Patent Description:
Power distribution systems, such as on aircraft, commonly include cabling to convey electric power to various electrical devices connected to the power distribution system. The cabling extends between terminations and joints interconnecting components of the system and generally includes a conductor sheathed within an insulator and reinforced with external shield. The shield typically extends continuously along the length of the insulation and is removed at the joints and terminations for purposes of mechanically connecting the cable to the joint or termination. Removal of the shield interrupts the effect that the shield otherwise provides to the electric field associated with electric current flowing through the cabling. The electric field extends radially through the insulator along the unshielded portion of the cabling and exerts stress on the insulator according to voltage.

In some electric systems the stress can potentially cause electrical breakdown of the insulator. To limit stress in such systems field grading device can be employed. For example, in high voltage systems, capacitive field grading devices like stress-cones can be attached to the unshielded portion of the cable to limit stress in the underlying insulator. In low and medium voltage applications resistive field grading devices cylindrical grading element with high conductivity, or field strength-dependent conductivity can be attached to the unshielded cabling portion. Such capacitive and resistive field grading devices limit electrical stress by distributing the electric field along the length of the unshielded portion of the cabling.

Such systems and methods have generally been acceptable for their intended purpose. However, there remains a need in the art for improved field grading members, cables, and methods of making field grading members. <CIT> relates to a cable fitting for a high voltage direct current transmission cable. <CIT> relates to an electroconductive compound in flake form. <CIT> relates to voltage switchable dielectric material. <CIT> relates to a method of building a cable termination.

A field grading member is provided in claim <NUM>. The field grading member includes a polymeric matrix and a particulate filler of particulate bodies distributed within the polymeric matrix. The particulate bodies of the particulate filler include a core formed from a semiconductor material, an oxide mixed layer deposited on the core, and a conducting oxide layer deposited on the oxide mixed layer to provide an electrical percolation path through the polymeric matrix triggered by strength of an electric field extending through the field grading member.

In addition to one or more of the features described above, or as an alternative, further examples of the field grading member may include that the semiconductor material forming the cores of the particulate bodies is a semiconductor oxide.

In addition to one or more of the features described above, or as an alternative, further examples of the field grading member may include that the semiconductor material forming the cores of the particulate bodies is zinc oxide.

In addition to one or more of the features described above, or as an alternative, further examples of the field grading member may include that the semiconductor material forming the cores of the particulate bodies includes unincorporated oxygen.

In addition to one or more of the features described above, or as an alternative, further examples of the field grading member may include that the oxide mixed layer of the particulate bodies also includes an oxide of the semiconductor material forming the cores of the particulate bodies and that the conducting layer does not include the oxide of the semiconductor material forming the cores of the particulate bodies.

In addition to one or more of the features described above, or as an alternative, further examples of the field grading member may include that the oxide mixed layer of the particulate bodies consists of zinc oxide and tin oxide.

In addition to one or more of the features described above, or as an alternative, further examples of the field grading member may include that the conducting layer of the particulate bodies consists of tin oxide.

In addition to one or more of the features described above, or as an alternative, further examples of the field grading member may include that the cores of the particulate bodies consist of zinc oxide, a dopant, and unincorporated oxygen; that the oxide mixed layers of the particulate bodies consist of zinc oxide and tin oxide; and that the conducting oxide layers of the particulate bodies consist of tin oxide.

A cable includes a conductor member, an insulator member extending about the conductor member, and a field grading member as described above. The field grading member abuts the insulator member and extends along a portion of the insulator member.

In addition to one or more of the features described above, or as an alternative, further examples of the cable may include that the cable has a shielded portion and an unshielded portion, a shield extending about the shielded portion of the cable and removed from the unshielded portion of the cable, and that the field grading member overlays the unshielded portion of the cable.

In addition to one or more of the features described above, or as an alternative, further examples of the cable may include a joint including the field grading member.

In addition to one or more of the features described above, or as an alternative, further examples of the cable may include a termination including the field grading member.

In addition to one or more of the features described above, or as an alternative, further examples may include that the cable electrically connects a high voltage power source to an electrical load.

