A method for internal throughflow conductor voltage inversion by cable accessory space electric field

Abstract

The present application relates to the technical field of cable voltage measurement data processing, in particular to a method for inverting internal through-flow conductor voltage through cable accessory space electric field, the steps of the method comprising: measuring the external electric field of the cable accessory, determining the type of the cable accessory, determining the inversion path based on the type of the cable accessory, arranging a certain number of sensor nodes on the inversion path of the cable accessory, and inverting calculation through a certain integral algorithm to obtain the cable voltage value, thereby completing the measurement of the cable voltage. The present application inverts and measures the voltage of the external electric field of the cable accessory through the arrangement of non-contact sensors, which can not only perceive the voltage distribution on the cable, but also further invert the partial fault condition of the cable accessory; and the present application adopts different fixed integral methods for the cable terminal and the cable intermediate joint of different accessories of the high-voltage cable to improve the inversion accuracy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cable voltage measurement data processing, in particular to a method for inverting internal through-flow conductor voltage through cable accessory space electric field. BACKGROUND

[0002] At present, contact measurement such as electromagnetic and capacitive mutual inductor is the most widely used means in power grid measurement field, but electromagnetic mutual inductor contains a large number of cores, and when facing high voltage measurement, the transformer is easy to work in the nonlinear region, thereby affecting the accuracy of the whole mutual inductor measurement, and easy to cause ferromagnetic resonance between the mutual inductor and the power grid; and the capacitive mutual inductor contains a large number of inertial elements such as capacitors, which is easy to cause voltage measurement phase lag and other problems. With the further development of smart grid and energy internet, the traditional contact voltage measurement means is not suitable for cable voltage measurement, and the current method cannot meet the demand of power grid. Therefore, we urgently need to develop a new method to solve the problem of how to measure the cable voltage by non-contact sensor. SUMMARY

[0003] The purpose of the present application is to provide a method for inverting internal through-flow conductor voltage through cable accessory space electric field, which is used to solve the above technical problems.

[0004] The embodiments of the present application are realized by the following technical solutions:

[0005] A method for inverting internal through-flow conductor voltage through cable accessory space electric field, the steps of the method comprising:

[0006] Measuring the external electric field of the cable accessory, determining the type of the cable accessory, determining the inversion path based on the type of the cable accessory, arranging a certain number of sensor nodes on the inversion path of the cable accessory, and performing inversion calculation through a certain integral algorithm to obtain the cable voltage value, thereby completing the measurement of the cable voltage.

[0007] Optionally, the type of the cable accessory is specifically a cable terminal and a cable joint.

[0008] Optionally, when the type of the cable accessory is a cable terminal, the inversion path of the cable terminal is determined, and the highest point of the external electric field of the cable terminal is taken as the limit to segment, the same number of sensor nodes are arranged in the set region of the segmented inversion path, and the first set integral algorithm is used for inversion calculation to obtain the cable voltage value.

[0009] 4. The method for inverting internal through-flow conductor voltage through cable accessory space electric field according to claim 3, wherein the first set integral algorithm is specifically a Chebyshev integral algorithm.

[0010] Optionally, when the type of the cable accessory is a cable joint, a set part between two stress cones of the cable joint is selected as the inversion path, a set number of sensor nodes are arranged in the set area of the inversion path, and inversion calculation is performed through the second set integral algorithm to obtain the cable voltage value.

[0011] Optionally, the second set integral algorithm is specifically a Gauss Legendre integral algorithm.

[0012] Optionally, the sensor node is specifically a non-contact sensor node.

[0013] The technical scheme of the embodiment of the present application has at least the following advantages and beneficial effects:

[0014] The embodiment of the present application measures the voltage of the external electric field of the cable accessory through the arrangement of the non-contact sensor, which can not only perceive the voltage distribution on the cable, but also further invert the partial fault condition of the cable accessory; and the embodiment of the present application adopts different fixed integral methods for the cable terminal and the cable intermediate joint of the high-voltage cable to improve the inversion precision. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A flowchart of a method for inverting the voltage of an internal current-carrying conductor through a spatial electric field of a cable accessory is provided.

