Protective casing for a high voltage cable

A protective casing for a joint, termination or cross-connection of at least one high voltage cable. The protective casing includes a first material portion of a first metal material having good strength properties. The protective casing includes a second material portion of a second metal material which is fixedly attached to the first material portion. The second metal material has good soft soldering properties such that it is possible to provide a strong and tight connection between the second material portion of the protective casing and a sheath of at least one of the cable parts by a soft soldering process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European patent application 08155452.9 filed 30 Apr. 2008.

TECHNICAL FIELD

The invention relates to a protective casing for a joint, termination or cross-connection of at least one high voltage cable, wherein the protective casing comprises a first material portion of a first metal material.

BACKGROUND OF THE INVENTION

A long deep-sea high voltage cable consist of a large number of cable parts which are joined together. The joining process of the cable parts is performed in situ on a cable ship or the like before the cable is laid in the sea. High voltage sea cables have a water tight sheath of lead or copper. The high pressure and the corrosive environment in the deep sea require that the joints between different cable parts have a very good protection. The same requirements apply to cable terminations or cross-connections of cables. It is known to protect the joints, terminations or cross-connections by a casing of a stainless steel material. Such a casing has the required strength to withstand the high pressure and it is resistant to corrosion. However, it is a problem to create a strong and tight connection between a stainless steel casing and the lead or copper sheath of the cable parts.

Stainless steel materials have relatively bad soft soldering properties. It is therefore difficult to make a strong and tight connection between a protective casing of a stainless steel material and a sheath of a high voltage cable by means of a soft soldering process. It is possible to connect a stainless steel casing to the sheath of a high voltage cable by means of a hard soldering process. However, due to the high temperature during a hard soldering process, there is a risk that the heat damages the sheath of the cable or other sensitive components in the vicinity of the hard soldering joint. Especially, in the relatively tough environment on a cable ship, it is difficult to construct a faultless soldering joint by means of a hard soldering process.

SUMMARY OF THE INVENTION

The object of the present invention is to enable the establishment of a strong and tight connection between a protective casing of a metal material and the sheath of a high voltage cable in a relatively tough environment.

This object is achieved according to the initially mentioned protective casing, which is characterised in that it comprises a second material portion of a second metal material which is fixedly attached to the first material portion, wherein the second metal material has good soft soldering properties such that it is possible to provide a strong and tight connection between the second material portion of the protective casing and a sheath of at least one of the cable parts by means of a soft soldering process.

According to one embodiment the first material portion preferably has a shape such that it completely encloses a connection area, such as a cable joint, a cable termination or a cross-connection of at least one cable part. Thereby, the connecting area, the termination or the cross-connection of the at least one cable is protected from external forces such as the high surrounding pressure in deep sea. Deep-sea high voltage cables have usually a sheath of lead or copper. Lead and copper are materials with good soft soldering properties. Since, the second material portion also has good soft soldering properties, it is possible to accomplish a strong and tight soldering joint between the second material portion of the protective casing and the sheath of a cable by means of a soft soldering process. The low temperature during a soft soldering process guarantees that the sheath of the cable parts or other sensitive components in the vicinity of the soldering joint will not be damage.

According one embodiment the material and the thickness of the material in the protective casing is chosen in dependence on the desired strength, corrosion resistance or other desired properties of the protective casing. Preferably the metal material of the casing should have high strength properties.

According to another embodiment of the invention, the first material portion is tubular and it has a first end part with an opening dimensioned to receive a cable part. A tubular first material portion encloses the connecting area between the cable parts in an effective manner. Such an opening enables insertion of a cable part to the connecting area inside the protective cover. Advantageously, the second material portion is fixedly attached to an outer surface of the first material portion in the vicinity of the first end portion. In this case, the second material portion will be positioned in the vicinity of the sheath of the cable. Thereby, it is possible to apply a solder to an area comprising the second material portion and the sheath of the cable and provide a soft soldering process such that a soft soldering joint is obtained connecting the protecting casing and the sheath of the cable to each other. The second material portion may have an annular shape. It is easy to accomplish a soft soldering joint having an extension around the whole periphery of the cable by means of an annular second material portion.

According to another embodiment of the invention, the protective casing comprises at least one prefabricated part comprising a first material portion and a fixedly connected second material portion. In this case, the second material portion has been attached to the first material portions in a factory or the like. The prefabricated part may comprise a second material portion fixedly attached to a first material by means of a hard soldering connection. Since the prefabricated part is prefabricated, the high temperature during the hard soldering process will not cause damage to the cables. Furthermore, it is possible to check the prefabricated part in the factory such that the first material portion and the second material portion have no damages.

