Potential-isolating transformer for energy transmission under relatively high insulation voltages, powers and operating frequencies

Abstract

The present invention relates to a transformer (1) which comprises a primary conductor (2) and a secondary conductor (3) which is electrically insulated with respect to the primary conductor (2). The secondary conductor (3) is designed as a sleeve which encloses the primary conductor (2). The secondary conductor is sheathed by a core (4) made of magnetically soft material. The secondary conductor (3) defines a winding together with the primary conductor enclosed by it.

Description

[0001] Potential-isolating transformer for energy transmission under relatively high insulation voltages, power levels and operating frequencies

[0002] TECHNICAL FIELD

[0003] The present invention relates to a potential-isolating transformer, which is particularly suitable for energy transmission under relatively high isolation voltages, power levels and operating frequencies, a high-performance transformer for energy transmission in medium-voltage networks, a system consisting of several transformer modules, each comprising such a transformer, and to a method for manufacturing such a transformer.

[0004] BACKGROUND OF THE INVENTION

[0005] Transformers are used for voltage conversion with a selectable conversion factor and for galvanic isolation between circuits. They comprise a primary and secondary winding, which are mechanically and electromagnetically coupled to each other via a core made of soft magnetic material.

[0006] As is well known, when operating at frequencies above 20 kHz, the size can be reduced by one to two orders of magnitude compared to operation at typical mains frequency, which has already proven successful in the low power range up to 100 kW.

[0007] However, in the high-power sector, where several megawatts need to be switched or converted, particular technical challenges arise. These include connection to medium-voltage networks with operating voltages of, for example, 20 kV, compliance with high test voltage requirements, and the increased material and insulation stresses at higher operating frequencies.

[0008] Ensuring reliable insulation between the primary and secondary sides of the transformer presents a particular challenge. While partial discharge effects are less relevant in low-voltage applications, very high test voltages and the prevention of partial discharges are essential in high-voltage applications.

[0009] A known solution for meeting such high insulation requirements is to spatially and structurally separate the primary and secondary sides of the transformer. Such transformers are used for wireless power transmission. Further improving insulation performance involves inserting additional insulating materials, for example, in the form of plastic plates. However, the spatial separation of the primary and secondary sides generally has the disadvantage of reducing magnetic coupling. It also entails design limitations and increases the transformer's dimensions. These disadvantages lead to a deterioration of both power density and power factor. The invention aims to overcome these disadvantages and to make a transformer, particularly for high operating frequencies in the high-power range, more efficient and compact.

[0010] SUMMARY

[0011] According to a first aspect of the invention, a transformer is provided comprising a primary conductor having several turns, a secondary conductor which is electrically insulated from the primary conductor, and a core made of soft magnetic material. The secondary conductor is designed as a sleeve that encloses the primary conductor.

[0012] The core is designed to enclose or encase the secondary conductor, thereby electromagnetically coupling it to the primary conductor. The secondary conductor, together with the encased primary conductor, describes a spatial curve that electromagnetically represents a single turn.

[0013] The spatial curve of the secondary conductor representing the winding is preferably circular, but can also have other geometries. In principle, it is sufficient for the secondary conductor to have a beginning and an end that are spatially close together. In this sense, and depending on the desired application, a U-shaped path for the extension of the secondary conductor or the sleeve it forms can also be advantageous.

[0014] With regard to the turns ratio, several turns of the primary conductor are preferably paired with a single turn of the secondary conductor. The number of turns of the primary conductor is also preferably low, e.g., between 3 and 10, preferably 3 to 6 turns, but with a relatively large cable diameter for high power applications.

[0015] The secondary conductor should preferably completely enclose the primary conductor, which consists of several turns, for which purpose the turns of the primary conductor must describe the same spatial curve as specified by the enclosing secondary conductor.

[0016] The secondary conductor can be made of aluminum, the primary conductor of copper. Aluminum has sufficient conductivity, at least at higher frequencies, and can be easily processed into a sleeve to encase the primary conductor.

