A cable partial discharge signal calculation method and device considering temperature effect

Abstract

The application discloses a kind of cable partial discharge signal calculation method and device considering temperature effect, belong to the technical field of power distribution and utilization, including the following steps: S1: measuring cable structure parameters and material parameters;S2: measuring each defect parameter of cable, cable barrier height and work function;S3: measuring cable impedance value, cable conductor layer actual operating temperature after current flow, calculate defect tip field strength;S4: calculate the partial discharge current considering the effect of temperature;S5: output partial discharge signal, obtain the corresponding relationship of defect and partial discharge signal.The application calculates barrier height, work function, operating temperature and field strength value and other parameters, then accurately calculates the partial discharge signal caused by defect, obtains the real discharge amount of partial discharge, can more accurately judge the running state of cable, judge whether cable can continue to use, whether it needs to be overhauled to reduce the influence of defect.

Description

Technical Field

[0001] This invention belongs to the field of power distribution technology, specifically relating to a method and apparatus for calculating partial discharge signals of cables that takes into account temperature effects. Background Technology

[0002] 10kV distribution lines are an important component of the power system, characterized by numerous points, wide coverage, and complex routes. During operation, they are susceptible to various external uncertainties, resulting in a high failure rate. Once a failure occurs, it can cause large-scale power outages, affecting industrial and agricultural production and the normal lives of many residents. This not only causes huge economic losses but also hinders the healthy development of my country's power industry. Therefore, the research and analysis of common faults and preventive measures of 10kV distribution lines is particularly important.

[0003] Due to internal factors such as electric field distortion caused by installation defects, as well as external factors such as mechanical force and temperature, insulation defects have a high probability of developing into insulation faults. This makes insulation faults of 10kV cables a major type of common fault in 10kV distribution lines. Partial discharge, as an early sign of insulation degradation in 10kV cables, has been proven to be an effective fault warning information through research and analysis. Therefore, conducting partial discharge detection on 10kV distribution lines is an effective measure to promptly detect potential insulation defects or faults in 10kV cables and avoid unplanned power outages. At the same time, accurate measurement of partial discharge in 10kV cables allows operators to promptly and accurately grasp the insulation status of 10kV cables, assess their insulation condition, and improve the operation and maintenance level of distribution networks.

[0004] Most existing methods for partial discharge detection of 10kV cables are based on ambient temperature. However, the conductor temperature of 10kV cables still in service is higher than ambient temperature, which leads to differences in the detected partial discharge and reduces the accuracy of the insulation condition assessment of 10kV cables. Summary of the Invention

[0005] This invention provides a method and apparatus for calculating partial discharge signals of cables that takes into account temperature effects. It also takes into account the influence of field strength and temperature, and can reflect the true discharge quantity to obtain accurate partial discharge signals.

[0006] To achieve the above objectives, the present invention provides a method for calculating cable partial discharge signals considering temperature effects, comprising the following steps:

[0007] S1: Measure the given cable structure parameters, and simultaneously measure the dielectric constant, thermal conductivity and effective electron mass of each layer of the cable material;

[0008] S2: Measure various defect parameters of a given cable; measure the barrier height and work function of a given cable;

[0009] S3: Measure the given cable impedance value to obtain the phase difference between the given cable rated voltage and current; measure the actual operating temperature T of the conductor layer after current flows through the cable;

[0010] S4: Calculate the maximum electric field strength of the defect based on the cable structure parameters and various defect parameters of the cable;

[0011] S5: Substitute the barrier height, work function, actual operating temperature, and maximum electric field strength of the defect into the partial discharge current signal calculation formula to calculate the partial discharge current considering the effect of temperature.

[0012] S6: Outputs partial discharge signal based on the phase difference between partial discharge current and voltage;

[0013] S7: Obtain the correspondence between defects and partial discharge signals.

[0014] Furthermore, before step S5, the calculation formula for the partial discharge current signal is corrected, and the partial discharge current signal is updated according to the calculation formula for the corrected partial discharge current signal.

[0015] Furthermore, after step S6 is completed, a different given cable is used, which has different defect parameters than the given cable used in the previous steps; steps S1-S7 are repeated to obtain the correspondence between different defects and partial discharge signals.

[0016] Furthermore, in step S2, the various defect parameters of the cable include the location, shape, and size of the defect, and the partial discharge area is calculated based on the shape and size of the defect.

