A device and method for measuring surface trap distribution characteristics of an insulating material

Abstract

The application provides a device and method for measuring surface trap distribution characteristics of insulating materials, which comprises a test cavity and a data acquisition system; the test cavity comprises a cavity shell, a rotating connecting rod, a clamping plate, a needle electrode, a grid electrode and a sample surface grounding ring electrode; the rotating connecting rod is fixed on the cavity shell; the clamping plate is fixed on the rotating connecting rod; the clamping plate comprises an upper end clamping plate, a middle clamping plate and a lower end clamping plate; the needle electrode is fixed on the upper end clamping plate; the grid electrode is fixed on the lower end clamping plate; the needle electrode applies high voltage and is used for generating charged particles through corona discharge; the grid electrode applies low voltage and is used for uniformizing the electric field between the needle electrode and the sample; the sample surface grounding ring electrode is arranged on the sample surface, a circular hole is formed in the center of the sample surface grounding ring electrode, and the needle electrode is opposite to the center of the circular hole during corona charging; and the data acquisition system is used for recording the sample surface potential. The device and method can improve the electric field distribution on the sample surface after corona charging and effectively measure the surface trap distribution characteristics of insulating materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of measurement, and particularly relates to a device and method for measuring surface trap distribution characteristics of insulating materials. BACKGROUND

[0002] With the rapid development of the power system in China, compared with AC power transmission, the advantage of UHV DC power transmission is more and more obvious. However, the insulation problem of UHV DC power transmission is still in the bottleneck stage, and the main difficulty is that a large number of traps exist in the insulating medium, causing space charge accumulation, resulting in electric field distortion and thus causing partial discharge. In order to master the formation, distribution and migration law of space charge in insulating medium, and then inhibit the method of charge accumulation, it has become an important topic in the field of high-voltage DC transmission insulation.

[0003] At present, researchers have proposed various measurement methods for the trap distribution characteristics of accumulated space charges of insulating materials, among which the widely used methods include thermally stimulated current (TSC), pulsed eletro-acoustic (PEA) and surface potential decay (SPD). The SPD method is a convenient and low-cost method for measuring space charge and space traps, which can provide relevant physical information such as space charge injection, migration, relaxation process and charge trap distribution, and is therefore widely used in the characterization of internal trap distribution of insulating materials.

[0004] According to the current research on the surface potential decay method (SPD), the trap distribution characteristics in the body of the insulating material are mainly characterized. The current SPD measurement method is divided into two stages: 1. Corona charging process: the needle electrode is applied with a high voltage to generate charged particles, and the grid electrode is applied with a low voltage to uniformly distribute the electric field between the needle electrode and the sample, so as to ensure uniform distribution of the charges reaching the sample surface; 2. Charge dissipation process: after the charging is completed, the surface potential decay process of the insulating material is measured. During the measurement, the sample is placed on the back electrode, and the back electrode is grounded. In the above measurement method, during the charge dissipation process, there is a high potential difference between the sample surface charge and the back electrode, and the electric force lines emitted by the sample surface charge mainly point to the back electrode, that is, the normal component of the electric field intensity is much larger than the tangential component. The process of trapping and de-trapping during charge dissipation is completed through the body of the insulating material, and therefore the measured potential decay curve is mainly caused by the traps in the body of the insulating material. Therefore, the trap distribution calculated according to the potential decay curve is also a characterization of the trap distribution in the body of the insulating medium. However, the existing SPD measurement method cannot characterize the surface trap distribution characteristics of the insulating material. SUMMARY

[0005] In view of the above problems, the application provides a device and a method for measuring surface trap distribution characteristics of insulating materials.

[0006] In one aspect, the application provides a device for measuring surface trap distribution characteristics of insulating materials, comprising an experimental cavity and a data acquisition system; the experimental cavity comprises a cavity shell, a rotating link, a clamping plate, a needle electrode, a grid electrode and a sample surface grounding ring electrode; the rotating link is fixed on the cavity shell; the clamping plate is fixed on the rotating link; the clamping plate comprises an upper end clamping plate, a middle clamping plate and a lower end clamping plate; the needle electrode is fixed on the upper end clamping plate; the grid electrode is fixed on the lower end clamping plate; the needle electrode applies high voltage to generate charged particles through corona discharge; the grid electrode applies low voltage to uniform the electric field between the needle electrode and the sample; the sample surface grounding ring electrode is arranged on the sample surface and has a circular hole in the center; the needle electrode is opposite to the center of the circular hole during corona charging; and the data acquisition system is used to record the surface potential of the sample.

[0007] Preferably, the sample is placed on a sample placement platform, and an insulating pad is arranged below the sample placement platform.

[0008] Preferably, the cavity shell and the rotating link are made of stainless steel.

[0009] Preferably, the rotating link is fixed on the cavity shell by a bearing connection.

[0010] Preferably, the clamping plate is fixed on the rotating link by screws.

