A reliability prediction method for cross-linked polyethylene cable insulation materials

Abstract

The present application belongs to the field of cable technology, and in particular to a reliability prediction method for cross-linked polyethylene cable insulation materials. The present application provides a reliability prediction method for cross-linked polyethylene cable insulation materials, which includes: firstly, obtaining the enthalpy values ​​of the cross-linking reaction exothermic peaks of several groups of cross-linked polyethylene and several groups of cross-linked materials by cross-linking reaction of several groups of cross-linked materials, then establishing a reliability prediction curve for the cross-linked polyethylene cable insulation layer, and finally inputting the cross-linking reaction exothermic enthalpy values ​​of the cross-linked materials to be predicted into the reliability prediction curve for the cross-linked polyethylene cable insulation materials to obtain the elongation under load of the cross-linked polyethylene; utilizing the negative correlation between the enthalpy value of the cross-linking agent and the elongation under load of the polyethylene cable insulation materials, the reliability of the cross-linked polyethylene cable insulation materials can be quickly predicted, which solves the technical problem of the lack of reliability prediction methods for cross-linked polyethylene cable insulation materials in the prior art.

Description

Technical Field

[0001] The present application belongs to the field of cable technology, and in particular relates to a reliability prediction method for a cross-linked polyethylene cable insulation material. Background Art

[0002] Due to its excellent electrical properties, cross-linked polyethylene (XLPE) insulation materials are widely used as insulation materials for long-distance overhead power transmission lines and urban underground cables.

[0003] The preparation method of cross-linked polyethylene is to use the active free radicals generated by the decomposition of the cross-linking agent to connect the linear molecular chains into a cross-linked polyethylene insulation material with a mesh structure and excellent electrical properties. Before the cross-linking agent is used as a cross-linkable granular material to manufacture the cross-linked polyethylene cable insulation layer, the cross-linking agent will spontaneously decompose due to storage temperature and storage time. For example, cross-linking agents such as diisopropylbenzene peroxide need to be stored at low temperature and dark light conditions, and their decomposition half-life decreases exponentially with increasing temperature. Therefore, cross-linked granules under different storage conditions will affect the cross-linking degree of the cross-linking reaction, and the elongation under load of cross-linked polyethylene is closely related to its cross-linking degree, that is, the elongation under load of cross-linked polyethylene prepared from cross-linked granules under different storage conditions is different.

[0004] When cross-linked polyethylene with too high elongation under load is used as the insulation material of the cable insulation layer, the cable insulation layer will be unreliable. The part about thermal elongation test in GB / T 18890.2-2015 stipulates that the elongation under load of XLPE material for 220kV cable insulation shall not exceed 100%. At present, the evaluation method of the reliability of cross-linked polyethylene cable insulation material requires thermal elongation test on the cross-linked polyethylene cable insulation material, and lacks prediction method. Summary of the invention

[0005] In view of this, the present application provides a reliability prediction method for a cross-linked polyethylene cable insulation material. By calculating the enthalpy value of the exothermic peak of the cross-linking reaction of the cross-linkable material and utilizing the negative correlation between the enthalpy value and the elongation under load of the polyethylene cable insulation layer material, the elongation under load of the polyethylene cable insulation material is judged, thereby quickly predicting the reliability of the cross-linked polyethylene cable insulation material, solving the technical problem of the lack of a reliability prediction method for cross-linked polyethylene cable insulation material in the prior art.

