things to do. New and retrofit projects along with added system requirements have increased the workload for designing, setting, installing, and maintaining protection systems. It is not uncommon for engineers to look back at the "good old days" with nostalgia. This paper performs a component-by-component and line-by-line comparison of protection schemes from the electromechanical, microprocessor, and distributed microprocessor architectures. For a complete line protection system, the comparison includes the protective relays, auxiliary logic, settings, firmware reliability, wiring, and testing (both periodic and scheme). Recognizing that engineers want only the best, yet practically attainable protection system, this paper includes measurements and calculations of reliability to bring a scheme online. Fault tree analysis techniques are used to bring numerical values to scheme comparisons. Finally, observations regarding functional requirements of old and modern systems allow engineers and management to evaluate the technological effectiveness of overall control systems.