CN114279607B - Cable joint interface pressure monitoring method and device based on acoustic elastic effect - Google Patents
Cable joint interface pressure monitoring method and device based on acoustic elastic effect Download PDFInfo
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- CN114279607B CN114279607B CN202111610676.9A CN202111610676A CN114279607B CN 114279607 B CN114279607 B CN 114279607B CN 202111610676 A CN202111610676 A CN 202111610676A CN 114279607 B CN114279607 B CN 114279607B
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Abstract
The invention discloses a cable joint interface pressure monitoring method based on an acoustic elastic effect, which comprises the following steps: s1: establishing a relation between the ultrasonic propagation time of the cold-shrink tube in the expanded state and the internal stress; s2: establishing a theoretical rule of radial space-time distribution of stress in the cold-shrink tube under the swelling action of silicone grease; s3: obtaining an expression of radial distribution of stress in the expanded cold-shrink tube; s4: correlating the relation between the stress in the cold-shrink tube in the expansion state and the interface pressure; s5: obtaining the interface pressure of the cold-shrinkage pipe in the expansion state; the invention also provides a cable joint interface pressure monitoring device based on the acoustoelastic effect, which comprises a cable body, a cold shrinkage pipe, an ultrasonic probe, a concave acoustic lens, an ultrasonic/stress analysis module and a stress/interface pressure conversion module. According to the invention, by improving the ultrasonic acoustic-elastic algorithm of the cold-shrink tube and combining the silicone swelling effect, the interface pressure of the cable joint can be monitored in time, the occurrence of fire and explosion accidents of the cable joint caused by insufficient interface pressure is reduced, and the power supply reliability is improved.
Description
Technical Field
The invention belongs to the technical field of fireproof and explosion-proof early warning of electrical equipment, and particularly relates to a cable joint interface pressure monitoring method based on an acoustic-elastic effect.
Background
Compared with overhead transmission lines, the power cable has the advantages of light weight, small occupied area, convenience in maintenance, small environmental influence and the like, so that the power cable is widely applied to a power system, and the operation reliability of the power cable is directly related to the stability and safety of the operation of a power grid system. Due to the restriction of factors such as manufacturing level, construction conditions, environmental conditions and the like, the cable joint is easy to become a weak link of the cable, and partial discharge or insulation aging and other conditions occur during operation, so that the interface pressure between the silicone rubber/polyethylene interface of the cable joint is reduced, and finally the interface discharge can be caused when the interface pressure is reduced beyond an allowable range, even explosion can be caused when the interface pressure is serious, and serious economic loss and casualties can be caused. Therefore, the online monitoring of the interface pressure of the power cable has important application value for the operation reliability of the power system.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a method and a device for monitoring the interface pressure of a cable connector based on the acoustoelastic effect, aiming at the defects of the prior art.
