Non-contact type insulating material surface property testing device and method

Abstract

This invention provides a non-contact device and method for assessing the surface characteristics of insulating materials, comprising: a housing, an equalizing element, and a ground electrode; the housing contains insulating oil to simulate the internal operating environment of power equipment; the equalizing element and the ground electrode are immersed in the insulating oil and are arranged vertically opposite each other, forming a surface discharge region between them; the equalizing element has a cavity containing a high-voltage lead, the lower end of which has a hanging part for suspending the insulating sample to be tested, such that the main body of the insulating sample is located on the central axis between the equalizing element and the ground electrode, and the lower end of the insulating sample is in contact with the ground electrode. This invention enables the surface discharge to develop stably along the surface of the insulating sample, effectively suppressing preferential breakdown of oil gaps, thereby simulating low surface field strength conditions under high voltage conditions, accurately and reliably reflecting the surface discharge characteristics of the insulating sample, and significantly improving the authenticity and repeatability of the test results.

Description

Technical Field

[0001] This invention relates to the field of insulation testing technology for high-voltage electrical equipment, and more specifically, to a non-contact device and method for assessing the surface properties of insulating materials. Background Technology

[0002] In recent years, with the advancement of China's "West-to-East Power Transmission" strategy and the goals of carbon peaking and carbon neutrality, ultra-high voltage direct current (UHVDC) transmission technology has developed rapidly, driving a continuous increase in market demand for converter transformers. The promotion of high-voltage levels has placed more stringent requirements on the safety and reliability of the insulation systems of key equipment such as transformers and instrument transformers. In large transformers, solid insulating materials such as insulating paper and cardboard, together with liquid insulating media such as mineral oil, constitute a composite insulation system, the performance of which directly determines the electric field distribution and insulation margin of the equipment. Studies have shown that approximately 35%–45% of insulation structure failures are related to surface discharge in solid insulation. Especially in oil-immersed environments, factors such as electric field concentration, electrical tree expansion, and interface bubble formation can all trigger surface flashover, leading to severe equipment damage.

[0003] Currently, in the study of surface discharge and surface breakdown characteristics of insulating materials, the academic and engineering communities widely adopt the finger electrode structure for evaluation. This involves clamping the insulating sample between a pair of opposing hemispherical electrodes and applying a high voltage between them to create a concentrated electric field and induce surface discharge. However, this structure requires direct contact between the electrodes and the sample, which has the following significant drawbacks: Firstly, the radius of curvature at the electrode ends is small, resulting in a significant concentration of the local electric field at the electrode edges and adjacent oil gap regions. When a high voltage is applied, the dielectric strength of the insulating oil is lower than that of the solid paperboard surface, and discharge often occurs first in the oil gap, forming a discharge channel of "electrode-oil gap-opposite electrode." This phenomenon means that the test primarily assesses the oil gap breakdown characteristics, rather than the actual surface breakdown behavior of the insulating paperboard surface. Secondly, due to the unevenness of the paperboard surface roughness, oil film thickness, and contact pressure, microbubbles easily form at the contact interface. The dielectric constant of these bubbles is much lower than that of the insulating oil, causing electric field lines to accumulate around the bubbles, significantly enhancing the local electric field strength and distorting the electric field distribution. This phenomenon alters the true electric field characteristics of the solid-liquid interface, causing surface discharge to no longer develop naturally along the paperboard surface, making it difficult to reflect the intrinsic surface discharge law of the material.

