Overhead conductor with self-cleaning coating

Abstract

A single coated conductor for an overhead power transmission or distribution line is provided comprising one or more electrical conductors (400) and a first coating (401) provided on at least a portion of the one or more electrical conductors (400). The first coating (401) comprises: (i) an inorganic binder comprising an alkali metal silicate; (ii) a polymerisation agent comprising nanosilica (“nS”) or colloidal silica (SiO.sub.2); and (iii) a photocatalytic agent, wherein the photocatalytic agent comprises ≥70 wt % anatase titanium dioxide (TiO.sub.2) having an average particle size (“aps”) ≤100 nm. The first coating (401) has an average thermal emissivity coefficient E≥0.90 across the infrared spectrum 2.5-30.0 μm and has an average solar reflectivity coefficient R≥0.90 and/or an average solar absorptivity coefficient A≤0.10 across the solar spectrum 0.3-2.5 μm.

Claims

1. A single coated conductor for an overhead power transmission or distribution line comprising: one or more electrical conductors; and a first coating provided on at least a portion of the one or more electrical conductors, wherein the first coating comprises: (i) an inorganic binder comprising an alkali metal silicate; (ii) a polymerisation agent comprising nanosilica (“nS”) or colloidal silica (SiO2); and (iii) a photocatalytic agent, wherein the photocatalytic agent comprises ≥70 wt % anatase titanium dioxide (TiO2) having an average particle size (“aps”) ≤100 nm; wherein the first coating has an average thermal emissivity coefficient E≥0.90 across the infrared spectrum 2.5-30.0 μm and has an average solar reflectivity coefficient R≥0.90 and/or an average solar absorptivity coefficient A≤0.10 across the solar spectrum 0.3-2.5 μm.

2. A single coated conductor as claimed in claim 1, wherein the alkali metal silicate comprises potassium silicate (K2SiO3), sodium silicate, or lithium silicate (Li2SiO3).

3. A single coated conductor as claimed in claim 2, wherein the sodium silicate comprises sodium metasilicate (Na2SiO3), sodium orthosilicate (Na4SiO4) or sodium pyrosilicate (Na6Si2O7).

4. A single coated conductor as claimed in claim 1, wherein the alkali metal silicate comprises a water based coating which is dehydrated, dried or cured after the first coating is provided on at least a portion of the one or more electrical conductors.

5. A single coated conductor as claimed in claim 1, wherein the photocatalytic agent comprises ≥75 wt % anatase titanium dioxide (TiO2).

6. A single coated conductor as claimed in claim 1, further comprising a reflective agent comprising rutile titanium dioxide.

7. A single coated conductor as claimed in claim 6, wherein the rutile titanium dioxide (TiO2) has an average particle size (“aps”) ≥100 nm.

8. A single coated conductor as claimed in claim 6, wherein the rutile titanium dioxide (TiO2) comprises substantially spherical particles.

9. A single coated conductor as claimed in claim 6, wherein the reflective agent comprises sodium aluminosilicate (AlNa12SiO5).

10. A single coated conductor as claimed in claim 6, wherein the reflective agent comprises a white filler which comprises: (i) magnesium oxide (MgO); (ii) calcium oxide (CaO); (iii) aluminum oxide (Al2O3); (iv) zinc oxide (ZnO); (v) calcium carbonate (CaCO3); (vi) aluminum silicate (Al2SiO5); (vii) kaolin (Al2O3.2SiO2); (viii) titanium dioxide (TiO2); or (viii) barium sulphate (BaSO4).

11. A single coated conductor as claimed in claim 1, further comprising an emissive agent which comprises an inorganic filler.

12. A single coated conductor as claimed in claim 11, wherein the inorganic filler comprises either: (i) calcium carbonate (CaCO3); (ii) calcined kaolin (Al.sub.2O.sub.3.2SiO2); or (iii) talc (hydrated magnesium silicate (H2Mg3(SiO3)4 or Mg3Si4O10(OH)2)).

13. A single coated conductor as claimed in claim 1, further comprising a curing agent selected from: (i) zinc oxide (ZnO); (ii) zinc stearate (C36H70O4Zn); (iii) trimagnesium orthophosphate (Mg3O8P2); (iv) magnesium oxide (MgO); (v) magnesium carbonate (MgCO3); and (vi) magnesium hydroxide (Mg(OH)2).

14. A single coated conductor as claimed in claim 1, further comprising an emulsion agent and/or a rheology agent selected from (i) hydroxyethyl cellulose; and (ii) polydimethylsiloxane.

15. A single coated conductor as claimed in claim 1, wherein the first coating is substantially white in colour has a L*≥80.

16. A single coated conductor as claimed in claim 1, wherein the first coating has an average thermal emissivity coefficient E≥0.90 across the infrared spectrum 2.5-30.0 μm when tested in accordance with ASTM E408 (2013) and/or an average solar reflectivity coefficient R≥0.90 and/or an average solar absorptivity coefficient A≤0.10 across the solar spectrum 0.3-2.5 μm when tested in accordance with ASTM E903 (2012).

17. A single coated conductor as claimed in claim 1, wherein the single coated conductor when tested in accordance with ANSI C19.4-2004 operates at a lower temperature than the temperature of the same one or more electrical conductors without the first coating.

18. A single coated conductor as claimed in claim 1, wherein the first coating has a thickness in the range >1 micron.

19. A kit for coating one or more electrical conductors to form a single coated conductor for an overhead power transmission or distribution line, the kit comprising: a first part comprising: (i) an inorganic binder comprising an alkali metal silicate; (ii) a polymerisation agent comprising nanosilica (“nS”) or colloidal silica (SiO2); and (iii) a photocatalytic agent, wherein the photocatalytic agent comprises ≥70 wt % anatase titanium dioxide (TiO2) having an average particle size (“aps”) ≤100 nm; and a second part comprising: (i) a curing agent; wherein, in use, the first and second parts are mixed together to form a first mixture and the first mixture is then sprayed, painted, coated or applied on to at least a portion of one or more electric conductors to form a first coating, wherein the first coating has an average thermal emissivity coefficient E≥0.90 across the infrared spectrum 2.5-30.0 μm and an average solar reflectivity coefficient R≥0.90 and/or an average solar absorptivity coefficient A≤0.10 across the solar spectrum 0.3-2.5 μm.

20. A kit as claimed in claim 19, wherein the inorganic binder comprises a water based inorganic binder.

21. A method of coating one or more electrical conductors to form a single coated conductor for an overhead power transmission or distribution line comprising: spraying, painting, coating or applying a first coating on to at least a portion of one or more electrical conductors, wherein the first coating comprises: (i) an inorganic binder comprising an alkali metal silicate; (ii) a polymerisation agent comprising nanosilica (“nS”) or colloidal silica (SiO2); and (iii) a photocatalytic agent, wherein the photocatalytic agent comprises ≥70 wt % anatase titanium dioxide (TiO.sub.2) having an average particle size (“aps”) ≤100 nm; wherein the first coating has an average thermal emissivity coefficient E≥0.90 across the infrared spectrum 2.5-30.0 μm and has an average solar reflectivity coefficient R≥0.90 and/or an average solar absorptivity coefficient A≤0.10 across the solar spectrum 0.3-2.5 μm.

22. A method as claimed in claim 21, wherein the inorganic binder comprises a water based inorganic binder and the method further comprises dehydrating, drying or curing the inorganic binder.

23. A method as claimed in claim 21, further comprising thermally curing the first coating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments of the present invention together with other arrangements given for illustrative purposes will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1 illustrates some of the heat transfer mechanisms associated with an overhead electrical conductor including gaining energy by solar radiation and losing energy by conductor radiation and by convection (wind);

(3) FIG. 2A shows a side view of a known coated conductor and FIG. 2B shows a cross-sectional view of the known coated conductor;

(4) FIG. 3A shows a cross-sectional view of a known single coated conductor, FIG. 3B shows a cross-sectional view of a known 6/1 ACSR conductor with a coating, FIG. 3C shows a cross-sectional view of a known 26/7 ACSR conductor with a coating and FIG. 3D shows a cross-sectional view of a known 54/19 ACSR conductor with a coating;

(5) FIG. 4 shows a single coated conductor according to a preferred embodiment of the present invention;

(6) FIG. 5 shows how the ampacity of different types of conductors varies as a function of solar irradiance;

(7) FIG. 6 shows UV-VIS-NIR absorbance spectra of a layer having a high solar reflectance according to an embodiment of the present invention;

(8) FIG. 7 shows the solar spectrum from 0.3-2.5 μm for comparison purposes with FIG. 6;

(9) FIG. 8 shows a test aluminium conductor;

(10) FIG. 9 shows test data relating to the mean temperatures of different test conductors over a peak solar irradiation period;

(11) FIG. 10 shows test data relating to the mean temperatures of different test conductors over a peak solar irradiation period and illustrates the significantly improved performance of a single coated conductor according to a preferred embodiment of the present invention operating at elevated temperatures up to 250° C.;

(12) FIG. 11 shows the reflectance of anatase and rutile titanium dioxide (TiO.sub.2) pigments as a function of wavelength;

(13) FIG. 12 shows the results of a current cycling test and shows that a preferred coated conductor according to an embodiment of the present invention was particularly effective in reducing the temperature of an Aluminium Conductor Steel Reinforced (“ACSR”) conductor;

(14) FIG. 13 shows the results of a current cycling test performed on a preferred coated conductor according to an embodiment of the present invention in terms of the temperature reduction (%) per cycle;

(15) FIG. 14 shows the results of an outdoor cooling performance test performed on a preferred coated conductor according to an embodiment of the present invention; and

(16) FIG. 15 shows the temperature reduction (%) difference between a preferred coated conductor according to an embodiment of the present invention and an uncoated conductor during a week in the month of May in the United Kingdom.

DETAILED DESCRIPTION

(17) Various embodiments of the present invention together with conventional arrangements given for illustrative purposes will now be discussed in more detail.

(18) FIG. 1 illustrates some of the heat transfer mechanisms associated with an overhead conductor 100.

(19) There are two predominate heat transfer mechanisms which will cause the temperature of the conductor 100 to rise. The first heat transfer mechanism is solar radiative heating of the conductor 100. It will be understood that incident solar radiation upon the conductor 100 will result in the temperature of the electrical conductor 100 increasing.

(20) The second heat transfer mechanism (not shown in FIG. 1) which will cause the temperature of the conductor 100 to rise is the effect of Ohmic losses due to the transmission of electrical current through the conductor 100. The resistance of the conductor 100 to the transmission of electrical current through the conductor 100 will result in Joule heating of the conductor 100.

(21) Accordingly, the combined effect of solar radiative heating of the conductor 100 and Joule heating will cause the temperature of the conductor 100 to rise.

(22) The gain in energy of the conductor 100 may be offset by three thermal transfer mechanisms through which the conductor 100 may lose energy namely by radiation, conduction and convection.

(23) Heat loss by conduction is negligible. Heat loss by convection (i.e. due to air currents or wind) will be dependent upon the geographic location of the conductor 100. A conductor 100 may be deployed in a hot region of the world such as Southern USA, the Middle East or Australia. Winds in non-coastal regions may be relatively light and hence heat loss by convection may not normally be a significant consideration. Accordingly, the predominant mechanism by which a conductor 100 may lose energy is by thermal radiation.

(24) It will be understood by those skilled in the art that overhead bare conductors as are conventionally deployed in regions of the world such as Southern USA, the Middle East and Australia can reach significantly elevated temperatures. Accordingly, the issue of being able to reduce the operational temperature of an overhead conductor deployed in a region of the world such as Southern USA, the Middle East and Australia is of considerably commercial concern to e.g. utilities companies.

(25) High voltage power lines in many countries are considered to form part of the national infrastructure and hence may be state owned and controlled.

