Current limiting fuse

Abstract

The invention relates to a current limiting fuse which comprises a first terminal end cap (3), a second terminal end cap (3´), and a fusible element (1) disposed between and connected to the first terminal end cap (3) and the second terminal end cap (3´). The fusible element (1) consists of or comprises a tubular element. The tubular element allows the fusible element to have a larger diameter as compared to a fusible element according to the prior art. The larger diameter of the fusible element results in reduced dielectric stress and this again leads to less partial discharges.

Description

[0001] CURRENT LIMITING FUSE

[0002] BACKGROUND

[0003] The present disclosure relates to a current limiting fuse, particularly to a high voltage current limiting fuse, such as, for example, to a high voltage current limiting fuse for a transformer, for example a distribution, dry, and / or power transformer.

[0004] A current limiting fuse generally responds to fault currents or other over-currents in a circuit by interrupting the current to protect the circuit. Such response is brought about by the inclusion in the fuse of a fusible element made of a materiel which melts when the heating effect of the fault current therein exceeds a predetermined value. Further, a current limiting fuse limits the magnitude of the fault current to a maximum value while interrupting it.

[0005] High voltage current limiting fuses generally play a crucial role in protecting transformers as well as in preventing damage to electrical systems. It is typically requested to use current limiting fuses e. g. in distribution and dry transformers. Very often, such fuses are used in pad-mounted transformers and submersible single phase and three-phase transformers and oil-filled switching units. Pad-mounted transformers are usually manufactured in power ratings from around 100 kVA to around 10,000 kVA and typically include built-in fuses and switches. Specifically, it is known to use current limiting fuses for protecting the transformer.

[0006] Fig. 1 shows a corresponding current limiting fuse according to prior art. The fuse comprises a first terminal end cap 300, a second terminal end cap 300', and a fusible element 100 disposed between and connected to the first terminal end cap 300 and the second terminal end cap 300'. The terminal end caps are configured as contacts between a network and a transformer. The fusible element 100 extends along a longitudinal axis L' that runs between the terminal end caps. The fuse further comprises a housing 500 which is filled with a medium, typically sand 400 such that the sand contacts and surrounds the fusible element 100.

[0007] Experience has shown that the fuse may generate a comparatively high safety risk and high level of partial discharges. These pose increased risks both for the user and for the device, i. e. the transformer in question. The partial discharges can be generated by melts or by the terminal end caps 300, 300'.

[0008] Therefore, there is a need for an improved current limiting fuse, particularly for an improved current limiting fuse having improved safety features.

[0009] SUMMARY

[0010] According to the present disclosure a current limiting fuse is provided which comprises a first terminal end cap, a second terminal end cap, and fusible element disposed between and connected to the first terminal end cap and the second terminal end cap. The fusible element consists of or comprises a tubular element. The current limiting fuse may be a high voltage current limiting fuse.

[0011] The tubular element allows the fusible element to have a larger diameter as compared to a correspondingly dimensioned fusible element according to the prior art. In operation, the larger diameter of the fusible element results in reduced dielectric stress and this again leads to less and / or lower partial discharges.

[0012] Thus, regarding a transformer having a current limiting fuse which is positioned at a specific distance to a metallic part of the transformer - such as a tank wall or a winding of the transformer - which is connected to ground or which has a certain electrical potential, a maximum dielectric stress is lower in case of a current limiting fuse according to the present description than in case of a respective current limiting fuse according to prior art.

[0013] For example, in case of a distribution transformer having a 6 MVA, 44 kV / 5 kV, situated at 40 mm from the tank wall, the maximum dielectric stress is 2.7 times lower in the transformer configuration with a high voltage current limiting fuse according to the present description as compared to a transformer configuration with a high voltage current limiting fuse according to prior art.

[0014] If the distance is increased to 60 mm, the dielectric stress is 3.1 times lower in case of a high voltage current limiting fuse according to the present description.

[0015] For both distances, 40 mm and 60 mm, the risk of partial discharge created by the fuse and the risk of breakdown are high when using a prior art current limiting fuse.

[0016] Fig. 6a shows equipotential lines in case of a high voltage current limiting fuse according to the present description positioned at a certain distance to a transformer part 6 such as a tank wall or a high voltage winding. Fig. 6b shows field lines of the considered configuration.

