Abstract: An arrangement for electrically conductively connecting two electrical units by means of a bipolar high voltage direct current transmission, in which between the units are arranged at least two electrical direct current cables constructed as superconductive cables. The superconductive cables are mounted separately from each other in a cryostat (1,2) suitable for conducting a cooling agent which has at least one metal pipe provided with a thermal insulation. The cryostats (1,2) are connected with at least one of their ends to a cooling plant (7) supplying the cooling agent and a pipeline (3) is placed parallel to the two cryostats (1,2). The pipeline (3) is connected at both its ends to the two cryostats (1,2) through valves (15,16,17) which are closed during uninterrupted operation and, in the case of an interruption at one of the superconductive cables, the pipeline (3) serves with the then open valves for conducting the cooling agent intended for the cryostat of the impaired cable.

Abstract: Provided is a method of forming a superconducting wire. In the method, a buffer layer is formed on a substrate. Then, a superconducting precursor film is formed on the substrate formed with the pinning seed layer. Thereafter, the substrate formed with the superconducting precursor film is heat-treated to form a superconducting film including magnetic flux pinning centers on the substrate. The magnetic flux pinning centers comprise at least one element included in the pinning seed layer, and at least one element included in the superconducting precursor film.

Abstract: A method for manufacturing a superconducting wire includes the following steps. A laminate metal having a first metal layer and a Ni layer formed on the first metal layer is prepared. An intermediate layer (20) is formed on the Ni layer of the laminate metal. A superconducting layer (30) is formed on the intermediate layer (20). By subjecting the laminate metal to a heat treatment after at least either of the step of forming a intermediate layer (20) and the step of forming a superconducting layer (30), a nonmagnetic Ni alloy layer (12) is formed from the laminate metal.

Abstract: A cryogenically-cooled HTS cable is configured to be included within a utility power grid having a maximum fault current that would occur in the absence of the cryogenically-cooled HTS cable. The cryogenically-cooled HTS cable includes a continuous liquid cryogen coolant path for circulating a liquid cryogen. A continuously flexible arrangement of HTS wires has an impedance characteristic that attenuates the maximum fault current by at least 10%. The continuously flexible arrangement of HTS wires is configured to allow the cryogenically-cooled HTS cable to operate, during the occurrence of a maximum fault condition, with a maximum temperature rise within the HTS wires that is low enough to prevent the formation of gas bubbles within the liquid cryogen.

Abstract: The present invention is configured such that, in a low AC loss oxide superconductor constituted by providing an oxide superconducting layer 6 on a substrate 1, said oxide superconducting layer 6 is separated into a plurality of filament conductors 2 in parallel to the lengthwise direction of said substrate 1 by dividing grooves 3 plurally formed in the widthwise direction of said substrate, and a high-resistance oxide 8 is formed in said dividing grooves 3. Because of the invention, it is possible to increase the insulation properties of individually divided mated filament conductors, and to obtain an oxide superconductor that has low AC loss.

Abstract: An oxide superconductor wire includes: a tape-shaped oxide superconductor laminate that is formed by providing an intermediate layer on a front surface side of a metal tape-shaped substrate, providing an oxide superconductor layer on the intermediate layer, and providing a protective layer on the oxide superconductor layer; and a coating member that includes a metal tape and a low melting point metal layer, in which the metal tape has a wider width than that of the oxide superconductor laminate and covers the protective layer surface of the oxide superconductor laminate, both side surfaces of the oxide superconductor laminate, and both end portions of a substrate back surface side in a width direction thereof, and both end portions of the metal tape in a width direction thereof are provided to cover both the end portions of the substrate back surface.

Abstract: A superconducting cable for power lead and transmission applications is disclosed. The high performance power cable comprises two type of different superconducting cable structures arranged co-axially, and the magnetic fields of their transport currents mutually enhance their performances. A further object is a power distribution cable that minimizes the cryogenic losses by a design of the compact cable cross-sections.

Abstract: A device and method for making a persistent joint allowing end terminations of superconducting MgB2 wire to be joined with a superconducting bridge. Superconducting electromagnetic coils may be joined in series or joining of coil assemblies to current sources and the two ends of a persistent switch. The device includes wire filaments with end preparation exposing reacted MgB2, inserted into a block and surrounded with Mg+B and/or MgB2 in powder, solid, slurry or sol-gel form and subsequently reacted to establish a bridge of superconducting MgB2 electrically connecting the superconducting MgB2 wires. Autonomous operation of the superconducting background magnet coils in magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) devices are allowed, or similar devices where autonomous operation of an MgB2 based superconducting magnet is required. The low resistant joint will also be beneficial for other superconducting applications such as fault current limiters, motors, generators, etc.

