Joint testing device and method for space charge and conductivity of insulating material in multi-physical field

Abstract

The invention discloses a combined testing device and method for space charges and conductance of an insulating material under multiple physical fields. The combined testing device comprises a testing box, a sample to be tested, a space charge testing system, a high-voltage direct-current system, a data storage and processing module, an electrode system, a temperature control system, a stress loading system and a conductance current testing system. The space charge testing system is arranged in the testing box and used for testing space charges of a to-be-tested sample, the electrode system comprises a high-voltage electrode and a grounding electrode which are tightly attached to the surfaces of the two sides of the to-be-tested sample respectively, and the conductance current testing system is used for measuring current of the to-be-tested sample; the temperature control system is used for regulating and controlling the test temperature of the test box; the stress loading system is used for applying stress to the to-be-tested sample; the data storage and processing module is connected with the space charge test system, the temperature control system, the stress loading system and the conductance current test system. According to the invention, the space charge and the conductance current of the insulating material can be comprehensively, accurately and simultaneously measured in situ in multiple physical fields.

Description

Technical Field

[0001] The invention belongs to the technical field of insulating material testing, and in particular relates to a device and method for jointly testing space charge and conductivity of insulating materials under multi-physical fields. Background Art

[0002] In recent years, as the demand for solid insulating materials in industries such as energy and power electronics continues to increase, capacitors often use the highest possible working electric field strength to obtain higher energy storage density. When solid insulating materials are exposed to high temperature and high pressure for a long time, charge injection and retention will occur, thus forming space charge, causing internal electric field distortion, and forming significant conduction current, causing significant losses, and ultimately leading to insulation breakdown. Therefore, it is very important to measure and evaluate the space charge distribution and conduction current conditions inside solid insulating materials.

[0003] In terms of analyzing the intrinsic correlation between space charge and conductivity current, the measurements of space charge and conductivity current are mostly step-by-step measurements. Considering the possible displacement current component of the external current and the influence of material structure heterogeneity, the experimental results obtained by testing the same material separately cannot be strictly analyzed together, which will also cause uncertainty in the experimental conclusions. In addition, solid insulating materials are often under the action of multiple physical fields in actual working conditions. Existing devices can only be carried out under the action of electricity, heat, and electric-thermal coupling. There is a lack of research on the joint test method of space charge and conductivity of insulating materials under multiple physical fields. Summary of the invention

[0004] The purpose of the present invention is to provide a device and method for jointly testing the space charge and conductivity of insulating materials under multiple physical fields. The present invention can comprehensively and accurately measure the space charge and conductivity current of insulating materials in situ at the same time under multiple physical fields.

[0005] The technical solution of the present invention is as follows: a device for testing space charge and conductivity of insulating materials under multi-physical fields, comprising a test box, a sample to be tested, a space charge test system, a high-voltage direct current system and a data storage and processing module; the space charge test system is arranged in the test box for testing the space charge of the sample to be tested, and also comprises an electrode system, a temperature control system, a stress loading system and a conductance current testing system; the electrode system comprises a high-voltage electrode and a grounding electrode respectively attached to the surfaces of both sides of the sample to be tested, the high-voltage electrode is electrically connected to the high-voltage direct current system, and the grounding electrode is electrically connected to the conductance current testing system; the conductance current testing system is used to measure the current of the sample to be tested; the temperature application end of the temperature control system is arranged on the test box, and the temperature control system is used to adjust the test temperature of the test box; the stress loading system comprises a sample fixture for clamping both ends of the sample to be tested, one end of the sample fixture passes through the side of the test box and is connected to a stress testing device; the stress loading system is used to apply stress to the sample to be tested; the data storage and processing module is respectively connected to the space charge test system, the temperature control system, the stress loading system and the conductance current testing system.

[0006] In the aforementioned device for joint testing of space charge and conductivity of insulating materials under multiple physical fields, the sample to be tested is a solid insulating material, and coating electrodes are provided on both sides of the sample to be tested.

