Tangibl was requested to provide preliminary engineering and detailed design services for the replacement of a pilot wire protection scheme for a distribution utility in New York. The 34.5kV two-ended line that was part of the project included a tap for backup supply to a hospital. Intermittent unavailability of the associated telephone pairs, with consequent line tripping, had resulted in significant deterioration of reliability for the backup supply to this critical customer.
Microprocessor distance relaying combined with a POTT scheme utilizing audio tone was chosen as the replacement scheme. This eliminated the dependence on DC telephone pairs for reliable performance of the protection scheme. The existing electromechanical relays were replaced with SEL 311 and RFL 9745 for audio tone communications. One of the stations had completely metal-clad construction, with no control house and therefore a new pre-wired relay panel in an outdoor, dustproof, weatherproof stainless-steel enclosure was provided to replace the existing relay and control panel for the line terminal breaker.
Tangibl prepared scope and detailed design documents and requisitioned the necessary material. Preliminary engineering work included development of a project schedule and a cost estimate using the client’s cost estimating tools. Tangibl also prepared detailed design drawings for the construction work packages, and incorporated field changes into as-built drawings.