CN215182001U - Interdigital capacitive sensor for cable insulation detection - Google Patents
Interdigital capacitive sensor for cable insulation detection Download PDFInfo
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- CN215182001U CN215182001U CN202120814693.3U CN202120814693U CN215182001U CN 215182001 U CN215182001 U CN 215182001U CN 202120814693 U CN202120814693 U CN 202120814693U CN 215182001 U CN215182001 U CN 215182001U
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Abstract
The utility model discloses an interdigital capacitive sensor for cable insulation detection, which comprises a metal conductor layer, wherein the metal conductor layer is wrapped with an insulating layer, the insulating layer is wrapped with a sheath layer, and the sheath layer is wrapped with a flexible basal layer; interdigital electrodes are arranged between the sheath layer and the flexible base layer along the circumferential direction; the interdigital electrode comprises an induction electrode and an excitation electrode, a gap is formed between the induction electrode and the excitation electrode, and an insulating medium is filled in the gap; the flexible substrate layer is wrapped with a metal back plate, the metal back plate is wrapped with a flexible protective layer, and the thickness D1 of the interdigital electrode is 18-36 μm. The utility model discloses a carry out optimal design to capacitive sensor's structure, if change electrode pair number, electrode width, electrode spacing isoparametric, can promote its sensitivity and other performances.
Description
Technical Field
The utility model belongs to the sensor field especially provides an interdigital capacitive sensor for cable insulation detects.
Background
The crosslinked polyethylene cable has the advantages of good heat resistance, high breakdown strength, large insulation resistance coefficient, small dielectric constant, low dielectric loss factor and the like, and is widely applied to power transmission lines and power distribution networks of various voltage grades of a power system. However, due to structural defects of the cable itself and the influence of the operating environment (high temperature, external force, external electric field, moisture, etc.) and operating time, the crosslinked polyethylene cable inevitably undergoes an insulation aging phenomenon, which easily causes a serious accident. In order to ensure reliable operation of the cable, the insulation state of the cable needs to be detected frequently.
To this end, the present company discloses a capacitive sensor for cable insulation detection, but requires adjustment of its various structural parameters to achieve optimum results.
SUMMERY OF THE UTILITY MODEL
In order to solve the problem, the utility model provides an interdigital capacitive sensor for cable insulation detects. The utility model discloses a carry out optimal design to capacitive sensor's structure, if change electrode pair number, electrode width, electrode spacing isoparametric, can promote its sensitivity and other performances.
In order to achieve the above technical effects, the technical scheme of the utility model is that:
an interdigital capacitive sensor for cable insulation detection comprises a metal conductor layer, wherein an insulating layer wraps the metal conductor layer, a sheath layer wraps the insulating layer, and a flexible substrate layer wraps the sheath layer; interdigital electrodes are arranged between the sheath layer and the flexible substrate layer along the circumferential direction; the interdigital electrode comprises an induction electrode and an excitation electrode, a gap is formed between the induction electrode and the excitation electrode, and an insulating medium is filled in the gap; the flexible substrate layer is wrapped with a metal back plate, the metal back plate is wrapped with a flexible protective layer, and the thickness D1 of the interdigital electrode is 18-36 μm.
In a further refinement, the flexible substrate layer has a thickness D2 of 50 μm.
In a further improvement, the length of the interdigital electrode is 5 cm.
In a further improvement, the dielectric constant of the insulating medium is 4.
In a further improvement, the number of pairs of the interdigital electrodes is 3-9.
The utility model has the advantages that:
the utility model discloses a carry out optimal design to capacitive sensor's structure, if change electrode pair number, electrode width, electrode spacing isoparametric, can promote its sensitivity and other performances.
Drawings
FIG. 1 is a schematic diagram of a sensor configuration;
FIG. 2a is a graphical representation of the effect results from the factor analysis of signal intensity;
FIG. 2b is a graphical representation of the effect results from the factor analysis of sensitivity;
FIG. 2c is a graphical representation of the effect impact results from factor analysis of penetration depth;
FIG. 3a is a graph of sensitivity variance analysis;
FIG. 3b is a graph of signal intensity variance analysis;
FIG. 4a is a graph of the estimated margin average result for N-3;
FIG. 4b is a graph of the estimated margin average result for N6;
fig. 4c shows the result of the estimated margin average value of N-9.
Detailed Description
The technical solution of the present invention will be described in detail below with reference to specific embodiments.
