Gas-insulated medium or high-voltage electrical apparatus including carbon dioxide, oxygen, and heptafluoro-isobutyronitrile
09837801 · 2017-12-05
Assignee
Inventors
- Yannick KIEFFEL (Saint Jean de Bournay, FR)
- Alain Girodet (Chassieu, FR)
- Christophe Creusot (Pizay, FR)
- Jacques Porte (Lyons, FR)
Cpc classification
International classification
Abstract
The present invention provides medium- or high-voltage equipment including a leaktight enclosure in which there are located electrical components and a gas mixture for providing electrical insulation and/or for extinguishing electric arcs that are likely to occur in said enclosure, the gas mixture comprising heptafluoroisobutyronitrile, carbon dioxide, and oxygen in small quantities. Electrical components covered in a solid dielectric layer of varying thickness are located inside said leaktight enclosure of the equipment of the invention.
Claims
1. Medium- or high-voltage equipment including a leaktight enclosure in which there are located electrical components and a gas mixture for providing electrical insulation and/or for extinguishing electric arcs that are likely to occur in said enclosure, wherein the gas mixture consists of heptafluoroisobutyronitrile, carbon dioxide, and oxygen, the oxygen being present in said gaseous medium at a molar percentage lying in the range 1% to 25%.
2. Equipment according to claim 1, wherein the oxygen is present in said gas mixture at a molar percentage lying in the range 2% to 15% and, in particular, in the range 2% to 10%.
3. Equipment according to claim 1, wherein said heptafluoroisobutyronitrile is present in said gas mixture at a molar percentage (M.sub.he) that is not less than 80% of the molar percentage M, determined by formula (II):
M=(P.sub.he/P.sub.mixture)×100 (II) in which P.sub.mixture represents the total pressure of the mixture at 20° C. in the equipment and P.sub.he represents the partial pressure, expressed in the same units, that is equivalent at 20° C. to the saturated vapor pressure presented by heptafluoro-isobutyronitrile as defined above at the minimum utilization temperature of the equipment.
4. Equipment according to claim 1, wherein said heptafluoroisobutyronitrile is present in said gas mixture at a molar percentage (M.sub.he) that lies in the range 95% to 130%, better still in the range 97% to 120%, ideally in the range 99% to 110% of the molar percentage M, determined by formula (II):
M=(P.sub.he/P.sub.mixture)×100 (II) in which P.sub.mixture represents the total pressure of the mixture at 20° C. in the equipment and P.sub.he represents the partial pressure, expressed in the same units, that is equivalent at 20° C. to the saturated vapor pressure presented by heptafluoroisobutyronitrile as defined above at the minimum utilization temperature of the equipment, said equipment being medium-voltage or high-voltage equipment in which having some of the mixture in the liquid state does not reduce insulation.
5. Equipment according to claim 1, wherein said heptafluoroisobutyronitrile is present in said gas mixture at a molar percentage (M.sub.he) that lies in the range 95% to 100%, in particular in the range 98% to 100% of the molar percentage M, determined by formula (II):
M=(P.sub.he/P.sub.mixture)×100 (II) in which P.sub.mixture represents the total pressure of the mixture at 20° C. in the equipment and P.sub.he represents the partial pressure, expressed in the same units, that is equivalent at 20° C. to the saturated vapor pressure presented by heptafluoroisobutyronitrile as defined above at the minimum utilization temperature of the equipment, said equipment being medium-voltage or high-voltage equipment in which insulation may be affected by the presence of a liquid phase.
6. Equipment according to claim 1, wherein electrical components covered in a solid dielectric layer of varying thickness are located inside said leaktight enclosure.
7. Equipment according to claim 6, wherein, the thickness of said solid dielectric layer is a function of the utilization factor of the electric field, η, defined as the ratio of the mean electric field (U/d) divided by the maximum electric field Emax (η==U/(Emax*d)), and said solid dielectric layer is a thick layer presenting a thickness greater than 1 mm and less than 10 mm for utilization factors lying in the range 0.2 to 0.4.
8. Equipment according to claim 7, wherein the material(s) selected for making said thick solid dielectric layer present(s) relative permittivity that is less than or equal to 6.
9. Equipment according to claim 7, wherein the material(s) selected for making said thick solid dielectric layer present(s) relative permittivity that is less than or equal to 4 and in particular less than or equal to 3.
