阅读说明：本技术 一种高压交流电缆绝缘用预交联料存储寿命检测方法 (Method for detecting storage life of pre-crosslinked material for high-voltage alternating-current cable insulation ) 是由 黎小林 傅明利 侯帅 惠宝军 朱闻博 伍国兴 谢宏 陈潇 徐曙 冯宾 张逸凡 于 2020-11-11 设计创作，主要内容包括：本发明公开一种高压交流电缆绝缘用预交联料存储寿命检测方法,包括：取新预交联料压片得交联聚乙烯,测量其交联度、力学特性及介电性能,将测量结果作为参考值；通过加热加速老化预交联料,并测量加速老化后的预交联料压片得的交联聚乙烯的交联度、力学特性及介电性能,将该测量结果与参考值对比,当结果落在误差允许范围内时,根据预设步长加长加热时间,直到结果不全落在误差允许范围内；根据交联剂分解率计算公式与半衰期随温度变化计算公式,将加热时间减去步长后转化为常温时间,得到预交联料存储寿命,本发明通过加热加速老化预交联料,取交联度、力学特性及介电性能作为活性标准,根据交联剂分解率和半衰期计算得预交联料存储寿命。(The invention discloses a method for detecting the storage life of a pre-crosslinked material for high-voltage alternating-current cable insulation, which comprises the following steps: tabletting the new pre-crosslinked material to obtain crosslinked polyethylene, measuring the crosslinking degree, the mechanical property and the dielectric property of the crosslinked polyethylene, and taking the measurement result as a reference value; heating and accelerating aging of the pre-crosslinked material, measuring the crosslinking degree, mechanical properties and dielectric properties of crosslinked polyethylene obtained by tabletting the accelerated aged pre-crosslinked material, comparing the measurement result with a reference value, and lengthening the heating time according to a preset step length when the result falls within an error allowable range until the result does not fall within the error allowable range; according to a cross-linking agent decomposition rate calculation formula and a half-life period along with temperature change calculation formula, the heating time is converted into normal temperature time after subtracting the step length, and the storage life of the pre-cross-linking material is obtained.)

1. A method for detecting the storage life of a pre-crosslinked material for high-voltage alternating-current cable insulation is characterized by comprising the following steps:

tabletting a pre-crosslinking material to obtain reference crosslinked polyethylene, wherein the pre-crosslinking material is a new non-aged pre-crosslinking material;

measuring the crosslinking degree of the reference crosslinked polyethylene to obtain crosslinking degree reference data;

testing the mechanical property of the reference crosslinked polyethylene to obtain mechanical property reference data;

heating the pre-crosslinking material at a preset temperature for a preset time to obtain an accelerated aging pre-crosslinking material;

tabletting the pre-crosslinked material with accelerated aging to obtain crosslinked polyethylene;

measuring the crosslinking degree of crosslinked polyethylene prepared from the accelerated aging pre-crosslinking material to obtain crosslinking degree detection data;

testing the mechanical property of the crosslinked polyethylene prepared from the accelerated aging pre-crosslinking material to obtain mechanical property detection data;

comparing the cross-linking degree reference data with the cross-linking degree detection data to obtain a first comparison result;

comparing the mechanical characteristic reference data with the mechanical characteristic detection data to obtain a second comparison result;

when the first comparison result falls within a first error allowable range and the second comparison result falls within a second error allowable range, extending the heating preset time according to a preset step length, retesting the crosslinking degree detection data and the mechanical property detection data, and comparing the crosslinking degree detection data with the crosslinking degree reference data and the crosslinking degree detection data until the first comparison result does not fall within the first error allowable range or the second comparison result does not fall within the second error allowable range;

when the first comparison result does not fall within the first error allowable range or the second comparison result does not fall within the second error allowable range, recording the heating time, wherein the accelerated aging pre-crosslinking material is an overdue pre-crosslinking material;

obtaining a calculation formula based on the decomposition rate of the cross-linking agent in the pre-cross-linked material:

wherein τ is the half-life of the crosslinking agent at the temperature T and T is the time elapsed for the crosslinking agent to remain at the temperature T;

and (3) converting the heating time of the overdue pre-crosslinking material into normal temperature time after subtracting the step length by combining a calculation formula of the half-life period of the crosslinking agent along with the temperature change, so as to obtain the storage life of the pre-crosslinking material.