According to another embodiment of the invention, the protective casing comprises two casing halves each comprising a first material portion and a fixedly attached second material portion such that the respectively casing halves are connectable to a sheath of a respective cable by means of a soft soldering process. The casing halves can be applied on the respective free ends of the cables before they are connected to each other. As soon as the cables have been connected to each other, the casing halves are pushed together such that they enclose the connecting area between the cable halves. Thereafter, the second material portions of the casing halves are connected to the sheaths of respective cables by means of a soft soldering process. Preferably, each of the casing halves comprise a third material portion of a third metal material fixedly attached to the first material portion wherein the third metal material has good soft soldering properties such that it is possible to provide a strength and tight connection between the third material portions of the casing halves by means of a soft soldering process. When the casing halves have been displaced to a closed together state, it is possible to accomplish a soft soldering joint between the third material portions of the casing halves, which holds the casing halves together in a safe manner. Preferably, the third material portions have an annular shape. In this case, it is easy to accomplish a soft soldering joint having an extension around the whole periphery of the casing halves.

According to another embodiment of the invention the first material portion comprises a stainless steel material. Deep-sea high voltage cables are subjected to high pressures and a corrosive environment. Stainless steel materials are strong and resistant to corrosion. Due to these properties, it is suitable to use a stainless steel material as a first material portion in casings for protecting joints between high voltage cable parts.

According to another embodiment of the invention, the second material portion comprises copper or a copper alloy or brass or a brass alloy. All these materials have good soft soldering properties and can with advantage be used in a second material portion of the protective casing. Preferably, the third material portion also comprises copper or a copper alloy or brass or a brass alloy. However, it is possible to use other materials than the above-mentioned with good soldering properties in the second material portion and in the third material portion of the protective casing. A prefabricated half of the protective casing may also include a fixedly attached third material portion. The third material portion has here been attached to the first material portions in a factory or the like. The prefabricated part may comprise a third material portion fixedly attached to the first material by means of a hard soldering connection. In this case, the high temperature during the hard soldering process will not case cause damage to the cable parts. Since the hard soldering process is performed in a factory, it is possible to check the first material portion and the third material portion such that they have no damages in the vicinity of the hard soldering joint.

FIG. 1shows a joint between a first cable1and a second cable2of a deep-sea high voltage cable. The first cable1,2is provided with a water tight sheath1aand the second cable2is provided with a water tight sheath2a.The water tight sheaths1a,2aare manufactured of lead or copper. The conductors of the cables1,2, which not are visible inFIG. 1, are connected to each other in a connecting area3. The connecting process of the conductors and the construction of the connecting area3are performed in a conventional manner with a cable joint. The connecting area3has a larger cross section area than the cables1,2. A protective casing4encloses the connecting area3. The protective casing4constitutes of a first casing half4aand a second casing half4bwhich are mounted together such that they completely encloses the connecting area3. The first casing half4aand the second casing half4bare prefabricated components.

The first casing half4acomprises a first material portion5having a tubular shape. The first material portion5is made of a metal material, which is strong and resistant to corrosion. Such a metal material is here exemplified as a stainless steel material. The first material portion5comprises a first end part5ahaving a substantially constant cross section area and an end opening dimensioned to receive the first cable1. The first material portion5comprises a second end part5bhaving a larger cross section than the first end part5a.The second end part5bhas also a substantially constant cross section area. An intermediate part5cof the first material portion5constitutes a connecting area between the first end part5aand the second end part5b.The intermediate part5chas a cross section area increasing in a direction from the first end part5ato the second end part5b.

The first casing half4acomprises a second material portion7having an annular shape. The second material portion7is fixedly attached to an outer surface of the first end part5aof the first material portion5in the vicinity of the end opening. The second material portion7is made of a metal material having good soft soldering properties. The second material portion is preferably made of copper or a copper alloy or brass or a brass alloy. In this case, the second material portion7is fixedly attached to the outer surface of the first end part5aby means a hard soldering connection. The first casing half4acomprises a third material portion8having an annular shape. The third material portion8is fixedly attached to an outer surface of the second end part5bof the first material portion5. The third material portion8is also made of a metal material having good soft soldering properties. The third material portion8can be made of copper or a copper alloy or brass or a brass alloy. Advantageously, the third material portion8is also fixedly attached to the outer surface of the first end part5aby means a hard soldering connection.

The second casing half4bhas a substantially corresponding construction as the first casing half4a.The second casing half4bcomprises a first material portion9having a tubular shape. The first material portion9is made of a metal material which is very strong and resistant to corrosion. The metal material is here exemplified as a stainless steel material. The first material portion9comprises a first end part9ahaving a substantially constant cross section area and an opening dimensioned to receive the second cable2. The first tubular material portion9comprises a second end part9bhaving a larger cross section than the first end part9a.The second end part9bhas also a substantially constant cross section area. An intermediate part9cof the first material portion9constitutes a connecting area between the first end part9aand the second end part9b.The intermediate part9chas a cross section area increasing in a direction from the first end part9ato the second end part9b.