[0007] In the aforementioned joint test device for space charge and conductivity of insulating materials under multi-physical fields, the space charge test system comprises a nanosecond pulse laser, a photoelectric trigger circuit, a double-sided transmission optical path, a coupling capacitor, a first protection circuit, a switch, a signal amplifier, and an oscilloscope; the laser light generated by the pulse laser is divided into two paths through a 1 / 9 beam splitter, wherein 10% of the laser light enters the photoelectric trigger circuit in one path and 90% of the laser light enters the double-sided transmission optical path in the other path; the photoelectric trigger circuit comprises a photodiode, the photodiode is connected to the oscilloscope, and the oscilloscope is connected to the signal amplifier; the double-sided transmission optical path comprises three 45° reflectors No. 1, No. 2, and No. 3 and a 5 / 5 beam splitter, the 5 / 5 beam splitter has a rotatable reset function and serves as a switching point for the double-sided transmission optical path, and the double-sided measurement circuit comprises front-side measurement and back-side measurement; When measuring the front side, the 5 / 5 beam splitter is rotated away, and the incident laser directly passes through the No. 1 45° reflector to be incident on the front side coating electrode; when measuring the back side, the 5 / 5 beam splitter is reset, and the incident laser passes through the 5 / 5 beam splitter, the No. 2 45° reflector and the No. 3 45° reflector in sequence to be incident on the back side coating electrode; the high-voltage electrode is in close contact with the back side coating electrode, and the grounding electrode is in close contact with the front side coating electrode; the high-voltage DC system includes a DC high-voltage power supply connected to the high-voltage electrode and a high-voltage protection resistor therebetween; the grounding electrode is grounded, and the high-voltage electrode is connected to the moving end of a single-pole double-throw switch through a coupling capacitor, and the two fixed ends of the single-pole double-throw switch are respectively connected to the ground and the first protection circuit, and the first protection circuit is connected to the signal amplifier; the nanosecond pulse laser is connected to a data storage and processing module through a serial port line.

[0008] In the aforementioned joint test device for space charge and conductivity of insulating materials under multiple physical fields, the conductivity current test system includes a relay and an electrometer. The relay is connected to the ground electrode and the second protection circuit respectively through a coaxial cable. The second protection circuit is connected to the electrometer, and the electrometer is grounded through a coaxial cable.

[0009] In the aforementioned joint test device for space charge and conductivity of insulating materials under multiple physical fields, a metal shielding box is provided inside the test box, and the metal shielding box is used to place the coupling capacitor of the space charge test system, the first protection circuit, the switch and the high-voltage protection resistor of the high-voltage DC system; the temperature control system includes a silicone rubber heating plate arranged on the upper and lower surfaces of the test box.

[0010] In the aforementioned joint test device for space charge and conductivity of insulating materials under multiple physical fields, the electrode system also includes an insulating support column and an electrode slide rail; the insulating support column is connected to the high-voltage electrode and the test box by a threaded connection; the grounding electrode is placed on the surface of the electrode slide rail; the electrode slide rail is made of insulating material and fixed inside the test box.

[0011] In the aforementioned joint test device for space charge and conductivity of insulating materials under multiple physical fields, the sample fixture includes a fixed fixture and a movable fixture, the fixed fixture and the movable fixture clamp the two ends of the sample to be tested, and the fixed fixture is fixed to the surface of the metal shielding box by bolts; a mechanical stretching adjustment device is arranged below the stress testing device, and the mechanical stretching adjustment device includes a fixed platform and a stretching platform that can slide longitudinally relative to the fixed platform; a lead screw is arranged on the fixed platform, and a connecting piece threadedly connected to the lead screw is arranged at the bottom of the stretching platform, and a rotating handle is arranged at the tail of the lead screw, and the longitudinal sliding of the stretching platform on the fixed platform is achieved by rotating the handle; the stress testing device is fixed to the sliding platform by bolts.

[0012] The test method of the aforementioned multi-physical field insulation material space charge and conductivity joint test device comprises the following steps:

[0013] S1. After cleaning the surface of the sample to be tested with alcohol, fix it with a sample fixture and make it close to the high-voltage electrode and the ground electrode. Then load the stress loading system to apply the corresponding stress to the preset level, and then turn on the temperature control system and set the preset temperature.