[0004] Furthermore, if the local field concentration effect is eliminated through electrode optimization or structural improvement, the overall electric field of the system tends to be uniform, but the voltage required for the test increases sharply, exceeding the capabilities of conventional laboratory platforms. Moreover, the background noise of partial discharge is high under high voltage, making it difficult to meet the requirements of low partial discharge and high precision measurement environment for the study of surface discharge characteristics of insulating materials. Summary of the Invention

[0005] In view of this, the present invention proposes a non-contact surface discharge characteristic assessment device and method for insulating materials, aiming to solve the problem that existing surface discharge assessment devices are prone to electric field distribution distortion, premature partial discharge and oil gap breakdown under high voltage, making it difficult to truly and efficiently reflect the surface discharge characteristics of insulating materials under high voltage and low field strength conditions. This invention proposes a non-contact device for evaluating the surface properties of insulating materials, comprising: a housing, an equalizing element, and a ground electrode; wherein, The housing contains insulating oil to simulate the internal operating environment of power equipment. The equalizing element and the ground electrode are immersed in the insulating oil and are arranged opposite each other in the vertical direction, forming a surface discharge area between them; The equalizing component has a cavity with a high-voltage lead inside. The lower end of the high-voltage lead has a hanging part for suspending the insulation sample to be tested, so that the main body of the insulation sample to be tested is located on the central axis between the equalizing component and the ground electrode, and the lower end of the insulation sample to be tested is in contact with the ground electrode.

[0006] Furthermore, in the aforementioned non-contact insulating material surface characteristic assessment device, the equalizing component is a columnar conductive cavity with annular flanges bent towards the central axis at both ends, used to eliminate electric field concentration and suppress partial discharge.

[0007] Furthermore, in the aforementioned non-contact insulating material surface characteristic assessment device, the equalizing component is made of aluminum, and its surface is polished.

[0008] Furthermore, in the above-mentioned non-contact insulation material surface characteristic assessment device, two layers of annular laminated insulating paperboard are provided between the equalizing component and the ground electrode. The annular laminated insulating paperboard is provided near the edge of the equalizing component and the ground electrode to regulate the edge electric field distribution and suppress local breakdown caused by curvature abrupt change.

[0009] Furthermore, in the aforementioned non-contact insulating material surface characteristic assessment device, several insulating support blocks are provided between the two layers of the annular laminated insulating paperboard to maintain a fixed distance between them, so as to form a stable oil gap electric field region.

[0010] Furthermore, in the aforementioned non-contact insulation material surface characteristic assessment device, the ground electrode is adjustablely sleeved on a vertically arranged grounding connecting rod to accommodate insulation samples of different lengths.

[0011] Furthermore, the aforementioned non-contact insulating material surface characteristic testing device further includes: an insulating support frame disposed within the housing; wherein, The insulating support frame includes an upper support portion and a lower support portion. The lower support portion is disposed on the bottom plate of the housing and is used to support the ground electrode. The upper support portion is located above the lower support portion and is used to support the equalizing component.

[0012] The non-contact surface characteristic assessment device for insulating materials provided in this invention, by vertically aligning the equalizing element and the ground electrode in insulating oil, and suspending the insulating sample under test below the equalizing element, with only the lower end of the insulating sample in contact with the ground electrode, effectively avoids the interface bubbles and local electric field distortion caused by the mechanical clamping of the test sample by traditional finger electrodes. At the same time, the equalizing element forms a quasi-uniform electric field distribution under high voltage, allowing the surface discharge to develop stably along the surface of the insulating sample, effectively suppressing preferential breakdown of oil gaps. Thus, it can simulate the low surface field strength condition under high voltage conditions, accurately and reliably reflecting the surface discharge characteristics of the insulating sample under test, and significantly improving the authenticity and repeatability of the test results.

[0013] On the other hand, the present invention also proposes a method for evaluating the surface properties of non-contact insulating materials, comprising the following steps: The insulation sample to be tested is suspended in the insulating oil between the equalizing component and the ground electrode in a non-contact manner. An adjustable high voltage is applied between the equalizing element and the ground electrode, and the partial discharge signal and loop current are monitored simultaneously. Gradually increase the high voltage. When the local discharge exceeds the background noise level, record the corresponding voltage as the surface discharge initiation voltage. When the circuit current suddenly increases and is accompanied by a voltage drop or the test circuit overcurrent protection is activated, record the corresponding voltage as the surface flashover voltage. The surface electrical properties of the insulation sample under test are evaluated based on the surface discharge initiation voltage and surface flashover voltage.

