Alternative Insulating Fluids to SF6 gas: What we know and don’t know. CO2 + O2 Alternative Insulating Fluids to SF6 gas: What we know and don’t know. George Becker, Daniel Schiffbauer, and Karla Trost C4 - Fluoronitrile C5 - Fluoroketone

Standards and the Industry New gases and gas mixtures have emerged and have potential for replacing SF6 IEC, CIGRE and Current Zero Club are continually investigating and have published papers, studies and pilot projects IEEE Switchgear ADSCOM Committee approved forming a Joint Task Force with IEEE Substations Committee - Spring 2016. Goal – understand the impact of Alternate Gases on the Standards http://resourcecenter.ieee-pes.org/pes/product/technical-publications/PES_TR0064_062018

136 Pages Report Includes: Background Historical Perspective (Such as: What factors were and were not relevant in the move from bulk oil to SF6? And Comparison of SF6 Alternatives to Bulk Oil Transition) Technical Considerations Stability Aspects Environmental and Regulatory Toxicity evaluation assessment and classifications Cost and Availability IEEE Standard Review Review of other industry activities Conclusions and recommendations

Report Conclusions & Recommendations:

The Utility Perspective “The quest for a Single Solution” Utilities are questioning why manufacturers are not converging on a single gas or gas mixture to replace SF6?? Some operating concerns: Multiple variations of filling equipment types Multiple procedures for gas processing Multiple labelling criteria The need for failsafe connections (different valves for different mixtures) Multiple gas handling standards and guides Multiple MDS sheets Varied arcing decomposition by-products Multiple gas detection equipment variations From the manufacturer’s perspective, the process of vetting multiple solutions in the lab and piloting in the field is necessary and long-term valuable for the customer. Research and development of four major alternatives now will reveal the strengths and weaknesses of each prior to consolidation.

The Utility Perspective “What about a direct replacement” Utilities are questioning why manufacturers are not working on a replacement gas or mixture that doesn’t require circuit breaker redesign?? Different gas properties and thermal capabilities require modification to some or all of the following: Interrupter gas flow cross section Interrupter nozzle contours Interrupter gas diffusion & electric field control Grounding switches Density sensors Pressure relief devices Filling valves Moisture absorber elements O-Rings, gaskets and other seals Capacitive/inductive switching performance (long arcing times) Short line faults (thermal interruption performance) High short circuit currents (high temperature and pressure)

The Utility Perspective “What about gas mixture handling” Utilities are asking about how handling procedure changes will affect personnel, projects and maintenance?? Some potential matters to consider: Development new handling standards, guides and recommended practices (Industry) Development of new filling and reclaiming procedures (Users) Pre-mixed gas cylinders Inventory methods Topping off of equipment (what is the correct mixture?) Addressing the toxicity of the new mixtures and the individual gases in the mixture Time frame to update industry standards, guides and recommended practices

Carbon Dioxide and Oxygen SF6 N2 + O2 CO2 + O2 C4 - Fluoronitrile C5 - Fluoroketone Sulfur-hexafluoride Clean-Air Carbon Dioxide and Oxygen C4-Fluoronitrile C5-Fluroketone Base Gas Chemical Formula SF6 80% N2 + 20% O2 70% CO2 + 30% O2 (CF3) 2CFCN (CF3) 2CFC(O)CF3 CO2e(GWP) 23,500 <1 2,210 1 Boiling Point -64°C <-183°C -50C -5°C +27°C Dielectric Strength 1.00 0.43 0.77 2.20 1.70 Gas Mixture Background (gases) Pure or with N2 or CF4 ~90% CO2 ~90% O2 With N2 or CO2 ~380 Lowest Operating Temperature -30°C * -50°C -30°C 0°C to +5°C -20°C possible Internal Arc Reaction Decomposition Products HF, SXFY, SOFX, F2, SOX, CF4 If applicable: O3, NOX CO, HF, O3 CO, HF, CnF2n+2, other Fluorinated Compounds CO, HF, COF2, CXFY, other Fluorinated Compounds Toxicity of Decomposition Products Slightly toxic (Hodge-Sterner) Typically None Relatively harmless (Hodge-Sterner) Practically non-toxic (Hodge-Sterner) *HV typical – some products -40°C

General Facts C5-Fluoroketone-based gas mixture is a chemical compound developed for switchgear applications in collaboration with 3MTM. Fluorinated molecule is non-flammable and neither the substance itself nor the effects of decomposition would deplete the ozone layer. The molecule has a chemical composition that decomposes under ultraviolet light, extreme heat, electrical arcing and its lifetime is less than 15 days versus 3,200 years with SF6 The use of the fluorinated molecule requires that the pure gas be mixed with a carrier gas such CO2, N2 or O2. The gas mixtures used for insulating and current interruption must operate at higher pressures than SF6 in order to achieve the same performance with equipment of similar size.

Vapor Pressures of Gases 3MTM NovecTM 4710 Pressure vs. Temperature Diagram One of the alternative gases has vapor pressure characteristics that are quite different from SF6. When condensation occurs, gas density drops rapidly along with performance.