Abstract: A multilayer superconducting wire 7 with essentially round cross sectional area where the outer surface of the round wire is provided with a high temperature superconductor layer 3 and where at least the high temperature superconductor layer 3 is fabricated as a spiral running along the length of the superconductor wire 7 in parallel lanes 15.

Abstract: A rotating machine includes a stator and a rotor configured to rotate within the stator. Rotor windings are supported in the rotor and are formed of a laminated electrical conductor in a single-layer saddle coil configuration. The conductor includes a first support lamina, a second support lamina, an insert including a high temperature superconductor disposed between the first and second support lamina, and a filler material surrounding the insert that bonds the insert to each of the first and second support lamina. At the location between the first support lamina and second support lamina corresponding to the location of the insert, the width dimension of the filler material on each side of the insert is at least 10 percent of a width of the conductor. The conductor is configured to carry at least 600 Amperes per turn and have a C-axis tensile strength of at least 21 MPa.

Abstract: An insulated high-temperature wire superconductor includes a wire of a noninsulated high temperature wire superconductor, the width of which is at least 10 times its thickness and in which a high-temperature superconductor is introduced into a matrix or is applied to a substrate. The wire is provided with an electrically non-conducting insulating layer on both sides such that the two insulating layers have an insulating edge width in a range from 2 mm to 200 mm which projects in relation to the wire.

Abstract: An arrangement with at least one superconductive cable (1) is indicated which is arranged in a cryostat (KR) serving for guiding a cooling agent, wherein the cryostat (KR) includes at least one thermally insulated metal pipe. To the outside of the cryostat (KR) is applied an electrically well conductive material that is composed of at least two strands (6, 7) which are wound one around the other with oppositely pitched direction around the cryostat (KR). The strands are connected fixedly and immovably to the cryostat (KR) at fixed points (8) mounted longitudinally spaced along an axial length of said cryostat.

Abstract: An oxide superconductor wire includes: a superconductor laminate that comprises a substrate which is formed in a tape shape and an intermediate layer, an oxide superconductor layer, and a metal stabilizing layer which are laminated on the substrate; and an insulating coating layer that covers an outside surface of the superconductor laminate, Also, either the entire outside surface or the entire inside surface of the insulating coating layer is coated with a coating layer formed of a fluororesin.

Abstract: An RE123-based superconducting wire includes a base material, an intermediate layer formed on the base material, and an oxide superconducting layer which is formed on the intermediate layer and includes an oxide superconductor having a composition formula represented by RE1Ba2Cu3O7?? (RE represents one or two or more rare earth elements), in which the oxide superconducting layer includes 0.5 to 10 mol % of a Hf-including compound dispersed in the oxide superconducting layer as an artificial pinning center, a film thickness d of the oxide superconducting layer is d>1 ?m, and a current characteristic of Jcd/Jc1?0.9 (Jc1 represents a critical current density when the thickness of the oxide superconducting layer is 1 ?m, and Jcd represents the critical current density when the thickness of the oxide superconducting layer is d ?m) is satisfied.

Abstract: A junction box is provided which allows serial connection of the individual conductors of at least one high temperature superconductor (HTS) wire bundle. The junction box includes an electrical interface device disposed within a junction box housing. The interface device is configured receive both ends of each conductor of each HTS wire bundle, and to provide a superconductive electrical connection between respective first ends of conductors to respective second ends of other wire bundle conductors to form at least one superconductive multi-turn electromagnetic winding.

Abstract: A conductor for transmitting electrical power having a cylindrical core (1) clad with a strip of metallic material (2), possibly comprising a superconductor, placed, in the shape of a tube, longitudinally around said core (I), its longitudinal edges being welded to each other along a weld seam (3). The core (1) has a slot (4, 4?) placed under said weld seam (3).