[0014] Furthermore, in the above-mentioned method for evaluating the surface properties of non-contact insulating materials, two layers of annular laminated insulating paperboard are provided between the equalizing element and the ground electrode. The annular laminated insulating paperboard is disposed near the edge of the equalizing element and the ground electrode to regulate the edge electric field distribution and suppress local breakdown caused by curvature abrupt changes.

[0015] Furthermore, the above-mentioned method for evaluating the surface characteristics of non-contact insulating materials also includes: after surface flashover occurs, observing the morphology of the ablation marks on the surface of the insulating sample to be tested, and confirming the surface discharge path by combining the dendritic carbonization marks.

[0016] The non-contact method for evaluating the surface properties of insulating materials provided by this invention suspends the insulating sample between an equalizing element and a ground electrode in insulating oil, and simultaneously monitors partial discharge signals and loop current. It can use the partial discharge exceeding the background noise level as the criterion for the surface discharge initiation voltage, and the sudden increase in loop current accompanied by a voltage drop or the overcurrent protection action of the test loop as the criterion for the surface flashover voltage. This achieves an objective and repeatable evaluation of the surface electrical performance. This method effectively avoids misjudgment of partial discharge caused by contact between the electrode and the sample, ensures that the discharge path truly reflects the insulation performance of the insulating material surface, and significantly improves the reliability and engineering applicability of the test results. Attached Figure Description

[0017] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic diagram of the non-contact insulating material surface characteristic assessment device provided in an embodiment of the present invention; Figure 2 A schematic diagram of the electric field simulation distribution of the voltage equalization component in the non-contact insulating material surface characteristic assessment device provided in an embodiment of the present invention; Figure 3 The image shows the surface discharge path morphology of the insulating paperboard under test in the non-contact insulating material surface characteristic assessment method provided in this embodiment of the invention. Detailed Implementation

[0018] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] Device Example: See Figure 1The non-contact insulating material surface characteristic testing device of this invention includes: a housing 1, an equalizing element 2, and a ground electrode 3; wherein, the housing 1 contains insulating oil to simulate the internal operating environment of power equipment; the equalizing element 2 and the ground electrode 3 are immersed in the insulating oil and are arranged opposite each other in the vertical direction, forming a surface discharge area between them; the equalizing element 2 has a cavity, and a high-voltage lead 5 is provided inside it. The lower end of the high-voltage lead 5 is provided with a hanging part for suspending the insulating sample 4 to be tested, so that the main body of the insulating sample 4 to be tested is located on the central axis between the equalizing element 2 and the ground electrode 3, and the lower end of the insulating sample 4 to be tested is in contact with the ground electrode 3.

[0020] Specifically, the equalizing element 2 is located at the top, serving as a high-potential electrode, and is connected to an external high-voltage power supply via an internal high-voltage lead; the ground electrode 3 is located at the bottom, serving as a low-potential reference electrode, and is connected to the housing 1 and the earth via a grounding connection rod, forming a stable zero-potential reference. Together, they form an axisymmetric electric field in the insulating oil, pointing from the equalizing element 2 to the ground electrode 3, causing surface discharge to preferentially develop along the surface of the insulating sample 4 under test. All electrical connections of the test apparatus are sealed and shielded to ensure a stable dielectric environment during testing, avoiding external interference and thus guaranteeing the accuracy and repeatability of the test results.

[0021] The surface characteristic assessment device of this invention connects to an external high-voltage source through a high-voltage lead 5. The upper end of the high-voltage lead 5 is connected to a high-voltage bushing 6 (e.g., a 550kV bushing), through which the high voltage is safely introduced into the cavity of the equalizing component 2.

[0022] The hanging part at the lower end of the high-voltage lead 5 can be a conductive clamping ring or a conductive support structure. The insulation sample 4 to be tested is spatially positioned and electrically connected through the support structure or clamping ring, placing it in a high-potential state. This arrangement ensures that surface discharge preferentially develops along the surface of the insulation sample 4 to be tested, rather than through the oil gap or container wall. The sample surface does not directly contact the equalizing component 2 or the ground electrode 3, thus achieving true non-contact electric field loading. During the test, different insulation samples 4 to be tested can be quickly replaced through the hanging part, facilitating continuous testing of multiple insulation samples 4 to be tested under the same test conditions, greatly improving experimental efficiency.

