Heating Assembly and Method for Insulation System Restoration of a Power Cable

Abstract

A heating assembly configured to receive a power cable for restoring an insulation system of the power cable, the heating assembly including: a central pressurisation and heating structure, and a first and second lateral structure provided at a respective axial end of the central pressurisation and heating structure, the first and second lateral structure each having at least a 20 cm long axially extending section primarily made of a material at most having a conductivity of the order of 1000 S/m at 20° C.

Claims

1. A heating assembly configured to receive a power cable joint of a power cable for restoring an insulation system of the power cable, the heating assembly comprising: a central pressurisation and heating structure comprising: a first part, including a first central channel configured to receive a portion of the power cable, a second part including a second central channel configured to receive a portion of the power cable, wherein the central pressurisation and heating structure is configured to be set in a closed state in which the first central channel faces the second central channel to thereby form a central heating chamber extending from a first end to a second end, opposite the first end, of the central pressurisation and heating structure, wherein the central pressurisation and heating structure is configured to be pressurised to obtain a first pressure higher than atmospheric pressure inside the central heating chamber when the power cable is arranged sealed in the central heating chamber; and a pressure compensator system comprising: a first lateral structure extending laterally from the first end of the central pressurisation and heating structure, the first lateral structure having a first lateral channel aligned with the central heating chamber and configured to receive a portion of the power cable, a second lateral structures extending laterally from the second end of the central pressurisation and heating structure, the second lateral structure having a second lateral channel aligned with the central heating chamber and configured to receive a portion of the power cable, wherein the first lateral structure is configured to be pressurised to obtain a second pressure higher than atmospheric pressure in the first lateral channel when the power cable is arranged sealed in the first lateral structure, and wherein the second lateral structure is configured to be pressurised to obtain a third pressure higher than atmospheric pressure in the second lateral channel when the power cable is arranged sealed in the second lateral structure, and wherein each of the first lateral structure and the second lateral structure has an at least 20 cm long axially extending section which is primarily made of material at most having a conductivity of the order of 1000 S/m at 20° C.

2. The heating assembly as claimed in claim 1, wherein the material at most has a conductivity of the order of 100 S/m at 20° C., such as 10 S/m at 20° C., such as 1 S/m at 20° C., such as 0.1 S/m at 20° C., such as 0.01 S/m at 20° C., such as 0.001 S/m at 20° C., such as 0.0001 S/m at 20° C.

3. The heating assembly as claimed in claim 1, wherein each of the second pressure and the third pressure is within ±50% of the first pressure such as within ±40% of the first pressure, such as within ±30% of the first pressure, such as within ±20% of the first pressure, such as within ±10% of the first pressure.

4. The heating assembly as claimed in claim 1, wherein the second pressure and the third pressure are equal to the first pressure.

5. The heating assembly as claimed in claim 1, wherein the first lateral structure and the second lateral structure have smaller radial dimensions than the central pressurisation and heating structure.

6. The heating assembly as claimed in claim 1, wherein the first pressure is a plurality of bar, such as at least 4 bar.

7. The heating assembly as claimed in claim 1, wherein the central pressurisation and heating structure primarily includes metal.

8. The heating assembly as claimed in claim 1, wherein each of the axially extending section of the first lateral structure and the axially extending section of the second lateral structure has a wall or walls primarily made of said material having at most a conductivity of the order of 1000 S/m at 20° C.

9. The heating assembly as claimed in claim 8, wherein the wall or walls of each of the first lateral structure and the second lateral structure includes at least 80% of said material.

10. The heating assembly as claimed in claim 1, comprising a heating device configured to heat the central heating chamber.

11. The heating assembly as claimed in claim 1, comprising an induction heating device including: a first high frequency, HF, heating coil configured to be arranged around the first lateral structure and a second HF heating coil configured to be arranged around the second lateral structure.