[0017] The core encasing or sheathing the secondary conductor is preferably made of soft magnetic concrete, into which the secondary conductor, along with the primary conductor it encloses, is cast. This type of sheathing is cost-effective while offering high efficiency and is understandably well-suited for construction. The term "core" is thus to be understood as such a sheathing of the secondary conductor with soft magnetic material. The soft magnetic concrete contains soft magnetic particles, for example, ferrite. These soft magnetic particles can be evenly distributed and mixed into conventional concrete or cement. Alternatively, the soft magnetic particles can be mixed into asphalt to obtain soft magnetic asphalt, which can then be used as a core. The soft magnetic particles can be derived from a recycling process or manufactured from recycled materials.Depending on its composition, soft magnetic concrete can have a relative permeability of 40 to 180.

[0018] By designing the secondary conductor as a coiled sleeve that accommodates the primary conductor or the windings of the primary conductor, the coupling factor between the primary and secondary sides of the transformer can be maximized, among other things.

[0019] This enables the transformer to operate at high frequencies and high power. A further advantage of the arrangement according to the invention is that the effects of skin and proximity effects on the current distribution in the conductors are minimized. Both advantages are significant for operation at high frequencies and high power.

[0020] The term "primary conductor" refers to an electrical conductor on the primary side of a transformer. The term "secondary conductor" refers to an electrical conductor on the secondary side of a transformer. The secondary side of the transformer can be the side with a lower voltage than the primary side. The number of turns (Np) on the primary side and the number of turns (Ns) on the secondary side define a specific turns ratio (k = Ns / Np), which determines the voltage (Us = k - Up), where Us is the secondary voltage and Up is the primary voltage. As explained, the secondary conductor typically has only a single turn.

[0021] Unless otherwise specified, "electrically insulated" refers to electrical insulation that is dimensioned and material-selected to meet all insulation requirements during transformer operation. It reliably prevents any electrical connection or short circuits between two electrical conductors, in this case the primary and secondary conductors, as well as between the transformer and its earth potential.

[0022] The primary conductor can be a cable whose sheath is made of electrically insulating material. The sheath can be designed to electrically insulate the primary conductor from the secondary conductor.

[0023] The use of a cable that meets the transformer's insulation requirements regarding the primary conductor from the secondary conductor and / or from other potentials, such as the transformer's earth potential, opens up degrees of freedom in the transformer's design and configuration, which can lead to an increase in power density. In particular, the flexible routing of the primary conductor within the sleeve-shaped secondary conductor allows for application-specific transformer shapes to be realized.

[0024] The primary conductor is preferably designed as a high-voltage cable. High-voltage cables are technologically mature and could therefore be used in transformers. However, they are not used in conventional transformers with windings around a magnetic core because the permissible bending radii cannot be maintained. By designing the secondary conductor as a bent or coiled sleeve, the radii of the sleeve can be flexibly selected, thus enabling the use of high-voltage cables and cables with suitable insulation.

[0025] The cable or high-voltage cable may include one or more of the following components: one or more flexible aluminum or copper strands, one or more silicone sheaths, a copper braid shield, and / or a tape made of aluminum and / or polyethylene terephthalate (PET).

[0026] To reduce the increased losses in the primary conductors at high operating frequencies, stranded wires are used, which consist of a plurality of parallel and fine wires.

[0027] The sheath of the primary conductor may, at least in sections, touch the secondary conductor. The sleeve of the secondary conductor may have a structure, in particular a retaining structure, that corresponds to the number of turns Np of the primary conductor and secures it.

[0028] The structure can be designed in such a way that it compresses the windings of the primary conductor for the purpose of fixing them together.

[0029] The structure can have the same number of slots as the number of turns Np of the primary conductor. Each slot can partially or completely accommodate one of the turns of the primary conductor.

[0030] The sleeve can consist of two half-shells, which are fixed together after the primary conductor has been inserted.

[0031] The sleeve can approximately describe a circle, an ellipse, or an oval. The sleeve can have an insulating layer made of electrically insulating material. The insulating layer can be designed to electrically insulate the primary conductor from the secondary conductor. In particular, the thickness of the insulating layer can be dimensioned to meet the insulation requirements of the transformer with respect to the secondary conductor against the soft magnetic core and / or against other potentials, such as the transformer's earth potential.

[0032] Alternatively, the insulating layer can provide part of the electrical insulation or be used as supplementary insulation. For example, the primary conductor sheath and the sleeve's insulating layer can be designed so that together, but not separately, they achieve the electrical insulation required for the transformer's operation.

[0033] The insulating layer can be an oxide layer, preferably made of aluminum oxide.

