An ultrasonic characteristic simulation device and detection and evaluation method for the interface aging of a cable joint

Abstract

The present invention discloses an ultrasonic characteristic simulation device and a detection and evaluation method for the interface aging of a cable joint. The ultrasonic characteristic simulation device of the present invention includes a mechanical pressurizing device, a pressure sensor, and an ultrasonic probe, which can simultaneously simulate the aging of the interface material of the cable joint and the change of the interface contact pressure with aging, and reproduce the insulation aging state of the cable joint interface; the detection and evaluation method comprehensively considers the changes in the reflection coefficient, sound velocity, and nonlinear coefficient of the ultrasonic signal, establishes an aging evaluation model for the insulation / rubber interface of the cable joint, and can more comprehensively reflect the changes in the interface pressure, roughness, and interface material properties; by using an aging evaluation coefficient closely related to the interface contact state, the reliability of the interface insulation can be evaluated more directly. The present invention realizes the ultrasonic non-destructive detection of the insulation / rubber interface aging.

Description

Technical Field

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

[0002] Current research shows that the insulation / rubber interface fault between the cable body and the intermediate joint is the most significant fault type, 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 inevitably age, resulting in a decline in their various performances, leading to the deterioration or even failure of the electrical performance of the insulation / rubber interface.

[0003] Due to its characteristics of fast speed, non-destructiveness, and safety, ultrasonic detection technology has been widely studied and applied in the defect detection of electrical insulating materials. 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, and the existing ultrasonic detection means 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 is of great guiding significance for the non-destructive detection technology of cable intermediate joints. Summary of the Invention

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

[0006] For this purpose, the present invention adopts the following technical solutions.

[0007] In a first aspect, the present invention provides an ultrasonic characteristic simulation device for the aging of the cable intermediate joint interface, which includes:

[0008] A mechanical pressurizing device for simulating the pressure between the insulation / rubber interfaces of the cable intermediate joint, including an insulating top plate, a first insulating bottom plate, a second insulating bottom plate, and insulating columns. The ends of the insulating top plate, the first insulating bottom plate, and the second insulating bottom plate are connected by insulating columns. The rubber specimen and the insulating specimen to be simulated are placed between the insulating top plate and the first insulating bottom plate. A first fastener is provided on the insulating columns above the insulating top plate. An elastic member is provided between the first fastener and the insulating columns. The pressure between the insulation / rubber interfaces of the cable intermediate joint is adjusted by rotating the first fastener.

[0009] A pressure sensor, located between the first insulating base plate and the second insulating base plate, is used to test the pressure between the insulation / rubber interface of the cable joint; and

[0010] An ultrasonic probe, placed on the surface of the rubber specimen to be simulated, is used to detect the ultrasonic echo signal of the insulation / rubber interface of the cable joint.

[0011] Further, the material of the insulating specimen to be simulated is cross-linked polyethylene or polypropylene used in the cable joint.

[0012] Further, the material of the rubber specimen to be simulated is silicone rubber or ethylene propylene diene monomer rubber used in the cable joint.

[0013] Further, there are at least two insulating columns and they are symmetrically distributed. A second fastener connected to the insulating columns is provided below the second insulating base plate.

[0014] Further, holes are opened on the insulating top plate, the ultrasonic probe is embedded in the holes and contacts with the upper surface of the rubber specimen to be simulated.

[0015] Further, the frequency of the ultrasonic probe is 1 MHz to 5 MHz.

[0016] In a second aspect, the present invention provides an ultrasonic detection and evaluation method for the interface aging of a cable joint, which uses the above ultrasonic characteristic simulation device for ultrasonic detection, and includes:

[0017] Simulating the interface pressure, stacking the insulating specimen and the rubber specimen to be simulated between the insulating top plate and the first insulating base plate, and applying a preset simulated pressure;

[0018] Testing the ultrasonic primary echo signal of the rubber specimen;

[0019] Calculating echo parameters according to the ultrasonic primary echo signal, and constructing an aging evaluation model for the insulation / rubber interface of the cable joint;

[0020] Obtaining the interface aging coefficient and evaluating the interface aging state.

[0021] Further, before simulating the interface pressure, specimen thermal aging is also carried out: wiping the insulating specimen and the rubber specimen to be simulated clean with anhydrous ethanol, putting them into a drying oven for thermo-mechanical aging, and setting the elongation rate, aging temperature and aging time; the elongation rate is 0% to 100%, and the aging temperature is 50 °C to 200 °C.

[0022] Further, the preset simulated pressure is 0 Mpa to 5 MPa.