[0017] Furthermore, in step S2, the specific method for measuring the barrier height and work function of the cable material is as follows: cut a sample of uniform thickness from a given cable containing spike defects, cut a sample sheet containing only the insulation layer (3) and only the conductor layer (1) from the sample, use a Kelvin probe scanner in semi-contact working mode to measure the surface potential difference of the sample sheet through secondary scanning technology, obtain the Fermi level and vacuum level of the cable material, and calculate the barrier height and work function of the cable material based on the potential difference, wherein the barrier height is the difference between the work functions of the conductor layer (1) and the insulation layer (3).

[0018] Furthermore, in step S3, the specific method for measuring the impedance value of the cable material is to measure the impedance value of a given cable using an impedance analyzer.

[0019] Furthermore, in step S3, the specific method for measuring the actual operating temperature of the cable conductor layer (1) is as follows: the detection part of the temperature sensor is brought into contact with the cable conductor layer (1) under test, current is applied to the cable and pressure is applied, and the operating temperature of the cable conductor layer (1) is detected by the temperature sensor.

[0020] Furthermore, in step S4, the method for calculating the maximum electric field strength of the defect is as follows: a simulation model of the cable body and the spike defect is constructed based on the cable structure parameters using the finite element simulation method, current constraints are set, and then the simulation model is meshed and calculated. The maximum electric field strength at the tip of the defect and the field strength distribution on the spike surface are obtained using the Poisson equation.

[0021] Furthermore, in step S5, the formula for calculating the partial discharge current signal I is:

[0022]

[0023] in, I 1 represents the tunneling current formed by the high field strength; I 2 represents the Schottky effect current formed at high temperature; S represents the partial discharge area; q represents the absolute electron charge; m represents the electron mass; m* represents the effective electron mass; and h represents Planck's constant. is the barrier height; E is the maximum electric field strength of the spike defect; is Richardson's constant; T is the operating temperature; k is Boltzmann's constant; W is the work function.

[0024] A device for calculating cable partial discharge signals considering temperature effects, comprising:

[0025] The input module is used to collect the structural parameters of the cable, the dielectric constant, thermal conductivity and effective electron mass of each layer of the cable material, defect parameters, barrier height, work function, impedance value, and the actual operating temperature of the conductor layer after the cable is filled with current.

[0026] The first calculation module is used to calculate the maximum electric field strength of the defect based on the cable structure parameters and cable defect parameters.

[0027] The second calculation module is used to calculate the partial discharge current considering the effect of temperature based on the barrier height, work function, actual operating temperature, and maximum electric field strength at the defect tip.

[0028] Output module: Used to output partial discharge signals based on the phase difference between partial discharge current and voltage; to obtain the correspondence between defects and partial discharge signals.

[0029] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0030] This invention first measures or calculates parameters such as barrier height, work function, operating temperature, and field strength. Then, it calculates the partial discharge current signal caused by the defect using the calculation formula for the partial discharge current signal. Since the actual operating temperature of the cable is taken into account in the calculation, the calculated partial discharge current signal is closer to the actual operating conditions. Therefore, the true discharge amount of the partial discharge can be obtained. In application scenarios, by utilizing the correspondence between defects and partial discharge signals, the actual discharge amount of the partial discharge can be measured to more accurately determine the defects in the power cable. Based on the cable defects, it can be determined whether the cable can continue to be used and whether it needs to be repaired to reduce the impact of the defects.

[0031] Furthermore, after calculating the partial discharge current signal, the calculation formula for the partial discharge current signal is corrected. The partial discharge signal of the cable measured by the instrument used in the experiment is compared with the calculated partial discharge signal, and the calculation formula for the partial discharge current signal is corrected. Then, the final partial discharge current signal is calculated using the corrected calculation formula, so that the calculated partial discharge current signal is more accurate.

[0032] Furthermore, the calculation method proposed in this invention can calculate partial discharge signals under temperature fluctuation conditions, which is highly adaptable and easy to match with the partial discharge signals of power cables in service in the power grid. Attached Figure Description

[0033] Figure 1 Flowchart of the cable partial discharge signal calculation method considering temperature effects according to the present invention;

[0034] Figure 2 This is a schematic diagram of the cable structure of the present invention;

[0035] Figure 3 A schematic diagram of the module structure for calculating cable partial discharge signals provided by the present invention;

[0036] In the diagram: 1. Conductor layer; 2. Conductor shielding layer; 3. Insulation layer; 4. Insulation shielding layer; 5. Armoring layer; 6. Outer sheath layer. Detailed Implementation

[0037] To make the objectives and technical solutions of this invention clearer and easier to understand, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0038] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] Taking a 10 kV XLPE cable with spike defects as an example, the calculation method for other defects is the same as that for spike defects. Its internal structure, from the inside out, consists of conductor layer 1, conductor shielding layer 2, XLPE insulation layer 3, insulation shielding layer 4, packaging and armor 5, and outer sheath 6. Insulation layer 3 is an XLPE insulation layer, and the outer semiconductor shielding layer and grounding shield together form insulation shielding layer 4. Spike defects appear on the outer surface of conductor layer 1, and their tips extend into the XLPE insulation layer 3.

