Ultrasonic characteristic simulation device for interface aging of cable intermediate joint and detection and evaluation method

Abstract

The invention discloses an ultrasonic characteristic simulation device for interface aging of a cable intermediate joint and a detection and evaluation method. The ultrasonic characteristic simulation device comprises a mechanical pressurization device, a pressure sensor and an ultrasonic probe, aging of a cable intermediate joint interface material and changes of interface contact pressure along with aging can be simulated at the same time, and the interface insulation aging state of the cable intermediate joint can be reproduced; the detection and evaluation method comprehensively considers the reflection coefficient, sound velocity and nonlinear coefficient change of an ultrasonic signal, establishes a cable intermediate joint insulation / rubber interface aging evaluation model, and can more comprehensively reflect the change of interface pressure, roughness and interface material properties; the aging evaluation coefficient closely related to the interface contact state is adopted, so that the reliability of interface insulation can be evaluated more directly. According to the invention, ultrasonic nondestructive testing of insulation / rubber interface aging is realized.

Description

Technical Field

[0001] The invention belongs to the field of power cable detection, and relates to an ultrasonic characteristic simulation device and a detection and evaluation method for aging of insulation / rubber interface of a cable intermediate joint. Background Art

[0002] Current research shows that the insulation / rubber interface failure between the cable body and the intermediate joint is the most significant type of failure, which usually causes serious damage to the cable intermediate joint. During the actual operation of the cable, the insulation and rubber materials at the cable intermediate joint will inevitably age, causing their various performances to decline, resulting in the degradation of the electrical performance of the insulation / rubber interface or even failure.

[0003] Ultrasonic testing technology has been widely studied and applied in defect detection of electrical insulation materials due to its fast, non-destructive and safe characteristics. However, in existing research, the focus is on detecting the aging of the rubber material itself. In practice, it is often the earlier failure of the insulation / rubber interface that causes the overall failure of the cable joint. Existing ultrasonic testing methods lack the ability to evaluate the aging of the insulation / rubber interface.

[0004] Therefore, obtaining the aging ultrasonic characteristics of the insulation / rubber interface between the cable body and the intermediate joint has important guiding significance for the nondestructive testing technology of the cable intermediate joint. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art and provide an ultrasonic characteristic simulation device and a detection and evaluation method for the aging of the insulation / rubber interface of the cable intermediate joint. The ultrasonic characteristic simulation device is used to simultaneously simulate the aging of the interface material of the cable intermediate joint and the change of the interface contact pressure with aging; the detection and evaluation method comprehensively reflects the changes in the interface pressure, roughness and properties of the interface material to comprehensively evaluate the interface aging state.

[0006] To this end, the present invention adopts the following technical solution.

[0007] In a first aspect, the present invention provides an ultrasonic characteristic simulation device for cable intermediate joint interface aging, comprising: A mechanical pressurizing device, used for simulating the pressure between the insulation / rubber interface of the cable intermediate joint, comprises an insulating top plate, a first insulating bottom plate, a second insulating bottom plate and an insulating support, wherein the ends of the insulating top plate, the first insulating bottom plate and the second insulating bottom plate are connected by the insulating support, and the rubber sample and the insulating sample to be simulated are placed between the insulating top plate and the first insulating bottom plate; a first fastener on the insulating support is provided above the insulating top plate, and an elastic member is provided between the first fastener and the insulating support, and the pressure between the insulation / rubber interface of the cable intermediate joint is adjusted by rotating the first fastener; A pressure sensor, located between the first insulating base plate and the second insulating base plate, for testing the pressure between the insulation / rubber interface of the cable intermediate joint; and The ultrasonic probe is placed on the surface of the rubber sample to be simulated and is used to detect the ultrasonic echo signal of the insulation / rubber interface of the cable intermediate joint.

[0008] Furthermore, the material of the insulation sample to be simulated is cross-linked polyethylene or polypropylene used in the cable intermediate joint.

[0009] Furthermore, the material of the rubber sample to be simulated is silicone rubber or EPDM rubber used in cable intermediate joints.

[0010] Furthermore, there are at least two insulating pillars which are symmetrically distributed, and a second fastener connected to the insulating pillar is provided below the second insulating bottom plate.

[0011] Furthermore, a hole is opened on the insulating top plate, and the ultrasonic probe is embedded in the hole and contacts the upper surface of the rubber sample to be simulated.

[0012] Furthermore, the frequency of the ultrasonic probe is 1 MHz to 5 MHz.