A method of making a field grading member is additionally provided in claim <NUM>. The method includes receiving a particulate include two or more cores formed from a semiconductor material, depositing an oxide mixed layer on each of the two or more cores, depositing a conducting oxide layer on each of the oxide mixed layers of the cores, and distributing the particulate as a particulate filler within a polymeric matrix to form a field grading member.

In addition to one or more of the features described above, or as an alternative, further examples of the method may include that depositing at least one of the oxide mixed layer and the conducting oxide layer includes immersing the two or more cores in a metal halide solution.

In addition to one or more of the features described above, or as an alternative, further examples of the method may include doping the semiconductor material with halide ions contained within the metal halide solution, that depositing the oxide mixed layer also includes depositing an oxide of the semiconductor material and an oxide of the metal contained within the metal halide solution on the two or more cores, and that depositing the conducting oxide layer also includes depositing a metal oxide formed from the metal contained within the metal halide solution.

In addition to one or more of the features described above, or as an alternative, further examples of the method may include that depositing one or more of the oxide mixed layer and the conducting oxide layer also includes exposing the two or more cores to a humidified vapor phase of a metal halide.

In addition to one or more of the features described above, or as an alternative, further examples of the method may include, at a cable including a conductor member and an insulator member extending about the conductor member, fixing the field grading member about a portion of the insulator member to limit magnitude of an electric field extending through the insulator member and associated with current flow through the conductor member.

Technical effects of the present disclosure include field grading filler materials with relatively high non-linearity in the resistivity (or conductivity) as a function of electric field magnitude. Technical effects also include the capability to limit electric stress associated with relatively high voltage for a given filler fraction of field grading material. Technical effects also include the capability to limit electric stress for a given voltage with a relatively low filler fraction, limiting the impact that the filler could otherwise have on the structure formed from an insulating matrix and field grading filler material.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an example implementation of a field grading member constructed in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other examples of field grading members, cables having field grading members, and methods of making field grading members and cables in accordance with the present disclosure, or aspects thereof, are provided in <FIG>, as will be described. The systems and methods described herein can be used for regulating electrical stress in cables communicating electrical power, such as high voltage power distribution systems on aircraft, though the present disclosure is not limited to aircraft or to high voltage power distribution systems in general.

Referring to <FIG>, a vehicle <NUM>, e.g., an aircraft, is shown. The vehicle <NUM> includes an electrical system <NUM> having a power source <NUM>, an electrical load <NUM>, and a cable <NUM>. The cable <NUM> electrically connects the power source <NUM> to the electrical load <NUM> through one or more of a joint <NUM> and a termination <NUM>. The joint <NUM> and/or the termination <NUM> include the field grading member <NUM> to regulate an electric field <NUM> (shown in <FIG>) within the cable <NUM> that is associated with an electric current <NUM> flowing through the cable <NUM>. Although shown and described herein as being part of the joint <NUM> or the termination <NUM> it is to be understood and appreciated that the field grading member <NUM> can also regulate electric fields in other structures of the cable <NUM>, such as portions of the cable that have been repaired by way of non-limiting example. In certain examples the power source <NUM> can be a direct current (DC) power source and the cable <NUM> configured to communicate DC power, e.g., DC power at upwards of <NUM> volts. It is also contemplated that the power source <NUM> can be an alternating current (AC) power source and that the cable <NUM> by configured to communicate AC power, e.g., upwards of <NUM> volts.

With reference to <FIG>, the field grading member <NUM> is shown. The field grading member <NUM>. The field grading member <NUM> includes polymeric matrix <NUM> and a particulate filler <NUM>. The polymeric matrix <NUM> includes an electrically insulative polymeric material <NUM>. Examples of suitable polymeric materials include ethylene diene rubber (EPDM) and silicone rubbers, and also thermoplastics such as polyethylene, polypropylene, and mixes thereof.