(26) Overhead electricity transmission lines generally comprise a core formed of one or more conductive wires. Various different types of overhead conductors are known.

(27) All Aluminium Conductors (“AAC”) comprise hard drawn aluminium wires stranded in successive layers in opposite directions to form the conductor as per BS EN 50182 or IEC 61089. AAC conductors may be used for aerial distribution lines having relatively short spans, aerial feeders and bus bars of substations. AAC conductors have a high corrosion resistance since steel is not present. Conventional AAC conductors are typically rated up to a maximum operating temperature of 80° C.

(28) All Aluminium Alloy Conductors (“AAAC”) comprise All Aluminium Alloy (“ALMELEC”) wires stranded in successive layers in opposite directions to form the conductor as per IEC 61089, BS EN 50182 or ASTM B 399. AAAC conductors are mainly used for overhead lines in transmission and distribution electrical networks having relatively long spans. They are also used as a messenger to support overhead electrical cables. AAAC conductors have a high corrosion resistance since steel is not present. Conventional AAAC conductors are typically rated up to a maximum operating temperature of 80° C.

(29) Aluminium Conductor Steel Reinforced (“ACSR”) conductors comprise an outer layer of aluminium conductor concentrically stranded over a central core of galvanized or stranded steel wires to form the conductor as per BS EN 50182, ASTM B 232 or IEC 61089. ACSR conductors are widely used for electrical power transmission over long distances. ACSR conductors may also be used as a messenger for supporting overhead electrical cables. Conventional ACSR conductors are typically rated up to a maximum operating temperature of 80° C.

(30) Aluminium Conductor Aluminium Clad Steel Reinforced (“ACSR/AW”) conductors comprise an outer layer of aluminium conductor concentrically stranded over a central core of aluminium clad steel solid or stranded cable to form the conductor as per ASTM B 549. ACSR/AW conductors are used for electrical power transmission and are ideal for long overhead lines spans like ACSR conductors but with slightly better resistance and current carrying capacity in addition to good corrosion resistance. Conventional ACSR/AW conductors are typically rated up to a maximum operating temperature of 80° C.

(31) Areal Bundled Cables (“ABC”) are made from aluminium conductors which are insulated by XLPE insulation and assembled to form two (Duplex), three (Triplex), four (Quadruplex) or more conductors as per ICEA S 474-76 or BS EN 50182. They are used for secondary overhead lines (in circuits not exceeding 600 V phase to phase) on poles or as feeders to residential premises.

(32) Various High Temperature Low Sag (“HTLS”) conductors are also known which are designed to operate at significantly higher operational temperatures of up to 150-250° C.

(33) Known HTLS conductors include Aluminium Conductor Composite Core (“ACCC”) conductors, Aluminium Conductor Steel Supported (“ACSS/MA”) conductors, Aluminium Conductor Aluminium Clad Steel Supported (“ACSS/AW”) conductors, Thermal Resistant Aluminium Alloy Conductor Steel Reinforced (“TACSR”) conductors, Thermal Resistant Aluminium Alloy Conductor Aluminium Clad Steel Reinforced (“TACSR/AW”) conductors and Super Thermal Resistant Aluminium Alloy Conductor Aluminium Clad Invar Reinforced (“STACIR/AW”) conductors.

(34) Aluminium Conductor Composite Core (“ACCC”) conductors comprise a concentrically stranded conductor with one or more layers of trapezoidal shaped annealed 1350-O aluminium wires on a central core of light weight carbon-glass fibre composite. ACCC conductors comprising a hybrid carbon composite core are stronger and lighter than traditional steel cores. ACCC conductors are capable of carrying twice the current of traditional ACSR conductors as ACCC conductors are designed for continuous operating temperatures of up to 180° C. in addition to its lighter core which allows approx. 30% more aluminium to be used without increasing the total weight. Usage of ACCC conductors reduces line losses by 30-40% under equal load conditions compared with traditional ACSR conductors of the same diameter and weight. ACCC conductors have greater strength, effective self-damping, superior fatigue resistance and a low coefficient of expansion thereby reducing conductor sag under heavy electrical load conditions. As a result, ACCC conductors can be used to increase spans between fewer or shorter structures. ACCC conductors have greater corrosion resistance than traditional ACSR conductors.

(35) ACCC conductors are used for overhead distribution and transmission lines and are particularly useful in reconductoring applications requiring increased current with existing tensions and clearances, new line applications where structures can be economised due to reduced conductor sag, new line applications requiring high emergency loading and lines where vibration due to wind is a problem. ACCC conductors can also be used at corrosive and coastal environments due to their good corrosion resistance. Conventional ACCC conductors are typically rated up to a maximum operating temperature of 180° C.

(36) Aluminium Conductor Steel Supported (“ACSS/MA”) conductors comprise one or more layers of annealed aluminium 1350-O wires stranded over a central core of zinc-5% aluminium mischmetal alloy coated steel wires that are designed to withstand most or all of the mechanical load on the ACSS conductor. ACSS conductors may be manufactured according to ASTM B 856.

(37) ACSS/MA conductors are similar to traditional ACSR conductors except that ACSS/MA conductors can be operated continuously at high temperatures up to 250° C. without damage. ACSS/MA conductors sag less under emergency loading than ACSR conductors, have self-damping properties and final sag is not affected by long time creep of the aluminium.

(38) ACSS/MA conductors are used for overhead distribution and transmission lines and are particularly useful in reconductoring applications requiring increased current with existing tensions and clearances. ACSS/MA conductors are also used for new line applications where structures can be economised due to reduced conductor sag, new line applications requiring high emergency loadings and lines where vibration due to wind is a problem. Conventional ACSS/MA conductors are typically rated up to a maximum operating temperature of 250° C.

(39) Aluminium Conductor Aluminium Clad Steel Supported (“ACSS/AW”) conductors comprise one or more layers of annealed aluminium 1350-O wires stranded over a central core of aluminium clad steel wires that are designed to withstand most or all of the mechanical load on ACSS/AW conductors. ACSS/AW conductors may be manufactured according to ASTM B 856.

(40) ACSS/AW conductors can operate continuously at high temperatures up to 200° C. without damage. The aluminium clad steel core which consists of a thick layer of aluminium (approx. 10% of the nominal wire radius) over steel gives ACSS/AW conductors the advantages of ACSS conductors along with light weight and good conductivity of aluminium with the high tensile strength and ruggedness of steel.

(41) ACSS/AW conductors are used for overhead distribution and transmission lines and are especially useful in reconductoring applications requiring increased current with existing tensions and clearances. ACSS/AW conductors are also used for new line applications where structures can be economised due to reduced conductor sag, new line applications requiring high emergency loadings and lines where vibration due to wind is a problem.

(42) ACSS/AW conductors have strength characteristics similar to ACSS conductors along with slightly greater ampacity and resistance to corrosion due to aluminium cladding of the steel core wires. Conventional ACSS/AW conductors are typically rated up to a maximum operating temperature of 200° C.

(43) Thermal Resistant Aluminium Alloy Conductor Steel Reinforced (“TACSR”) conductors comprise one or more layers of thermal resistant aluminium zirconium alloy (AT1) wires stranded over a central core of zinc coated steel wire(s) as per IEC 62004 and IEC 60888 and generally according to IEC 61089.

(44) TACSR conductors are able to carry higher (150%) load current than traditional ACSR conductors as they are designed for continuous operating temperatures of up to 150° C. TACSR conductors have the same installation technique as ACSR conductors.

(45) TACSR conductors are used for overhead distribution and transmission lines and are particularly useful in new line applications requiring increased current. Conventional TACSR conductors are typically rated up to a maximum operating temperature of 150° C.

(46) Thermal Resistant Aluminium Alloy Conductor Aluminium Clad Steel Reinforced (“TACSR/AW”) conductors comprise one or more layers of thermal resistant aluminium zirconium alloy (AT1) wires stranded over a central core of stranded aluminium clad steel (20SA Type A) wire(s) as per IEC 62004 and IEC 61232 and generally according to IEC 61089.

(47) TACSR/AW conductors are able to carry higher load current than traditional ACSR conductors as they are designed for continuous operating temperatures of up to 150° C. TACSR/AW conductors have increased corrosion resistance and lower electrical resistance and lower mass than TACSR conductors. TACSR/AW conductors have the same installation technique as ACSR conductors.

(48) TACSR/AW conductors are used for overhead distribution and transmission lines and are particularly useful in new line applications requiring increased current. TACSR/AW may be used at corrosive and coastal environments due to their good corrosion resistance. Conventional TACSR/AW conductors are typically rated up to a maximum operating temperature of 150° C.

(49) Super Thermal Resistant Aluminium Alloy Conductor Aluminium Clad Invar Reinforced (“STACIR/AW”) conductors comprise one or more layers of super thermal resistant aluminium zirconium alloy (AT3) wires stranded over a central core of stranded aluminium clad invar wires as per IEC 62004 and generally according to IEC 61089 and IEC 61232. Invar is a special Fe/Ni alloy having a very low coefficient of linear expansion.

(50) STACIR/AW conductors are able to carry higher (200%) load current than traditional ACSR conductors as they are designed for continuous operating temperatures of up to 210° C. Beyond knee point STACIR/AW conductors experience a sag increase due to the expansion of the Invar core alone (extremely low value ≤3.7×10.sup.−6/° C.) which controls sag at high operating temperatures. STACIR/AW conductors have increased corrosion resistance and have the same installation technique as ACSR conductors.

(51) STACIR/AW conductors are used for overhead distribution and transmission lines and are particularly useful in new line applications requiring increased current. STACIR/AW conductors may be used at corrosive and coastal environments due to their good corrosion resistance. Conventional STACIR/AW conductors are typically rated up to a maximum operating temperature of 210° C.

(52) Accordingly, known HTLS conductors enable high voltage overhead electric conductors to be operated at significantly higher operating temperatures up to a maximum operating temperature typically in the range 150-250° C.

(53) FIG. 2A shows a side view and FIG. 2B shows a cross-sectional view of a known coated conductor 200 as disclosed in WO 2015/105972 (Ranganathan). The known conductor 200 comprises 19 aluminium cables or wires 202 surrounded by an outer polymeric coating 201. Gaps 203 may be present between the outer polymeric coating 201 and the individual conductive cables or wires 202. The outer polymeric coating 201 is provided in order to decrease the temperature of the conductor 200 when the conductor 200 is tested in accordance with ANSI C119.4.

(54) FIG. 3A shows a cross-sectional view of another known conductor having a central aluminium core 301 and a single outer polymeric coating 302.

(55) FIG. 3B shows a cross-sectional view of a known 6/1 ACSR conductor comprising a central steel reinforcing element 303 surrounded by a ring of six aluminium electrical wires 310. Each of the six aluminium wires 310 has a polymeric coating 302.

(56) FIG. 3C shows a cross-sectional view of a known 26/7 ACSR conductor comprising seven central steel reinforcing elements 303 surrounded by a first ring of aluminium wires 310 which in turn are surrounded by a second ring of aluminium wires 310. The second outer ring of aluminium wires are enclosed by an outermost polymeric coating 302.

(57) FIG. 3D shows a known 54/19 ACSR conductor comprising 19 central steel reinforcing elements 303 surrounded by a first ring of aluminium wires 310 which are in turn surrounded by a second ring of aluminium wires 310. The second ring of aluminium wires 310 are in turn surrounded by a third ring of aluminium wires 310. The third outer ring of aluminium wires 310 is enclosed by an outermost polymeric coating 302.

(58) FIG. 4 shows a single coated conductor according to a preferred embodiment of the present invention. The single coated conductor comprises an inner metallic conductor 400 preferably of aluminium. The inner metallic conductor 400 may comprise one or more steel reinforcing elements (not shown) and/or one or more composite elements.