10. Equipment according to claim 8, wherein said material(s) are selected from: polytetrafluoroethylene, polyimide, polyethylene, polypropylene, polystyrene, polycarbonate, polymethyl methacrylate, polysulfone, polyetherimide, polyether ether ketone, parylene N™, Nuflon™, silicone, and epoxy resin.
11. Equipment according to claim 6, wherein the thickness of said solid dielectric layer is a function of the utilization factor of the electric field, η, defined as the ratio of the mean electric field (U/d) divided by the maximum electric field, Emax (η=U/(Emax*d)), and said solid dielectric layer is a thin layer presenting a thickness less than 1 mm, advantageously less than 500 μm, in particular lying in the range 60 to 100 μm for utilization factors greater than 0.5, and in particular greater than 0.6.
12. Equipment according to claim 11, wherein the material(s) selected for making said thin solid dielectric layer present relative permittivity lying in the range 2 to 4 and in particular in the range 2.5 to 3.5.
13. Equipment according to claim 11, wherein said material(s) is/are selected from polytetrafluoroethylene, polyimide, polyethylene, polypropylene, polystyrene, polyamide, ethylene-monochlorotrifluoroethylene, parylene N™, Nuflon™, HALAR™, and HALAR C™.
14. Equipment according to claim 1, wherein said equipment is a gas-insulated electrical transformer, a gas-insulated line for transporting or distributing electricity, an element for connecting to other pieces of equipment in the network, or a connector/disconnector.
15. A method for electrical insulation and/or for electric arc extinction comprising a step of utilizing equipment according to claim 6.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1)
(2)
(3)
(4)
(5)
(6)
DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS
(7) The invention is based on the use of a gas mixture having low environmental impact, combining heptafluoroisobutyronitrile as described above, at least one dilution gas, also called neutral gas or buffer gas, constituted by carbon dioxide, and oxygen.
(8) In the present invention, the expressions “dilution gas”, “neutral gas”, or “buffer gas” are equivalent and may be used interchangeably.
(9) Advantageously, heptafluoroisobutyronitrile is present in the equipment in entirely gaseous form whatever the utilization temperature of the equipment. It is therefore advisable for the pressure of the heptafluoroisobutyronitrile inside the equipment to be selected as a function of the saturated vapor pressure (SVP) presented by heptafluoroisobutyronitrile at the lowest utilization temperature of said equipment.
(10) However, since the equipment is usually filled with gas while at ambient temperature, the reference pressure of the heptafluoroisobutyronitrile used while filling the equipment is the pressure that corresponds to the SVP presented by heptafluoroisobutyronitrile at the lowest utilization temperature of said equipment, as raised to the filling temperature, e.g. 20° C.
(11) By way of example, the Table III below gives the saturated vapor pressures, referenced SVP.sub.i-C3F7CN and expressed in hectopascals, presented by heptafluoroisobutyronitrile at temperatures of 0° C., −5° C., −10° C., −15° C., −20° C., −25° C., −30° C., and −40° C., as well as the pressures, referenced P.sub.i-C3F7CN and expressed in hectopascals, which correspond to those saturated vapor pressures raised to 20° C.
(12) TABLE-US-00003 TABLE III saturated vapor pressure of i-C.sub.3F.sub.7CN SVP.sub.i-C3F7CN P.sub.i-C3F7CN Temperatures (hPa) (hPa) 0° C. 1177 1264 −5° C. 968 1058 −10° C. 788 877 −15° C. 634 720 −20° C. 504 583 −25° C. 395 466 −30° C. 305 368 −35° C. 232 286 −40° C. 173 218
Example of Application and Filling
(13) Depending on the equipment, the recommended pressure for filling with an electric insulation medium and/or an electric arc extinction medium varies. However, it is typically a pressure of several bars (i.e. a few thousand hectopascals).
(14) Heptafluoroisobutyronitrile is used in a mixture with carbon dioxide and various amounts of oxygen in order to be able to obtain the recommended filling pressure level.
(15) Thus, for example, equipment designed firstly for being used at a minimum temperature of −30° C., and secondly for being filled to 5 bars (i.e. 5000 hPa), at an ambient temperature of 20° C., should be filled with 0.368 bars (i.e. 368 hPa) of heptafluoroisobutyronitrile and 4.632 bars (i.e. 4632 hPa) of a dilution gas at that ambient temperature.