[0014] S2, after the temperature and stress are stable, turn on the high voltage DC system to apply the electric field to the sample to be tested;

[0015] S3, detect whether there is a large current flowing through both sides of the sample to be tested. When the current signal is stable, the conductive current test system is connected to the ground electrode to form a closed loop and perform data acquisition, and save the data to the data storage and processing module;

[0016] S4, synchronously open the space charge test system to perform front and back measurements on the space charge, and save them to the data storage and processing module;

[0017] S5. Use the scale transformation method to calculate the electric field distribution curve and charge density distribution curve of the insulating material, and retain the data within the last 10 seconds of the current data recorded in the conductivity current test system to calculate the corresponding conductivity.

[0018] The test method of the aforementioned joint test device for space charge and conductivity of insulating materials under multiple physical fields, the process of measuring space charge by the space charge test system is to set the laser frequency and laser energy of the pulsed laser, emit a certain number of lasers to the sample to be tested, and transmit the test current to the signal amplifier through the coupling capacitor, switch, and first protection circuit in the circuit, and use the oscilloscope trigger function to record the amplifier signal.

[0019] In the aforementioned test method of the space charge and conductivity joint test device for insulating materials under multiple physical fields, the calculation formula for obtaining the electric field distribution curve and the charge density distribution curve of the insulating material is:

[0020]

[0021] In the formula, E 0 is the electric field strength, ρ 0 is the charge density, M ST is the correction coefficient, ω represents the angular frequency, γ is a complex term, Represents the difference between the real and imaginary amplitudes of the current spectrum I(ω), represents the difference between the real and imaginary parts of the product of the complex term γ and the current spectrum I(ω);

[0022] The calculation formula of the complex term γ is as follows:

[0023]

[0024] In the formula, j is a complex unit, and D is the thickness of the sample to be tested;

[0025] The formula for calculating the corresponding conductivity is as follows:

[0026]

[0027] Where, I is the conductance current measured in the conductance current test system; L is the thickness of the sample to be tested; S is the contact area between the sample to be tested and the high-voltage electrode; U is the voltage applied by the high-voltage DC system.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention proposes a device and method for jointly testing space charge and conductivity of insulating materials under multi-physical fields, and establishes an ultra-high resolution space charge and conductivity current joint measurement device under multi-physical field collaboration, which can comprehensively and accurately measure the space charge and conductivity current characteristics of solid insulating materials in situ at the same time, overcoming the problems of inaccurate evaluation and incomplete experimental conditions in existing measurement technologies, thereby playing an important role in further improving the quality standards of solid insulating materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of the present invention;

[0031] Figure 2 It is a plan view of the mechanical structure of the present invention;

[0032] Figure 3 It is a three-dimensional diagram of the mechanical structure of the present invention;

[0033] Figure 4 It is the test principle diagram of the present invention;

[0034] Figure 5 is the electric field distribution curve obtained by this method;

[0035] Figure 6 is the charge density distribution curve obtained by this method;

[0036] Figure 7 is the conductivity curve obtained by this method.

[0037] The markings in the attached drawings are: 1. sample to be tested; 2. insulating support column; 3. high voltage electrode; 4. grounding electrode; 5. electrode slide rail; 6. test box; 7. metal shielding box; 8. movable clamp; 9. fixed clamp; 10. stress testing device; 11. sliding stretching table; 12. lead screw; 13. fixed platform; 14. rotating handle; 15. silicone rubber heating plate. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0039] Embodiment 1: Joint test device for space charge and conductivity of insulating materials under multi-physical fields, such as Figure 1-3 As shown, it includes a test box, a sample to be tested 1, a space charge test system, a high voltage direct current system and a data storage and processing module; the space charge test system is arranged in the test box for testing the space charge of the sample to be tested. The device also includes an electrode system, a temperature control system, a stress loading system and a conduction current testing system. The electrode system includes a high voltage electrode 3 and a ground electrode 4 respectively attached to the surfaces of both sides of the sample to be tested 1, the high voltage electrode 3 is electrically connected to the high voltage direct current system, and the ground electrode 4 is electrically connected to the conduction current testing system; the conduction current testing system is used to measure the conduction current of the sample to be tested 1; the temperature application end is arranged on the test box, and the temperature control system is used to adjust the test temperature of the test box; the stress loading system includes a sample fixture for clamping the two ends of the sample to be tested 1, and one end of the sample fixture passes through the side of the test box and is connected to a stress testing device 10; the stress loading system is used to apply stress to the sample to be tested 1; the data storage and processing module is respectively connected to the space charge test system, the temperature control system, the stress loading system and the conduction current testing system.