[0017] Effects that can be achieved by a current limiting fuse according to the present description particularly comprise:

[0018] • Security: increase in the safety of users and reduction or even elimination of the risk of damages to electrical systems caused by a faulty transformer

[0019] • Transformer protection: particularly suitable protection of a transformer from overcurrent and short-circuit currents, as well as prevention of damage to electrical systems caused by a faulty transformer

[0020] • High engineering transformer design effort: No or at least reduced design limitations due to thermal, magnetic and mechanical effects caused by short circuit currents

[0021] • Transformer cost: No or at least reduced limitations due to the short circuit currents, stress and forces - more economical design having similar performances

[0022] • Partial discharges: reduced partial discharge levels

[0023] • Extension of voltages: increased voltage ratings and extended application possibilities

[0024] • Transformer maintenance cost: eliminated or at least reduced risk of overload and short circuits and their respective effects

[0025] • No or at least reduced fuse maintenance: no need for additional care or maintenance for the fuse, and / or

[0026] • Fuse cost: very low fuse costs as compared to transformer costs

[0027] Various embodiments may implement one or more of the following features:

[0028] Preferably, the fusible element is made from a highly temperature resistant material.

[0029] The tubular element may define a longitudinal axis which passes through the first terminal end cap and the second terminal end cap. For the avoidance of doubt, the tubular element is hollow, i.e., it defines an interior lumen extending therethrough.

[0030] The tubular element may comprise a cylindrical outer surface with respect to the longitudinal axis, preferably wherein the cylindrical outer surface is a circular cylindrical outer surface. With suitable electrical properties of the fuse, this enables advantageously simple manufacturing thereof. The tubular element may comprise a cylindrical inner surface with respect to the longitudinal axis, preferably wherein the cylindrical inner surface is a circular cylindrical inner surface. With suitable electrical properties of the fuse, this enables advantageously simple manufacturing thereof.

[0031] The tubular element may have a length along the longitudinal axis and an outer radius with respect to the longitudinal axis. For example, the length may be greater than twice the outer radius. Preferably the relation 1 < X / R < 6 is fulfilled, further preferably the relation 1 < X / R < 4. These are particularly suitable relations.

[0032] The length of the tubular element may be at least 5 cm, preferably at least 15 cm. This is particularly advantageous in the case of a current limiting fuse for a transformer.

[0033] The length of the tubular element may be at most 50 cm, preferably at most 40 cm. This is particularly advantageous in the case of a current limiting fuse for a transformer.

[0034] Exemplary preferred length ranges of the tubular element depend on the rated and test voltages and may be 5 to 50 cm, 5 to 40 cm, 15 to 50 cm or 15 to 40 cm.

[0035] The tubular element may comprise a first end region with respect to the longitudinal axis, the first end region forming an electrical contact surface contacting the first terminal end cap. The electrical contact surface contacting the first terminal end cap may have a closed ring shape. This may allow a particularly suitable electrical contact between the first terminal end cap and the fusible element.

[0036] The tubular element may comprise a second end region with respect to the longitudinal axis opposite to the first end region, the second end region forming an electrical contact surface for contacting the second terminal end cap. The electrical contact surface contacting the second terminal end cap may have a closed ring shape. This may allow a particularly suitable electrical contact between the second terminal end cap and the fusible element.

[0037] The first terminal end cap and / or the second terminal end cap may have an electrical contact surface for electrical contact with the fusible element, said electrical contact surface being of a ring-shaped groove, wherein the tubular element extends into the ring-groove. This may allow a particularly suitable electrical contact between the fusible element and the respective terminal end cap.

[0038] The first terminal end cap and / or the second terminal end cap may be made from an electrically conductive material, particularly from a material with good electrically conductive properties such as copper, aluminum and / or silver.

[0039] The current limiting fuse may further comprise an electrically insulated support element for supporting the fusible element. The support element may extend along the length of the fusible element between the first terminal end cap and the second terminal end cap. The fusible element may directly contact the support element. Preferably, the support element extends coaxially with the fusible element along the longitudinal axis.

[0040] The support element may directly contact the first and / or the second terminal end cap. The configuration may be such that the support element extends together with the fusible element into the ring-groove of the first and / or second terminal end cap.

[0041] The support element may comprise a cylindrical inner and / or outer surface, wherein the fusible element directly contacts the cylindrical inner and / or outer surface of the support element. The support element may be tube shaped, for example it may have the shape of a cylindrical tube, preferably the shape of a circular cylindrical tube.