[0023] In this embodiment, the insulating paperboard to be tested is suspended inside the equalizing component 2, so that the sample is positioned on the electric field symmetry axis and hangs naturally. This arrangement method completely eliminates the problems of interface bubbles and local field strength distortion caused by electrode pressing or fixing in traditional contact structures, ensuring that the discharge is determined only by the electric field distribution and the surface properties of the material.

[0024] The insulation sample 4 to be tested can be insulating paperboard. The insulating oil can be transformer oil. The equalizing element 2 and the ground electrode 3 are immersed in the insulating oil to simulate the actual oil-paper insulation environment inside an ultra-high voltage transformer. By filling the insulating oil medium, air discharge and surface bubble generation can be effectively suppressed, reducing the disturbance of the external environment on the surface discharge path, so that the discharge behavior is completely determined by the solid-liquid interface characteristics. At the same time, the environment in the insulating oil can reduce the probability of electric field abrupt changes and corona effects, ensuring uniform voltage rise and controlled discharge development during the test, thereby obtaining more realistic surface breakdown data and repeatable material performance evaluation results.

[0025] In this embodiment, the equalizing component 2 is a columnar conductive cavity with annular flanges bent toward the central axis at both ends, which is used to eliminate electric field concentration and suppress partial discharge.

[0026] The equalizing element 2 is made of aluminum, and its surface is polished to form a continuous and smooth electric field boundary, suppressing electric field concentration at the ends. In practice, the equalizing element 2 can be made of a highly conductive metal (such as an aluminum 900H structure), with an outer diameter of approximately φ360 mm and no insulating coating on the surface; its outer contour is a smooth curved surface to achieve natural diffusion of electric field lines and smooth transition of the electric field gradient. The insulating sample 4 to be tested is vertically suspended between the equalizing ring and the ground electrode 3. The high-voltage equalizing element 2 is a high-field region and does not directly contact the sample; the electric field loading is achieved by relying on the spatial potential distribution.

[0027] The ground electrode 3 can also be an aluminum electrode, which is set opposite to the equalizing element 2 to form a stable and symmetrical field boundary below the equalizing ring, so that the electric field lines are axially symmetrically distributed along the top of the sample, thereby ensuring that the surface discharge mainly occurs on the surface of the sample to be tested rather than in the oil gap or container wall.

[0028] The position of the ground electrode 3 is adjustablely sleeved on the vertically arranged grounding connecting rod 10 to accommodate insulation samples 4 of different lengths to be tested.

[0029] Specifically, the ground electrode 3 can be a spherical, dome-shaped, flat, or other shapes. It can be connected to the grounding connection rod by bolts.

[0030] In this embodiment, the ground electrode 3 is a disc-shaped structure with a rounded edge and a through hole in the center. It is fitted onto the grounding connecting rod. By loosening the fastening bolt, the ground electrode 3 can be moved up and down along the grounding connecting rod, for example, from position A to position B. Then, the bolt is tightened to achieve positioning, thereby maintaining the optimal gap matching between the equalizing component 2 and the ground electrode 3 and avoiding electric field distortion caused by changes in sample size.

[0031] In this embodiment, it further includes: an insulating support frame 7 disposed within the housing 1; wherein the insulating support frame 7 includes an upper support portion 71 and a lower support portion 72, the lower support portion 72 is disposed on the bottom plate of the housing 1 and is used to support the ground electrode 3; the upper support portion 71 is located above the lower support portion 72 and is used to support the equalizing member 2.

[0032] Specifically, the insulating support frame 7 is a vertically arranged double-layer (e.g., U-shaped) frame structure. The lower support can be placed on the bottom plate of the housing 1 by screws or slots; the upper support 71 is located on the upper inner side of the lower support 72, and is integrally formed with the lower support 72 or fixedly connected by an insulating connector. The two maintain a preset distance in the vertical direction to support the bottom edge of the pressure equalizing component 2. Preferably, the upper support 71 is located at the bottom of the annular laminated insulating paperboard 8, and supports both the annular laminated insulating paperboard 8 and the pressure equalizing component 2.

