Patent Description:
A fluid-filled inductive device, e.g. a transformer, comprises solid insulation and cooling fluid. A sufficient circulation of the cooling fluid is needed for efficient cooling of the inductive device. Thus, the solid insulation should allow the cooling fluid to pass and circulate in the device. For example, the top and bottom winding insulators, so called winding tables or pressplates, may be comprised in arrangements of several separate but combined parts, i.e. pressplates and common spacer rings, to allow the cooling fluid to pass the solid insulation.

<CIT> discloses a pressplate for a transformer. The pressplate is provided with groves or bars on one face to form oil channels.

Similarly, <CIT> discloses an insert for isolating two windings of a coil. The insert comprises a polyaramid plate having spacers placed on one of the faces of the plate to define channels for dielectric fluid.

<CIT>, discloses an oil transformer with a cooling channel.

<CIT>, <CIT> and <CIT> disclose related art.

It is an objective of the present invention to provide an improved electrical insulator for an inductive device <NUM> filled with an electrically insulating cooling fluid, for allowing the fluid to pass the insulator.

According to an aspect of the present invention, there is provided an electrical insulator. The insulator is configured to be used in an inductive device filled with an electrically insulating cooling fluid. The insulator defines a plurality of internal channels for allowing the electrically insulating cooling fluid to flow there through to improve circulation of the fluid within the inductive device.

According to another aspect of the present invention, there is provided an inductive device comprising a housing, an electrically insulating cooling fluid contained within the housing, a winding arrangement submerged in the cooling fluid, and at least one insulator of the present disclosure.

By the insulator having internal channels for the cooling fluid, the circulation of the cooling fluid can be improved without the need for spacers or the like which would increase the spatial footprint of the insulator. The insulator, and thus the whole inductive device, may be made more compact.

It is to be noted that any feature of any of the aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of any of the aspects may apply to any of the other aspects.

<FIG> illustrates an inductive device <NUM>, e.g. an electrical power transformer or reactor, typically a transformer. The device <NUM> comprises a conventional winding arrangement <NUM> of wound electrical conductor(s) in a housing <NUM>, e.g. a transformer tank. The housing <NUM> is filled with an electrically insulating cooling fluid <NUM>, e.g. a liquid or a gas, preferably a liquid such as a mineral oil or ester liquid, e.g. a transformer oil. The inductive device <NUM> comprises solid insulators <NUM>, e.g. pressplates as illustrated in the figure. The winding <NUM> may be pressed between the pressplates <NUM> to stabilize the winding and separate it from e.g. a core or other elements in the inductive device. The insulators <NUM> of the present disclosure may additionally or alternatively to pressplates be used as any other solid insulation in an inductive device <NUM>, e.g. spacers in the winding <NUM> or a cylinder around the winding <NUM>.

The insulator <NUM> may be cellulose based, e.g. pressboard or wood/wood laminate, synthetic, e.g. aramid or epoxy based, and/or a laminate or composite. The insulator may e.g. comprise a fibre-resin composite of fibres, e.g. synthetic fibres such as glass fibres, in a resin matrix, e.g. comprising a curable or otherwise hardenable resin such as an epoxy or polyester resin, preferably epoxy.

<FIG> illustrates an embodiment of a substantially flat insulator <NUM> in the having a central axial through hole <NUM>. The flat insulator <NUM> has a first main surface <NUM>, here an upper surface, and a second main surface <NUM>, here a bottom surface, as well as an outer edge surface <NUM> and an inner edge surface <NUM> defining the through hole <NUM>. Internal channels <NUM> are formed in the insulator. Each of the internal channels are configured for allowing cooling fluid <NUM> to enter the channel from outside of the insulator, pass though the insulator within the channel, and exit the channel to the outside of the insulator. The channels <NUM> may be separate from each other, or may intersect to form a network of channels. This implies that each end of each channel has an opening in one of the outer surfaces <NUM>-<NUM> of the insulator, or has an opening into another of the channels.