2. The method for detecting the storage life of a pre-crosslinked material for insulation of a high-voltage AC cable according to claim 1, further comprising,

measuring the dielectric property of the reference crosslinked polyethylene to obtain dielectric property reference data;

measuring the dielectric property of the crosslinked polyethylene prepared from the overdue pre-crosslinked material to obtain dielectric property detection data;

and comparing the dielectric property reference data with the dielectric property detection data to verify the deterioration of the overdue pre-crosslinking material.

3. The method for detecting the storage life of the pre-crosslinked material for high-voltage alternating-current cable insulation according to claim 1, wherein the crosslinking degree of the reference crosslinked polyethylene is measured to obtain crosslinking degree reference data, specifically:

and measuring the crosslinking degree of the reference crosslinked polyethylene through DSC test and thermal extension test to obtain crosslinking degree reference data.

4. The method for detecting the storage life of the pre-crosslinked material for insulation of the high-voltage alternating-current cable according to claim 1, wherein the crosslinking degree of the crosslinked polyethylene prepared from the accelerated aging pre-crosslinked material is measured to obtain crosslinking degree detection data, and specifically comprises the following steps:

and measuring the crosslinking degree of the crosslinked polyethylene prepared from the accelerated aging pre-crosslinking material through DSC test and thermal extension test to obtain crosslinking degree detection data.

5. The method for detecting the storage life of the pre-crosslinked material for insulation of the high-voltage alternating-current cable according to claim 1, wherein the mechanical properties comprise: tensile strength, modulus of elasticity, and elongation at break.

6. The method for detecting the storage life of the pre-crosslinked material for insulation of the high-voltage alternating-current cable according to claim 1, wherein the dielectric properties comprise: direct current conductivity, alternating current breakdown field strength, relative dielectric constant, and dielectric loss tangent.

Technical Field

The invention relates to the field of performance test of high-voltage alternating-current cable insulation materials, in particular to a method for detecting the storage life of a pre-crosslinked material for high-voltage alternating-current cable insulation.

Background

The insulating layer of the high-voltage alternating-current cable takes crosslinked polyethylene as a main insulating material, the most widely used method for realizing polyethylene crosslinking is a chemical crosslinking method, the principle is that the polyethylene with a linear structure is crosslinked into crosslinked polyethylene with a net structure by means of free radicals generated by thermal decomposition of a peroxide crosslinking agent, and the crosslinked extruded material is a crosslinked polyethylene pre-crosslinking material. The production process of the pre-crosslinking material comprises the steps of adding 0.2 mass percent of antioxidant into polyethylene at the mixing temperature of 130-250 ℃, uniformly mixing in a screw mixer, adding 2 mass percent of crosslinking agent, usually Dicumyl Peroxide (DCP), at the mixing temperature of 110-120 ℃, uniformly mixing, extruding and pelletizing by a screw extruder, and dehydrating by a vibrating screen to form the finished product of the pre-crosslinking material.

The crosslinking agent DCP is a strong oxidant, and a certain amount of DCP can be spontaneously decomposed in the storage process before the pre-crosslinked particles are put into the cable manufacturing link, so that the content of DCP in the pre-crosslinked material is reduced. In the formal crosslinking extrusion of the pre-crosslinking material, DCP is an initiator of crosslinking reaction, and has obvious influence on the efficiency of the crosslinking reaction and the crosslinking density of a final product, so that the pre-crosslinking materials with different storage times have activity difference due to different DCP contents, and the performance of the finished cable insulation layer is directly influenced.

Therefore, the activity and shelf life of the pre-crosslinking material is critical to the performance of the cable insulation. However, at present, no mature detection method is available for judging the activity and the storage life of the pre-crosslinking material for the high-voltage alternating-current cable insulation, and no determination method for the aging time and the temperature required by the accelerated aging test of the pre-crosslinking material is available.

