Patent Description:
Document <CIT> refers to a static electric induction device.

A static electric induction device according to the preamble of present claim <NUM> is known from document <CIT>.

Documents <CIT>, <CIT>, <CIT> and <CIT> refer to transformers with cooling arrangements.

A problem to be solved is to provide a static electric induction device that can be cooled efficiently.

This object is achieved by the static electric induction device according to claim <NUM> and by the method as defined in claim <NUM>. Exemplary further developments constitute the subject-matter of the dependent claims.

The static electric induction device is defined in present claim <NUM>.

Static means, for example, that the device does not move in the intended operation. The heat generated by the heat-generating component during the intended operation may result from reversal of magnetism and/or from an electric resistivity of the heat-generating component. The heat-generating component is, for example, a power transformer.

The duct system can be considered as part of a cooling system, and the duct system may include at least two or exactly two types of internal ducts, that is, the longitudinal channels and the cross channels. However, in addition to the cross channels and the longitudinal channel which can be located directly at the heat-generating component, there may also be supply pipes, for example, running from the longitudinal channels to a pump and/or a cooler of the cooling system.

The number of cross channels may exceed a number of the longitudinal channels, for example, by at least a factor of two or by at least a factor of three. A cross-sectional area of the longitudinal channels may be larger than a cross-sectional area of the cross channels, for example, by at least a factor of two.

A cooling design of power transformers impacts both size and the energy efficiency of the transformer. Improved cooling allows the transformer to be made smaller, or alternatively to improve its energy efficiency because losses increase with temperature. The highest losses occur in the transformer winding. The most effective cooling of liquid-filled power transformers is Oil-Directed, OD, cooling. For simplicity, the term 'oil' is at times used herein as designation for the coolant, also this term includes any dielectric liquid suitable for transformer cooling, which can include mineral oil, natural esters, synthetic esters, isoparaffinic liquids, and other liquids.

For example, the winding has a number of radial and axial cooling ducts where oil can flow, that is, the cross channels and the longitudinal channels, respectively. In particular, old oil is distributed azimuthally through a pressure chamber installed below the winding and enters the axial cooling ducts at the bottom. After absorbing heat from the winding, hot oil exits the axial cooling ducts at a top into a transformer tank. A pump sucks oil from the top of the tank and forces it through a cooler where the oil is cooled down before reentering the pressure chamber.

Typically, barriers like oil guiding rings can be placed in the axial cooling ducts to force the oil to traverse the radial cooling ducts. Because of fluid dynamic effects, the oil does not distribute evenly among the radial ducts. Some radial ducts will have higher local oil velocity and other radial ducts will have lower local oil velocity. Cooling performance increases with oil velocity. Higher pump flow rate will generate higher oil velocities in the winding and can therefore be used to improve cooling compared to a lower pump flow rate.

However, high oil velocities also amplify the fluid dynamic effects that cause uneven distribution of oil within the winding. Therefore, local oil velocities can become lower at a high pump flow rate. This means that there is a maximum flow rate of the pump that can be used before the maximum winding temperature, also known as the winding hot spot temperature, starts to increase. Fluid dynamic effects are non-linear, so a small deviation from the thermal design calculation due to manufacturing tolerances might lead to excessive temperatures.

The winding hot spot for OD cooling typically occurs just above the location of an oil guiding ring due to the Venturi effect. The Venturi effect is a reduction of pressure corresponding to an increase of fluid velocity in a constricted flow passage point. The low local pressure may be insufficient to force oil into the adjacent radial oil duct and may lead to recirculating flow.

In the static electric induction device described herein, the problem of low radial oil speed can be solved by allowing a controlled amount of oil to bypass the oil guide and pass straight on up through the axial duct. The upwards flow in the axial duct opposite the oil guide induces increased oil flow in the radial duct directly above the oil guide and will counteract recirculating flow. Thereby the winding hot spot temperature is reduced.