(59) The single coated conductor according to a preferred embodiment of the present invention preferably comprises a first inorganic coating 401 surrounding the metallic conductor 400. The first coating 401 includes a self-cleaning photocatalytic agent comprising anatase titanium dioxide (TiO.sub.2).

(60) According to the present invention one or more electrical conductors 400 are provided which have a first coating or layer 401 which has an average thermal emissivity coefficient E≥0.90 and an average solar reflectivity coefficient R≥0.90 and/or an average solar absorptivity coefficient A≤0.10.

(61) The one more electrical conductors 400 may form part of an overhead power transmission or distribution line.

(62) The first coating or layer 401 preferably comprises: (i) an inorganic binder optionally comprising an alkali metal silicate; (ii) a polymerisation agent optionally comprising nanosilica (“nS”) or colloidal silica (SiO.sub.2); (iii) optionally a reflective agent such as rutile titanium dioxide (TiO.sub.2) having an average particle size ≥250 nm; and (iv) a photocatalytic agent, wherein the photocatalytic agent optionally comprises ≥70 wt % anatase titanium dioxide (TiO.sub.2) optionally having an average particle size ≤100 nm.

(63) The first coating or layer 401 preferably has an average thermal emissivity coefficient E≥0.90 across at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the infrared spectrum 2.5-30.0 μm.

(64) The first coating or layer 401 preferably has an average solar reflectivity coefficient R≥0.90 and/or an average solar absorptivity coefficient A≤0.10 across at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the solar spectrum 0.3-2.5 μm.

(65) According to an embodiment the first coating 401 may be provided on at least a portion of the one or more electrical conductors 400.

(66) A single coated conductor according to the present invention has been tested and found to have a good or excellent corrosion resistance when tested in accordance with ASTM B117 (Salt spray) testing procedure.

(67) Using the industry standard CIGRE 207-2002 method of calculating conductor temperature the importance of utilising a single coated conductor having a high solar reflectivity coating in regions with high solar radiation will now be demonstrated. For illustrative purposes only, a power line may be considered which is deployed at a location 30° North in latitude and which is exposed to 12 hours of August solar radiation. The air temperature is modelled as being 40° C.

(68) Under the above conditions a Drake ACSR overhead electrical conductor with different coatings transmitting a constant current of 1000 A will have the following characteristics:

(69) TABLE-US-00001 TABLE 1 Conductor Conductor temperature resistance Optical characteristics (° C.) Ohms/km Uncoated conductor 99.1 0.0945 Emissivity: 0.5 Absorptivity: 0.5 Reflectivity: 0.5 Conductor having a grey emissive 91.1 0.0921 coating Emissivity: 0.86 Absorptivity: 0.55 Reflectivity: 0.45 A single coated conductor according 83.3 0.0898 to a preferred embodiment of the present invention having both high emissivity and high reflectivity Emissivity: 0.95 Absorptivity: 0.1 Reflectivity: 0.9

(70) The figures shown above in Table 1 were calculated using the industry standard CIGRE model and demonstrate that a single coated conductor according to a preferred embodiment of the present invention having both high reflectivity and high emissivity results in nearly a doubling of the cooling effect (×1.975 15.8° C. c.f. 8.0° C.) relative to a conventional conductor having a grey coating. As detailed below, the above calculations were further confirmed through empirical testing using two different test rigs.

(71) A single coated conductor according to a preferred embodiment of the present invention having both an increased emissivity and at the same time a high reflectivity (i.e. without increasing solar absorption) is shown to be particularly effective and to provide a significantly improved performance relative to conventional arrangements operating at temperatures up to 100° C. (as per Table 1 above) and also at elevated temperatures in the range 150-250° C. (data shown below).

(72) The first coating 401 may comprise a white filler. The white filler may, for example, comprise: (i) magnesium oxide (MgO); (ii) calcium oxide (CaO); (iii) aluminium oxide (Al.sub.2O.sub.3); (iv) zinc oxide (ZnO); (v) calcium carbonate (CaCO.sub.3); (vi) aluminium silicate (Al.sub.2SiO.sub.5); (vii) kaolin (Al.sub.2O.sub.3.2SiO.sub.2); (viii) titanium dioxide (TiO.sub.2); or (viii) barium sulphate (BaSO.sub.4). The first coating 401 may include one or more other white fillers.

(73) Inorganic Coatings

(74) According to various embodiments the first coating 401 preferably comprises an inorganic binder, preferably a water based inorganic binder.

(75) The inorganic binder preferably comprises an alkali (or alkaline) metal silicate. For example, the alkali (or alkaline) metal silicate may comprise potassium silicate (K.sub.2SiO.sub.3). Alternatively, the alkali (or alkaline) metal silicate may comprise sodium silicate. The sodium silicate may comprise sodium metasilicate (Na.sub.2SiO.sub.3), sodium orthosilicate (Na.sub.4SiO.sub.4) or sodium pyrosilicate (Na.sub.6Si.sub.2O.sub.7).

(76) According to an embodiment the alkali (or alkaline) metal silicate may comprise lithium silicate (Li.sub.2SiO.sub.3).

(77) According to another embodiment the alkali (or alkaline) metal silicate may comprise calcium silicate (Ca.sub.2SiO.sub.4) or calcium orthosilicate.

(78) According to another embodiment the alkali (or alkaline) metal silicate may comprise magnesium aluminium silicate (AlMgSiO.sub.4).

(79) The first inorganic coating 401 may comprise one or more braids, ceramic fibres, adhesives yarns or special tapes.

(80) The first inorganic coating 401 may be semi-conductive and may have a volume resistivity of 10.sup.12 ohm-cm or less, preferably a volume resistivity of 10.sup.10 ohm-cm or less, further preferably a volume resistivity of 10.sup.8 ohm-cm or less.

(81) The first inorganic coating 401 may have a thermal deformation temperature in the range 140-150° C., 150-160° C., 160-170° C., 170-180° C., 180-190° C., 190-200° C., 200-210° C., 210-220° C., 220-230° C., 230-240° C., 240-250° C., 250-260° C., 260-270° C., 270-280° C., 280-290° C., 290-300° C. or >300° C.

(82) The first inorganic coating 401 may have a retention of elongation at break of 50% or more after 2000 hours of exterior weathering test in accordance with ASTM 1960.

(83) The first inorganic coating 401 may have a heat conductivity of 0.15 W/m or more.

(84) The first coating 401 may less preferably have a lightness value L* in the range 0-10, 10-20, 20-30, 30-40, 40-50, 50-60, 60-70, 70-80. More preferably, the first coating 401 is white and has a lightness value L* in the range 80-90 or 90-100 wherein when L*=0 the observed colour is black and wherein when L*=100 the observed colour is white. According to the preferred embodiment the coating 401 has a L*≥80.

(85) The first inorganic coating 401 may be substantially free of hydrorepellent additives, a hydrophilic additive and/or a dielectric fluid.

(86) Fillers

(87) In a similar manner to the arrangements disclosed in WO 2015/105972 (Ranganathan) according to various embodiments of the present invention the first inorganic coating 401 may include one or more fillers. The first inorganic coating 401 may contain one or more fillers at a concentration of 0-50% (by weight of the total composition) and the one or more fillers may have an average particle size of 0.1-50 μm. The filler particles may be spherical, hexagonal, flake like, fibres or ribbon like.

(88) IR Reflective Additives

(89) In a similar manner to the arrangements disclosed in WO 2015/105972 (Ranganathan) according to various preferred embodiments of the present invention, the first inorganic coating 401 may comprise one or more infrared reflective pigments or additives. The one or more infrared reflective (“IR”) pigments or additives may be included in the first inorganic coating 401 at a concentration from e.g. 0.1-10 wt %. The IR reflective additives are preferably white.

(90) Stabilisers

(91) In a similar manner to the arrangements disclosed in WO 2015/105972 (Ranganathan) according to various preferred embodiments of the present invention one or more stabilisers may be included in the first inorganic coating 401 at a concentration of e.g. 0.1-5% (by weight of the total composition or coating).

(92) The one or more stabilisers may comprise a light stabiliser and/or a dispersion stabiliser such as bentonite. The stabiliser is preferably white.

(93) Coating Process

(94) The first inorganic coating 401 or a first mixture may be applied to one or more conductors 400 such as an overhead cable by being sprayed or painted on. The first coating or first mixture is preferably water based and may be dehydrated or dried e.g. by thermal curing optionally over a period of hours.

(95) One or more pre-treatment processes may be used to prepare a surface of the conductor 400 or one or more conductive wires for the first inorganic coating 401. For example, according to various embodiments the conductor 400 or one or more conductive wires may be subjected to chemical treatment, pressurised air cleaning, hot water treatment, steam cleaning, brush cleaning, heat treatment, sand blasting, ultrasound, deglaring, solvent wipe, plasma treatment and the like.

(96) A surface of one or more overhead conductors 400 may be deglared by sand blasting. An overhead conductor may be heated to temperatures between 23-250° C. as part of a heat treatment process to prepare the surface of the conductor 400 or one or more conductive wires for the first coating 401. The temperature may be selected dependent upon the first coating 401.

(97) In certain embodiments, the coating processes may be solvent free or essentially solvent free. Solvent free, or essentially solvent free may mean that no more than about 1% of a solvent is used in any of the processes relative to the total weight of the product.

(98) Characteristics of Coated Conductors

(99) As will be appreciated, the application of a single coating or monolayer 401 provides cables, such as overhead conductors, with a number of superior characteristics including self-cleaning properties.

(100) The first inorganic coating 401 may provide a cable with a uniform thickness around the exterior of the conductor 400 or one or more conductive wires. Each method of applying the first inorganic coating 401 may compensate for differing amounts of unevenness.

(101) The first coating layer 401 according to various preferred embodiments of the present invention may provide the conductor 400 or one or more conductive wires with an increased mechanical strength relative to that of a bare conductor. For example, according to various embodiments a single coated conductor 400 or one or more conductive wires may have a minimum tensile strength of 10 MPa and may have a minimum elongation at break of 50% or more.

(102) As another advantage, a single coating 401 may in a similar manner to the arrangements disclosed in WO 2015/105972 (Ranganathan) serve as a protective layer against corrosion and bird caging in the conductor 400 or one or more conductive wires.

(103) As may be appreciated, bare or liquid coated conductors may lose their structural integrity over time and may become vulnerable to bird caging in any spaces between the conductor wire strands. In contrast, a conductor 400 or one or more conductive wires having a single coating 401 are shielded and may eliminate bird caging problems.

(104) As another advantage, the first inorganic coating 401 may eliminate water penetration, may reduce ice and dust accumulation and may improve corona resistance.

(105) As another advantage, a conductor 400 or one or more conductive wires coated with a single coating 401 may have an increased heat conductivity, an increased emissivity and decreased absorptivity characteristics.

(106) As an additional advantage, the first inorganic coating 401 may have a thermal deformation resistance at higher temperatures including temperatures of 140-150° C., 150-160° C., 160-170° C., 170-180° C., 180-190° C., 190-200° C., 200-210° C., 210-220° C., 220-230° C., 230-240° C., 240-250° C., 250-260° C., 260-270° C., 270-280° C., 280-290° C., 290-300° C. or >300° C.

(107) Advantageously, the first inorganic coating 401 may maintain flexibility at lower temperatures and may have improved shrink back and low thermal expansion at the lower temperature range.

(108) The addition of the first inorganic coating 401 may add relatively little weight to an overhead conductor 400. For example, the weight increase of a single coated overhead conductor according to a preferred embodiment of the present invention may be <5%, 5-10%, 10-15% or 15-20%.

(109) A yet further significant advantage is that the first inorganic coating 401 have either a good or excellent corrosion resistance in contrast to some known single coatings.

