CN111505472A - A kind of preparation method of thermoplastic insulation sample for electrical tree degradation experiment - Google Patents

Abstract

The invention belongs to the technical field of electrical tree resistance research of thermoplastic cable insulating materials, and relates to a method for preparing a thermoplastic insulating sample for electrical tree deterioration experiments. It includes four steps: single-piece hot pressing, needle sticking, secondary hot pressing, and sample taking. In the invention, the experimental sample is subjected to secondary hot pressing by a self-made electrical branch pressing device, and the obtained electrical branch experimental sample has a thinner thickness and can be applied to insulating materials with lower light transmittance. The needle electrode is effectively fixed, ensuring the dielectric strength required in the electrical tree experiment.

Description

A kind of preparation method of thermoplastic insulation sample for electrical tree degradation experiment

technical field

The invention belongs to the technical field of electrical tree resistance research of thermoplastic cable insulating materials, and relates to a method for preparing a thermoplastic insulating sample for electrical tree deterioration experiments.

Background technique

Thermoplastic cable insulation represented by polypropylene has gradually been used in high-voltage power cables due to its advantages of being free from cross-linking and recyclability. In the actual operation of the power cable, due to the inevitable occurrence of impurities or defects inside the cable, the insulating layer is prone to local electric field concentration and gradually induces electrical tree branches. In addition, the long-term aging of the thermoplastic insulated cable by electricity, heat and other factors will also produce electrical trees. For thermoplastic insulating materials, it is of great significance to evaluate its electrical tree resistance performance and to grasp the initiation and growth mechanism of its electrical tree for evaluating the reliability and safety of power cable systems.

The electrical branch samples used in the laboratory studies were all prepared by the experimental method of melting the pins. The method of melting the needle is to heat the insulating material to be tested to a molten state, insert the needle into the sample and cool it to form a usable high-voltage needle electrode, and paste the copper foil on the other side of the sample as the ground electrode. This method can effectively fabricate the needle-plate electrode system that meets the experimental requirements. However, for polypropylene insulating materials, the light transmittance of polypropylene is small, and the experimental samples made by the traditional fusion pin method are thick, and it is difficult to observe the needle tips and induced electrical branches inside the polypropylene samples under the microscope. When the thickness of the experimental sample is reduced, the needle tip inserted in the molten state will be resisted by the polypropylene matrix, and will shift to both sides during the insertion process, thus penetrating the polypropylene, which does not meet the experimental requirements of the needle-plate electrode. Therefore, there is currently a lack of methods for preparing electrical dendritic specimens for opaque thermoplastic materials.

SUMMARY OF THE INVENTION

The purpose of the present invention is to introduce a method for preparing a thermoplastic insulating sample for electrical tree deterioration experiment. Meet the microscope observation of the electric tree experimental platform. At the same time, ensure that the needle electrode is located in the center of the experimental sample, and will not shift to both sides to affect the insulation effect of the high-voltage electrode.

The technical scheme of the present invention is as follows: a method for preparing a thermoplastic insulating sample for electrical tree degradation experiment, comprising four steps of single-piece hot pressing, needle sticking, secondary hot pressing, and sample taking;

1) The single-piece hot pressing step:

Use a single stainless steel plate, put the raw material in the sample tank, place the iron plate between two layers of PET film, place the film and iron plate on the iron plate of the flat vulcanizer, and raise the temperature of the iron plate to At any temperature between 170°C and 210°C, pressure is applied to the whole stacked film and iron plate through a flat vulcanizer, and the pressure is any pressure between 0.1MPa and 20MPa;

Turn off the heating system after holding for more than 5 minutes;

Wait for the sample to cool to room temperature, remove the applied pressure, and take out the stainless steel plate;

Repeat this step for another piece of stainless steel;

2) The needle sticking steps:

For one of the stainless steel plates, insert the needle tail of the needle electrode into the small groove of the stainless steel plate, and place the needle tip on the surface of the sample groove and face the bottom surface of the sample groove;

Fix the needle tail;

Cover the other stainless steel plate above the placement needle, align the two stainless steel plates, and clamp them to fix them;

3) described secondary hot pressing step:

Place the fixed double-layer stainless steel plate on the iron plate of the flat vulcanizer, and cover the upper and lower surfaces of the double-layer stainless steel plate with PET film;

Raise the temperature of the iron plate to any temperature between 170 ℃ and 210 ℃, and apply pressure to the whole stacked film and iron plate through the flat vulcanizer, and the pressure is any pressure between 5MPa and 20MPa;

Turn off the heating system after holding for more than 5 minutes;

Wait for the sample to cool to room temperature, remove the applied pressure, and remove the stainless steel plate.