The technical scheme adopted by the invention is as follows: a cable joint interface pressure monitoring method based on an acoustic elastic effect comprises the following steps:
s1: establishing a relation between the ultrasonic propagation time of the cold-shrink tube in the expanded state and the internal stress, and comprising the following steps of:
1) Selecting zero-stress silicon rubber with different thicknesses;
2) Carrying out ultrasonic monitoring by utilizing a cable joint interface pressure monitoring device based on an acoustic elastic effect;
3) Recording the time difference between the propagation sound path and the echo;
4) Obtaining zero stress propagation velocity V 0 ；
5) Applying tension perpendicular to the ultrasonic wave propagation direction and a direct current electric field parallel to the ultrasonic wave propagation direction to the silicon rubber;
6) Obtaining the ultrasonic wave propagation speed V under the internal stress;
7) Calculating the acoustic elasticity coefficient K of the ultrasonic wave;
8) Changing a tension value to obtain ultrasonic wave propagation speed V and an acoustic elastic coefficient K under different tensions;
9) Changing the direct-current field intensity to obtain the ultrasonic wave propagation speed V and the acoustic elastic coefficient K under different direct-current field intensities;
10 Establishing an acoustic-elastic equation of any radial position r and time t of the cold-shrink tube in the expanded state, and recording the equation as:
in the formula, K r 、K φ And K z Respectively the acoustoelastic coefficients in the radial direction, the circumferential direction and the axial direction of the cold-shrinkable tube, sigma r 、
And σ z The internal stresses in three directions are respectively, for the cold-shrink tube after expanding, the radial stress and the axial stress can be ignored relative to the circumferential stress, and then the formula can be rewritten as follows:
11 Establishing the relation between the ultrasonic propagation time and the internal stress of the cold-shrink tube in the expanded state, and regarding the cold-shrink tube with the wall thickness d after expanding, as the propagation speed of the ultrasonic is far greater than the relaxation speed of the cold-shrink tube, the corresponding ultrasonic propagation speed at any position of the cold-shrink tube can be considered to be kept constant during single detection, and is only related to the position and not related to the time; the time difference T of the ultrasonic echo in the cold-shrink tube is
In the formula t 0 The time difference between the ultrasonic detection time and the cold shrink tube installation time is obtained;
12 Establishing a relationship between the propagation time T of the ultrasonic wave in the cold-shrink tube and the internal stress thereof, i.e.
S2: establishing a theoretical rule of radial space-time distribution of stress in a cold-shrink tube under the swelling action of silicone grease, comprising the following steps of:
1) Developing a silicone grease absorption experiment of the cold-shrink tube, and respectively selecting two conditions of silicone grease absorption and silicone grease non-absorption of the cold-shrink tube;
2) Keeping the direct current electric field, the expansion strain and the temperature environment condition of the cold-shrinkable tube unchanged, and measuring the stress sigma of the cold-shrinkable tube at different radial positions r in the experimental process φ ；
3) Changing the direct current electric field, expansion strain and temperature environment conditions of the cold-shrinkable tube, and measuring again;
4) Obtaining the absorption silicone grease and the stress sigma of the cold-shrink tube φ The relationship of variation, denoted as σ φ ＝σ φ (r,t)；
5) Correlating the acoustic elastic equation of the cold-shrinkage tube in the expanded state with the stress relaxation characteristic expression to obtain the expanded stateThe theoretical law of radial space-time distribution of stress in cold-shrink tube is recorded as sigma φ ＝σ φ (r, t, k), wherein k is a parametric vector in a mathematical expression of the circumferential stress;
s3: obtaining an expression of the radial distribution of the stress in the expanded cold-shrink tube:
T(t 0 )＝f(t 0 ；d,k)
ultrasonic detection is carried out at different moments with longer intervals to obtain a series of t 0 Establishing a multi-order matrix with d and k as unknowns according to the corresponding series T, and obtaining d and k according to a matrix theory;
s4: relating the relation between the stress in the cold-shrink tube in the expanded state and the interface pressure:
f 1 ＝ε circular (x 1 )·E(x 1 ,t)
in the formula f 1 At radial position x for time t of cold-shrink tube 1 Internal stress of (e) of circular For cold-shrink tube shape variables, E is the cold-shrink tube elastic modulus, f is the cold-shrink tube interface pressure, D 0 For cold-shrink tube thickness, R 0 The inner diameter of the cold shrink tube is in an expanded state;
s5: and obtaining the interface pressure f of the cold-shrink tube in the expanded state.
Preferably, the propagation sound path is twice the thickness of the silicone rubber, and the echo time difference is the time difference between the first echo and the initial wave or the time difference between the first echo and the second echo after the ultrasonic pulse propagates in the silicone rubber.
Preferably, the zero stress propagation velocity V 0 The average value of the zero stress propagation speed corresponding to the silicon rubber with different thicknesses is obtained.
Preferably, the cold shrink tube silicone grease absorption experiment is carried out based on an optimized orthogonal experiment technology, so that the time-varying rule of the expansion stress and the silicone grease absorption amount of the silicone rubber under different environmental condition combinations is obtained.
