Case Study | Utility Engineering & Consulting

Fast Trip No Reclose Relay Program

Tangibl was retained by a mid-Atlantic utility to provide preliminary engineering and detailed design for its multi-year Fast Trip No Reclose (FTNR) Program. FTNR enables low-set instantaneous protective-relay trip settings, and disables circuit-breaker reclosing, as part of clearing circuits via SCADA for safe work by aerial linemen. Our client established this program to ensure that FTNR was available on eligible circuits not already provided with this protection scheme.

Affected substations either had instrument and control (I&C) panels and relay panels in a control house, or indoor, non-walk-in metal-clad switchgear with I&C and relay panels integrated into the switchgear assembly. Primary and backup SEL 751 relays paired with one Electro Switch LSR each for instantaneous and no-reclosing were specified. The SEL 751s replaced either electromechanical distance or overcurrent protective relays. Bitronics meters were specified to replace existing ammeters and watt meters.

Tangibl prepared AC and DC single schematics, wiring diagrams and panel views, cable schedules, demolition/removal drawings, requisitioned the necessary material, and prepared clearance requests for review. Upon acceptance, Tangibl prepared issue-for-construction construction work packages, and incorporated field changes into as-built drawings. Tangibl further contributed to the overall program by a) developing an improved scoping document based on lessons learned across the program, and b) recommending that one of the substations in the program be deferred as a result of knowledge, through our other work at this client, of its planned unloading due to new distribution substation capacity being installed nearby.

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