[0042] In particular, the contact between the support element and the fusible element can be configured so that it is gas-tight. This enables even more extensive protection against partial discharge.

[0043] The tubular element may directly contact the cylindrical surface of the support element continuously between the first terminal end cap and the second terminal end cap.

[0044] The cylindrical surface of the support element which is directly contacted by the fusible element may be an outer surface or an inner surface with respect to the longitudinal axis.

[0045] The support element may comprise a lumen extending therethrough, along the longitudinal axis. In other words, the support element may have a tubular shape, in other words a hollow cylindrical shape.

[0046] The fusible element may be or may comprise a metallic foil which is disposed on the support element. The fusible element may be placed on the support element or may be deposited on the support element by means of a deposition technique, preferably via a plasma deposition or a vapor deposition. The fusible element may be placed or deposited on the support element gas-tight and / or oil-tight and / or ester-tight.

[0047] The current limiting fuse may further comprise an insulated casing element extending between the first terminal end cap and the second terminal end cap, wherein the casing element surrounds the fusible element with respect to the longitudinal axis. The casing element may be cylindrically shaped defining an axis which coincides with the longitudinal axis.

[0048] The casing element may be made from an oil-tight and / or ester-tight material. In this way the fuse may also be suitable for use in an oil or ester environment, for example in an oil- filled tank of a transformer.

[0049] The current limiting fuse may further comprise a material for enhancing an arc extinguishing capability of the fuse, the material being disposed in contact with the fusible element. The material may be for example a silica-based material or sand, particularly quartz sand.

[0050] Particularly, the end caps are configured to provide electrical contacts between a network and a transformer. Preferably, the end caps are made from a highly electrically conductive material. This may enhance reduction of electrical stress in the area between the terminal end caps.

[0051] The first terminal end cap and / or the second terminal end cap may have a recess, wherein the fusible element is arranged to extend into the recess.

[0052] The first terminal end cap and / or the second terminal end cap may have a flat surface area facing the respective other terminal end cap and extending in a plane normal to the longitudinal axis.

[0053] The first terminal end cap and / or the second terminal end cap may have a convexly rounded surface area on a side facing radially and / or axially away from the fusible element. The rounded surface area of the respective terminal end cap allows for a reduction in the maximum dielectric stress within the region of the respective cap. It is noted that the maximum dielectric stress tends to be most critical close to the fusible element and close to the terminal end caps.

[0054] The convexly rounded surface area may be shaped rotationally symmetrical with respect to the longitudinal axis.

[0055] The convexly rounded surface area may be shaped like a section of a spherical surface.

[0056] The spherical surface may show a radius which is larger than an outer radius of the tubular element.

[0057] The current limiting fuse may further comprise at least one contacting element which is configured and arranged to increase the electrical conducting contact area between the first terminal end cap and the fusible element or between the second terminal end cap and the fusible element.

[0058] The contacting element may comprise a cylindrical surface which contacts an inner and / or outer surface portion of the fusible element and a surface portion of the first terminal end cap and / or the second terminal end cap.

[0059] The contacting element and the respective terminal end cap may form an integral component.

[0060] The current limiting fuse may be a fuse for a distribution transformer and / or a dry transformer and / or a power transformer, preferably wherein the transformer has a rating of between 1 MVA and 50 MVA.

[0061] According to a further aspect of the present description, a current limiting fuse is provided which comprises a first terminal end cap, a second terminal end cap, and fusible element disposed between and connected to the first terminal end cap and the second terminal end cap. The first terminal end cap and / or the second terminal end cap may have a convexly rounded surface area on a side facing away from the fusible element. The rounded surface area of the respective terminal end cap allows for a reduction in the maximum dielectric stress within the region of the respective cap. It is noted that the maximum dielectric stress tends to be most critical close to the fusible element and close to the terminal end caps.

[0062] According to a further aspect of the present description, a transformer is provided which comprises a high-voltage winding and a current limiting fuse as described herein, wherein the current limiting fuse is arranged at a distance from the high-voltage winding, preferably wherein the distance is at least 20 mm, preferably at least 30 mm.

[0063] According to a further aspect of the present description, a transformer is provided which comprises a high-voltage winding, an oil-filled tank, wherein the high-voltage winding is arranged within the tank, and a current limiting fuse as described herein, wherein the current limiting fuse is arranged at a distance from the tank, preferably wherein the distance is at least 20 mm, preferably at least 30 mm.