Heat Energy and Thermal Performance Thermal breakdown of the Fluoroketones, Fluoronitriles and buffer gases such as CO2 and N2 does not occur until at least 600°C to 650°C. Reduction in the temperature limits due to thermal decomposition is not expected. Working groups (IEEE C37.20.9) have tentatively recommended use of the “In air” limits for conductors due to the presence of Oxygen in many proposed gas mixtures.

Making, Breaking and Switching Stresses Terminal faults will test the hot dielectric recovery capability of the arc quenching gas. TRV’s for 145 kV breaker; first pole to clear factor of 1.5

Making, Breaking and Switching Successful terminal fault performance includes management of hot exhaust gases. Long arcing times are the most severe condition for the exhaust because it supplies the most arc energy to the interruption process. Hot gas generated during interruption must eventually exit the interrupter and enter the stressed regions across the gap and/or from high voltage to ground. The hot dielectric strength of pure SF6 is well understood. The same level of understanding is possible for each SF6 alternative and requires investments in Computational Fluid Dynamics simulations as well as validation power tests which measure gas pressure and gas temperature as a function of time. Axisymmetric CFD simulation showing hot gas exiting the interrupter

Electrical Endurance Pure SF6, CO2 and O2 mostly recombine after arcing and disassociation. Fluoroketones and Fluoronotriles do not recombine after arcing and disassociation. In addition to contact and nozzle wear, we must concern ourselves with degradation of the gas and its long term effects on the performance of the equipment. Reconsideration of the service capability tests should be made in light of the possibility for permanent gas decomposition. Standards may be revised to require that type testing demonstrate performance after the accumulation of significant fault duty.

Making, Breaking and Switching: CO2 + C4-Fluoronitrile   CO2 + Fluoronitrile Fault Interruption (dielectric phase) 145 kV, 40 kA, 50 Hz successful for T10, T30, T100a and OP2 Fault Interruption (thermal phase) 145 kV, 40 kA, 50 Hz SLF successful after adaptation to the physical characteristics of CO2. The authors describe the size of the chamber as, “comparable with existing SF6 self-blast chambers”. Low Current GCB Switching 145 kV, 40 kA, 50 Hz capacitive switching test was successful but the specific rating is not disclosed. GIS Switching 145 kV, 40 kA, 50 Hz Disconnect Switch and High Speed Grounding Switch 1600 A bus transfer current successful with behavior similar to SF6. Bus-charging is not required but successfully completed. Induced current tests of the grounding switch successful with behavior similar to SF6. 420 kV, 50 Hz Disconnect Switch Total test pressure 0.55 MPa-abs (0.51 MPa CO2 + 0.04 MPa C4F7N) Successful 1600 A, 20 V bus transfer test with stable arcing time and contact wear similar to SF6. Practical Experience 420 kV GIL at National Grid (2016), 123kV GIS at Swiss Axpo Power (2017)

Gas Stability Buffer Gases: CO2 is the most promising candidate for switching applications due to its arc quenching properties Gas Mixtures: CO2 + O2 + C5-Ketones with a GWP of <1 (Air PlusTM) Limited minimum operating temperature (-5 to -20 deg. C) CO2 + O2 + C4-Nitriles usable for -30°C with GWP of about 380 to 690. known as g3 CO2 + O2 mixture applicable to -50° or -55°C with GWP of <1. N2 + O2 Clean Air mixture applicable to -50°C with GWP=0

Toxicity – Constituent Gases C4-Fluoronitrile C5-Fluoroketone SF6 CO2 *All values shown are new gas (no arc by-products present)

Design Console – C4-Fluoronitrile Mixture ** SF6 CO2+O2+ C5 F-ketone C4 F-nitrile CO2+O2 N2+O2 (VI) Gas Selector Rated Pressure (psig @ 20 deg. C) 50 87 125 163 200 *Shown for typical HV breaker (-30C) ** Inconsistent data in the public literature

Design Console – C5-Fluoroketone Mixture SF6 CO2+O2+ C5 F-ketone C4 F-nitrile CO2+O2 N2+O2 (VI) Gas Selector Rated Pressure (psig @ 20 deg. C) 50 87 125 163 200 *Shown for typical HV breaker (-30C)

Design Console – CO2 + O2 *Shown for typical HV breaker (-30C) SF6 C5 F-ketone C4 F-nitrile CO2+O2 N2+O2 (VI) Gas Selector Rated Pressure (psig @ 20 deg. C) 50 87 125 163 200 *Shown for typical HV breaker (-30C)

Design Console – N2 + O2 *Shown for typical HV breaker (-30C) SF6 CO2+O2+ C5 F-ketone C4 F-nitrile CO2+O2 N2+O2 (VI) Gas Selector Rated Pressure (psig @ 20 deg. C) 50 87 125 163 200 *Shown for typical HV breaker (-30C)

Alternative Insulating Fluids to SF6 gas: What we know and don’t know. George Becker – Power Engineers, Inc – george.becker@powereng.com Daniel Schiffbauer – Toshiba International – daniel.schiffbauer@Toshiba.com Karla Trost – G&W Electric – ktrost@gwelec.com