12. A method of restoring an insulation system around a conductor of a power cable, using the heating assembly as claimed in claim 1, the method comprising: a) placing the power cable joint including a conductor having a restoration insulation system layer arranged around a conductor in one of the first central channel and the second central channel, b) placing the power cable in each of the first lateral structure and the second lateral structure, c) setting the central pressurisation and heating structure in the closed state, d) placing a first high frequency, HF, heating coil around the axially extending section of the first lateral structure and a second HF heating coil around the axially extending section of the second lateral structure, e) pressurising the central heating chamber to the first pressure, the first lateral channel to the second pressure, and the second lateral channel to the third pressure, and f) heating the restoration insulation system layer by outer heating inside the central pressurisation and heating structure and by inner heating of the restoration insulation system layer by feeding the first HF heating coil and the second HF heating coil with current to induce a current in the conductor.

13. The method as claimed in claim 12, comprising performing steps a)-f) for each of a plurality of restoration insulation system layers.

14. The method as claimed in claim 12, wherein in step f) the outer heating and the inner heating are performed simultaneously.

15. The heating assembly as claimed in claim 2, wherein each of the second pressure and the third pressure is within ±50% of the first pressure such as within ±40% of the first pressure, such as within ±30% of the first pressure, such as within ±20% of the first pressure, such as within ±10% of the first pressure.

16. The heating assembly as claimed in claim 2, wherein the second pressure and the third pressure are equal to the first pressure.

17. The heating assembly as claimed in claim 2, wherein the first lateral structure and the second lateral structure have smaller radial dimensions than the central pressurisation and heating structure.

18. The heating assembly as claimed in claim 2, wherein the first pressure is a plurality of bar, such as at least 4 bar.

19. The heating assembly as claimed in claim 2, wherein the central pressurisation and heating structure primarily includes metal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

[0047] FIG. 1 schematically shows a top view of a heating assembly in an open state;

[0048] FIG. 2 shows a longitudinal section of a heating assembly while heating a restoration insulation system layer of a power cable; and

[0049] FIG. 3 is a flowchart of a method of restoring the insulation system of a power cable.

DETAILED DESCRIPTION

[0050] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

[0051] FIG. 1 schematically shows a top view of a heating assembly 1 in an open state. The heating assembly 1 is adapted for heating an insulation system layer of a power cable when restoring an insulation system of a power cable over a conductor joint or in case the power cable has been damaged. The heating may in some examples involve curing of the restoration insulation system layer.

[0052] The pressurisation and heating device 1 may be suitable for heating restoration insulation system layers of medium voltage or high voltage AC or DC power cables.

[0053] The heating assembly 1 comprises a central pressurisation and heating structure 3. The central pressurisation and heating structure 3 comprises a first part 3a and a second part 3b.

[0054] The first part 3a has a first central channel 3c extending from one end of the first part 3a to an opposite end of the first part 3a. The first central channel 3c is straight. The first central channel 3c is configured to receive a power cable including a power cable joint.

[0055] The second part 3b has a second central channel 3d extending from one end of the second part 3b to an opposite end of the second part 3b. The second central channel 3d is straight. The second central channel 3d is configured to receive a power cable including a power cable joint.

[0056] The first part 3a and the second part 3b are configured to be assembled with each other to thereby set the central pressurisation and heating structure 3 in a closed state. The central pressurisation and heating structure 3 is thus openable and closable.

[0057] The first part 3a and the second part 3b may for example be hingedly connected, or they may be completely separable from each other.

[0058] In the closed state of the central pressurisation and heating structure 3, the first central channel 3c faces the second central channel 3d. The first central channel 3c is axially aligned with the second central channel 3d. The first central channel 3c and the second central channel 3d thus form a central heating chamber extending from a first end 4a of the central pressurisation and heating structure 3 to a second end 4b, opposite to the first end 4a, of the central pressurisation and heating structure 3. The central heating chamber is thus configured to circumferentially enclose the power cable including the power cable joint along the length of the central pressurisation and heating structure 3.

[0059] The heating assembly 1 may comprise a heating device 3e configured to heat the central heating chamber to a predefined temperature. The predefined temperature is according to some examples a curing temperature for curing a thermosetting polymer such as polyethylene. According to some example the predefined temperature is a melting temperature for heating a thermoplastic polymer such as polyethylene until it melts.

[0060] The central pressurisation and heating structure 3 may according to one example comprise the heating device 3e. The heating device 3e may be configured to directly heat the central heating chamber for example by means of heating coils or similar means arranged around the first central channel 3c and the second central channel 3d. Alternatively, the heating device may be external to the central pressurisation and heating structure 3. In this case the heating device may be configured to externally heat gas such as noble gas introduced into the central heating chamber.

