SUBSEA FUSE DEVICE

Abstract

 The present invention relates to a subsea fuse device (20) comprising a fuse housing (21) and a fuse wire. The fuse wire comprises a first end section (22), a second end section (23), and a central section (24). The fuse housing (21) comprises a one-piece outer envelope which completely encloses a hollow space (27) and provides a first feedthrough opening (25) and a second feedthrough opening (26). The central section (24) of the fuse wire is arranged within the hollow space (27), the first end section (22) of the fuse wire is extending through the first feedthrough opening (25), and the second end section (23) of the fuse wire is extending through the second feedthrough opening (26). At the first feedthrough opening (25), an outer circumferential surface of the first end section (22) is in contact with an inner circumferential surface of the first feedthrough opening (25) and seals the first feedthrough opening (25). At the second feedthrough opening (26), an outer circumferential surface of the second end section (23) of the fuse wire is in contact with an inner circumferential surface of the second feedthrough opening (26) and seals the second feedthrough opening (26).

Description

Field of the invention

[0001] The present invention relates to a subsea fuse device which may be used in electrical and electronic circuits in subsea equipment. Furthermore, the present invention relates to a subsea device comprising an electric circuitry comprising the subsea fuse device.

Background of the invention

[0002] In subsea applications, for example subsea oil production, subsea devices may comprise electric and electronic circuitry. The subsea devices, which may comprise for example so-called subsea canisters, may be arranged in a depth of several hundred or even several thousand metres, for example in a depth of 3000 m. Subsea devices may be pressure compensated such that the inside pressure essentially corresponds to an environmental pressure which may be in a range of a few hundred bars, for example 300 bars in a depth of 3000 m. Such pressure compensated subsea devices may be filled with a fluid, for example oil, which may be pressurized with ambient pressure. Consequently, this very high ambient pressure is also acting on the electric or electronic circuitry arranged within the subsea device.

[0003] In electronic and electrical circuitry fuses are used to protect partial circuits, so-called sub circuits, from overload and short circuits. A usual fuse may work by melting or vaporizing a conductive element arranged within the fuse. By melting or vaporizing the conductive element the fuse becomes not conducting and isolates for example a sub circuit from the rest of the circuit or a system.

[0004] However, when a usual fuse is used in a subsea device, it shows that such a fuse fails to protect sub circuits when being used in oil at high ambient pressure, for example at 300 bars. Furthermore, the oil which is typically used as an isolating dielectric fluid, may be contaminated by the melted or vaporized conductive element of the fuse. This may influence the insulating properties of the oil which are depending on the cleanliness of the oil.

[0005] Therefore, there is a need for a fuse which operates reliably in an oil-filled subsea device at high pressures.

Summary of the invention

[0006] According to the present invention, this object is achieved by a subsea fuse device and a subsea device as defined in the independent claims. The dependent claims define embodiments of the present invention.

[0007] According to the present invention, a subsea fuse device is provided. The subsea fuse device comprises a fuse housing and a fuse wire. The fuse wire comprises a first end section, a second end section, and a central section along a longitudinal direction of the fuse wire. The fuse housing comprises a one-piece outer envelope which completely encloses a hollow space. Furthermore, the housing provides a first feedthrough opening and second feedthrough opening. The feedthrough openings are connecting the hollow space inside the fuse housing with an environment surrounding the subsea fuse device. The central section of the fuse wire is arranged completely within the hollow space of the fuse housing. The first end section of the fuse wire extends through the first feedthrough opening, and the second end section of the fuse wire extends through the second feedthrough opening. At the first feedthrough opening, an outer circumferential surface of the first end section of the fuse wire is in contact with an inner circumferential surface of the first feedthrough opening such that it seals the first feedthrough opening. Likewise, at the second feedthrough opening, an outer circumferential surface of the second end section of the fuse wire is in contact with an inner circumferential surface of the second feedthrough opening thus sealing the second feedthrough opening. In other words, the interior of the fuse housing comprising the central section of the fuse wire is completely sealed from an outside of the fuse housing. Thus, the central section of the fuse wire does not come into contact with, for example, a dielectric fluid surrounding the fuse housing, and the interior of the fuse housing may be protected from high pressure outside the fuse housing. Therefore, operation of the fuse wire inside the fuse housing becomes reliable, and an isolating dielectric fluid outside the fuse housing may not be contaminated by a melting or vaporizing fuse wire. Moreover, as the fuse housing is formed as a one-piece outer envelope, a reliable tightness of the fuse housing can be achieved even at high environmental pressure.

