Assessment of Eco-friendly Gases for. Electrical Insulation to Replace the Most. Potent Industrial Greenhouse Gas SF 6

Transcription

1 Assessment of Eco-friendly Gases for Electrical Insulation to Replace the Most Potent Industrial Greenhouse Gas SF 6 1 Mohamed Rabie and Christian M. Franck Power Systems and High Voltage Laboratories, ETH Zurich, 8092 Zurich rm@ethz.ch Supporting information: Total Pages: 7 Number of Figures: The supporting information contains: Text Section S1: SF 6 emissions at SF 6 production Text Section S2: SF 6 emissions at equipment production Text Section S3: SF 6 emissions at use phase Figure S4: Vapor pressure curves for various gases 11 S 1

2 12 Text Section S1: SF 6 emissions at SF 6 production Emissions during production of the gas quantity necessary to fill an electrical apparatus are part of its environmental footprint. The IPCC estimates an emission factor of 0.2% (total emissions during the manufacturing process divided by the total quantity of produced SF 6 ) for applications that do not require highly purified SF 6 gas (e.g., electrical equipment) and a factor of 8% for applications that require highly purified SF 6 gas (e.g., semiconductor manufacturing). 1 For Germany, an emission factor of 0.5% has been reported for the production of SF 6 that is subsequently used in electrical equipment. 2 For China, emission factors during SF 6 production of % have been estimated S 2

3 23 Text Section S2: SF 6 emissions at equipment production The major manufacturers of electrical equipment are located in Asia and Europe. 4 During the production of equipment, SF 6 emissions depend on the production process, in particular whether SF 6 or e.g. helium is used for the tightness tests, 5 or whether SF 6 is used to fill up micro-cavities in the resin insulation of instrument transformers or bushings. 1 The IPCC suggests for the production of medium voltage equipment emission factors (total emissions during the manufacturing process divided by the total quantity of SF 6 contained in electrical equipment) of 7% and 29% for Europe and Japan, respectively, and for high voltage equipment emission factors of 8.5% and 29% S 3

4 34 Text Section S3: SF 6 emissions at use phase During the use phase of equipment, SF 6 might be emitted due to major failure/arc faults, due to maintenance losses and gas handling mistakes as well as due to natural leakage e.g. through sealings. SF 6 leakage rates vary strongly with the equipment s type, e.g. whether the pressure systems are closed or sealed. Sealed gas volumes (often medium voltage GIS) do not need to be re-filled, whereas closed gas volumes (mostly high voltage GIS) need to be regularly re-filled during the operating life. The IEC (International Electrotechnical Commission) standard limits the maximum annual leakage rate of SF 6 to 0.5% for closed pressure systems, such as high voltage GIS. Most medium voltage GIS are sealed pressure systems with annual leakage rates of < 0.1%. In contrast to the IEC standard, the IPCC suggests in its "Guidelines for National Greenhouse Gas Inventories (2006)" emission factors (total annual emissions divided by the total quantity of SF 6 contained in electrical equipment including leakage, major failures/arc faults, maintenance losses) of 0.2% and 0.7% for medium voltage GIS for Europe and Japan, respectively, and values of 2.6%, 0.7% and 14% for high voltage GIS in Europe, Japan and in the US, respectively. 1 These values might be outdated, since e.g. in the US, emission factors within EPA s Emission Reduction Partnership have decreased from 14% in 1999 to 2% in New equipment typically complies with the IEC standard and leakage rates are often far below 0.5% during testing. However, after about 20 years in operation, SF 6 leakage rates from high voltage GIS start increasing drastically with time. The average leakage rates can exceed 2% after 30 years in operation, due to corrosion of flanges and deterioration of sealings. 5,7 Whether electrical equipment produced today will show a similar increase of emission rates with time cannot yet be answered. Moreover, the measurement of small leakage rates under realistic conditions is challenging. 8 For the installed high voltage equipment in China s network, a relatively low averaged annual leakage of 0.08% and an annual maintenance/disposal emission factor of 4.3% have been given, 3 which result in good agreement of bottom-up with top-down estimates. 9 S 4

5 61 62 Figure S4: Vapor pressure curves for various gases 63 (a) 10 0 p (MPa) (b) p (MPa) N 2 O 2 CO 2 SF 6 CF 3 I C 4 F 7 N C 5 F 10 0 C 6 F 12 0 HFO 1234ze(Z) HFO 1234ze(E) HFO 1234yf T ( C) Figure S4: Vapor pressure curves for various gases, namely (a) N 2, 10 O 2, 11 CO 2, 12 SF 6, 13 CF 3 I, 14 C 4 F 7 N, 15 C 6 F 12 O 16 as well as (b) the 3 isomers of C 3 H 2 F 4 : HFO-1234yf, 17 HFO- 1234ze(Z) 18 and HFO-1234ze(E). 19 The vapor pressure curve of a pure compound defines the liquid-vapor phase transition. It is needed for the estimation of the dew point of a gas mixture, which defines the minimum operating temperature of equipment. 20 S 5

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