[0013] In a second aspect, the present invention provides an ultrasonic detection and evaluation method for the aging of the interface of the intermediate cable joint, which uses the above-mentioned ultrasonic characteristic simulation device to perform ultrasonic detection, and comprises: Simulating interface pressure, stacking the insulation sample and the rubber sample to be simulated between the insulation top plate and the first insulation bottom plate, and applying a preset simulation pressure; Test the ultrasonic primary echo signal of the rubber sample; Calculate echo parameters based on ultrasonic primary echo signal and build an aging assessment model for the insulation / rubber interface of the cable intermediate joint; The interface aging coefficient is obtained and the interface aging status is evaluated.

[0014] Furthermore, thermal aging of the samples was performed before simulating the interface pressure: the insulation samples and rubber samples to be simulated were wiped clean with anhydrous ethanol, placed in a drying oven for thermal mechanical aging, and the elongation, aging temperature and aging time were set; the elongation was 0%~100%, and the aging temperature was 50℃~200℃.

[0015] Furthermore, the preset simulation pressure is 0 MPa~5 MPa.

[0016] Furthermore, the cable intermediate joint insulation / rubber interface aging assessment model is as follows: Ultrasonic echo velocity and material modulus E The following relationship exists: (4) In the formula, is the density of the rubber sample; According to the phase screen approximation theory, the ultrasonic first echo reflection coefficient R and interface roughness S q The following relationship exists: (5) In the formula, R 0 is the reflection coefficient of an ideal smooth interface, k is the number of echoes; Ultrasonic first echo nonlinear coefficient Interface pressure P There is approximately the following relationship between them: (6) In the formula, is the first correction coefficient; is the second correction coefficient; is the third correction factor; Based on the Gaussian distribution model of the rough interface, the actual contact area of ​​the rough interface Nominal contact area The following relationship exists: (7) In the formula, is the composite elastic modulus of the interface contact material; It is the material surface morphology parameter, which is used to describe the spherical radius of the protrusions on the rough surface; According to equations (4) to (7), the interface aging evaluation coefficient is defined as K age : (8) In the formula, is the fourth correction coefficient.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: The ultrasonic characteristic simulation device of the present invention can simultaneously simulate the aging of the cable intermediate joint interface material and the change of the interface contact pressure with aging, which is consistent with the aging state of the cable intermediate joint interface insulation, and solves the problem of difficulty in reproducing the aging state of the cable intermediate joint interface.

[0018] The ultrasonic detection and evaluation method of the present invention comprehensively considers the multi-parameter changes of ultrasonic signals, and the established model can comprehensively reflect the changes in interface pressure, roughness and interface material properties, and the evaluation of the interface aging state is more comprehensive; the interface aging evaluation coefficient proposed by the present invention is closely related to the interface contact state, and can more directly evaluate the reliability of interface insulation, and achieve a more accurate evaluation of the interface state; the present invention realizes ultrasonic non-destructive detection of insulation / rubber interface aging, which has important guiding significance for the non-destructive detection technology of cable intermediate joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0020] Figure 1 It is a structural schematic diagram of an ultrasonic characteristic simulation device for cable intermediate joint interface aging according to the present invention; Figure 2 is an ultrasonic time domain spectrogram of the insulation / rubber interface at different aging times in a specific embodiment of the present invention; Figure 3 is an ultrasonic frequency domain spectrogram of the insulation / rubber interface at different aging times in a specific embodiment of the present invention; Figure 4 is a graph showing changes in the ultrasonic primary echo reflection coefficient with interface aging time in a specific embodiment of the present invention; Figure 5 is a graph showing changes in the ultrasonic primary echo velocity with interface aging time in a specific embodiment of the present invention; Figure 6 is a graph showing changes in the nonlinear coefficient of the ultrasonic primary echo with the interface aging time in a specific embodiment of the present invention; Figure 7 It is a graph showing the change of the interface aging coefficient with the interface aging time in a specific implementation manner of the present invention.

[0021] Figure 1 In the figure: 1-insulating sample; 2-rubber sample; 3-insulating top plate; 4-first insulating bottom plate; 5-second insulating bottom plate; 6-insulating support pillar; 7-first fastener; 8-elastic member; 9-pressure sensor; 10-ultrasonic probe; 11-second fastener. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below in conjunction with specific implementation methods and accompanying drawings.

[0023] Example 1 This embodiment provides an ultrasonic characteristic simulation device for aging of insulation / rubber interface of cable intermediate joint, such as Figure 1As shown, the device includes: a mechanical pressurizing device, a pressure sensor 9 and an ultrasonic probe 10.

