CN104198823A - System for acquiring trap parameters of solid dielectric material - Google Patents

Abstract

The invention discloses a solid dielectric material trap parameter acquisition system, which includes a constant temperature box and a three-electrode corona charging system, a surface potential measurement system, a rotating support system and a temperature control system arranged in the constant temperature box; the three-electrode corona charging system It includes a multi-needle electrode coaxially arranged from top to bottom and a grounded metal disk electrode; the surface potential measurement system includes a capacitive electrostatic probe set on an adjustable insulating fixture; the rotating support system includes an insulating support frame, a metal aluminum plate The upper surface is provided with a metal turntable and a metal heating box; the temperature control system includes a first heating device and a second heating device. The invention can accurately collect trap energy levels and trap density parameters of solid dielectric materials, has the characteristics of wide application range, high measurement accuracy, simple and convenient operation, and is a solid dielectric surface charging phenomenon and its influence on flashover performance along the surface. The research provides an effective analysis method.

Description

A solid dielectric material trap parameter acquisition system

technical field

The invention relates to a device for testing dielectric properties of insulating materials, in particular to a trap parameter acquisition system for solid dielectric materials.

Background technique

At present, polymer insulation materials and oil-impregnated insulation are widely used in the field of electrical insulation because of their good dielectric properties. However, with the improvement of the voltage level of the power system and the development of DC transmission technology, the space charge effect of polymer insulation has become more and more prominent, which leads to the distortion of the electric field inside the polymer material, causing partial discharge and the development of electric trees, resulting in material aging and The problem of insulation failure, how to suppress and eliminate the space charge in the insulation has become a research hotspot in the field of electrical insulation at home and abroad.

At present, there are many studies on the mechanism of polymer aging, among which Kwan-Chi Kao of Canada and Tu Demin of Xi'an Jiaotong University in China proposed the thermal electron-induced polymer degradation theory. Under the action of a high electric field, electrons/holes are injected from the electrode into the polymer through the Schottky effect or the Fowler-Nordheim effect. In the trap state, the average free path of electrons/holes is short, so they are quickly trapped by traps to form space charges. During the trapping/recombination process of space charges, when the charge migrates from a high-energy state to a low-energy state, the excess energy is transferred to another electron in a non-radiative form, making the latter a thermal electron. Hot electrons with sufficient energy will cause molecular degradation to form a large number of macromolecular free radicals, which will further trigger free radical chain reactions and lead to further degradation of polymers. The generation of hot electrons and the energy of hot electrons are determined by the density and depth of traps. Changing the trap depth or density of polymers can change the formation probability and energy of hot electrons. Therefore, measuring and analyzing the trap properties of materials, such as energy level and density, is of great significance for the formation and suppression mechanism of space charge of materials and the characterization and evaluation of the aging state of polymer materials.

On the other hand, in the embedded electrode system, the trap charge injection, transport, recombination, and desorption processes near the electrode will also have an important impact on the flashover phenomenon along the surface. The trapping characteristics and surface charging characteristics of dielectrics have been widely concerned for a long time, and it is believed that they are closely related to the surface flashover characteristics of dielectrics under vacuum conditions.

Based on the above analysis, the trap characteristics significantly affect the dielectric and discharge characteristics of solid dielectric materials, and may become a more intrinsic performance characterization parameter of solid dielectric materials. Therefore, it is very important to measure and analyze the trap parameters of solid insulating materials. meaning. At present, domestic researchers generally obtain the decay current by measuring the isothermal surface potential decay, and then obtain the trap information on the material surface. However, most measurement systems have problems such as uneven system charging effect, insufficient charge injection, and manual operation for measurement records, resulting in large dispersion of measurement results, poor repeatability, and low accuracy.

At present, with regard to the measurement and recording of surface potential, most of them are recorded manually at equal intervals, which is time-consuming and the recording is not accurate enough. After the completion of corona charging, most measurement systems need to manually replace the needle tip with a potential probe to measure the surface potential attenuation. This process takes a long time and it is difficult to measure the instantaneous potential information after the charging is completed.