Abstract: A rolled superconducting article includes: a cylindrical bobbin having a post in a cylindrical shape; a superconducting strip wound on the cylindrical bobbin in a rolled shape with a predetermined tension applied, wherein the superconducting strip is formed of a superconducting thin film, which is coated with a metal coating layer on a facing surface of the superconducting thin film, and a stabilizing substrate wound on the superconducting strip, wherein the stabilizing substrate is coated with a metal coating layer on a facing surface of the stabilizing substrate; an anti-bonding substrate wound on an outer surface of the stabilizing substrate with a predetermined tension applied; wherein the superconducting thin film is thermally adhered to the stabilizing substrate by heat-treating the rolled superconducting strip with the anti-bonding substrate wound therearound.

Abstract: A device and method for continuously forming superconducting wire, and products made therefrom. The method may include providing at least one continuous metal sheathing strip and at least one metal form, continuously forming the at least one continuous metal sheathing strip to form a partially open configuration, continuously filling the partially open configuration with magnesium diboride precursor comprising boron, and a metal form, and closing the partially open configuration thereby enclosing the magnesium diboride precursor comprising boron, and a metal form, to form a closed configuration. Subsequent reduction in diameter and elongation in length of the closed configuration, followed by heat treatment, catalyzes the transformation of the magnesium diboride precursor comprising boron, and the metal form, to magnesium diboride to form the superconducting wire.

Abstract: An arrangement for electrically conductively connecting two superconductive strip-shaped electrical conductors (1, 2) having at least approximately the same width, where the two conductors (1, 2) rest against each other with their end faces against each other in a connecting point (V). A strip (6) of superconductive material is soldered to the two conductors (1, 2), where the strip extends beyond both conductors so as to cover the connecting point (V). A strip (6) is used which has, only in the area of the connecting point (V) between the two conductors (1, 2), at least approximately the same width as the conductors, and where the strip narrows on both sides of the connecting point (V) and facing away from the connecting point (V).

Abstract: A system is specified having at least one superconducting cable (SK) which has at least one superconducting conductor (2), and having a cryostat (KR) which surrounds the same and has two metallic tubes, an inner tube (6) and an outer tube (7), which are arranged concentrically at a distance from one another, are corrugated transversely with respect to their longitudinal direction and between which vacuum insulation (8) is arranged. The cable (SK) has a central tubular support (1) for passing a coolant through, on which the superconducting conductor (2) rests. The cable (SK) is surrounded all around by a buffer layer (5) which protects the same against mechanical damage and consists of insulating material, and the inner tube (6) of the cryostat (KR) at least rests in a sealed manner on the buffer layer (5).

Abstract: In a coated high-temperature superconducting wire 1 in which a superconducting yttrium-based wire (high-temperature superconducting wire) 2 having a rectangular cross section is coated by an insulating layer 6, the insulating layer 6 is an electrodeposited film made of block copolymerized polyimide which contains siloxane bonds in a polyimide main chain and which has molecules with anionic groups. A coil formed from the superconducting yttrium-based wire 2 is impregnated with epoxy resin, and the epoxy resin is cured. The coil is configured such that the epoxy resin is completely separated from the superconducting yttrium-based wire 2 by the insulating layer 6.

Abstract: A superconducting device (1; 1a, 1b), having a coated conductor (2) with a substrate (3) and a quenchable superconducting film (4), wherein the coated conductor (2) has a width W and a length L, is characterized in that 0.5?L/W?10, in particular 0.5?L/W?8, and that the coated conductor (2) has an engineering resistivity ?eng shunting the superconducting film (4) in a quenched state, with ?eng>2.5?, wherein RIntShunt=?eng*L/W, with RIntShunt: internal shunt resistance of the coated conductor (2). The risk of a burnout of a superconducting device in case of a quench in its superconducting film is thereby further reduced.

Abstract: A coated conductor with a substantially round cross section has a high temperature superconductor layer which is sandwiched between an inner substrate layer and an outer substrate layer to place the high temperature superconductor layer in the region of neutral strain axis.

Abstract: An MgB2 superconducting wire excellent in critical current density property is supplied by using a crystalline boron powder which is low in costs and easy to obtain. For the wire, a precursor of the MgB2 superconducting wire is used, the precursor having a linear structure including a core region containing a magnesium powder and a boron powder, and a sheath region formed of a metal covering an outer circumferential portion of the core region. The boron powder is crystalline, and has a volume-mean particle size of 2 ?m or less.