[0040] In this embodiment, the sample to be tested 1 is selected as a solid insulating material, such as a polymer film. The sample to be tested 1 is sprayed with electrodes on both sides of the solid insulating material by magnetron sputtering or thermal evaporation. The materials of the double-sided electrodes include but are not limited to metals such as gold, silver, aluminum, and platinum. Under the condition of being as thin as possible, the sample to be tested 1 is opaque and resistant to laser ablation, and the surface is guaranteed not to be damaged to prevent the sample to be tested 1 from being broken during the pressurization process. The height of the sample to be tested 1 should be slightly larger than the diameter of the high-voltage electrode 3 to prevent surface discharge. The length depends on the distance from the sample fixture to the high-voltage electrode 3 and should not be less than 2 times the height. The sample to be tested 1 in this embodiment uses a 5.8um polypropylene film, which is cut into a size of 5cm*12cm, and a double-sided gold electrode with a radius of 2.5mm is sprayed in a magnetron sputtering instrument. The high-voltage electrode 3 and the grounding electrode 4 are both brass rings, and the central light holes of the two electrodes are located on an axis to ensure that the positive and negative laser beams can hit the same position. In this embodiment, the electrode radius of the ground electrode 4 in contact with the sample 1 to be tested is 2.5 mm, which is consistent with the diameter size of the sputtering electrode of the sample 1 to be tested, and the radius of the light hole is 1 mm; the radius of the high-voltage electrode 3 is 2.5 cm, and the radius of the light hole is 1 mm.

[0041] Specifically, the space charge test system includes a nanosecond pulse laser, a photoelectric trigger circuit, a double-sided transmission optical path, a coupling capacitor, a first protection circuit, a switch, a signal amplifier, and an oscilloscope. Figure 4 As shown. The laser light generated by the pulse laser is divided into two paths through a 1 / 9 beam splitter, wherein 10% of the laser light enters the photoelectric trigger circuit in one path, and 90% of the laser light enters the double-sided transmission optical path in the other path; the photoelectric trigger circuit includes a photodiode, the photodiode is connected to an oscilloscope, and the oscilloscope is connected to a signal amplifier; the double-sided transmission optical path includes three 45° reflectors No. 1, No. 2, and No. 3 and a 5 / 5 beam splitter, the 5 / 5 beam splitter has a rotatable reset function and serves as a switching point of the double-sided transmission optical path, and the double-sided measurement circuit includes a front measurement circuit and a back measurement circuit.

[0042] Furthermore, when measuring the front side, the 5 / 5 beam splitter is rotated away, and the incident laser directly passes through the No. 1 45° reflector to be incident on the front side coating electrode; when measuring the back side, the 5 / 5 beam splitter is reset, and the incident laser passes through the 5 / 5 beam splitter, the No. 2 45° reflector and the No. 3 45° reflector in sequence to be incident on the back side coating electrode; the high-voltage electrode 3 is in close contact with the back side coating electrode, and the ground electrode 4 is in close contact with the front side coating electrode.