[0016] Figure 2 A schematic diagram of the surface potential distribution of a cable terminal is provided. DETAILED DESCRIPTION

[0017] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0018] As Figure 1 shown, the present application provides one of the embodiments: a method for inverting the voltage of an internal current-carrying conductor through a spatial electric field of a cable accessory, the steps of the method comprising:

[0019] measuring the external electric field of the cable accessory, determining the type of the cable accessory, determining the inversion path based on the type of the cable accessory, arranging a set number of sensor nodes on the inversion path of the cable accessory, and performing inversion calculation through a set integral algorithm to obtain the cable voltage value, thereby completing the measurement of the cable voltage.

[0020] In the embodiment, the cable accessory is an important part of the cable transmission system, and its reliability determines the reliability of the power system. More than half of the failures of the cable transmission system are caused by cable accessory failures. The cable accessory mainly includes a cable terminal and a cable joint. Since the grounding part does not cover the entire cable accessory in the two cable accessories of the cable terminal and the cable intermediate joint, the external electric field caused by the cable voltage can be measured in the external air of the cable terminal and the cable intermediate joint, and then the corresponding voltage value on the cable terminal is inversely calculated. The method of measuring the voltage of the cable accessory by the electric field inversion voltage can not only perceive the voltage distribution on the cable, but also further inversely calculate the partial failure of the cable accessory.

[0021] Since the surface of the cable terminal itself is a nonlinear structure, and the electric field and voltage distribution at both ends of the cable terminal are not symmetrical, the entire cable terminal surface electric field distribution presents a very high degree of nonlinearity. Therefore, when the cable accessory is the cable terminal, the cable terminal surface electric field highest point is segmented as a boundary, and 3 sensing nodes are respectively placed on the left and right faces to perform Chebyshev integration to inversely calculate the cable voltage value.

[0022] Unlike the cable terminal, the cable intermediate joint presents very good symmetry. Therefore, half of the part between the two stress cones of the cable intermediate joint is selected as the integral inversion path. On the integral path, the monotonicity of the electric field distribution is very good, so when the cable accessory is the cable intermediate joint, half of the part between the two stress cones of the cable intermediate joint is selected as the integral inversion path, and the cable voltage value can be obtained by Gauss-Legendre integral inversion at 5 nodes.

[0023] The basic principle of the electric field inversion voltage is shown in the following formula:

[0024]

[0025] Wherein, U ba represents the potential difference between points b and a, and the negative sign before the integral represents that the direction of the electric field intensity is opposite to the direction of the voltage rise. E represents the electric field value along the integral path. The integral formula is approximately equal to the superposition of N discrete points, which is the description of the physical meaning of the integral, and the larger N is, the smaller the error after discretization is. Using the inversion scheme, a certain number of sensors need to be placed on the electric field integral path.

[0026] Based on the numerical integral scheme of the above integral inversion method, in the embodiment, Gauss-Legendre integral and Chebyshev integral can be used.

[0027] In this embodiment, the integral scheme is Gauss-Legendre integral, i.e., a variant of Gauss integral, which is a special Gauss integral with the weight function set as p(x) = 1 and the integral interval changed to [-1, 1], as shown in the following formula, in which the weight and position are determined by using Legendre polynomials with orthogonal properties.

[0028]

[0029] The Legendre polynomials used to solve the weight and integral node position in the Gauss-Legendre integral are shown in the following formula:

[0030]

[0031] In solving the integral constant under N integral nodes, the zero point corresponding to the N-order Legendre polynomial is the corresponding integral node. Since the Gauss-Legendre integral range can only be [-1, 1], and the actual electric field integral range is [a, b], the original integral object dx needs to be converted, and the conversion formula is as follows:

[0032]

[0033] The Gauss-Legendre integral formula is put into the integral formula for solving the voltage of the actual electric field to obtain the Gauss-Legendre integral formula for electric field inversion voltage as follows:

[0034]

[0035] The actual Gauss-Legendre polynomial integral node position and weight can be found in Table 1. In actual electric field inversion voltage, the integral node number is first determined, and then the corresponding electric field sensor placement position is determined according to Table 1 for inversion.