Abstract: A termination unit for a multi-phase superconductor cable has, for each phase, a cylindrical modular element (1, 2, 3) having a thermally insulating external envelope (1A, 2A, 3A) containing a superconductor cable portion (7, 8, 9) contained in an internal envelope (1B, 2B, 3B) containing a cooling fluid. A branch element (4, 5, 6) of each phase, provided with an electrical connection element (4A, 5A, 6A), is arranged at the end of each said modular element, where each branch element (4, 5, 6) is directly connected to the corresponding cable portion (7, 8, 9) and only the electrical connection element (4A, 5A, 6A) projecting from the modular elements (1, 2, 3).

Abstract: A method of compensating for thermal contraction of superconducting and cryo-resistive cables. The method includes the steps of determining a compensation length for a cable such that when the cable is subjected to an operating temperature, the cable is in or near a stress-free state, and installing the cable into a pipe such that portions of the cable extend outwardly past ends of the pipe. The method further includes the steps of marking each end of the cable such that the determined compensation length is visibly shown, forcing the cable into the pipe at an ambient installation temperature such that a cable pattern is formed therein, and maintaining the cable in the pipe to prevent the cable from being pushed out of the pipe.

Abstract: A superconducting wire (1; 31), contains NbTi superconducting material and Cu, with one enclosing tube (2), in particular, a copper enclosing tube. At least three Al blocks (3a-3c) are disposed peripherally distributed in the enclosing tube (2) and at least three sections containing NbTi (4a-4c) are also disposed peripherally distributed in the enclosing tube (2) and separate the Al blocks (3a-3c) from one another in the peripheral direction. The Al blocks (3a-3c) each make large-surface contact with their adjacent sections containing NbTi (4a-4c). A stabilized NbTi superconducting wire is thereby provided, which has low weight and which can be manufactured at low cost. The superconducting wire has a reduced risk of crack formation, in particular, during wire drawing.

Abstract: A superconducting wire includes a superconductor layer and a carbon nanotube layer. The superconductor layer and the carbon nanotube layer are stacked on each other and rolled to form the superconducting wire. Thus, the superconductor layer and the carbon nanotube layer are simultaneously rolled and alternately stacked on each other.

Abstract: A method and composition for doped HTS tapes having directional flux pinning and critical current.

Abstract: A superconducting wire includes a linear superconductor and a carbon nanotube structure. The carbon nanotube structure is located on the linear superconductor.

Abstract: There is provided a superconductive cable wherein an efficiency of an electric power transmission is increased to a maximum and the superconductive cable is miniaturized by strengthening a longitudinal magnetic field in a superconductive material.

Abstract: Impurities are reduced in an oxide superconducting layer and in an interface between the oxide superconducting layer and an intermediate layer. A superconducting wire rod 1 has a structure including a substrate (10), an intermediate layer (20) formed on the substrate (10), a reaction suppressing layer (28) formed on the intermediate layer (20) and mainly containing polycrystalline SrLaFeO4+?1 or CaLaFeO4+?2, in which the ?1 and the ?2 each represent an amount of non-stoichiometric oxygen, and an oxide superconducting layer (30) formed on the reaction suppressing layer (28) and mainly containing an oxide superconductor.

Abstract: An arrangement is provided having a superconductive cable (SK) which consists of a superconductive conductor (1) and a superconductive screen (3) that encloses the latter with the interposition of a dielectric (2) and which is enclosed, with the inclusion of a free space (FR) for conveying a refrigerant, by a cryostat (KR) which consists of two metal tubes (4,5) arranged mutually concentrically, between which vacuum insulation (6) is arranged. Outside the screen (3), a tubularly closed layer (7, 8) of a ferromagnetic material is provided over the entire length of the cable (SK). It is preferably arranged on the outer circumference of the cryostat (KR).

Abstract: A method of managing thermal contraction of a superconductor cable (2) having a cable body surrounded by an external screen (2A) made form wound metal elements and installed between its ends in an enclosure (1) or cryostat filled with a cryogenic liquid, where the method includes mechanically applying a locking force loading only said screen (2A) at a so-called locking point (5A, 5B) in the vicinity of the ends of the cable.

Abstract: An MgB2 compound sheath superconducting wire includes a high stable metal having a specific electric resistance 7 ??cm or below at a room temperature and a high strength metal having a Vickers hardness 50 or above at a room temperature, both of which are assembled therewith to realize a high strength and a lengthy superconductor.

