115kV Line Relay Replacement and DFR Installations

Tangibl was requested by the client to provide preliminary engineering and detailed design services for a series of transmission system upgrades that were triggered by the interconnection of a ~100 MW (nameplate capacity) wind farm in northern New England. The work involved three different substations connected by a 115kV loop at the edge of the transmission network. Primary work involved the replacement, at one station only, of an existing 115kV OCB and related disconnects with a new 115kV GCB, plus new CCVTs and wave traps. Protection and control work involved replacement of line protection packages at all three stations, installation of new digital frequency meters and new digital fault recorders (DFRs) at two of the stations.

Tangibl finalized the project scope documents for each project, and prepared protection and control descriptions, outage and energization plans, and testing and commissioning plans. The scope documents included proposed changes to key schematic and switching diagrams. The protection and control descriptions detailed the replacement, with microprocessor technology, of existing regular and backup distance protection schemes including the use of carrier and transfer trip where required. The outage and energization plans described the switching steps for each outage to a level of detail necessary for the client’s transmission control center to schedule the outages with ISO New England. The testing and commissioning plans, developed after detailed design engineering was under way, laid out the testing sequence for each protection package and DFR.

Tangibl prepared detailed design drawings for 30%, (elementaries, schematics and panel views), 70% (wiring diagrams), 100% (complete package) and issue for construction (IFC) submittals. Engineering and design was complicated by the fact that outages at each station were scheduled at different intervals, with the resultant impact on deliverable schedule, even though the line protection packages had to be designed simultaneously for each end of the multi-terminal lines. The remote location of the project (three hours’ drive from the nearest major airport) provided significant logistical challenges. Field verification was accomplished with the assistance of Tangibl’s Project Specialist, based two hours away, in the same state as the project.

Tangibl provided additional services for this project, beyond its routine engineering and design responsibilities. At the client’s request, Tangibl proposed and was contracted separately to fabricate, test and ship relay panels for the line terminal regular and backup protection packages and the frequency meter. Material was specified by Tangibl as part of the engineering and design process, and the panels were assembled at Tangibl’s facilities, wired, and tested by Tangibl’s utility-grade wiring subcontractor and tested by that company’s utility-grade testing affiliate. The panels were shipped in a timely manner to the client’s receiving location, where they were acceptance-tested by the client and then shipped to the substation. Finally, Tangibl’s Project Specialist supervised the testing and commissioning of the protection packages and DFR’s at all three substations.