Method of determining compatibility between polymeric insulation material and foreign material

Abstract

To provide a method of determining the compatibility between a polymeric electrical insulation material for an insulation layer of a high voltage power cable and a foreign material.SOLUTION: The method includes: a) preparing a test sample from A) an insulation plate comprising the polymeric electrical insulation material, and B) the foreign material; b) applying a voltage to the test sample; c) determining a conductivity of the test sample based on measurements taken during the step b); d) comparing the conductivity of the test sample with a reference conductivity; and e) concluding whether the foreign material is compatible with the polymeric electrical insulation material based on the comparison in the step d).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates generally to high voltage power cables. [Background technology]

[0002] Power cables have an insulation system that electrically insulates the conductors, which typically comprises an inner semiconducting layer, an insulating layer and an outer semiconducting layer.

[0003] The DC performance of the insulation system is governed by the electrical conductivity of the insulating layers. The insulating layers may come into direct or indirect contact with other layers in the power cable or may come into direct or indirect contact with materials during handling. There is a risk that the insulating layers may become contaminated by one or more of these layers or from materials that come into contact with the insulation system during handling. This can result in a greater electrical conductivity of the insulating material and an increased risk of failure of the power cable during service and / or inspection. Summary of the Invention

[0004] In view of the above, it is an object of the present disclosure to provide a method for solving or at least alleviating the problems of the prior art.

[0005] Thus, there is provided a method for determining compatibility between a polymeric electrical insulating material for an insulation layer of a high voltage power cable and a dissimilar material, comprising the steps of: a) preparing a test sample from A) an insulating plate made of a polymeric electrical insulating material, and B) the dissimilar material; b) applying a voltage to the test sample; c) determining the conductivity of the test sample based on measurements obtained during step b); d) comparing the conductivity of the test sample with a reference conductivity; and e) concluding whether the dissimilar material is compatible with the polymeric electrical insulating material based on the comparison of step d).

[0006] The term "compatible" should be understood to mean that the inherent electrical conductivity of the polymeric electrically insulating material remains sufficiently unaffected under test conditions by the presence of the foreign material after preparation of the test specimen. Thus, the foreign material should not contaminate the polymeric electrically insulating material to an extent greater than an acceptable amount from the nominal electrical conductivity.

[0007] The method allows the selection of materials for power cables that are compatible with the polymeric electrical insulating material that forms part of the insulation system, without the need to carry out testing by constructing an actual test high-voltage power cable for this purpose. Thus, the low electrical conductivity of the polymeric electrical insulating material can be ensured for high-voltage power cables in a fast, simple and inexpensive manner, as required for the application.

[0008] The polymeric electrically insulating material may be, for example, a polyethylene such as cross-linked polyethylene (XLPE), a polypropylene, an ethylene propylene diene monomer rubber (EPDM), an ethylene propylene rubber (EPR), or any other suitable extrudable polymeric electrically insulating material.

[0009] According to one embodiment, step e) comprises concluding that the dissimilar material is compatible with the polymeric electrically insulating material if the deviation of the electrical conductivity from the reference electrical conductivity is no more than a predetermined amount, and concluding that the dissimilar material is incompatible with the polymeric electrically insulating material otherwise.

[0010] A conductivity deviation refers to a conductivity that is greater than a reference conductivity by more than a predetermined amount.

[0011] According to one embodiment, steps b) and c) are carried out in a conductivity cell.

[0012] According to one embodiment, in step a), the insulating plate is brought into direct contact with the dissimilar material.

[0013] According to one embodiment, step a) further comprises pressing the insulating plate and the dissimilar material together in a press.

[0014] According to one embodiment, step a) comprises heat treating the insulating plate and the dissimilar material when they are in direct contact.

[0015] According to one embodiment, the heat treatment comprises heating at a temperature in the range of 70-110° C. The temperature may be selected based on, for example, the maximum allowable operating temperature of a high voltage power cable using the polymeric electrical insulating material as a material of an insulating layer of its insulation system. For example, if the maximum allowable temperature is 70° C., 80° C., or 90° C., the temperature of the heat treatment step is 70° C., 80° C., or 90° C., respectively.

[0016] According to one embodiment, the heat treatment comprises subjecting the insulating plate and the dissimilar material to temperature cycling between room temperature and said temperature in the range of 70-110° C. This simulates the load changes during operation of a high voltage power cable.

[0017] According to one embodiment, the reference conductivity is the conductivity of an uncontaminated reference sample of the polymeric electrically insulating material.

[0018] According to one embodiment, the electric field applied to the test specimen in step b) is in the range of 15-50 kV / mm.

[0019] According to one embodiment, the insulating plate has a thickness in the range of 0.5 to 2 mm. For example, the insulating plate may have a thickness in the range of 0.8 to 1.5 mm.

[0020] According to one embodiment, the dissimilar material is one of a polymeric material, a lubricious material, a metal, and a semiconductor material.

[0021] According to one embodiment, the dissimilar material is a conductive tape or a swelling tape. A swelling tape is typically a water-swellable tape that includes a superabsorbent polymer.

[0022] According to one embodiment, the polymeric electrically insulating material is a DC insulating material.