[0043] The high-voltage direct current system includes a direct current high-voltage power supply connected to the high-voltage electrode 3 and a high-voltage protection resistor arranged at the output end of the direct current high-voltage power supply; the ground electrode 4 is grounded, the high-voltage electrode 3 is connected to the moving end of the single-pole double-throw switch through a coupling capacitor, and the two fixed ends of the single-pole double-throw switch are respectively connected to the ground and the first protection circuit, and the first protection circuit is connected to the signal amplifier; the nanosecond pulse laser is connected to the data storage and processing module through a serial port line. The coupling capacitor, the protection circuit, and the switch are interconnected through a coaxial cable line, fixed inside the test box 6, and connected to the coaxial cable seat on the surface of the test box 6, wherein the coupling capacitor is used to isolate the direct current high voltage on the one hand and for signal coupling on the other hand. The switch is located between the coupling capacitor and the protection circuit, and is used to connect and disconnect the connection between the capacitor and the measurement circuit to ensure the safety of the signal amplifier.

[0044] In this embodiment, in order to ensure that the sample 1 to be tested is a current source, the coupling capacitor is required to be more than 100 times larger than the sample capacitor. In this embodiment, a 22nF capacitor is used. The pulse laser uses a Nd:YAG solid laser with a wavelength of 1064nm and a pulse width of about 10ns. The laser energy on both sides is preferably adjusted to 1-1.5mJ. The nanosecond pulse laser is connected to the data storage and processing module via a serial line.

[0045] In this embodiment, the signal amplifier is connected to the coaxial cable holder on the surface of the test box 6 and the oscilloscope through a coaxial cable. The amplifier adopts a low-noise, broadband high-frequency current amplifier with a bandwidth of DC-400kHz and a low-frequency gain of 1×10 7 Up to 1×10 9 V / A, input resistance is less than 10Ω.

[0046] Furthermore, the high-voltage DC power supply is connected to a high-voltage protection resistor via an insulated wire, wherein the protection resistor is placed in the test box 6 and connected to the high-voltage electrode 3 via an insulated wire; the resistance of the high-voltage protection resistor should ensure that the electrometer and the signal amplifier are not damaged when the sample breaks down, and is much smaller than the sample resistance. In this embodiment, the protection resistor is 300MΩ.

[0047] Specifically, the conduction current test system includes relays and electrometers, such as Figure 4 As shown, the relay is connected to the ground electrode 4 and the second protection circuit respectively through a coaxial cable, the second protection circuit is connected to the electrometer, and the electrometer is grounded through the coaxial cable.

[0048] In this embodiment, the relay is a single-pole double-throw high-voltage vacuum relay, which can withstand a maximum voltage greater than the rated value of the DC high-voltage power supply. In the circuit, the main input end of the relay is connected to the output end of the measurement circuit, the normally open contact is connected to the electrometer, and the normally closed contact is grounded. Its main function is to switch the working state of the main measurement circuit and effectively protect the safety of the low-current measurement equipment; the controller of the relay is mainly a communication module with MCU as the core, and its main function is to read the instructions sent by the program monitoring and control module through the RS232 serial port and control the connection and disconnection of the normally open and normally closed contacts of the high-voltage vacuum relay in real time.

[0049] In this embodiment, the electrometer is a Keithley 6517B electrometer, and the maximum allowable current of the electrometer is 20 mA.

[0050] Specifically, a metal shielding box 7 is provided inside the test box 6, and the metal shielding box 7 is used to place the coupling capacitor of the space charge test system, the first protection circuit, the switch and the high-voltage protection resistor of the high-voltage DC system; the metal shielding box 7 should maintain a good tightness to reduce external electromagnetic interference. The temperature control system includes a silicone rubber heating plate 15 arranged on the upper and lower surfaces of the test box 6. The temperature control system realizes variable temperature control through the silicone rubber heating plate 15 and applies different temperature fields. The maximum rated temperature of the silicone rubber heating plate 15 should be greater than 100°C.

[0051] Specifically, the electrode system also includes an insulating support column 2 and an electrode slide rail 5; the insulating support column 2 is connected to the high-voltage electrode 3 and the test box 6 by a threaded connection; the grounding electrode 4 is placed on the surface of the electrode slide rail 5; the electrode slide rail 5 is made of insulating material and fixed inside the test box 6.