Sufficient charge injection is the key to accurately measure the trap characteristics of materials. Solid dielectric materials need to be injected at relatively high temperatures (varies with materials, generally 60-80°C). The existing test system has no heating conditions, and it is difficult to realize the preheating of solid dielectric materials, which seriously affects the experimental results.

Contents of the invention

The purpose of the present invention is to provide a solid dielectric material trap parameter acquisition system, which can accurately collect the trap energy level and trap density parameters of the solid dielectric material, and has the characteristics of wide application range, high measurement accuracy, and simple and convenient operation.

The present invention adopts following technical scheme:

A solid dielectric material trap parameter acquisition system, including a constant temperature box and a three-electrode corona charging system, a surface potential measurement system, a rotating support system and a temperature control system arranged in the constant temperature box;

The three-electrode corona charging system includes a multi-needle electrode coaxially arranged from top to bottom and a grounded metal disc electrode. The multi-needle electrode is connected to a DC charging power supply, and the upper surface of the metal disc electrode is used to place the electrode to be tested. In the same way, the metal disc electrode includes copper electrodes and aluminum electrodes that are in contact with each other up and down and are arranged eccentrically;

The surface potential measurement system includes a capacitive electrostatic probe arranged on an adjustable insulating mount, and the output end of the capacitive electrostatic probe is sequentially connected to a signal conditioning circuit and a signal acquisition circuit outside the incubator;

The rotary support system includes an insulating support frame with a metal aluminum plate on the upper surface of the thermostatic box, a metal turntable is arranged on the upper surface of the metal aluminum plate, a metal heating box is arranged on the upper surface of the metal turntable, and the metal disc electrodes are placed on the The upper surface of the metal heating box; when the charge injection of the sample to be tested is performed, the sample to be tested is located under the multi-needle electrode; when the surface potential decay measurement is performed, the sample to be tested is located under the capacitive electrostatic probe;

The temperature control system includes a first heating device arranged in a metal heating box, and a second heating device arranged on an insulating support frame under the metal aluminum plate, and a temperature controller outside the thermostat controls and connects the first heating device and the second heating device. Two heating devices.

The multi-needle electrode adopts stainless steel needles, and the radius of curvature of the needle tip is 5 μm; the outermost needle electrodes in the multi-needle electrode are distributed in a regular hexagon, and each vertex and the midpoint of each side of the regular hexagon are provided with needles. Electrodes, the length of the outermost multiple needle electrodes is 9mm; the multiple needle electrodes in the second outer layer of the multi-needle electrodes are distributed in a regular hexagon, and each vertex and the midpoint of each side of the regular hexagon are provided with needles. The length of the plurality of needle electrodes on the second outer layer is 11 mm; the inner plurality of needle electrodes in the multi-needle electrode are distributed in a regular hexagon, and each vertex of the regular hexagon and the center of the regular hexagon are provided with needle electrodes. The length of multiple needle electrodes is 12mm, and the inner multiple needle electrodes are 40mm away from the upper surface of the sample to be tested; the outermost multiple needle electrodes, the second outer layer multiple needle electrodes and the inner multiple needle electrodes are composed of A regular hexagon with the same center and decreasing side lengths.

Among the metal disk electrodes, the copper electrode has a diameter of 120 mm and a thickness of 10 mm; the aluminum electrode has a diameter of 250 mm and a thickness of 10 mm; the eccentric distance between the copper electrode and the aluminum electrode is 60 mm, and the copper electrode and the aluminum electrode are fixed by bolts.

The adjustable insulating fixing frame includes an insulating fixing frame and a position adjustment mechanism, and the capacitive electrostatic probe is fixed on the position adjustment mechanism.

The metal rotating disk, the metal heating box and the aluminum electrodes in the metal disk electrodes are arranged from bottom to top and fixed by bolts.