[0023] According to one embodiment, the DC insulating material is designed for voltages above 300 kV.

[0024] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to "elements, devices, components, means," and the like should be interpreted non-exclusively as referring to at least one example of the element, device, component, means, etc., unless otherwise specified. [Brief description of the drawings]

[0025] Specific embodiments of the inventive concept will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] 1 shows a schematic of an electrode system for measuring electrical conductivity. [Diagram 2] 4 is a flow chart of a method for determining compatibility between a polymeric electrical insulating material and a dissimilar material for an insulation layer of a high voltage power cable. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. However, the inventive concept may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather, these embodiments are provided as examples 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 specification.

[0027] 1 shows a schematic of an electrode system or conductivity cell 1 in a laboratory setup for determining the conductivity of a test sample 3. Based on the determined conductivity, the compatibility of dissimilar materials with the polymeric electrically insulating material forming the test sample 3 can be determined.

[0028] The electrode system 1 comprises a high voltage connection 5 connected to a high voltage unit. The electrode system 1 comprises a measurement connection 7 connected to a measuring instrument such as a galvanometer or electrometer.

[0029] Furthermore, the electrode system 1 comprises a high voltage electrode 9 electrically connected to the high voltage connection 5 and a measurement electrode 11 electrically connected to the measurement connection 7 .

[0030] The electrode system 1 may comprise a guard electrode 13. The guard electrode 13 is connected to ground and may be arranged coaxially with the measurement electrode 11.

[0031] The test sample 3 is placed between the high voltage electrode 9 and the measurement electrode 11 in contact with the high voltage electrode 9 and the measurement electrode 11 .

[0032] This allows the leakage current through the test sample 3 to be measured by a measuring instrument. In this way, the conductivity of the test sample 3 can be determined.

[0033] The test sample 3 is composed of an insulating plate 3a made of a polymeric electrically insulating material and a different material 3b.

[0034] A method for determining compatibility between a polymeric electrically insulating material and a dissimilar material 3b will now be described in more detail with reference to the flow chart of FIG.

[0035] In step a), a test specimen is prepared: the test specimen 3 is made of an insulating plate 3a made of a polymeric electrically insulating material and a dissimilar material 3b.

[0036] The insulating plate 3a and the dissimilar material 3b are preferably arranged in direct contact with each other. The dissimilar material 3b may be arranged on only one side of the insulating plate 3a in direct contact with the insulating plate 3a, or on both sides of the insulating plate 3b such that the insulating plate 3a is sandwiched between the dissimilar materials 3b as shown in Figure 1. Alternatively, the insulating plate 3a and the dissimilar material 3b may be arranged in indirect contact with each other.

[0037] The insulating plate 3a may have a thickness of, for example, 0.5 to 2 mm.

[0038] The polymeric electrical insulating material may include, for example, polyethylene, such as XLPE, polypropylene, EPDM, or EPR. The polymeric electrical insulating material may be, for example, a DC insulating material designed for voltages greater than 300 kV.

[0039] The dissimilar material 3b may be, for example, a polymeric material, a lubricating material such as grease, a metal such as lead, copper, a copper alloy, aluminium, an aluminium alloy or a stainless steel grade, or a semiconductor material. The dissimilar material 3b may, according to one example, be a tape such as a conductor tape or a swelling tape, i.e. a water-swellable tape.

[0040] In one example, the insulating plate 3a may be made in the same way as an insulating layer of a high voltage power cable, and thus the insulating plate 3b may for example be cross-linked and degassed after cross-linking.

[0041] In one example, the insulating plate 3a and the dissimilar material 3b may be pressed against each other. The insulating plate 3a and the dissimilar material 3b may be pressed against each other in a press. The pressed test specimen 3 thus obtained may comprise a single layer of the dissimilar material 3a in direct contact with the insulating plate 3b, or the pressed test plate 3 may comprise the insulating plate 3a arranged between two layers of the dissimilar material 3b in a sandwich configuration and in direct contact with the two layers of the dissimilar material 3b.

[0042] The test specimen 3 may be subjected to a heat treatment. Thus, the heat treatment may be performed when the insulating plate 3a and the dissimilar material 3b are in direct or indirect contact with each other. The heat treatment may include heating the test specimen 3 at a temperature in the range of 70-110°C. In one example, the heat treatment includes subjecting the test plate 3 to a temperature cycle between room temperature and a range of 70-110°C.

[0043] The prepared test sample 3 is placed in the electrode system / conductivity cell 1 .

[0044] In step b), a voltage is applied to the test specimen 3. In step b), the electric field on the test specimen 3 may be in the range of 15-50 kV / mm. A voltage may, as an example, be applied to the test sample 3 in step b) for 24 hours.

[0045] In one example, the thickness of the test plate 3 may be 1 mm and the applied voltage may be 30 kV / mm.

[0046] In step c), the conductivity of the test sample 3 is determined based on the measurements taken in step b), i.e. while a voltage is applied to the test sample 3. Thus, the leakage current through the test sample 3 can be determined. From the leakage current the volume resistivity can be determined and based on the volume resistivity the conductivity of the test sample 3 can be determined.