(110) Experimental Data

(111) Various simulations were performed following CIGRE technical specification 601, further details of which are given below.

(112) For steady state situations, fixed weather and conductor parameters were assumed in order to calculate the maximum expected ratings or conductor temperatures. The environmental data were chosen to represent a hot, cloudless, sunny subtropical desert location, as detailed below.

(113) TABLE-US-00002 TABLE 2 Environmental data Location 30 Degrees North Date 10.sup.th June Time 12 hours Ambient temperature (° C.) 40 Wind velocity perpendicular to 0.6096 conductor (m/s) Conductor orientation E-W Atmospheric conditions Clear Albedo 0.1 Calculated solar irradiance (W/m.sup.2) Varied from night to noon
Reduction in Operating Temperature

(114) Generally, a new uncoated conductor will have an emissivity E=0.5 and solar absorptivity A=0.5. Over the course of a year the emissivity E of an uncoated conductor will increase to e.g. approx. 0.8 as the surface of conductor becomes coated with organic matter and/or is exposed to pollution. Similarly, the absorptivity will also increase during the course of the year to 0.8. These figures are dependent upon location and it will be understood, for example, that if the conductor is located in a less polluted location then the final values may end up being different (e.g. higher/lower).

(115) Table 3 below shows current and temperature as a function of surface characteristics.

(116) TABLE-US-00003 TABLE 3 Aged uncoated Conductor having Drake New uncoated a preferred conductor Drake conductor coating E = 0.8 E = 0.5 E = 0.95 A = 0.8 A = 0.5 A = 0.1 Current at 100° C. (A) 907 908 1126 Temperature (° C.) at n/a 99.9 78.75 976 Amps Increase in current n/a 1 119 I.sup.2R power savings (running at a cooler n/a n/a 6% temperature)

(117) It will be understood that Drake ACSR conductors are commonly used for CIGRE simulations.

(118) Increase in Ampacity

(119) Table 4 below shows how the ampacity varies with time of day and corresponding solar irradiance for a perfect conductor, an aged conductor, a new uncoated conductor and coated conductor according to a preferred embodiment.

(120) TABLE-US-00004 TABLE 4 Drake conductor (26/7) Theoretical Drake with a preferred coating perfect conductor New E = 0.95 Drake (26/7) Drake A = 0.1 conductor after 1 conductor % % Total (26/7) year (26/7) Uplift Uplift Solar E = 1.0 E = 0.8 E = 0.5 on on Time of Irradiance A = 0.0 A = 0.8 A = 0.5 E = 0.8 E = 0.5 Day (W/m.sup.2) Current (A) Current (A) Current (A) Current (A) A = 0.8 A = 0.5 04:00:00 0 1161 1115 1043 1149  3% 10% 05:00:00 0 1161 1115 1043 1149  3% 10% 06:00:00 266 1161 1078 1018 1145  6% 12% 07:00:00 463 1161 1044 996 1141  9% 15% 08:00:00 689 1161 1006 971 1137 13% 17% 09:00:00 911 1161 967 946 1133 17% 20% 10:00:00 1093 1161 935 926 1129 21% 22% 11:00:00 1210 1161 914 912 1127 23% 24% 12:00:00 1251 1161 907 908 1126 24% 24%

(121) FIG. 5 shows a plot of ampacity or current capacity against time of day solar intensity for a new, aged and dual coated conductor (included for illustrative purposes only) compared against a theoretical perfect conductor.

(122) FIG. 5 shows that the ampacity of a modified conductor performs close to the performance of a theoretical perfect conductor (wherein the ampacity does not reduce with increasing solar irradiance). In particular, it is noted from FIG. 5 that the performance of a modified conductor shows a high level of performance after 8 hours in marked contrast to conventional conductors.

(123) Technology Validation in a Laboratory Environment

(124) Initial lab-scale prototypes were manufactured and tested based on the performance of flat aluminium sheeting of the same grade as power lines but configured flat for ease of testing. Accordingly, coatings were applied to flat sheeting rather than to cylindrical cables.

(125) Optical proof of concept was demonstrated by demonstrating that the first coating 401 has the necessary optical performance (e.g. high reflectivity, high emissivity) in the specific wavelengths required to produce optimal radiative cooling.

(126) Furthermore, electrical proof of concept was demonstrated by demonstrating that a modified conductor operates at a significantly cooler temperature than that of an uncoated conductor when transmitting a relatively high current.

(127) The electrical proof of concept testing involved both: (i) constant current testing wherein multiple flat coated conductors were tested outdoors with their temperatures being the output; and (ii) constant temperature testing involving testing multiple different coatings at the same temperature but with the wattage required to heat each being the output.

(128) Solar Reflective Layer

(129) UV-VIS-NIR spectral analysis of a solar reflective layer was carried out by a third party using a JASCO® V670 UV-VIS-NIR spectrometer with ISN-723 integrating sphere attachment. An integrating sphere attachment allowed collection of diffuse radiation (about 180°) reflected by the sample. Analysis was undertaken in reflectance mode, with specular reflectance excluded. One spectrum was collected from each side of the sample. The sample was also turned 90° around the incident beam for analysis of the second side. This should have low absorbance in the solar spectrum (0.3-2.5 μm). The modified conductor demonstrates this.

(130) FIG. 6 shows UV-VIS-NIR absorbance or reflectivity spectra of a solar reflective layer according to an embodiment of the present invention. The absorbance or reflectivity spectra demonstrates that over 90% of solar energy is not absorbed thereby promoting cooling under direct sunlight. Notably the reflectivity reduces towards 2.5 μm which is advantageous so as not to prevent or interfere with thermal emission of infra-red radiation in the wavelength range 2.5-30.0 μm. The particular solar reflective layer which was tested with reference to FIG. 6 comprised a single layer reflective/emissive silicate coating according to a preferred embodiment.

(131) FIG. 7 shows the solar spectrum for comparison purposes with FIG. 6. The solar spectrum at the top of the atmosphere broadly corresponds with a 5250° C. blackbody spectrum. The solar radiation at sea level shows various absorption bands due to absorption by O.sub.2, H.sub.2O and CO.sub.2 molecules.

(132) Constant Current Electrical Proof of Concept

(133) Rig Design and Experimental Method

(134) Further testing was performed in order demonstrate that a modified coating 401 according to a preferred embodiment of the present invention functions to lower the operating temperature of an electrical conductor. A series of conductors comprising several lengths of flat aluminium conductor of allot 1350 were connected in series and tested with at least one of the conductors being uncoated.

(135) The upper surface of each of the conductor(s) was exposed to the atmosphere whilst the lower surface of the conductor(s) was thermally insulated by being adhered to CELOTEX® foam board. DC current was then applied to the conductors which then became hot due to Joule heating. Temperature measurements of the coated and uncoated conductors were taken to demonstrate the efficacy of the single coating 401 according to a preferred embodiment of the present invention in terms of reducing the temperature of an aluminium conductor 400. Sensors were mounted behind the conductors and were located between the conductors and the insulation in order to reduce influences of poor thermal connections which might otherwise introduce errors if they were connected to the side directly exposed to solar radiation.

(136) Several rigs were designed and iteratively optimised in order to remove the possibility of performance measurements being due to artefacts of experimental design. It was desired to explore the performance of different coatings when exposed to sunlight and natural convection, as these environmental conditions represent the operating conditions of the end product.

(137) As no standards exist for constant current testing in an external environment a new purpose built rig was designed specifically for testing outdoors. When testing outdoors and under sunlight and using insulated surface mounted thermocouples to measure temperature a number of problems may arise. Thermocouples may introduce an optical irregularity into the surface of the conductor. Also, a temperature gradient may form from the surface of the conductor to air, where small deviations in the distance from thermocouple to the conductor can lead to large differences in the temperature measuring accuracy between thermocouples.

(138) In turn, a test rig was designed which equally thermally insulated thermocouples and which minimised potential differences in thermal gradients between the sensors and the conductors. A piece of CELOTEX® insulation, with dimensions 50×450×600 mm was used as the base for the test rig.

(139) CELOTEX® has a lower thermal conductivity than air and can operate at the higher temperatures required for the constant current testing. Holes were drilled in the rear of the CELOTEX® insulation and thermocouple sensors were threaded through to the surface. A few millimetres of the sensor cable were then pulled through allowing the sensor to lie parallel to the CELOTEX® surface. Thermocouples sensors were kept electrically insulated from the test strips by a 0.1 mm thick high temperature double sided adhesive tape which was placed on top in order to secure thermocouples to lie within 1 mm of the central line of the conductor. The aluminium conductors were then placed on top of the sensors so that thermocouples were concealed between the CELOTEX® and the aluminium conductor thereby minimising the potential for thermal gradients to exist between the sensors and the conductors. The number of connections between the conductors and the power source was minimised by utilising a single piece of conductor which was cut into a wave-like or serpentine pattern or shape as shown in FIG. 8.

(140) FIG. 8 shows an aluminium test conductor with various dimensions indicated. The conductor was arranged to comprise ten rows of which the outer two were used for making electrical connections and the inner eight were for coating testing. The wave-like or serpentine shaped conductor was then placed on top of the sensors and was secured underneath using double sided thermally stable tape. The aluminium conductor comprised alloy 1350 and had a thickness of 0.7 mm. The transition point from one type of coating to another was arranged to be midway through the semi-circular connecting curve portions.

(141) Temperature Testing Up to 100° C.

(142) Four different conductor strips were tested namely: (i) an uncoated bright aluminium (control) conductor; (ii) a conductor having a grey emissive coating comprising 10 wt % silicon carbide in a condensation cured silicone rubber binder; (iii) a conductor having a black emissive coating comprising a carbon black layer comprising 1 wt % carbon black in acetone; and (iv) a conductor 400 according to a preferred embodiment comprising a first or single layer 401 comprising a photocatalytic agent, wherein the photocatalytic agent comprised ≥70 wt % anatase titanium dioxide (TiO.sub.2) having an average particle size (“aps”) ≤100 nm.

(143) Samples were tested outdoors under low wind conditions with solar radiation levels greater than 800 W/m.sup.2. Two nominal temperature ranges were tested. A low voltage DC power supply comprising 1.5 V batteries supplying currents up to 100 A were connected continuously to the test rig which resulted in the conductors increasing in temperature to a temperature of approx. 0-100° C. above ambient. Ambient temperature was typically 20° C. but in the range 10-30° C.

(144) Mean temperatures were calculated for each of the coatings at peak. The key environmental conditions were: (i) 10-30° C. ambient temperature; (ii) low wind (Beaufort scale typically 2-3); and (iii) ≥800 W/m.sup.2 perpendicular solar irradiation.

(145) The results are shown in FIG. 9 which shows the mean temperatures of the different conductors over the peak period. At these temperatures it is apparent that a single coated conductor according to a preferred embodiment of the present invention is particularly advantageous. The empirical test data is consistent with the calculated values shown and described above with reference to Table 1. The test data accordingly demonstrates the significant performance benefits which result from increasing the solar reflectivity in the presence of sunlight by utilising a single coated conductor according to a preferred embodiment of the present invention.

(146) Temperature Testing Up to 250° C.

(147) Three different conductor strips were tested namely: (i) an uncoated bright aluminium (control) conductor; (ii) a conductor having a black emissive coating comprising a carbon black layer comprising 1 wt % carbon black in acetone; (iii) a conductor according to a preferred embodiment having a white coating which includes a photocatalytic agent, wherein the photocatalytic agent comprises ≥70 wt % anatase titanium dioxide (TiO.sub.2) having an average particle size s 100 nm.

(148) Samples were tested outdoors under low wind conditions. A 6V lead acid battery with 70 AH nominal capacity was used. The battery was shorted with jump leads in order to heat the strip up to around 250° C. The current was set between 100-150 A and was connected continuously to the test rig which resulted in the conductors increasing in temperature such that the uncoated control conductor reached an average temperature of 249.5° C.

