Life cycle experiences with micro-processor based relays and roadmap to sustainability

Microprocessor based protective relays have been widely used to provide many benefits including system performance, monitoring, technology and compliance. Recently utilities have started to replace earlier generation of microprocessor-based protective devices with modern protection and control Intelligent Electronic Devices (IEDs). The upgrade is partially due to increased failure rates of the earlier generation of devices, as well as to benefit from the new functionalities including system integration, Synchrophasor applications, IEC61850 communication and cyber security. The process to upgrade numerical relays is quite different and is more complex than upgrading of traditional electromechanical or solid-state relays with a functionally equivalent device. In addition to the hardware replacement, functions related to cyber security, protection, automation and control, event recording and digital communications must be considered. The protection and control system practitioners need to manage the asset and set the strategies, with inputs from other stakeholders across lines of business as well as externally with manufacturers, regulators, consultants or even neighboring utilities because the selection and application criteria have expanded with the introduction of new features and functions. This paper discusses the existing asset management, performance, replacement, and technology considerations based on utility practices at the T&D level. Strategies and practical concerns including hardware and firmware compatibility, protection settings, or other features such as automation or other possible functions integrated and associated set point considerations, as well as commissioning and testing when upgrading or replacing a microprocessor device are described in detail. This paper will assist utility or industry electrical engineers that have an on-going relay upgrade project or are planning to upgrade their aging microprocessor relays in lessons learned from some major power companies in North America.