4) Steps of taking the sample: Use a blade to cut along the two layers of stainless steel plates, take out the sample from between the two layers of stainless steel plates, cut the sample into small pieces that are convenient for experiment by scissors or cutting machine, and put it into the test sample. Sample bags for use in electrical branch experiments.

The upper and lower surfaces of the sample groove are the planes of the sample groove parallel to the thickness surface, and the bottom surface of the sample groove is the thickness surface away from the small strip groove.

The raw material of the invention is thermoplastic insulating cable material.

The cooling method in the present invention cooling to room temperature includes, but is not limited to, cooling at room temperature, accelerated cooling by electric fans, and water cooling, and cooling to room temperature is further expressed as any temperature between room temperature and 100°C.

The thickness of the stainless steel plate of the present invention is below 0.75mm, and its length and width are smaller than the side length of the flat vulcanizer;

It has a sample slot for placing the polypropylene matrix and a small slot for placing the needle tail, wherein the sample slot is a transparent slot that runs through the upper and lower surfaces of the stainless steel plate, and the small slot is an open slot that does not contact the lower surface.

In the present invention, the distance between the bottom surface of the sample groove and the point of the small groove close to the sample groove is determined according to the needle electrode, so that after the needle tail of the needle electrode is attached to the small groove, the needle tip is located in the sample groove, and the needle tip is in the sample groove. The distance between the lower and bottom surfaces of the sample groove complies with the experimental requirements for the distance between the needle and the plate electrode in the electrical tree experiment.

Compared with the sample obtained by the existing fusion pin scheme, the electrical branch experimental sample obtained by the present invention has the following advantages:

1. The thickness of the electrical branch test sample obtained in the present invention is thinner, and can be applied to insulating materials with lower light transmittance, so as to observe accurate needle tip and electrical branch morphology.

2. The needle tip of the electrical branch experimental sample obtained by the present invention is located in the center of the experimental sample and will not be inclined like both sides, which effectively ensures the insulation strength near the needle tip.

3. In the present invention, the experimental sample is subjected to secondary hot pressing through a self-made electrical branch pressing device, and the obtained electrical branch experimental sample has a thinner thickness and can be applied to insulating materials with lower light transmittance. The needle electrode is effectively fixed, ensuring the dielectric strength required in the electrical tree experiment.

Description of drawings

Fig. 1 is a schematic diagram of a stainless steel plate in the preparation device of the present invention: a-front view, b-left view, c-top view.

Fig. 2 is a customized physical diagram of the stainless steel plate of the preparation device of the present invention.

FIG. 3 is a schematic diagram of the experimental sample finally obtained by the preparation method.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

The following presents a brief summary of the invention in order to provide a basic understanding of certain aspects of the invention. The invention provides a sample preparation device and method for electrical tree experiment of thermoplastic insulating materials such as polypropylene, including two aspects: device and method.

The experimental device of the present invention is two layers of identical stainless steel plates and a flat vulcanizer. The main shape requirements of the stainless steel plate are shown in Figure 1, and its main features are the sample groove for placing the polypropylene matrix and the small groove for placing the needle tail. The needle tail here refers to the portion of the cylinder with a larger diameter at the tail of the needle electrode than near the tip of the needle. The upper and lower surfaces of the sample groove described herein are the planes of the sample groove parallel to the thickness surface, and the bottom surface of the sample groove is the thickness surface away from the small strip groove.

The sample groove is a transparent groove running through the upper and lower surfaces of the steel plate, and the small strip groove is an open groove that does not contact the lower surface.