The invention also provides a cable joint interface pressure monitoring device based on the acoustoelastic effect, which comprises a cable body, a cold shrinkage pipe, an ultrasonic probe, a concave acoustic lens, an ultrasonic/stress analysis module and a stress/interface pressure conversion module, and is characterized in that: the ultrasonic probe has an ultrasonic transmitting and receiving function, the concave acoustic lens can gather ultrasonic signals and perfectly attach to the surface of the cold-shrink tube, and the ultrasonic/stress analysis module and the stress/interface pressure conversion module are realized based on the algorithm in the steps S1-S5.
Compared with the prior art, the method and the device for monitoring the interface pressure of the cable joint based on the acoustoelastic effect have the following advantages that:
1. the invention can fully consider the problem of stress relaxation acceleration caused by the swelling effect of silicone grease after the cold shrink tube is installed, so that the monitoring of the cold shrink tube has practical significance;
2. the invention can realize effective monitoring under the environmental conditions of different direct current electric fields, expansion strain and temperature aiming at cold shrinkage pipes with different thicknesses, and has strong universality;
3. the ultrasonic acoustoelastic algorithm of the expansion cold-shrink tube is improved, and the ultrasonic acoustoelastic algorithm is applied to the cable joint interface pressure online monitoring device, so that the innovation is strong.
4. The equation form established by the invention is suitable for all cable joint cold-shrinkable tubes, only the coefficients are different, the coefficients only need to be determined by testing different cold-shrinkable tubes, and any physical parameters of the cold-shrinkable tubes and the silicon rubber thereof do not need to be known.
Drawings
FIG. 1 is a flow chart of the experimental principle of the present invention;
FIG. 2 is a schematic structural view of the present invention;
FIG. 3 is a schematic view of the ultrasonic propagation path of the present invention;
FIG. 4 is a schematic diagram of the time difference T of the ultrasonic echo according to the present invention;
FIG. 5 shows the circumferential stress f at a certain position of the cold shrink tube of the cable joint 1 And an explanatory diagram of the interfacial pressure f.
In the figure: the device comprises a cable body 1, a cold shrinkage pipe 2, an ultrasonic probe 3, a concave acoustic lens 4, an ultrasonic/stress analysis module 5 and a stress/interface pressure conversion module 6.
Detailed Description
The invention will be described in further detail with reference to the following drawings and specific embodiments.
1-5, a method for monitoring the interface pressure of a cable joint based on the acoustoelastic effect comprises the following steps:
s1: establishing a relation between the ultrasonic propagation time of the cold-shrink tube in the expanded state and the internal stress, and comprising the following steps of:
1) Selecting zero-stress silicon rubber with different thicknesses;
2) Carrying out ultrasonic monitoring by utilizing a cable joint interface pressure monitoring device based on an acoustic elastic effect;
3) Recording the time difference between the propagation sound path and the echo;
4) Obtaining zero stress propagation velocity V 0 ；
5) Applying tension perpendicular to the ultrasonic wave propagation direction and a direct current electric field parallel to the ultrasonic wave propagation direction to the silicon rubber;
6) Obtaining the ultrasonic wave propagation speed V under the internal stress;
7) Calculating the acoustic elasticity coefficient K of the ultrasonic wave;
8) Changing a tension value to obtain ultrasonic wave propagation speed V and an acoustic elastic coefficient K under different tensions;
9) Changing the direct-current field intensity to obtain the ultrasonic wave propagation speed V and the acoustic elastic coefficient K under different direct-current field intensities;
10 Establishing an acoustic-elastic equation of any radial position r and time t of the cold-shrink tube in the expanded state, and recording the equation as:
in the formula, K r 、K φ And K z Respectively the acoustic elastic coefficient, sigma, in the radial direction, the circumferential direction and the axial direction of the cold-shrinkable tube r 、
And σ z The internal stresses in three directions are respectively, for the expanded cold-shrink tube, the radial and axial stresses can be ignored relative to the circumferential stress, and then the above formula can be rewritten as follows:
11 Establishing the relation between the ultrasonic propagation time and the internal stress of the cold-shrink tube in the expanded state, and regarding the cold-shrink tube with the wall thickness d after expanding, as the propagation speed of the ultrasonic is far greater than the relaxation speed of the cold-shrink tube, the corresponding ultrasonic propagation speed at any position of the cold-shrink tube can be considered to be kept constant during single detection, and is only related to the position and not related to the time; the time difference T of the ultrasonic echo in the cold-shrink tube is
In the formula t 0 The time difference between the ultrasonic detection time and the cold-shrink tube installation time is obtained;
12 To establish a relationship between the propagation time T of the ultrasonic wave in the cold-shrink tube and the internal stress thereof, i.e.