[0040] Please see Figure 1 The present invention provides the following technical solution: a method for calculating partial discharge signals of cables considering temperature effects, comprising the following steps:

[0041] S1: Measure the given cable structural and material parameters. The cable structural parameters include the cable dimensions and the thickness of each layer. (Refer to...) Figure 2 The material parameters of the cable include the dielectric constant, thermal conductivity, and effective electron mass of the outer sheath layer 6, armor layer 5, insulation shield layer 4, insulation layer 3, conductor shield layer 2, and conductor layer 1. The inherent properties of the materials of conductor layer 1 and insulation layer 3 determine the value of the barrier width d. At the same time, the properties of the materials themselves also determine the shape of the barrier. That is, under the action of the gate electric field, the rectangular barrier of the oxide layer is deformed into a triangular barrier, and the barrier width will decrease accordingly.

[0042] S2: Measure the structural parameters of various defects in a given cable. These parameters include the location, shape, and size of the defect. When the surface of conductor layer 1 is not smooth enough and burrs are present, the presence of these burrs will lead to the formation of spike defects after current is applied and pressure is applied. The partial discharge generated by these spike defects is called tip discharge. The appearance of the spike defect is considered to be conical. Since the spike defect appears on the surface of the conductor layer, its material is the same as that of the conductor layer. Assuming the measured defect shape is conical, the base area of ​​the defect is S1, the height is m, and the distance L from the center of the bottom to the end of the cable material is n, the lateral area S2 of the discharge tip is calculated using the base radius r1 and the busbar l. Then, the partial discharge area S is calculated using the base area S1 and the lateral area S2 of the discharge tip.

[0043] The calculation formula is as follows:

[0044] S2=πlr1;

[0045] S = S1 + S2.

[0046] S3: Cut a uniform 1mm-2mm thick sample from a given cable containing spike defects or a cable of the same type as the given cable. Cut a thin sample sheet containing only insulation layer 3 and conductor layer 1 from this sample. Measure the Fermi level E of the sample using a Kelvin probe scanner in semi-contact mode via a double-scan technique. f And the vacuum energy level E0, and calculate the barrier height of the cable material. The work function W, where the barrier height is... The work function W1 of conductor layer 1 and the material work function W3 of insulating layer 3 are the difference.

[0047] Barrier height The calculation formula is:

[0048] =W1-W3

[0049] The formula for calculating the work function W is:

[0050] W=E f - E0

[0051] S4: Measure the impedance value of the given cable using an E4991B impedance analyzer to determine the phase relationship between the partial discharge current signal and the applied voltage signal of the given cable, obtain the degree of current lag or voltage lead, and output the final partial discharge signal.

[0052] S5: Dissect the outer sheath 6, armor layer 5, insulation shield layer 4, insulation layer 3 and conductor shield layer 2 of the given cable, and bring the detection part of the temperature sensor into contact with the conductor layer 1 of the cable under test, apply current and pressure to the cable, and the temperature sensor detects the accurate operating temperature T of the cable conductor layer 1.

[0053] S6: Using the finite element simulation method, a simulation model of the cable body and spike defect is constructed based on the cable structure parameters. Current constraints are set, and then the simulation model is meshed before finite element calculation is performed: the Poisson equation is used to obtain the maximum electric field strength of the spike defect and the electric field distribution on the spike surface.

[0054] S7: Substitute the parameters calculated in S2-S6 into the partial discharge current signal calculation formula to calculate the partial discharge current I considering the effect of temperature. The calculation formula for the partial discharge current signal I is as follows:

[0055]

[0056]

[0057]

[0058] Where I1 is the tunneling current formed by high field strength; I2 is the Schottky effect current formed by high temperature; q is the absolute electron charge; m is the electron mass, with a value of 9.10956×10-31 kg; and h is Planck's constant, with a value of 6.63×10-34 J•m. is Richardson's constant, with a value of 120 A / cm²•K²; m* is the effective electron mass; k is Boltzmann's constant, with a value of 1.38 × 10⁻²³ J / K. E is the maximum electric field strength of the spike defect; S is the discharge area, in m2. The barrier height is expressed in eV; W is the work function, expressed in eV; and T is the operating temperature, expressed in K.