[0036] Table 1

[0037]

[0038] In this embodiment, the integral scheme is Chebyshev integral. The weight of Chebyshev integral is a fixed value, and its integral point is mainly derived by Taylor expansion, and has better accuracy for inversion of functions with low-order polynomials of electric field and distance. Its original integral equation is consistent with Gauss-Legendre integral, and the calculation of its weight is as follows:

[0039]

[0040] The principle of Chebyshev integral is as follows. On the basis of the original integral equation, the function on the left is first Taylor expanded to obtain the following formula:

[0041] f(x) = a0 + a1x + a2x2 +…+a n x n

[0042] Further, the above formula is brought into the left and right ends of the original integral equation, and the integral or summation is performed on the left and right ends simultaneously. The left integral obtains the following formula, and the summation on the right obtains the formula:

[0043]

[0044] The corresponding Chebyshev integral positions are shown in Table 2 by comparing the same parts of the above two formulas:

[0045] Table 2

[0046]

[0047] Considering the general case when the integral interval is [0, d], the Chebyshev original positions in Table 2 can be converted into positions represented by d as shown in Table 3:

[0048] Table 3

[0049]

[0050] Further, the original Chebyshev integral is corresponded to the electric field inversion voltage, the transformation of the integral object is as follows:

[0051]

[0052]

[0053] In the specific application of the embodiment, it can be known from the derivation process that the Chebyshev integral and the Gauss-Legendre integral can be derived from the number of integral points and the starting position of the integral, without the need to analyze the specific electromagnetic field physical model. If the Gauss-Legendre integral or the Chebyshev integral encounters a complex electric field environment, for example, the electric field distribution is highly nonlinear and does not exhibit obvious monotonicity, in order to ensure that a relatively high precision is inverted under the condition that the number of sensors is relatively small, it is generally considered to perform segmented inversion processing on this basis.

[0054] The embodiment also provides an application example: the final voltage inversion value is obtained according to the actual electric field value and the theoretical electric field value. Since the corresponding electric field value cannot be actually measured in the current research, the theoretical formula is used to calculate the electric field value as the theoretical electric field value, and the simulation electric field value is used as the measured electric field value for inversion analysis. Therefore, before inversion, the electric field distribution in the entire cable needs to be solved first, and in the application example, COMSOL Multiphysics software is used for simulation.

[0055] Because of the different material structure inside the cable, and also need to care about the cable inside the electric field voltage distribution, so only use finite element simulation analysis, can not be used in the simulation of boundary element. Using COMSOL in the current module, set the voltage size of the symmetric line part is 10kV, set the ground part voltage is 0kV.

[0056] In COMSOL simulation first of all by using steady-state research method for solid heat transfer calculation, after the completion of the entire solid heat transfer calculation, further in the frequency domain, set its frequency is 50Hz, current module simulation analysis. Get the final phase is 0 under the condition of electric field voltage distribution.

[0057] In this application example, the cable terminal or cable intermediate joint in the inversion of electromagnetic field environment is relatively complex, using inverse problem optimization algorithm can be more convenient to inverse, but the inverse problem optimization algorithm solving time is long, can not meet the real-time of inversion, therefore mainly consider using integral method for inversion research.

[0058] In this application example, because the cable terminal surface voltage or electric field distribution can not be calculated by theoretical formula, only the simulation solution to the cable accessory related electric field voltage value, therefore in the absence of actual electric field measurement value can not evaluate the precision of Gauss integral inversion method in this inversion situation, only the Gauss integral inversion process and integral point, weight calculation. In order to simulate the actual Gauss integral inversion process, in this study, the COMSOL directly calculated electric field intensity as the measured electric field intensity, the difference value of surface voltage as the theoretical electric field intensity for analysis. The cable terminal surface voltage distribution in COMSOL is exported as shown in Figure 2 .