[0064] The transformer may further comprise a box, preferably an oil-tight and / or ester- tight box, wherein the current limiting fuse is arranged within the box and the box is arranged within the tank. Alternatively, the current limiting fuse can be placed for example in a liquid insulation of the transformer, for example oil or ester etc. In particular, the present disclosure comprises the following aspects:

[0065] 1. A current limiting fuse, comprising a first terminal end cap (3), a second terminal end cap (3'), and a fusible element (1) disposed between and connected to the first terminal end cap (3) and the second terminal end cap (3'), the fusible element (1) consisting of or comprising a tubular element.

[0066] 2. The current limiting fuse of aspect 1, wherein the tubular element defines a longitudinal axis (L) which passes through the first terminal end cap (3) and the second terminal end cap (3').

[0067] 3. The current limiting fuse of aspect 2, wherein the tubular element comprises a cylindrical outer surface (12) with respect to the longitudinal axis (L), preferably wherein the cylindrical outer surface (12) is a circular cylindrical outer surface.

[0068] 4. The current limiting fuse of any of aspects 2 to 3, wherein the tubular element comprises a cylindrical inner surface (14) with respect to the longitudinal axis (L), preferably wherein the cylindrical inner surface (14) is a circular cylindrical inner surface.

[0069] 5. The current limiting fuse of any of aspects 2 to 4, wherein the tubular element has a length (A.) along the longitudinal axis (L) and an outer radius (R) with respect to the longitudinal axis (L), preferably fulfilling the relation 1 < X / R < 6, further preferably fulfilling the relation 1 < X / R < 4.

[0070] 6. The current limiting fuse of aspect 5, wherein the length (X) of the tubular element is at least 5 cm, preferably at least 15 cm. 7. The current limiting fuse of any of aspects 5 to 6, wherein the length (A.) of the tubular element is at most 50 cm, preferably at most 40 cm.

[0071] 8. The current limiting fuse of any of aspects 2 to 7, wherein the tubular element comprises a first end region (16) with respect to the longitudinal axis (L), the first end region forming an electrical contact surface contacting the first terminal end cap (3), preferably wherein the electrical contact surface contacting the first terminal end cap has a closed ring shape.

[0072] 9. The current limiting fuse of aspect 8, wherein the tubular element comprises a second end region (18) with respect to the longitudinal axis (L) opposite to the first end region (16), the second end region forming an electrical contact surface for contacting the second terminal end cap (3'), preferably wherein the electrical contact surface contacting the second terminal end cap has a closed ring shape.

[0073] 10. The current limiting fuse of any of the preceding aspects, wherein the first terminal end cap (3) and / or the second terminal end cap (3') has an electrical contact surface for electrical contact with the fusible element (1), said electrical contact surface being of a ring-shaped groove, wherein the tubular element extends into the ring-groove.

[0074] 11. The current limiting fuse of any of the preceding aspects, wherein the first terminal end cap (3) and / or the second terminal end cap (3') is made from a good electrically conductive material such as for example copper, aluminum and / or silver.

[0075] 12. The current limiting fuse of any of the preceding aspects, further comprising an insulated support element (2) for supporting the fusible element (1), the support element (2) extending along the length of the fusible element (1) between the first terminal end cap (3) and the second terminal end cap (3'), wherein the fusible element (1) directly contacts the support element (2). 13. The current limiting fuse of aspect 12, wherein the support element (2) comprises a cylindrical surface (22, 22'), wherein the fusible element (1) directly contacts the cylindrical surface (22, 22') of the support element.

[0076] 14. The current limiting fuse of aspect 13, wherein the tubular element directly contacts the cylindrical surface (22, 22') of the support element (2) continuously between the first terminal end cap (3) and the second terminal end cap (3').

[0077] 15. The current limiting fuse of any of aspects 13 to 14, wherein the cylindrical surface (22, 22') of the support element (2) is an outer surface (22) or an inner surface (22') with respect to the longitudinal axis (L).

[0078] 16. The current limiting fuse of any of aspects 12 to 15, wherein the support element (2) comprises a lumen (24) extending therethrough along the longitudinal axis (L).

[0079] 17. The current limiting fuse of any of aspects 12 to 16, wherein the fusible element (1) is placed on the support element or deposited on the support element (2) by means of a deposition technique, preferably via a plasma deposition or a vapor deposition.