Disclosure of Invention

The embodiment of the invention provides a method for detecting the storage life of a pre-crosslinked material for high-voltage alternating-current cable insulation, which can determine the aging time and temperature required by an accelerated aging test on the pre-crosslinked material and detect the storage life of the pre-crosslinked material for the high-voltage alternating-current cable insulation.

An embodiment of the invention provides a method for detecting storage life of a pre-crosslinked material for insulation of a high-voltage alternating-current cable, which comprises the following steps:

tabletting a pre-crosslinking material to obtain reference crosslinked polyethylene, wherein the pre-crosslinking material is a new non-aged pre-crosslinking material;

measuring the crosslinking degree of the reference crosslinked polyethylene to obtain crosslinking degree reference data;

testing the mechanical property of the reference crosslinked polyethylene to obtain mechanical property reference data;

heating the pre-crosslinking material at a preset temperature for a preset time to obtain an accelerated aging pre-crosslinking material;

tabletting the pre-crosslinked material with accelerated aging to obtain crosslinked polyethylene;

measuring the crosslinking degree of crosslinked polyethylene prepared from the accelerated aging pre-crosslinking material to obtain crosslinking degree detection data;

testing the mechanical property of the crosslinked polyethylene prepared from the accelerated aging pre-crosslinking material to obtain mechanical property detection data;

comparing the cross-linking degree reference data with the cross-linking degree detection data to obtain a first comparison result;

comparing the mechanical characteristic reference data with the mechanical characteristic detection data to obtain a second comparison result;

when the first comparison result falls within a first error allowable range and the second comparison result falls within a second error allowable range, extending the heating preset time according to a preset step length, retesting the crosslinking degree detection data and the mechanical property detection data, and comparing the crosslinking degree detection data with the crosslinking degree reference data and the crosslinking degree detection data until the first comparison result does not fall within the first error allowable range or the second comparison result does not fall within the second error allowable range;

when the first comparison result does not fall within the first error allowable range or the second comparison result does not fall within the second error allowable range, recording the heating time, wherein the accelerated aging pre-crosslinking material is an overdue pre-crosslinking material;

obtaining a calculation formula based on the decomposition rate of the cross-linking agent in the pre-cross-linked material:

wherein τ is the half-life of the crosslinking agent at the temperature T and T is the time elapsed for the crosslinking agent to remain at the temperature T;

and (3) converting the heating time of the overdue pre-crosslinking material into normal temperature time after subtracting the step length by combining a calculation formula of the half-life period of the crosslinking agent along with the temperature change, so as to obtain the storage life of the pre-crosslinking material.

Further, measuring the dielectric property of the reference crosslinked polyethylene to obtain dielectric property reference data, measuring the dielectric property of the crosslinked polyethylene prepared by the overdue pre-crosslinked material to obtain dielectric property detection data, and comparing the dielectric property reference data with the dielectric property detection data to verify the deterioration of the overdue pre-crosslinked material.

Wherein the degree of crosslinking of the reference crosslinked polyethylene and the degree of crosslinking of the crosslinked polyethylene prepared from the accelerated aging pre-crosslink are measured by DSC test and thermal elongation test.

Moreover, the mechanical properties include: tensile strength, modulus of elasticity, and elongation at break; the dielectric properties include: direct current conductivity, alternating current breakdown field strength, relative dielectric constant, and dielectric loss tangent.