In the embodiment of <FIG>, the internal channels <NUM> comprises a plurality of radial channels extending in a plane within the insulator <NUM>, which plane is parallel to opposing first and second main surfaces <NUM> and <NUM> of the insulator. Specifically, each of the radial channels <NUM> extends from the outer edge surface <NUM>, having an opening in said outer edge surface, to the inner edge surface <NUM>, having an opening in said inner edge surface. Typically, the radial channels are separate from each other, without intersecting with each other. Typically, the radial channels are straight.

In the embodiment of <FIG>, the internal channels <NUM> are bores in the insulator <NUM>, typically formed by drilling through the insulator <NUM>. Alternatively, in some embodiments, the channels <NUM> may be formed in an inner layer of a multilayer structure, e.g. a laminate. Such an inner layer may be corrugated, thus forming channels <NUM> there through. In some other embodiments, the inner layer may comprise spacers, e.g. in the form of discrete ribs, thus forming channels <NUM> there through.

<FIG> illustrates an insulator <NUM> in the form of a laminate comprising an inner layer <NUM> formed between a first outer layer <NUM>, having the first main surface <NUM> of the insulator, and a second outer layer <NUM>, having the second main surface <NUM> of the insulator. The insulator <NUM> is in the embodiment of <FIG> arranged as a pressplate at one end of a winding <NUM>, e.g. comprising a plurality of windings, in the example of the figure a low voltage (LV) winding 30a, a high-voltage (HV) winding 30b and regulation winding 30c. Internal radial channels <NUM> are formed in the inner layer <NUM>, e.g. by the means of radial spacers arranged between the first and second outer layers <NUM> and <NUM>, typically fastened (e.g. glued) to the first and second outer layers. The radial channels allow cooling fluid to flow radially within the insulator <NUM>, outward from the axial through hole <NUM> (as indicated by the arrows) or vice versa.

In the embodiment of <FIG>, the channels <NUM> also comprise axial channels <NUM>, each corresponding to a hole through the second outer layer <NUM> which open up into a radial channel. More generally, each of the axial channels <NUM> extends through at least one of the first and second main surfaces <NUM> and <NUM> and into at least one of the radial channels for allowing the cooling fluid to pass between the axial and radial channels. Looking at the example embodiment of <FIG>, cooling fluid may flow through the axial channels until they intersect with radial channels and may then continue to flow through said radial channels (as indicated by the arrows in the figure) or vice versa. Thus, if the insulator <NUM> is an upper pressplate, the cooling fluid may flow upwards along or within the winding <NUM> until the fluid reaches the insulator <NUM>, whereby the cooling fluid enters the insulator via the axial channels <NUM> and/or the axial through hole <NUM> into the radial channels which conducts the fluid flow outwards. Thus, efficient circulation of the cooling fluid may be obtained.

Internal channels <NUM> may reduce the mechanical strength of the insulator <NUM>, why it may in some embodiments be advantageous to use a fibre-resin composite material in the insulator to improve mechanical strength without increasing the thickness of the insulator. Thus, the first outer layer <NUM> and/or the second outer layer <NUM> may be made of a composite material of fibres in a resin matrix. The inner layer <NUM> may e.g. comprise spacers fastened (e.g. glued) to the first and second outer layers to form internal (radial) channels <NUM>, which spacers may be of the same composite material or of another suitable material e.g. cellulose-based such as pressboard or wood. The fibres are typically electrically insulating, e.g. synthetic fibres such as glass fibres. The resin is typically a hardenable resin such as a curable or thermosetting resin, e.g. an epoxy or polyester resin, preferably an epoxy resin.