(149) Mean temperatures were calculated for each of the coatings at peak.

(150) The results are shown in FIG. 10 which shows the mean temperatures of the different conductors over the peak period. At these elevated temperatures it is again apparent that a single coated conductor according to a preferred embodiment of the present invention is particularly advantageous. In particular, the test results show that compared to the control conductor, the single coated provides a temperature reducing effect of 55.4° C. which represent a very significant performance advantage.

(151) Self-Cleaning Photonic Coatings to Increase the Capacity of Overhead Conductors

(152) The present invention is particularly concerned with the inclusion of a photocatalytic agent in the coating 401 provided on an overhead conductor 400 in order to render the coating self-cleaning. In particular, it should be understood that the coating is self-cleaning in the sense that when the photocatalytic agent is excited with ultra-violet (“UV”) light then the photocatalytic agent preferably creates hydroxyl (OH.sup.−) and superoxide (O.sub.2.sup.−) radicals which preferably decompose surface organic matter which may have accreted onto the overhead conductor into carbon dioxide (CO.sub.2) and water (H.sub.2O).

(153) The coating 401 provided on the overhead conductor 400 according to the preferred embodiment is preferably white (or less preferably may be considered as having a high degree of whiteness). According to the preferred embodiment white may be defined as L*≥80.

(154) Two particularly preferred embodiments will now be discussed in more detail below namely: (i) a single inorganic layer 401 formed from a two-part kit; and (ii) a single inorganic layer 401 formed from a one part kit.

(155) Surface modification has emerged recently as a cost effective method to increase the performance of overhead conductors. These work by optimising the external surface of the overhead conductor in terms of its solar reflectivity and thermal emissivity. Having high values (e.g. ≥0.9) for both solar reflectivity (R) and thermal emissivity (E) promotes a significant cooling effect on overhead conductors. This reduction in operating temperature reduces the resistance of the conductor and increases the current carrying capacity.

(156) Several coating based solutions have been proposed to achieve this. For example, various inorganic and organic based coatings are known to lower the operating temperature of overhead lines.

(157) However, the known coatings are predominantly non-white. Furthermore, a known problem with white conductors is that they suffer from discoloration over time.

(158) It will be appreciated by those skilled in the art that conventional single layer (or monolayer) white coating products will accrete dirt and invariably darken over time as they are exposed to environmental pollutants.

(159) As such, there is a particular emphasis in conventional arrangements in promoting thermal emissivity which in turn increases the solar absorptivity. As overhead conductors may operate above 90° C., this approach does result in a net cooling effect.

(160) However, according to the present invention the solar reflectivity (R) is also maximised which advantageously can increase the cooling power.

(161) Thus, substantial performance benefits exist by providing both a highly reflective and a highly emissive coating for a conductor in a manner according to various embodiments of the present invention.

(162) In contrast, conventional arrangements such as those disclosed, for example, in FR-2971617 (Nexan) and WO 2007/034248 (Simic) are considered to be ineffective from a commercial perspective due to the propensity for white coatings to darken and discolour over time.

(163) The progressive darkening of initially white coatings over a period of time makes conventional white coatings preclusive as solutions for overhead conductors as network operators need to be able confidently to thermally rate their lines according to stable levels of solar reflectivity and thermal emissivity.

(164) Thus, end users and network operators must plan according to an aged solar reflectance not the new or initial solar reflectance. It will be appreciated that significant and variable drops in solar reflectance are not practical from a network operators perspective who need to be able to thermally rate their overhead lines.

(165) The dirt resistance of a distribution or power line could in theory be increased by using a coating having an additive such as colloidal silica (SiO.sub.2). However, the use of such additives has been shown to result in up to a 20% reduction in the solar reflectance.

(166) The surface of the conductor might also be washed with a high powered jet wash. However, a person skilled in the will understand this to be impractical from a commercial, safety and cost perspective especially when considering that the distribution or power line will be a high voltage overhead line.

(167) The provision of a coating having a photocatalytic agent according to the present invention which provides a self-cleaning effect will immediately be recognised as being advantageous.

(168) A particular advantage of incorporating a self-cleaning photocatalyst into the coating according to the present invention is the ability to provide a durable white coating which requires little or no maintenance overtime. According to various embodiments of the present invention the (white) coating will maintain a high degree of whiteness (i.e. L*≥80) for a substantially longer period of time than conventional white coatings. According to an embodiment the coating may remain white having a L*≥80 for an indefinite period of time when subjected to standard levels of airborne pollution.

(169) According to various embodiments self-cleaning capabilities are preferably integrated into a white reflective monolayer.

(170) Self-cleaning coatings may have a number of operating mechanisms. According to various embodiments the coating may be simultaneously: (i) anti-static thereby reducing the ability of particles to stick to the surface; (ii) super-hydrophilic thereby reducing the water contact angle of surface water thereby acting to collect and clear surface particulate matter on the surface more effectively in the presence of atmospheric water; and (iii) photocatalytic.

(171) According to a particularly preferred embodiment anatase titanium dioxide (TiO.sub.2) may be utilised as a photocatalytic agent. Anatase titanium dioxide (TiO.sub.2) is a semi-conductor with a band gap of 3.2 eV, which when excited with UV light, creates hydroxyl (OH.sup.−) and superoxide (O.sub.2.sup.−) radicals which preferably act to decompose surface organic matter accreted onto the coating into carbon dioxide (CO.sub.2) and water (H.sub.2O).

(172) Single Inorganic Layer Formed from a Two-Part Kit

(173) A self-cleaning white photonic coating according to an embodiment of the present invention may be formed by mixing together two parts of a kit.

(174) The two part composition may comprise a first composition (part A) comprising: (i) a coating binder 50-70 wt % (of part A); (ii) optionally nanosilica (“nS”) 2-5 wt % (of part A); (iii) optionally one or more optically active pigments e.g. rutile titanium dioxide (TiO.sub.2) 10-20 wt % (of part A); (iv) a photocatalytic e.g. anatase titanium dioxide (TiO.sub.2) 1.76%-2.75 wt % (of part A); (v) optionally inert fillers 10-20 wt % (of part A); and (vi) optionally zinc based co-curatives 0.4-1 wt % (of part A).

(175) The two part composition preferably comprises a second composition (part B) comprising: (i) water 50-70 wt % (of part B); (ii) optionally a rheology modifier 0.3-1 wt % (of part B); (iii) optionally magnesium based co-curatives 10-15 wt % (of part B); (iv) optionally zinc based co-curative 1-3 wt % (of part B); and (v) optionally an aqueous emulsion 7-15 wt % (of part B).

(176) Coating Binder

(177) As the photocatalytic agent preferably performs a self-cleaning function by oxidising organic materials, organic binders are preferably not used for this purpose at least not to any significant degree. As such the binder preferably comprises an inorganic binder or a substantially inorganic binder.

(178) According to a particularly preferred embodiment the binder may comprise an alkali or alkaline metal silicate binder and the binder may be water based. For example, the alkali (or alkaline) metal silicate preferably comprises potassium silicate (K.sub.2SiO.sub.3).

(179) Alternatively, the alkali (or alkaline) metal silicate may comprise sodium silicate. The sodium silicate may comprise sodium metasilicate (Na.sub.2SiO.sub.3), sodium orthosilicate (Na.sub.4SiO.sub.4) or sodium pyrosilicate (NaSi.sub.2O.sub.7).

(180) According to an embodiment the alkali (or alkaline) metal silicate may comprise lithium silicate (Li.sub.2SiO.sub.3).

(181) According to another embodiment the alkali (or alkaline) metal silicate may comprise calcium silicate (Ca.sub.2SiO.sub.4) or calcium orthosilicate.

(182) According to another embodiment the alkali (or alkaline) metal silicate may comprise magnesium aluminium silicate (AlMgSiO.sub.4).

(183) Nanosilica (“nS”) or Colloidal Silica (SiO.sub.2)

(184) Nanosilica (“nS”) or colloidal silica (SiO.sub.2) may be added to increase the Si:alkali metal ratio and thereby increase the polymerisation of a coating according to a preferred embodiment. The resulting coating may comprise a siloxane polymer. The nanosilica (“nS”) or colloidal silica (SiO.sub.2) can increase the abrasion resistance and adhesion of the silicate to aluminium. Further, the addition of nanosilica (“nS”) or colloidal silica (SiO.sub.2) preferably further increases the inherent emissivity of the silicate binder further improving the cooling effect.

(185) Siloxane (Silicone) Polymers

(186) According to various embodiments of the present invention a single coating may be formed which may at least partially comprise a siloxane (silicone) polymer.

(187) For reference purposes the chemical structure of several different siloxanes is shown below in Table 5:

(188) TABLE-US-00005 TABLE 5 Hexamethylcyclo- Octamethylcyclo- Decamethylcyclo- Name trisiloxane (D3) tetrasiloxane (D4) pentasiloxane (D5) Molecular C.sub.6—H.sub.18—O.sub.3—Si.sub.3 C.sub.8—H.sub.24—O.sub.4—Si.sub.4 C.sub.10—H.sub.30—O.sub.5—Si.sub.5 formula Structural formula Molecular 222.46 296.64 370.80 weight CAS-no 541-05-9 556-67-2 541-02-6 Synonyms Dimethylsiloxane cyclic Cyclic dimethylsiloxane Cyclic dimethylsiloxane (among trimer tetramer, pentamer, others) KF994 KF995 Part of Cyclomethicone Dow Corning 245 fluid. Part of Cyclomethicone Dodecamethylcyclo- Hexamethyldisiloxane Name hexasiloxane (D6) HMDS Molecular formula C.sub.12—H.sub.36—O.sub.6—Si.sub.6 C.sub.6—H.sub.18—O—Si.sub.2 Structural formula Molecular weight 444.93 162.42 CAS-no 540-97-6 107-46-0 Synonyms Cyclohexasiloxane Oxybis(trimethyisilane), (among others) Bis(trimethylsilyl)ether
Emulsion and/or Rheology Additive

(189) In order to improve the rheological properties, flexibility and coating applicability an emulsion additive and/or rheology additive may optionally be added to the coating. According to an embodiment aqueous polydimethylsiloxane (“PDMS”) ((C.sub.2H.sub.6OSi).sub.n) of 40-50% solids may be used as an additive for the coating. Although polydimethylsiloxane (“PDMS”) ((C.sub.2H.sub.6OSi).sub.n) is organic, the main building block is siloxane based, which is not oxidised by the photocatalytic agents in the coating. In any case, the emulsion additive and/or rheology additive preferably comprises less than 5% of the dry film weight.

(190) Photocatalytically Active Pigments

(191) According to a particularly preferred embodiment a photocatalytic agent is preferably included in the conductor coating.

(192) According to a preferred embodiment the photocatalytic agent may comprise 70 wt % anatase titanium dioxide (TiO.sub.2) further preferably having an average particle size 100 nm.

(193) The photocatalytic agent preferably results in the photocatalytic conversion of organic matter which may have adhered to the coating provided on the conductor. In particular, when anatase titanium dioxide (TiO.sub.2) is excited by UV light it creates hydroxyl (OH.sup.−) and superoxide (O.sub.2.sup.−) radicals which preferably decompose surface organic matter into carbon dioxide (Co.sub.2) and water (H.sub.2O).

(194) According to an embodiment the photocatalytic agent may comprise a commercially available form of titanium dioxide (TiO.sub.2) known either as DEGUSSA (EVONIK)® P25 or AEROXIDE® TiO.sub.2 P25.

