IEEE PES T&D Conference & Exposition 2022 - 134

table 1: Phase-out dates for implementing
SF6 gas-insulated equipment in California
Voltage Capacity
(kV)
38< kV ≤ 145
145< kV ≤ 245
>245
Short-Circuit
Current Rating (kA)
< 63
≥ 63
< 63
≥ 63
All
Phase
Out Date
Jan. 1, 2025
Jan. 1, 2028
Jan. 1, 2027
Jan. 1, 2031
Jan. 1, 2033
The report concluded that SF6-free alternative policy intervention
is likely to be needed to trigger a transition from SF6.
Industry sustainability and environmental leadership are
challenging their transmission substation departments to
establish criteria and plans to phase out SF6 in high-voltage
gas-insulated equipment. Utility sourcing departments, for
example, are responsible for purchasing equipment and evaluating
suppliers for value and risk. These departments are in
the process of identifying SF6-alternative suppliers for gasinsulated
switchgear. Based on feedback from a few large
utilities, vacuum-switching, air-insulation technology is the
preferred option considering technical, commercial, and
quality evaluation criteria, including technical performance,
global warming potential, availability of suppliers, and no
F-gas-reporting requirements.
Governments are also establishing criteria for phasing out
SF6. California, for example, is the first state that has taken
regulatory action through the California Air Resource Board
to limit SF6 emissions and phase out SF6. Beginning with
reporting year 2025, the requirement changes to an emissions
limit rather than a rate. The revised regulation order of
reducing GHG emissions for all gas-insulated equipment and
phase-out of SF6 has been approved for adoption. SF6 phaseout
dates for gas-insulated equipment are shown in Table 1.
Lab Evaluation and Results
Manufacturing lab evaluations have determined that eliminating
SF6 gas offers comparably high reliability and
increased performance, making it the most sustainable alternative
for health, safety, and the environment.
Intensive research was conducted on more than 200 gases
for insulating and switching performance. The most promising
gases compared to SF6 are clean air or an F-gas mix
based on fluoronitrile and fluorketone. See Figure 3.
Performance of Alternative Gasses
The insulating gas within a circuit breaker provides the
dielectric strength, or insulation, to electric current flow. The
dielectric strength is the maximum electrical field or voltage
that can be withstood before the electrical current breaks
through and the material can no longer electrically insulate.
In some cases, the insulating gas can act as an electrical arcquenching
medium, meaning it is used to cool and extinguish
an electrical arc as part of the circuit breaker design.
The switching performance of a breaker can be defined as
how the product performs its duty of protecting equipment/
grids from damage caused by excess current from an overload
or short circuit. A breaker's most basic function is to
interrupt current flow after a fault is detected.
The results of the evaluations for both the basic insulation
components and the integral switching functions for these
selected gases are shown in Figure 4.
When evaluating insulation during performance, clean
air insulation technology (left figure in blue) has the best
values for health, safety, environment, and long-term stability
because of its natural properties using clean air as an
Sulfur Hexafluoride
Fluoronitrile
C5-Fluoroketone
Clean Air
* SF6
* GWP = 23,000
* Excellent Di-Electric
* Temp. Up to -30 °C
* Toxic L-50 = 100,000
* Reporting Required
* Leakage Penalty Apply
* Bi-Product - H2SO4,
SO2
* (CF3)2 CFCN
* GWP = 2,100
* Di-Electric Up to 70%
* Temp. Up to -30 °C
* Toxic L-50 = 20,000
* Reporting Required
* Leakage Penalty Apply
* Bi-Product - CO, HF,
COF2
* (CF3)2 CFC(O)CF3
* GWP = 1
* Di-Electric Up to 70%
* Temp. Up to 0 °C
* Toxic L-50 = 15,000
* Reporting Required
* Leakage Penalty Apply
* Bi-Product - HF, COF2
* N2 + O2
* GWP = 0
* Di-Electric Up to 50%
* Temp. Up to -60 °C
* Toxic L-50 = 0
* No Reporting Required
* No Leakage Penalty
Apply
* Bi-Product - None
figure 3. Known properties of SF6 and alternative insulating mediums.
134
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