[0023] Furthermore, the aging evaluation model for the insulation / rubber interface of the cable joint in the middle is as follows:

[0024] The ultrasonic primary echo sound velocity and the material modulus E have the following relationship:

[0025] (4)

[0026] In the formula, is the density of the rubber specimen;

[0027] According to the phase screen approximation theory, the ultrasonic primary echo reflection coefficient R and the interface roughness S q have the following relationship:

[0028] (5)

[0029] In the formula, R 0 is the reflection coefficient of the ideal smooth interface, k is the number of echo times;

[0030] The ultrasonic primary echo nonlinear coefficient and the interface pressure P approximately have the following relationship:

[0031] (6)

[0032] In the formula, is the first correction coefficient; is the second correction coefficient; is the third correction coefficient;

[0033] Based on the Gaussian distribution model of the rough interface, the true contact area of the rough interface and the nominal contact area have the following relationship:

[0034] (7)

[0035] In the formula, is the composite elastic modulus of the interface contact materials; is the material surface topography parameter, used to describe the spherical radius of the protrusions on the rough surface;

[0036] From formulas (4) to (7), define the interface aging evaluation coefficient K age :

[0037] (8)

[0038] In the formula, is the fourth correction coefficient.

[0039] Compared with the prior art, the present invention has at least the following beneficial effects:

[0040] The ultrasonic characteristic simulation device of the present invention can simultaneously simulate the aging of the interface material of the cable joint and the change of the interface contact pressure with aging, which is consistent with the interface insulation aging state of the cable joint, and solves the problem of difficult reproduction of the interface aging state of the cable joint.

[0041] The ultrasonic detection and evaluation method of the present invention comprehensively considers the multi-parameter changes of ultrasonic signals. The established model can comprehensively reflect the changes of interface pressure, roughness and interface material properties, and evaluate the interface aging state more comprehensively. The interface aging evaluation coefficient proposed by the present invention is closely related to the interface contact state, can more directly evaluate the reliability of interface insulation, and realize a more accurate evaluation of the interface state. The present invention realizes the ultrasonic non-destructive detection of the aging of the insulation / rubber interface, which has important guiding significance for the non-destructive detection technology of cable joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0043] Figure 1 is a schematic structural diagram of the ultrasonic characteristic simulation device for the interface aging of the cable joint of the present invention;

[0044] Figure 2 is the ultrasonic time-domain spectrogram of the insulation / rubber interface at different aging times in the specific embodiment of the present invention;

[0045] Figure 3 is the ultrasonic frequency-domain spectrogram of the insulation / rubber interface at different aging times in the specific embodiment of the present invention;

[0046] Figure 4 is a graph showing the change of the ultrasonic primary echo reflection coefficient with the interface aging time in the specific embodiment of the present invention;

[0047] Figure 5 is a graph showing the change of the ultrasonic primary echo sound velocity with the interface aging time in the specific embodiment of the present invention;

[0048] Figure 6 is a graph showing the change of the ultrasonic primary echo nonlinear coefficient with the interface aging time in the specific embodiment of the present invention;

[0049] Figure 7 is a graph showing the change of the interface aging coefficient with the interface aging time in the specific embodiment of the present invention.

[0050] Figure 1 Among them: 1 - insulating specimen; 2 - rubber specimen; 3 - insulating top plate; 4 - first insulating bottom plate; 5 - second insulating bottom plate; 6 - insulating support; 7 - first fastener; 8 - elastic member; 9 - pressure sensor; 10 - ultrasonic probe; 11 - second fastener. Specific embodiments

[0051] The present invention will be further described in detail below in conjunction with specific embodiments and the accompanying drawings of the specification.

[0052] Embodiment 1

[0053] This embodiment provides an ultrasonic characteristic simulation device for the aging of the insulation / rubber interface of a cable joint. As Figure 1 shown, the device includes: a mechanical pressurizing device, a pressure sensor 9, and an ultrasonic probe 10.

[0054] The mechanical pressurizing device is used to simulate the pressure between the insulation / rubber interfaces of the cable joint.

[0055] The pressure sensor 9 is located between the first insulating bottom plate and the second insulating bottom plate and is used to measure the pressure between the insulation / rubber interfaces of the cable joint.

[0056] The ultrasonic probe 10, with a frequency of 1 MHz to 5 MHz, is placed on the surface of the rubber specimen and is used to detect the ultrasonic echo signal of the insulation / rubber interface of the cable joint.

[0057] 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 materials of the insulating top plate 3, the first insulating bottom plate 4, the second insulating bottom plate 5, and the insulating support 6 are epoxy resin, which is insulating and heat-resistant. Other materials such as polytetrafluoroethylene or acrylic resin can also be used.