[0034] The oxide layer can be produced by an anodizing process.

[0035] The primary conductor can have a number of turns Np, with Np greater than 1, preferably with Np from 3 to 30, particularly preferably with Np from 4 to 6. The soft magnetic concrete can at least partially encase or surround the sleeve of the secondary conductor.

[0036] The use of soft magnetic concrete allows for the production of relatively large components or transformer blocks with largely unrestricted design possibilities. Selecting the appropriate thickness of the concrete sheathing around the secondary conductor allows for adjustments to achieve the desired maximum induction within the material, as well as optimization in terms of weight and remagnetization losses.

[0037] Alternative soft magnetic materials suitable for high operating frequencies include ferrites, iron powder materials, or amorphous metal foils. Of these alternative soft magnetic materials, only amorphous metal foils offer a relatively high maximum induction, approaching the values ​​of silicon-iron sheets. Furthermore, their permeability is also relatively high compared to the other materials. However, shaping can be limited because the metal foils can only be processed into ring cores. Soft magnetic concrete, on the other hand, allows for more flexible shaping.

[0038] The soft magnetic concrete can completely encase or surround the sleeve.

[0039] The core can essentially form a concrete block made of magnetic concrete in which the transformer is cast and thus enclosed.

[0040] The sleeve can completely enclose the primary conductor.

[0041] The secondary conductor sleeve can have one or more slots along its winding. Two opposing slots can also be provided. The slots can be closed at the ends of the sleeve. In this case, the sleeve forms a contact ring at each end, electrically connecting the sleeve segments or half-shells separated by the slots in parallel.

[0042] Electrical connections for connecting the transformer to an external power grid can be made to the ends of the sleeve. The electrical connections can, for example, be soldered to the ends of the sleeve.

[0043] The secondary conductor can consist of only one turn, which is less than 360°. The required voltage transformation can be achieved by the corresponding number of turns in the primary conductor, assuming that the secondary conductor consists of only one turn. Preferably, the secondary conductor can have a turn of 270° to less than 360°, preferably 330° to 355°.

[0044] The secondary conductor can extend along the axis in a helical shape. According to a second aspect of the invention, a method for manufacturing the transformer according to the first aspect is provided, wherein the sleeve consists of two half-shells. The method comprises the following steps: - laying the primary conductor in one of the half-shells,

[0045] - Closing the sleeve by attaching the second half-shell, and

[0046] - mechanically fixing the two half-shells to each other.

[0047] The latter can involve welding the two half-shells together.

[0048] According to a third aspect of the invention, a high-performance transformer for energy transmission in medium-voltage networks with operating voltages of 1 to 50 kV is provided, which comprises the transformer according to the first aspect.

[0049] According to a fourth aspect of the invention, a system consisting of several transformer modules, each comprising a transformer according to the first aspect, is provided, the core of which is preferably formed from a soft magnetic concrete block into which the secondary and primary conductors are cast. The inputs and outputs of the secondary and primary conductors (i.e., the electrical connections) are interconnected according to the requirements of the system to form a complete electrical system.

[0050] In this way, even with a small turns ratio of a single block, optimal adaptation can be achieved depending on the application. If the respective primary conductors are connected in series and the secondary conductors in parallel, the effective turns ratio can be increased accordingly. The number of turns in the primary conductors adds up, while the number of turns in the secondary conductor remains at 1.

[0051] However, it is also possible, instead of increasing the number of turns, to increase the input voltage and for this purpose to supply the primary side of the modules with a separate input voltage each, while connecting the secondary conductors in parallel.

[0052] Alternatively, the respective primary conductors can be connected in parallel, and the respective secondary conductors in series. This connection allows for a higher output voltage that cannot be achieved with a single transformer by increasing the effective turns ratio. This is particularly advantageous when the sleeve is wound in only two dimensions, i.e., with only one turn of less than 360°.

[0053] A cooling structure may be incorporated into the concrete blocks to dissipate the heat generated by the ladders.