[0052] Specifically, the sample fixture includes a fixed fixture 9 and a movable fixture 8, which clamp the two ends of the sample 1 to be tested, and the fixed fixture 9 is fixed to the surface of the metal shielding box 7 by bolts; a mechanical stretching adjustment device is arranged below the stress testing device, and the mechanical stretching adjustment device includes a fixed platform 13 and a stretching platform that can slide longitudinally relative to the fixed platform 13; a lead screw 12 is arranged on the fixed platform 13, and a connecting piece threadedly connected to the lead screw 12 is arranged at the bottom of the stretching platform, and a rotating handle 14 is arranged at the tail of the lead screw 12, and the longitudinal sliding of the stretching platform on the fixed platform 13 is realized by rotating the handle 14; the stress testing device 10 is fixed to the sliding platform by bolts.

[0053] In this embodiment, the stress testing device 10 adopts a common digital dynamometer with a maximum tension limit of 5N and an accuracy of 0.5%, and can be connected to a data storage and processing module via RS232.

[0054] In this embodiment, the data is stored in the labview program developed by the laboratory, which can display temperature, tension, laser energy, laser frequency, DC voltage amplitude, conductance current curve, and oscilloscope real-time current curve in real time. The data processing module is a self-developed matlab program, which can process the conductance current curve and oscilloscope real-time current curve to obtain the electric field distribution, charge density distribution curve, and conductivity results.

[0055] Embodiment 2: Based on the testing device in Embodiment 1, this embodiment provides a testing method, the steps are as follows:

[0056] S1. After cleaning the surface of the sample to be tested with alcohol, fix it with a sample fixture and make it close to the high-voltage electrode and the ground electrode. Then load the stress loading system to apply the corresponding stress to the preset level, and then turn on the temperature control system and set the preset temperature.

[0057] S2, after the temperature and stress are stable, turn on the high voltage DC system to apply the electric field to the sample to be tested;

[0058] S3, detect whether there is a large current flowing through both sides of the sample to be tested. When the current signal is stable, the conductive current test system is connected to the ground electrode to form a closed loop and perform data acquisition, and save the data to the data storage and processing module;

[0059] S4, synchronously open the space charge test system to perform front and back measurements on the space charge, and save them to the data storage and processing module;

[0060] S5. Use the scale transformation method to calculate the electric field distribution curve and charge density distribution curve of the insulating material, and retain the data within the last 10 seconds of the current data recorded in the conductivity current test system to calculate the corresponding conductivity.

[0061] The calculation formula for obtaining the electric field distribution curve and charge density distribution curve of the insulating material is:

[0062]

[0063] In the formula, E 0 is the electric field strength, ρ 0 is the charge density, M ST is the correction coefficient, ω represents the angular frequency, γ is a complex term, Represents the difference between the real and imaginary amplitudes of the current spectrum I(ω), represents the difference between the real and imaginary parts of the product of the complex term γ and the current spectrum I(ω);

[0064] The calculation formula of the complex term γ is as follows:

[0065]

[0066] Where j is a complex unit and D is the thickness of the sample to be tested.

[0067] The formula for calculating the corresponding conductivity is as follows:

[0068]

[0069] Wherein, I is the conductance current measured in the conductance current test system; L is the thickness of the sample to be tested; S is the contact area between the sample to be tested 1 and the high-voltage electrode 3; and U is the voltage applied by the high-voltage DC system.

[0070] In this embodiment, an electric field of 100 kV / mm is applied to a 5.8 μm polypropylene film, and the obtained electric field distribution curve is as follows: Figure 5 The charge density distribution curve is shown in Figure 6 The conductivity curve obtained is shown in Figure 7 As shown, the calculated conductivity is 4e-15 S / cm.

[0071] In summary, the present invention proposes a device and method for jointly testing space charge and conductivity of insulating materials under multi-physical fields, and establishes an ultra-high resolution space charge and conductivity current joint measurement device under multi-physical field collaboration, which can relatively comprehensively and accurately measure the space charge and conductivity current characteristics of solid insulating materials in situ at the same time. The resolution of space charge test can reach sub-micron level, overcoming the problems of inaccurate evaluation and incomplete experimental conditions in existing measurement technologies, thereby playing an important role in further improving the quality standards of solid insulating materials.

