Patent Application
20240055850
The present invention relates to high voltage electric cable connections. More particularly, the invention relates to a thermoplastic insulation system for jointing of high voltage conductors and to a method for jointing of high voltage conductors.
JPH0847154 describes pre-moulded insulator sleeve into which a conductor having a semi-conductive layer is inserted. After insertion, the insulator sleeve is heated to cure and integrate with the conductor and the semi-conductive layer.
GB1381770 describes a junction sleeve for a cable, the sleeve being of the type consisting of an elongate member formed of a flexible material such as plastics and formed as a cylinder terminating at either end in a frustoconical end section with a central opening for receiving a cable and provided with a longitudinal slit extending from end to end.
EP0724789 relates to the protection of a connection between two pieces of high voltage electrical equipment, especially between a power cable and other electrical equipment.
EP2639264 describes a field grading material including a polymeric matrix and an electrically conducting organic filler, as well as to field grading element, including said field grading material.
EP3365952 relates to a joint for medium/high voltage electric cables having a thermoplastic insulation system, and to a method for manufacturing the same.
Several solutions for insulation system for jointing of high voltage conductors are known, but all have various disadvantages that should be overcome. One such problem is that the traditional lapping method may not be viable anymore since the lack of cross-linking will allow material deformation during the melting procedure. An alternative is to use a direct injection moulding procedure. However, this procedure requires highly specialized equipment and the jointing needs to be performed in two steps in order to account for density/volume change in the material.
The goal of the present invention is to provide a new and advantageous insulation system for jointing of high voltage conductors. In particular, the present invention provides thermoplastic insulation system for jointing of high voltage conductors.
The present invention is defined by the appended claims and in the following.
In a first aspect, the present invention provides a method for manufacturing an electric cable joint, the method comprising the steps of:
In other words, the terminal portion of the first electric conductor is placed axially adjacent to the terminal portion of the second electric conductor when the electric conductors are joined.
Thermoplastic are defined as polymers that can be melted and recast almost indefinitely. They are molten when heated and harden upon cooling. The polymer network of a thermoplastic material forms and/or breaks up as the temperature is changed.
In an embodiment of the method, any of the inner thermoplastic semiconducting material and the outer thermoplastic semiconducting material may be provided in the form of a at least one pre-moulded element.
In another embodiment of the method, each of the inner thermoplastic semiconducting material, the thermoplastic insulating material and the outer thermoplastic semiconducting material may be provided separately in the form of at least one pre-moulded element.
In an embodiment of the method, either the inner thermoplastic semiconducting material or outer thermoplastic semiconducting material may be provided in the form of a at least one pre-moulded element together with the thermoplastic insulating material. In other words, such that steps c) and d) or steps d) and e) may be performed at the same time.
In another embodiment of the method, the inner thermoplastic semiconducting material, the thermoplastic insulating material and an outer thermoplastic semiconducting material may be provided in the form of the least one pre-moulded element. In other words, such that steps c), d) and e) may be performed at the same time.
In another embodiment of the method, the materials are heated above their crystalline melting point and pressure is applied to shape each layer into a cylinder after any of the steps c), d), and e).
In another embodiment of the method, the materials are heated above their crystalline melting point and pressure is applied to shape the joint into a cylinder only after step e).
In a second aspect, the present invention provides a pre-moulded thermoplastic insulation for an electrical conductor joint. The pre-moulded thermoplastic insulation comprises at least one joint element, wherein each joint element comprises an insulating layer made of a thermoplastic insulating material, and
The person skilled in the art will understand that a cylindrical layer refers to a hollow cylindrical layer or a tube-shaped cylindrical layer.
In an embodiment of the pre-moulded thermoplastic insulation, the pre-moulded thermoplastic insulation may further comprise an inner layer made of a first thermoplastic semiconducting material, covering an internal surface of the insulating layer, and adapted for abutting the electric conductor joint.
In another embodiment of the pre-moulded thermoplastic insulation, the pre-moulded thermoplastic insulation may further comprise an outer layer made of a second thermoplastic semiconducting material surrounding the insulating layer of the pre-moulded element.
In another embodiment of the pre-moulded thermoplastic insulation, the at least one or more joint elements are connectable through heat treatment.
In an embodiment of the pre-moulded thermoplastic insulation, the insulation is a tubular cylinder and each joint element is a sector of the tubular cylinder, wherein n elements form a full cylinder; and n is an integer between 2 and 10, preferably between 2 and 5.
The person skilled in the art will understand that a sector of the tubular cylinder refers to a hollow cylindrical sector or a tube sector.
In an embodiment of the pre-moulded thermoplastic insulation according to the invention, the pre-moulded insulation comprises two joint elements.
In another embodiment of the pre-moulded thermoplastic insulation according to the invention, the pre-moulded thermoplastic insulation may be in the form of a tubular cylinder with at least one slit.
In a third aspect, the invention provides an electric cable joint, comprising a pre-moulded thermoplastic insulation according to the second aspect of the invention.
The present invention is described in detail by reference to the following drawings:
Jointing cables with a thermoplastic insulation system is challenging. The specific properties of thermoplastic polymers make it difficult if not impossible to adapt procedures known in the art, for example traditionally used with crosslinked polymer, where once set each layer will not be affected by the heating of the subsequent layer.
