Test method for low-frequency submarine cable flexible joint detection

Abstract

The invention discloses a test method for detecting a low-frequency submarine cable flexible joint. The test method comprises the following steps: step S100, sleeving a metal guide sleeve on one submarine cable of which the flexible joint needs to be manufactured; s200, manufacturing a flexible joint between the end parts of the two submarine cables, wherein the flexible joint comprises a conductor, an inner shielding layer, an insulating layer and an outer shielding layer which are arranged from inside to outside; s300, the metal guide sleeve is moved, specifically, the metal guide sleeve is moved to the position of the soft connector so that the soft connector can be located in the metal guide sleeve; step S400, making a disconnection point; step S500, grounding the metal guide sleeve; step S600, applying a test voltage to the metal guide sleeve and keeping the test voltage for a set time; s700, the test voltage is removed, and the metal guide sleeve is removed; s800, observing whether insulation shielding of the flexible joint is broken down or not; according to the invention, the detection position is more accurate, and irreversible damage to submarine cable body insulation and manufactured qualified flexible joints caused by repeated withstand voltage tests is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of submarine cable connection detection, and in particular to a test method for detecting low-frequency submarine cable soft joints. Background Art

[0002] my country's offshore wind energy resources are mainly concentrated in the southeast coast and the attached islands, and the wind energy density is basically over 300w / m2. According to the results of the previous wind energy resource survey, my country's offshore wind power development potential at a water depth of 5-25m and a height of 50m is about 200GW; and the offshore wind power development potential at a water depth of 5-50m and a height of 70m is about 500GW. Therefore, my country has a good offshore wind power development resource foundation. With the increase in water depth and offshore distance, low-frequency submarine cable transmission systems have emerged to fill the gap between industrial frequency AC and DC. In the production of low-frequency submarine cables, soft joints are a key part of the long-length delivery of submarine cables, which directly affects the service life and reliability of submarine cables. Therefore, the production and testing of submarine cable soft joints are very important links.

[0003] Before the flexible joint is made, a certain voltage is applied to the submarine cables on both sides of the joint for a withstand voltage test. After the flexible joint is made, a secondary withstand voltage test is performed on the entire submarine cable after the joint is completed. If there is no insulation breakdown, it verifies that the manufacturing quality of the flexible joint is qualified. With the delivery of long-length submarine cables, there will be multiple flexible joints in a single submarine cable. Multiple repetitive withstand voltage tests will cause irreversible damage to the insulation of the submarine cable body and the qualified flexible joints, affecting the long-term operation stability and reliability of the submarine cable. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the present invention provides a test method for detecting low-frequency submarine cable flexible joints, which has the advantage of accurately detecting the position of the flexible joints.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A test method for detecting a low-frequency submarine cable flexible joint comprises the following steps:

[0007] Step S100, inserting a metal guide sleeve into one of the submarine cables for which a flexible joint is to be made;

[0008] Step S200, making a flexible joint between the ends of two submarine cables, the flexible joint comprising a conductor, an inner shielding layer, an insulating layer and an outer shielding layer arranged from the inside to the outside;

[0009] Step S300, moving the metal guide sleeve: moving the metal guide sleeve to the flexible joint so that the flexible joint is located inside the metal guide sleeve;

[0010] Step S400, making a disconnection point: annular grooves are provided on both sides of the outer shielding layer of the metal guide sleeve, so that the outer shielding layer is completely disconnected at the two annular grooves;

[0011] Step S500, grounding the metal guide sleeve: connecting a grounding wire to the metal guide sleeve to access the grounding system;

[0012] Step S600, applying a test voltage to the metal guide sleeve and maintaining it for a set time;

[0013] Step S700, removing the test voltage and removing the metal guide sleeve;

[0014] Step S800, observe whether the insulation shielding of the flexible joint is broken; if not, it proves that the flexible joint is qualified, and then use semi-conductive paint to repair the disconnection point to restore the function of the outer shielding layer, and then repair the outer sheath; if broken, remove the flexible joint and repeat step S100.

[0015] By adopting the above technical solution, high voltage is applied to the metal guide sleeve for a certain period of time. During this process, since the outer shielding layer is located on both sides of the metal guide sleeve with annular grooves, the voltage will not be transmitted to the entire submarine cable along the outer shielding layer, but will only act on the flexible joint part in the metal guide sleeve. In this way, the detection position is more accurate, and multiple repetitive voltage withstand tests are avoided to avoid irreversible damage to the insulation of the submarine cable body and the qualified flexible joints, which is beneficial to protecting the submarine cable body and the qualified flexible joints.