[0033] In this embodiment, the insulating support frame 7 ensures a stable relative position between the equalizing element 2 and the ground electrode 3 within the housing 1, thereby creating a highly symmetrical axial electric field distribution when voltage is applied. This also avoids electric field distortion, which helps ensure the authenticity and repeatability of the test results.

[0034] The non-contact surface characteristic assessment device of the present invention can be widely used in the basic research and performance evaluation of electrical insulation materials. Through a controllable high-voltage oil immersion environment and uniform electric field structure, the device can systematically characterize the surface breakdown characteristics of different paperboards, composite papers, laminates and coating structures, providing experimental basis for material selection, process improvement and aging life prediction.

[0035] At the engineering application level, the device of this invention can be used to verify the insulation structure of oil-immersed transformers, converter transformers, and reactors of 750 kV and above. It simulates the internal electric field distribution and oil temperature environment of the transformer under actual operating conditions to evaluate the safety margin and surface discharge risk of different insulation structures. Combined with online monitoring and electric field simulation technology, the device can also be expanded into a comprehensive testing and diagnostic platform for the insulation performance of transformer oil-paper systems, providing crucial support for the development and verification of new environmentally friendly insulating oils, composite paper, and solid insulation systems, and possessing significant scientific research and engineering application value.

[0036] It is evident from the above that the non-contact insulating material surface characteristic assessment device provided in this embodiment, by vertically aligning the equalizing element 2 and the ground electrode 3 in the insulating oil, and suspending the insulating sample 4 to be tested below the equalizing element 2, with only the lower end of the insulating sample 4 in contact with the ground electrode 3, effectively avoids the interface bubbles and local electric field distortion caused by the mechanical clamping of the test piece by the traditional finger electrode; at the same time, the equalizing element 2 forms a quasi-uniform electric field distribution under high voltage, so that the surface discharge develops stably along the surface of the insulating sample, effectively suppressing the preferential breakdown of the oil gap, thereby simulating the low surface field strength working condition under high voltage conditions, accurately and reliably reflecting the surface discharge characteristics of the insulating sample 4 to be tested, and significantly improving the authenticity and repeatability of the test results.

[0037] Continue to combine Figure 2 The electric field simulation results show that there is an electric field concentration phenomenon at the maximum arc curvature of the equalizing component 2. This region is prone to forming a local high field strength, which may cause the breakdown to occur first on the surface of the equalizing component 2, rather than on the insulation sample 4 to be tested.

[0038] To avoid such non-target discharge, in this embodiment, two layers of annular laminated insulating paperboard 8 are provided between the equalizing component 2 and the ground electrode 3. The annular laminated insulating paperboard 8 is located near the edge of the equalizing component 2 and the ground electrode 3 to regulate the edge electric field distribution and suppress local breakdown caused by curvature abrupt change.

[0039] Specifically, in regions with high electric field gradients, two layers of annular laminated insulating paperboard 8 are placed between the equalizing element 2 and the ground electrode 3 to allow the electric field to transition smoothly at the edges of the insulating paperboard, significantly reducing extreme field strength peaks. The annular laminated insulating paperboard 8 is approximately 3 mm thick to optimize the local electric field distribution and guide the surface discharge path.

[0040] Furthermore, a number of insulating support blocks 9 are provided between the two layers of annular laminated insulating paperboard 8 to maintain a fixed distance between them, so as to form a stable oil gap electric field region.

[0041] Method Implementation Examples: This invention also provides a method for evaluating the surface properties of non-contact insulating materials, comprising the following steps: Step S1: The insulation sample 4 to be tested is suspended in a non-contact manner between the equalizing component 2 and the ground electrode 3 in the insulating oil.