Claims

1. A device for testing space charge and conductivity of insulating materials under multi-physical fields, comprising a test box, a sample to be tested (1), a space charge test system, a high voltage direct current system and a data storage and processing module; the space charge test system is arranged in the test box for testing the space charge of the sample to be tested; and characterized in that: It also includes an electrode system, a temperature control system, a stress loading system and a conduction current testing system; the electrode system includes a high-voltage electrode (3) and a grounding electrode (4) respectively attached to the surfaces of both sides of the sample to be tested (1), the high-voltage electrode (3) is electrically connected to the high-voltage direct current system, and the grounding electrode (4) is electrically connected to the conduction current testing system; the conduction current testing system is used to measure the current of the sample to be tested (1); the temperature application end of the temperature control system is arranged on the test box, and the temperature control system is used to adjust the test temperature of the test box; the stress loading system includes a sample clamp for clamping the two ends of the sample to be tested (1), one end of the sample clamp passes through the side of the test box and is connected to a stress testing device (10); the stress loading system is used to apply stress to the sample to be tested (1); the data storage and processing module is respectively connected to the space charge testing system, the temperature control system, the stress loading system and the conduction current testing system.

2. The device for testing space charge and conductivity of insulating materials under multi-physical fields according to claim 1, characterized in that: The sample to be tested (1) is made of solid insulating material, and coating electrodes are arranged on the front and back sides of the sample to be tested (1).

3. The device for testing space charge and conductivity of insulating materials under multi-physical fields according to claim 2, characterized in that: The space charge test system comprises a nanosecond pulse laser, a photoelectric trigger circuit, a double-sided transmission optical path, a coupling capacitor, a first protection circuit, a switch, a signal amplifier, and an oscilloscope; the laser light generated by the pulse laser is divided into two paths through a 1 / 9 beam splitter, wherein 10% of the laser light enters the photoelectric trigger circuit in one path and 90% of the laser light enters the double-sided transmission optical path in the other path; the photoelectric trigger circuit comprises a photodiode, the photodiode is connected to the oscilloscope, and the oscilloscope is connected to the signal amplifier; the double-sided transmission optical path comprises three 45° reflectors No. 1, No. 2, and No. 3 and a 5 / 5 beam splitter, the 5 / 5 beam splitter has a rotatable reset function and serves as a switching point for the double-sided transmission optical path, and the double-sided measurement circuit comprises front measurement and back measurement; when measuring the front side, the 5 / 5 beam splitter is rotated away and the incident laser light is directly The laser beam is incident on the front coating electrode through a No. 1 45° reflector; when measuring the back side, the 5 / 5 beam splitter is reset, and the incident laser beam is incident on the back coating electrode through the 5 / 5 beam splitter, the No. 2 45° reflector and the No. 3 45° reflector in sequence; the high-voltage electrode (3) is in close contact with the back coating electrode, and the grounding electrode (4) is in close contact with the front coating electrode; the high-voltage DC system comprises a DC high-voltage power supply connected to the high-voltage electrode (3) and a high-voltage protection resistor between the two; the grounding electrode (4) is grounded, the high-voltage electrode (3) is connected to the moving end of a single-pole double-throw switch through a coupling capacitor, and the two fixed ends of the single-pole double-throw switch are respectively connected to the ground and a first protection circuit, and the first protection circuit is connected to a signal amplifier; the nanosecond pulse laser is connected to a data storage and processing module through a serial port line.

4. The device for testing space charge and conductivity of insulating materials under multiple physical fields according to claim 3, characterized in that: The conduction current testing system comprises a relay and an electrometer, wherein the relay is respectively connected to a grounding electrode (4) and a second protection circuit via a coaxial cable, the second protection circuit is connected to the electrometer, and the electrometer is grounded via the coaxial cable.