[0061] The first part 3a has a wall or walls 3f primarily comprising metal. The second part 3b has a wall or walls 3g primarily comprising metal.

[0062] The heating assembly 1 comprises a pressure compensator system which includes a first lateral structure 5 and a second lateral structure 7.

[0063] The first lateral structure 5 extends laterally from the first end 4a of the central pressurisation and heating structure 3.

[0064] The first lateral structure 5 is has an axially extending section primarily made of material at most having a conductivity of the order of 1000 S/m at 20° C. The material may for example be or comprise glass fibre or carbon fibre reinforced polymer, such as glass fibre or carbon fibre reinforced epoxy or polyamide.

[0065] The axially extending section is at least 20 cm long but could according to one variation be the entire length of the first lateral structure 5, which is the case in the example shown in FIGS. 1 and 2. In this case, the first lateral structure 5 is primarily made of material at most having a conductivity of the order of 1000 S/m at 20° C.

[0066] The axially extending section of the first lateral structure 5 has a wall or walls 5a of which for example at least 80% or at least 90% is made of material at most having a conductivity of the order of 1000 S/m at 20° C., such as 100 S/m at 20° C., such as 10 S/m at 20° C., 1 S/m at 20° C., such as 0.1 S/m at 20° C., such as 0.01 S/m at 20° C., such as 0.001 S/m at 20° C., such as 0.0001 S/m at 20° C., such as 10{circumflex over ( )}-4 S/m at 20° C., such as 10{circumflex over ( )}-5 S/m at 20° C., such as 10{circumflex over ( )}-6 S/m at 20° C., such as 10{circumflex over ( )}-7 S/m at 20° C., such as 10{circumflex over ( )}-8 S/m at 20° C., such as 10{circumflex over ( )}-9 S/m at 20° C., such as 10{circumflex over ( )}-10 S/m at 20° C.

[0067] The second lateral structure 7 extends laterally from the second end 4b of the central pressurisation and heating structure 3. The first lateral structure 5 and the second lateral structure 7 extend away from the central pressurisation and heating structure 3 in opposite directions.

[0068] The second lateral structure 7 has an axially extending section primarily made of material at most having a conductivity of the order of 1000 S/m at 20° C. The material may for example be or comprise glass fibre or carbon fibre reinforced polymer, such as glass fibre or carbon fibre reinforced epoxy or polyamide.

[0069] The axially extending section is at least 20 cm long but could according to one variation be the entire length of the second lateral structure 7. which is the case in the example shown in FIGS. 1 and 2. In this case, the second lateral structure 7 is primarily made of material at most having a conductivity of the order of 1000 S/m at 20° C.

[0070] The axially extending section of the second lateral structure 7 has a wall or walls 7a of which for example at least 80% or at least 90% is made of material at most having a conductivity of the order of 1000 S/m at 20° C., such as 100 S/m at 20° C., such as 10 S/m at 20° C., 1 S/m at 20° C., such as 0.1 S/m at 20° C., such as 0.01 S/m at 20° C., such as 0.001 S/m at 20° C., such as 0.0001 S/m at 20° C., such as 10{circumflex over ( )}-4 S/m at 20° C., such as 10{circumflex over ( )}-5 S/m at 20° C., such as 10{circumflex over ( )}-6 S/m at 20° C., such as 10{circumflex over ( )}-7 S/m at 20° C., such as 10{circumflex over ( )}-8 S/m at 20° C., such as 10{circumflex over ( )}-9 S/m at 20° C., such as 10{circumflex over ( )}-10 S/m at 20° C.

[0071] The first lateral structure 5 may be integrated with the central pressurisation and heating structure 3. Alternatively, the first lateral structure 5 may be configured to be connected to or attached in a sealed manner to the central pressurisation and heating structure 3.

[0072] The second lateral structure 7 may be integrated with the central pressurisation and heating structure 3. Alternatively, the second lateral structure 7 may be configured to be connected in a sealed manner to the central pressurisation and heating structure 3.