S2: establishing a theoretical rule of radial space-time distribution of stress in a cold-shrink tube under the swelling action of silicone grease, and comprising the following steps of:
1) Developing a silicone grease absorption experiment of the cold-shrink tube, and respectively selecting two conditions of silicone grease absorption and silicone grease non-absorption of the cold-shrink tube;
2) Keeping the direct current electric field, the expansion strain and the temperature environment condition of the cold-shrinkable tube unchanged, and measuring the stress sigma of the cold-shrinkable tube at different radial positions r in the experimental process φ ；
3) Changing the direct current electric field, expansion strain and temperature environment conditions of the cold-shrinkable tube, and measuring again;
4) Obtaining the absorption silicone grease and the stress sigma of the cold-shrink tube φ Relationship of variation, denoted as σ φ ＝σ φ (r,t)；
5) Associating the acoustic elastic equation of the cold-shrink tube in the expanded state with a stress relaxation characteristic expression to obtain a radial space-time distribution theoretical rule of the stress in the cold-shrink tube in the expanded state, and recording the radial space-time distribution theoretical rule as sigma φ ＝σ φ (r, t, k), wherein k is a parameter vector in the mathematical expression of the circumferential stress;
s3: obtaining an expression of the radial distribution of the stress in the expanded cold-shrink tube:
T(t 0 )＝f(t 0 ；d,k)
ultrasonic detection is carried out at different moments with longer intervals to obtain a series of t 0 Establishing a multi-order matrix with d and k as unknowns according to the corresponding series T, and obtaining d and k according to a matrix theory;
s4: relating the relation between the stress in the cold-shrink tube in the expanded state and the interface pressure:
f 1 ＝ε circular (x 1 )·E(x 1 ,t)
in the formula f 1 At radial position x for time t of the cold shrink tube 1 Internal stress of (e) circular For cold-shrink tube shape variation, E is the cold-shrink tube elastic modulus, f is the cold-shrink tube interface pressure, D 0 For cold-shrink tube thickness, R 0 The inner diameter of the cold-shrink tube is in an expanded state;
s5: and obtaining the interface pressure f of the cold-shrink tube in the expansion state.
The invention also provides a cable joint interface pressure monitoring device based on the acoustoelastic effect, which comprises a cable body, a cold shrinkage pipe, an ultrasonic probe, a concave acoustic lens, an ultrasonic/stress analysis module and a stress/interface pressure conversion module, and is characterized in that: the ultrasonic probe has an ultrasonic transmitting and receiving function, the concave acoustic lens can gather ultrasonic signals and perfectly attach to the surface of the cold-shrink tube, and the ultrasonic/stress analysis module and the stress/interface pressure conversion module are realized based on the algorithm in the steps S1-S5.
Example 1
1. Mounting a concave acoustic lens on the surface of the cable joint cold-shrink tube to enable the concave acoustic lens to be perfectly attached to the surface of the cold-shrink tube;
2. mounting an ultrasonic probe to make the ultrasonic probe vertical to the incidence of the concave acoustic lens;
3. connecting an ultrasonic/stress analysis module, a stress/interface pressure conversion module and a starting device to carry out ultrasonic monitoring;
4. obtaining an ultrasonic echo time difference T, and obtaining the stress in the cold-shrink tube through an ultrasonic/stress analysis module;
5. and outputting the interface pressure of the cable joint through the stress/interface pressure conversion module.