[0058] The ends of the insulating top plate 3, the first insulating bottom plate 4, and the second insulating bottom plate 5 are connected by 4 symmetrically distributed insulating supports 6. Between the insulating top plate 3 and the first insulating bottom plate 4, a rubber specimen 2 to be simulated and an insulating specimen 1 to be simulated are placed. Above the insulating top plate 3, there is a first fastener 7 sleeved on the insulating support. The first fastener 7 and the insulating support 6 are provided with an elastic member 8, and the pressure between the insulation / rubber interfaces of the cable joint is adjusted by rotating the first fastener 7. Below the second insulating bottom plate 5, there is a second fastener 11 connected to the insulating support 6, and the second fastener remains stationary during the use of the device. The elastic member 8 is a spring, and other similar elastic members can also be used.

[0059] The material of the insulating specimen 1 to be simulated is cross-linked polyethylene or polypropylene used in cable joints. The material of the rubber specimen 2 to be simulated is silicone rubber or ethylene propylene diene monomer (EPDM) rubber used in cable joints.

[0060] Both the first fastener and the second fastener are nuts, and other similar fasteners can also be used.

[0061] An opening is made on the insulating top plate 3, and the ultrasonic probe 10 is embedded in the hole and contacts the upper surface of the rubber specimen 2.

[0062] During the actual operation of the cable, the cable joint is in a long-term high-temperature state, and the materials on both sides of the insulating / rubber interface of the cable joint are in a long-term thermal aging state. In Figure 1 the insulating specimen 1 and the rubber specimen 2 with different thermal aging times stacked in the ultrasonic characteristic simulation device for the aging of the insulating / rubber interface of the cable joint shown can reproduce and simulate the aging states of the materials on both sides of the cable joint interface. Since the rubber of the cable joint is in a long-term expanded and stressed state, stress relaxation of the material will occur as the rubber material ages, and the pressure at the insulating / rubber interface of the cable joint will gradually decrease. The ultrasonic characteristic simulation device of the present invention can tighten the first fastener 7, and the insulating top plate 3 and the first insulating bottom plate 4 will squeeze the insulating specimen 1 and the rubber specimen 2, thereby simulating the change of the pressure at the insulating / rubber interface of the cable joint with the aging of the interface. The pressure sensor 9 placed between the first insulating bottom plate 4 and the second insulating bottom plate 5 is subjected to the same force as the insulating specimen 1 and the rubber specimen 2. By reading the pressure indication of the pressure sensor 9, the specific value of the interface pressure can be obtained. There are 4 elastic members 8, which are respectively sleeved on the four insulating columns 6 to evenly distribute the pressure on the insulating top plate 3.

[0063] Embodiment 2

[0064] This embodiment provides an ultrasonic detection and evaluation method for the aging of the cable joint interface, which uses the ultrasonic characteristic simulation device described in Embodiment 1 for ultrasonic detection, and the steps are as follows:

[0065] Step S1, specimen thermal aging: Wipe the insulating specimen to be simulated and the rubber specimen to be simulated clean with anhydrous ethanol, put them into a drying oven for thermo-mechanical aging, and set the elongation rate, aging temperature and aging time; after aging is completed, take out the specimen and proceed to Step S2;

[0066] Step S2, simulate interface pressure: Stack the insulating specimen and the rubber specimen between the insulating top plate and the first insulating bottom plate of the ultrasonic characteristic simulation device; tighten the first fastener, observe the indication of the pressure sensor, and after the indication of the pressure sensor reaches the simulated pressure, proceed to Step S3;

[0067] Step S3, ultrasonic signal test: Apply vaseline between the ultrasonic probe and the rubber specimen, and test the ultrasonic primary echo signal;

[0068] Step S4, Repeat steps S1 to S3 to conduct ultrasonic tests on rubber specimens and insulating specimens with different aging times and different interface pressures;

[0069] Step S5, Calculate 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;

[0070] Step S6, Based on the parameters calculated in step S5, establish an aging evaluation model for the insulation / rubber interface of the cable joint, obtain the interface aging coefficient, and evaluate the interface aging state.

[0071] Specifically, the elongation rate in step S1 is 0% to 100%, and the aging temperature is 50°C to 200°C.

[0072] Specifically, the simulated pressure for the insulation / rubber interface aging in step S2 is 0 Mpa to 5 MPa.

[0073] Specifically, in step S5, the ultrasonic primary echo parameters are calculated by the following formulas.