The first heating device and the second heating device are connected in parallel and controlled by a temperature controller outside the incubator. The first heating device includes two thermocouples connected in series, and the second heating device adopts a quartz infrared heating tube.

The thermostat is also provided with a humidity control device, and the humidity control device uses a solid desiccant.

Conductive silicone grease is arranged between the copper electrode and the sample to be tested.

The present invention has the following beneficial effects:

The invention can measure the trap energy level and trap density parameters of the solid dielectric material, and can distinguish two kinds of traps, electron type and hole type, and is easy to operate. Wide applicability, the invention is not only suitable for testing the trap characteristics of inorganic insulating materials, such as alumina, machinable ceramics and other insulating materials, but also suitable for testing the trap characteristics of polymer insulating materials and oil-impregnated paper insulation.

The present invention is designed with double heating devices, which are heated in parallel and controlled by an external temperature controller; one of the heating devices is placed in a metal heating box fixedly connected to the metal disc electrode to realize the treatment Direct preheating of the test sample; another heating device is fixed on the insulating support frame under the metal aluminum plate, and the ambient temperature is controlled by heating the surrounding air. The design of the double heating device can realize the direct preheating of the test sample, so that the dielectric material can obtain sufficient charge injection, and at the same time ensure that the temperature distribution in the constant temperature box is relatively uniform, and the control accuracy of the temperature in the constant temperature box is improved.

The metal turntable is placed on a metal aluminum plate supported by an insulating support frame. The design of the metal turntable can realize the adjustment of the position and angle of the sample to be tested, and can realize free and rapid measurement of the charge injection and surface potential decay of the sample to be tested. switch.

The present invention adopts multi-needle electrodes, and the distribution position of each needle, the length of the needles, and the distance between the needle tip and the surface of the sample to be tested can be calculated by the finite element analysis method, so that the multi-needle electric field can reach a state of uniform distribution, and achieve the desired effect on the surface of the sample. The effect of fully and uniformly injecting charge.

Description of drawings

Fig. 1 is the structural representation of three-electrode corona charging system among the present invention;

Fig. 2 is the schematic diagram of surface potential automatic measurement recording system among the present invention;

Fig. 3 is the schematic diagram of metal turntable among the present invention;

Fig. 4 is a schematic diagram of the rotating support system in the present invention;

Fig. 5 is a schematic diagram of the distribution of multi-needle electrodes in the present invention.

Detailed ways

As shown in Figures 1 to 5, the solid dielectric material trap parameter acquisition system of the present invention includes a constant temperature box 11 and a three-electrode corona charging system, a surface potential measurement system, a rotating support system and temperature control system. The three-electrode corona charging system is used to inject charge into the test sample 3, the surface potential measurement system is used to test the Fast switching between injection mode and surface potential attenuation measurement to accurately measure the instantaneous potential information after charging is completed; the temperature control system is used to realize the adjustment of the experimental environment temperature to obtain more sufficient charge injection and ensure the experimental effect.

In the present invention, the three-electrode corona charging system includes a multi-needle electrode 1 coaxially arranged from top to bottom and a grounded metal disc electrode 2. The multi-needle electrode 1 is connected to a DC charging power supply. The multi-needle electrode 1 adopts stainless steel needles. The radius of curvature is 5 μm; the outermost needle electrodes in the multi-needle electrode 1 are distributed in a regular hexagon, and each vertex and the midpoint of each side of the regular hexagon are provided with needle electrodes, and the outermost needle electrodes The length of the multi-needle electrode 1 is 9mm; the multiple needle electrodes of the sub-outer layer in the multi-needle electrode 1 are distributed in a regular hexagon, and each vertex and the midpoint of each side of the regular hexagon are provided with needle electrodes, and the multiple needle electrodes of the sub-outer layer The length of the electrode is 11 mm; the inner multiple needle electrodes in the multi-needle electrode 1 are distributed in a regular hexagon, and each vertex of the regular hexagon and the center of the regular hexagon are provided with needle electrodes, and the length of the inner multiple needle electrodes is 12mm, the inner multiple needle electrodes are 40mm away from the upper surface of the sample 3 to be tested; the outermost multiple needle electrodes, the second outer layer multiple needle electrodes and the inner multiple needle electrodes form the same center and the side lengths decrease hexagon. Due to the use of the multi-needle electrode 1, the distribution position of each needle in the multi-needle electrode 1, the length of the needle and the distance between the needle tip and the sample surface can be calculated by the finite element analysis method, so that the electric field of the multi-needle can be evenly distributed, and the treatment can be achieved. The effect of fully and uniformly injecting charge on the surface of test sample 3.

