34.5kV Line Terminal and Pilot Wire Relay Replacement

When a distribution utility in New York faced challenges with their existing pilot wire protection scheme, Tangibl was brought in to provide innovative solutions. This case study highlights our approach to a critical pilot wire relay replacement project, aimed at improving the reliability of a backup power supply for a hospital, a vital customer in the region. The existing system’s limitations were causing significant reliability issues that required prompt and effective resolution.

The project focused on a 34.5kV two-ended line, which included a crucial tap that provided backup power to a hospital. Unfortunately, the intermittent unavailability of associated telephone pairs resulted in frequent line tripping, severely affecting the reliability of the backup power supply. This was a critical concern as the hospital relied on continuous power for essential services. To address these issues, Tangibl recommended a more reliable and advanced solution to replace the outdated pilot wire protection scheme.

We implemented a modern solution based on microprocessor distance relaying combined with a POTT (Permissive Overreach Transfer Trip) scheme using audio tone. This new approach completely eliminated the need for DC telephone pairs, thus ensuring a more stable and consistent protection system. The replacement involved updating the existing electromechanical relays with advanced SEL 311 relays and RFL 9745 for audio tone communication, providing a more reliable and efficient solution. Additionally, the station with metal-clad construction, which lacked a control house, required a custom solution. Tangibl designed and installed a pre-wired relay panel housed in a stainless steel, outdoor weatherproof enclosure, ensuring optimal performance in all weather conditions.

Tangibl’s involvement in this project covered the full spectrum of engineering services, from preliminary design to final construction. Our team developed detailed project schedules and cost estimates using the client’s tools. We prepared comprehensive scope and design documents, ensuring all specifications were met. Detailed drawings for construction work packages were created, and field changes were incorporated into as-built drawings to finalize the project.

Through this pilot wire relay replacement, Tangibl successfully resolved the utility’s reliability challenges. The solution provided long-term sustainability and reliability for the hospital’s critical backup power. This project underscores our commitment to delivering innovative and dependable engineering solutions for essential infrastructure.