[0074] (1)

[0075] In formula (1), is the ultrasonic primary echo sound velocity, d is the thickness of the rubber specimen, t r is the echo time.

[0076] (2)

[0077] In formula (2), R is the ultrasonic primary echo reflection coefficient, r 1 is the amplitude of the primary echo, r 0 is the amplitude of the fundamental wave.

[0078] (3)

[0079] In formula (3), is the ultrasonic primary echo nonlinear coefficient, A 2 is the amplitude of the second harmonic in the frequency domain after the primary echo is Fourier-transformed, A 1 is the amplitude of the fundamental wave in the frequency domain after the primary echo is Fourier-transformed.

[0080] Specifically, the aging evaluation model for the insulation / rubber interface of the cable joint in step S6 is as follows:

[0081] The ultrasonic primary echo sound velocity and the material modulus E have the following relationship:

[0082] (4)

[0083] In the formula, is the density of the rubber specimen;

[0084] According to the phase screen approximation theory, the ultrasonic primary echo reflection coefficient R and the interface roughness S q have the following relationship:

[0085] (5)

[0086] In the formula, R 0 is the reflection coefficient of the ideal smooth interface, k is the number of echo times;

[0087] The ultrasonic primary echo nonlinear coefficient and the interface pressure P approximately have the following relationship:

[0088] (6)

[0089] In the formula, is the first correction coefficient; is the second correction coefficient; is the third correction coefficient;

[0090] Based on the Gaussian distribution model of the rough interface, the true contact area of the rough interface and the nominal contact area have the following relationship:

[0091] (7)

[0092] In the formula, is the composite elastic modulus of the interface contact material; is the material surface topography parameter, used to describe the spherical radius of the protrusions on the rough surface;

[0093] From formulas (4) to (7), define the interface aging evaluation coefficient K age :

[0094] (8)

[0095] In the formula, represents the fourth correction coefficient.

[0096] The ultrasonic detection and evaluation method of the present invention comprehensively considers the reflection coefficient, sound velocity, and change of the non-linear coefficient of ultrasonic signals, establishes an aging evaluation model for the insulation / rubber interface of cable joints, and can more comprehensively reflect the changes in interface pressure, roughness, and interface material properties; the proposed aging evaluation coefficient closely related to the interface contact state can more directly evaluate the reliability of interface insulation.

[0097] Application Example

[0098] The ultrasonic detection and evaluation method for the insulation / rubber interface aging of cable joints described in Example 2 was used for the following application.

[0099] The insulation specimen to be simulated and the silicone rubber specimen to be simulated are rectangles with dimensions of 30 mm × 60 mm × 2 mm. The unaged specimen was selected as the insulation specimen. The silicone rubber specimens were respectively specimens that had undergone thermo-mechanical aging for 0 h, 10 h, 240 h, 480 h, 720 h, and 1200 h in an oven at 150 °C. The first fastener was rotated to adjust the interface pressure between the insulation specimen and the silicone rubber specimen to 0.10 MPa.

[0100] The ultrasonic spectrograms of the insulation / rubber interface with different aging times are as Figure 2 shown. Ultrasonic waves are reflected at the insulation / rubber interface, generating a primary echo.

[0101] The Fourier transform was performed on the ultrasonic time-domain signal. The frequency-domain signals of the primary echoes of the insulation / rubber interface with different aging times are as Figure 3 shown.

[0102] As the insulation / rubber interface ages, the amplitude of the primary echo gradually decreases and the reflection coefficient decreases. The change of the reflection coefficient with the interface aging state can be calculated; as the insulation / rubber interface ages, the primary echo time advances, and the echo sound velocity with the interface aging state can be calculated based on the specimen thickness and echo time; according to the fundamental wave and harmonic wave of the ultrasonic frequency-domain spectrum, the change of the non-linear coefficient with the interface aging state can be calculated. The calculation results are as Figure 4 、 Figure 5 and Figure 6 shown.

[0103] The three groups of coefficients were substituted into the aging evaluation model for fitting, and the interface aging evaluation coefficient K age was calculated, as Figure 7 shown. When C0 = 0, C1 = 0.000752, C2 = 0.012, and C3 = 1.00E-06, the interface aging evaluation coefficient K age is highly correlated with the interface aging time. Compared with the evaluation results of the interface aging by a single parameter, the interface aging evaluation coefficient Kage The evaluation result of the interface aging state has a better correlation with the aging time.