The upper surface of the metal disk electrode 2 is used to place the sample 3 to be tested, and the metal disk electrode 2 includes a copper electrode and an aluminum electrode that are in contact with each other up and down and arranged eccentrically. The diameter of the copper electrode 2 in the metal disk electrode 2 is 120 mm, and the thickness is 10 mm; the diameter of the aluminum electrode is 250 mm, and the thickness is 10 mm; the eccentric distance between the copper electrode and the aluminum electrode is 60 mm, and the copper electrode and the aluminum electrode are fixed by bolts. The surface of the copper electrode is finely polished to ensure good electrical contact between the sample 3 to be tested and the copper electrode, and conductive silicone grease is arranged between the copper electrode and the sample 3 to be tested.

The surface potential measurement system includes a capacitive electrostatic probe 4 arranged on an adjustable insulating fixture 5, the adjustable insulating fixture 5 includes an insulating fixture 5 and a position adjustment mechanism 6, and the capacitive electrostatic probe 4 is fixed at a position adjustment On the mechanism 6 , the distance between the capacitive electrostatic probe 4 and the upper surface of the sample 3 to be tested can be precisely adjusted through the position adjusting mechanism 6 . The output end of the capacitive electrostatic probe 4 is sequentially connected to the signal conditioning circuit 7 and the signal acquisition circuit 8 outside the thermostat 11, and the signal acquisition circuit 8 sends the signal to the computer, and the computer can process the measured signal to be measured by the existing software. The surface potential decay of sample 3 was automatically sampled and recorded continuously.

The rotating support system includes an insulating support frame 13 whose upper surface is a metal aluminum plate 12 arranged in a constant temperature box 11 , and a metal turntable 9 is arranged on the upper surface of the metal aluminum plate 12 . A metal heating box 10 is provided on the upper surface of the metal turntable 9 . The size of the metal heating box 10 is 250mm×250mm×20mm. The metal disk electrode 2 is placed on the upper surface of the metal heating box 10 . The metal turntable 9, the metal heating box 10 and the aluminum electrodes in the metal disc electrode 2 are arranged from bottom to top and fixed by bolts. The metal turntable 9 can realize the adjustment of the position and angle of the sample 3 to be tested, and can realize free switching between the two states of the sample 3 to be tested, charge injection and surface potential decay measurement. When the charge injection of the sample 3 to be tested is performed, the sample 3 to be tested is located under the multi-needle electrode 1; when the surface potential attenuation measurement is performed, the metal turntable 9 can be rotated so that the sample 3 to be tested is located on the capacitive electrostatic probe 4 below.

The temperature control system includes a first heating device 14 arranged in the metal heating box 10, and a second heating device 15 arranged on the insulating support frame 13 under the metal aluminum plate 12, and the temperature controller outside the thermostat 11 controls the connection A first heating device 14 and a second heating device 15 . After the first heating device 14 and the second heating device 15 are connected in parallel, they are controlled by a temperature controller outside the thermostat 11 to ensure that the temperature control accuracy is ±0.1°C. The first heating device 14 includes two thermocouples connected in series, and the second heating device 15 adopts a quartz infrared heating tube.

