Case study of digital control systems for high-voltage substations

This paper describes the design, implementation, and commissioning of a complete protection and control system retrofit project at a large transmission substation. Fort Thompson Substation, located in South Dakota, has two 345/230 kV step-down transformers with two 345 kV lines and twelve 230 kV lines. Western Area Power Administration (Western) undertook a project several years ago to completely renovate all the protection and control systems at this substation. They used the automation practices that Western had developed to reduce costs of new substation construction. While it is easy to cost justify integrating and automating systems when building a new substation, it is traditionally more difficult to justify automation system upgrade schemes when doing a renovation project. However, recent innovations in the integration capabilities of microprocessor-based protective relays, and other substation IEDs, make a complete integration system upgrade, including automation, cost effective compared to selective replacement of individual IEDs, wiring, and testing. This paper describes the justification and special challenges of automating an existing substation. It also discusses the overall system design concept of the integration and automation schemes that were employed. Topics covered in the paper include: Extensive use of fiber-optic cables to replace all control wiring in the yard Extensive use of multifunctional protection devices to eliminate wiring and equipment that would be required in a traditional design Replacement of hardwired lockout relays with "soft" logic Elimination of hardwired I/O to the RTU Project management tools used to ensure completion dates and to maintain budget Challenges of designing operator interface screens Impact on the workforce in migrating to a completely automated substation Insights gained in testing and commissioning the substation.