The shape of the sample slot described here is not limited to the cuboid shown in the figure, and can be any three-dimensional figure that meets the requirements of the electrical tree experiment. The number of the small grooves is not limited to the five shown in the figure, and the shape may be a rectangular parallelepiped groove or a semicircular groove. The thickness dimension of a single stainless steel plate is less than 0.75mm, and the length and width of the stainless steel plate are less than the side length of the iron plate of the flat vulcanizer. The distance between the bottom surface of the stainless steel plate sample groove and the point where the small groove is close to the sample groove is determined according to the needle electrode, so that after the needle tail of the needle electrode is attached to the small groove, the needle tip is located in the sample groove, and the needle tip is located in the sample groove. The distance from the bottom surface of the sample tank meets the experimental requirements for the distance between the needle and the plate electrode in the electrical tree experiment.

The experimental method of the present invention comprises the following steps:

(1) Single-piece hot pressing: use a single stainless steel plate, put polypropylene raw material in the sample tank, place the iron plate between two layers of PET film, and place the film and iron plate together in the flat vulcanizer. On the iron plate, raise the temperature of the iron plate to any temperature between 170 ℃ and 210 ℃, and apply pressure to the whole stacked film and iron plate through the flat vulcanizing machine. The pressure is any between 0.1MPa and 20MPa. A pressure. After holding for more than 5min, turn off the heating system, wait for the sample to cool to room temperature, remove the applied pressure, and take out the stainless steel plate. Repeat this round of steps for the other stainless steel plate.

(2) Needle sticking: For one of the stainless steel plates, insert the needle tail of the needle electrode into the small groove of the stainless steel plate, and place the needle tip on the surface of the sample groove and face the bottom surface of the sample groove. Secure the needle tail. Put another stainless steel plate on the top of the needle, align the two stainless steel plates, and clamp them to fix it.

(3) Secondary hot pressing: place the fixed double-layer stainless steel plate on the iron plate of the flat vulcanizer, and cover the upper and lower surfaces of the double-layer stainless steel plate with PET film. Raise the temperature of the iron plate to any temperature between 170 °C and 210 °C, and apply pressure to the whole stacked film and iron plate through a flat vulcanizer, and the pressure is any pressure between 5MPa and 20MPa. After holding for more than 5min, turn off the heating system, wait for the sample to cool to room temperature, remove the applied pressure, and take out the stainless steel plate.

(4) Take the sample: cut along the two layers of stainless steel plate, take out the sample from between the two layers of stainless steel plate, cut the sample into small pieces that are convenient for experiment by scissors or cutting machine, and put it into the sample bag for use in electric branch experiments. The final sample is shown in FIG. 3 .

The sample in the step is not limited to polypropylene, and can be any thermoplastic insulating material.

The cooling methods of Step 1 and Step 3 include, but are not limited to, various cooling methods such as room temperature cooling, accelerated cooling by electric fans, and water cooling.

The cooling to room temperature in the steps 1 and 3 can be further expressed as any temperature between room temperature and 100°C.

A typical production process is as follows:

(1) 50 g of isotactic polypropylene (produced by Borealis) was prepared, placed in a paper bowl and dried in an oven at 160° C. for 24 hours to remove residual moisture in the experimental sample.

(2) Put polypropylene raw material in the sample tank of the stainless steel plate, place the iron plate between two layers of PET films, place the film and the iron plate on the iron plate of the flat vulcanizer, and place the iron plate on the iron plate of the flat vulcanizer. When the temperature rises to 180°C, pressure is applied to the whole stacked film and iron plate through the flat vulcanizer, and the pressure is 10MPa. After holding for 8 min, turn off the heating system, wait for the sample to cool to room temperature, remove the applied pressure, and repeat the same process for another piece of stainless steel plate.

(3) For one of the stainless steel plates, insert the needle tail of the needle electrode into the small groove of the stainless steel plate, and place the needle tip on the surface of the sample groove and face the bottom surface of the sample groove. Secure the needle tail with clear tape. Put another stainless steel plate on top of the needle, align the two stainless steel plates, and fix them with clips.

(4) Place the fixed double-layer stainless steel plate on the iron plate of the flat vulcanizer, and cover the upper and lower surfaces of the double-layer stainless steel plate with PET film. The temperature of the iron plate was raised to 180°C, and pressure was applied to the whole stacked film and iron plate through a flat vulcanizer, and the pressure was 10MPa. After holding for 8 min, turn off the heating system, wait for the sample to cool to room temperature, remove the applied pressure, and take out the stainless steel plate.