Abstract: Disclosed herein is a superconducting wire which is used in, for example, superconducting magnet energy storage systems. The superconducting wire includes: a wire comprising a metal substrate, a superconducting layer and a buffer interposed between the metal substrate and the superconducting layer; and a stabilizer layer plated on the wire, wherein an epoxy resin insulating layer coats the entire surface of the stabilizer layer. The superconducting wire makes it possible to reduce damage to an insulating material when forming the insulating material during the production of the superconducting wire, and it has a uniform surface and can be produced in a simple manner.

Abstract: An induction heating apparatus that can operate at current frequencies of greater than 60 Hz and at least 1 kW. The induction heating apparatus includes a high frequency power supply, a superconductive induction coil, and a fluid cooling system. A fluid cooling system is designed to cause a cooling fluid to flow at least partially about and/or through the superconductive induction coil.

Abstract: A method of controlling fault currents within a utility power grid is provided. The method may include coupling a superconducting electrical path between a first and a second node within the utility power grid and coupling a non-superconducting electrical path between the first and second nodes within the utility power grid. The superconducting electrical path and the non-superconducting electrical path may be electrically connected in parallel. The superconducting electrical path may have a lower series impedance, when operated below a critical current level, than the non-superconducting electrical path. The superconducting electrical path may have a higher series impedance, when operated at or above the critical current level, than the non-superconductor electrical path.

Abstract: An improved process for the preparation of oxide superconducting rods. The present invention provides a process for the preparation of oxide superconducting rods. The process includes the steps of a cold isopressing process without addition of binder, particularly thin and those based on Ag-added (Bi,Pb)2 Sr2 Ca2 Cu3 O10+x is disclosed.

Abstract: Provided is an oxide superconducting wire material, wherein pinning of magnetic flux, under an environment in which magnetic field is applied, can be conducted efficiently towards any magnetic-field applying angle direction, to secure a high superconductive property. The oxide superconducting wire material (100) is provided with a metal substrate (110), an intermediate layer (120) formed upon the metal substrate (110), and a REBaCuO-system superconductive layer (140) formed upon the intermediate layer (120). RE comprises one or more elements selected from Y, Nd, Sm, Eu, Gd, and Ho. Oxide particles including Zr are distributed within the superconductive layer (140) as magnetic-flux pinning points (145), and the mole ratio (y) of Ba included within the superconductive layer (140) is, when the mole ratio of Zr is assumed to be x, within a range of (1.2+ax)?y?(1.8+ax), wherein 0.5?a?2.

Abstract: The invention relates to a high temperature superconducting tape conductor having a flexible metal substrate that comprises at least one intermediate layer disposed on the flexible metal substrate and comprising terraces on the side opposite the flexible metal substrate, wherein a mean width of the terraces is less than 1 ?m and a mean height of the terraces is more than 20 nm, and that comprises at least one high temperature superconducting layer disposed on the intermediate layer, which is disposed on the at least one intermediate layer and comprises a layer thickness of more than 3 ?m. The ampacity of the high temperature superconducting tape conductor relative to the conductor width is more than 600 A/cm at 77 K.

Abstract: A superconducting structure (1) has a plurality of coated conductor tapes (2; 2a-2o), each with a substrate (3) which is one-sided coated with a superconducting film (4), in particular an YBCO film, wherein the superconducting structure (1) provides a superconducting current path along an extension direction (z) of the superconducting structure (1), wherein the coated conductor tapes (2; 2a-2o) provide electrically parallel partial superconducting current paths in the extension direction (z) of the superconducting structure (1), is characterized in that the coated conductor tapes (2; 2a-2o) are superconductively connected among themselves along the extension direction (z) continuously or intermittently. A more stable superconducting structure with which high electric current strengths may be transported is thereby provided.

Abstract: In some embodiments of the invention, superconducting structures are described. In certain embodiments the superconducting structures described are thin films of iron-based superconductors on textured substrates; in some aspects a method for producing thin films of iron-based superconductors on textured substrates is disclosed. In some embodiments applications of thin films of iron-based superconductors on textured substrates are described. Also contemplated is the formation of a film of iron-based superconductor having a thickness and an in-plane lattice constant formed on a textured substrate having a thickness and an in-plane lattice constant similar to the in-plane lattice constant of the iron-based superconductor.