The particulate filler <NUM> is distributed within the polymeric matrix <NUM> and includes a plurality of particulate bodies <NUM>. In certain examples the particulate bodies are composite particulate bodies <NUM> and in this respect are formed from one or more conductive material and one or more insulative or semiconducting material. In accordance with certain examples the field grading member <NUM> is generally cylindrical in shape. In accordance with certain examples the field grading member <NUM> can have a contoured shape, e.g., tapering along an axial length of the field grading member <NUM>.

With reference to <FIG>, a particulate body <NUM> is shown according to an illustrative example. The particulate body <NUM> includes a core <NUM>, an oxide mixed layer <NUM>, and a conducting oxide layer <NUM>. The core <NUM> is formed from a semiconductor material <NUM>. The oxide mixed layer <NUM> is deposited on the core <NUM>. The conducting oxide layer <NUM> is deposited on the oxide mixed layer <NUM> to provide an electrical percolation path <NUM> through the polymeric matrix <NUM> triggered by strength of the electric field <NUM> (shown in <FIG>) extending through the field grading member <NUM>.

In certain examples the semiconductor material <NUM> forming the core <NUM> includes a semiconductor oxide. In accordance with certain examples the semiconductor material <NUM> forming the core <NUM> includes zinc oxide. It is also contemplated that the semiconductor material <NUM> forming the core <NUM> can include unincorporated oxygen <NUM>. In further examples the semiconductor material <NUM> forming the core <NUM> can include a dopant <NUM>. In certain examples the dopant includes one or more dopants selected from a group including aluminum, gallium, nitrogen, and fluorine. In accordance with certain examples the dopant includes an ion selected from a group including one or more of aluminum ions, gallium ions, nitrogen ions, and fluoride ions. It is contemplated that, in accordance with certain examples, that the dopant consists of (or consist essentially of) fluoride ions.

The zinc oxide forming the core <NUM> provides high electron mobility, high thermal conductivity, and an N-type semi-conductive electrical transition of relatively wide band gap, e.g., on the <NUM> electron-volts. As will be appreciated by those of skill in the art in view of the present disclosure, semiconductors having relatively wide band gaps can operate at higher voltages, higher frequencies, and higher temperatures than semiconductor materials with smaller band gaps, such as silicon and gallium arsenide for example. Further, each vacancy within the zinc oxide forming the core <NUM> provides two (<NUM>) electrons, the number of vacancies within the core can be adjusted according to the technique used to form the core <NUM>, and conductivity of the core <NUM> is sensitive (and therefore tunable) to surface modification.

In certain examples the oxide mixed layer <NUM> of the particulate body <NUM> include an oxide <NUM> of the semiconductor material <NUM> forming the core <NUM> of the particulate body <NUM>. In accordance with certain examples the oxide mixed layer <NUM> of the particulate body <NUM> can include the oxide <NUM> of the semiconductor material <NUM> forming the core <NUM> of the particulate body <NUM> and another oxide <NUM>. For example, it is contemplated that the oxide mixed layer <NUM> can consist, or consist essentially, of zinc oxide and tin oxide. Including a conducting oxide contained within a matrix of the mixed oxide layer enhances the electrical performance of the underlying core. Specifically, the conductive oxide in conjunction with the dopant (such as fluoride ions) helps move electric field relatively efficiently between particles within the insulting polymer matrix. The mixed oxide layer also affords an additional transport medium for electrons that helps extend beyond the electron transport properties of the semiconductor core.

In certain examples the conducting oxide layer <NUM> include an oxide <NUM> that does not include the oxide of the semiconductor material <NUM> forming the core <NUM> of the particulate body <NUM>. In accordance with certain examples the conducting oxide layer <NUM> of the particulate body <NUM> consists, or consists essentially, of tin oxide. Advantageously, the conducting oxide layer <NUM> provides additional assistance in transport of electrons between particles to particle relative to the electron transport between semiconductor particles not having the conducting oxide layer <NUM>.

In the illustrated example the core <NUM> of the particulate body <NUM> consists of zinc oxide, fluorides ions, and unincorporated oxygen. The oxide mixed layer <NUM> of the particulate body <NUM> consists of zinc oxide and tin oxide. The conducting oxide layer <NUM> of the particulate body <NUM> consists of tin oxide. Zinc oxide and other wide band gap oxide-based semiconductors are desirable due to the versatility of the temperature and voltage range that wide band gap semiconductors can operate in compared to non-wide band gap semiconductors. Without being bound by a particular theory, it is believed that conducting oxides within the conducting oxide layer <NUM> improve the charge transfer compared to using a semiconductor particle without the conducting oxide layer <NUM>.