[0006] The first aspect of the present application provides a reliability prediction method for a cross-linked polyethylene cable insulation material, comprising the following steps:

[0007] Step 1, a plurality of groups of cross-linkable materials undergo a cross-linking reaction to obtain enthalpy values ​​of exothermic peaks of cross-linking reactions of a plurality of groups of cross-linked polyethylenes and a plurality of groups of cross-linkable materials;

[0008] Step 2, performing a heat extension test on a plurality of groups of cross-linked polyethylene to obtain a plurality of groups of elongation under load of the cross-linked polyethylene;

[0009] Step 3, establishing a reliability prediction curve of a cross-linked polyethylene cable insulation material based on the enthalpy values ​​of the cross-linking reaction exothermic peaks of several groups of cross-linkable materials and the elongation under load of several groups of cross-linked polyethylene;

[0010] Step 4, performing a cross-linking reaction on the cross-linkable material to be predicted, and obtaining a thermal enthalpy value of the cross-linkable material to be predicted at an exothermic peak of the cross-linking reaction;

[0011] Step 5, comparing the thermal enthalpy value of the cross-linkable material to be predicted at the cross-linking reaction exothermic peak with the thermal enthalpy standard value;

[0012] The cross-linkable material contains a cross-linking agent and polyethylene.

[0013] Preferably, after step 5, the method further comprises:

[0014] Step 6: input the enthalpy value of the cross-linking reaction exothermic peak of the cross-linkable material to be predicted into the reliability prediction curve of the cross-linked polyethylene cable insulation material to obtain the elongation under load of the cross-linked polyethylene to be predicted;

[0015] Step 7: Compare the elongation under load of the cross-linked polyethylene to be predicted with the standard value.

[0016] It should be noted that the standard value described in this application can be the standard value of elongation under load (<100%) of XLPE material for 220kV cable insulation specified in the thermal elongation test section of GB / T 18890.2-2015, or it can be a custom value or a standard value defined in other national standards. The standard value of thermal enthalpy in this application is 8.08655 J / g.

[0017] Preferably, the reliability prediction curve of the cross-linked polyethylene cable insulation material is a cross-linked polyethylene elongation prediction curve under load.

[0018] It should be noted that the method for establishing the prediction curve of the elongation under load of the cross-linked polyethylene is based on the thermal enthalpy value as the horizontal axis and the elongation under load of the cross-linked polyethylene as the vertical axis.

[0019] Preferably, the heat enthalpy values ​​of the cross-linking reaction exothermic peaks of the cross-linking reaction of the several groups of cross-linkable materials to obtain the several groups of cross-linked polyethylenes and the several groups of cross-linkable materials include:

[0020] A plurality of groups of cross-linkable materials are subjected to a cross-linking reaction in a differential scanning calorimeter to obtain enthalpy values ​​of exothermic peaks of cross-linking reactions of a plurality of groups of cross-linked polyethylenes and a plurality of groups of cross-linkable materials.

[0021] Preferably, obtaining the enthalpy values ​​of the cross-linking reaction exothermic peaks of the plurality of cross-linkable materials comprises: obtaining the enthalpy values ​​of the cross-linking reaction exothermic peaks of the plurality of cross-linkable materials by using the integral area of ​​the heat flow-time image of a differential scanning calorimeter.

[0022] Preferably, the integral area of ​​the heat flow-time image is calculated by taking the heat flow image before the exothermic peak of the cross-linking reaction as the baseline and taking the intersection point of the baseline and the heat flow curve as the upper and lower limits of the integral.

[0023] Preferably, the cross-linking agent is a peroxide.

[0024] Preferably, the peroxide is dicumyl peroxide (DCP).

[0025] Preferably, the cross-linking reaction of the plurality of groups of cross-linkable materials in a differential scanning calorimeter comprises:

[0026] 5 mg to 10 mg of several groups of cross-linkable materials with a size of 0.5 mm×0.5 mm×0.5 mm were respectively subjected to cross-linking reaction in a differential scanning calorimeter crucible.

[0027] Preferably, placing several groups of cross-linkable materials into a differential scanning calorimeter for cross-linking reaction comprises: after purging the differential scanning calorimeter with nitrogen, placing 5 mg to 10 mg of several groups of cross-linkable materials with a size of 0.5 mm×0.5 mm×0.5 mm in a special crucible for the differential scanning calorimeter for cross-linking reaction.

[0028] Preferably, the purity of the nitrogen is greater than 99.999%.