[0080] 18. The current limiting fuse of any of the preceding aspects, further comprising an insulated casing element (5) extending between the first terminal end cap (3) and the second terminal end cap (3'), wherein the casing element (5) surrounds the fusible element (1) with respect to the longitudinal axis (L).

[0081] 19. The current limiting fuse of aspect 18, wherein the casing element (5) is cylindrically shaped defining an axis which coincides with the longitudinal axis (L). 20. The current limiting fuse of any of aspects 18 to 19, wherein the casing element (5) is made from an oil-tight and / or ester-tight material.

[0082] 21. The current limiting fuse of any of the preceding aspects, further comprising a material (4) for enhancing an arc extinguishing capability of the fuse, the material being disposed in contact with the fusible element (1).

[0083] 22. The current limiting fuse of any of the preceding aspects, wherein the first terminal end cap (3) and / or the second terminal end cap (3') has a recess (32), wherein the fusible element (1) is arranged to extend into the recess.

[0084] 23. The current limiting fuse of aspect 22, wherein the first terminal end cap (3) and / or the second terminal end cap (3') has a flat surface area (34) facing the respective other terminal end cap (3', 3) and extending in a plane (E) normal to the longitudinal axis (L).

[0085] 24. The current limiting fuse of any of aspects 22 to 23, wherein the first terminal end cap (3) and / or the second terminal end cap (3') has a convexly rounded surface area (36) on a side facing away from the fusible element (1).

[0086] 25. The current limiting fuse of aspect 24, wherein the convexly rounded surface area (36) is shaped rotationally symmetrical with respect to the longitudinal axis (L).

[0087] 26. The current limiting fuse of any of aspects 24 to 25, wherein the convexly rounded surface area (36) is shaped like a section of a spherical surface.

[0088] 27. The current limiting fuse of aspect 26, wherein the spherical surface shows a radius (R2) which is larger than an outer radius

[0089] (R) of the tubular element. 28. The current limiting fuse of any of the preceding aspects, further comprising at least one contacting element (7) which is configured and arranged to increase the electrical conducting contact area between the first terminal end cap (3) and the fusible element (1) or between the second terminal end cap (3') and the fusible element (1).

[0090] 29. The current limiting fuse of aspect 28, wherein the contacting element (7) comprises a cylindrical surface (72) which contacts a surface portion of the fusible element (1) and a surface portion of the first terminal end cap (3) and / or the second terminal end cap (3').

[0091] 30. The current limiting fuse of any of aspects 28 to 29, wherein the contacting element (7) and the respective terminal end cap (3, 3') form an integral component.

[0092] 31. The current limiting fuse of any of the preceding aspects, wherein the current limiting fuse is a fuse for a distribution transformer and / or a dry transformer and / or a power transformer, preferably wherein the transformer has a rating of between 1 MVA and 50 MVA.

[0093] 32. A current limiting fuse, comprising a first terminal end cap (3), a second terminal end cap (3'), and a fusible element (1) disposed between and connected to the first terminal end cap (3) and the second terminal end cap (3'), wherein the first terminal end cap (3) and / or the second terminal end cap (3') has a convexly rounded surface area (36) on a side facing away from the fusible element (1).

[0094] SHORT DESCRIPTION OF THE DRAWINGS

[0095] The subject-matter of the disclosure will be explained in more detail with reference to preferred exemplary embodiments which are illustrated in the attached drawings. Fig. 1 is a schematic cross-section of a current limiting fuse according to prior art.

[0096] Fig. 2 shows an example of a current limiting fuse according to the present description, comprising a tube-shaped fusible element and a tube-shaped support element.

[0097] Fig. 3 shows a detail of Fig. 2 around a first terminal end cap of the current limiting fuse.

[0098] Fig. 4 shows a further example of a current limiting fuse, having a cylindrical support element arranged within the fusible element.

[0099] Fig. 5 shows a further example of a current limiting fuse, having a tube-shaped support element surrounding the fusible element.

[0100] Fig. 6a is a schematic representation of equipotential lines inside a transformer between a current limiting fuse according to the present description and a metallic part of the transformer, for example a tank wall.

[0101] Fig. 6b is a corresponding representation showing field lines.

[0102] Figures 7a and 7b show examples of a current limiting fuse, comprising terminal end caps having a convexly rounded surface area.

