Solution
The project was strategically located between the Carnegie Mellon and University of Pittsburgh campuses in the Panther Hollow residential area. The project was conceptualized under the principle of being a good neighbor, with a minimized footprint, architectural designs for exterior facades that were consistent with nearby structures, and underground cabling for high-voltage power lines and medium-voltage feeder circuits connecting the substation with the area distribution grid.
Riazzi Substation is 138/23-kV substation with associated 138-kV and 23-kV underground infrastructure. The station consists of a four-position 138-kV gas insulated ring bus switchgear, two 138/23-kV power transformers and 23-kV metal clad switchgear. A two-story structure houses all switchgear and associated protection and control systems, shielding this sensitive equipment from the effects of severe weather. The 138-kV supply is derived by splitting an existing underground 138-kV power line encased in a high-pressure, fluid-filled (HPFF) conduit near the property. Six 23-kV feeder lines originate from the new station in a configuration that is expandable to accommodate at least a dozen additional lines.
Burns & McDonnell managed all aspects of this integrated engineer-procure-construct (EPC) project, including site development, stormwater management and permitting, foundations, above- and below-grade electrical, the GIS building and switchgear, protection and controls, SCADA, the underground 23-kV distribution and underground 138-kV transmission.
Upon commencing construction, site preparation work included installation of a retaining wall along a large portion of the property boundary to stabilize a steep grade adjacent to key electrical equipment.
The two-story substation building was constructed of precast concrete with an exterior designed to closely resemble exteriors of university operations facilities located nearby. The design avoids the typical industrial feel of a conventional substation by incorporating green textural elements running vertically on exterior walls, along with landscaping and revegetation of areas around the site. The structure design reduced the required footprint by a factor of five over the space needed for conventional outdoor substations with equivalent capacity.
Discrete, underground power cables were installed to and from the substation, mitigating neighborhood concerns about the appearance of poles and above-ground lines. The underground cable routes were installed using stainless steel pipe, requiring hundreds of welds and turns, while navigating aging underground utility infrastructure, including a 16-inch water main and a 68-inch storm sewer, both more than 100 years old.
On one of the selected underground cable routes for three distribution circuits exiting the substation, a large steam main running beneath an arterial street posed an obstacle that made installation of manholes and conduit along that portion of the route infeasible. The solution was a new aerial cable installation spanning 20 poles, capped at each end by riser poles where the cable connects back to the underground conduit.