[0047] In step d) the conductivity of the test sample 3 is compared with a reference conductivity, which may be the conductivity of an uncontaminated reference sample of the polymeric electrical insulating material under test. The reference sample is thus a piece of insulating plate of the same polymeric electrical insulating material as the polymeric electrical insulating material currently being evaluated.

[0048] In step e), based on the comparison in step d), it is concluded whether the foreign material 3b is compatible with a polymeric electrical insulating material. The foreign material 3b is compatible with a polymeric electrical insulating material if the electrical conductivity determined in step c) deviates from the reference electrical conductivity by no more than a predefined amount. In particular, it is concluded that the foreign material 3b is compatible with a polymeric electrical insulating material if the electrical conductivity determined in step c) is equal to or greater than the reference electrical conductivity but the deviation is equal to or less than a predefined threshold value. Otherwise, it is concluded that the foreign material 3b is not compatible with a polymeric electrical insulating material.

[0049] Steps d) and / or e) may be computer implemented, eg performed by processing circuitry, or may be performed manually, eg by a test operator.

[0050] Steps a)-e) can be repeated for a number of different test specimens 3, each of which comprises the same polymeric electrical insulating material as the insulating plate 3a, but with a different dissimilar material 3b. For example, the dissimilar material can be a number of different types of tape, such as different types of conductor tape or different types of swelling tape, in order to find candidates for conductor tape or swelling tape compatible with the polymeric electrical insulating material. Thus, a number of test specimens 3 can be created, each of which comprises the same polymeric electrical insulation, but each of which has a different dissimilar material 3 of the same general type, e.g., conductor tape or swelling tape. Furthermore, such testing can be performed for a number of different components of a high voltage power cable, such as lubricating material, metallic water barrier, etc. A number of test specimens can be created for each component to be tested for compatibility with the polymeric electrical insulating material.

[0051] Once a compatible dissimilar material is found based on this method, a high voltage power cable can be constructed using the polymeric electrical insulating material for the insulation layers and compatible dissimilar materials for other components of the high voltage power cable, e.g., conductor tapes, swelling tapes, etc.

[0052] The high voltage power cable thus constructed may be a submarine power cable or an underground power cable.

[0053] The inventive concept has been described above primarily with reference to a few examples, however, as will be readily apparent to those skilled in the art, other embodiments besides those disclosed above are equally possible within the scope of the inventive concept as defined by the appended claims.

Claims

1. 1. A method for determining compatibility between a polymeric electrical insulating material for an insulating layer of a high voltage power cable and a dissimilar material (3b), comprising the steps of: a) preparing a test sample (3) from A) an insulating plate (3a) made of the polymeric electrically insulating material, and B) the dissimilar material (3b); b) applying a voltage to the test sample (3); c) determining the conductivity of the test sample (3) based on the measurements obtained during step b); and d) comparing the conductivity of the test sample (3) with a reference conductivity; e) concluding whether the dissimilar material (3b) is compatible with the polymeric electrical insulating material based on the comparison of step d); A method comprising:

2. 2. The method of claim 1, wherein step e) comprises concluding that the dissimilar material (3b) is compatible with the polymeric electrically insulating material if the deviation of the electrical conductivity from the reference electrical conductivity is no more than a predetermined amount, and concluding that the dissimilar material (3b) is incompatible with the polymeric electrically insulating material otherwise.

3. The method of claim 1 or 2, wherein steps b) and c) are carried out in a conductivity cell.

4. The method according to any one of claims 1 to 3, wherein in step a) the insulating plate (3a) is brought into direct contact with the dissimilar material (3b).

5. The method according to claim 4, wherein step a) further comprises pressing the insulating plate (3a) and the dissimilar material (3b) together in a press.

6. 5. The method according to claim 4, wherein step a) comprises heat treating the insulating plate (3a) and the dissimilar material (3b) when the insulating plate (3a) and the dissimilar material (3b) are in direct contact.

7. The method of claim 6, wherein the heat treatment comprises heating at a temperature in the range of 70 to 110°C.

8. The method according to claim 7, wherein said heat treatment comprises subjecting said insulating plate (3a) and said dissimilar material (3b) to a temperature cycle between room temperature and said temperature in the range of 70-110°C.

9. The method of any one of claims 1 to 8, wherein the reference conductivity is the conductivity of an uncontaminated reference sample of the polymeric electrically insulating material.

10. The method according to any one of the preceding claims, wherein the electric field on the test specimen (3) in step b) is in the range of 15-50 kV / mm.

11. The method according to any one of the preceding claims, wherein the insulating plate (3a) has a thickness in the range of 0.5 to 2 mm.

12. The method of any one of claims 1 to 11, wherein the dissimilar material is one of a polymeric material, a lubricious material, a metal, and a semiconductor material.

13. The method according to any one of claims 1 to 11, wherein the dissimilar material is a conductor tape or a swelling tape.

14. The method of any one of claims 1 to 13, wherein the polymeric electrically insulating material is a DC insulating material.

15. The method of claim 14 , wherein the DC insulating material is designed for voltages greater than 300 kV.

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