Compared with the prior art, the embodiment of the invention provides the method for detecting the storage life of the pre-crosslinking material for the insulation of the high-voltage alternating-current cable, the new pre-crosslinking material is tabletted to obtain crosslinked polyethylene, the crosslinking degree, the mechanical property and the dielectric property of the crosslinked polyethylene are measured, and the measurement result is used as a reference value; heating and accelerating aging of the pre-crosslinked material, measuring the crosslinking degree, mechanical properties and dielectric properties of crosslinked polyethylene obtained by tabletting the accelerated aged pre-crosslinked material, comparing the measurement result with a reference value, and lengthening the heating time according to a preset step length when the result falls within an error allowable range until the result does not fall within the error allowable range; and (3) according to a cross-linking agent decomposition rate calculation formula and a half-life period along with temperature change calculation formula, converting the heating time minus the step length into the normal temperature time to obtain the storage life of the pre-cross-linked material. According to the invention, the accelerated aging is carried out by adopting a heating mode, the test period is shortened, the material consumption is reduced, the crosslinking degree and the mechanical property of the crosslinked polyethylene prepared by measuring the pre-crosslinking material with accelerated aging are compared with those of reference crosslinked polyethylene, and the aging time and temperature required by the accelerated aging test of the pre-crosslinking material are determined by combining the decomposition rate of a crosslinking agent in the pre-crosslinking material and the rule that the half-life period changes along with the temperature change, so that the storage life of the pre-crosslinking material is detected.

Drawings

Fig. 1 is a schematic flow chart of a method for detecting a storage life of a pre-crosslinked material for insulation of a high-voltage ac cable according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

To illustrate the determination and calculation of the accelerated aging test parameters, the theory of the half-life and decomposition rate of DCP, a short-cut one, is presented here.

The research shows that the crosslinking of polyethylene is a first-order reaction, and the reaction kinetic equation is

In the formula (1), v is a reaction rate, C is a DCP concentration, and K is a reaction rate constant.

Can be solved by the formula (1):

C＝C₀·e^-K·t，(2)

c in formula (2)₀Is the initial concentration of DCP in the pre-crosslinking material.

Therefore, the calculation formula of the decomposition rate X of the DCP in the pre-crosslinking material at the moment t can be obtained through a reaction kinetics theory as follows:

formula (3) shows that the decomposition rate of DCP increases with longer storage time, and therefore influences the reactivity of the precrosslinker. The calculation formula of the reaction rate constant K can be obtained from the Arrhenius formula:

in the formula (4), R is a gas constant, E is an apparent activation energy, and A is a frequency factor. Thus, at different temperatures, the ratio of the reaction rate constants is:

the decomposition half-life τ of DCP is defined as the time required for the DCP concentration to drop to half the initial concentration at some ambient temperature. Substituting tau into the calculation formula of the decomposition rate of the DCP can be solved:

the decomposition rate calculation formula (3) is substituted with the formula (6) to obtain:

meanwhile, the half-life period of the DCP in the pre-crosslinking material at other temperatures is calculated by combining a relation (6) of the decomposition half-life period tau and the reaction rate constant K of the DCP and a calculation formula (5) of the ratio of the reaction rate constant with the measured half-life period of the DCP at a certain temperature, wherein the calculation formula is as follows:

in the formula (8) < tau >₀To know a certain temperature T₀(iv) the half-life of DCP.

According to the existing experimental data and conclusions, the half-life of DCP decomposition at normal temperature (30 ℃) can be calculated to be 490 years, and the half-lives at other temperatures can also be calculated, and the complete calculation result is shown in the following table 1.

TABLE 1 decomposition half-life of DCP in precrosslinked charge at different temperatures

The content of DCP in the pre-crosslinking material can be calculated by combining the data in the table 1 and the calculation formula (7) of the decomposition rate of DCP after being stored for a certain time at room temperature. In order to achieve the same DCP decomposition rate in the accelerated aging test of the pre-crosslinking material and realize the effect of storing the pre-crosslinking material at equivalent room temperature for a corresponding period of time, the problems of the stability of a pre-crosslinking material mixing system and the reasonability of the aging test period should be considered at the same time.

It is added here that increasing the storage temperature does accelerate the spontaneous decomposition of DCP for the purpose of accelerating the aging of the precrosslinking material. But also can affect polyethylene molecules in the pre-crosslinking material, so that the polyethylene molecules can generate weak crosslinking automatically due to the increase of the number of active free radicals in a pre-crosslinking material mixing system, and the subsequent test result is affected. However, since the set accelerated aging test temperature is usually less than the actual crosslinking process temperature (about 180 ℃), the polyethylene crosslinking phenomenon induced during aging is negligible. In addition, from the perspective of the chemical reaction principle, because the crosslinking reaction is an exothermic reaction, the temperature is increased, the reaction balance can be moved to the left, the crosslinking reaction can be inhibited to a certain extent, the proportion of the crosslinking product in the pre-crosslinking material system is reduced, and the influence of the accelerated aging test on the activity of the pre-crosslinking material is considered to be mainly caused by the spontaneous decomposition of DCP rather than the influence on polyethylene molecules.