Abstract: An AC superconducting cable with an insulating layer on the external circumference of a conductor, and wherein: the insulating layer includes a first insulating layer, a second insulating layer and a third insulating layer, from the inside layer to the outside layer; the insulating layer is impregnated with liquid nitrogen; the product of the dielectric constant ?1 of the first insulating layer and the dielectric loss tangent tan ?1 and the product of the dielectric constant ?2 of the second insulating layer and the dielectric loss tangent tan ?2 fulfilling the relationship ?1×tan ?1>?2×tan ?2; and the product of the dielectric constant ?2 of the second insulating layer and the dielectric loss tangent tan ?2 and the product of the dielectric constant ?3 of the third insulating layer and the dielectric loss tangent tan ?3 fulfilling the relationship ?2×tan ?2<?3×tan ?3.

Abstract: A crystalline article includes a single-crystal ceramic fiber, tape or ribbon. The fiber, tape or ribbon has at least one crystallographic facet along its length, which is generally at least one meter long. In the case of sapphire, the facets are R-plane, M-plane, C-plane or A-plane facets. Epitaxial articles, including superconducting articles, can be formed on the fiber, tape or ribbon.

Abstract: This invention provides a rare earth-type tape-shaped oxide superconductor having excellent mechanical strength and superconducting properties and a composite substrate using for the same. Non-oriented and non-magnetic Ni-9 at % W alloy tapes (11, 21) were bonded onto both sides of a non-oriented and non-magnetic hastelloy tape (100) by a normal temperature bonding process, and an Ni-3 at % W alloy tape (12) having a cubic texture was bonded onto the surface of the tape (11) by a normal temperature bonding process. Thereafter, the heat-treatment was given in a reducing atmosphere and a bonding layer (50a) etc. was formed on the adhesive interface of each layer. Next, a (Ce, Gd)O2 intermediate layer (13) and a Ce2Zr2O7 intermediate layer (14) by an MOD process, a CeO2 intermediate layer (15), a YBCO superconducting film (16) by a TFA-MOD method, and a silver stabilization layer (17) were stacked sequentially on the surface of the tape (12). A critical current value (Ic) of this superconductor showed 150 A.

Abstract: An HTS cable assembly is provided which includes a cryostat or housing, an HTS wire bundle disposed longitudinally within the cryostat, and plural support members disposed between the HTS wire bundle and the cryostat. The support members are elongate, tubular members having resiliency in both the axial and radial directions. The support members are disposed between the HTS wire bundle and the inner surface of the cryostat in an arrangement that maintains and supports the HTS wire bundle in a spaced-apart relationship with respect to the inner surface of the cryostat. In addition, the plural support members are configured to substantially prevent relative movement between the HTS wire bundle and the cryostat.

Abstract: In a superconducting cable line in which a superconducting cable is connected to a terminal connecting part or an intermediate connecting part, an offset part in which a superconducting cable is laid in a curved-shape is provided near the terminal connecting part or the intermediate connecting part. Further, when it is assumed that the superconducting cable is movable in the offset part, an external tube of the superconducting cable is fixed such that a maximum amplitude part which maximizes the amount of movement of the superconducting cable following thermal expansion and contraction of a cable core becomes immovable.

Abstract: The phase transition temperature, at which the crystal lattice of LMO that constitutes an oxide layer as an intermediate layer or as a part of an intermediate layer becomes cubic, is lowered. A substrate for a superconducting wire rod includes an oxide layer (LMO layer (22)) which contains, as a principal material, a crystalline material represented by the compositional formula: Laz(Mn1?xMx)wO3+? (wherein M represents at least one of Cr, Al, Co or Ti, ? represents an oxygen non-stoichiometric amount, 0<w/z<2, and 0<x?1).

Abstract: The invention relates to power cable comprising, at least one HTS-tape and a cooling system comprising a fluid cooling medium for cooling the at least one HTS-tape. The at least one HTS-tape being at least partly surrounded by a cooling layer comprising said fluid cooling medium and an electrical insulation at least partly impregnated with said fluid medium. The power cable of the invention has shown to reduce the risk of fault current and electrically breakdown. When extra cooling is needed for stable operation the cooling medium may evaporate in the cooling layer for providing the cooling.