[0073] The first lateral structure 5 may be openable. The first lateral structure 5 may comprise a first lateral structure part 5b and a second lateral structure part 5c which are configured to be assembled with each other. The first lateral structure part 5b has a straight open channel 5d, extending from one end to an opposite end of the first lateral structure part 5b. The second lateral structure part 5c has a straight open channel 5e, extending from one end to an opposite end of the second lateral structure part 5c. The channels 5d and 5e form a first lateral channel which is circumferentially closed when the first lateral structure part 5b and the second lateral structure part 5c are assembled with each other and the first lateral structure 5 is closed. The first lateral channel is configured to receive a power cable. The first lateral channel 5c is axially aligned with the central heating chamber.

[0074] The first lateral structure part 5b and the second lateral structure part 5c may for example be hinged or they may be completely separable from each other.

[0075] The second lateral structure 7 may be openable. The second lateral structure 7 may comprise a third lateral structure part 7b and a fourth lateral structure part 7c which are configured to be assembled with each other. The third lateral structure part 7b has a straight open channel 7d, extending from one end to an opposite end of the third lateral structure part 7b. The fourth lateral structure part 7c has a straight open channel 7e, extending from one end to an opposite end of the fourth lateral structure part 7c. The channels 7d and 7e form a second lateral channel which is circumferentially closed when the third lateral structure part 7b and the fourth lateral structure part 7c are assembled with each other and the second lateral structure 7 is closed. The second lateral channel is configured to receive a power cable. The second lateral channel 7c is axially aligned with the central heating chamber.

[0076] The third lateral structure part 7b and the fourth lateral structure part 7c may for example be hinged or they may be completely separable from each other.

[0077] Instead of an openable first lateral structure, the first lateral structure could be a pipe that is disposable after use. It could for example be sawed into two or more pieces to remove it from around the power cable.

[0078] Instead of an openable second lateral structure, the second lateral structure could be a pipe that is disposable after use. It could for example be sawed into two or more pieces to remove it from around the power cable.

[0079] With reference to FIGS. 2 and 3, a method of curing an uncured insulation system layer of power cable joint, using the heating assembly 1 will now be described.

[0080] The use of the curing assembly 1 will now be described in the context of a jointing operation. The process is similar in case the insulation system of a power cable that has been damaged is restored. Further, the insulation system that is being restored in the present example is being cured because in the example the restoration insulation system layer comprises a thermosetting polymer. The process is however similar in case a thermoplastic is used, except that the temperatures used in the step of heating may be adapted to the characteristics of the thermoplastic.

[0081] FIG. 2 schematically shows a power cable 9 comprising two cable lengths 9a and 9b that are in the process of being jointed inside the heating assembly 1. The central pressurisation and heating structure 3 is in the closed state and the power cable 9 extends through the central pressurisation and heating structure 3 inside the central heating chamber 10.

[0082] The power cable 9 also extends through the first lateral structure 5 and the second lateral structure 7 which are arranged at opposite axial ends of the central pressurisation and heating structure 3.

[0083] In the state shown in FIG. 2, the conductors 11a and 11 b of the two cable lengths 9a and 9b have been jointed and a conductor joint 11c has thus been created. The two conductors 11a, 11 b thus form a single conductor.

[0084] The jointing of the conductors 11a, 11 b may for example be performed by welding, brazing or by using mechanical connectors.

[0085] Each cable length 9a, 9b has an insulation system 13a, 13b which has been shaped conically adjacent to the conductor joint 11c. A region comprising the conically shaped insulation systems 13a, 13b and the conductor joint 11c is the power cable joint.

[0086] The joint insulation system, i.e. the insulation system around the conductor joint 11c and between the conically shaped ends of the insulation systems 13a and 13b is then rebuilt layer by layer.

[0087] A first restoration insulation system layer 15, which is uncured, is provided around the conductor joint 11c and arranged overlappingly with the corresponding insulation layer of the insulation systems 13a, 13b at their conically shaped ends. The first restoration insulation system layer 15 may for example be formed by tape wound around the exposed conductor.

[0088] The central heating chamber 10 may be pressurised to a first pressure higher than atmospheric pressure. The first pressure is a plurality of bar, such as in a range of 4-15 bar, for example 4-10 bar.