(195) DEGUSSA (EVONIK)® P25 titanium dioxide (TiO.sub.2) is a powdered form of titanium dioxide (TiO.sub.2). The properties of P25 titanium dioxide (TiO.sub.2) have been investigated in detail and reference is made to the Journal of Photochemistry and Photobiology A: Chemistry, 216(2-3): 179-182 which refers to the powdered form of titanium dioxide (TiO.sub.2) as comprising a mixture of anatase, rutile and amorphous titanium dioxide (TiO.sub.2) in the ratio anatase:rutile:amorphous 78:14:8.

(196) It is noted that DEGUSSA (EVONIK)® P25 titanium dioxide (TiO.sub.2) is often (incorrectly) reported as comprising 70:30, 80:20 or 85:15 anatase:rutile crystallites. Accordingly, the presence of the amorphous form of titanium dioxide (TiO.sub.2) in DEGUSSA (EVONIK)® P25 titanium dioxide (TiO.sub.2) seems often (incorrectly) to be ignored.

(197) It has been reported that the average particle size (“aps”) of the anatase titanium dioxide (TiO.sub.2) in DEGUSSA (EVONIK)® P25 is approximately 85 nm and the average particle size (“aps”) of rutile titanium dioxide (TiO.sub.2) in DEGUSSA (EVONIK)® P25 is approximately 25 nm.

(198) Titanium dioxide (TiO.sub.2) may be used as a photocatalyst for decomposition of organic pollutants because it is chemically stable and biologically benign. The band gap of titanium dioxide (TiO.sub.2) is larger than 3 eV (˜3.0 for rutile and ˜3.2 for anatase) thus making pure titanium dioxide (TiO.sub.2) primarily active for UV light.

(199) It is believed that the specific phase mixture of different polymorphs of titanium dioxide (TiO.sub.2) as are present in DEGUSSA (EVONIK)® P25 has a synergistic effect and an increased photocatalytic activity is observed compared to pure phases (i.e. either relative to pure rutile titanium dioxide (TiO.sub.2) or to pure anatase titanium dioxide (TiO.sub.2)).

(200) It is also generally accepted that pure anatase titanium dioxide (TiO.sub.2) exhibits a higher photocatalytic activity than pure rutile titanium dioxide (TiO.sub.2).

(201) It is known that anatase titanium dioxide (TiO.sub.2) has a larger band gap than rutile titanium dioxide (TiO.sub.2). While this reduces the light that can be absorbed, it may raise the valence band maximum to higher energy levels relative to redox potentials of adsorbed molecules. Accordingly, the oxidation power of electrons may be increased and electron transfer may be facilitated from the titanium dioxide (TiO.sub.2) to the adsorbed molecules.

(202) Optically Active Pigments

(203) Depending on the composition the coating may further comprise non-photocatalytic pigments. The pigments are preferably white in colour. According to a particularly preferred embodiment the coating may be arranged to have over 90% total solar reflectivity. This may be achieved in part by including optically active pigments in the coating which preferably promote solar reflectance without increasing absorption of visible light.

(204) The optically active pigments may include rutile titanium dioxide (TiO.sub.2).

(205) According to other embodiments the optically active pigment may comprise silicon dioxide (SiO.sub.2) or cerium hydroxide (Ce(OH).sub.3).

(206) Fillers

(207) An inorganic filler may be included for a number of purposes including pigment extension and increasing the thermal emissivity. The pigments preferably do not increase the absorption of solar radiation. According to various embodiments the filler may comprise calcium carbonate (CaCO.sub.3), calcined kaolin (Al.sub.2O.sub.3.2SiO.sub.2) or talc (e.g. hydrated magnesium silicate (H.sub.2Mg.sub.3(SiO.sub.3).sub.4 or Mg.sub.3Si.sub.4O.sub.10(OH).sub.2)).

(208) According to another embodiment a filler with a high brightness such as sodium alumino silicate may be used to increase the total solar reflectivity.

(209) Curing Agent—Co-Curative Metal Salts

(210) According to various embodiments the coating may comprise a metal salt. In particular, polyvalent metal cations, such as Zn2+, Ca2+ and Mg2+ can increase the viscosity of alkali metal silicate coatings (and siloxane coatings) and decrease the curing time. These can be added to make a two part solution. The solubility of the metal salt added determines the pot-life of the coating. For example, highly soluble metal salts such as magnesium sulphate (MgSO.sub.4) will react readily with the alkali metal silicate coating (or siloxane coating) and reduce the pot-life substantially. Preferred salts include zinc oxide (ZnO), zinc stearate (C.sub.36H.sub.70O.sub.4Z.sub.n), trimagnesium orthophosphate (Mg.sub.3O.sub.8P.sub.2), magnesium oxide (MgO) and magnesium carbonate (MgCO.sub.3).

(211) Reference to the “pot-life” of the coating is intended to be understood in the conventional sense of a two-pack or multi-component coating systems that cure through a chemical reaction. These systems generally consist of a base component (often called the “Part A”) and a catalyst or hardener component (often called the “Part B”). When these components are mixed together a chemical reaction starts which will lead to the curing of the coating. In practical terms the term “pot-life” may be considered as the time from combining the components of the coating to the point at which the mixed coating is no longer useable. Pot-life is commonly thought of as the length of time that a mixed (catalysed) coating system retains a viscosity low enough to be applied to a surface (although this is not strictly true).

(212) These materials can be combined to make a two part silicate coating with self-cleaning properties which adheres strongly to aluminium and provides sufficient flexibility required to be applied on conductors which are wrapped around cylindrical drums. The zinc based co-curative is important in both part A and part B to allow for rapid curing and the formation of insoluble films. The following section demonstrates how self-cleaning rates compare with dirt accretion on white surfaces.

(213) Self-Cleaning Rates Versus Elemental Carbon Deposition

(214) When black carbon (BC) is deposited upon a white surface, it will strongly absorb incident light, decrease solar reflectance and degrade aesthetic appearance. This increase in absorbance results in an increase in surface temperature meaning a reduction in cooling power of such a photonic coatings. In order to maintain cooling power in this scenario, black carbon will need to be removed.

(215) Conductors according to various embodiments may become soiled by particulate matter (PM) such as soot which is an elemental carbon (EC). A simple and non-destructive method of measuring the amount of elemental carbon on a surface is by measuring it's whiteness (L*) relative to its clean state, wherein L*=0 is the darkest black and L*=100 is the brightest white.

(216) It will be understood that by measuring L* it is possible to estimate how clean a surface is. It is also possible to predict the performance of a photocatalytic self-cleaning coating in various locations around the world and to assess its effectiveness as a method to maintain solar reflectivity.

(217) Methodology

(218) Two metrics will be compared in order to assess the effectiveness of a photocatalytic titanium dioxide (TiO.sub.2) layer namely: (i) the amount of time taken for 8 μg cm.sup.−2 of black carbon to accumulate on the coating surface; and (ii) the amount of time needed to clear 8 μg cm.sup.−2 of black carbon from the surface.

(219) The coating being analysed is a white silicate coating with concentration of photocatalytic fixed to 1.6 wt %.

(220) The time taken for 8 μg cm.sup.−2 of black carbon to accumulate on the surface depends on the average concentration of black carbon in the atmosphere and the deposition velocity of the particles.

(221) The deposition velocity is governed by the particle's aerodynamic equivalent diameter (“aed”). Black carbon is an elemental carbon (EC) and is mainly hosted by PM.sub.2.5.

(222) PM.sub.2.5 are a group of particles having an aerodynamic equivalent diameter (“aed”) ≤2.5 μm and the corresponding deposition velocity for particles of this size is 1.89×10.sup.−4 ms.sup.−1.

(223) The average concentration of black carbon in the atmosphere can change rapidly in a small area with concentrations peaking next to busy roads and industrial areas.

(224) The concentration also varies widely with time of day, temperature and humidity. The data used below is taken as a yearly average and where possible on multiple sites around the city/country.

(225) The black carbon concentration in Singapore, Delhi, London and Gent are found in the literature.

(226) The other black carbon concentrations referred to below were estimated from PM.sub.2.5 concentrations combined with data collected by the Surface PARTiculate mAtter Network (“SPARTAN”).

(227) SPARTAN collects data on the composition of PM.sub.2.5 in different environments all over the world using a filter sampler (TEFLON® and NUCLEPORE®) and a nephelometer.

(228) According to SPARTAN data the average fraction of black carbon in PM.sub.2.5 was 11.9% (±8.2%). A deposition rate was established then scaled up to obtain a total time for 8 μg cm.sup.−2 of black carbon to accumulate.

(229) The concentration of black carbon in the atmosphere is strongly correlated to industry and density of automotive traffic rather than location, so a more generalised approach to this problem can be taken and the following estimates have been calculated: (i) rural 1.2-1.7 μg m.sup.−3; (ii) small cities 2.4-3.0 μg m.sup.−3; and (iii) large cities 4.6-7.9 μg m.sup.−3.

(230) For a fixed photocatalytic titanium dioxide (TiO.sub.2) concentration, the time taken to clear 8 μg cm.sup.−2 of black carbon is primarily dependant on the intensity of light incidence on the surface as this drives the photocatalytic process.

(231) The intensity of light will vary from location to location. Accumulated total solar radiation on a horizontal surface per calendar year for each of the locations was sourced from the NASA POWER (Prediction of Worldwide Energy resources) project. This data was an average over the past 10 years where data allowed. In the case of countries, the accumulated total solar radiation figure was obtained by averaging the solar data for each major city in the country.

(232) The accumulated solar radiation data was then used to calculate a surface recovery rate, which is an estimation of the rate at which the surface whiteness (L*) is recovered by the photocatalytic cleaning per day. This was done by multiplying the mean solar insolation at each location with a scalar, called the effective self-maintenance (“SM”) factor. The self-maintenance (“SM”) factor is a scalar that represents the total colour (L*) change by 8 μg cm.sup.−2 of black carbon normalized by the corresponding total solar irradiation (i.e. the product of the solar intensity and irradiation duration) in the study environment. For 1.6 wt % photocatalytic titanium dioxide (TiO.sub.2) with a black carbon loading of 8 μg cm.sup.−2 the self-maintenance factor was found to be 1.9×10.sup.−4 m.sup.2h.sup.−1 W.sup.−1.

(233) The surface recovery rate was then used to calculate the total number of days needed to fully recover the surface whiteness (L*) lost by a surface soiled by 8 μg cm.sup.−2 of black carbon.

(234) For 1.6 wt % titanium dioxide (TiO.sub.2) the loss of L* was observed to be 11.2.

(235) Results

(236) TABLE-US-00006 TABLE 6 Deposition of 8 μg cm.sup.−2 Surface recovery of 8 μg Location BC (days) cm.sup.−2 BC (days) Singapore 1814 15 Delhi 471 14 *Dubai 968 12 *Saudi Arabia 392 11 *Beijing 557 18 London 1339 25 *Brazil 2745 14 *South Africa 1328 12 *Australia 5881 12 *China 792 17 Gent 1376 24 *UAE 722 12
*Note: No empirical data for elemental carbon (EC) is available. Instead, it was estimated using a global percentage (11.9%) of PM.sub.2.5 empirical data with the percentage coming from the Surface PARTiculate mAtter Network (“SPARTAN”) project.

(237) For the locations evaluated, the average surface recovery time is roughly 100 times faster than the deposition rate of 8 μg cm.sup.−2 of black carbon.

(238) Accordingly, 1.6 wt % photocatalytic titanium oxide (TiO.sub.2) in silicate will act as a very effective self-cleaning layer for the standard conditions that the coatings are likely to face.

Non-Photocatalytic Example 1A

(239) The following example relates to a base non-photocatalytic coating composition.

(240) A two part water based inorganic photonic coating was manufactured comprising a first composition (part A) and a second composition (part B).