[0016] Optionally, the conductors of the two submarine cables are connected via a sinusoidal conductor; an axial cross-section of the sinusoidal conductor and an outer edge line parallel to the axis thereof are in a sinusoidal wave shape.

[0017] By adopting the above technical solution, the conductor connection adopts sinusoidal conductor connection, so that the outer diameter of the conductor at the crest is the largest, and the outer diameter of the conductor at the trough is the smallest. The larger the outer diameter, the smaller the resistance; then when the same current passes through, the loss at the crest is the smallest, and the heat is also the smallest; the heat will be transferred from high to low, so the temperature at the trough will be lower, and then the current carrying capacity of the entire joint can be improved.

[0018] Optionally, the outer diameter of the crest of the sinusoidal conductor is 9-11 mm larger than the outer diameter of the trough.

[0019] By adopting the above technical solution, when the difference between the outer diameter of the crest and the trough is 9-11mm, the loss is reduced to the minimum.

[0020] Optionally, the inner diameter of the metal guide sleeve is 1-3 mm larger than the outer diameter of the outer shielding layer.

[0021] By adopting the above technical solution, the inner diameter of the metal guide sleeve is 1-3mm larger than the outer diameter of the outer shielding layer. When a certain force is applied, the metal guide sleeve can move along the flexible joint; when no external force is applied, the metal guide sleeve is not easy to move on the flexible joint. In this way, when high pressure is applied, the metal guide sleeve is not easy to shift, which is conducive to the smooth progress of the detection.

[0022] Optionally, in step S500, the grounding wire is wound around the metal guide sleeve and clamped on the metal guide sleeve using a clamp.

[0023] By adopting the above technical solution, the connection between the grounding wire and the metal guide sleeve is stable, which prevents the grounding wire from accidentally detaching during detection and affecting the detection.

[0024] Optionally, in step S600, the test voltage applied to the metal guide sleeve is 318KV, and the setting time is 30 minutes.

[0025] By adopting the above technical solution, the test voltage is 318KV and the test setting time is 30min, which meets the requirements of time working scenarios and performance testing.

[0026] Optionally, in step S400, the axial width of the annular groove is at least 5 mm.

[0027] By adopting the above technical solution, the annular groove with a width of 5 mm can be ensured to be disconnected, and it is relatively easy to open the annular groove of this width.

[0028] Optionally, step S200 specifically includes the following steps:

[0029] Step S201, removing the outer sheath, outer shielding layer, insulating layer and inner shielding layer from the connecting end of the submarine cable, so that the end of the conductor exceeds the end of the inner shielding layer, the end of the inner shielding layer exceeds the end of the insulating layer, and the end of the insulating layer exceeds the end of the outer shielding layer;

[0030] Step S202, hot-melt welding the conductor ends of the two submarine cables;

[0031] Step S203, using the same material as the inner shielding layer to wrap around to form the inner shielding layer of the flexible joint, so as to be connected to the original inner shielding layer as a whole;

[0032] Step S204, using the same material as the insulating layer to melt and form the insulating layer of the flexible joint so as to be connected to the original insulating layer as a whole;

[0033] Step S205, using the same material as the outer shielding layer to wrap around to form the outer shielding layer of the flexible joint, so as to be connected with the original outer shielding layer as a whole.

[0034] By adopting the above technical solution, during the production process of the flexible joint, the end of the conductor is made to extend beyond the end of the inner shielding layer, the end of the inner shielding layer extends beyond the end of the insulating layer, and the end of the insulating layer extends beyond the end of the outer shielding layer. When the flexible joint is completed, the outer shielding layer of the flexible joint will cover the connection point of the insulating layer of the flexible joint, the insulating layer of the flexible joint will cover the connection point of the inner shielding layer of the flexible joint, and the inner shielding layer of the flexible joint will cover the connection point of the conductor of the flexible joint, thereby achieving a good insulation and shielding effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural diagram of embodiment 1 of the present invention.

[0036] Figure 2 It is a process schematic diagram of embodiment 1 of the present invention.

[0037] Figure 3 It is a structural diagram of embodiment 2 of the present invention.

[0038] Description of reference numerals:

[0039] 10. Conductor;

[0040] 20. Inner shielding layer;

[0041] 30. Insulation layer;

[0042] 40, outer shielding layer; 400, annular groove;

[0043] 50. Outer sheath;

[0044] 60. Metal guide sleeve;

[0045] 70. Sinusoidal conductor;

[0046] 80. Experimental wire. DETAILED DESCRIPTION

[0047] The following is combined with Figure 1 The present invention is described in further detail.