A humidity control device is also arranged in the thermostat 11, and the humidity control device adopts a solid desiccant. In this embodiment, the solid desiccant can be desiccant silica gel for transformers to ensure that the humidity is controlled below 40% to meet the experimental requirements.

When the present invention is in use, at first the sample 3 to be tested is pasted on the copper electrode upper surface in the metal disc electrode 2 with conductive silicone grease, the distance between the multi-needle electrode 1 and the sample 3 to be tested is kept at 40mm, and then the multi-needle electrode 1 Apply a charging voltage of +10kV or -10kV, and the charging time for each injection is 10 to 30 minutes. When charging, use the temperature control system to heat the metal disk electrode 2 and keep it at 70°C to ensure sufficient charge injection. Under the action of high voltage, corona discharge occurs at the tip of the multi-needle electrode 1, the air is ionized to generate a large number of charged particles, and an ionization zone is formed around the tip of the multi-needle electrode 1. Taking the application of a negative polarity voltage as an example, under the action of an electric field, the negative ions drift to the surface of the sample 3 to be tested. Since the electric field distribution between the multi-needle electrode 1 and the metal disk electrode 2 located below the multi-needle electrode 1 is relatively uniform, the negative ions will A uniform charge drift area is formed between the multi-needle electrode 1 and the test sample 3, and the electrons in the negative ions will be captured by the trap states on the surface of the test sample 3, thereby obtaining a uniform surface charging effect.

During the experiment, after the charge injection of the sample was completed, the DC charging voltage was removed, and the surface of the sample 3 to be tested was covered with aluminum foil and discharged in a short circuit. trap charge). After the short-circuit discharge, by rotating the metal turntable 9, the metal disk electrode 2 is driven to move the charging area on the surface of the sample 3 to be tested to the capacitive electrostatic probe 4, and the surface potential attenuation of the sample 3 to be tested is measured in a non-contact manner. The distance between the capacitive electrostatic probe 4 and the surface of the sample 3 to be tested is 2 mm. After the signal output by the capacitive electrostatic probe 4 is conditioned by the signal conditioning circuit 7, it is connected to the signal acquisition circuit 8 connected to the computer, and the surface potential of the test sample 3 can be continuously sampled by the computer. In the experiment, the signal acquisition circuit 8 is generally set to sample once every 1s. Since the attenuation characteristics of the surface potential are greatly affected by the environment, the entire experiment must be carried out in the incubator 11. During the experiment, the temperature was kept strictly constant, and the relative humidity inside the incubator 11 was controlled to be lower than 40% by placing a solid desiccant. According to the isothermal current decay theory, during the isothermal decay of the surface potential, the charges in the shallow traps in the medium are released first, while the charges in the deep traps are released later. The heat release current changes with time at a constant temperature, and the change of this current reflects the distribution of trap energy levels.

According to the surface potential decay characteristics of the sample under isothermal conditions, the isothermal decay current can be calculated, and then the trap energy level and trap density parameters of the sample can be calculated.

The invention can measure the trap energy level and trap density parameters of the solid dielectric material, and can distinguish two kinds of traps, electron type and hole type, and is easy to operate. The invention is not only suitable for testing the trap characteristics of inorganic insulating materials, such as aluminum oxide and machinable ceramics, but also for testing the trap characteristics of polymer insulating materials and oil-immersed paper. The invention provides theoretical and technical support for the study of trap characteristics of solid dielectric materials, and can be used for trap parameters to characterize the aging status of polymer insulating materials and research on the aging law of polymers, as well as the charging phenomenon on the surface of solid dielectric materials and its influence on surface flashover performance, etc. Aspect research provides an effective means of analysis.