(241) The first composition (part A) comprised: (i) potassium silicate (BETOLIN® K35, Wöllner GmbH, Ludwigshafen) 68.3 p.b.w.; (ii) rutile titanium dioxide (TiO.sub.2) having an average particle size of 500 nm 20 p.b.w.; (iii) calcined kaolin (Al.sub.2O.sub.3.2SiO.sub.2) 7.4 p.b.w.; (iv) talc (e.g. hydrated magnesium silicate (H.sub.2Mg.sub.3(SiO.sub.3).sub.4 or Mg.sub.3Si.sub.4O.sub.10(OH).sub.2)) 9.6 p.b.w.; (v) zinc stearate (C.sub.36H.sub.70O.sub.4Z.sub.n) 0.3 p.b.w.; and (vi) zinc oxide (ZnO) 0.2 p.b.w.

(242) The second composition (part B) comprised: (i) water 56.7 p.b.w.; (ii) hydroxyethyl cellulose (CH.sub.2CH.sub.2OH) 0.6 p.b.w.; (iii) trimagnesium orthophosphate (Mg.sub.3O.sub.8P.sub.2) 9.4 p.b.w.; (iv) magnesium carbonate (MgCO.sub.2) 6 p.b.w.; and (v) zinc oxide (ZnO) 2.3 p.b.w.

(243) It will be understood that “p.b.w.” refers to “parts by weight” and can be used to indicate the relative proportion of components to be included in each composition.

(244) The reagents were mixed in that order in two separate beakers. These were then mixed in a 1:1 ratio and mixed with a high speed mixer until uniform dispersal was achieved.

(245) It is to be noted that this example is not photocatalytically active as no photocatalytically active nanoparticles were included in this formulation.

(246) However, as a based formulation, the following tests were performed: (i) coating finish; (ii) mandrel bend test; and (iii) coating finish. The results are presented in Table 7 below.

Non-Photocatalytic Example 1B

(247) The following example relates to a base non-photocatalytic coating composition.

(248) A two part water based inorganic photonic coating was manufactured comprising a first composition (part A) and a second composition (part B).

(249) The first composition (part A) comprised: (i) potassium silicate (BETOLIN® K35, Wöllner GmbH, Ludwigshafen) 68.3 p.b.w.; (ii) rutile titanium dioxide (TiO.sub.2) having an average particle size of 500 nm 20 p.b.w.; (iii) calcined kaolin (Al.sub.2O.sub.3.2SiO.sub.2) 7.4 p.b.w.; (iv) talc (e.g. hydrated magnesium silicate (H.sub.2Mg.sub.3(SiO.sub.3).sub.4 or Mg.sub.3Si.sub.4O.sub.10(OH).sub.2)) 9.6 p.b.w.; (v) zinc stearate (C.sub.36H.sub.70O.sub.4Z.sub.n) 0.3 p.b.w.; and (vi) zinc oxide (ZnO) 0.2 p.b.w.

(250) The second composition (part B) comprised: (i) water 56.7 p.b.w.; (ii) hydroxyethyl cellulose (CH.sub.2CH.sub.2OH) 0.6 p.b.w.; (iii) trimagnesium orthophosphate (Mg.sub.3O.sub.8P.sub.2) 9.4 p.b.w.; (iv) magnesium carbonate (MgCO.sub.2) 6 p.b.w.; (v) zinc oxide (ZnO) 2.3 p.b.w.; and (vi) 40% solids acrylic latex emulsion additive 3.5 p.b.w.

(251) The reagents were mixed in that order in two separate beakers. These were then mixed in a 1:1 ratio and mixed with a high speed mixer until uniform dispersal was achieved.

(252) It is to be noted that this example is not photocatalytically active as no photocatalytically active nanoparticles were included in this formulation.

(253) However, as a based formulation, the following tests were performed: (i) coating finish; (ii) mandrel bend test; and (iii) coating finish. The results are presented in Table 7 below.

Non-Photocatalytic Example 1C

(254) The following example relates to a base non-photocatalytic coating composition.

(255) A two part water based inorganic photonic coating was manufactured comprising a first composition (part A) and a second composition (part B).

(256) The first composition (part A) comprised: (i) potassium silicate (BETOLIN® K35, Wöllner GmbH, Ludwigshafen) 68.3 p.b.w.; (ii) rutile titanium dioxide (TiO.sub.2) having an average particle size of 500 nm 20 p.b.w.; (iii) calcined kaolin (Al.sub.2O.sub.3.2SiO.sub.2) 7.4 p.b.w.; (iv) talc (e.g. hydrated magnesium silicate (H.sub.2Mg.sub.3(SiO.sub.3).sub.4 or Mg.sub.3Si.sub.4O.sub.10(OH).sub.2)) 9.6 p.b.w.; (v) zinc stearate (C.sub.36H.sub.70O.sub.4Z.sub.n) 0.3 p.b.w.; (vi) zinc oxide (ZnO) 0.2 p.b.w.

(257) The second composition (part B) comprised: (i) water 56.7 p.b.w.; (ii) hydroxyethyl cellulose (CH.sub.2CH.sub.2OH) 0.6 p.b.w.; (iii) trimagnesium orthophosphate (Mg.sub.3O.sub.8P.sub.2) 9.4 p.b.w.; (iv) magnesium carbonate (MgCO.sub.2) 6 p.b.w.; (v) zinc oxide (ZnO) 2.3 p.b.w.; and (vi) 40% solids acrylic latex emulsion additive 7.55 p.b.w.

(258) The reagents were mixed in that order in two separate beakers. These were then mixed in a 1:1 ratio and mixed with a high speed mixer until uniform dispersal was achieved.

(259) It is to be noted that this example is not photocatalytically active as no photocatalytically active nanoparticles were included in this formulation.

(260) However, as a based formulation, the following tests were performed: (i) coating finish; (ii) mandrel bend test; and (iii) coating finish. The results are presented in Table 7 below.

Non-Photocatalytic Example 1D

(261) The following example relates to a base non-photocatalytic coating composition.

(262) A two part water based inorganic photonic coating was manufactured comprising a first composition (part A) and a second composition (part B).

(263) The first composition (part A) comprised: (i) potassium silicate (BETOLIN® K35, Wöllner GmbH, Ludwigshafe) 68.3 p.b.w.; (ii) rutile titanium dioxide (TiO.sub.2) having an average particle size of 500 nm 20 p.b.w.; (iii) calcined kaolin (Al.sub.2O.sub.3.2SiO.sub.2) 7.4 p.b.w.; (iv) talc (e.g. hydrated magnesium silicate (H.sub.2Mg.sub.3(SiO.sub.3).sub.4 or Mg.sub.3Si.sub.4O.sub.10(OH).sub.2)) 9.6 p.b.w.; (v) zinc stearate (C.sub.36H.sub.70O.sub.4Z.sub.n) 0.3 p.b.w.; and (vi) zinc oxide (ZnO) 0.2 p.b.w.

(264) The second composition (part B) comprised: (i) water 56.7 p.b.w.; (ii) hydroxyethyl cellulose (CH.sub.2CH.sub.2OH) 0.6 p.b.w.; (iii) trimagnesium orthophosphate (Mg.sub.3O.sub.8P.sub.2) 9.4 p.b.w.; (iv) magnesium carbonate (MgCO.sub.2) 6 p.b.w.; (v) zinc oxide (ZnO) 2.3 p.b.w.; and (vi) 40% solids polydimethylsiloxane (“PDMS” (C.sub.2H.sub.6OSi).sub.n) latex emulsion additive 3.5 p.b.w.

(265) The reagents were mixed in that order in two separate beakers. These were then mixed in a 1:1 ratio and mixed with a high speed mixer until uniform dispersal was achieved.

(266) It is to be noted that this example is not photocatalytically active as no photocatalytically active nanoparticles were included in this formulation.

(267) However, as a based formulation, the following tests were performed: (i) coating finish; (ii) mandrel bend test; and (iii) coating finish. The results are presented in Table 7 below.

Non-Photocatalytic Example 1E

(268) The following example relates to a base non-photocatalytic coating composition.

(269) A two part water based inorganic photonic coating was manufactured comprising a first composition (part A) and a second composition (part B).

(270) The first composition (part A) comprised: (i) potassium silicate (BETOLIN® K35, Wöllner GmbH, Ludwigshafen) 68.3 p.b.w.; (ii) rutile titanium dioxide (TiO.sub.2) having an average particle size of 500 nm 20 p.b.w.; (iii) calcined kaolin (A.sub.2O.sub.3.2SiO.sub.2) 7.4 p.b.w.; (iv) talc (e.g. hydrated magnesium silicate (H.sub.2Mg.sub.3(SiO.sub.3).sub.4 or Mg.sub.3Si.sub.4O.sub.10(OH).sub.2)) 9.6 p.b.w.; (v) zinc stearate (C.sub.36H.sub.70O.sub.4Z.sub.n) 0.3 p.b.w.; and (vi) zinc oxide 0.2 p.b.w.

(271) The second composition (part B) comprised: (i) water 56.7 p.b.w.; (ii) hydroxyethyl cellulose (CH.sub.2CH.sub.2OH) 0.6 p.b.w.; (iii) trimagnesium orthophosphate (Mg.sub.3O.sub.8P.sub.2) 9.4 p.b.w.; (iv) magnesium carbonate (MgCO.sub.2) 6 p.b.w.; (v) zinc oxide (ZnO) 2.3 p.b.w.; and (vi) 40% solids polydimethylsiloxane (“PDMS” (C.sub.2H.sub.6OSi).sub.n) latex emulsion additive 7.55 p.b.w.

(272) The reagents were mixed in that order in two separate beakers. These were then mixed in a 1:1 ratio and mixed with a high speed mixer until uniform dispersal was achieved.

(273) It is to be noted that this example is not photocatalytically active as no photocatalytically active nanoparticles were included in this formulation.

(274) However, as a based formulation, the following tests were performed: (i) coating finish; (ii) mandrel bend test; and (iii) coating finish. The results are presented in Table 7 below.

(275) Results—Application/Applicability, Adhesion and Coating Finish/Flexibility

(276) Examples 1A-1E detailed above were subjected to the following tests.

(277) Mandrel Bend Test: The samples were bent round a 6 mm cylindrical mandrel. If the coating cracked and detached from the aluminium sample this was counted as a fail.

(278) Cross Hatch Adhesion Test: The samples adhesion to aluminium was tested with a cross hatch adhesion test.

(279) Coating Finish: The general usability of the coating was rated as “Fail”, “Acceptable” or “Pass” according to the number of coating defects and ease of application of the coating.

(280) TABLE-US-00007 TABLE 7 Coating Example Application/applicability Adhesion finish/flexibility 1C Pass 4 A Fail 1B Pass 4 A Fail 1E Poor 4 A Fail 1D Pass 4 A Pass 1A Pass 4 A Pass

(281) This demonstrates that whilst acrylic latex additives can improve the rheology and usability of the coating it generally vitiates the mechanical properties of the coating. PDMS ((C.sub.2H.sub.6OSi).sub.n) emulsion additives should be minimised to below 5 wt % to ensure there is no significant effect on usability or flexibility.

(282) Photocatalytic Coating Compositions

(283) The previous section demonstrated it was feasible to get flexible coatings with high solar reflectance for aluminium. The following section outlines formulation variants to incorporate photocatalytic capabilities within the silicate layer in accordance with various embodiments of the present invention.

Inventive Example 2

(284) A water based coating was prepared by mixing together two compositions.

(285) The first composition (part A) comprised: (i) potassium silicate (BETOLIN® K35, Wöllner GmbH, Ludwigshafen) 26 p.b.w.; (ii) photocatalytic titanium dioxide (TiO.sub.2) (DEGUSSA (EVONIK)® P25) 15 p.b.w.; (iii) colloidal silica (SiO.sub.2) (LUDOX® SK, Grace GMBH and Co) 18 p.b.w.; (iv) calcium carbonate (CaCO.sub.3) 5 μm 30 p.b.w.; (v) sodium aluminiosilicate (AlNa.sub.12SiO.sub.5) 1.5 p.b.w.; and (vi) stabiliser 1.5 p.b.w.