[0054] FIGURES

[0055] Preferred embodiments of the invention are explained in more detail below with reference to the drawings:

[0056] Figure 1 shows a schematic structure of a transformer according to a first embodiment of the invention in perspective view; Figures 2A-C show schematic sectional views through the secondary conductor designed as a sleeve with variants of a structure for the sleeve as they can be used in the transformer from Figure 1;

[0057] Figure 3 shows an embodiment of the secondary conductor designed as a sleeve with two half-shells, as can be used in the transformer from Figure 1; and

[0058] Figure 4 shows a schematic construction of a slotted sleeve, as it can be used as a secondary conductor in the transformer from Figure 1.

[0059] DESCRIPTION

[0060] Figure 1 shows a schematic diagram of a transformer 1 according to a first embodiment of the invention in perspective view. The transformer 1 can be used for energy transmission in medium-voltage networks with operating voltages from 1 to 50 kV.

[0061] The transformer 1 comprises a primary conductor 2 and a secondary conductor 3, which is electrically insulated from the primary conductor 2. The secondary conductor 3 is designed as a sleeve that encloses the primary conductor 2. The primary conductor 2 and the secondary conductor 3 are wound around the same axis A. In the illustrated embodiment, the primary conductor 2 comprises four turns that are guided within the circularly wound secondary conductor 3. The secondary conductor 3 approximately defines one turn that is not completely closed. Thus, the transformer 1 defines a turns ratio of k = 1 / 4, i.e., the voltage on the secondary side is reduced to one-quarter of that on the primary side.

[0062] The assembly consisting of the sleeve of the secondary conductor 3 and the primary conductor 2 is embedded or cast into a soft magnetic concrete block 4, which then serves as core 4 for electromagnetic coupling between the secondary conductor 2 and the primary conductor 3.

[0063] The soft magnetic concrete block 4 consists of conventional concrete to which soft magnetic particles, such as ferrite, have been uniformly added. Suitable composite materials are known, among others, from the scientific publication Ellithy, Ibrahim; Esguerra, Mauricio; Radhakrishnan, Rewanth (2024), "Soft Magnetic Materials: High Permeability Magnetic Composites with Cement, Asphalt, and Epoxy Binders for Enhanced Performance across Diverse Applications," e.g., the soft magnetic concrete developed by MAGMENT GmbH under the name MC60®. The transformer 1 includes electrical connections 21, 31. The electrical connections 21, 31 are connected to the primary conductor 2 and the secondary conductor 3, respectively, and extend from the magnetic concrete block for connection to an external power grid, such as a medium-voltage network.

[0064] The primary conductor 2 is designed as a cable, as shown in the sectional view through the secondary conductor 3, which is designed as a sleeve, in Figure 2A. The sheath 22 of the cable consists of electrically insulating material and insulates the primary conductor 2 from the secondary conductor 3.

[0065] Alternatively or additionally, the insulation requirements can be met by an insulating layer 7, for example an aluminum oxide layer, which is produced by an anodizing process on the inner circumference of the secondary conductor 3 designed as a sleeve.

[0066] As shown in Figure 2A, the secondary conductor 3, designed as a sleeve, has a tubular structure that accommodates all four turns of the primary conductor 2, designed as a cable, and compresses them together for mechanical fixation. This fixation can be achieved by designing the sleeve with two half-shells 33, 34, as shown in Figure 3. After the cable is laid, the half-shells 33, 34 can be brought together in one of the first of the two half-shells and fixed to each other. During this process, the four turns of the cable can be compressed. The structure of the two half-shells preferably encloses the multiple turns of the primary conductor in a form-fitting manner to ensure good heat dissipation.

[0067] As an alternative to a tubular design, the sleeve can have a "cloverleaf-shaped" structure, as shown in Figure 2C. The rounded bulges of the cloverleaf define grooves 35 for the partial or complete reception of each of the turns of the primary conductor 2.

[0068] In another embodiment of the sleeve, as shown in Figure 2B, the outer wall of the sleeve can be tubular and the inner circumference cloverleaf-shaped.

[0069] Figure 4 shows a schematic diagram of another embodiment of the sleeve, as it can be used as a secondary conductor 3 in the transformer 1 according to Figure 1. In this embodiment, a slot is incorporated along the winding path. Two opposing slots can also be provided.

[0070] With the transformer according to the invention, particularly also in the version with a casing of the secondary conductor made of soft magnetic concrete, coupling factors in the range above 0.9, preferably above 0.95 and particularly preferably above 0.98 can be achieved.