(16) Such equipment is in particular high-voltage equipment of the 145 kV (kilovolt) gas-insulated equipment (GIS) type as sold by Alstom under reference B65, designed for an application at −30° C. filled with a dilution gas/i-C.sub.3F.sub.7CN. For this equipment having a minimum application temperature of −30° C., heptafluoro-isobutyronitrile should be at a pressure of 0.368 bars absolute measured at 20° C. Buffer gas should be added in order to obtain the final properties of the gas mixture. More particularly, in the context of the present invention, CO.sub.2 is added in order to obtain the total pressure of the mixture. Some of the CO.sub.2 was replaced by oxygen so as to determine the contribution of oxygen to the total dielectric strength. Various molar ratios of oxygen were tested: 0%, 2%, 4%, 6%, 8%, and 10%.
(17) Since the partial pressure of heptafluoroisobutyronitrile is 0.368 bars absolute measured at 20° C. and the total pressure of the gas is 5 bars absolute, the molar ratio of i-C.sub.3F.sub.7CN is thus 0.368/5, i.e. about 7.4%.
(18) In order to determine the composition of the gas mixture for use during filling, a molar percentage M is determined for heptafluoroisobutyronitrile at the recommended filling pressure of the equipment, which percentage represents the maximum proportion of heptafluoroisobutyronitrile that the mixture of heptafluoroisobutyronitrile/(carbon dioxide+oxygen, if any), should include in order for there not to be any liquid in the enclosure of the equipment. The molar percentage M is given by the formula M=(P.sub.he/P.sub.mixture)×100, with P.sub.he representing the pressure, at the filling temperature (typically of the order of 20° C.), equivalent to the saturated vapor pressure SVP of heptafluoroisobutyronitrile at the minimum utilization temperature T.sub.min of the equipment (P.sub.he=(SVP.sub.he×293)/(273+T.sub.min)).
(19) Then, the molar percentage M.sub.he is selected as a function of M. In some circumstances, it is imperative that M.sub.he does not exceed M in order to avoid the presence of any liquid.
(20) However, it is sometimes possible, for example at medium voltage or for some high-voltage equipment for which insulation is not affected by the presence of a liquid phase, to have a little liquid at low or very low temperature, and then M.sub.he may reach 110% or even 130% of M. In addition, as heptafluoro-isobutyronitrile has better dielectric strength than neutral gases, it is desirable to optimize filling using heptafluoro-isobutyronitrile: therefore, it is preferable for M.sub.he to be selected so that it is not less than 80% of M, better still not less than 95% of M, better still not less than 98% of M, e.g. equal to 99% of M.
Example of Filling for 0% Oxygen (Comparative Example)
(21) Since the partial pressure of heptafluoroisobutyronitrile is 0.368 bars absolute measured at 20° C. and the total pressure of the gas is 5 bars absolute, the molar ratio of i-C.sub.3F.sub.7CN is thus 0.368/5, i.e. about 7.4%. To achieve this, additional CO.sub.2 was added until a total pressure of 5 bars absolute (4 bars relative) was reached.
(22) The equipment can be filled by adding gases starting with i-C.sub.3F.sub.7CN, which presents the lower saturated vapor pressure at the filling temperature (relative to CO.sub.2), then by adding CO.sub.2 until the total pressure of the mixture (4 bars relative) is reached, or it can be filled by means of a gas mixer enabling the ratio between i-C.sub.3F.sub.7CN and the carrier gas CO.sub.2 to be controlled, this ratio being held constant and equal to about 7.4% by pressure for the duration of filling by using a precision mass flowmeter.
Example of Filling for 2% Oxygen (Invention)
(23) Since the partial pressure of heptafluoroisobutyronitrile is 0.368 bars absolute measured at 20° C., firstly, pure O.sub.2 at 0.1 bars absolute was added and then CO.sub.2 was added until a total pressure of 5 bars absolute (4 bars relative) was reached. The molar ratio of i-C.sub.3F.sub.7CN was thus 0.368/5 i.e. about 7.4%; the molar ratio of O.sub.2 was 0.1/5 i.e. 2%; and the molar ratio of CO.sub.2 was 4.53/5 i.e. about 90.6%.