(286) The second composition (Part B) comprised: (i) water 70.4 p.b.w.; (ii) hydroxyethyl cellulose (CH.sub.2CH.sub.2OH) 0.6 p.b.w.; (iii) magnesium carbonate (MgCO.sub.2) 9.2 p.b.w.; (iv) magnesium oxide (MgO) 4.6 p.b.w.; and (v) zinc oxide (ZnO) 2 p.b.w.

(287) The reagents or compositions were mixed in the order as listed above in two separate beakers. The contents of the two beakers were then mixed in a 1:1 ratio and mixed with a high speed mixer until uniform dispersal was achieved.

Inventive Example 3

(288) A water based coating was prepared by mixing together two compositions.

(289) The first composition (part A) comprised: (i) potassium silicate (BETOLIN® K35, Wöllner GmbH, Ludwigshafen) 26 p.b.w.; (ii) photocatalytic titanium dioxide (TiO.sub.2) (DEGUSSA (EVONIK)® P25) 15 p.b.w.; (iii) colloidal silica (SiO.sub.2) (LUDOX® SK, Grace GMBH and Co) 18 p.b.w.; (iv) calcined kaolin (Al.sub.2O.sub.3.2SiO.sub.2) 12 p.b.w.; (v) talc (e.g. hydrated magnesium silicate (H.sub.2Mg.sub.3(SiO.sub.3).sub.4 or Mg.sub.3Si.sub.4O.sub.10(OH).sub.2)) 18 p.b.w.; (vi) sodium aluminiosilicate (AlNa.sub.12SiO.sub.5) 1.5 p.b.w.; and (vii) stabiliser 1.5 p.b.w.

(290) The second composition (part B) comprised: (i) water 70.4 p.b.w.; (ii) hydroxyethyl cellulose (CH.sub.2CH.sub.2OH) 0.6 p.b.w.; (iii) trimagnesium orthophosphate (Mg.sub.3O.sub.8P.sub.2) 9.2 p.b.w.; (iv) magnesium carbonate (MgCO.sub.2) 4.6 p.b.w.; and (v) zinc oxide (ZnO) 2 p.b.w.

(291) The reagents or compositions were mixed in the order as listed above in two separate beakers. The contents of the two beakers were then mixed in a 1:1 ratio and mixed with a high speed mixer until uniform dispersal was achieved.

(292) In Example 2 and Example 3, high solar reflectivity is achieved with relatively high volumes or wt % of titanium dioxide (TiO.sub.2) (DEGUSSA (EVONIK)® P25) or equivalent and other high brightness materials including sodium aluminosilicate (AlNa.sub.2SiO.sub.5). These examples combine the coating properties of Example 1A with photocatalytic properties to provide a durable, self-cleaning coating for cooling overhead lines. Once the first coating or mixture is applied to an electrical conductor, the first coating or mixture is preferably dehydrated or dried. According to a preferred embodiment the conductor and applied coating is preferably thermally cured.

(293) Examples have been given above of various two-part compositions. However, according to various further embodiments of the present invention the components necessary for providing the first coating 401 may be provided in a single composition which is formed or mixed and then sprayed or painted on to the conductor 400. Accordingly, although a two-part kit may be preferred it is not essential to provide the various components which form the single coating in a multi-part kit. Instead, all the components may be provided in a single mixture.

(294) Water Based Alkali Metal Silicate Inorganic Coatings

(295) According to the preferred embodiment the coating or mixture which is provided on the electrical conductor comprises an inorganic binder which preferably comprises a water based alkali metal silicate binder. Water based silicate coatings include a silicate anion stabilised by an alkali metal cation as shown in Eqn. 3 below:

(296) ##STR00006##

(297) Eqn. 3 above illustrates equilibrium between undissociated silanol (Si—OH) groups and an alkali metal stabilised silicate anion (Si—O.sup.−).

(298) According to various embodiments the alkali metal cation may comprise either sodium, potassium or lithium creating sodium silicate, potassium silicate or lithium silicate.

(299) The above preferred water-based coatings may be cured by a condensation reaction whereby the silicate anions condense to form a siloxane chain and produce water as shown below:

(300) ##STR00007##

(301) Eqn. 4 above shows equilibrium between two silanol groups and a siloxane bond, with water as a by-product.

(302) The full removal of water is desirable for the silicate polymer to form completely i.e. the equilibrium needs to be driven completely to the right. Without the full removal of water, the film might resolubilise and the coating might degrade.

(303) The coatings according to various embodiments of the present invention may be self-cured through the addition of divalent metal cations and/or may be post-cured with dilute phosphoric acid. According to various embodiments dried films may be assisted by the addition of divalent metal cations such as Mg.sup.2+ and Ca.sup.2+. The resultant coatings according to various embodiments are moisture stable at ambient temperatures.

(304) According to various embodiments the alkali metal silicate film or coating may be cured. According to an embodiment the coating may be subjected to a stepwise thermal curing process over a period of several hours. The thermal curing process may according to various embodiments be for a period of 4-24 hours. According to various embodiments, the alkali metal silicate film or coating may be thermally cured for a period of <1 hour, 1-2 hours, 2-3 hours, 3-4 hours, 4-5 hours, 5-6 hours, 6-7 hours, 7-8 hours, 8-9 hours, 9-10 hours, 10-11 hours, 11-12 hours, 12-13 hours, 13-14 hours, 14-15 hours, 15-16 hours, 16-17 hours, 17-18 hours, 18-19 hours, 19-20 hours, 20-21 hours, 21-22 hours, 22-23 hours, 23-24 hours or >24 hours.

(305) According to various embodiments the thermal curing process may be arranged to dehydrate the silicate film or inorganic coating which includes a self-cleaning photocatalytic agent.

(306) According to various embodiments the thermal curing process may comprise a stepwise curing process in order to incrementally dehydrate the film and cause the first coating or mixture to solidify or otherwise harden.

(307) According to various embodiments the final curing temperature may in the range 50-80° C. For example, the final curing temperature may be in the range 50-60° C., 60-70° C. or 70-80° C. In particular, if the coating is applied to a conductor which has a maximum operating temperature of 80° C. then the final curing temperature may be arranged to be s 80° C., s 90° C. or s 100° C.

(308) According to other embodiments the final curing temperature may in the range 150-250° C. For example, the final curing temperature may be in the range 150-160° C., 160-170° C., 170-180° C., 180-190° C., 190-200° C., 200-210° C., 210-220° C., 220-230° C., 230-240° C. or 240-250° C. In particular, if the coating is applied to a conductor which has a maximum operating temperature of 250° C. then the final curing temperature may be arranged to be ≤250° C., ≤260° C., ≤270° C., ≤280° C., ≤290° C. or ≤300° C.

(309) The silicate coating which is applied to conductors according to various embodiments may have a long lifetime due to their purely inorganic nature, which makes degradation by UV and general atmospheric exposure very limited.

(310) The silicate inorganic coating including a photocatalytic agent is also particularly effective as a self-cleaning layer which maintains the substantially white coating to a high level of whiteness for an extended period of time.

Inventive Example 4

(311) A particularly preferred water based coating was prepared by mixing together two compositions. The first composition (part A) comprised: (i) potassium silicate (BETOLIN® 20 K35, Wollner GmbH, Ludwigshafen) 64 p.b.w.; (ii) rutile titanium dioxide (500 nm APS) 8 p.b.w.; (iii) photocatalytic titanium dioxide (TiO.sub.2) (DEGUSSA (EVONIK)® P25) 3.2 p.b.w.; (iv) calcined kaolin (Mattex Pro BSF) 1.88 p.b.w.; (v) sodium aluminiosilicate (AlNa.sub.12SiO.sub.5) 1.5 p.b.w.; and (vi) a stabiliser 1.5 p.b.w.

(312) The second composition (Part B) comprised: (i) water 15 p.b.w.; (ii) 25 hydroxyethyl cellulose (CH.sub.2CH.sub.2OH) 0.6 p.b.w.; (iii) trimagensium orthophosphate (4.5 p.b.w) and (iv) zinc oxide (ZnO) 2 p.b.w.

(313) The reagents or compositions were mixed in the order as listed above in two separate beakers. The contents of the two beakers were then mixed in a 1:1 ratio and mixed with a high speed mixer until uniform dispersal was achieved.

Tests Performed on Inventive Example 4

(314) The following tests were performed on Inventive Example 4.

(315) Coating Finish: The general usability of the coating was rated as “Fail”, “Acceptable” or “Pass” according to the number of coating defects and ease of application of the coating.

(316) Cross Hatch Adhesion Test: The sample's adhesion to aluminium was tested with a cross hatch adhesion test.

(317) Mandrel Bend Test: The sample was bent round a 6 mm cylindrical mandrel. If the coating cracked and detached from the aluminium sample then this was counted as a fail.

(318) Solar Reflectivity: UV-VIS-NIR analysis was carried out using a Jasco V670 UVVIS-NIR spectrometer with ISN-723 integrating sphere attachment. An integrating sphere attachment allowed collection of diffuse radiation (about 180°) reflected by the sample. The total solar reflectance was calculated.

(319) Thermal Emissivity: In accordance with ASTM C 1371-15 Standard Test Method for Determination of Emittance of Materials Near Room Temperature Using Portable Emissometers. Emissivity was measured using a D & S emissometer without traceability to reference standards as described in Clause 6.1.5 of the standard. The results are for five different positions of the sample surface which have then been averaged.

(320) Current Cycling: A circuit was set up with a coated and uncoated conductor connected in series. The conductor comprised an Aluminium Conductor Steel Reinforced (“ACSR”) conductor. Thermocouples were inserted into the conductor core. A specified level of current was transmitted through the conductor for 30 minutes which had the effect of increasing the temperature of the conductor. The conductor was then allowed to cool for 30 minutes. The process was then repeated and cycled. This test demonstrates a compatible coefficient of thermal expansion between the coating and the aluminium conductor.

(321) Outdoor Cooling Performance: An uncoated and coated Aluminium Conductor Steel Reinforced (“ACSR”) conductor were connected in series and were suspended two metres above the ground with full exposure to meteorological conditions. The conductors were subjected to 200 A current and the resulting temperatures were recorded every second for a week by thermocouples which were inserted into the conductor cores. This test demonstrated real world cooling performance of coated conductors compared with uncoated conductors in the United Kingdom during the month of May.

Results of Testing Inventive Example 4

(322) The results of testing Inventive Example 4 are summarised below:

(323) TABLE-US-00008 Coating Finish Pass Crosshatch adhesion 5 B Mandrel Bend Test Pass Solar Reflectance 0.903 Thermal Emissivity 0.93

(324) FIG. 12 shows the results of the current cycling test and shows that Inventive Example 4 was particularly effective in reducing the temperature of the Aluminium Conductor Steel Reinforced (“ACSR”) conductor.

(325) FIG. 13 shows the results of the current cycling test performed on Inventive Example 4 in terms of the temperature reduction (%) per cycle.

(326) FIG. 14 shows the results of the outdoor cooling performance test performed on Inventive Example 4.

(327) FIG. 15 shows the temperature reduction (%) difference between Inventive Example 4 and an uncoated conductor during a week in the month of May in the United Kingdom.

(328) The above results and testing illustrate that Inventive Example 4 comprises a particularly beneficial composition which, in use, forms a first coating on a conductor which is particularly effective in reducing the temperature of the conductor as well as having beneficial self-cleaning properties.

(329) Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the accompanying claims.