Pressurisation and Heating Device and Method for Insulation System Restoration of a Power Cable

Abstract

A pressurisation and heating device for restoring an insulation system of a power cable, the pressurisation and heating device including: a first part including a first channel configured to receive a portion of the power cable, a second part including a second channel configured to receive a portion of the power cable, wherein the pressurisation and heating device is configured to be set in a closed state in which the first channel faces the second channel thereby forming a heating chamber extending from a first end to a second end, opposite the first end, of the pressurisation and heating device, wherein the pressurisation and heating device is configured to be pressurised to obtain a pressure higher than atmospheric pressure inside the heating chamber when the power cable is arranged sealed in the heating chamber, wherein the pressurisation and heating device 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 moo S/m at 20° C.

Claims

1. A pressurisation and heating device for restoring an insulation system of a power cable pressurisation and heating device comprising: a first part including a first channel configured to receive a portion of the power cable, a second part including a second channel configured to receive a portion of the power cable, wherein the pressurisation and heating device is configured to be set in a closed state in which the first channel faces the second channel thereby forming a heating chamber extending from a first end to a second end, opposite the first end, of the pressurisation and heating device, wherein the pressurisation and heating device is configured to be pressurised to obtain a pressure higher than atmospheric pressure inside the heating chamber when the power cable is arranged sealed in the heating chamber, wherein the pressurisation and heating device 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 pressurisation and heating device 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 pressurisation and heating device as claimed in claim 1, wherein the axially extending section is at least 30 cm long, such as at least 40 cm long.

4. The pressurisation and heating device as claimed in claim 1, wherein at least 70%, such as at least 80% of the axially extending section is made of material at most having a conductivity of the order of 1000 S/m at 20° C.

5. The pressurisation and heating device as claimed in claim 1, wherein the material comprises fibre reinforced polymer.

6. The pressurisation and heating device as claimed in claim 1, comprising a high frequency, HF, heating coil extending around the heating chamber in the axially extending section when the pressurisation and heating device is in the closed state.

7. The pressurisation and heating device as claimed in claim 6, wherein the HF heating coil extends around the heating chamber at a location which is in a range of ±30% from a centre of the pressurisation and heating device measured from the first end towards the second end.

8. The pressurisation and heating device as claimed in claim 7, wherein the range is ±10%.

9. A heating assembly comprising the pressurisation and heating device as claimed in claim 1, and at least one external HF heating coil configured to be arranged around the pressurisation and heating device in the axially extending section.

10. A method of restoring an insulation system around a conductor of a power cable, using the pressurisation and heating device as claimed in claim 1, the method comprising: a) placing the power cable having a restoration insulation system layer arranged around a conductor in one of the first channel and the second channel, b) setting the pressurisation and heating device in the closed state, c) pressurising the heating chamber, and d) heating the restoration insulation system layer while the heating chamber is pressurised, by outer heating inside the pressurisation and heating device and by inner heating of the restoration insulation system layer by feeding a high frequency, HF, heating coil arranged around the heating chamber in the axially extending section with current to induce a current in the conductor.

11. The method as claimed in claim 10, comprising performing steps a)-d) for each of a plurality of restoration insulation system layers.

12. The method as claimed in claim 10, wherein in step d) the outer heating and the inner heating are performed simultaneously.

13. The method as claimed in claim 10, wherein the outer heating and inner heating is performed in a noble gas atmosphere inside the heating chamber.

14. The method as claimed in claim 10, wherein prior to step d) the restoration insulation system layer is an uncured insulation system layer, and wherein in step d) the outer heating and the inner heating is for curing the restoration insulation system layer.

15. The pressurisation and heating device as claimed in claim 2, wherein the axially extending section is at least 30 cm long, such as at least 40 cm long.

16. The pressurisation and heating device as claimed in claim 2, wherein at least 70%, such as at least 80% of the axially extending section is made of material at most having a conductivity of the order of 1000 S/m at 20° C.

17. The pressurisation and heating device as claimed in claim 2, wherein the material comprises fibre reinforced polymer.

18. The pressurisation and heating device as claimed in claim 2, comprising a high frequency, HF, heating coil extending around the heating chamber in the axially extending section when the pressurisation and heating device is in the closed state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

[0053] FIG. 1 schematically shows a top view of a pressurisation and heating device in an open state;

[0054] FIG. 2 shows a longitudinal section of an example of a heating assembly comprising the pressurisation and heating device in FIG. 1 while heating a restoration insulation system layer of a power cable;

[0055] FIG. 3 shows a longitudinal section of another example of a pressurisation and heating device while heating a restoration insulation system layer of a power cable; and

[0056] FIG. 4 is a flowchart of a method of restoring the insulation system of a power cable.