[0024] The mechanical pressurizing device is used to simulate the pressure between the insulation and rubber interface of the cable intermediate joint.

[0025] The pressure sensor 9 is located between the first insulating base plate and the second insulating base plate and is used to test the pressure between the insulation / rubber interface of the cable intermediate joint.

[0026] The ultrasonic probe 10 has a frequency of 1 MHz to 5 MHz and is placed on the surface of the rubber sample to detect the ultrasonic echo signal of the insulation / rubber interface of the cable intermediate joint.

[0027] The mechanical pressurizing device is composed of an insulating top plate 3, a first insulating bottom plate 4, a second insulating bottom plate 5 and an insulating support 6. The insulating top plate 3, the first insulating bottom plate 4, the second insulating bottom plate 5 and the insulating support 6 are made of epoxy resin, which is insulating and high temperature resistant. Other materials, such as polytetrafluoroethylene or acrylic resin, may also be used.

[0028] The ends of the insulating top plate 3, the first insulating bottom plate 4 and the second insulating bottom plate 5 are connected by four symmetrically distributed insulating pillars 6. The rubber sample 2 to be simulated and the insulating sample 1 to be simulated are placed between the insulating top plate 3 and the first insulating bottom plate 4. A first fastener 7 sleeved on the insulating pillar is provided above the insulating top plate 3. The first fastener 7 and the insulating pillar 6 are provided with an elastic member 8. The pressure between the insulation / rubber interface of the cable intermediate joint is adjusted by the rotation of the first fastener 7. A second fastener 11 connected to the insulating pillar 6 is provided below the second insulating bottom plate 5. The second fastener is fixed when the device is in use. The elastic member 8 is a spring, and other similar elastic members can also be used.

[0029] The material of the insulation sample 1 to be simulated is cross-linked polyethylene or polypropylene used in the cable intermediate joint. The material of the rubber sample 2 to be simulated is silicone rubber or EPDM rubber used in the cable intermediate joint.

[0030] The first fastener and the second fastener are both nuts, and other similar fasteners may also be used.

[0031] The insulating top plate 3 has a hole, and the ultrasonic probe 10 is embedded in the hole and contacts the upper surface of the rubber sample 2 .

[0032] In the actual cable operation process, the cable joints are in a long-term high temperature state, and the materials on both sides of the insulation / rubber interface of the cable intermediate joints are in a long-term heat aging state. Figure 1The insulation sample 1 and rubber sample 2 with different heat aging times stacked in the ultrasonic characteristic simulation device for aging of the insulation / rubber interface of the cable intermediate joint shown can reproduce the aging state of the materials on both sides of the interface of the cable intermediate joint. Since the rubber of the cable intermediate joint is in an expansion stress state for a long time, the stress relaxation of the material will occur with the aging of the rubber material, and the pressure of the insulation / rubber interface of the cable intermediate joint will gradually decrease. The ultrasonic characteristic simulation device of the present invention can tighten the first fastener 7, and the insulation top plate 3 and the first insulation bottom plate 4 will squeeze the insulation sample 1 and the rubber sample 2, thereby simulating the change of the pressure of the insulation / rubber interface of the cable intermediate joint with the aging of the interface. The pressure sensor 9 placed between the first insulation bottom plate 4 and the second insulation bottom plate 5 is subjected to the same force as the insulation sample 1 and the rubber sample 2. By reading the pressure reading of the pressure sensor 9, the specific value of the interface pressure can be obtained. There are 4 elastic members 8, which are respectively mounted on the four insulation pillars 6 to evenly distribute the pressure on the insulation top plate 3.

[0033] Example 2 This embodiment provides an ultrasonic detection and evaluation method for the aging of the cable intermediate joint interface, which uses the ultrasonic characteristic simulation device described in Example 1 to perform ultrasonic detection, and the steps are as follows: Step S1, thermal aging of samples: wipe the insulation sample and the rubber sample to be simulated clean with anhydrous ethanol, put them into a drying oven for thermal mechanical aging, set the elongation, aging temperature and aging time; after aging, take out the sample and proceed to step S2; Step S2, simulating interface pressure: stacking the insulating sample and the rubber sample between the insulating top plate and the first insulating bottom plate of the ultrasonic characteristic simulation device; tightening the first fastener, observing the pressure sensor reading, and entering step S3 after the pressure sensor reading reaches the simulated pressure; Step S3, ultrasonic signal testing: applying vaseline between the ultrasonic probe and the rubber sample, and testing the ultrasonic primary echo signal; Step S4, repeating steps S1 to S3, performing ultrasonic testing on rubber samples and insulation samples with different aging times and different interface pressures; Step S5, calculating the ultrasonic primary echo parameters, including the ultrasonic primary echo sound velocity, the ultrasonic primary echo reflection coefficient and the ultrasonic primary echo nonlinear coefficient; Step S6, establishing a cable intermediate joint insulation / rubber interface aging assessment model based on the parameters calculated in step S5, obtaining an interface aging coefficient, and assessing the interface aging state.