[0059] Substituting the parameters obtained in step 1 into the calculation formulas for the tunneling effect current I1 and the Schottky effect current I2, the numerical values ​​of the tunneling current and Schottky current are obtained. The resulting diagrams of the tunneling and Schottky currents can be plotted and used as the partial discharge input waveform for studying the partial discharge propagation model. Building upon previous studies that only investigated the influence of field strength on the partial discharge signal, this invention proposes a method for calculating the partial discharge current signal that considers the effect of temperature. Furthermore, it considers the influence of impedance parameters on the phase during the calculation, thereby obtaining an accurate original partial discharge signal.

[0060] S8: Formula for calculating the corrected partial discharge current signal:

[0061] Due to differences in cable materials, the obtained parameters may vary slightly. This invention proposes to modify and correct the calculation formula in practical engineering applications. At room temperature, the partial discharge signal of the cable measured by instruments in the experiment is compared with the partial discharge signal calculated by the formula proposed in this invention. The formula is then modified to obtain a correction coefficient. This correction coefficient ensures that the calculation result at room temperature is consistent with the result obtained from actual measurement.

[0062] S9: Outputs partial discharge signal;

[0063] By using the corrected partial discharge current signal calculation formula, the partial discharge current signal caused by the defect can be accurately calculated. The actual discharge amount of partial discharge within a certain time period can be obtained according to the formula Q=I×t. Then, based on the degree of current lag or voltage lead obtained from S4, the final partial discharge signal is output.

[0064] S10: Replace the given cable with one whose defect parameters are different from those of the given cable used in the previous steps;

[0065] S10: Repeat steps S1-S8 to obtain the correspondence between different defects and partial discharge signals.

[0066] In application scenarios:

[0067] The partial discharge signal of the tested cable is measured. Based on the correspondence between the partial discharge signal and different defects and partial discharge signals, the defect parameters are determined. Based on the defect parameters, it is determined whether the actual operating cable of the same model needs maintenance. The partial discharge current signal calculation model considering the effect of temperature proposed in this invention can reflect the actual partial discharge quantity of power cable defects and obtain accurate partial discharge signals. Therefore, this method can more accurately determine the operating status of power cables, whether the cable can continue to be used, and whether maintenance is needed to reduce the impact of defects.

[0068] In practical engineering applications, due to fluctuations in power grid load, the actual operating temperature of cables will also fluctuate to some extent with the load fluctuations. The calculation method proposed in this invention can calculate the partial discharge signal under temperature fluctuation conditions, which is convenient for matching with the partial discharge signal of power cables in service in the power grid.

[0069] Example 2

[0070] This invention provides a cable partial discharge signal calculation device that considers temperature effects, such as... Figure 3 As shown, it includes:

[0071] The input module is used to collect the structural parameters of the cable, the dielectric constant, thermal conductivity and effective electron mass of each layer of the cable material, defect parameters, barrier height, work function, impedance value, and the actual operating temperature of the conductor layer after the cable is filled with current.

[0072] The first calculation module is used to calculate the maximum electric field strength of the defect based on the cable structure parameters and cable defect parameters.

[0073] The second calculation module is used to calculate the partial discharge current considering the effect of temperature based on the barrier height, work function, actual operating temperature, and maximum electric field strength at the defect tip.

[0074] Output module: Used to output partial discharge signals based on the phase difference between partial discharge current and voltage; to obtain the correspondence between defects and partial discharge signals.

[0075] Example 3

[0076] The present invention provides a computer device comprising an electrically connected memory and a processor, wherein the memory stores a computer program that can run on the processor, and when the processor executes the computer program, it implements the cable partial discharge signal calculation method considering temperature effects as described in Embodiment 1.

[0077] The computer program can be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete the present invention.

[0078] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0079] The memory can be used to store the computer program and / or modules. The processor implements various functions of the cable partial discharge signal calculation device / terminal equipment that takes temperature effects into account by running or executing the computer program and / or modules stored in the memory and calling the data stored in the memory.