5. The device for testing space charge and conductivity of insulating materials under multi-physical fields according to claim 3, characterized in that: A metal shielding box (7) is provided inside the test box (6), and the metal shielding box (7) is used to place a coupling capacitor of a space charge test system, a first protection circuit, a switch, and a high-voltage protection resistor of a high-voltage direct current system; the temperature control system comprises a silicone rubber heating plate (15) arranged on the upper and lower surfaces of the test box (6).

6. The device for testing space charge and conductivity of insulating materials under multi-physical fields according to claim 5, characterized in that: The electrode system further comprises an insulating support column (2) and an electrode slide rail (5); the insulating support column (2) is connected to the high voltage electrode (3) and the test box (6) by means of a threaded connection; the grounding electrode (4) is placed on the surface of the electrode slide rail (5); the electrode slide rail (5) is made of insulating material and is fixed inside the test box (6).

7. The device for testing space charge and conductivity of insulating materials under multi-physical fields according to claim 5, characterized in that: The sample clamp comprises a fixed clamp (9) and a movable clamp (8), the fixed clamp (9) and the movable clamp (8) clamp the two ends of the sample to be tested (1), and the fixed clamp (9) is fixed to the surface of the metal shielding box (7) by bolt connection; a mechanical stretching adjustment device is arranged below the stress testing device, and the mechanical stretching adjustment device comprises a fixed platform (13) and a stretching platform that can slide longitudinally relative to the fixed platform (13); a lead screw (12) is arranged on the fixed platform (13), a connecting piece threadedly connected to the lead screw (12) is arranged at the bottom of the stretching platform, and a rotating handle (14) is arranged at the tail of the lead screw (12), and the longitudinal sliding of the stretching platform on the fixed platform (13) is realized by rotating the handle (14); the stress testing device (10) is fixed to the sliding platform by bolt connection.

8. The testing method of the device for testing space charge and conductivity of insulating materials under multi-physical fields according to any one of claims 1 to 7, characterized in that: The steps include: S1. After cleaning the surface of the sample to be tested with alcohol, fix it with a sample fixture and make it close to the high-voltage electrode and the ground electrode. Then load the stress loading system to apply the corresponding stress to the preset level, and then turn on the temperature control system and set the preset temperature. S2, after the temperature and stress are stable, turn on the high voltage DC system to apply the electric field to the sample to be tested; S3, detect whether there is a large current flowing through both sides of the sample to be tested. When the current signal is stable, the conductive current test system is connected to the ground electrode to form a closed loop and perform data acquisition, and save the data to the data storage and processing module; S4, synchronously open the space charge test system to perform front and back measurements on the space charge, and save them to the data storage and processing module; S5. Use the scale transformation method to calculate the electric field distribution curve and charge density distribution curve of the insulating material, and retain the data within the last 10 seconds of the current data recorded in the conductivity current test system to calculate the corresponding conductivity.

9. The testing method of the device for testing space charge and conductivity of insulating materials under multi-physical fields according to claim 8, characterized in that: The process of measuring space charge in the space charge test system is to set the laser frequency and laser energy of the pulse laser, emit the laser a certain number of times to the sample to be tested, transmit the test current to the signal amplifier through the coupling capacitor, switch, and first protection circuit in the circuit, and use the oscilloscope trigger function to record the amplifier signal.

10. The testing method of the device for testing space charge and conductivity of insulating materials under multi-physical fields according to claim 8, characterized in that: The calculation formula for obtaining the electric field distribution curve and charge density distribution curve of the insulating material is: Where E0 is the electric field intensity, ρ0 is the charge density, M ST is the correction coefficient, ω represents the angular frequency, γ is a complex term, Represents the difference between the real and imaginary amplitudes of the current spectrum I(ω), represents the difference between the real and imaginary parts of the product of the complex term γ and the current spectrum I(ω); The calculation formula of the complex term γ is as follows: In the formula, j is a complex unit, and D is the thickness of the sample to be tested; The formula for calculating the corresponding conductivity is as follows: Where, I is the conductance current measured in the conductance current test system; L is the thickness of the sample to be tested; S is the contact area between the sample to be tested and the high-voltage electrode; U is the voltage applied by the high-voltage DC system.

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