2021-090 Hickory Gas-Insulated SubstationOctober 22, 2021 Report No. 2021-090
INFORMAL STAFF REPORT
TO CITY COUNCIL
SUBJECT:
Provide a description and photo simulation of the electric transmission, substation, and
distribution infrastructure around the new Hickory Gas-Insulated Substation (GIS).
EXECUTIVE SUMMARY:
The new Hickory GIS is to be built adjacent to an entry corridor to the City of Denton for its
downtown, University of North Texas, and historic district areas. Therefore, aesthetics along this
entry corridor were of particular interest to the Council who wanted the new substation to fit the
area. DME is aware that the substation wall treatment was presented to Council on a number of
occasions; however, DME is unclear if the Council has ever seen aesthetic information related to
the overhead to underground conversion of the transmission lines. The information in this
document should provide Council with further information on this topic.
On June 21, 2016, the City Council (ID 16-7111) was requested to provide DME staff direction
regarding the Hickory Substation site related to options to the substation’s configuration and
aesthetic treatment. The presentation included background information on the Hickory Substation
site, displayed the recommendation of the Aesthetic Committee, as well as estimated construction
costs. It was during this Council meeting that DME was given direction to build the new Hickory
Substation with GIS technology to minimize its footprint as well as the Council’s preference for a
façade/wall which is shown in Figure 1 below.
Figure 1 - Facade/Wall Treatment chosen by Aesthetic Committee
1 City of Denton Meeting Agenda – City Council, June 21, 2016
October 22, 2021 Report No. 2021-090
Additional direction from Council included DME moving forward with underground transmission
circuits appropriate to the construction of this substation as well as converting existing overhead
distribution circuits, in the same general area, to underground. Figure 2 below shows where the
existing overhead distribution (red) and transmission lines (blue) are located.
Figure 2 - Location of Existing Overhead Transmission and Distribution Circuits
Transitioning overhead transmission and distribution lines to underground requires “riser”
structures to facilitate the transition. For distribution lines, riser structures are typically smaller and
often go unnoticed.
However, for the transmission lines, riser structures require larger than normal transmission line
poles that are approximately 120’ tall, 25’ wide, and manufactured from galvanized steel. The
reason for the larger structures is to allow for the underground transmission cables (shown in red
below) to route along these structures to connect to the overhead transmission line conductors. For
“deadened” poles, or where the transmission conductor stops, it is necessary to increase the size,
and thus the pole strength, to support the deadened weight or force due to the conductor stopping.
Additionally, there are many energized components on these structures which need adequate
spacing to ensure National Electric Safety Code (NESC) clearances are maintained and ensure safe
operation. Figure 3 provides a typical transmission line riser structure.
October 22, 2021 Report No. 2021-090
Figure 3 - Sketch of Transmission Overhead to Underground Riser
Two of these structures will be located along Oak Street on City owned property (where the old
Hickory Substation is currently located) with one additional structure, for a total of three (3),
located on Stella Street in an electric easement. These structures are located approximately one
block from the new substation site as shown in Figure 4 below. With only small changes needed,
all three existing transmission lines, connecting to the new Hickory GIS riser structures, will
remain in their current alignments.
October 22, 2021 Report No. 2021-090
Figure 4 – Proposed Transmission Riser Structures
Photo simulations from an Oak Street and Bonnie Brae perspective of the “BEFORE [Figures 5
and 7]” and “AFTER [Figures 6 and 8]” transmission lines are included for reference. These risers
are needed to support the transition between overhead transmission lines to underground for the
new Hickory GIS.
October 22, 2021 Report No. 2021-090
Figure 5 - BEFORE: View from Oak Street looking East toward the existing Hickory Substation
Figure 6 - AFTER: View from Oak Street looking East toward the existing Hickory Substation
October 22, 2021 Report No. 2021-090
Figure 7 - BEFORE: View from Bonnie Brae looking South toward existing Hickory Substation
Figure 8 - AFTER: View from Bonnie Brae looking South toward existing Hickory Substation
DME is currently evaluating proposals to contract the construction of the Hickory GIS project and
includes the new GIS Sand the overhead to underground conversions of the area’s distribution and
transmission lines. DME expects to bring the contract to the City Council for consideration in
December 2021 or January 2022. The transmission poles, which include the riser poles, required
for this project are anticipated to be ordered in the next few weeks. There are limited options
available at this time; however, some include having the poles delivered with a green color (for
October 22, 2021 Report No. 2021-090
UNT) or corten steel poles which intentionally rust and turn brown over time. Either of these
options will be more costly. Since galvanized steel structures are cost effective and consistent
with other existing structures in the area, DME intends to move forward with the purchase of the
standard, galvanized steel poles unless directed otherwise by the Council.