The challenge is that after an additional thermoplastic layer is applied to build a joint, the additional thermoplastic layer needs to be heated to form a cylinder and insure the best contact with the previous layer. However, this additional thermoplastic layer (and potentially the layer underneath too, if it is also made of thermoplastic material) may lose its shape during this step. This will in turn cause deformation and uniformity/homogeneity problems at the joint. These are critical parameters to insure a good insulation in the joint.
By already having at least the insulation layer of the insulating system in its final form the problem of material flow may be solved. Equal pressure may be applied on the outer surface of the layer of interest during heating so that the material is held in place.
This is not as easy when dealing with a tape-lapped layer because the volume change is different in the joint compared to the surrounding cable due to the voids introduced between laps. The inventive method reduces drastically these voids, and virtually eliminates them.
Compared to the traditional tape-lapping procedure, the amount of material interfaces is significantly reduced and thus reduces the risk for contamination, since cleanliness will usual be a key factor for success.
This method also presents the advantage of being a much less labour-intensive method.
The present invention provides an improved method for manufacturing an electric cable joint 300, the method illustrated in
After assembly of a new thermoplastic material on a previous layer, to form the definitive new layer, it is required to apply heat and pressure to said layer, so that the thermoplastic material is heated above its crystalline melting point and shaped into a cylinder. There are different approaches for when to do this step. It can be advantageous to apply heat and pressure after each addition of a new thermoplastic material, for example to ensure that the current layer is well in place before continuing the method or to avoid the formation of bubbles between the layers; but it can also be advantageous to apply heat and pressure only after certain layers are in place, for example to avoid deformation of certain layers, or of the thermoplastic cables when heating in order to form a new layer.
This heating step will also ensure the connection between the different layers of the joint 310, 311, 312, 313.
For example, after preparing the electric cables 100; 200, the respective terminal portions of the electric conductors 110; 210 are joined, forming the electric conductor joint 310, as shown in
In a second step, the electric conductor joint 310 is surrounded with a first thermoplastic semiconducting material, forming a joint inner layer 311, as shown
It may be beneficial to prepare the joint inner layer 311 in a separate step, especially when using the tape-lapping method, in order to fill out voids where the material contacts the conductor as this can reduce the risk for transplantation of defects.
Then, in a third step, illustrated in
Then in a fourth step, illustrated in
Alternatively, in another example the only heating and shaping step may be after the addition of the joint outer layer 313. This would avoid multiple heating step and thus protect the different layers of thermoplastic in the cables to be joined.
Thermoplastic are defined as polymers that can be melted and recast almost indefinitely. They are molten when heated and harden upon cooling. The polymer network of a thermoplastic material forms and/or breaks up as the temperature is changed.
For example, the insulating material could be made of thermoplastic polyolefins (TPO), polypropylene, polypropylene and its copolymers with ethylene, HDPE, LLDPE, LDPE, MDPE, PE-based copolymers etc. or any combination thereof. For example, an insulating material could comprise PP, TPO and LLDPE.
For example, the semiconducting material could be made of thermoplastic polyolefins (TPO), polypropylene, polypropylene and its copolymers with ethylene, HDPE, LLDPE, LDPE, MDPE, PE-based copolymers etc. or any combination thereof, and of a conductive filler such as furnace black, acetylene black, etc. or any combination thereof.
In order to achieve desired material properties, both the insulating and the semiconducting materials may further comprise additives such as plasticizers, fillers (including nanomaterials), stabilizers, processing aids, etc.
In a second example illustrated in
The person skilled in the art will understand that even though the joint inner layer 311 and the joint outer layer 313 are described to both be made of 2 pre-moulded joint elements 340; 360; the assembly of each of these layer is an independent step and could be replaced by a suitable method in the art, including tape-lapping.
In this second example each layer 311, 312, 313 is applied on the previous layer 310, 311, 312 respectively. The material is heated above the crystalline melting point and shaped into a cylinder around the conductor after each layer addition.
In a third example, the joint inner layer 311 and the joint outer layer 313 are also each made of 2 pre-moulded joint elements 340; 360, in the shape of halves of a tubular cylinder and made of a first and second thermoplastic semiconducting material, respectively.
Just as in the second example, the person skilled in the art will understand that even though the joint inner layer 311 and the joint outer layer 313 are described to both be made of 2 pre-moulded joint elements 340; 360; the assembly of each of these layer is an independent step and could be replaced by a suitable method in the art, including tape-lapping.
In this third example each layer 311, 312, 313 is applied on the previous layer 310, 311, 312 respectively. Finally, the material is heated above the crystalline melting point and shaped into a cylinder around the conductor when all elements 310, 311, 312, 313 of the joint are assembled.
Different types of pre-moulded joint elements that are used to produce the thermoplastic joint of interest are illustrated in
By producing pre-moulded joint elements already having multiple layers of interest, the number of step in the jointing procedure is reduced, and the procedure will be much less labour-intensive. This also reduces the risk for contamination, as cleanliness is usually a key factor for success. Finally producing these pre-moulded joint elements will also ensure a better contact between the layers.
The person skilled in the art will understand that even though the slits are evenly distributed in
The person skilled in the art will understand that even though the sectors are all of the same size in
The person skilled in the art will also understand the structures illustrated in
The person skilled in the art will also understand that the structures of the at least one joint element (350, 351, 353, 355) and of the optional pre-moulded joint elements 340; 360 or of the equivalent structure obtained by a method known in the art, are made to achieve close contact, that is to say opposite sides have interlocking design.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21305225.1 | Feb 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/054450 | 2/22/2022 | WO |