Claims (8)

1. A solid dielectric material trap parameter acquisition system, characterized in that: comprising a thermostat and a three-electrode corona charging system, a surface potential measurement system, a rotating support system and a temperature control system arranged in the thermostat; The three-electrode corona charging system includes a multi-needle electrode coaxially arranged from top to bottom and a grounded metal disc electrode. The multi-needle electrode is connected to a DC charging power supply, and the upper surface of the metal disc electrode is used to place the electrode to be tested. In the same way, the metal disc electrode includes copper electrodes and aluminum electrodes that are in contact with each other up and down and are arranged eccentrically; The surface potential measurement system includes a capacitive electrostatic probe arranged on an adjustable insulating mount, and the output end of the capacitive electrostatic probe is sequentially connected to a signal conditioning circuit and a signal acquisition circuit outside the incubator; The rotary support system includes an insulating support frame with a metal aluminum plate on the upper surface of the thermostatic box, a metal turntable is arranged on the upper surface of the metal aluminum plate, a metal heating box is arranged on the upper surface of the metal turntable, and the metal disc electrodes are placed on the The upper surface of the metal heating box; when the charge injection of the sample to be tested is performed, the sample to be tested is located under the multi-needle electrode; when the surface potential decay measurement is performed, the sample to be tested is located under the capacitive electrostatic probe; The temperature control system includes a first heating device arranged in a metal heating box, and a second heating device arranged on an insulating support frame under the metal aluminum plate, and a temperature controller outside the thermostat controls and connects the first heating device and the second heating device. Two heating devices. 2. The solid dielectric material trap parameter acquisition system according to claim 1, characterized in that: the multi-needle electrodes adopt stainless steel needles, and the radius of curvature of the needle tip is 5 μm; the outermost needle electrodes in the multi-needle electrodes are positive six. Hexagonal distribution, and each vertex of the regular hexagon and the midpoint of each side are provided with needle electrodes, the length of the outermost needle electrodes is 9mm; the multiple needle electrodes in the second outer layer of the multi-needle electrodes are positive six Hexagonal distribution, and each vertex of the regular hexagon and the midpoint of each side are equipped with needle electrodes, the length of the multiple needle electrodes on the second outer layer is 11mm; the multiple needle electrodes on the inner side of the multi-needle electrodes are regular hexagons distribution, and each vertex of the regular hexagon and the center of the regular hexagon are provided with needle electrodes, the length of the inner multiple needle electrodes is 12mm, and the inner multiple needle electrodes are 40mm away from the upper surface of the sample to be tested; the outermost A plurality of needle electrodes, a plurality of needle electrodes in the second outer layer and a plurality of inner needle electrodes form a regular hexagon with the same center and decreasing side lengths. 3. The solid dielectric material trap parameter acquisition system according to claim 2, characterized in that: the diameter of the copper electrode in the metal disc electrode is 120mm, and the thickness is 10mm; the diameter of the aluminum electrode is 250mm, and the thickness is 10mm; the copper electrode and the aluminum electrode The eccentric distance is 60mm, and the copper electrode and the aluminum electrode are fixed by bolts. 4. The solid dielectric material trap parameter acquisition system according to claim 3, characterized in that: the adjustable insulating fixing frame includes an insulating fixing frame and a position adjustment mechanism, and the capacitive electrostatic probe is fixed on the position adjustment mechanism. 5. The solid dielectric material trap parameter acquisition system according to claim 4, characterized in that: the metal turntable, the metal heating box and the aluminum electrodes in the metal disk electrodes are arranged from bottom to top and fixed by bolts. 6. The solid dielectric material trap parameter acquisition system according to claim 5, characterized in that: the first heating device and the second heating device are connected in parallel and controlled by a temperature controller outside the thermostat box, and the first heating device includes Two thermocouples are connected in series, and the second heating device adopts a quartz infrared heating tube. 7. The system for collecting parameters of solid dielectric material traps according to claim 6, wherein a humidity control device is provided in the constant temperature box, and the humidity control device uses a solid desiccant. 8. The solid dielectric material trap parameter acquisition system according to claim 7, characterized in that: conductive silicone grease is arranged between the copper electrode and the sample to be tested.