A controlled amount of oil flow through the oil guide can be achieved by making one or more holes of predefined shape in the oil guiding. The holes might be circular. The at least one hole might not necessarily be a hole in the oil guiding ring itself, but a constricted flow passage bounded by the oil guiding ring, vertical insulation cylinders, and vertical spacers, for example.

The static electric induction device makes it possible to use a higher pump flow rate, thereby improving cooling beyond what is possible with conventional OD technology. The improved cooling can be used to make the transformer more compact, thereby saving material cost or increasing loading capability for locations where transformer size is limited such as offshore wind platforms or urban environments. Alternatively, the improved cooling can be used to reduce the overall temperature of the transformer, thereby improving energy efficiency, because losses increase with temperature. The static electric induction device allows to increase the robustness of the device design in case there are deviations between the thermal design calculations and the manufactured unit.

Thus, the static electric induction device allows high-speed OD cooling of power transformers, for example.

In at least one embodiment, the static electric induction device may comprise a tank filled with a dielectric liquid, a heat-generating component comprising two vertical cooling ducts, a multitude of horizontal cooling ducts connecting the two vertical cooling ducts, at least one flow obstruction within one of the vertical cooling ducts, a pump configured to generate a flow of dielectric liquid through the cooling ducts, wherein the flow obstruction is configured to allow a controlled amount of oil flow, in particular less than <NUM>, to bypass the flow obstruction.

The flow obstruction can be mechanically attached to the heat-generating device and/or can be mechanically attached to an insulating surface bounding the axial cooling duct. For example, the flow obstruction is a guiding ring. For example, the bypass flow is through at least one opening partially bounded by the oil guiding ring and/or the bypass flow is through at least one hole in the oil guiding ring. The at least one hole in the oil guiding ring could be circular.

The heat-generating component comprises a plurality of electric conductor sections. The electric conductor sections are stacked one above the other, in particular along a direction of main extent of the longitudinal channels.

The cross channels run in each case between adjacent ones of the electric conductor sections. In other words, the cross channels are configured as ducts through the electric conductor sections.

Along the direction of main extent the at least one flow obstruction is thinner than the electric conductor sections. Hence, seen in cross-section perpendicular to the cross channels, an overall area of the electric conductor sections may exceed an overall area of the cross channels.

The heat-generating component is a transformer, in particular a power transformer. Power transformer could mean that the heat-generating component is configured for a power of at least <NUM> MVA or at least <NUM> MVA. Alternatively or additionally, the heat-generating component is configured for a power of at most <NUM> GVA or of at most <NUM> GVA. Thus, the electric conductor sections are transformer windings.

For example, the winding comprises a cable that comprises a multitude of electric conductors. The cable is wound around the transformer core with a certain number of turns. Several turns of the cable may be configured close together in the shape of a disc. This may be referred to as a transformer disc winding. Hence, the term `winding' also includes a disc winding.

The duct system can be applied at high voltage windings and/or at low voltage windings. If the heat-generating component is a transformer, it may be of a core type or also of a shell type.

According to at least one embodiment, the at least one flow obstruction is mechanically permanently connected with the duct system and/or the heat-generating component. For example, the at least one flow obstruction is attached to the respective component by gluing, clamping, soldering, welding, screwing and/or riveting.

According to at least one embodiment, the at least one flow obstruction is free of parts which are configured to be movable in the intended use of the static electric induction device. Hence, the at least one flow obstruction may consist of fix parts and/or may be rigid in the intended operation of the static electric induction device. In particular, the at least one flow obstruction is free of flaps or valves or the like.

The at least one flow obstruction comprises an obstruction plate having a plurality of bypass openings. The bypass openings are configured to be passed through by the coolant. For example, the bypass openings are permanently open and are not configured to be closed at times.

According to at least one embodiment, the at least one obstruction plate is arranged in elongation with at least one of the cross channels. For example, the at least one obstruction plate is located in the at least one assigned longitudinal channel. Hence, the respective channel comprises a constriction or narrowing realized by the at least one flow obstruction.