[0029] In summary, the present application provides a reliability prediction method for cross-linked polyethylene cable insulation materials, the prediction method comprising: firstly, obtaining the enthalpy values ​​of the cross-linking reaction exothermic peaks of several groups of cross-linked polyethylene and several groups of cross-linked materials by subjecting several groups of cross-linkable materials to cross-linking reactions, then establishing a reliability prediction curve for cross-linked polyethylene cable insulation materials, and finally obtaining the enthalpy values ​​of the cross-linking reaction exothermic peaks of the cross-linkable materials to be predicted and inputting them into the reliability prediction curve for cross-linked polyethylene cable insulation materials to obtain the elongation under load of the cross-linked polyethylene; wherein, during the cross-linking reaction of several groups of cross-linkable materials, the cross-linkable material pellets first violently While absorbing heat to melt the polyethylene resin, the cross-linking agent DCP gradually decomposes. When the temperature further rises, the cross-linking reaction begins, and a relatively weak cross-linking reaction exothermic peak appears in the heat flow curve, and its intensity is positively correlated with the degree of completion of the cross-linking reaction. Therefore, the activity of different cross-linkable materials can be evaluated by calculating the enthalpy value of the cross-linking reaction exothermic peak during the heating process. Cross-linkable materials with different activities will affect the cross-linking degree of the cross-linking reaction, and the elongation under load of cross-linked polyethylene is closely related to its cross-linking degree, and is in direct proportion. That is, the lower the activity of the cross-linked pellets, the greater the elongation under load of the cross-linked polyethylene. Therefore, the present application calculates the enthalpy value of the cross-linking agent at the exothermic peak of the cross-linking reaction, and utilizes the negative correlation between the enthalpy value of the cross-linking agent and the elongation under load of the polyethylene cable insulation material to determine the elongation under load of the polyethylene cable insulation material. When the elongation under load is lower than the standard value, it is determined that the cross-linked polyethylene cable insulation material prepared with this cross-linked polyethylene is unreliable. There is no need to conduct experiments such as thermal extension again, and the reliability of the cross-linked polyethylene cable insulation material can be quickly predicted, thereby solving the technical problem of the lack of a reliability prediction method for cross-linked polyethylene cable insulation material in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor.

[0031] Figure 1 A schematic flow chart of a reliability prediction method for a cross-linked polyethylene cable insulation material provided in Example 3 of the present application;

[0032] Figure 2 A schematic diagram of a method for calculating the enthalpy value of a cross-linkable material at an exothermic peak of a cross-linking reaction provided in Example 1 of the present application;

[0033] Figure 3 A schematic diagram of a reliability prediction curve of a cross-linked polyethylene cable insulation material is established for Example 2 of the present application. DETAILED DESCRIPTION

[0034] The present application provides a reliability prediction method for a cross-linked polyethylene cable insulation material. The elongation of the polyethylene cable insulation material under load is judged by the enthalpy value of the exothermic peak of the cross-linking reaction of the cross-linkable material and the relationship between the enthalpy value of the cross-linkable material and the elongation of the polyethylene cable insulation material under load, thereby quickly predicting the reliability of the cross-linked polyethylene cable insulation material, solving the technical problem of the lack of a reliability prediction method for the cross-linked polyethylene cable insulation material in the prior art.

[0035] The technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0036] Wherein, the reagents or raw materials used in the following examples are all commercially available or homemade.