(24) The equipment can be filled by adding gases starting with i-C.sub.3F.sub.7CN, which presents the lowest saturated vapor pressure at the filling temperature (relative to CO.sub.2 and O.sub.2), then beginning by adding oxygen for greater accuracy, and then by adding CO.sub.2, until the total pressure of the mixture (4 bars relative) is reached, or it can be filled by means of a gas mixer enabling the ratio between i-C.sub.3F.sub.7CN and O.sub.2 with CO.sub.2, this ratio being held constant and equal to 7.4% by pressure for the duration of filling by using a precision mass flowmeter.
(25) Electric Results: Strength Tests at Power Frequency and Under a Lightning Impact at High Voltage
(26) These tests were carried out on a set of busbars of an ALSTOM B65 shielded substation having a rated voltage of 145 kV, in accordance with IEC standard 62271-1 relating to high-voltage equipment.
(27) The Table IV below shows the results obtained for a gaseous medium containing only CO.sub.2, only dry air, only SF.sub.6, or a mixture of CO.sub.2 and of heptafluoroisobutyronitrile (CO.sub.2/C.sub.3F.sub.7CN) in a molar ratio of 7.4/92.6, for an identical total pressure, i.e. 4 bars relative.
(28) TABLE-US-00004 TABLE IV Positive Negative Gaseous Power lightning lightning medium frequency (kV) impact (kVc) impact (kVc) CO.sub.2 176 366 −310 Dry air 211 334 −369 SF.sub.6 456 890 −889 CO.sub.2/i-C.sub.3F.sub.7CN 367 820 −685
(29) In addition, the dielectric strength of the mixtures CO.sub.2/i-C.sub.3F.sub.7CN (−30° C.) for various oxygen contents (0% to 10%) were measured: at 50 Hz: the minimum striking voltage (Min), the maximum striking voltage (Max), and the mean value over 30 measurements (mean) are given; under a lightning impact (negative (LI−) and positive (LI+) polarity): the voltage U50 that represents the voltage at which 50% breakdown takes place, as obtained by the rise and fall method, and the voltage U0, which is a withstand voltage (0% breakdown) are given.
(30) The results are presented below in Table V.
(31) TABLE-US-00005 TABLE V C.sub.3F.sub.7CN Bar abs 0.367 0.369 0.37 0.371 0.371 0.37 O.sub.2 Bar abs 0 0.105 0.207 0.308 0.405 0.506 CO.sub.2 Bar abs 4.683 4.576 4.473 4.361 4.284 4.174 Total pressure Bar abs 5.05 5.05 5.05 5.04 5.06 5.05 % C.sub.3F.sub.7CN % 7.3% 7.3% 7.3% 7.4% 7.3% 7.3% % O.sub.2 % 0.0% 2.1% 4.1% 6.1% 8.0% 10.0% 50 Hz mean 367 396 397 408 393 407 Min 286 347 354 355 331 324 Max 410 429 450 437 402 438 LI+ U50 820 869 874 888 880 894 U0 780 850 840 840 860 870 LI− U50 −685 −693 −701 −689 −665 −710 U0 −670 −680 −690 −670 −650 −690
(32) Using some of the results in Table V,
(33) From results shown in Table V, Table VI below shows the relative dielectric strengths relative to the mixture i-C.sub.3F.sub.7CN+CO.sub.2.
(34) TABLE-US-00006 TABLE VI 0 2 4 6 8 10 C.sub.3F.sub.7CN Bar abs 0.367 0.369 0.37 0.371 0.371 0.37 O.sub.2 Bar abs 0 0.105 0.207 0.308 0.405 0.506 CO.sub.2 Bar abs 4.683 4.576 4.473 4.361 4.284 4.174 Total pressure Bar abs 5.05 5.05 5.05 5.04 5.06 5.05 % C.sub.3F.sub.7CN % 7.3% 7.3% 7.3% 7.4% 7.3% 7.3% % O.sub.2 % 0.0% 2.1% 4.1% 6.1% 8.0% 10.0% mean 1.00 1.08 1.08 1.11 1.07 1.11 50 Hz Min 1.00 1.21 1.24 1.24 1.16 1.13 Max 1.00 1.05 1.10 1.07 0.98 1.07 LI+ U50 1.00 1.06 1.07 1.08 1.07 1.09 U0 1.00 1.09 1.08 1.08 1.10 1.12 LI− U50 1.00 1.01 1.02 1.01 0.97 1.04 U0 1.00 1.01 1.03 1.00 0.97 1.03
(35) Using some of the results in Table VI,
(36) An improvement in the dielectric properties of the mixtures is observed starting from the addition of 2% oxygen, in particular for the dielectric strength values: the minimum breakdown value at 50 Hz and the lightning impact value U0 especially in positive polarity, the improvement being smaller in negative polarity.