DETAILED DESCRIPTION

[0057] 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.

[0058] FIG. 1 schematically shows a top view of a pressurisation and heating device 1 in an open state. The pressurisation and heating device 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. 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.

[0059] The pressurisation and heating device 1 comprises a first part 3 and a second part 5.

[0060] The first part 3 has a first channel 3a extending from one end of the first part 3 to an opposite end of the first part 3. The first channel 3a is straight. The first channel 3a is configured to receive a power cable including a power cable joint.

[0061] The second part 5 has a second channel 5a extending from one end of the second part 5 to an opposite end of the second part 5. The second channel 5a is straight. The second channel 5 is configured to receive a power cable including a power cable joint.

[0062] The first part 3 and the second part 5 are configured to be assembled with each other to thereby set the pressurisation and heating device 1 in a closed state. The pressurisation and heating device 1 is thus openable and closable.

[0063] The first part 3 and the second part 5 may for example be hingedly connected, or they may be completely separable from each other.

[0064] In the closed state of the pressurisation and heating device 1, the first channel 3a faces the second channel 5a. The first channel 3a is axially aligned with the second channel 5a. The first channel 3a and the second channel 5a thus form a heating chamber extending from a first end 4a of the pressurisation and heating device 1 to a second end 4b, opposite to the first end 4a, of the pressurisation and heating device 1. The heating chamber is thus configured to circumferentially enclose the power cable including the power cable joint along the length of the pressurisation and heating device 1.

[0065] The pressurisation and heating device 1 may according to some examples comprise a heating device 7 configured to heat the 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 examples the predefined temperature is a melting temperature for heating a thermoplastic polymer such as polyethylene until it melts. The heating device 7 may be configured to directly heat the heating chamber for example by means of heating coils or similar means arranged around the first channel 3a and the second channel 5a.

[0066] Alternatively, the heating device may be external to the pressurisation and heating device 1. In this case the heating device may be configured to externally heat gas such as noble gas introduced into the heating chamber.

[0067] The pressurisation and heating device 1 has an axially extending section 9 which is primarily made of material at most having a conductivity of the order of moo S/m at 20° C. The axially extending section 9 is at least 20 cm long, such as at least 30 cm long, such as at least 40 cm long.

[0068] The axially extending section 9 may according to one example be the entire length of the pressurisation and heating device 1, i.e. from the first end 4a to the second end 4b.

[0069] The material may according to examples at most have a conductivity of the order of moo 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∧-4 S/m at 20° C., such as 10∧-5 S/m at 20° C., such as 10∧-6 S/m at 20° C., such as 10∧-7 S/m at 20° C., such as 10∧-8 S/m at 20° C., such as 10∧-9 S/m at 20° C., such as 10∧-10 S/m at 20° C.

[0070] 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.

[0071] In the axially extending section 9 of the pressurisation and heating device 1, the first part 3 and the second part 5 each has a wall or walls 3b of which at least 70% or at least 80% is material at most having a conductivity of the order of moo S/m at 20° C.

[0072] FIG. 2 schematically shows a longitudinal section of a heating assembly 10 comprising the pressurisation and heating device 1 with a power cable 11, including a power cable joint, arranged inside.

[0073] The power cable 11 comprises two cable lengths 11a and 11b that are in the process of being jointed inside the pressurisation and heating device 1. The pressurisation and heating device 1 is in the closed state and the power cable 11 extends through the pressurisation and heating device 1 inside the heating chamber 13.

[0074] In the state shown in FIG. 2, the conductors 15a and 15b of the two cable lengths 11a and 11b have been jointed and a conductor joint 15c has thus been created. The two conductors 15a, 15b form a single conductor.

[0075] The jointing of the conductors 15a, 15b may for example be performed by welding, brazing or by using mechanical connectors.

[0076] Each cable length 11a, 11b has an insulation system 17a, 17b which has been shaped conically adjacent to the conductor joint 15c. A region comprising the conically shaped insulation systems 17a, 17b and the conductor joint 15c is the power cable joint.

[0077] The heating assembly 10 comprises an induction heating device. The induction heating device comprises at least one HF heating coil 19a, 19b. The at least one heating coil 19a, 19b is arranged around the axially extending section 9 of the pressurisation and heating device 1. The at least one heating coil 19a is thus arranged radially outside the axially extending section 9.