[0037] Example 1

[0038] This embodiment 1 provides a method for calculating the enthalpy value of a cross-linkable material at an exothermic peak of a cross-linking reaction, comprising the following steps:

[0039] 1.1. Cut several groups of cross-linkable pellets into 0.5mm×0.5mm×0.5mm chips, and then place the cut chips in a special aluminum crucible for DSC experiment. The mass of material required for each DSC experiment is 5mg~10mg. When placing the chips, ensure that they are in good contact with the bottom of the crucible. Cover the crucible with a lid and press and package to complete the sample preparation required for the DSC experiment;

[0040] 1.2. Place the crucible containing the cross-linkable material and the reference crucible (empty crucible) on the sample holder in the DSC experimenter. The experimental procedure includes two heating processes (the second heating process confirms the first experimental effect). The temperature is raised from 30°C to 220°C in both heating processes, and the heating rate is 10°C / min. The heat flow through the sample and the heat flow through the empty crucible are measured during the heating process, and finally the heat flow through the cross-linkable material itself is obtained;

[0041] 1.3. Use the DSC instrument to measure the heat flow data of the sample when it is heated for the first time and draw a heat flow-time graph to calculate the exothermic enthalpy of the cross-linking reaction;

[0042] Taking the heat flow image before the cross-linking reaction exothermic peak as the baseline, and the tangent point between the baseline and the heat flow curve as the upper and lower limits of integration, the area within the integrated closed region can be obtained to obtain the cross-linking reaction exothermic enthalpy of the cross-linkable material during the entire heating process, as shown in the following appendix to the specification: Figure 2 Inner shaded area shown;

[0043] The sample mass should be weighed accurately to 0.01 mg, and the mass difference between the new pellets and the pellets after storage should be less than 5%. At the same time, the DSC tester should ensure that the nitrogen (purity ≥ 99.999%) is purged in the environment to avoid oxidation reactions during the melting and crystallization of the sample, which may affect the experimental accuracy. If the cross-linking reaction exothermic enthalpy calculated by the heat flow curve during the second heating process of the same sample is greater than 0.1 J / g, it means that the cross-linkable material in the sample is not fully cross-linked during the first heating process, and the experiment needs to be repeated.

[0044] Example 2

[0045] This embodiment 2 provides an embodiment of establishing a reliability prediction curve of a cross-linked polyethylene cable insulation material based on the thermal enthalpy value of the cross-linked material at the exothermic peak of the cross-linking reaction and the elongation under load of the cross-linked material:

[0046] Step 1, cross-linking reaction of new pellets, 220kV high-voltage cross-linked cable insulation layer cross-linkable materials stored for one year, five years and ten years in a differential scanning calorimeter to obtain cross-linked polyethylene prepared from new pellets, cross-linkable materials stored for one year, five years and ten years and enthalpy values ​​of cross-linking reaction exothermic peaks of new pellets, cross-linkable materials stored for one year, five years and ten years, wherein the calculation of the enthalpy value of the cross-linking material at the cross-linking reaction exothermic peak refers to Example 1, and the specific values ​​are shown in Table 1;

[0047] Step 2, the cross-linked polyethylene prepared from the new pellets, the cross-linked materials stored for one year, five years and ten years is subjected to a heat extension test according to the national standard GB / T 18890.2-2015, and the specific values ​​are shown in Table 2;

[0048]

[0049] Table 1

[0050]

[0051] Table 2

[0052] It can be seen from Table 1-2 that as the storage time increases, the exothermic peak of the cross-linking reaction of the cross-linkable material measured in the DSC experiment weakens and the heat release gradually decreases. When the storage time reaches 5 years, the measured exothermic enthalpy of the cross-linking reaction of the cross-linkable material decreases by about 30%. This is because during long-term storage, the DCP in the cross-linkable material gradually decomposes and the activity of the cross-linkable material decreases, resulting in insufficient cross-linking reaction of the cross-linkable material when the temperature is raised to the cross-linking temperature. At the same time, it can be seen from the results of the thermal extension experiment in Table 2 that with the extension of the storage time, the elongation under load of the cross-linkable material measured in the thermal extension experiment gradually increases, that is, the elongation under load of the cross-linked polyethylene can be determined by the enthalpy value obtained by the cross-linking reaction of several groups of cross-linked materials in a differential scanning calorimeter. The enthalpy value is negatively correlated with the elongation under load of the cross-linked polyethylene. Therefore, the reliability prediction curve of the cross-linked polyethylene cable insulation material can be established based on the enthalpy value of the cross-linking reaction exothermic peak of the new pellets, the cross-linked materials stored for one year, five years and ten years, and the elongation under load of several groups of cross-linked polyethylene. According to the existing experimental data, it can be obtained Figure 3 The reliability prediction curve is shown in Figure 2. Figure 3 It can be seen that the elongation under load and the thermal enthalpy value of cross-linked polyethylene should conform to a linear relationship, and the characteristic equation of the elongation under load and the thermal enthalpy value can be obtained by curve fitting. The horizontal dotted line in the figure is the standard line of 100% elongation under load, and its intersection with the fitted straight line in the figure is 8.08655 J / g. Therefore, it can be considered that in this example, when the exothermic enthalpy value of the cross-linking reaction of the cross-linkable material is greater than 8.08655 J / g, the activity of the cross-linkable material still meets the required performance requirements, and the reliability of the cross-linked polyethylene cable insulation material made therefrom meets the national standard.