According to at least one embodiment, the bypass openings are arranged in a center region of the obstruction plate. Hence, the respective bypass openings can be located centrically in the respective longitudinal channel.

Thus, the at least one flow obstruction comprises a plurality of the bypass openings. All the bypass openings in the respective flow obstruction can be of the same shape, or there are bypass openings of different shapes.

According to at least one embodiment, the cross channels and/or the longitudinal channels have a cross-section with an aspect ratio of at least <NUM> or of at least <NUM> so that a length of the respective cross-section exceeds a width of the respective cross-section by a factor equal to the aspect ratio. Alternatively or additionally, said factor is at most <NUM>.

According to an example, not forming part of the present invention, the at least one flow obstruction is part of a coolant guiding ring surrounding the heat-generating component along a circumference for at least <NUM>° or for at least <NUM>° or completely, or being surrounded by the heat-generating component for at least <NUM>° or at least <NUM>° or completely, seen in top view of the coolant guiding ring.

The coolant guiding ring may extend over a plurality of the longitudinal channels, the respective longitudinal channels may be arranged in parallel with one another along an axial direction of the heat-generating component. For example, the coolant guiding ring may serve for mechanically supporting the heat-generating component.

The coolant guiding ring may be located between two adjacent sub-stacks of the electric conductor sections. Preferably, in a first one of said sub-stacks the coolant is configured to run in an antiparallel manner in the cross channels compared with a second one of said sub-stacks. The sub-stacks may follow one another along the assigned longitudinal channels. For example, per sub-stack there are at least <NUM> or at least <NUM> of the cross channels. Alternatively or additionally, there are at most <NUM> or at most <NUM> of the cross channels per sub-stack. It is possible that there are exactly two of the longitudinal channels for all the sub-stacks that are stacked one above the other along the axial direction of the heat-generating component.

For example, seen in top view, the cross channels have the shape of a circular ring sector, and seen in cross-section the cross channels may be of rectangular or approximately rectangular shape.

The coolant guiding ring may be annulus and comprises a plurality of the flow obstructions so that a plurality of the corresponding longitudinal channels are arranged in parallel with each other. It is possible that adjacent ones of said longitudinal channels are separated from one another by spacer ribs. For example, the spacer ribs run between adjacent coolant guiding rings and may be limited by the respective coolant guiding rings.

According to at least one embodiment, the at least one flow obstruction narrows the cross-section of the respective longitudinal channel by at least <NUM>% or by at least <NUM> or by at least <NUM>%. Alternatively or additionally, said value is at most <NUM>% or at most <NUM>% or at most <NUM>%.

According to at least one embodiment, the cross channels are oriented in a horizontal manner and the longitudinal channels are oriented in a vertical manner. This applies, for example, with a tolerance of at most <NUM>° or of at most <NUM>°.

According to at least one embodiment, the static electric induction device further comprises one, any two or all of the following components:.

According to at least one embodiment, the tank is configured to be filled with the coolant and the duct system is configured to lead the coolant from the pump and the cooler through the tank. This applies, for example, for at least <NUM>% or for at least <NUM>% of the coolant, concerning one round trip through the duct system. It is possible that there is a separate bypass allowing a small part of the coolant to bypass the heat-generating component.

According to at least one embodiment, the pump and the cooler are located outside the tank. Hence, only part of the duct system and the heat-generating component may be located within the tank. It is possible that the duct system together with the tank is a closed system in intended operation so that the coolant does not leave the duct system, the tank and, if present, the pump as well as the cooler.

If there is a plurality of the flow obstructions, it is possible that all the flow obstructions are of the same design. Otherwise, different kinds of flow obstructions can be combined with each other.

A method for operating the static electric induction device is additionally provided by present claim <NUM>.

By means of the method, a static electric induction device is operated as indicated in connection with at least one of the above-stated embodiments. Features of the static electric induction device are therefore also disclosed for the method.