[0008] According to an embodiment, the outer envelope is pressure resistant. This means that, in a sealed state of the outer envelope, a pressure inside the outer envelope is independent from an environmental pressure prevailing outside the outer envelope. For example, a pressure inside the outer envelope may comprise approximately 1 bar while an outside pressure may vary in a range from 0 to 300 bars. For accomplishing this, the outer envelope may be made of a rigid material having a shape which supports to maintain the shape under pressure varying conditions.

[0009] According to an embodiment, the outer envelope has a tubular form and the first and second feedthrough openings are arranged at opposite ends of the tubular envelope. The tubular form supports a high stability of the fuse housing against high external pressure.

[0010] Furthermore, the outer envelope may be hermetically sealed apart from the first and second feedthrough openings. This enables that the hollow space within the outer envelope may be filled with gas or air with a pressure far below an operating pressure in subsea environments. For example, a pressure of about one bar may be present in the hollow space. Furthermore, the hermetically sealed outer envelope may enable the hollow space to be evacuated. Thus, a reliable operation of the fuse wire within the hollow space of the fuse housing is enabled.

[0011] According to another embodiment, the outer envelope is made of an electrically isolating material. The material may comprise for example glass, ceramics or resin. Therefore, in case the fuse wire is melted or vaporized inside the hollow space and does not provide an electrical conduction any more, the whole fuse device interrupts reliably an electric current flow to an electrical circuit or sub circuit protected by the subsea fuse device.

[0012] In case a glass material is used for the outer envelope, the subsea fuse device may be manufactured as follows. The fuse wire may be passed through the opposite ends of a glass tube such that the central section is arranged within the glass tube and the first end section and the second end section are arranged at the opposite ends of the glass tube. The ends of the glass tube are heated so that they seal around the first and second end sections, respectively. For example, infrared absorbing glass may be used such that an infrared heat source can concentrate the heat in a small sealing zone of the glass tube. The thermal coefficient of expansion of the glass material and the fuse wire may be similar to prevent breaking the glass-to-metal seal. The glass used may contain no volatile components such as lead oxide and fluorides to support the isolating property.

[0013] According to another embodiment, a cross section of the central section of the fuse wire is smaller than a cross section of each of the first and second end sections. The cross section of the central section may be selected depending on the cutoff current required for protecting the electrical circuits which are to be protected by the subsea fuse device. The cross section of the end sections may be selected significantly larger. This enables that only the central section of the fuse wire is melting or vaporizing at the cutoff current, whereas the first and second end sections are not heated significantly such that the sealing at the first and second feedthrough openings is not significantly loaded by thermal expansion during fusing the subsea fuse device.

[0014] In another embodiment of the present invention, the central section of the fuse wire comprises a first material and at least one of the first and second end sections of the fuse wire comprises a second material which is different from the first material. For example, the second material of the first and second end sections may comprise a metal material having a low coefficient of expansion or a coefficient of expansion which corresponds to a coefficient of expansion of a material of the fuse housing. This may improve the sealing of the first and second end sections of the fuse wire within the first and second feedthrough openings. The first material of the central section of the fuse wire may be selected in consideration of a reliable melting of the wire in case of the cutoff current being applied. For example, the first and second materials may each comprise zinc, copper, silver or aluminum. However, the central section and the first and second end sections of the fuse wire may also be made of the same material.

[0015] According to another aspect of the present invention, a subsea device is provided which comprises an enclosure and an electric circuitry arranged within the enclosure. The electric circuitry comprises the above described subsea fuse device for protecting the electric circuitry from overcurrent or short circuit.

[0016] According to an embodiment, the enclosure of the subsea device is filled with a fluid, for example oil, and comprises a volume and pressure compensator which balances the pressure inside the enclosure to the pressure prevailing in an environment of the enclosure. In other words, the subsea device is pressure compensated and the fluid filled into the enclosure is pressurized with essentially the same pressure prevailing outside the subsea device. For example, in a subsea environment in a depth of 3000 m, the pressure may be approximately 300 bars. However, the electric circuitry inside the enclosure can reliably be protected from overcurrent by the subsea fuse device as the fuse wire inside the subsea fuse device is completely sealed from this environmental pressure and the oil filled into the enclosure.

[0017] Although specific features are described in the above summary and the following detailed description in connection with specific embodiments and aspects of the present invention, it is to be understood that the features of the embodiments and aspects may be combined with each other unless specifically noted otherwise.

Brief description of the drawings

[0018] The present invention will now be described in more detail with reference to the accompanying drawings.

Fig. 1 shows schematically a subsea device according to an embodiment of the present invention.

Fig. 2 shows schematically a subsea fuse device according to an embodiment of the present invention.