[0053] Example 3

[0054] This embodiment 3 provides a reliability prediction method for a cross-linked polyethylene cable insulation material, comprising the following steps:

[0055] Step 1, crosslinking reaction is carried out on new pellets, crosslinkable materials stored for one year, five years and ten years to obtain four groups of enthalpy values ​​of crosslinking reaction exothermic peaks of crosslinked polyethylene and crosslinkable materials, wherein the calculation of the enthalpy value of the crosslinking material at the crosslinking reaction exothermic peak is based on Example 1, and the specific values ​​are shown in Table 1;

[0056] Step 2: Perform heat extension experiments on new pellets, cross-linked polyethylene stored for one year, five years and ten years to obtain the elongation under load of new pellets, cross-linked polyethylene stored for one year, five years and ten years. For specific values ​​of the elongation under load, see Table 2.

[0057] Step 3, establishing a reliability prediction curve of cross-linked polyethylene cable insulation material based on the enthalpy values ​​of the cross-linking reaction exothermic peaks of several groups of cross-linkable materials and several groups of elongations of cross-linked polyethylene under load; wherein the enthalpy value is negatively correlated with the elongation of the cross-linked polyethylene under load, and thus a reliability prediction curve of cross-linked polyethylene cable insulation material can be established based on the enthalpy values ​​of the cross-linking reaction exothermic peaks of new pellets, cross-linkable materials stored for one year, five years, and ten years, and several groups of elongations of cross-linked polyethylene under load.

[0058] Step 4: The cross-linkable material to be predicted undergoes a cross-linking reaction to obtain a thermal enthalpy value of the cross-linkable material to be predicted at an exothermic peak of the cross-linking reaction; wherein the cross-linkable material to be predicted is a cross-linked material stored for any time, at any temperature, or under other storage conditions.

[0059] Step 5, the enthalpy value of the cross-linking reaction exothermic peak of the cross-linkable material to be predicted is input into the reliability prediction curve of the cross-linked polyethylene cable insulation material to obtain the elongation under load of the cross-linked polyethylene to be predicted;

[0060] It should be noted that in the process of heating the cross-linked pellets, before the temperature is raised to 110°C, the pellets absorb heat violently, resulting in an obvious endothermic peak in the DSC heat flow curve. At this stage, the polyethylene resin in the cross-linkable material melts and the cross-linking agent DCP gradually decomposes. When the temperature is further increased, the cross-linking reaction begins, and a relatively weak cross-linking reaction exothermic peak appears in the heat flow curve, and its intensity is positively correlated with the degree of completion of the cross-linking reaction. Therefore, the strength of the cross-linking degree of different cross-linkable materials can be evaluated by calculating the enthalpy value of the cross-linking reaction exothermic peak during the heating process, and then the thermal extension properties of the XLPE material can be predicted. Compared with the prior art, the present invention proposes to use DSC experiments to link the cross-linking reaction exothermic enthalpy of the cross-linkable material with the thermal extension properties of the obtained XLPE material, and flexibly and quickly realizes the prediction of the reliability of cross-linked polyethylene.