[0034] Specifically, the stretching rate in step S1 is 0% to 100%, and the aging temperature is 50° C. to 200° C.

[0035] Specifically, the simulation pressure of insulation / rubber interface aging in step S2 is 0 MPa to 5 MPa.

[0036] Specifically, in step S5, the ultrasonic primary echo parameters are calculated by the following formula.

[0037] (1) In formula (1), is the velocity of the first ultrasonic echo, d is the thickness of the rubber sample, t r is the echo time.

[0038] (2) In formula (2), R is the ultrasonic first echo reflection coefficient, r 1 is the amplitude of an echo, r 0 is the fundamental amplitude.

[0039] (3) In formula (3), is the nonlinear coefficient of the ultrasonic primary echo, A 2 is the second harmonic amplitude of the first echo in the frequency domain after Fourier transform, A 1 is the fundamental amplitude of the first echo in the frequency domain after Fourier transform.

[0040] Specifically, the cable intermediate joint insulation / rubber interface aging assessment model in step S6 is as follows: Ultrasonic echo velocity and material modulus E The following relationship exists: (4) In the formula, is the density of the rubber sample; According to the phase screen approximation theory, the ultrasonic first echo reflection coefficient R and interface roughness S q The following relationship exists: (5) In the formula, R 0 is the reflection coefficient of an ideal smooth interface, k is the number of echoes; Ultrasonic first echo nonlinear coefficient Interface pressure P There is approximately the following relationship between them: (6) In the formula, is the first correction coefficient; is the second correction coefficient; is the third correction factor; Based on the Gaussian distribution model of the rough interface, the actual contact area of ​​the rough interface Nominal contact area The following relationship exists: (7) In the formula, is the composite elastic modulus of the interface contact material; It is the material surface morphology parameter, which is used to describe the spherical radius of the protrusions on the rough surface; According to equations (4) to (7), the interface aging evaluation coefficient is defined as K age : (8) In the formula, represents the fourth correction coefficient.

[0041] The ultrasonic detection and evaluation method of the present invention comprehensively considers the reflection coefficient, sound velocity and nonlinear coefficient changes of the ultrasonic signal, and establishes an aging evaluation model for the insulation / rubber interface of the cable intermediate joint, which can more comprehensively reflect the changes in interface pressure, roughness and interface material properties; the proposed aging evaluation coefficient that is closely related to the interface contact state can more directly evaluate the reliability of interface insulation.

[0042] Application Examples The ultrasonic detection and evaluation method for the aging of the insulation / rubber interface of the cable intermediate joint described in Example 2 was used as follows.

[0043] The insulation specimen and the silicone rubber specimen to be simulated are rectangular with a size of 30 mm × 60 mm × 2 mm. The insulation specimen is selected as the specimen that has not been aged. The silicone rubber specimen is selected as the specimen that has been thermomechanically aged in an oven at 150°C for 0 h, 10 h, 240 h, 480 h, 720 h and 1200 h. The first fastener is rotated to adjust the interface pressure between the insulation specimen and the silicone rubber specimen to 0.10 MPa.

[0044] Ultrasonic spectra of insulation / rubber interface at different aging times Figure 2 As shown, the ultrasonic wave is reflected at the insulation / rubber interface, generating an echo.

[0045] The ultrasonic time domain signal is transformed by Fourier transform, and the frequency domain signal of the ultrasonic primary echo of the insulation / rubber interface with different aging times is as follows: Figure 3 shown.

[0046] As the insulation / rubber interface ages, the amplitude of the first echo gradually decreases and the reflection coefficient decreases. The calculation shows that the reflection coefficient changes with the interface aging state; as the insulation / rubber interface ages, the first echo time advances, and the echo sound velocity changes with the interface aging state can be calculated based on the sample thickness and echo time; based on the fundamental wave and harmonic wave of the ultrasonic frequency domain spectrum, the nonlinear coefficient changes with the interface aging state can be calculated. The calculation results are as follows Figure 4 , Figure 5 and Figure 6 shown.