[0104] Those skilled in the art can obviously make various modifications to the above embodiments easily, and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art to the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. An ultrasonic detection and evaluation method for the interface aging of cable joints in the middle, which uses an ultrasonic characteristic simulation device for ultrasonic detection. The ultrasonic characteristic simulation device includes: A mechanical pressure device for simulating the pressure between the insulation / rubber interfaces of cable joints in the middle, including an insulation top plate, a first insulation bottom plate, a second insulation bottom plate, and insulation columns. The ends of the insulation top plate, the first insulation bottom plate, and the second insulation bottom plate are connected by the insulation columns. Between the insulation top plate and the first insulation bottom plate is used to place the rubber specimen and the insulation specimen to be simulated; above the insulation top plate is provided a first fastener on the insulation columns. The first fastener and the insulation columns are provided with elastic members, and the pressure between the insulation / rubber interfaces of the cable joints in the middle is adjusted by rotating the first fastener; A pressure sensor located between the first insulation bottom plate and the second insulation bottom plate for testing the pressure between the insulation / rubber interfaces of cable joints in the middle; And An ultrasonic probe placed on the surface of the rubber specimen to be simulated for detecting the ultrasonic echo signal of the insulation / rubber interface of the cable joint in the middle; It is characterized in that the ultrasonic detection and evaluation method includes: Step S1, specimen thermal aging. After aging is completed, take out the specimen and enter step S2; Step S2, simulate the interface pressure: Stack the insulation specimen and the rubber specimen between the insulation top plate and the first insulation bottom plate of the ultrasonic characteristic simulation device; Tighten the first fastener and observe the reading of the pressure sensor. After the reading of the pressure sensor reaches the simulated pressure, enter step S3; Step S3, apply vaseline between the ultrasonic probe and the rubber specimen and test the ultrasonic primary echo signal; Step S4, repeat steps S1 to S3 to perform ultrasonic tests on the rubber specimens and insulation specimens with different aging times and different interface pressures; Step S5, calculate 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, according to the parameters calculated in step S5, establish an aging evaluation model for the insulation / rubber interface of the cable joint in the middle, obtain the interface aging evaluation coefficient, and evaluate the interface aging state; Define the interface aging evaluation coefficient K age As follows: Nonlinear coefficient of ultrasonic primary echo There is approximately the following relationship with the interface pressure P as follows: （6） Wherein, is the first correction coefficient; is the second correction coefficient; is the third correction coefficient; is the fourth correction coefficient; is the ultrasonic primary echo sound velocity; R is the ultrasonic primary echo reflection coefficient.

2. The ultrasonic detection and evaluation method 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 joints in the middle.

3. The ultrasonic detection and evaluation method according to claim 1, characterized in that, The material of the rubber specimen to be simulated is silicone rubber or ethylene propylene diene monomer rubber used in cable joints in the middle.

4. The ultrasonic detection and evaluation method according to claim 1, wherein There are at least two insulation columns and they are symmetrically distributed. Below the second insulation bottom plate is provided a second fastener connected to the insulation columns.

5. The ultrasonic detection and evaluation method according to claim 1, characterized in that, The insulation top plate is provided with holes, and the ultrasonic probe is embedded in the holes and is in contact with the upper surface of the rubber specimen to be simulated.

6. The ultrasonic detection and evaluation method according to claim 1, wherein The frequency of the ultrasonic probe is 1 MHz to 5 MHz.

7. The ultrasonic detection and evaluation method according to claim 1, characterized in that The specimen thermal aging is as follows: Wipe the insulation specimen and the rubber specimen to be simulated clean with anhydrous ethanol, put them into a drying oven for thermo-mechanical aging, and set the elongation rate, aging temperature, and aging time; The elongation rate is 0% to 100%, and the aging temperature is 50 °C to 200 °C.

8. The ultrasonic detection and evaluation method according to claim 1, characterized in that, The simulated pressure is 0 Mpa to 5 MPa.

9. The ultrasonic detection and evaluation method according to claim 1, characterized in that, The establishment process of the aging evaluation model for the insulation / rubber interface of the cable joint in the middle is as follows: Ultrasonic primary echo sound velocity and the material modulus E have the following relationship: （4） In the formula, is the density of the rubber sample; According to the phase screen approximation theory, the ultrasonic primary echo reflection coefficient R and the interface roughness S q have the following relationship: （5） In the formula, R 0 is the reflection coefficient of the ideal smooth interface, k is the number of echo times; Gaussian distribution model based on a rough interface, true contact area of the rough interface and the nominal contact area have the following relationship: （7） In the formula, is the composite elastic modulus of the interfacial contact material; is the material surface topography parameter, which is used to describe the spherical radius of the protrusions on the rough surface; Define the interface aging evaluation coefficient according to formulas (4) to (7). K age .

Images