PREVIOUS CITY COUNCIL ACTIVITY:
On December 2, 2014, a City Council Work Session report (ID 14-0764), directed DME to enlist
input from citizens through the creation of an Aesthetics Committee to discuss the appearance of
the façade for Hickory Substation. Reviewing the City Council agenda for this date provided
identification of item ID 16-711 to “receive a report, hold a discussion, and provide staff direction
regarding the DME Hickory Substation site, … and concerning the options related to the station’s
configuration and aesthetic treatment2.” Direction given at this meeting established an Aesthetic
Committee to look at options for Hickory Substation’s façade.
(Time unknown) As result of citizen comment, the idea of a gas insulated substation was
introduced into the deliberations.
At the City Council meeting on November 17, 2015, DME provided (ID15-10373) Council a
presentation, and requested guidance, regarding the potential utilization of GIS technology for
DME electric substations. The substation of topic was the proposed Eagle Substation. The
presentation included information on AIS/GIS cost differences, personnel requirements,
footprints, performance/reliability, operations/maintenance, as well as photo simulations4 for AIS
vs. GIS.
On June 21, 2016, the City Council (ID 16-7115) was requested to provide DME staff direction
regarding the Hickory Substation site related to options to the station’s configuration and aesthetic
treatment. The presentation included background information on the Hickory Substation site,
displayed the recommendation of the Aesthetic Committee, and estimated construction costs. It
was during this Council meeting that DME was given direction to build the new Hickory
Substation with GIS technology as well as the Council’s preference for a façade/wall which is
shown in the image below.
Additional direction from this Council meeting included DME to move forward with underground
transmission circuits appropriate to the construction of this substation as well as converting
existing overhead distribution circuits, in the same general area, to underground.
2 City of Denton Meeting Agenda – City Council, July 21, 2014
3 City of Denton Meeting Agenda – City Council, November 17, 2015
4 City of Denton Council Minutes, November 17, 2015
5 City of Denton Meeting Agenda – City Council, June 21, 2016
October 22, 2021 Report No. 2021-090
On July 18, 2017, Council approved (ID 17-8646/Consent Agenda) a Professional Services
Agreement for Architectural and Design Services relating to the Hickory Substation Gas Insulated
Substation Equipment Building and Screening Wall.
The current timeline for the design and construction of Hickory Substation is to complete its
technical specifications, on or before, March 2021; issue an RFP, on or before, May 2021; and
request Council approval of the design/build contract, on or before, December 2021. Hickory
Substation is currently scheduled to be on-line, on or before, the summer of 2024. Please know
these dates are subject to change based on conditions or other factors that may be out of the control
of DME.
The original cost estimate for the Hickory Substation was $25 million and current cost estimate
for the Hickory Substation and associated costs is now $32.5 million. While this represents an
increase from the initial budget, the combined cost estimate for the Hickory Substation and the
Council approved Eagle Substation was $51.2 million. Elimination of the Eagle Substation
coupled with changes that DME Engineering Division has recommended to the distribution
system, the net capital cost savings is now estimated to be $18.6 million with increased reliability
as compared to the prior two new substation plan and no change to the overall timing of planned
future substations.
MAJOR MILESTONE SCHEDULE:
April 2021 – Solicit RFQ
May 2021 – Select Qualified Firms from RFQ Process
May 2021 – Provide project specification package to Qualified Firms and request proposals
October 2021 – Select Firm for the Project
December 2021 – PUB and Council Approval
December 2021 to May 2022 – Project Design
June 2022 – Construction Starts
January 2024 – Energization
June 2024 – Construction Complete
STAFF CONTACT:
Jerry Fielder, P.E; Division Engineering Manager; 940-349-7173
6 City of Denton Meeting Agenda – City Council, July 18, 2017