[0071] One embodiment particularly suitable for practical application involves manufacturing such transformers as concrete modules. Each concrete module contains a transformer according to the invention, which is cast in soft magnetic concrete. The cast secondary conductor has one turn, designed as a sleeve, into which a primary conductor with several turns is inserted. The electrical connections of the primary and secondary conductors are accessible for coupling with other modules. In this way, despite the small turns ratio of a single module, optimal adaptation can be achieved depending on the application. If the respective primary conductors are connected in series and the secondary conductors in parallel, the effective turns ratio increases accordingly. The number of turns of the primary conductors adds up, while the number of turns of the secondary conductor remains at 1.

[0072] However, it is also possible, instead of increasing the number of turns, to increase the input voltage and for this purpose to supply the primary side of the modules with a separate input voltage each, while connecting the secondary conductors in parallel.

[0073] Each module can achieve outputs of one megawatt, and thus several megawatts can be achieved via the module structure.

[0074] Preferably, the transformer incorporates a cooling structure to facilitate heat transfer from the interior of the secondary conductor casing to the outside. Water circuits are suitable for this purpose, as are cooling fins integrated into the concrete structure. Particularly due to the challenges of adequate cooling, the aforementioned modular structure offers advantages, as multiple blocks can be cooled more effectively individually. This improved cooling increases efficiency.

[0075] Electromagnetically, increasing the diameter of the secondary conductor's winding (with the enclosed primary conductor consisting of several windings) means lengthening the aluminum conductor or the aluminum sleeve. Therefore, increasing the diameter of the ring shown in Figure 1 increases the maximum possible operating voltage and thus the maximum possible power. The proposed solution is therefore particularly scalable, simply by increasing the winding diameter.

Claims

Claims 1. Transformer (1) comprising: a primary conductor (2) with several turns, a secondary conductor (3) which is electrically insulated from the primary conductor (2), wherein the secondary conductor is designed as a sleeve which encloses the primary conductor, a core (4) made of soft magnetic material which encloses the secondary conductor, wherein the secondary conductor describes one turn with the primary conductor it encloses.

2. Transformer according to claim 1, wherein the winding of the secondary conductor describes a circle, an oval, an ellipse or a U-shape.

3. Transformer according to claim 1 or 2, wherein the core consists of soft magnetic concrete.

4. Transformer according to one of the preceding claims, wherein the core consists of a block of soft magnetic concrete in which the secondary and primary conductors are cast.

5. Transformer according to claim 4, wherein a cooling structure is incorporated into the block of soft magnetic concrete, which dissipates the heat generated by the conductors.

6. Transformer according to one of the preceding claims, wherein the primary conductor is designed as a cable whose sheath (22) consists of electrically insulating material, and wherein the sheath electrically insulates the primary conductor from the secondary conductor.

7. Transformer according to one of the preceding claims, wherein the sleeve of the secondary conductor has a structure that corresponds to the number of turns Np of the primary conductor and fixes the turns of the primary conductor.

8. Transformer according to claim 6, wherein the structure has the same number of slots (35) as the number of turns Np of the primary conductor, and the slots are designed to partially or completely accommodate one of the turns of the primary conductor.

9. Transformer according to one of the preceding claims, wherein the sleeve has an insulating layer (7) made of electrically insulating material, wherein the insulating layer is designed such that it electrically insulates the primary conductor from the secondary conductor or provides part of the electrical insulation.

10. Transformer according to one of the preceding claims, wherein the primary conductor has a number of turns Np, with Np greater than 1, preferably with Np from 3 to 30, particularly preferably with Np from 4 to 6.

11. Transformer according to one of the preceding claims, wherein the material of the secondary conductor is aluminium and the material of the primary conductor is copper.

12. System consisting of several transformer modules, each comprising a transformer according to claim 4 or 5, wherein the inputs and outputs of the secondary and primary conductors are interconnected according to the requirements of the system to form an overall electrical system.

13. Method for manufacturing the transformer according to any one of claims 1 to 11, wherein the sleeve consists of two half-shells, and the method comprises the following steps: - Laying the primary line in one of the half-shells, - Closing the sleeve by attaching the second half-shell, and - mechanically fixing the two half-shells to each other.

14. High-performance transformer for energy transmission in medium-voltage networks with operating voltages of 1 to 50 kV comprising the transformer according to any one of claims 1 to 11.

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