(37) The improvement in the dielectric properties is observed for an oxygen content of 2% to 10% with optimum dielectric properties for the addition of 2% to 6%, and a central value of 4%.
(38) In this context, the dielectric strengths of the reference gases (CO.sub.2, N.sub.2, SF.sub.6, CO.sub.2/i-C.sub.3F.sub.7CN) and of the CO.sub.2/i-C.sub.3F.sub.7CN/4 v % O.sub.2 mixture for an application temperature of −30° C. at power frequency were measured at power frequency as well as under a positive or a negative wave lightning impact in accordance with IEC standard 62271-1 in the same configurations (GIS 145 kV sold under Alstom reference B65 designed for application at −30° C.) The results are presented below in Table VII.
(39) TABLE-US-00007 TABLE VII CO.sub.2/ CO.sub.2/ i-C.sub.3F.sub.7CN i-C.sub.3F.sub.7CN/4% O.sub.2 CO.sub.2 N.sub.2 (−30° C.) (−30° C.) SF.sub.6 Power 176 211 367 397 456 frequency (kV) Positive 366 334 820 874 890 lightning impact (kVc) Positive −310 −369 −685 −701 −889 lightning impact (kVc)
(40) The addition of 4% oxygen makes it possible to improve in a significant manner the dielectric strength of the total gas mixture at power frequency and under lightning impact (positive and negative polarities) and to reach 87% of the strength of SF.sub.6 in the equipment at 50 Hz, 98% under positive polarity lightning impact, and 78% under negative polarity lightning impact.
(41) Toxicity
(42) Heptafluoroisobutyronitrile presents no specific toxicity for humans and has an LC50 (lethal concentration, 50%) that is greater than 15,000 ppm. In addition, by diluting it to about 7% in CO.sub.2 or in air, toxicity is further reduced by the molar or volume ratio of the mixture in order to reach an LC50 of the order of 70,000 ppm for the mixture, which classifies it in the field of gases considered to be “practically non-toxic” (toxicity classification 5, according to the Hodge and Sterner toxicity scale).
(43) Flammability
(44) Pure heptafluoroisobutyronitrile, as well as the i-C.sub.3F.sub.7CN/CO.sub.2 mixtures having a low oxygen content are non-flammable.
(45) Environmental Impact/GWP
(46) The global warming potential or GWP of heptafluoro-isobutyronitrile is of the order of 2400, i.e. 9.5 times lower than that of SF.sub.6 and more than 3.1 times lower than that of a mixture of SF.sub.6 and nitrogen at 10% by volume of SF.sub.6.
(47) Heptafluoroisobutyronitrile presents a molar mass of 195 grams per mole (g/mol).
(48) The GWP of the gas mixture is calculated in accordance with the May 17, 2006 Regulation (EC) No. 842/2006 of the European Parliament and of the Council on certain fluorinated greenhouse gases, Part 2 “Method of calculating the total global warming potential (GWP) for a preparation”. According to that text, the GWP factor of a gas mixture is a weighted average, using the weight fraction of each substance multiplied by its GWP factor.
(49) In use in a mixture at 7.4% molar percent in CO.sub.2 (44 g/mol) plus oxygen at 4%, the fraction by weight of heptafluoro-isobutyronitrile is 26%, therefore the GWP of the mixture is of the order of 630, which represents a reduction of the order of 97.2% compared with the carbon equivalent for pure SF.sub.6 (Table VIII).
(50) TABLE-US-00008 TABLE VIII Weight Molar P molar % fraction Gas mass GWP (bar abs) (% P) (w %) i-C.sub.3F.sub.7CN 195 2400 0.37 7.40% 26.21% O.sub.2 32 0 0.207 3.71% 2.16% CO.sub.2 44 1 5 89.65% 71.64% Total P 6 GWP of mixture = 630 Reduction/SF.sub.6 = 97.2%
(51) End of Life
(52) At the end of its life or after circuit-breaking tests, the gas can be recovered by means of conventional recovery techniques using a compressor and a vacuum pump. The heptafluoroisobutyronitrile is then separated from the carbon dioxide and oxygen using a zeolite capable of trapping only the smaller-sized carbon dioxide and the oxygen; alternatively, a selective separation membrane allows the carbon dioxide and the oxygen to escape and retains the heptafluoroisobutyronitrile, which has greater size and molar mass; any other option may be envisaged.
