Nelson Dewey Substation Asset Renewal

Grant County, WI, USA

Communications & SCADA, Substation & Switchyard, Transmission & Distribution

Project Highlights

  • Replaced two 1958 vintage 138/69 kV autotransformers with a new single 60 MVA transformer.
  • Installed security upgrades which included new yard lighting.
  • Modeled and updated ground grid.
  • Reconductored 69 kV lattice box structure.

ECI provided scoping and complete detailed design services for an asset renewal project at a 161/138/69 kV substation on a retired coal-fired power plant site. The principal scope was to replace two sixty-year-old 138/69 kV autotransformers with a single 60 MVA unit to align with capacity needs of the new system configuration. The new autotransformer foundation was integrated with a concrete oil containment basin in an area congested with structure foundations and other below grade infrastructure. The 69 kV and 138 kV circuit breaker bushing arresters and bus arresters were replaced with station class line arresters on the bus structures. The 161 kV and 69 kV bus VT junction boxes were replaced and the 69 kV bus was reinsulated and reconductored. A portable substation was used during the 69 kV bus outage to supply local distribution.

Cable trench was installed for new control cables to the 69 kV equipment and new transformer. Physical security mitigation measures were installed, including all new LED instant-on yard lighting and a fence expansion to enclose the control house within the perimeter fence. The substation ground grid was modeled in CDEGS and remediation was performed to mitigate step and touch potential violations under all design criteria conditions.

Wiring changes in the control house were necessary to connect the new transformer to existing protection, control and SCADA equipment. The 69 kV bus differential protection was replaced along with a breaker failure and control relay.

ECI worked with suppliers to add oil monitoring equipment to the new transformer, as well as an existing transformer with poor documentation. ECI provided support to field crews through the installation process and was ready to respond with design changes as the need arose.

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