[0103] Figures 8a to 8c show examples of a current limiting fuse, comprising ring-shaped contacting elements each for increasing the electrical contact area between a respective terminal end cap and the fusible element, the ring-shaped contacting elements arranged to contact the fusible element from outside.

[0104] Figures 9a and 9b show examples of a current limiting fuse, comprising cylindrically shaped contacting elements, the cylindrically shaped contacting elements arranged to contact the fusible element from inside. DETAILED DESCRIPTION

[0105] Fig. 2 shows an example of a current limiting fuse according to the present disclosure. The current limiting fuse may be configured for use in distribution, dry or power transformers, preferably wherein the transformer has a rating of between 1 MVA and 50 MVA.

[0106] The current limiting fuse comprises a first terminal end cap 3, a second terminal end cap 3', and a fusible element 1. The fusible element 1 consists of a tubular element which defines a longitudinal axis L. The tubular element has a cylindrical outer surface 12 extending around the longitudinal axis L and a cylindrical inner surface 14 extending around the longitudinal axis L. Preferably, the outer surface 12 and the inner surface 14 both exhibit a circular cross-section normal to the longitudinal axis L. Accordingly, the tubular element has, with respect to the longitudinal axis L, an inner radius r and an outer radius R.

[0107] The length A. of the tubular element measured along the longitudinal axis L may be for example between 5 cm and 50 cm, preferably between 15 cm and 40 cm.

[0108] The thickness of the wall of the tubular element, i. e. R - r is preferably between 1 mm and 30 mm, preferably between 2 mm and 20 mm, preferably between 3 mm and 15 mm.

[0109] The length X and the outer radius R are preferably chosen such that the relation 1 < X / R < 6, further preferably the relation 1 < X / R < 4 is fulfilled.

[0110] The tubular element comprises a first end region 16 with respect to the longitudinal axis L which forms an electrical contact surface for electrically contacting the first terminal end cap 3 to the tubular element. Fig. 3 shows a detail of Fig. 2 around the first terminal end cap 3. Preferably, the first terminal end cap 3 has a recess 32, for example in form of a groove, wherein the first end region 16 extends into the recess 32, preferably electrically contacting an inner wall region of the recess 32. The recess 32 may be ring shaped such that it extends around the longitudinal axis L. Fig. 3 illustrates an example in which the tubular element contacts the radially outer, i. e. inward-facing wall of the recess 32 and, preferably, also the axially facing bottom surface of the recess 32.

[0111] The tubular element further comprises a second end region 18 wherein the connection between the second end region 18 and the second terminal end cap 3' preferably is identical or corresponding to the connection between the first end region 16 and the first terminal end cap 3. The first and second terminal end caps 3, 3' are formed of a good electrically conductive material such as for example copper, aluminum, or silver.

[0112] The current limiting fuse further comprises a support element 2 for supporting the fusible element 1. The support element 2 extends along the length of the fusible element 1 between the first terminal end cap 3 and the second terminal end cap 3'. Preferably, the support element 2 is directly connected to both the first terminal end cap 3 and to the second terminal end cap 3'. The connection can by physical and / or chemical. The support element of his example is tube-shaped. As illustrated in Fig. 2, the wall thickness of the support element 2 may be greater than the wall thickness of the fusible element 1.

[0113] The support element 2 consists of an electrically insulating material. The fusible element 1 directly contacts the support element 2 along an uninterrupted or continuous path between the first terminal end cap 3 and the second terminal end cap 3'. The support element 2 may have a cylindrical surface 22 to which the fusible element 1 is attached. In the example, the cylindrical surface 22 is a surface pointing radially outwards with respect to the longitudinal axis. But it may alternatively be a radially inward facing surface.

[0114] For example, the fusible element 1 may be a metallic foil which is attached to the surface of the support element 2, preferably in a gas-tight and / or oil-tight and / or ester-tight manner. Alternatively, the fusible element 1 can be placed on the support element or may be for example deposited on the support element 2 by means of a deposition technique such as a plasma deposition or vapor deposition. This may be advantageous because it allows a practically gas-tight connection to be created between the fusible element and the support element, which reduces the likelihood of partial discharges. Preferably, the fusible element 1 contacts the entirety of the cylindrical surface 22 of the support element 2.