Detailed description of the drawings

[0019] In the following, exemplary embodiments of the invention will be described in more detail. It is to be understood that the features of the various exemplary embodiments described herein may be combined with each other unless specifically noted otherwise. Same reference signs in the various drawings refer to similar or identical components.

[0020] Fig. 1 shows a subsea device 10, for example a subsea canister, which may be arranged in a subsea environment for housing electrical components or electric circuitry 11. For communicating with other components arranged in other subsea devices and for supplying the electric circuitry 11 with electrical energy, a data and energy supply connection 12 may be provided extending from an interior of the subsea device 10 to an exterior of the subsea device 10. The subsea device 10 may be arranged and operated in deep sea environments, for example in a depth of 3000 m. Therefore, the subsea device 10 comprises an enclosure 13 which protects the interior of the enclosure 13 from the environment, for example from salt water.

[0021] For the construction of such subsea devices two solutions are proposed for dealing with the high pressures present in deep sea environments. A pressure resistant enclosure can be provided, which has a close to atmospheric internal pressure, enabling the use of conventional electric and electronic components. Such enclosures need to have relatively thick walls and are thus bulky and heavy, since they have to withstand high differential pressures. Another solution is the use of pressurized (or pressure compensated) enclosures, which comprise a volume/pressure compensator which balances the pressure in the enclosure to the pressure prevailing in the ambient seawater. The enclosure 13 shown in Fig. 1 comprises such a volume/pressure compensator indicated by reference sign 14. The pressure compensated enclosure 13 is generally filled with a fluid 17, for example oil, and components operated inside the pressure compensated enclosure 13 are made to be operable under high pressures. The pressure/volume compensator 14 compensates variations in the volume of the fluid 17 filling the enclosure 13, which may occur due to variations in ambient pressure or in temperature. Temperature changes can be caused by deployment at the subsea location or by internal heating, for example due to electric losses.

[0022] The electric circuitry 11 may comprise partial or sub circuits 15 and 16. Some of the sub circuits 15, 16 may have to be protected from overload and short circuits. Therefore, in the power supply connection 12 to the sub circuit 15 a subsea fuse device 20 is provided. The electric circuitry 11 may comprise for example a printed circuit board on which the subsea fuse device 20 and the sub circuits 15, 16 are arranged.

[0023] As described above, the interior of the enclosure 13 may be filled with fluid 17, for example an isolating dielectric oil. Therefore, the subsea fuse device 20 may be surrounded and may be in direct contact with the fluid 17. Furthermore, due to the pressure compensation of the enclosure 13 via the pressure compensator 14, the fluid 17 may be pressurized at essentially the same pressure as it is prevailing outside the enclosure 13. In subsea applications this pressure may be for example 300 bars. Therefore, the subsea fuse device 20 has to be capable of operating reliably under such pressure conditions.

[0024] Fig. 2 shows the subsea fuse device 20 of Fig. 1 in more detail. The subsea fuse device 20 comprises a fuse housing 21 and a fuse wire. The fuse wire is composed of three sections in its longitudinal direction: a first end section 22, a second end section 23 and a central section 24. The sections 22 to 24 of the fuse wire may each have different properties. For example, the end sections 22 and 23 may have a different cross section then the central section 24. Furthermore, the end sections 22 and 23 may be made of a different material than the central section 24. However, the sections 22 to 24 may also be made of the same material and may have the same properties, such that the whole fuse wire is made of a continuous homogeneous material.

[0025] The fuse housing 21 may have a tubular form and may be made of a glass tube. In general, the fuse housing 21 may be made as a one-piece outer envelope which completely encloses a hollow space 27 through which the fuse wire is extending. The tubular housing 21 has at each end a feedthrough opening. In Fig. 2 the housing 21 has a first feedthrough opening 25 at the left-hand side and a second feedthrough opening 26 at the right-hand side. The central section 24 of the fuse wire is arranged within the hollow space 27 of the fuse housing 21 and the first end section 22 of the fuse wire is extending through the first feedthrough opening 25. The second end section 23 of the fuse wire is extending through the second feedthrough opening 26. At the first feedthrough opening 25, an outer circumferential surface of the first end section 22 is in direct contact with an inner circumferential surface of the first feedthrough opening 25 and seals the first feedthrough opening 25. At the second feedthrough opening 26, an outer circumferential surface of the second end section 23 is in contact with an inner circumferential surface of the second feedthrough opening 26 and seals the second feedthrough opening 26. Due to the direct contact, no additional sealing means are needed.

[0026] The central section 24 of the fuse wire is dimensioned and made of a material such that it melts or vaporizes when a predetermined electrical current flowing through the fuse wire is exceeded.