[0078] In the present example the heating assembly 10 comprises two HF heating coils 19a and 19b. Both HF heating coils 19a and 19b are arranged axially spaced apart around the axially extending section 9 of the pressurisation and heating device 1. Alternatively, if the pressurisation and heating device comprises two axially extending sections, each HF heating coil may be arranged around a respective axially extending section.

[0079] The HF heating coils 19a, 1913 may be arranged symmetrically at the two sides of the conductor joint 15c. The HF heating coils 19a, 1913 may thus be arranged at the same axial distance, in a respective axial direction, from the conductor joint 15c. 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, such as 0.1-0.5 m from the conductor joint 11c.

[0080] If only one HF heating coil 19a is employed, it may be centred over the conductor joint 15c.

[0081] The induction heating device may comprise a power supply. The at least one HF heating coil 19a, 19b is powered by the power supply. The power supply is configured to generate an alternating current in the kilohertz range.

[0082] The induction heating device may comprise a water-cooling system configured to cool the least one HF heating coil.

[0083] The at least one HF heating coil 19a, 19b may be one or more external HF heating coils, as shown in FIG. 2. In this case the at least one HF heating coil 19a, 19b may be provided around and removed from the pressurisation and heating device 1. Alternatively, the at least one HF heating coil may be integrated with the pressurisation and heating device 1. In this case, the pressurisation and heating device 1 comprises at least one HF heating coil, as shown in FIG. 3. The same considerations with respect to placement may apply as mentioned above in case the pressurisation and heating device 1 comprises one or two integrated HF heating coils.

[0084] With reference to FIG. 2 and to FIG. 4, a method of restoring an insulation system around a conductor of a power cable will now be described. In the present example, the restoration of the insulation system concerns curing an uncured insulation system layer of a power cable joint, using the pressurisation and heating device 1 or the heating assembly 10. The method could also be used for restoring an insulation system of a power cable that has been damaged without involving jointing.

[0085] The joint insulation system, i.e. the insulation system around the conductor joint 15c and between the conically shaped ends of the insulation systems 17a and 17b is rebuilt layer by layer.

[0086] A first restoration insulation system layer 21 is provided around the conductor joint 15c and arranged overlappingly with the corresponding insulation layer of the insulation systems 17a, 17b at their conically shaped ends.

[0087] The restoration uncured insulation system layer 21 may for example be formed by tape wound around the exposed conductor.

[0088] In the process of heating the restoration insulation system layer 21, in a step a) the power cable joint including the conductor with the conductor joint 15c and the restoration insulation system layer 21 arranged around the conductor joint 15c is placed in one of the first channel 3 and the second channel 5.

[0089] In case of restoring the insulation system of a power cable due repair, the restoration insulation system layer is provided around the conductor.

[0090] In a step b) the pressurisation and heating device 1 is set in the closed state. The heating chamber 10 is thus formed around the power cable joint.

[0091] The pressurisation and heating device 1 may comprise sealing members such as gaskets to seal the heating chamber 10 against the power cable 11. The first part 3 and the second part 5 are sealed against each other too.

[0092] In a step c) the heating chamber 13 is pressurised. The heating chamber 13 is pressurised to a pressure higher than atmospheric pressure. The pressure is a plurality of bar, such as in a range of 4-15 bar, for example 4-10 bar.

[0093] The heating chamber 13 may be filled with noble gas during curing in conjunction with step c), to prevent oxidation while rebuilding the insulation system over the conductor joint 15c. The noble gas obtains the pressure present inside the heating chamber 13.

[0094] In a step d) the restoration insulation system layer 21 is heated. The heating typically involves curing the restoration insulation system layer 21 but could involve melting without curing in case the restoration insulation system layer 21 is made of a thermoplastic.

[0095] The heating is performed by outer heating of the restoration insulation system layer 21 inside the pressurisation and heating device 1 and by inner heating of the restoration insulation system layer 21 by feeding the at least one HF heating coil 19a, 19b, 19c arranged around the heating chamber 13 in the axially extending section 9 with current to induce a current in the conductor.

[0096] The at least one HF coil 19a, 19b may for example be openable or splittable into several parts to facilitate the placement around the power cable 11 before step d).

[0097] In case the pressurisation and heating device 1 comprises one or more sections made of a material with higher electrical conductivity than the axially extending section 9, the at least one HF heating coil 19a, 19b, 19c is placed around the axially extending section at a proper distance from the interface between the two materials.

[0098] In step d) the outer heating and the inner heating are typically performed simultaneously.

[0099] Steps a)-d) are typically performed for each of a plurality of restoration insulation system layers of the power cable joint. After each iteration, the heated insulation system layer(s) is/are cooled down to a predefined temperature such as to 60° C. or less.

[0100] 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.