[0115] The current limiting fuse further comprises an insulated casing element 5 extending between the first terminal end cap 3 and the second termina end cap 3'. The casing element 5 surrounds the fusible element 1 with respect to the longitudinal axis L. Preferably, the casing element 5 is cylindrically shaped. The casing element 5 may define an axis which coincides with the longitudinal axis L. The casing element 5 may be made from an oil-tight and / or ester- tight material. In this way, the current limiting fuse is suited to be arranged for operation immersed in oil or ester within an oil-filled or ester-filed transformer tank.

[0116] The current limiting fuse further comprises a material 4 for enhancing an arc extinguishing capability of the fuse. The material 4 may be for example sand. It is disposed in contact with the fusible element 1. The material 4 may be filled in an area between the fusible element 1 and the casing element 5 and / or inside the tubular fusible element 1.

[0117] In the example of Figures 2 and 3, the support element 2 comprises a lumen 24 or through hole which extends therethrough along the longitudinal axis L. The lumen 24 may be filled with the material 4 for enhancing an arc extinguishing capability of the fuse.

[0118] The first terminal end cap 3 and / or the second terminal end cap 3' may have a flat surface area 34 facing the respective other terminal end cap 3', 3 and extending in a plane E normal to the longitudinal axis L. The recessed groove may be recessed with regard to said plane E.

[0119] Fig. 6a is a schematic representation of equipotential lines inside a transformer between a current limiting fuse according to the present description and a metallic part 6 of the transformer. The metallic part may be for example a tank wall or a high voltage winding of the transformer. Fig. 6b is a corresponding representation showing electrical field lines. As can be taken from these figures, the maximum dielectric stress is potentially critical close to the fusible element 1 and / or close to the first or second terminal end cap 3, 3'.

[0120] Fig. 4 shows a further example of a current limiting fuse. Unless otherwise described, the fuse may be designed in the same way as the example above.

[0121] The current limiting fuse according to this example has a cylindrical support element 2 which is not tube-shaped but which has the shape of a solid cylinder. The axis of the cylinder preferably coincides with the longitudinal axis L. The fusible element 1 is attached to or provided on the radially outward-facing surface 22 of the support element 2.

[0122] Fig. 5 shows a further example of a current limiting fuse. Here, the support element 2 is again tube-shaped, however, the fusible element 1 is attached to the radially inside facing surface 22' of the support element 2. With this design, a separate casing element is not necessary because the support element 2 can be designed in such a way that it also has a corresponding casing or housing function.

[0123] To reduce the maximum dielectric stress close to the first or second terminal end cap, cap configurations as exemplarily illustrated in Figures 7a and 7b can be provided. Fig. 7a shows an example where the first terminal end cap 3 and / or the second terminal end cap 3' has a convexly rounded surface area 36 on a side facing axially away from the fusible element 1. Preferably, the rounded surface area 36 is shaped rotationally symmetrical with respect to the longitudinal axis L. The rounded shape effectuates a further reduction in the maximum dielectric stress near the respective terminal end cap.

[0124] As illustrated in Fig. 7b, the convexly rounded surface area 36 may be shaped like a section of a spherical surface, for example like a hemispheric surface. As can be seen in Fig. 7b, the outer radius R of the fusible element 1 is smaller than the radius R2 of the first terminal end cap 3.

[0125] The first and second terminal end caps 3, 3' may be configured identical or correspondingly.

[0126] In the examples shown in Figures 7a and 7b, both terminal end caps 3, 3' are provided with a ring-shaped groove 32. The end regions 16, 18 of the fusible element 1 each extend into a respective one of these grooves 32.

[0127] Figures 8a to 8c show examples of a current limiting fuse, having differently shaped terminal end caps. The end caps shown in Fig. 8a are essentially shaped flat or plane on their sides facing axially away from the fusible element 1, the end caps shown in Fig. 8b are moderately rounded and the end caps shown in Fig. 8c are essentially spherically rounded. The more pronounced the rounded surface area, the more suitable the fuse is for higher voltages. Accordingly, the example of Fig. 8a may be suited for low voltages, the example of Fig. 8b for high voltages, and the example of Fig. 8c for ultra high voltages.

[0128] Further, the current limiting fuses of Figures 8a to 8c comprise ring-shaped contacting element 7 configured to increase the electrical contact area between a respective terminal end cap 3, 3' and the fusible element 1. A ring-shaped contacting element 7 is arranged on the respective flat surface area 34 of a terminal end cap. Alternatively, a terminal end cap 3 and the respective contacting element 7 together may form an integral component, i. e. they may be designed in one piece.