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A reliability prediction method for cross-linked polyethylene cable insulation material, characterized in that: The following steps are involved: Step 1, a plurality of groups of cross-linkable materials undergo a cross-linking reaction to obtain enthalpy values ​​of exothermic peaks of cross-linking reactions of a plurality of groups of cross-linked polyethylenes and a plurality of groups of cross-linkable materials; Step 2, performing a heat extension test on a plurality of groups of cross-linked polyethylene to obtain a plurality of groups of elongation under load of the cross-linked polyethylene; Step 3, establishing a reliability prediction curve of a cross-linked polyethylene cable insulation material based on the enthalpy values ​​of the cross-linking reaction exothermic peaks of several groups of cross-linkable materials and the elongation under load of several groups of cross-linked polyethylene; Step 4, performing a cross-linking reaction on the cross-linkable material to be predicted, and obtaining a thermal enthalpy value of the cross-linkable material to be predicted at an exothermic peak of the cross-linking reaction; Step 5, comparing the thermal enthalpy value of the cross-linkable material to be predicted at the exothermic peak of the cross-linking reaction with the thermal enthalpy standard value; the cross-linking material is a cross-linking agent and polyethylene; Step 6: input the enthalpy value of the cross-linkable material to be predicted at the exothermic peak of the cross-linking reaction into the reliability prediction curve of the cross-linked polyethylene cable insulation material to obtain the elongation under load of the cross-linked polyethylene to be predicted; Step 7, comparing the elongation under load of the cross-linked polyethylene to be predicted with the standard value; The heat enthalpy values ​​of the exothermic peaks of the cross-linking reaction of the plurality of groups of cross-linkable materials to obtain the plurality of groups of cross-linked polyethylenes and the plurality of groups of cross-linkable materials include: The plurality of groups of cross-linked materials are subjected to a cross-linking reaction in a differential scanning calorimeter to obtain enthalpy values ​​of exothermic peaks of cross-linking reactions of the plurality of groups of cross-linked polyethylenes and the plurality of groups of cross-linkable materials; The step of obtaining the enthalpy values ​​of the cross-linking reaction exothermic peaks of the plurality of cross-linkable materials comprises: obtaining the enthalpy values ​​of the cross-linking reaction exothermic peaks of the plurality of cross-linkable materials by using the integral area of ​​the heat flow-time image of the differential scanning calorimeter; The method for confirming the integral area of ​​the heat flow-time image is: taking the heat flow image before the exothermic peak of the cross-linking reaction as the baseline, and taking the intersection point of the baseline and the heat flow curve as the upper and lower limits of the integral.

2. A reliability prediction method for cross-linked polyethylene cable insulation material according to claim 1, characterized in that: The cross-linking agent is peroxide.

3. A reliability prediction method for cross-linked polyethylene cable insulation material according to claim 2, characterized in that: The peroxide is dicumyl peroxide.

4. A reliability prediction method for cross-linked polyethylene cable insulation material according to claim 1, characterized in that: The cross-linking reaction of the plurality of cross-linkable materials in the differential scanning calorimeter comprises: placing 5 mg to 10 mg of the plurality of cross-linkable materials with a size of 0.5 mm×0.5 mm×0.5 mm in the crucible of the differential scanning calorimeter respectively for cross-linking reaction.

5. A reliability prediction method for cross-linked polyethylene cable insulation material according to claim 4, characterized in that: The method of placing several groups of cross-linkable materials into a differential scanning calorimeter for cross-linking reaction comprises: after purging the differential scanning calorimeter with nitrogen, placing 5 mg to 10 mg of several groups of cross-linkable materials with a size of 0.5 mm×0.5 mm×0.5 mm into the crucible of the differential scanning calorimeter for cross-linking reaction.

6. A reliability prediction method for cross-linked polyethylene cable insulation material according to claim 5, characterized in that: The purity of the nitrogen is greater than 99.999%.

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