6. And carrying out multiple measurements, and taking the average value of the multiple results as the finally measured interface pressure of the cable joint.
The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any modification and replacement based on the technical solution and inventive concept provided by the present invention should be covered within the scope of the present invention.
Claims (5)
1. A cable joint interface pressure monitoring method based on an acoustic elastic effect is characterized by comprising the following steps:
s1: establishing a relation between the ultrasonic propagation time of the cold-shrink tube in the expanded state and the internal stress, and comprising the following steps of:
1) Selecting zero-stress silicon rubber with different thicknesses;
2) Carrying out ultrasonic monitoring by utilizing a cable joint interface pressure monitoring device based on an acoustic elastic effect;
3) Recording the time difference between the propagation sound path and the echo;
4) Obtaining zero stress propagation velocity V 0 ；
5) Applying tension perpendicular to the ultrasonic wave propagation direction and a direct current electric field parallel to the ultrasonic wave propagation direction to the silicon rubber;
6) Obtaining the ultrasonic wave propagation speed V under the internal stress;
7) Calculating the acoustic elasticity coefficient K of the ultrasonic wave;
8) Changing a tension value to obtain ultrasonic wave propagation speed V and an acoustic elastic coefficient K under different tensions;
9) Changing the direct-current field intensity to obtain the ultrasonic wave propagation speed V and the acoustic elastic coefficient K under different direct-current field intensities;
10 Establishing an acoustic-elastic equation of any radial position r and time t of the cold-shrink tube in the expanded state, and recording the equation as:
in the formula, K r 、K φ And K z Respectively the acoustoelastic coefficients in the radial direction, the circumferential direction and the axial direction of the cold-shrinkable tube, sigma r 、
And σ z The internal stresses in three directions are respectively, for the cold-shrink tube after expanding, the radial stress and the axial stress can be ignored relative to the circumferential stress, and then the formula can be rewritten as follows:
11 For a cold-shrink tube with the wall thickness d after expanding, because the propagation speed of ultrasonic is far greater than the relaxation speed of the cold-shrink tube, the propagation speed of the ultrasonic corresponding to any position of the cold-shrink tube is considered to be kept constant during single detection, and is only related to the position and not to the time; the time difference T of the ultrasonic echo in the cold-shrink tube is
In the formula t 0 The time difference between the ultrasonic detection time and the cold-shrink tube installation time is obtained;
12 To establish a relationship between the propagation time T of the ultrasonic wave in the cold-shrink tube and the internal stress thereof, i.e.
S2: establishing a theoretical rule of radial space-time distribution of stress in a cold-shrink tube under the swelling action of silicone grease, comprising the following steps of:
1) Developing a silicone grease absorption experiment of the cold-shrink tube, and selecting two conditions of silicone grease absorption and silicone grease non-absorption of the cold-shrink tube respectively;
2) Keeping the conditions of the direct current electric field, the expansion strain and the temperature environment of the cold-shrinkable tube unchanged, and measuring the stress sigma of the cold-shrinkable tube at different radial positions r in the experimental process φ ；
3) Changing the direct current electric field, expansion strain and temperature environment conditions of the cold-shrinkable tube, and measuring again;
4) Obtaining the absorption silicone grease and the stress sigma of the cold-shrink tube φ The relationship of variation, denoted as σ φ ＝σ φ (r,t)；
5) Associating the acoustic elastic equation of the cold-shrink tube in the expanded state with a stress relaxation characteristic expression to obtain a radial space-time distribution theoretical rule of the stress in the cold-shrink tube in the expanded state, and recording the radial space-time distribution theoretical rule as sigma φ ＝σ φ (r, t, k), wherein k is a parametric vector in a mathematical expression of the circumferential stress;
s3: obtaining an expression of the radial distribution of the stress in the expanded cold-shrink tube:
T(t 0 )＝f(t 0 ；d,k)
ultrasonic detection is carried out at different moments with longer intervals to obtain a series of t 0 Establishing a multi-order matrix with d and k as unknowns according to the corresponding series T, and obtaining d and k according to a matrix theory;
s4: relating the relation between the stress in the cold shrink tube in the expanded state and the interface pressure:
f 1 ＝ε circular (x 1 )·E(x 1 ,t)
in the formula f 1 At radial position x for time t of the cold shrink tube 1 Internal stress of (e) circular For cold-shrink tube shape variation, E is the cold-shrink tube elastic modulus, f is the cold-shrink tube interface pressure, D 0 For cold-shrink tube thickness, R 0 The inner diameter of the cold-shrink tube is in an expanded state;
s5: and obtaining the interface pressure f of the cold-shrink tube in the expansion state.