The method is for operating the static electric induction device, wherein in operation the pump pumps the coolant through the cooler and the duct system so that the heat-generating component is cooled by means of a flow of the coolant. Seen along the longitudinal channels, at most <NUM> or at most <NUM>% of a coolant flow is through the at least one flow obstruction.

A static electric induction device and an operating method described herein are explained in greater detail below by way of exemplary embodiments with reference to the drawings. Elements which are the same in the individual figures are indicated with the same reference numerals. The relationships between the elements are not shown to scale, however, but rather individual elements may be shown exaggeratedly large to assist in understanding.

<FIG> illustrates an embodiment of a static electric induction device <NUM>. The static electric induction device <NUM> comprises a tank <NUM> in which a heat-generating component <NUM>, like a power transformer, is located. As an option, the heat-generating component <NUM> could comprise an inner winding <NUM>, for example, a low voltage winding, and an outer winding <NUM>, for example, a high voltage winding. The power transformer can be of a core type as illustrated in <FIG>, but can alternatively also be of a shell type.

Further, the device <NUM> comprises a duct system <NUM> having various ducts and optionally a pressure chamber in which the heat-generating component <NUM> is accommodated. The ducts connect the pressure chamber with a pump <NUM> and a cooler <NUM>, and the pressure chamber is located inside the tank <NUM>. As a further option, there can be a separate bypass <NUM> that allows flow of a coolant <NUM> outside of the pressure chamber. A flow direction F of the coolant <NUM> is symbolized by arrows.

<FIG> illustrate cross-sectional views through the heat-generating component <NUM> of a modified static electric induction device <NUM> wherein for simplicity of the drawing only a part of one of the windings <NUM>, <NUM> of <FIG> is schematically illustrated.

The duct system <NUM>, compare in particular <FIG>, comprises longitudinal channels <NUM> having a direction M of main extent, and further comprises a plurality of cross channels <NUM>. The windings are stacked one above the other and may be composed of an electric conductor section <NUM> and of an electric insulation <NUM>; however, an inner configuration of the windings could be much more complex than illustrated in <FIG>. Hence, adjacent windings are distant from one another and the cross channels <NUM> run between adjacent conductor sections <NUM> and connect the assigned longitudinal channels <NUM> with one another. In a lateral direction, on a side remote from the heat-generating component <NUM>, the longitudinal channels <NUM> are limited by duct walls <NUM>. The duct walls <NUM> can be wall of the pressure chamber of <FIG>.

For example, a height of the cross channels along the direction M of main extent is at least <NUM> and/or at most <NUM>. Alternatively or additionally, a width of the cross channels <NUM> perpendicular to the plane of projection of <FIG> is at least <NUM> and/or is at most <NUM>. Alternatively or additionally, a thickness of the windings between adjacent cross channels <NUM> is at least <NUM> and/or is at most <NUM>. Alternatively or additionally, a breadth of the longitudinal channels <NUM> perpendicular to the direction M of main extent is at least <NUM> and/or is at most <NUM>. Optionally, in the direction perpendicular to the plane of projection of <FIG>, the cross channels <NUM> and the longitudinal channels <NUM> can have the same width.

The conductor sections <NUM> can be grouped into sub-stacks <NUM>, <NUM>. For example, per sub-stack <NUM>, <NUM> there are at least <NUM> and/or at most <NUM> of the windings and, thus, of the cross channels <NUM>. Within a specific sub-stack <NUM>, <NUM>, intentionally the coolant <NUM> flows in the same direction, indicated by the arrows that symbolize the flow direction F. Between adjacent sub-stacks <NUM>, <NUM> there is a redirection flow obstruction <NUM> in one of the associated longitudinal channels <NUM>. These redirection flow obstructions <NUM> are impermeable for the coolant <NUM>. Hence, by means of the redirection flow obstructions <NUM> all the arriving coolant is redirected, for example, by <NUM>°.

