2021-035 Hickory SubstationJune 4, 2021 Report No. 2021-035
INFORMAL STAFF REPORT
TO CITY COUNCIL
SUBJECT:
Provide an overview of the safety of Gas Insulated Switchgear (GIS) for the Hickory GIS
Substation Project including a review of the sites considered for the substation.
EXECUTIVE SUMMARY:
Through independent research and information obtained from GIS manufacturers, Denton
Municipal Electric has learned of several safety improvements gained from this technology. These
improvements are briefly described below along with a high-level overview of the technology.
In a traditional air-insulated electric substation (AIS), energized equipment is insulated from other
equipment using air. This means the energized equipment is usually outdoors and requires large
metdistances for insulation. GIS technology uses SF6 gas to insulate the energized equipment
rather than air. For a GIS substation, energized components are contained in a metal enclosure
with SF6 inside. This allows for much less space required than a traditional air-insulated substation
and thus a smaller substation size. However, GIS technology has a two to three times higher
overall cost than traditional air insulated substations. The size of the site selected by Council
(purple site in the map below) required GIS technologies to be considered. An overview of the
history of the project is shown below in the section called “Previous Council Activity”.
The amount of SF6 used in a GIS substation is several times higher than an AIS substation. DME
tracks the amount of SF6 used in our substations. Since the design for Hickory Substation is not
complete, DME does not know how much SF6 will be needed. The EPA requires reporting SF6
inventory when you exceed a threshold and it is expected Hickory Substation will put DME over
the reporting threshold. The EPA is interested in SF6 because it is a greenhouse gas. Any
maintenance required on the substation equipment that will involve the SF6 environment will be
done by certified professionals. As a component of the project, all equipment required to safely
capture and store the SF6 gas will be included and be stored on-site. Efforts will be made during
the design to limit the amount of SF6 used and investigate the use of alternative gases. Hickory
will have SF6 density indication and leakage monitors constantly monitoring the station.
Safety Improvements:
Since all high voltage equipment will be housed inside a building, the noise levels at the
adjacent properties will be significantly lower than a traditional substation.
Since all energized equipment is housed inside a grounded metal tube, electric fields are
eliminated, and electromagnetic fields (EMF) are near zero around the energized
equipment.
All transmission lines and distribution lines will be underground in the block surrounding
the site.
Employee safety is improved due to reduced exposure to high voltage equipment.
June 4, 2021 Report No. 2021-035
On October 21, 2014, at closed session meeting (ID 14-0625), DME presented to Council the sites
being considered for the new Hickory Substation. Five (5) sites were presented to Council for
consideration and are shown in the map below including the number of displaced homes and
businesses.
Orange Site – Seven single family houses and one business
Purple Site – Five single family homes
Green Site – Twelve multi-until apartment buildings
Blue Site – Twelve multi-until apartment buildings
Yellow Site – Seven multi-unit apartment buildings and one church
June 4, 2021 Report No. 2021-035
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 treatment1.” 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 (ID15-10372) 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 simulations3 for AIS
vs. GIS.
On June 21, 2016, the City Council (ID 16-7114) 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.
1 City of Denton Meeting Agenda – City Council, July 21, 2014
2 City of Denton Meeting Agenda – City Council, November 17, 2015
3 City of Denton Council Minutes, November 17, 2015
4 City of Denton Meeting Agenda – City Council, June 21, 2016
June 4, 2021 Report No. 2021-035
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.
On July 18, 2017, Council approved (ID 17-8645/Consent Agenda) a Professional Services
Agreement for Architectural and Design Services relating to the Hickory Substation Gas Insulated
Substation Equipment Building and Screening Wall.
When deliberations for both the Eagle and Hickory Substations were initiated, the plan was to have
both substations equipped with two (2) transformers in each substation to provide a combined
service capacity of 100 MW. With the August 18, 2020 direction from the Council to not build
Eagle Substation, the design of the Hickory GIS was adjusted to compensate for the additional
load serving capacity originally planned for a Hickory & Eagle Substation scenario. DME’s
current plans for Hickory Substation is for it to be equipped with four (4) transformers which
provides the same 100 MW capacity. Only two (2) transformers will be installed initially with the
others installed as demand grows and they are justified. However, please know the footprint for
Hickory Substation GIS will not change; plus, no changes are currently anticipated for the planned
façade. All needed adjustments will be inside the façade.
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 2023. Please know
these dates are subject to change based on conditions or other factors that may be out of the control
of DME.
5 City of Denton Meeting Agenda – City Council, July 18, 2017
June 4, 2021 Report No. 2021-035
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
August 2021 – Select Firm for the Project
November 2021 – PUB and Council Approval
November 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