[0048] Embodiment 1: A test method for detecting low-frequency submarine cable flexible joints is disclosed, referring to Figure 2 , specifically including the following steps:

[0049] Step S100, insert a metal guide sleeve 60 into one of the submarine cables that needs to make a flexible joint; the voltage level of the submarine cable is 220KV, the outer diameter of the conductor 10 is 38mm, the outer diameter of the core wire is 94mm, the inner diameter of the metal guide sleeve 60 is 95mm, and the length is 710mm; in addition, the material of the metal guide sleeve 60 can be selected from conductive metals such as copper and iron.

[0050] Step S200, making a flexible joint between the ends of two submarine cables, the flexible joint comprising a conductor, an inner shielding layer, an insulating layer and an outer shielding layer arranged from the inside to the outside; the length of the flexible joint is about 700 mm.

[0051] Step S201, remove the outer sheath 50, outer shielding layer 40, insulating layer 30 and inner shielding layer 20 from the connecting end of the submarine cable, so that the end of the conductor 10 exceeds the end of the inner shielding layer 20, the end of the inner shielding layer 20 exceeds the end of the insulating layer 30, and the end of the insulating layer 30 exceeds the end of the outer shielding layer 40; wherein the thickness of the outer shielding layer 40 is 1.5mm, the thickness of the insulating layer 30 is 24mm, the thickness of the inner shielding layer 20 is 1.5mm, the length of the end of the conductor 10 exceeding the end of the inner shielding layer 20, the length of the end of the inner shielding layer 20 exceeding the end of the insulating layer 30, and the length of the end of the insulating layer 30 exceeding the end of the outer shielding layer 40 are all 100mm, which is conducive to the formation of a flexible joint and to achieving better insulation shielding. Specifically comprising the following steps:

[0052] Step S202, hot-melt welding the ends of the conductors 10 of the two submarine cables;

[0053] Step S203, using the same material as the inner shielding layer to wrap around to form the inner shielding layer of the flexible joint, so as to be connected to the original inner shielding layer as a whole;

[0054] Step S204, using the same material as the insulating layer to melt and form the insulating layer of the flexible joint so as to be connected to the original insulating layer as a whole;

[0055] Step S205, using the same material as the outer shielding layer to wrap around to form the outer shielding layer of the flexible joint, so as to be connected with the original outer shielding layer as a whole.

[0056] Step S300, moving the metal guide sleeve 60: moving the metal guide sleeve 60 to the flexible joint so that the flexible joint is located inside the metal guide sleeve 60. Since the inner diameter of the metal guide sleeve 60 is 1 mm larger than the outer diameter of the core wire, the metal guide sleeve 60 can move along the core wire when it is stressed. When the metal guide sleeve 60 is not stressed, it is not easy for the metal guide sleeve 60 to move on the core wire, which is conducive to keeping the metal guide sleeve 60 in the experimental position; in order to achieve the above purpose, the inner diameter of the metal guide sleeve 60 can be 1-3 mm larger than the outer diameter of the core wire.

[0057] Step S400, making a disconnection point: annular grooves 400 are opened on both sides of the outer shielding layer 40 at the metal guide sleeve 60, so that the outer shielding layer 40 is completely disconnected at the two annular grooves 400; the axial length of the annular groove 400 is at least 5 mm and its radial thickness is 1.5 mm.

[0058] Step S500, grounding the metal guide sleeve 60: connecting a grounding wire to the metal guide sleeve 60 to access the grounding system. In order to increase the connection stability between the grounding wire and the metal guide sleeve 60, the grounding wire is wound around the metal guide sleeve 60 and clamped on the metal guide sleeve 60 using a clamp.

[0059] Step S600, apply 318kV test voltage to the metal guide sleeve 60 and maintain it for a set time of 30 minutes. During the test, the cross-section of the two connected submarine cables is as follows: Figure 1 As shown, an experimental wire 80 is connected to the metal guide sleeve 60; the experimental wire 80 is connected to an external transformer, and the transformer is connected to a power source.

[0060] Step S700, removing the test voltage and removing the metal guide sleeve 60; the metal guide sleeve 60 can be removed with the aid of scissors.

[0061] Step S800, observe whether the insulation shielding of the flexible joint is broken; if not, it proves that the flexible joint is qualified, and then use semi-conductive paint to repair the disconnection point to restore the function of the outer shielding layer, and then repair the outer sheath; if broken, remove the flexible joint and repeat step S100.