With reference to <FIG>, the cable <NUM> is shown with the field grading member <NUM> spaced apart from the cable <NUM> and abutting the cable <NUM>, respectively. The cable <NUM> is arranged to communicate the electric current <NUM> from the power source <NUM> (shown in <FIG>) to the electrical load <NUM> (shown in <FIG>) and includes a conductor member <NUM>, an insulator member <NUM>, and shielding <NUM>.

The conductor member <NUM> extends along a conductor axis <NUM> and is formed from an electrically conductive conductor material <NUM>. The conductor material <NUM> is selected to communicate the electric current <NUM> carried by the conductor member <NUM>. The conductor material <NUM> can include copper or a copper alloy by way of non-limiting example.

The insulator member <NUM> extends along the conductor member <NUM>, is fixed to the conductor member <NUM>, and is formed from an electrically insulative insulator material <NUM>. The insulator material <NUM> electrically isolates the conductor member <NUM> from the external environment <NUM> and is selected to accommodate the electric field <NUM> associated with the electric current <NUM> flowing through the conductor member <NUM>. The insulator material <NUM> can include a cross-linked polyethylene material by way of non-limiting example.

The shielding <NUM> extends partially along the insulator member <NUM>, is fixed along a shielded portion <NUM> of the cable <NUM>, is removed (absent) from an unshielded portion <NUM> of the cable <NUM> and is formed from an electrically conductive shielding material <NUM>. The shielding material <NUM> is selected to regulate the electric field <NUM> within the shielded portion <NUM> of the cable <NUM>, e.g., by distributing the electric field <NUM> within the conductor member <NUM> and the insulator member <NUM>. It is contemplated that the shielding <NUM> be electrically connected to a ground terminal <NUM>.

As will be appreciated by those of skill in the art in view of the present disclosure, shielding the cable <NUM> with the shielding <NUM> can limit the electrical stress exerted by the electric field <NUM> on the insulator member <NUM> by controlling uniformity of the electric field <NUM> axially within the insulator member <NUM> along the shielded portion <NUM> of the cable <NUM>. This is indicted schematically in <FIG> with the spacing shown between adjacent regulated electric field lines <NUM>, which extend axially within the insulator member <NUM> and along the shielded portion <NUM> of the cable <NUM>.

As will also be appreciated by those of skill in the art in view of the present disclosure, electrical stress exerted by the electric field <NUM> on the insulator member <NUM> within the unshielded portion <NUM> of the cable <NUM> can be greater than that within the shielded portion <NUM> of the cable <NUM>. This is also indicted schematically in <FIG> with the spacing shown between adjacent unregulated electric field lines <NUM>, which extend radially within the insulator member <NUM> and along the unshielded portion <NUM> of the cable <NUM>. The electrical stress can be relatively high at a terminal location <NUM> of the shielding <NUM>, varies in peak intensity according to voltage applied to the cable <NUM>, and in some cables can be of magnitude sufficient to cause electrical breakdown of the insulator material <NUM> forming the insulator member <NUM>. The field grading member <NUM> interacts with the electric field <NUM> to regulate the electrical stress within insulator member <NUM> associated with the electric current <NUM> flowing through the cable <NUM>.

With reference to <FIG>, the field grading member <NUM> is shown abutting the cable <NUM>. When integrated into the cable <NUM> the insulator member <NUM> underlays the field grading member <NUM> (the field grading member <NUM> thereby overlaying the insulator member <NUM>) and electrically separates the field grading member <NUM> from the conductor member <NUM>. More specifically, the field grading member <NUM> overlays the unshielded portion <NUM> of the cable <NUM>, the insulator member <NUM> thereby underlaying the field grading member <NUM> such that the field grading member <NUM> distributes the electric field <NUM> axially along the conductor axis <NUM>. Distribution of the electric field <NUM>, as indicated by the relatively large spacing between adjacent distributed regulated field lines <NUM> in relation to the unregulated field lines <NUM> (shown in <FIG>), limits the electrical stress exerted on the insulator member <NUM> by the electric field <NUM>. Limiting magnitude of the electrical stress in turn allows the insulator member <NUM> to be relatively small for a given voltage (and electric field magnitude) and/or have a higher voltage rating in comparison to cables not employing the field grading member <NUM>.