Accordingly, due to the Venturi effect at the winding next to the redirection flow obstruction <NUM> the flow direction can be inverted so that a circular flow around the respective winding results. However, such a circular flow leads to a decreased cooling of the respective winding so that a local hot spot H arises. This is shown only schematically in <FIG>, and in <FIG> the local hot spot H is illustrated in more detail by means of the hatchings.

The strength of the Venturi effect is dependent on the flow speed of the coolant <NUM>. For transformer oil, in order to avoid such local hot spots H, the maximum allowable speed is around <NUM>/s, for example, in a typical configuration. Because occurrence of only one local hot spot H may lead to severe damage of the device <NUM>, the maximum coolant speed is in particular limited to the case where no significant local hot spots H arise due to the Venturi effect.

In <FIG>, embodiments of the static electric induction device <NUM> are illustrated, wherein <FIG> provides a perspective view of a part of the device <NUM> and <FIG> show sectional views of slightly different embodiments.

Compared with the modified static electric induction device <NUM> of <FIG>, in the static electric induction device <NUM> of <FIG> the redirection flow obstructions <NUM> are replaced by flow obstructions <NUM> which allow a minor fraction of the coolant <NUM> to pass through. For example, a cross-sectional area of the respective longitudinal channel <NUM> is reduced by the assigned flow obstruction <NUM> by at least <NUM> and by at most <NUM>%. Hence, some of the coolant <NUM> flows through the respective flow obstructions <NUM>.

Thus, the strength of the Venturi effect at the adjacent cross channel <NUM> can be reduced and an overall higher flow speed of the coolant <NUM> through the channels <NUM>, <NUM> is enabled. For example, the flow speed can be increased by a factor between <NUM> and <NUM> compared with the modified static electric induction device <NUM> so that in the static electric induction device <NUM> flow speeds of the coolant <NUM> of up to <NUM>/s may be realized. By increasing the flow speed, the cooling can be improved.

For example, the flow obstructions <NUM> each comprise a obstruction plate <NUM> in which bypass openings <NUM> are formed. It is possible that the obstruction plates <NUM> are mounted onto the duct wall <NUM> or alternatively onto the respectively assigned winding, or onto both. Mounting could be achieved, for example, by means of a mounting plate <NUM> running in parallel with the direction M of main extent.

According to <FIG>, the flow obstructions <NUM> and consequently the part of the obstruction plates <NUM> having the bypass openings <NUM> run in elongation with a top side of the uppermost winding of the lower sub-stack <NUM>, seen along the direction M of main extent of the longitudinal channels <NUM>. Contrary to that, according to <FIG> the flow obstructions <NUM> and consequently the part of the obstruction plates <NUM> having the bypass openings <NUM> run in elongation with a bottom side of the lowermost winding of the upward sub-stack <NUM>, again seen along the direction M of main extent. It is also possible that the two variants of <FIG> are both realized in the static electric induction device <NUM>.

In <FIG> it is further illustrated that the flow obstructions <NUM> may alternatively be integrated in a coolant guiding ring <NUM> so that the coolant guiding ring <NUM> comprises at least one bypass opening <NUM> per associated longitudinal channel <NUM>. As an option, a plurality of the longitudinal channels <NUM> can be arranged in parallel with one another all around the heat-generating component <NUM>. Adjacent longitudinal channels <NUM> can be separated from one another by spacer ribs <NUM> which run along the direction M of main extent. Between adjacent windings, there can be conductor section spacers <NUM>.

Concerning the configuration of the ribs <NUM>, the spacers <NUM> and the channels <NUM>, <NUM>, reference is also made to document <CIT>, in particular to <FIG> and page <NUM>, lines <NUM> to <NUM>, as well as <FIG> and page <NUM>, line <NUM>, to page <NUM>, line <NUM>, the disclosure content of which is hereby included by reference.

Otherwise, the same as to <FIG> may also apply to <FIG>, and vice versa.