In conclusion, 70 ℃ is selected as the test temperature of the accelerated aging test. At this temperature, it is shown from table 1 that the half-life of decomposition of DCP is 157 days, and it is found from the calculation of formula (7) that the half-life of storage at 30 ℃ can be equivalently realized by performing accelerated aging for 3.8 hours, and that storage at normal temperature for 10 years can be equivalently realized by performing aging for 77 hours (about 3 days). And the temperature of 70 ℃ is far lower than the temperature of the crosslinking process, so the aging temperature gives consideration to the stability of the pre-crosslinking material system and the reasonability of the test duration.

Referring to fig. 1, a schematic flow chart of a method for detecting a storage life of a pre-crosslinked material for insulation of a high-voltage ac cable according to an embodiment of the present invention is shown. The method comprises the following steps:

s10, tabletting the pre-crosslinked material to obtain the reference crosslinked polyethylene, wherein the pre-crosslinked material is a new pre-crosslinked material which is not aged.

And S11, measuring the crosslinking degree of the reference crosslinked polyethylene to obtain crosslinking degree reference data.

And S12, testing the mechanical property of the reference crosslinked polyethylene to obtain mechanical property reference data.

For example, the steps S10 to S12 may specifically be:

the pre-crosslinked material which is newly delivered from a factory is crosslinked at 180 ℃, a flat vulcanizing machine is used for molding into sheets with the thickness of 0.2mm and 1.0mm, and then a cutter is used for cutting the sheets into round or dumbbell-shaped samples. Wherein the round sample with the thickness of 0.2mm is used for measuring the dielectric property, the dumbbell-shaped sample with the thickness of 1.0mm is used for measuring the thermal extension and the mechanical property, the crosslinking degree of the crosslinked polyethylene sample prepared from the newly-delivered pre-crosslinked material is obtained according to a method for measuring the crosslinking degree by a DSC test in GB/T36965-2018, and the measurement result is used as the standard for subsequently evaluating the activity and the service life of the pre-crosslinked material.

S13, heating the pre-crosslinking material at a preset temperature for a preset time to obtain the pre-crosslinking material with accelerated aging.

S14, tabletting the pre-crosslinked material subjected to accelerated aging to obtain the crosslinked polyethylene.

And S15, measuring the crosslinking degree of the crosslinked polyethylene prepared from the accelerated aging pre-crosslinking material to obtain crosslinking degree detection data.

And S16, testing the mechanical property of the crosslinked polyethylene prepared from the accelerated aging pre-crosslinking material to obtain the detection data of the mechanical property.

Wherein the degree of crosslinking can be measured by DSC test and thermal extension test; mechanical properties include tensile strength, modulus of elasticity and elongation at break; the dielectric properties include direct current conductivity, alternating current breakdown field strength, relative permittivity, and dielectric loss tangent.

For example, the steps S13 to S16 may specifically be:

and carrying out an accelerated aging test on the pre-crosslinked material which is newly delivered. And (3) placing the pre-crosslinked material which is newly delivered into a beaker, placing the beaker into a constant-temperature oven, setting the temperature of the oven to be 70 ℃, carrying out accelerated aging for 3.8 hours, and equivalently storing for half a year at 30 ℃. And standing the aged pre-crosslinked material for 24 hours at room temperature. Then, the tabletting, the crosslinking degree and the mechanical property are tested.

And S17, comparing the cross-linking degree reference data with the cross-linking degree detection data to obtain a first comparison result.

And S18, comparing the mechanical characteristic reference data with the mechanical characteristic detection data to obtain a second comparison result.