An interdigital capacitive sensor for cable insulation detection as shown in fig. 1 comprises a metal conductor layer 1, wherein an insulating layer 2 is wrapped outside the metal conductor layer 1, a sheath layer 3 is wrapped outside the insulating layer 2, and a flexible substrate layer 7 is wrapped outside the sheath layer 3; interdigital electrodes are arranged between the sheath layer 3 and the flexible substrate layer 7 along the circumferential direction; the interdigital electrode comprises an induction electrode 4 and an excitation electrode 5, a gap 6 is formed between the induction electrode 4 and the excitation electrode 5, and the gap 6 is filled with an insulating medium; the flexible substrate layer 7 is wrapped with a metal back plate 8, and the metal back plate 8 is wrapped with a flexible protective layer 9.
The method for optimizing the structural parameters of the interdigital capacitive sensor for detecting the insulation of the cable is disclosed. The method inspects three effect indexes of the sensor respectively, changes the structural parameters in a simulation mode, and obtains the positive and negative corresponding relation between the structural parameters and the effect of the sensor, thereby obtaining the effect of parameter optimization.
The portable interdigital capacitive sensor for cable insulation detection is shown in the structural diagram 1 and comprises an interdigital electrode, a flexible substrate, a grounding backboard, a flexible protection layer and a metal clamp. The interdigital electrodes mainly include two types: the device comprises an excitation electrode (red) and an induction electrode (blue), wherein the width of the excitation electrode (red) and the induction electrode (blue) are w, the number of the electrodes is even, the logarithm of the electrodes is N, the thickness of the electrodes is d, and the excitation electrode and the induction electrode are made of red copper with small resistivity and are used for applying an excitation voltage and generating induction current; the width of the electrode gap is g, and the electrode gap is filled with an insulating medium with dielectric constant of epsilon x; the electrode plate is deposited on a flexible substrate, and the substrate is made of flexible material PTFE and used for keeping insulation with the grounding back plate; the grounding back plate is made of brass with smaller thickness and is used for shielding radial external noise signals; the flexible protective layer is made of flexible materials, is attached to the clamp and is used for protecting the background plate, so that the damage of the clamp in use is avoided, the stress of the capacitive sensor is uniform, and an air gap between the electrode and the surface of the cable is reduced; the metal clamp enables the capacitive sensor to be in close contact with the tested cable, and a screw interface are additionally attached, so that the sensor can be further fixed, and the measurement accuracy is improved.
Designing a sensor: the penetration depth of the sensor is mainly determined by the electrode pair number, the electrode pair number and the penetration depth are in negative correlation, and the penetration depth can be determined according to the measured depth of the cable insulating layer so as to guide the design of the electrode pair number of the sensor; in order to improve the sensitivity of the sensor, an electrode structure with larger width and smaller gap can be selected; the thickness of the flexible substrate can be reduced to about 50 μm as appropriate in view of lowering the substrate effect, and the thickness of the electrode pad can be set to 18 to 36 μm for improving the output capacitance.
For the evaluation of the structural optimization of the sensor, three effect indexes of signal intensity, sensitivity and penetration depth are adopted. The main parameters that affect the sensor output are: the logarithm of the metal electrode N, the ratio K of the electrode width to the gap, the electrode thickness D1, the dielectric constant of the substrate material E, and the substrate thickness D2. In the multi-factor analysis, each parameter factor not only acts on the response result independently, but also acts in combination, namely the interaction between the factors. In order to comprehensively evaluate the influence of parameters and interaction thereof on the optimization index of the sensor in each two-dimensional model, a two-level full-factor experiment is carried out, and the test level of each factor is shown in the following table 1.
TABLE 1 level table of various factors
The factor design is a design test in which, when the test is performed, the levels of all the factors are changed simultaneously instead of one at a time, thereby studying the influence of a plurality of factors on the response and possibly studying the interaction between the factors. In a two-level full factorial design, each experimental factor has only two levels, and the entire experiment includes all combinations of these factor levels. Practical experience shows that the multi-level interaction is nonexistent or is small enough to be ignored, and part of the two-level interaction can be mainly considered, so that the design only considers the influence of the two-level interaction test on each index when the analysis is carried out by software.
In a normal probability plot of normalized effects, the normalized effect is shown relative to the distribution fit line when all effects are 0. As the factor value changes from a low level to a high level, the response of the positive effector increases, shown on the right side of 0, the negative effector decreases in response, shown on the left side of 0, and the more distant from 0, the more pronounced the effect.