In <FIG>, some possible examples of the flow obstructions <NUM> are illustrated. According to the exemplary embodiment of <FIG>, the flow obstruction <NUM> comprises the obstruction plate <NUM> and the mounting plate <NUM>. It is possible that the obstruction plate <NUM> is shorter than the mounting plate <NUM>.

The plates <NUM>, <NUM> are manufactured from one piece, for example, by bending. The flow obstruction <NUM> are of a dielectric material like a polymeric material. Composites of a plurality of materials are also possible.

In <FIG>, there is a plurality of the bypass openings <NUM> which may be arranged, for example, along a straight line. All the bypass openings <NUM> can be of the same shape. The bypass openings <NUM> completely run through the obstruction plate <NUM>. There can be more than the two bypass openings <NUM> shown in <FIG>, for example, there are at least three bypass openings <NUM> and/or at most eight bypass openings <NUM> per flow obstruction. In the direction perpendicular to the mounting plate <NUM>, the bypass openings <NUM> can be located in a middle third of the obstruction plate <NUM>.

In a lateral direction, in parallel with the line along which the bypass openings <NUM> are arranged, the mounting plate <NUM> and/or the obstruction plate <NUM> may directly adjoin the spacer ribs.

According to <FIG>, the bypass opening <NUM> is located next to the mounting plate <NUM>, that is, in an outermost third of the obstruction plate <NUM> and, thus, next to the duct wall <NUM>. Moreover, the bypass opening <NUM> does not need to be of circular shape as in <FIG>, but can be of square or rectangular shape, too. Again, there can be more than one bypass opening <NUM> per obstruction plate <NUM>.

According to the exemplary embodiment of <FIG>, there is a plurality of the bypass openings <NUM>, and the bypass openings <NUM> can have different shapes. As an option, one or some or all of the bypass openings <NUM> can be arranged at an edge of the obstruction plate <NUM>, in particular next to the spacer ribs.

Claim 1:
A static electric induction device (<NUM>) comprising:
- a heat-generating component (<NUM>) which is subject to electric induction, and
- a duct system (<NUM>) configured to lead a coolant (<NUM>) along the heat-generating component (<NUM>),
wherein
- the duct system (<NUM>) includes a plurality of cross channels (<NUM>) and longitudinal channels (<NUM>), each of the longitudinal channels (<NUM>) having a cross-sectional area and each one of the longitudinal channels (<NUM>) being assigned to at least some of the cross channels (<NUM>) and the assigned cross channels (<NUM>) connect the longitudinal channels (<NUM>) with each other,
- the duct system (<NUM>) further includes at least one flow obstruction (<NUM>) located in at least one of the longitudinal channels (<NUM>), the flow obstruction (<NUM>) is configured to allow flow of the coolant through it and locally narrows the cross-sectional area of the at least one of the longitudinal channels (<NUM>) by at least <NUM>% so that a bypass for the coolant (<NUM>) is realized,
- the heat-generating component (<NUM>) comprises a plurality of electric conductor sections (<NUM>) stacked one above the other along a direction (M) of main extent of the longitudinal channels (<NUM>), the cross channels (<NUM>) in each case run between adjacent ones of the electric conductor sections (<NUM>), and along the direction (M) of main extent the at least one flow obstruction (<NUM>) is thinner than the electric conductor sections (<NUM>),
- the heat-generating component (<NUM>) is a transformer and the electric conductor sections (<NUM>) are transformer windings,
- the at least one flow obstruction (<NUM>) comprises an obstruction plate (<NUM>) having a plurality of bypass openings (<NUM>) configured to be passed through by the coolant (<NUM>), and characterised in that
- the at least one flow obstruction (<NUM>) further comprises a mounting plate (<NUM>) running in parallel with the direction (M) of main extent, the obstruction plate (<NUM>) and the mounting plate (<NUM>) being manufactured from one piece of a dielectric material which is a polymeric material.