[0011] Preferably, the needle electrode and the grid electrode are made of red copper.

[0012] Preferably, the sample surface grounding ring electrode is made of aluminum alloy.

[0013] Preferably, the data measurement system comprises an active electrostatic probe, an electrostatic voltmeter, an oscilloscope and a computer; the active electrostatic probe is fixed on the middle clamping plate; after the corona charging process is completed, the rotating link is rotated to make the active electrostatic probe opposite to the sample, the surface potential of the sample is measured, the potential value displayed by the electrostatic voltmeter is displayed through the oscilloscope, and the computer records the discrete points of the potential decay over time, i.e., the U-t discrete curve.

[0014] In another aspect, the application provides a method for measuring surface trap distribution characteristics of insulating materials, which utilizes the above-mentioned measuring device; during the measurement, the needle electrode applies high voltage to generate charged particles through corona discharge; the grid electrode applies low voltage to uniform the electric field between the needle electrode and the sample; the needle electrode is opposite to the center of the circular hole of the sample surface grounding ring electrode during corona charging; after the corona charging is completed, the rotating link is rotated to make the active electrostatic probe opposite to the sample, the surface potential of the sample is measured, the potential value displayed by the electrostatic voltmeter is displayed through the oscilloscope, and the computer records the discrete points of the potential decay over time, i.e., the U-t discrete curve, which reflects the surface trap distribution characteristics of the sample.

[0015] Preferably, the distance of the clamping plate adjusts the distance between the needle electrode and the grid electrode, the grid electrode and the sample, the active electrostatic probe and the sample, realizes the measurement of samples of different sizes, and makes the surface charge distribution of the sample uniform. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a schematic diagram of an insulating material surface trap distribution characteristic measurement device of the present application;

[0017] Figure 2 is a schematic diagram of an experimental cavity in an insulating material surface trap distribution characteristic measurement device of the present application;

[0018] Figure 3 is a left view of the experimental cavity;

[0019] Figure 4 is a top view of the rotating structure in the experimental cavity. DETAILED DESCRIPTION

[0020] The embodiments will be described in detail below with reference to the accompanying drawings.

[0021] An insulating material surface trap distribution characteristic measurement device of the present application is composed of an experimental cavity and a data acquisition system, as shown in Figure 1 .

[0022] The experimental cavity includes an external cavity, internal electrodes, and a sample placement table, as shown in Figure 2 . The external cavity is used to fix the electrodes and bear the sample placement table, the internal electrodes have the function of pressurization, and the sample placement table is used to place the measurement sample. The data acquisition system is used to record the surface potential of the measurement sample.

[0023] As shown in Figure 2 , the external cavity mainly includes a cavity shell 1, a rotating connecting rod 2, a clamping plate 3, and an insulating pad 9. The cavity shell 1 and the rotating connecting rod 2 are preferably made of stainless steel, the rotating connecting rod 2 is fixed on the cavity shell 1, such as fixed by a bearing connection; the clamping plate 3 is fixed on the rotating connecting rod 2, such as fixed by screws, and the clamping plate 3 includes an upper end clamping plate, a middle clamping plate, and a lower end clamping plate; the insulating pad 9 mainly serves to bear the sample, and is located below the sample placement table (not shown).

[0024] The inner electrodes mainly include needle electrode 4, grid electrode 6 and sample surface grounding ring electrode 7. The needle electrode 4 and the grid electrode 6 are preferably made of red copper, and the sample surface grounding ring electrode 7 is preferably made of aluminum alloy. The needle electrode 4 is fixed on the upper end clamping plate, and the grid electrode 6 is fixed on the lower end clamping plate. The needle electrode 4 applies high voltage for generating charged particles (electric charges) by corona discharge, and the grid electrode 6 applies low voltage for uniforming the electric field between the needle electrode 4 and the sample 8, so as to ensure that the electric charges distributed on the surface of the sample 8 are uniform. The power supply 10 is used for applying voltage to the needle electrode and the grid electrode. The sample surface grounding ring electrode 7 is arranged on the surface of the sample 8, and a circular hole is formed in the center of the electrode 7. The needle electrode 4 is opposite to the center of the circular hole of the electrode 7 during corona charging. Within ten minutes after the electrode starts to be pressurized, the electric charges generated by the corona discharge of the needle electrode 4 in the gas environment move to the surface of the sample, so as to charge the surface of the sample, deposit the electric charges on the surface of the sample, and ensure that the sample 8 accumulated at the circular hole generates electric field mainly in the tangential direction of the surface of the sample 8. The sample 8 is placed on a sample placing table (not shown), and an insulating pad 9 is arranged below the sample placing table. The insulating pad 9 is used to reduce the dissipation of the electric charges along the body. The ring electrode 7 and the insulating pad 9 jointly change the electric field on the surface of the sample 8. The ring electrode 7 effectively increases the electric field generated by the electric charges on the surface of the sample in the direction along the surface of the sample (referred to as the tangential component of the electric field), and the insulating pad 9 weakens the electric field generated by the electric charges on the surface of the sample in the direction perpendicular to the surface (referred to as the normal component of the electric field). That is, due to the structure, the electric field for accumulating electric charges on the sample 8 in the normal component of the surface is far less than the tangential component of the electric field along the surface of the sample 8, so as to ensure that most of the electric charges dissipate along the surface of the sample to the sample surface grounding ring electrode 7 under the action of the tangential component of the electric field.