[0089] The central heating chamber 10 may be filled with noble gas during curing, to prevent oxidation while rebuilding the insulation system over the conductor joint 11c. The noble gas may be pressurised to the first pressure.

[0090] The first lateral channel 17 of the first lateral structure 5 may be pressurised to a second pressure. The second pressure is plurality of bar, such as in a range of 3-15 bar, for example 3-10 bar.

[0091] The second lateral channel 19 of the second lateral structure 7 may be pressurised to a third pressure. The third pressure is plurality of bar, such as in a range of 3-15 bar, for example 3-10 bar.

[0092] The second pressure and the third pressure is within ±50% of the first pressure such as within ±40% of the first pressure, such as within ±30% of the first pressure, such as within ±20% of the first pressure, such as within ±10% of the first pressure. At least one of or both the second pressure and the third pressure may according to one example be equal to the first pressure.

[0093] In a step a) the power cable joint including the conductor with the conductor joint 11c and the restoration insulation system layer 15 arranged around the conductor joint is placed in one of the first central channel 3c and the second central channel 3d.

[0094] In a step b) the power cable 9 is placed in each of the first lateral structure 5 and the second lateral structure 7. The first lateral structure 5 and the second lateral structure 7 may be open at this stage and the power cable 9 may be arranged in the channels 5d, 5e, 7d, 7e.

[0095] Steps a) and b) may be carried out simultaneously or essentially simultaneously.

[0096] In a step c) the central pressurisation and heating structure is set in the closed state, whereby the central heating chamber 10 is formed around the power cable joint. Step c) may also involve setting the first lateral structure 5 and the second lateral structure 7 in their closed state.

[0097] The heating assembly may comprise sealing members such as gaskets to seal the central heating chamber 10, the first lateral channel 17 and the second lateral channel 19 against the power cable 9.

[0098] As shown in FIG. 2, the first lateral structure 17 and the second lateral structure 19 may have smaller radial dimensions than the central pressurisation and heating structure 3.

[0099] The heating assembly 1 may comprise an induction heating device comprising a first HF heating coil 21 and a second HF heating coil 23. The induction heating device may comprise a power supply system configured to feed the first HF heating coil 21 and the second HF heating coil with an alternating current having a frequency in the kilohertz range. The induction heating device may comprise a water-cooling system configured to cool the first HF heating coil 21 and the second HF heating coil 23.

[0100] In a step d) the first HF heating coil 21 is placed around the axially extending section of the first lateral structure 5 and the second HF heating coil 23 is placed around the axially extending section of the second lateral structure 7. In case the first lateral structure 5 comprises also one or more sections made of a material with higher electrical conductivity than the axially extending section, the first HF heating coil 21 is placed around the axially extending section at a proper distance from the interface between the two materials. In case the second lateral structure 7 comprises also one or more sections made of a material with higher electrical conductivity than the axially extending section, the second HF heating coil 23 is placed around the axially extending section at a proper distance from the interface between the two materials.

[0101] The first HF heating coil 21 and the second HF heating coil 23 may for example be openable or splittable into several parts to facilitate the placement around the power cable 9 in step d).

[0102] The first HF heating coil 21 and the second HF heating coil 23 may be arranged at an equal axial distance from the conductor joint 11c. This distance may at most be 2-2.5 m from the conductor joint 11c, such as 1-2 m from the conductor joint 11c, such as 0.8-1 m from the conductor joint 11c.

[0103] In a step e) the central heating chamber 10 is pressurised to the first pressure, the first lateral channel 17 to the second pressure, and the second lateral channel 19 to the third pressure.

[0104] In a step f) the restoration insulation system layer 15 is heated by outer heating inside the central pressurisation and heating structure 3 by means of the heating device and by inner heating of the restoration insulation system layer 15 by feeding the first HF heating coil 21 and the second HF heating coil 23 with current to induce a current in the conductor. According to the present example, the heating in step f) involves curing the restoration insulation system layer 15.

[0105] In step f) the outer heating and the inner heating are typically performed simultaneously.

[0106] Steps a)-f) are typically performed for each of a plurality of restoration insulation system layers of the power cable joint, for example each being uncured before step f). After each iteration, the insulation system layer(s) is/are cooled down to a predetermined temperature such as to 60° C. or less.

[0107] The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.