Electric Transmission Texas (ETT) on Feb. 16 filed with the Public Utility Commission of Texas an application to amend its certificates of convenience and necessity for the Stewart Road 345-kV Transmission Line in Hidalgo County, Texas.
The proposed Stewart Road Project would be designed, built, and operated as a double-circuit, 345-kV transmission line that would begin at the existing AEP Texas Stewart Road substation, located south of the City of Donna, east of Farm-to-Market (FM) Road 2557/Stewart Road, and would extend to an interconnection point along the existing AEP Texas North Edinburg to Sharyland Utilities (SU) Palmito 345-kV transmission line.
The transmission line project would terminate at an expansion of the existing AEP Texas Stewart Road substation, ETT added.
ETT and SU were each certificated for about one-half of this transmission line, with ETT owning the western half of the transmission line from the AEP Texas North Edinburg substation to the east past the proposed tap locations.
The project would be built using double-circuit, single-pole steel structures, ETT added, noting that typical structures would range in height between 130 feet and 155 feet above grade; the estimated maximum height of structures is 200 feet above grade.
The miles of right of way (ROW) for all 15 alternative routes filed by ETT range from about 4.90 miles for “Route B3” to about 9.27 miles for “Route C7.” ETT also said that since the project would be a double-circuit line, the number of miles of circuit is twice the number of miles of ROW and ranges from 9.80 miles to 18.54 miles.
The area traversed by the alternative routes being evaluated – the study area – for the project is oriented in a west-to-east direction and entirely within Hidalgo County, ETT said. The existing AEP Texas Stewart Road substation is located in the western portion of the study area and the three potential interconnection points (A, B, and C) along the ETT portion of the existing AEP Texas North Edinburg to SU Palmito 345-kV transmission line are located in the eastern portion of the study area.
The study area, ETT added, is generally flat, primarily rural, and the entire area is predominantly cropland or rangeland/pastureland. Most of the habitable structures in the study area are associated with rural ranch or agricultural properties that would be considered low intensity development, ETT said.
Discussing the need for the proposed project, ETT noted that the load in the western Lower Rio Grande Valley (LRGV) is currently served by three 345-kV transmission lines from the north, at times by imports from an HVDC tie with Mexico, and previously by three combined cycle generation facilities. Most of the load in the western LRGV is concentrated around the cities of Edinburg, McAllen, Pharr, and the neighboring communities. ETT added that one of the three combined cycle generators is the Frontera generation facility located south of McAllen in the southernmost part of Hidalgo County.
Frontera in 2016 began exporting its entire 524-MW generating capacity to Mexico, ETT said, noting that the unavailability of the Frontera plant results in increased power flows north to south from the North Edinburg substation where the remaining generators are located, and two of the 345-kV transmission lines from the north terminate.
The 300-MW HVDC tie with Mexico is known as the Railroad DC Tie, and is located south of McAllen in the southernmost part of Hidalgo County near Frontera. ETT added that the operation of the Railroad DC Tie has a significant impact on the line loading levels in the area during outage conditions. If the Railroad DC Tie is exporting power to Mexico, the north to south line loading is further increased. ETT added that with the 300-MW export condition on the Railroad DC Tie, the unavailability of the Frontera generating plant, and the projected load increases in the area, the transmission system in Hidalgo County experiences facility overloads and system under voltages during certain transmission facility outages. Those overloads and under voltages issues result in the violation of NERC and ERCOT reliability criteria, and can result in loss of considerable electrical load in the area, ETT said.
ERCOT in June 2016 endorsed a transmission system improvement plan for the area that included the construction of a 345-kV double-circuit transmission line from the AEP Texas Stewart Road 138-kV substation to a tap point along the North Edinburg-SU Palmito 345-kV line, as well as expansion of the AEP Texas Stewart Road substation to include a 345-kV switchyard and two new 345/138-kV autotransformers. The ERCOT Technical Advisory Committee reviewed the plan and in June 2016, the ERCOT Board of Directors recommended the project as needed to support the reliability of the ERCOT regional transmission system.
The consensus opinion of its routing consultant, POWER Engineers, was to recommend Route B3 as the route that best addresses certain requirements, ETT said, adding that it determined that that route provides the best balance of routing characteristics and best addresses certain requirements.
According to the filing, Route B3 has an estimated cost of about $16.8m; the AEP Texas Stewart Road substation expansion has an estimated total cost of about $28m.
According to the estimated schedule, ROW and land acquisition would begin in March 2019, and be completed in September 2019; engineering and design would begin in March 2019, and be completed in August 2019; material and equipment procurement would begin in June 2019, and be completed in December 2019; and construction of the facilities would begin in November 2019, and be completed in May 2020, which is also when the facilities would be energized.