And S19, when the first comparison result falls within a first error allowable range and the second comparison result falls within a second error allowable range, prolonging the heating preset time according to a preset step length, retesting the crosslinking degree detection data and the mechanical property detection data, and comparing the crosslinking degree detection data and the mechanical property detection data with the crosslinking degree reference data and the crosslinking degree detection data until the first comparison result does not fall within the first error allowable range or the second comparison result does not fall within the second error allowable range.

And S20, when the first comparison result does not fall within the first error allowable range or the second comparison result does not fall within the second error allowable range, recording the heating time, wherein the pre-crosslinking material with accelerated aging is an expired pre-crosslinking material.

For example, the steps S19 to S20 may specifically be: if the performance measurement result of the aged pre-crosslinked material and the sample is basically unchanged compared with the performance measurement result of a newly-shipped pre-crosslinked material and the sample, the pre-crosslinked material still keeps good activity after being stored at room temperature for half a year, and the storage life at room temperature is longer than half a year.

In order to obtain the storage life of the pre-crosslinked material at normal temperature, aging is carried out for 3.8 hours at 70 ℃ as a step length, namely, the pre-crosslinked material is equivalently stored for half a year at 30 ℃. And gradually prolonging the aging time of the accelerated aging test to obtain the aged pre-crosslinked material with longer equivalent storage time at normal temperature. And (3) after the aging test for prolonging the aging time is completed, tabletting of corresponding materials and testing of the crosslinking degree and the mechanical property of the sample are carried out until the sample with obviously changed properties is obtained.

Furthermore, the test method also comprises the steps of measuring the dielectric property of the reference crosslinked polyethylene to obtain dielectric property reference data, measuring the dielectric property of the crosslinked polyethylene prepared from the overdue pre-crosslinked material to obtain dielectric property detection data, and comparing the dielectric property reference data with the dielectric property detection data to verify the deterioration of the overdue pre-crosslinked material.

S21, obtaining a calculation formula based on the decomposition rate of the cross-linking agent in the pre-cross-linked material:

wherein τ is the half-life of the crosslinking agent at the temperature T and T is the time elapsed for the crosslinking agent to remain at the temperature T;

and S22, converting the heating time of the overdue pre-crosslinking material into normal temperature time after subtracting the step length by combining a calculation formula of the half-life period of the crosslinking agent along with the temperature change, and obtaining the storage life of the pre-crosslinking material.

For example, step S22 may specifically be:

and subtracting a step length of the aging time extension from the accelerated aging time of the sample with obviously changed crosslinking degree and mechanical property, and converting the storage time at 70 ℃ and 30 ℃ to obtain the storage life of the pre-crosslinked material at 30 ℃.

The embodiment of the invention provides a method for detecting the storage life of a pre-crosslinked material for insulation of a high-voltage alternating-current cable, wherein a new pre-crosslinked material is taken for tabletting to obtain crosslinked polyethylene, the crosslinking degree, the mechanical property and the dielectric property of the crosslinked polyethylene are measured, and the measurement result is used as a reference value; heating and accelerating aging of the pre-crosslinked material, measuring the crosslinking degree, mechanical properties and dielectric properties of crosslinked polyethylene obtained by tabletting the accelerated aged pre-crosslinked material, comparing the measurement result with a reference value, and lengthening the heating time according to a preset step length when the result falls within an error allowable range until the result does not fall within the error allowable range; and (3) according to a cross-linking agent decomposition rate calculation formula and a half-life period along with temperature change calculation formula, converting the heating time minus the step length into the normal temperature time to obtain the storage life of the pre-cross-linked material. According to the invention, the test period can be shortened and the material consumption can be reduced by adopting a heating mode to accelerate aging, the crosslinking degree and the mechanical property of crosslinked polyethylene prepared from the pre-crosslinking material with accelerated aging are measured and compared with the crosslinking degree and the mechanical property of reference crosslinked polyethylene, and the aging time and the temperature required by the accelerated aging test of the pre-crosslinking material are determined by combining the decomposition rate of a crosslinking agent in the pre-crosslinking material and the rule that the half-life period changes along with the temperature change, so that the storage life of the pre-crosslinking material is detected.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.