Fig. 2 a-2 c are graphs of effect influence results obtained by performing factor analysis on simulation data, and it is obvious that for the signal intensity (a), the importance degree of each factor effect is: n (electrode pair) > K (electrode width gap ratio) > N × K (interaction of pair to width gap ratio) > D2 (substrate thickness) > D1 (electrode thickness) > N × D2 (interaction of pair to substrate thickness) > N × D1 (interaction of pair to electrode thickness) > K × D2 (interaction of width gap ratio to substrate thickness) > K × D1 (interaction of width gap ratio to electrode thickness) > E (substrate dielectric constant) > N × E (interaction of pair to substrate dielectric constant). Obviously, the logarithm of the electrode and the ratio of the width to the gap, and the interaction between them, have much larger influence on the signal strength than other factors, and thus the output signal strength of the sensor is mainly determined by the logarithm of the electrode and the ratio of the width to the gap. Both the electrode pair number and the electrode width-gap ratio have positive effect on the signal intensity, the larger the value of the electrode pair number and the electrode width-gap ratio is, the larger the area covered by the whole electrode is, the larger the capacitance value between the electrodes is, and the larger the signal intensity is.
For the sensitivity (b), the distribution of each factor obviously judges that the primary and secondary orders of the influencing factors are respectively: k > N > N x K > D2> D1> N x D2> N x D1> E > N x E, the number of electrode pairs N and the aspect ratio K predominate, but the effect of the two is completely different, the number of electrode pairs being a negative effect and the aspect ratio being a positive effect, the interaction being a negative effect.
For the penetration depth (c), the primary and secondary orders of the influence degree arrangement of each factor in the normal probability map are: n > K > N xK > D2> D1> E > D1 xD 2> E xD 2> N xD 1> N xD 2, the effect of the electrode logarithm N on the penetration depth is obviously higher than the effect of other factors, namely the electrode logarithm has a decisive effect on the penetration depth, and the effect is a negative effect. The aspect ratio K and the electrode logarithm N have the same negative effect, the interaction being a positive effect, but much less than the main effects of K and N.
When the interaction effect among the factors has a significant influence on the result, the effect of each factor needs to be subjected to simple effect test, and the change of one factor in the factor interaction items on different levels of another factor is respectively considered. As can be seen from the results of the simple analysis, when the dependent variable is the signal intensity Cp, there is a significant interaction effect to mask or distort the mechanism of action of the independent variable factor: for nxd 2, when the number N of electrode pairs is low, the significance level is greater than 0.05, i.e. the horizontal size of the substrate thickness D2 has less influence on the signal intensity, but when N is high, the substrate thickness D2 has a certain influence on the output signal intensity of the sensor; it can also be concluded that the electrode thickness D1 and the dielectric constant E of the substrate also have no major effect on the signal strength at low levels of N, while at high levels of N, variations in the levels of these factors will have an effect on the signal strength. Therefore, in designing a sensor, it is necessary to take into account the significant influence of the interaction between the thickness of the electrode and the substrate and the dielectric constant of the substrate on the signal strength as the number of pairs of electrodes increases.
FIG. 2 a-FIG. 2c are graphs of the effect results of factor analysis: when the signal strength (a), the sensitivity (b) and the penetration depth (c) satisfy the constraint conditions, the larger the values of K and N are, the larger the area covered by the whole electrode is, and the larger the capacitance value between the electrodes is, i.e., the larger the signal strength is. For the penetration depth, under the condition that the number N of electrode pairs is certain, the smaller the K value is, the larger the inter-polar distance s is, the electric field in the insulating layer is enhanced, and relatively speaking, the electric field of the sheath layer between the electrodes is weakened, so that the capability of the electric field penetrating the insulating layer is improved, and the penetration depth is increased. And when the electrode logarithm increases, the electrode distance s is reduced, the electric field is weakened with the surface of the cable sheath and the electric field of the internal insulating layer, and further the permeability is reduced. For the sensitivity, when the number of electrode pairs is constant, the larger the K value is, that is, the larger the area covered by the electrode is, the higher the sensitivity is, but when the number of electrode pairs is constant, the smaller the number of electrode pairs N is, the higher the sensitivity is, because at this time, with the increase of the electrodes, the electric field between the electrodes is mainly the fringe electric field, and is concentrated in the sheath layer near the surface, so the penetration ability is weakened, the penetration depth is reduced, and the sensitivity to the internal insulating layer is greatly weakened.