In some embodiments of the present invention, the insulator <NUM> is flat and the channels <NUM> comprise or consist of radial channels extending in a plane within the insulator, which plane is parallel to opposing first and second main surfaces <NUM> and <NUM> of the insulator. In some embodiments, the insulator <NUM> has an inner edge surface <NUM> defining a central through hole <NUM> through the insulator, said through hole being perpendicular to the plane of the insulator, in which plane the radial channels <NUM> extend. In this case, each of the radial channels <NUM> may extend from an outer (outward facing) edge surface <NUM> of the insulator to the inner edge surface <NUM> of the insulator. Additionally or alternatively, in some embodiments, the channels <NUM> comprise axial channels <NUM>, where each of the axial channels extends through at least one of the first and second main surfaces <NUM> and <NUM> and into at least one of the radial channels for allowing the cooling fluid to pass between the axial and radial channels (i.e. each of the axial channels has an inlet or outlet into/out from the a radial channel).

In some embodiments of the present invention, the insulator <NUM> is made of at least one electrically insulating material comprising a cellulose-based material, e.g. pressboard or wood laminate, preferably pressboard.

In some embodiments of the present invention, the insulator <NUM> is made of at least one electrically insulating material comprising a composite material of fibres, e.g. synthetic fibres such as glass fibres, in a resin matrix. The resin matrix may comprise a curable resin such as an epoxy or polyester resin, preferably epoxy.

In some embodiments of the present invention, the insulator <NUM> is a laminate wherein the channels <NUM> are formed by means of spacers <NUM> arranged between first and second outer layers <NUM> or <NUM> of the insulator. In some embodiments, the first outer layer <NUM> and/or the second outer layer <NUM> is made of a composite material of fibres, e.g. synthetic fibres such as glass fibres, in a resin matrix. The resin matrix may comprise a curable resin such as an epoxy or polyester resin, preferably epoxy. In some embodiments, the spacers <NUM> are formed by a continuous corrugated layer arranged between the first and second outer layers <NUM> or <NUM>. In some other embodiments, the spacers <NUM> are formed by discrete ribs arranged between the first and second outer layers <NUM> or <NUM>.

In some other embodiments of the present invention, the channels <NUM> are bores in the insulator <NUM>, typically formed by drilling.

In some embodiments of the present invention, the insulator <NUM> is arranged as a pressplate at the top and/or bottom of the winding arrangement <NUM>.

In some embodiments of the present invention, the inductive device <NUM> is a transformer or a reactor, preferably a transformer.

In some embodiments of the present invention, the cooling fluid is a liquid, e.g. a mineral oil or ester liquid, preferably a mineral oil.

Claim 1:
An electrical insulator (<NUM>), for an inductive device (<NUM>) filled with an electrically insulating cooling fluid (<NUM>), the insulator defining a plurality of internal channels (<NUM>) for allowing the fluid (<NUM>) to flow there through to improve circulation of the fluid within the inductive device,
wherein the insulator (<NUM>) is flat and the internal channels (<NUM>) comprise radial channels extending in a plane within the insulator (<NUM>) which is parallel to opposing first (<NUM>) and second (<NUM>) main surfaces of the insulator,
wherein the insulator (<NUM>) has an inner edge surface (<NUM>) defining a central through hole (<NUM>) through the insulator (<NUM>), perpendicular to the plane of the insulator (<NUM>),
wherein the channels (<NUM>) comprise axial channels (<NUM>), each of the axial channels extending through at least one of the first (<NUM>) and second (<NUM>) main surfaces and into at least one of the radial channels for allowing the cooling fluid to pass between the axial and radial channels, and
characterised in that each of the radial channels (<NUM>) extends from an opening in an outer edge surface (<NUM>) of the insulator (<NUM>) to an opening in the inner edge surface (<NUM>) of the insulator (<NUM>), and in that the insulator (<NUM>) is made of at least one electrically insulating material comprising a composite material of fibres, wherein the fibres are synthetic fibres such as glass fibres, in a resin matrix, comprising a curable resin such as an epoxy or polyester resin, preferably epoxy.