[0027] As the whole housing 21 is sealed including the feedthrough openings 25, 26, the central section 24 may melt or vaporize without contaminating the fluid 17 outside the fuse housing 21. Furthermore, the tubular form of the housing 21 provides a significant pressure resistance such that the subsea fuse device 21 may be used in the above described high-pressure environment without breaking.

[0028] The central section 24 of the fuse wire, whichis placed inside the glass tube, is dimensioned for carrying the current for the sub circuit 15. The hollow space 27 of the tubular fuse housing 21 may be filled with a gas or produced with vacuum depending on the voltage level which is used for supplying the sub circuit 15.

[0029] In case the fuse housing 21 is made of glass, the glass tube is bonded onto the metallic fuse wire at both ends ensuring a sealed tube. For example, during production the fuse wire may be arranged in a glass tube with open ends. Each of the end sections 21, 23 is arranged at a corresponding open end of the glass tube. Each end of the glass tube is heated such that it seals around the corresponding end sections 22, 23. The sealing areas at both ends of the glass tube are indicated in Fig. 2 by reference signs 28, 29. Thermal expansion coefficient of the metal of the fuse wire and glass may be selected similar to prevent cracks as they cool during production. As described above, the fuse wire may be uniform or non-uniform, and it may consist of one or several materials. The first and second end sections 22, 23 extending from the fuse housing 21 may be soldered to a printed circuit board of the electric circuitry 11.

[0030] The subsea fuse device 20 enables an isolation of a faulty sub circuit 15 in an oil-filled and pressurized environment. However, the subsea fuse device 20 may be used for other applications in subsea devices, for example implementation of redundancy and providing overcurrent protection. Using the subsea fuse device 20 may avoid an interrupted service, high cost of replacing the oil or a total failure of larger systems, when a fuse does not break as intended, in particular in subsea devices which are often placed in high ambient pressure environments which are inaccessible, for example at the seafloor, and which may make maintenance difficult and expensive.

Claims

1. A subsea fuse device, comprising:

- a fuse housing (21), and

- a fuse wire comprising a first end section (22), a second end section (23), and a central section (24),

wherein the fuse housing (21) comprises a one-piece outer envelope which completely encloses a hollow space (27) and provides a first feedthrough opening (25) and a second feedthrough opening (26),
wherein the central section (24) of the fuse wire is arranged within the hollow space (27) of the fuse housing (21), the first end section (22) of the fuse wire is extending through the first feedthrough opening (25), and the second end section (23) of the fuse wire is extending through the second feedthrough opening (26),
wherein, at the first feedthrough opening (25), an outer circumferential surface of the first end section (22) of the fuse wire is in contact with an inner circumferential surface of the first feedthrough opening (25) and seals the first feedthrough opening (25), and
wherein, at the second feedthrough opening (26), an outer circumferential surface of the second end section (23) of the fuse wire is in contact with an inner circumferential surface of the second feedthrough opening (26) and seals the second feedthrough opening (26).

2. The subsea fuse device according to claim 1, wherein the outer envelope is pressure resistant.

3. The subsea fuse device according to claim 1 or claim 2, wherein the outer envelope has a tubular form, and wherein the first and second feedthrough openings (25, 26) are arranged at opposite ends of the tubular envelope.

4. The subsea fuse device according to any one of the preceding claims, wherein the outer envelope is hermetically sealed apart from the first and second feedthrough openings (25, 26).

5. The subsea fuse device according to any one of the preceding claims, wherein the outer envelope is made of an electrically isolating material.

6. The subsea fuse device according to any one of the preceding claims, wherein the outer envelope is made of at least one material of a group comprising:

- glass,

- ceramics, and

- resin.

7. The subsea fuse device according to any one of the preceding claims, wherein a cross section of the central section (24) of the fuse wire is smaller than a cross section of each of the first and second end sections (22, 23).

8. The subsea fuse device according to any one of the preceding claims, wherein the central section (24) of the fuse wire comprises a first material and at least one of the first and second end sections (22, 23) of the fuse wire comprises a second material, wherein the first and second materials are different.

9. The subsea fuse device according to claim 8, wherein the first and second materials each comprise at least one of the group comprising:

- zinc,

- copper,

- silver, and

- aluminum.

10. A subsea device, comprising:

- an enclosure (13), and

- an electric circuitry (11) arranged within the enclosure (13),

wherein the electric circuitry (11) comprises a subsea fuse device (20) according to any one of the preceding claims.

11. The subsea device according to claim 10, wherein the enclosure (13) is filled with a fluid (17) and comprises a volume/pressure compensator (14) which balances the pressure in the enclosure (13) to the pressure prevailing in an environment of the enclosure (13).

Drawing