In summary, theoretically, the electrode pair number N and the width-gap ratio K have significant influence on design indexes, and the penetration depth is determined by measuring the thicknesses of the insulating layer and the sheath layer of the cable in practical application, so that the pair number of the sensor electrodes can be determined; considering sensitivity, because the electrode width-to-gap ratio K has a positive effect, the value of K can be larger under an ideal condition, N is 2, but the problem of untight bonding may exist in practical application, and certain errors are brought to measurement; then determining other parameters based on the signal intensity, wherein the substrate dielectric constant E has a negative effect on the signal intensity and the sensitivity, the substrate thickness D2 and the electrode thickness D1 have a positive effect, when the electrode logarithm is small, the substrate does not have a remarkable influence on the capacitance value, and when the logarithm is large, the influence on the interaction with the substrate parameters is considered to be remarkable, in order to weaken the contribution of the substrate, PI with the dielectric constant of 4 is selected as a substrate material, and the substrate thickness D2 is 50 μm; the effect of the electrode thickness is not significant when the number of electrode pairs is small, so an electrode with a thickness of 18 μm can be chosen as the electrode of the sensor to avoid axial disturbances as much as possible. When the number of pairs of electrodes is large, the interaction with the thickness of the electrodes is obvious, the thickness of the electrodes can be 36 micrometers, and therefore the signal intensity and the sensitivity are increased without influencing the measurement effect.
Results of simple effect analysis of interaction: nxd 2(a), nxd 1(b), nxe (c) are shown in table 2, table 3 and table 4, respectively:
TABLE 2
Dependent variable: cp
Based on estimating marginal mean
*. the level of significance of the difference in mean values was 0.05.
b. Multiple comparative adjustments: the Stark method.
TABLE 3
Dependent variable: cp
Based on estimating marginal mean
*. the level of significance of the difference in mean values was 0.05.
b. Multiple comparative adjustments: the Stark method.
TABLE 4
Dependent variable: cp
Based on estimating marginal mean
*. significance level of the mean difference was 0.05
b. Multiple comparative adjustments: the Stark method.
For the interdigital electrode, it is obvious that there is no correlation between the electrode length and the penetration depth of the sensor, so the optimized indexes in the 3D model are sensitivity and signal intensity, and the influence of the electrode pair number, the electrode width-gap ratio and the electrode length on the sensitivity and the signal intensity of the sensor is analyzed. Because the calculation speed is low in the three-dimensional simulation, the influence of the simultaneous change of the structural parameters of the plurality of electrodes on the performance indexes of the sensor is deeply known by adopting a general full-factor experimental design so as to research the factors with any level number.
In order to accelerate the running speed of the three-dimensional model simulation in COMSOL, the thickness of the electrode is 0.1mm, the relative dielectric constant of the substrate is 2.55, and the thickness of the substrate is 0.1 mm. Because the influence of the electrode length in the three-dimensional model needs to be considered in detail, a level table of full-factor design is shown in the following table 5, result analysis is performed on optimization indexes obtained by COMSOL simulation calculation in software, so that the influence of the electrode length on sensitivity and signal intensity is obtained, and whether the interaction of the length, the electrode logarithm and the aspect ratio has obvious influence on each index is researched.
Table 5 design level meter
Results of 3a and 3b were obtained as shown in tables 6 and 7 by analysis of variance for sensitivity and signal intensity.
TABLE 6
TABLE 7
For the signal strength Cp, the main factor effect plays a major significant role, the degree of influence of the interaction is weak, and the main and secondary orders of the influencing factors: l (electrode length) > N (electrode pair number) > K (electrode width to gap ratio) > N × L (electrode pair number interacting with electrode length) > K × L (electrode width to gap ratio interacting with electrode length) > N × K (electrode width to gap ratio interacting with electrode pair number), the signal strength increases as the electrode pair number and electrode width to gap ratio increases, and as described above, the signal strength is approximately in direct proportion to the electrode length of the sensor; for sensitivity S, stronger factor interaction exists, and the influence degrees sequentially include: k > N > N x K > L > N x L > K x L, as with signal strength, the electrode aspect ratio increases, the sensitivity also increases, the electrode logarithm increases, and the sensitivity decreases instead.
To further explore the effect results of each structural parameter at different levels, SPSS software was used to perform the analysis, and the results of estimating the marginal average values are shown in FIGS. 4a-4 c. For sensitivity, the effect of increasing the electrode length is not significant, remains substantially constant, and the larger the electrode aspect ratio, the greater the sensitivity, which is consistent with the conclusions that have been made above, but when N is gradually increased to a higher level, the effect of increasing the electrode length on the overall sensitivity begins to be prominent, i.e. the sensitivity begins to change as the electrode length increases. It is to be noted that when L is about 5cm, an "inflection point" appears in the increase in sensitivity, i.e., after L exceeds 5cm, the increase in sensitivity gradually decreases and tends to stabilize, and it can be determined that the electrode length has a preferable value of 5 cm.