With reference to <FIG>, a method <NUM> of making a field grading member is shown. As shown with box <NUM>, the method <NUM> includes receiving a particulate including cores formed from a semiconductor material, e.g., cores <NUM> (shown in <FIG>) formed from the semiconductor material <NUM> (shown in <FIG>). The semiconductor material forming the cores is doped with halide ions, e.g., the dopant <NUM> (shown in <FIG>), contained within a metal halide solution, as shown with box <NUM>. Doping can be accomplished by immersing the cores in a metal halide solution or by exposing the cores to a humidified vapor phase of the metal halide, as shown with box <NUM>.

As shown with box <NUM>, an oxide mixed layer, e.g., the oxide mixed layer <NUM> (shown in <FIG>) is deposited on each of the cores. In certain examples depositing the oxide mixed layer includes depositing an oxide of the semiconductor material and an oxide of the metal contained within the metal halide solution on the cores, as shown with box <NUM>. Depositing the oxide mixed layer can be accomplished by immersing (or continuing to immerse) the cores in the metal halide solution or by exposing (or prolonging exposure) the cores to the humidified vapor phase of the metal halide, as shown with boxes <NUM> and <NUM>.

As shown with box <NUM>, a conducting oxide layer, e.g., the conducting oxide layer <NUM> (shown in <FIG>) is deposited on the oxide mixed layer coating each core. In certain examples deposing the conducting oxide layer can include depositing a metal oxide formed from the metal contained within the metal halide solution, as shown with box <NUM>. Depositing the conducting oxide layer can be accomplished by immersing the coated cores in a metal halide solution or by exposing the cores to a humidified vapor phase of the metal halide, as shown with boxes <NUM> and <NUM>. The particles are thereafter disposed as a particulate filler within a polymeric matrix to form a field grading member, e.g., the field grading member <NUM> (shown in <FIG>), as shown with box <NUM>. The field grading member can in turn be fixed to a cable, e.g., the cable <NUM> (shown in <FIG>), as shown with box <NUM>.

Cable joints and terminations in electrical systems can require field grading to manage the electric field, and the associated potential for electrical breakdown, that could otherwise exist at the joint or termination. In high voltage electrical systems capacitive grading can be employed at the cable joint or termination, such as by fixation of a stress-cone formed from a two-part rubber composition and defining a profile selected for the electric field otherwise present at the cable joint or termination. In low and medium voltage electrical systems resistive grading can be employed at the cable joint and termination, such as be fixation of a cylindrical grading element with relatively high conductivity, which can be dependent upon field strength.

In examples described herein a composite body is employed to provide field grading at a cable joint or termination. The composite body includes an electrically insulating matrix and a semiconductor filler. The semiconductor filler is tailored, by incorporating therein a dopant, to provide electrical conductivity commensurate with strength of the magnetic field at the cable joint or termination. In certain examples the doped semiconductor filler has relatively high non-linearity and in this respect exhibits a rapid rate of adjustment to electric field strength change in comparison to field grading bodies not employing doped semiconductor fillers.

Claim 1:
A field grading member (<NUM>), comprising:
a polymeric matrix (<NUM>); and
a particulate filler (<NUM>) distributed within the polymeric matrix, particulate bodies (<NUM>) of the particulate filler comprising:
a core (<NUM>) that includes zinc oxide doped with fluoride ions;
an oxide mixed layer (<NUM>) deposited on the core; and
a conducting oxide layer (<NUM>) deposited on the oxide mixed layer to provide an electrical percolation path through the polymeric matrix triggered by strength of an electric field extending through the field grading member.