[0042] Specifically, the insulation sample 4 to be tested can be insulating paperboard. Before the test, the insulating paperboard needs to be thoroughly dried to eliminate internal and surface moisture, avoiding interference from humidity on surface discharge characteristics. The presence of moisture significantly reduces the volume resistivity and breakdown strength of the paperboard, and forms localized micro-discharge channels under the influence of an electric field, resulting in lower surface flashover voltage and poorer repeatability. To ensure the accuracy and comparability of the measurement results, this method uses constant-temperature vacuum drying to pre-treat the sample, keeping the moisture content within the standard allowable range. After drying, the insulating paperboard must be kept airtight during cooling to prevent moisture absorption and re-moistening, and then immediately immersed in pre-degassed insulating oil for storage until test use.

[0043] Step S2: Apply an adjustable high voltage between the equalizing element 2 and the ground electrode 3, and simultaneously monitor the partial discharge signal and the loop current.

[0044] In practice, a high-voltage AC power frequency of 50Hz is applied between the equalizing element 2 and the ground electrode 3, with a voltage increase rate of 10kV / min. During the test, the temperature of the insulating oil is controlled between 50 and 70℃ (e.g., 60℃) to simulate the oil temperature environment of equipment such as power transformers under rated operating conditions.

[0045] While boosting the voltage, a partial discharge detector is used to monitor the discharge signal, and a current sensor is used to collect the circuit current.

[0046] Step S3: Gradually increase the high voltage. When the local discharge exceeds the background noise level, record the corresponding voltage as the surface discharge initiation voltage. When the circuit current suddenly increases and is accompanied by a voltage drop or the test circuit overcurrent protection is activated, record the corresponding voltage as the surface flashover voltage.

[0047] Specifically, a background noise level (e.g., 10 pC) is set. When the partial discharge quantity is detected to continuously exceed this threshold and exhibit a typical discharge pulse pattern, it is determined to be the start of surface discharge, and the voltage at this time is recorded as the surface discharge initiation voltage. In some tests, a sharp increase in partial discharge quantity and oscillation of voltage waveform can be observed before surface flashover occurs. However, since such signals are easily affected by noise, this embodiment uses a sudden increase in loop current accompanied by a voltage drop or overcurrent protection action of the high-voltage power supply as the criterion for determining surface flashover, in order to improve the stability or repeatability of the test results.

[0048] Step S4: Evaluate the surface electrical properties of the insulation sample 4 under test based on the surface discharge initiation voltage and surface flashover voltage.

[0049] Furthermore, step S5 is included after step S4: after the surface flashover occurs, the morphology of the ablation marks on the surface of the insulation sample 4 to be tested is observed, and the surface discharge path is confirmed by combining the dendritic carbonization marks.

[0050] In practice, after the test, the insulation sample 4 to be tested is taken out and its surface morphology is observed, such as... Figure 3 As shown, the image on the left displays a symmetrical electrode outline, and black ablation marks are visible on the surface of the insulating cardboard under test. These are carbonization marks formed during the discharge process, indicating that the discharge spreads along the surface of the insulating cardboard. The magnified image on the right further shows that these marks have a typical dendritic morphology, visually proving that surface discharge occurs.

[0051] In this embodiment, the applied voltage, loop current, and partial discharge signal are synchronously recorded by the data acquisition system. Based on the synchronous data, the surface discharge initiation voltage and surface flashover voltage are determined (the partial discharge development rate and partial discharge abrupt change threshold can also be collected as auxiliary analysis). The average value and dispersion of the results obtained from multiple repeated tests are combined with the surface morphology of the insulation sample when flashover occurs to evaluate the surface electrical performance of the insulation sample 4 under test, so as to determine its tolerance level and stability.

[0052] The relevant parts of the method embodiments and the above-described device embodiments can be referred to each other, and will not be repeated here.