[0080] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0081] Example 4

[0082] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a processor-executable, non-volatile, computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0083] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for calculating partial discharge signals in cables considering temperature effects, characterized in that, Includes the following steps: S1: Measure the given cable structure parameters, and simultaneously measure the dielectric constant, thermal conductivity and effective electron mass of each layer of the cable material; S2: Measure various defect parameters of a given cable; Measure the barrier height and work function of a given cable; S3: Measure the given cable impedance value to obtain the phase difference between the given cable rated voltage and current; Measure the actual operating temperature T of the conductor layer (1) after the cable is filled with current; S4: Calculate the maximum electric field strength of the defect based on the cable structure parameters and various defect parameters of the cable; S5: Substitute the barrier height, work function, actual operating temperature, and maximum electric field strength of the defect into the partial discharge current signal calculation formula to calculate the partial discharge current considering the effect of temperature; the partial discharge current I is calculated by the following formula: in, I 1 represents the tunneling current formed by the high field strength; I 2 represents the Schottky effect current formed at high temperature; S represents the partial discharge area; q represents the absolute electron charge; m represents the electron mass; m* represents the effective electron mass; and h represents Planck's constant. is the barrier height; E is the maximum electric field strength of the spike defect; Richardson's constant; T is the operating temperature; k is Boltzmann's constant; W is the work function; S6: Outputs partial discharge signal based on the phase difference between partial discharge current and voltage; S7: Obtain the correspondence between defects and partial discharge signals.

2. The method for calculating cable partial discharge signals considering temperature effects according to claim 1, characterized in that, Before step S5, the partial discharge current signal calculation formula is corrected, and the partial discharge current signal is updated according to the corrected partial discharge current signal calculation formula.

3. The method for calculating cable partial discharge signals considering temperature effects according to claim 1, characterized in that, After step S6 is completed, a different given cable is used, which has different defect parameters than the given cable used in the previous steps; steps S1-S7 are repeated to obtain the correspondence between different defects and partial discharge signals.

4. The method for calculating cable partial discharge signals considering temperature effects according to claim 1, characterized in that, In step S2, the cable defect parameters include the location, shape, and size of the defect, and the partial discharge area is calculated based on the defect shape and size.

5. The method for calculating cable partial discharge signals considering temperature effects according to claim 1, characterized in that, In step S2, the specific method for measuring the barrier height and work function of the cable material is as follows: cut a uniform thickness sample from a given cable containing spike defects, cut a sample sheet containing only the insulation layer (3) and only the conductor layer (1) from the sample, use a Kelvin probe scanner in semi-contact working mode to measure the surface potential difference of the sample sheet through secondary scanning technology, obtain the Fermi level and vacuum level of the cable material, and calculate the barrier height and work function of the cable material based on the potential difference, wherein the barrier height is the difference between the work functions of the conductor layer (1) and the insulation layer (3).

6. The method for calculating cable partial discharge signals considering temperature effects according to claim 1, characterized in that, In step S3, the specific method for measuring the impedance value of the cable material is to measure the impedance value of a given cable using an impedance analyzer.

7. The method for calculating cable partial discharge signals considering temperature effects according to claim 1, characterized in that, In step S3, the specific method for measuring the actual operating temperature of the cable conductor layer (1) is as follows: the detection part of the temperature sensor is brought into contact with the cable conductor layer (1) under test, the current is applied to the cable and pressure is applied, and the operating temperature of the cable conductor layer (1) is detected by the temperature sensor.

8. The method for calculating cable partial discharge signals considering temperature effects according to claim 1, characterized in that, In step S4, the method for calculating the maximum electric field strength of the defect is as follows: a simulation model of the cable body and the spike defect is constructed based on the cable structure parameters using the finite element simulation method, current constraints are set, and then the simulation model is meshed and calculated. The maximum electric field strength at the tip of the defect and the field strength distribution on the spike surface are obtained using the Poisson equation.

9. A cable partial discharge signal calculation device considering temperature effects, used to implement the method of claim 1, characterized in that, include: The input module is used to collect the structural parameters of the cable, the dielectric constant, thermal conductivity and effective electron mass of each layer of the cable material, defect parameters, barrier height, work function, impedance value, and the actual operating temperature of the conductor layer after the cable is filled with current. The first calculation module is used to calculate the maximum electric field strength of the defect based on the cable structure parameters and cable defect parameters. The second calculation module is used to calculate the partial discharge current considering the effect of temperature based on the barrier height, work function, actual operating temperature, and maximum electric field strength at the defect tip using the partial discharge current calculation formula described in claim 1. Output module: Used to output partial discharge signals based on the phase difference between partial discharge current and voltage; to obtain the correspondence between defects and partial discharge signals.

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