[0062] Embodiment 2: The difference between Embodiment 2 and Embodiment 1 is that Figure 3 , the conductors 10 of the two submarine cables are connected by a sinusoidal conductor 70; the two ends of the sinusoidal conductor 70 are respectively hot-melt welded to the ends of the conductors 10 of the submarine cables on both sides; the axial cross-section of the sinusoidal conductor 70 is parallel to its axis and has a sinusoidal shape of the outer edge; in this way, the outer diameter of the conductor at the crest is the largest, and the outer diameter of the conductor at the trough is the smallest. The larger the outer diameter, the smaller the resistance; then when the same current passes through, the loss at the crest is the smallest, and the heat generation is also the smallest; the heat will be conducted from high to low, so the temperature at the trough will decrease, and then the current carrying capacity of the entire joint can be improved. In order to achieve the best effect, the crest outer diameter of the sinusoidal conductor 70 is 9-11mm larger than the trough outer diameter. In order to increase the connection strength, the diameters at both ends of the sinusoidal conductor 70 are the same as the diameters of the conductors 10 of the submarine cables on both sides.

[0063] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A test method for detecting low-frequency submarine cable flexible joints, characterized in that: The specific steps include: Step S100, inserting a metal guide sleeve into one of the submarine cables for which a flexible joint is to be made; Step S200, making a flexible joint between the ends of two submarine cables, the flexible joint comprising a conductor, an inner shielding layer, an insulating layer and an outer shielding layer arranged from the inside to the outside; Step S300, moving the metal guide sleeve: moving the metal guide sleeve to the flexible joint so that the flexible joint is located inside the metal guide sleeve; Step S400, making a disconnection point: annular grooves are provided on both sides of the outer shielding layer of the metal guide sleeve, so that the outer shielding layer is completely disconnected at the two annular grooves; Step S500, grounding the metal guide sleeve: connecting a grounding wire to the metal guide sleeve to access the grounding system; Step S600, applying a test voltage to the metal guide sleeve and maintaining it for a set time; Step S700, removing the test voltage and removing the metal guide sleeve; Step S800, observe whether the insulation shielding of the flexible joint is broken; if not, it proves that the flexible joint is qualified, and then use semi-conductive paint to repair the disconnection point to restore the function of the outer shielding layer, and then repair the outer sheath; if broken, remove the flexible joint and repeat step S100.

2. A test method for detecting low-frequency submarine cable flexible joints according to claim 1, characterized in that: The conductors of the two submarine cables are connected by a sinusoidal conductor; the outer edge of the axial section of the sinusoidal conductor parallel to its axis is in a sinusoidal wave shape.

3. A test method for detecting low-frequency submarine cable flexible joints according to claim 2, characterized in that: The outer diameter of the crest of the sinusoidal conductor is 9-11 mm larger than the outer diameter of the trough.

4. A test method for detecting low-frequency submarine cable flexible joints according to claim 1, characterized in that: The inner diameter of the metal guide sleeve is 1-3 mm larger than the outer diameter of the outer shielding layer.

5. A test method for detecting low-frequency submarine cable flexible joints according to claim 1, characterized in that: In step S500, the grounding wire is wound around the metal guide sleeve and clamped on the metal guide sleeve using a clamp.

6. A test method for detecting low-frequency submarine cable flexible joints according to claim 1, characterized in that: In step S600, the test voltage applied to the metal guide sleeve is 318KV, and the setting time is 30 minutes.

7. A test method for detecting low-frequency submarine cable flexible joints according to claim 1, characterized in that: In step S400, the axial width of the annular groove is at least 5 mm.

8. A test method for detecting low-frequency submarine cable flexible joints according to claim 1, characterized in that: Step S200 specifically includes the following steps: Step S201, removing the outer sheath, outer shielding layer, insulating layer and inner shielding layer from the connecting end of the submarine cable, so that the end of the conductor exceeds the end of the inner shielding layer, the end of the inner shielding layer exceeds the end of the insulating layer, and the end of the insulating layer exceeds the end of the outer shielding layer; Step S202, hot-melt welding the conductor ends of the two submarine cables; Step S203, using the same material as the inner shielding layer to wrap around to form the inner shielding layer of the flexible joint, so as to be connected to the original inner shielding layer as a whole; Step S204, using the same material as the insulating layer to melt and form the insulating layer of the flexible joint so as to be connected to the original insulating layer as a whole; Step S205, using the same material as the outer shielding layer to wrap around to form the outer shielding layer of the flexible joint, so as to be connected with the original outer shielding layer as a whole.

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