2. The method for monitoring the interface pressure of the cable joint based on the acoustic elastic effect as claimed in claim 1, wherein: the propagation sound path is twice the thickness of the silicon rubber, and the echo time difference is the time difference between the first echo and the initial wave or the time difference between the first echo and the second echo after the ultrasonic pulse propagates in the silicon rubber.
3. The method for monitoring the interface pressure of the cable joint based on the acoustic elastic effect as claimed in claim 1, wherein: zero stress propagation velocity V 0 The average value of the zero stress propagation speed corresponding to the silicon rubber with different thicknesses is obtained.
4. The method for monitoring the interface pressure of the cable joint based on the acoustic elastic effect as claimed in claim 1, wherein: the cold-shrink tube silicone grease absorption experiment is carried out based on an optimized orthogonal experiment technology, so that the time-varying rule of silicone rubber expansion stress and silicone grease absorption amount under different environmental condition combinations is obtained.
5. A monitoring device using the method for monitoring the interface pressure of the cable joint based on the acoustoelastic effect in claim 1, which comprises a cable body (1), a cold shrink tube (2), an ultrasonic probe (3), a concave acoustic lens (4), an ultrasonic/stress analysis module (5) and a stress/interface pressure conversion module (6), and is characterized in that: the ultrasonic probe (3) has an ultrasonic transmitting and receiving function, the concave acoustic lens (4) can gather ultrasonic signals and perfectly fit on the surface of the cold-shrink tube, and the ultrasonic/stress analysis module (6) and the stress/interface pressure conversion module (7) are realized based on the algorithm in the steps S1-S5.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05164631A (en) * | 1991-12-13 | 1993-06-29 | Suzuki Motor Corp | Method and apparatus for measuring stress |
| JP2008076387A (en) * | 2006-08-24 | 2008-04-03 | Toshiba Corp | Ultrasonic stress measuring method and instrument |
| CN109470400A (en) * | 2018-09-21 | 2019-03-15 | 浙江大学 | Measure the method and device of injection molding machine cavity pressure indirectly by sonication |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60163643A (en) * | 1984-02-07 | 1985-08-26 | テルモ株式会社 | Ultrasonic measuring method and apparatus |
| CN106404250B (en) * | 2016-03-21 | 2019-04-19 | 广州供电局有限公司 | The measuring device and its method of cable cold-shrinking intermediate joint interfacial pressure |
| CN113237587A (en) * | 2021-02-02 | 2021-08-10 | 国网电力科学研究院武汉南瑞有限责任公司 | Cable joint interface pressure measurement system |
| CN113138048A (en) * | 2021-03-25 | 2021-07-20 | 四川大学 | Nondestructive live-line detection method for cable joint interface pressure based on stress ultrasound |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05164631A (en) * | 1991-12-13 | 1993-06-29 | Suzuki Motor Corp | Method and apparatus for measuring stress |
| JP2008076387A (en) * | 2006-08-24 | 2008-04-03 | Toshiba Corp | Ultrasonic stress measuring method and instrument |
| CN109470400A (en) * | 2018-09-21 | 2019-03-15 | 浙江大学 | Measure the method and device of injection molding machine cavity pressure indirectly by sonication |
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