Through the optimization process, the logarithm N of the metal electrode, the ratio K of the electrode width to the gap, the electrode thickness D1, the dielectric constant E of the substrate material and the substrate thickness D2 are structurally optimized. The result obtained in this method is a trend, and the specific numerical value can be determined according to the actual application. Three effect indexes of signal intensity, sensitivity and penetration depth are adopted.
The electrode logarithm N and the width gap ratio K have obvious influence on design indexes, and the penetration depth is determined by the thickness of an insulating layer and a sheath layer of a measuring cable in practical application, so that the logarithm of the sensor electrode can be determined; considering sensitivity, because the electrode width-to-gap ratio K has a positive effect, the value of K can be larger under an ideal condition, N is 2, but the problem of untight bonding may exist in practical application, and certain errors are brought to measurement; then determining other parameters based on the signal intensity, wherein the substrate dielectric constant E has a negative effect on the signal intensity and the sensitivity, the substrate thickness D2 and the electrode thickness D1 have a positive effect, when the electrode logarithm is small, the substrate does not have a remarkable influence on the capacitance value, and when the logarithm is large, the influence on the interaction with the substrate parameters is considered to be remarkable, in order to weaken the contribution of the substrate, PI with the dielectric constant of 4 is selected as a substrate material, and the substrate thickness D2 is 50 μm; the effect of the electrode thickness is not significant when the number of electrode pairs is small, so an electrode with a thickness of 18 μm can be chosen as the electrode of the sensor to avoid axial disturbances as much as possible. When the number of pairs of electrodes is large, the interaction with the thickness of the electrodes is obvious, the thickness of the electrodes can be 36 micrometers, and therefore the signal intensity and the sensitivity are increased without influencing the measurement effect.
In short, the influence of the electrode logarithm N and the width gap ratio K on the performance of the sensor is large, and the electrode logarithm N and the width gap ratio K need to be selected according to actual needs; the influence of other factors is limited, and a determined value can be selected according to practical factors such as convenient bending and the like, as described above. In practice, if the signal intensity needs to be increased, N is increased and K is increased; if the sensitivity needs to be increased, N is reduced and K is increased by selecting selection; if the penetration depth needs to be increased, N is selected to be reduced, and K is selected to be reduced.
The above-mentioned is only a concrete direction embodiment of the utility model, nevertheless the utility model discloses a design concept is not limited to this, and all utilize this design right the utility model discloses carry out immaterial change, all should belong to the action of infringing the scope of protection of the utility model.
Claims (5)
1. An interdigital capacitive sensor for cable insulation detection comprises a metal conductor layer (1), wherein an insulating layer (2) is wrapped outside the metal conductor layer (1), a sheath layer (3) is wrapped outside the insulating layer (2), and a flexible substrate layer (7) is wrapped outside the sheath layer (3); interdigital electrodes are arranged between the sheath layer (3) and the flexible substrate layer (7) along the circumferential direction; the interdigital electrode comprises an induction electrode (4) and an excitation electrode (5), a gap (6) is formed between the induction electrode (4) and the excitation electrode (5), and an insulating medium is filled in the gap (6); the flexible substrate layer (7) is wrapped with a metal back plate (8), the metal back plate (8) is wrapped with a flexible protective layer (9), and the interdigital electrode is 18-36 μm in thickness D1.
2. The interdigital capacitive sensor for the detection of the insulation of cables according to claim 1, characterized in that the thickness D2 of the flexible substrate layer (7) is 50 μm.
3. The interdigital capacitive sensor for cable insulation detection of claim 1, wherein the interdigital electrode has a length of 5 cm.
4. The interdigital capacitive sensor for cable insulation detection of claim 1, wherein the dielectric medium has a dielectric constant of 4.
5. The interdigital capacitive sensor for cable insulation detection of claim 1, wherein the number of pairs of interdigital electrodes is 3-9.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114413745A (en) * | 2022-01-04 | 2022-04-29 | 华北电力科学研究院有限责任公司 | Device and method for detecting insulation moisture depth of generator stator |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114413745A (en) * | 2022-01-04 | 2022-04-29 | 华北电力科学研究院有限责任公司 | Device and method for detecting insulation moisture depth of generator stator |
| CN114413745B (en) * | 2022-01-04 | 2023-05-23 | 华北电力科学研究院有限责任公司 | Device and method for detecting insulation and moisture depth of generator stator |
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