[0129] Figures 9a and 9b show examples of a current limiting fuse, comprising cylindrically shaped contacting elements 7 which are shaped like solid cylinders to contact the fusible element 1 from radially inside. In this case, the support element is tube-shaped and contacts the radially outward facing surface of the fusible element 1.

Claims

CLAIMS1. A current limiting fuse, comprising a first terminal end cap (3), a second terminal end cap (3'), and a fusible element (1) disposed between and connected to the first terminal end cap (3) and the second terminal end cap (3'), the fusible element (1) consisting of or comprising a tubular element.

2. The current limiting fuse of claim 1, wherein the tubular element defines a longitudinal axis (L) which passes through the first terminal end cap (3) and the second terminal end cap (3').

3. The current limiting fuse of claim 2, wherein the tubular element comprises a cylindrical outer surface (12) with respect to the longitudinal axis (L), preferably wherein the cylindrical outer surface (12) is a circular cylindrical outer surface.

4. The current limiting fuse of any of claims 2 to 3, wherein the tubular element comprises a cylindrical inner surface (14) with respect to the longitudinal axis (L), preferably wherein the cylindrical inner surface (14) is a circular cylindrical inner surface.

5. The current limiting fuse of any of claims 2 to 4, wherein the tubular element has a length (A.) along the longitudinal axis (L) and an outer radius (R) with respect to the longitudinal axis (L), preferably fulfilling the relation 1 < X / R < 6, further preferably fulfilling the relation 1 < X / R < 4.

6. The current limiting fuse of claim 5, wherein the length (X) of the tubular element is at least 5 cm, preferably at least 15 cm, and / orwherein the length (A.) of the tubular element is at most 50 cm, preferably at most 40 cm.

7. The current limiting fuse of any of claims 2 to 6, wherein the tubular element comprises a first end region (16) with respect to the longitudinal axis (L), the first end region forming an electrical contact surface contacting the first terminal end cap (3), preferably wherein the electrical contact surface contacting the first terminal end cap has a closed ring shape, and / or wherein the tubular element comprises a second end region (18) with respect to the longitudinal axis (L) opposite to the first end region (16), the second end region forming an electrical contact surface for contacting the second terminal end cap (3'), preferably wherein the electrical contact surface contacting the second terminal end cap has a closed ring shape.

8. The current limiting fuse of any of the preceding claims, wherein the first terminal end cap (3) and / or the second terminal end cap (3') has an electrical contact surface for electrical contact with the fusible element (1), said electrical contact surface being of a ring-shaped groove, wherein the tubular element extends into the ring-groove.

9. The current limiting fuse of any of the preceding claims, further comprising an insulated support element (2) for supporting the fusible element (1), the support element (2) extending along the length of the fusible element (1) between the first terminal end cap (3) and the second terminal end cap (3'), wherein the fusible element (1) directly contacts the support element (2).

10. The current limiting fuse of claim 9, wherein the support element (2) comprises a cylindrical surface (22, 22'), wherein the fusible element (1) directly contacts the cylindrical surface (22, 22') of the support element.

11. The current limiting fuse of any of claim 10, wherein the cylindrical surface (22, 22') of the support element (2) is an outer surface (22) or an inner surface (22') with respect to the longitudinal axis (L).

12. The current limiting fuse of any of claims 9 to 11, wherein the fusible element (1) is placed on the support element or deposited on the support element (2) by means of a deposition technique, preferably via a plasma deposition or a vapor deposition.

13. The current limiting fuse of any of the preceding claims, further comprising an insulated casing element (5) extending between the first terminal end cap (3) and the second terminal end cap (3'), wherein the casing element (5) surrounds the fusible element (1) with respect to the longitudinal axis (L), and / or further comprising a material (4) for enhancing an arc extinguishing capability of the fuse, the material being disposed in contact with the fusible element (1).

14. The current limiting fuse of any of the preceding claims, wherein the first terminal end cap (3) and / or the second terminal end cap (3') has a convexly rounded surface area (36) on a side facing away from the fusible element (1).

15. The current limiting fuse of any of the preceding claims, further comprising at least one contacting element (7) which is configured and arranged to increase the electrical conducting contact area between the first terminal end cap (3) and the fusible element (1) or between the second terminal end cap (3') and the fusible element (1).

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