[0059] Because the cable terminal surface electric field has great nonlinearity, in the front and rear field value is very small, therefore do not consider the front and rear in the inversion process, consider the electric field greater than 25kV / m of the part is 85mm and 165mm interval section. In this part of the interval section COMSOL get the voltage difference is 8962.8V, this voltage value as the inversion reference value. With 3 sensor nodes for example calculation. Calculation of Gauss integral in m k As shown in table 4, m k Put into Gauss-Legendre integral calculation, can get the corresponding integral point and the corresponding coefficient as shown in table 5.

[0060] Table 4

[0061]

[0062] Table 5

[0063]

[0064] Since the theoretical electric field and the simulation electric field are calculated by COMSOL, the above Gauss integral inversion only has method reference significance, and the error in calculating the voltage is not significant.

[0065] In the application example, further fixed point integral inversion analysis is carried out, and Gauss-Legendre integral and Chebyshev integral are carried out in the [85mm, 165mm] section under the conditions of 3, 4, 5 sensors, respectively. The Chebyshev integral inversion results are shown in Tables 6, 7 and 8, and the Gauss-Legendre integral inversion results are shown in Tables 9, 10 and 11.

[0066] Table 6

[0067]

[0068] Table 7

[0069]

[0070] Table 8

[0071]

[0072] Table 9

[0073]

[0074] Table 10

[0075]

[0076] Table 11

[0077]

[0078] By analyzing the above tables, it can be found that when the Chebyshev integral has 3 sensors and the Gauss-Legendre integral has 4 sensors, the accuracy is the highest, and the errors are 3% and 2.25%, respectively. When the number of sensors is increased to 5, the accuracy of both inversion schemes is reduced, mainly due to the nonlinear distribution of the electric field distribution. The interval segmentation or another selection of the corresponding integral path can be used to further improve the inversion accuracy.

[0079] Since the electric field distribution of the cable terminal presents a nonlinear distribution, the integral is divided into left and right parts for inversion analysis, with 3 electric field sensors placed in each part. The two parts are [85mm, 103mm] and [103mm, 165mm], respectively. The Chebyshev integral and the Gauss-Legendre integral are shown in Tables 12 and 13, respectively.

[0080] Table 12

[0081]

[0082] Table 13

[0083]

[0084] It can be found from the above table that the segmented Chebyshev integral effectively improves the overall inversion accuracy, but the segmented Gauss-Legendre integral greatly reduces the inversion accuracy. Therefore, for the cable joint, the segmented Chebyshev integral has high integral accuracy. The accuracy of the cable internal conductor voltage inversion of the present application is verified.

[0085] The above is only the preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for inverting the voltage of an internal current-carrying conductor by means of the spatial electric field of a cable accessory, characterized in that, The steps of this method include: The external electric field of the cable accessory is measured to determine the type of cable accessory. Based on the type of cable accessory, the inversion path is determined. A set number of sensor nodes are deployed on the inversion path of the cable accessory. The inversion calculation is performed by setting an integration algorithm to obtain the cable voltage value and complete the measurement of the cable voltage. The cable accessories specifically include cable terminals and cable connectors; When the cable accessory is a cable terminal, the inversion path of the cable terminal is determined, and the cable terminal is divided into segments with the highest point of the external electric field of the cable terminal as the boundary. The same set number of sensor nodes are deployed in the set area of ​​the segmented inversion path, and the inversion calculation is performed by the first set integration algorithm to obtain the cable voltage value. When the cable accessory is a cable joint, the set portion between the two stress cones of the cable joint is selected as the inversion path. A set number of sensor nodes are set up in the set area of ​​the inversion path, and the inversion calculation is performed by the second set integral algorithm to obtain the cable voltage value.

2. The method for inverting the voltage of an internal current-carrying conductor by means of the spatial electric field of a cable accessory according to claim 1, characterized in that, The first set integration algorithm is specifically the Chebyshev integration algorithm.

3. The method for inverting the voltage of an internal current-carrying conductor by means of the spatial electric field of a cable accessory according to claim 2, characterized in that, The second set integration algorithm is specifically the Gaussler-Gande integration algorithm.

4. The method for inverting the voltage of an internal current-carrying conductor by means of the spatial electric field of a cable accessory according to any one of claims 1-3, characterized in that, The sensor node is specifically a non-contact sensor node.

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