[0053] In summary, the non-contact method for evaluating the surface properties of insulating materials provided by this invention suspends the insulating sample between an equalizing element and a ground electrode in insulating oil, and simultaneously monitors partial discharge signals and loop currents. It uses the partial discharge exceeding the background noise level as the criterion for the surface discharge initiation voltage, and uses a sudden increase in loop current accompanied by a voltage drop or overcurrent protection activation in the test loop as the criterion for the surface flashover voltage. This achieves an objective and repeatable evaluation of the surface electrical performance. This method effectively avoids misjudgments of partial discharge caused by electrode-sample contact, ensures that the discharge path truly reflects the insulation performance of the insulating material surface, and significantly improves the reliability and engineering applicability of the test results.

[0054] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A non-contact device for assessing the surface properties of insulating materials, characterized in that, include: The casing, equalizing element, and ground electrode; among which, The housing contains insulating oil to simulate the internal operating environment of power equipment. The equalizing element and the ground electrode are immersed in the insulating oil and are arranged opposite each other in the vertical direction, forming a surface discharge area between them; The equalizing component has a cavity with a high-voltage lead inside. The lower end of the high-voltage lead has a hanging part for suspending the insulation sample to be tested, so that the main body of the insulation sample to be tested is located on the central axis between the equalizing component and the ground electrode, and the lower end of the insulation sample to be tested is in contact with the ground electrode.

2. The non-contact insulating material surface characteristic testing device according to claim 1, characterized in that, The equalizing component is a cylindrical conductive cavity with annular flanges at both ends that bend toward the central axis to eliminate electric field concentration and suppress partial discharge.

3. The non-contact insulating material surface characteristic testing device according to claim 1, characterized in that, The pressure equalizing component is made of aluminum and its surface is polished.

4. The non-contact insulating material surface characteristic testing device according to claim 1, characterized in that, Two layers of annular laminated insulating paperboard are provided between the equalizing element and the ground electrode. The annular laminated insulating paperboard is disposed near the edge of the equalizing element and the ground electrode to regulate the edge electric field distribution and suppress local breakdown caused by curvature abrupt change.

5. The non-contact insulating material surface characteristic testing device according to claim 4, characterized in that, Several insulating support blocks are provided between the two layers of annular laminated insulating paperboard to maintain a fixed distance between them, so as to form a stable oil gap electric field region.

6. The non-contact insulating material surface characteristic testing device according to claim 1, characterized in that, The ground electrode is adjustablely fitted onto a vertically arranged grounding connecting rod to accommodate insulation samples of different lengths.

7. The non-contact insulating material surface characteristic testing device according to claim 1, characterized in that, Also includes: An insulating support frame is disposed within the housing; wherein... The insulating support frame includes an upper support portion and a lower support portion. The lower support portion is disposed on the bottom plate of the housing and is used to support the ground electrode. The upper support portion is located above the lower support portion and is used to support the equalizing component.

8. A method for evaluating the surface properties of a non-contact insulating material, characterized in that, Includes the following steps: The insulation sample to be tested is suspended in the insulating oil between the equalizing component and the ground electrode in a non-contact manner. An adjustable high voltage is applied between the equalizing element and the ground electrode, and the partial discharge signal and loop current are monitored simultaneously. Gradually increase the high voltage. When the local discharge exceeds the background noise level, record the corresponding voltage as the surface discharge initiation voltage. When the circuit current suddenly increases and is accompanied by a voltage drop or the test circuit overcurrent protection is activated, record the corresponding voltage as the surface flashover voltage. The surface electrical properties of the insulation sample under test are evaluated based on the surface discharge initiation voltage and surface flashover voltage.

9. The method for evaluating the surface properties of non-contact insulating materials according to claim 8, characterized in that, Two layers of annular laminated insulating paperboard are provided between the equalizing element and the ground electrode. The annular laminated insulating paperboard is disposed near the edge of the equalizing element and the ground electrode to regulate the edge electric field distribution and suppress local breakdown caused by curvature abrupt change.

10. The method for assessing the surface properties of non-contact insulating materials according to claim 8, characterized in that, Also includes: After a surface flashover occurs, the morphology of the ablation marks on the surface of the insulation sample to be tested is observed, and the surface discharge path is confirmed by combining the dendritic carbonization marks.

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