(5) Use a blade to cut along the two layers of stainless steel plates, take out the sample from between the two layers of stainless steel plates, cut the sample into small pieces that are convenient for the experiment by scissors or cutting machine, and put it into the sample bag for use in the electric branch experiment.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be an equivalent replacement manner, and all are included within the protection scope of the present invention.

Claims (6)

1. A preparation method of a thermoplastic insulation sample for an electric tree degradation experiment is characterized by comprising the following steps: the method comprises four steps of single-chip hot pressing, needle sticking, secondary hot pressing and sample taking;

1) the single-chip hot pressing step comprises:

using a single stainless steel plate, putting raw materials into a sample groove, placing an iron plate between two layers of PET films, placing the whole body formed by stacking the films and the iron plate on the iron plate of a flat vulcanizing machine, heating the iron plate to any temperature between 170 and 210 ℃, and applying pressure to the whole body formed by stacking the films and the iron plate through the flat vulcanizing machine, wherein the pressure is any pressure intensity between 0.1 and 20 MPa;

keeping for more than 5min, and then closing the heating system;

waiting for the sample to be cooled to room temperature, removing the applied pressure, and taking out the stainless steel plate;

repeating the step for another stainless steel plate;

2) the needle sticking step:

for one stainless steel plate, the needle tail of the needle electrode is embedded into a small groove of the stainless steel plate, and the needle tip is arranged on the surface of a sample in the sample groove and faces to the lower bottom surface of the sample groove;

fixing the needle tail;

covering the other stainless steel plate above the placing needle, aligning and sticking the two stainless steel plates, and clamping to fix the two stainless steel plates;

3) the secondary hot pressing step:

placing the fixed double-layer stainless steel plate on an iron plate of a flat vulcanizing machine, wherein the upper surface and the lower surface of the double-layer stainless steel plate are covered by PET films;

the temperature of the iron plate is raised to any temperature between 170 ℃ and 210 ℃, and the pressure is applied to the whole laminated film and the iron plate through a flat vulcanizing machine, wherein the pressure is any pressure intensity between 5MPa and 20 MPa;

keeping for more than 5min, and then closing the heating system;

waiting for the sample to be cooled to room temperature, removing the applied pressure, and taking out the stainless steel plate;

4) a sample taking step: and taking out the sample from between the two layers of stainless steel plates, shearing the sample into small pieces convenient for experiments, and putting the small pieces into a sample bag for the electric tree experiment.

2. The preparation method of the thermoplastic insulation sample for the electrical tree degradation experiment as claimed in claim 1, wherein the insulation sample comprises: the upper surface and the lower surface of the sample groove are sample groove planes parallel to the thickness surface, and the lower bottom surface of the sample groove is the thickness surface far away from the strip groove.

3. The preparation method of the thermoplastic insulation sample for the electrical tree degradation experiment as claimed in claim 1, wherein the insulation sample comprises: the raw material is thermoplastic insulating cable material.

4. The preparation method of the thermoplastic insulation sample for the electrical tree degradation experiment as claimed in claim 1, wherein the insulation sample comprises: cooling to room temperature includes, but is not limited to, cooling down to room temperature, accelerated cooling with an electric fan, water cooling, and cooling to room temperature is further expressed as any temperature between room temperature and 100 ℃.

5. The preparation method of the thermoplastic insulation sample for the electrical tree degradation experiment as claimed in claim 1, wherein the insulation sample comprises:

the thickness of the stainless steel plate is less than 0.75mm, and the length and the width of the stainless steel plate are less than the side length of the flat vulcanizing machine;

the test tube is provided with a sample groove for placing a polypropylene substrate and a small groove for placing a needle tail, wherein the sample groove is a penetrating groove which penetrates through the upper surface and the lower surface of a stainless steel plate, and the small groove is an open groove which is not in contact with the lower surface.

6. The preparation method of the thermoplastic insulation sample for the electrical tree degradation experiment as claimed in claim 5, wherein the insulation sample is prepared from the following raw materials in parts by weight: the distance between the lower bottom surface of the sample groove and the point of the small groove close to the sample groove is determined according to the needle electrode, so that the needle point is positioned in the sample groove after the needle tail of the needle electrode is pasted with the small groove, and the distance between the needle point and the lower bottom surface of the sample groove meets the experimental requirement on the distance between the needle and the plate electrode in the electrical tree branch experiment.

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