Energy Center Switchyard and Transmission Scopes

Confidential Location, Michigan

This EPC delivery of a 2×1 combined-cycle gas plant included switchyard and transmission line scopes. A 345kV, five-breaker switchyard has three bays connected to the plant’s generator step-up unit (GSU) transformers and two connected to the main auxiliary transformers. The GSU bays have 550kV breakers; the step-down transformer bays have 362kV breakers. Five-inch-diameter Schedule 80 rigid bus provides the electrical connection within the switchyard. Structures include seven H-frames: six for the strain bus to the GSU transformers and an outgoing dead-end structure to the transmission line, as well as a lightning mast.

Transmission line work included one mile of new 345kV line for the interconnect to the utility switchyard, along with associated structures and materials:

• Twelve steel monopole structures
• Bundled 1351-kcmil dipper aluminum conductor steel-reinforced cables
• Two optical ground wire (OPGW) circuits

The new transmission line crosses over 40kV and 13kV lines and under a double-circuit 345kV line and single-circuit 230kV line — all in one span. During wire pulling, MEC used batwing guard structures to protect against contact with the 40- and 13kV lines. Equipotential grounding mats prevented risk of electric shock from the 345- and 230kV transmission lines.