The second casing half4bcomprises a second material portion10having an annular shape. The second material portion10is fixedly attached to an outer surface of the first end part9aof the first material portion9in the vicinity of the end opening. The second material portion10is made of a metal material having good soft soldering properties. The second material portion10is preferably made of copper or a copper alloy or brass or a brass alloy. Preferably, the second material portion10is fixedly attached to the outer surface of the first end part9aby means a hard soldering. The second casing half4bcomprises a third material portion11having an annular shape. The third material portion11is fixedly attached to an outer surface of the second end part9bof the first material portion9. The third material portion11is also made of a metal material having good soft soldering properties. The third material portion11can be made of copper or a copper alloy or brass or a brass alloy. Preferably, the third material portion11is fixedly attached to the outer surface of the first end part9aby means a hard soldering connection.

The first end part5aof the first casing half4ahas been connected to the sheath1aof the first cable1by means of a soft soldering joint12. The soft soldering joint is formed by a suitable solder. The soft soldering joint12connects the annular second material portion7of the first casing half4aand the sheath1aof the first cable1. In a corresponding manner, the first end part9aof the second casing half4bhas been connected to the sheath2aof the second cable2by means of a soft soldering joint13. The soft soldering joint13connects the annular second material portion10of the second casing half4band the sheath2aof the first cable2. The second end part9bof the second casing half4bhas a somewhat smaller outer diameter than the second end part5bof the first casing half4a.The second end part5bof the first casing half4aand the second end part9bof the second casing half4bhave here been displaced to a close together state. In this state the outer end of the second end part9bof the second covering half4bhas been displaced a small distance into the second end part5bof the first casing half4a.One or several position elements14have been inserted through holes in the second end part5bof the second casing half4aand the second end part9bof the first casing half4bfor holding the halves4a,4btogether in this state during a soft soldering process. Thereafter, a soft soldering process is performed such that a soft soldering joint15is accomplished which connects the first casing half4aand the second casing half4bpermanently to each other.

FIG. 2ashows a first stage of the mounting process of the protective casing4. The mounting process is performed on a cable ship or the like before the cable is laid in the sea. The first casing half4ahas here been applied on a free end of the first cable1and the second casing half4bhas been applied on a free end of the second cable2. The first casing half4aand the second casing half4bare prefabricated components. Consequently, the annular second material portion7,10and the annular third material portions8,11have already been attached to the first material portions5,9of the respective casing halves4a,4bin a factory or the like. The annular second material portion7,10and the annular third material portions8,11have preferably been attached to the first material portions5,9by a hard soldering process.

The first casing half4aand the second casing half4bhave been pushed to a distance from each other on the respectively cables1,2such that it is possible to connect the conductors of the cables1,2to each other and to construct the connecting area3.FIG. 2bshows the finished connecting area3which has a larger cross section area than the cable parts2,3. Thereafter, the casing halves4a,4bare pushed to the close together state which is shown inFIG. 2c.Position elements14have here been inserted through correspondingly arranged holes such that the casing halves4a,4bare held in the close together state. A suitable solder layer is then applied around the whole periphery of the outer surfaces of the annular third material portions8,11. The solder is heated in a suitable manner to its melt temperature. The solder has a melt temperature which is lower than 450° C. during a soft soldering process. Therefore, the heat from the soldering process is too low to damage the connecting area3. After that, the solder is cooled and solidified such that it forms a joint15covering the outer surfaces of the third material portions8,11. Such a soldered joint15having an extension around the whole periphery of the third material portions8,11holds the casing halves4a,4btogether in a safe manner. Since both the third material portions8,11is made of a material having good soft soldering properties, the joint15will be strong and water tight.

After that, a solder layer is applied on the outer surfaces of the annular second material portion7of the first covering half4aand the adjacent sheath1aof the first cable1. The solder is heated to its melt temperature and cooled such that the solder forms a joint12covering the outer surfaces of the second material portion7and the adjacent area of the sheath1aof the first cable1. Since the second material portion7is made of a material having good soft soldering properties and the sheath1ais made of lead or copper, which also have good soft soldering properties, the joint12will be strong and tight. The heat from the soft soldering process is too low to damage the sheath1aof the first cable1. Finally, a solder layer is applied on the outer surfaces of the annular second material portion10of the second covering half4band the adjacent sheath2aof the second cable part2. The solder is heated to its melt temperature and cooled such that the solder forms a joint13covering the outer surfaces of the second material portion10and the adjacent area of the sheath2aof the second cable2. Since the second material portion10is made of a material having good soft soldering properties and the sheath2ais made of lead or copper, which also have good soft soldering properties, the joint13will be strength and tight. The heat from the soft soldering process is too low to damage the sheath2aof the second cable2.

The invention is not in any way restricted to the embodiment described in the figures, but may be varied freely within the scope of the claims. For example the protective casing4may be a protective casing for a termination of a high voltage cable or a protective casing for a cross-connection of high voltage cables.