[0047] Substitute the three sets of coefficients into the aging assessment model for fitting and calculate the interface aging assessment coefficients K age ,like Figure 7 When C0=0, C1=0.000752, C2=0.012, C3=1.00E-06, the interface aging evaluation coefficient K age It is highly correlated with the interface aging time. Compared with the evaluation results of interface aging by a single parameter, the interface aging evaluation coefficient K age The evaluation results of the interface aging state are better correlated with the aging time.

[0048] It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. An ultrasonic characteristic simulation device for cable intermediate joint interface aging, characterized in that: include: A mechanical pressurizing device, used for simulating the pressure between the insulation / rubber interface of the cable intermediate joint, comprises an insulating top plate, a first insulating bottom plate, a second insulating bottom plate and an insulating support, wherein the ends of the insulating top plate, the first insulating bottom plate and the second insulating bottom plate are connected by the insulating support, and the rubber sample and the insulating sample to be simulated are placed between the insulating top plate and the first insulating bottom plate; a first fastener on the insulating support is provided above the insulating top plate, and an elastic member is provided between the first fastener and the insulating support, and the pressure between the insulation / rubber interface of the cable intermediate joint is adjusted by rotating the first fastener; A pressure sensor, located between the first insulating base plate and the second insulating base plate, used to test the pressure between the insulation / rubber interface of the cable intermediate joint; as well as The ultrasonic probe is placed on the surface of the rubber sample to be simulated and is used to detect the ultrasonic echo signal of the insulation / rubber interface of the cable intermediate joint.

2. The ultrasonic characteristics simulation device according to claim 1, characterized in that: The material of the insulation specimen to be simulated is cross-linked polyethylene or polypropylene used in cable intermediate joints.

3. The ultrasonic characteristics simulation device according to claim 1, characterized in that: The material of the rubber sample to be simulated is silicone rubber or EPDM rubber used in cable intermediate joints.

4. The ultrasonic characteristics simulation device according to claim 1, characterized in that: There are at least two insulating pillars which are symmetrically distributed, and a second fastener connected to the insulating pillars is provided below the second insulating bottom plate.

5. The ultrasonic characteristics simulation device according to claim 1, characterized in that: A hole is opened on the insulating top plate, and the ultrasonic probe is embedded in the hole and contacts the upper surface of the rubber sample to be simulated.

6. The ultrasonic characteristics simulation device according to claim 1, characterized in that: The frequency of the ultrasonic probe is 1 MHz to 5 MHz.

7. A method for ultrasonic detection and evaluation of cable intermediate joint interface aging, which uses the ultrasonic characteristic simulation device according to any one of claims 1 to 6 for ultrasonic detection, characterized in that: include: Simulating interface pressure, stacking the insulation sample and the rubber sample to be simulated between the insulation top plate and the first insulation bottom plate, and applying a preset simulation pressure; Test the ultrasonic primary echo signal of the rubber sample; Calculate the echo parameters based on the ultrasonic primary echo signal and build the cable intermediate joint insulation / rubber interface aging assessment model; The interface aging coefficient is obtained and the interface aging status is evaluated.

8. The ultrasonic detection and evaluation method according to claim 7, characterized in that: Before simulating the interface pressure, the sample is thermally aged: the insulation sample and rubber sample to be simulated are wiped clean with anhydrous ethanol, placed in a drying oven for thermal mechanical aging, and the elongation rate, aging temperature and aging time are set; the elongation rate is 0%~100%, and the aging temperature is 50℃~200℃.

9. The ultrasonic detection and evaluation method according to claim 7, characterized in that: The preset simulation pressure is 0Mpa~5MPa.

10. The ultrasonic detection and evaluation method according to claim 7, characterized in that: The cable intermediate joint insulation / rubber interface aging assessment model is as follows: Ultrasonic echo velocity and material modulus E The following relationship exists: （4） In the formula, is the density of the rubber sample; According to the phase screen approximation theory, the ultrasonic first echo reflection coefficient R and interface roughness S q The following relationship exists: （5） In the formula, R 0 is the reflection coefficient of an ideal smooth interface, k is the number of echoes; Ultrasonic first echo nonlinear coefficient Interface pressure P There is approximately the following relationship between them: （6） In the formula, is the first correction coefficient; is the second correction coefficient; is the third correction factor; Based on the Gaussian distribution model of the rough interface, the actual contact area of ​​the rough interface Nominal contact area The following relationship exists: （7） In the formula, is the composite elastic modulus of the interface contact material; It is the material surface morphology parameter, which is used to describe the spherical radius of the protrusions on the rough surface; According to equations (4) to (7), the interface aging evaluation coefficient is defined as K age : （8） In the formula, is the fourth correction coefficient.

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