(53) Association with Solid Insulation
(54) So as to obtain dielectric equivalence with SF.sub.6, (reaching 100% of the strength of SF.sub.6), without reducing its performance at low temperature or increasing the total amount of pressure, the gas mixture presented above is used in combination with solid insulation having low dielectric permittivity that is applied on those conductive parts that are subjected to an electric field that is greater than the breakdown field of the system without solid insulation.
(55) The solid insulation implemented in the context of the present invention is in the form of a layer of thickness that varies for a given piece of equipment. The implemented insulating layer may present low thickness (thin or fine layer), or high thickness (thick layer).
(56) Since the thickness of the insulating layer is a function of the utilization factor of the electrical field, η, defined as the ratio of the mean electric field (U/d) divided by the maximum electric field Emax (η=U/(Emax*d)), the layer is thick for utilization factors close to 0.3, and the layer is thin for utilization factors approaching 0.9.
(57) The calculations presented in
(58) This solution therefore makes it possible to reduce, in significant manner, the maximum electric field on the gaseous phase and thus to increase the total dielectric strength of the “mixed” insulation that is made up in series of solid insulation and of gas insulation. This phenomenon of reducing the electrical field acting on the gaseous phase is more pronounced when the dielectric permittivity of the solid layer is low.
(59) In the example presented, the hybrid insulation is composed of solid spherical insulation of a thickness of 10 mm in combination with gas insulation of a thickness of 15 mm, the total insulation being of a thickness of 25 mm. Electric field calculation was performed for two different configurations of solid insulation presenting significantly different relative permittivities, typically of 5.3 and 2.9.
(60) In this precise example, the factor by which the electric field in the gaseous phase is reduced is of the order of 15% for solid insulation having dielectric permittivity of 5.3 and of the order of 30% for solid insulation having dielectric permittivity of 2.9. In the invention, a material presenting relative permittivity of the order of 3 or less is preferred for making the thick layers in the electrodes.
(61) These dielectric calculations have been confirmed by measurements performed on equipment presenting an improvement factor of the order of 20% in dielectric strength (relative to a non-covered electrode) for a thick layer made of epoxy resin presenting relative permittivity of the order of 5 and an improvement factor of the order of 30% (relative to a non-covered electrode) in dielectric strength for a thick layer made of silicone presenting relative permittivity of the order of 3.
(62) For the thin layers made on the electrical parts subjected to weaker electric fields, the materials used present dielectric permittivities of the order of 3 and they are applied in the form of thin layers having thickness that is typically of the order of 60 to 100 μm. The results obtained using equipment with thin layer deposits of the order of 60 to 100 μm of Nuflon™ (relative permittivity of 2.7) or parylene N (relative permittivity of 2.65) deposited on electrodes show improvement factors for dielectric strength of the order of 8% relative to a non-covered electrode.
(63) In the context of the present invention, the equipment that is shown in part in a diagram in
(64) The combination of the two technologies in one hybrid insulation, comprising both gas-insulation of the CO.sub.2/i-C.sub.3F.sub.7CN/O.sub.2 type and in particular O.sub.2 at 4 v % together with a solid insulation in the form of a thick layer at locations having a weak field utilization factor and in the form of a thin layer at locations having a strong field utilization factor, makes it possible to obtain total insulation equivalent to that of SF.sub.6 without any significant increase in pressure and without modifying the minimum utilization temperature.
REFERENCES
(65) [1] European patent application, in the name of Mitsubishi Denki Kabushiki Kaisha, having publication number 0 131 922 on Jan. 23, 1985. [2] U.S. Pat. No. 4,547,316, in the name of Mitsubishi Denki Kabushiki Kaisha, published on Oct. 15, 1985. [3] International application WO 2008/073790, in the name of Honeywell International Inc., published on Jun. 19, 2008. [4] International application WO 2012/080246, in the name of ABB Technology AG., published on Jun. 21, 2012. [5] European patent application, in the name of Mitsubishi Denki Kabushiki Kaisha, having publication number 1 724 802 on Nov. 22, 2006.