[0025] The data measurement system includes an active electrostatic probe 5, such as a Kelvin type, an electrostatic voltmeter 11, an oscilloscope 12 and a computer 13. The active electrostatic probe 5 is fixed on the middle clamping plate. After the corona charging process is completed, the active electrostatic probe 5 is opposite to the sample by rotating the rotating connecting rod 2, the surface potential of the sample is measured, the potential value displayed by the electrostatic voltmeter 11 is displayed through the oscilloscope 12, and the discrete points of the potential with time are recorded by the computer 13, that is, the U-t discrete curve, so that the surface potential value of the sample can be accurately displayed, the error during visual observation is reduced, and the test efficiency is improved. The U-t discrete curve can reflect the trap distribution characteristics of the surface of the insulating material. The distance between the needle electrode 4 and the grid electrode 6, the distance between the grid electrode 6 and the sample, and the distance between the active electrostatic probe 5 and the sample can be adjusted by adjusting the distance of the clamping plate 3, so as to facilitate the measurement of samples of different sizes, and make the electric charges on the surface of the sample as uniform as possible.

[0026] This embodiment is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. An insulating material surface trap distribution characteristic measuring device, comprising an experimental cavity and a data acquisition system; the experimental cavity comprises a cavity shell, a rotating link, a clamp plate, a needle electrode, a grid electrode and a sample surface grounding ring electrode, the rotating link is fixed on the cavity shell, the clamp plate is fixed on the rotating link, the clamp plate comprises an upper end clamp plate, a middle clamp plate and a lower end clamp plate; the needle electrode is fixed on the upper end clamp plate, and the grid electrode is fixed on the lower end clamp plate; the needle electrode applies high voltage for corona discharge to generate charged particles; the grid electrode applies low voltage to uniform the electric field between the needle electrode and the sample; the sample surface grounding ring electrode is arranged on the sample surface, a circular hole is provided in the center, and the needle electrode is opposite to the center of the circular hole during corona charging; and the data acquisition system is used for recording the surface potential of the sample. The data acquisition system comprises an active electrostatic probe, an electrostatic voltmeter, an oscilloscope and a computer; the active electrostatic probe is fixed on the middle clamp plate; after the corona charging process is completed, the rotating link is rotated to make the active electrostatic probe opposite to the sample, the surface potential of the sample is measured, the potential value displayed by the electrostatic voltmeter is displayed through the oscilloscope, and the computer records the discrete points of the potential decay with time, that is, the U-t discrete curve.

2. The apparatus for measuring surface trap distribution of an insulating material according to claim 1, wherein The sample is placed on a sample placement table, and an insulating pad plate is arranged below the sample placement table.

3. The apparatus of claim 1, wherein the insulating material is a dielectric material. The cavity shell and the rotating link are made of stainless steel.

4. The apparatus of claim 1, wherein the insulating material is a dielectric material. The rotating link is fixed on the cavity shell by a bearing connection.

5. The apparatus of claim 1, wherein The clamp plate is fixed on the rotating link by screws.

6. The apparatus of claim 1, wherein The needle electrode and the grid electrode are made of red copper.

7. The apparatus of claim 1, wherein the insulating material is a dielectric material. The sample surface grounding ring electrode is made of aluminum alloy.

8. An insulating material surface trap distribution characteristic measuring method, which utilizes the insulating material surface trap distribution characteristic measuring device of any one of claims 1-7 to measure, wherein the needle electrode applies high voltage to generate charged particles by corona discharge; the grid electrode applies low voltage to uniform the electric field between the needle electrode and the sample; the needle electrode is opposite to the center of the circular hole of the sample surface grounding ring electrode during corona charging; after the corona charging is completed, the rotating link is rotated to make the active electrostatic probe opposite to the sample, the surface potential of the sample is measured, the potential value displayed by the electrostatic voltmeter is displayed through the oscilloscope, and the computer records the discrete points of the potential decay with time, that is, the U-t discrete curve, which reflects the sample surface trap distribution characteristic.

9. The method of claim 8, wherein the surface-trap distribution of the insulating material is measured by: The distance between the needle electrode and the grid electrode, the grid electrode and the sample, and the active electrostatic probe and the sample is adjusted by the distance of the clamp plate, so that different size samples can be measured, and the surface charge distribution of the sample is uniform.

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