Method and device for monitoring cable insulation based on power quality monitoring data

Abstract

The application relates to the technical field of cable monitoring, and is a cable insulation monitoring method and device based on power quality monitoring data, which comprises the following steps: obtaining the high-voltage side harmonic voltage amplitude and phase corresponding to each end by using the voltage value of each end of the monitored cable; obtaining the equivalent impedance of the monitored cable by using the high-voltage side harmonic voltage amplitude and phase corresponding to each end; and comparing the equivalent impedance of the monitored cable with an impedance threshold value, and in response to the equivalent impedance being less than the impedance threshold value, the insulation state of the monitored cable is abnormal. The application has low cost, low applicable environment requirement, can realize real-time insulation monitoring, has low monitoring environment requirement, can adapt to cable insulation monitoring in various environments, can effectively avoid the limitations of the partial discharge online monitoring method, the sheath current monitoring method and the temperature monitoring method, and can reduce the complexity of existing cable insulation monitoring.

Description

Technical Field

[0001] This invention relates to the field of cable monitoring technology, specifically a cable insulation monitoring method and device based on power quality monitoring data. Background Technology

[0002] Insulation monitoring and early warning of cables are important safety issues for power equipment. The slow, gradual and insidious nature of cable insulation aging has always been a challenge for power safety.

[0003] Currently, there are three main research methods for cable insulation aging, as follows:

[0004] 1. Partial Discharge Online Monitoring Method: The signals generated during partial discharge mainly include various electrical and non-electrical signals. Electrical signals include electromagnetic waves and pulse currents; non-electrical signals include sound, light, and heat. Partial discharge measurement techniques for measuring electromagnetic wave signals include the ultra-high frequency sensor method, which has strong anti-interference capabilities but rapid signal attenuation. Partial discharge measurement techniques for measuring pulse current signals include the high-frequency current sensor method, capacitor-coupled sensor method, and metal-coupled sensor method. These methods are widely used, highly sensitive, and can measure the charge quantity of partial discharge, but are highly susceptible to electromagnetic interference. Therefore, partial discharge signals in the insulation of operating cables in the field are weak, subject to strong electromagnetic interference, and affected by factors such as sensor sensitivity and signal attenuation, making partial discharge signals difficult to extract and identify. Furthermore, the partial discharge method is relatively expensive.

[0005] 2. Sheath Current Monitoring Method: Before a cable insulation failure, an increase in sheath current often occurs. Therefore, online monitoring of the sheath current of high-voltage cables can reflect the cable's insulation status to a certain extent. Furthermore, a significant increase in sheath current can also cause cable temperature rise, increasing additional losses in the sheath, reducing the cable's current carrying capacity, and potentially even causing thermal breakdown. Currently, online sheath current monitoring technology still faces the following challenges: Firstly, for cross-connected cables, distinguishing between leakage current and sheath circulating current from the grounding current during online monitoring is a key and difficult research area.

[0006] 3. Temperature monitoring method: During normal operation of high-voltage cross-linked cables, the conductor temperature should not exceed 90℃. Monitoring the cable temperature can reflect some faults or defects in the cable. Furthermore, by monitoring the cable's operating temperature, the actual current-carrying capacity of the cable can be determined, ensuring safe operation within the current-carrying capacity range. However, temperature monitoring also has limitations. Traditional temperature measurement methods using thermocouples only monitor the temperature of critical parts of the cable, reflecting only the local temperature situation during operation and failing to reflect the overall situation. Distributed fiber optic temperature measurement requires the temperature-sensing fiber to be pre-laid on the outside of the power cable, between the sheath and the main insulation layer. It is not suitable for cables already in operation without temperature-sensing fiber optics, and this technology is significantly affected by different cable laying environments and operating conditions, such as humidity and temperature. Summary of the Invention

[0007] This invention provides a cable insulation monitoring method and device based on power quality monitoring data, which overcomes the shortcomings of the prior art and can effectively solve the problems of high cost and inability to achieve real-time insulation monitoring for various types of cables in existing cable insulation monitoring methods.

[0008] One of the technical solutions of this invention is achieved through the following measures: a cable insulation monitoring method based on power quality monitoring data, comprising:

[0009] By using the voltage value at each end of the monitored cable, the amplitude and phase of the high-voltage side harmonic voltage at each end are obtained;

[0010] The equivalent impedance of the monitored cable is obtained by using the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end.

[0011] The equivalent impedance of the monitored cable is compared with an impedance threshold. If the equivalent impedance is less than the impedance threshold, the insulation condition of the monitored cable is abnormal.

[0012] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0013] The above method utilizes the voltage value at each end of the monitored cable to obtain the amplitude and phase of the high-voltage side harmonic voltage at each end, including:

[0014] Two high-voltage transformers are used to convert the voltage value at each end of the monitored cable into the corresponding secondary voltage.

[0015] The amplitude and phase of the harmonic voltage output from the secondary side of the two high-voltage transformers are obtained using the secondary voltage.

[0016] The harmonic voltage amplitude and phase output from the secondary side of the two high-voltage transformers are restored to the high-voltage side harmonic voltage amplitude and phase corresponding to each end of the cable being monitored.

[0017] The equivalent impedance of the monitored cable is calculated by using the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end, including:

[0018] The amplitude and phase of the high-voltage side harmonic voltage corresponding to each end of the monitored cable are input into the cable impedance model to obtain the capacitance value of the monitored cable.

[0019] The capacitance value of the cable to be monitored is input into the equivalent model at both ends of the cable, and the equivalent impedance of the cable to be monitored is obtained by conversion.

[0020] The equivalent models of the two ends of the above cable are shown below:

[0021]

[0022] in, For Y c The estimated value of Y c Let be the admittance matrix. for The admittance in the first row and second column. for Admittance in the second row and first column.

[0023] The second technical solution of the present invention is achieved through the following measures: a cable insulation monitoring device based on power quality monitoring data, comprising:

[0024] The first monitoring and execution unit uses the voltage value at each end of the monitored cable to obtain the amplitude and phase of the high-voltage side harmonic voltage at each end.

[0025] The second monitoring and execution unit uses the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end to calculate the equivalent impedance of the monitored cable.

[0026] The anomaly detection unit compares the equivalent impedance of the monitored cable with an impedance threshold. If the equivalent impedance is less than the impedance threshold, the insulation condition of the monitored cable is abnormal.

[0027] The third technical solution of the present invention is achieved through the following measures: a storage medium storing a computer program that can be read by a computer, the computer program being configured to execute a cable insulation monitoring method based on power quality monitoring data during runtime.

[0028] The fourth technical solution of the present invention is achieved through the following measures: an electronic device, including a processor and a memory, wherein the memory stores a computer program, which is loaded and executed by the processor to implement a cable insulation monitoring method based on power quality monitoring data.

[0029] This invention is low in cost and has low environmental requirements. It obtains the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end of the monitored cable by measuring the voltage value at each end, and calculates the equivalent impedance of the monitored cable. Based on the equivalent impedance, it determines whether the insulation status of the monitored cable is abnormal, thereby enabling real-time insulation monitoring. It has low requirements for the monitoring environment and can adapt to cable insulation monitoring in various environments. It can also effectively avoid the limitations of partial discharge online monitoring methods, sheath current monitoring methods, and temperature monitoring methods, and reduce the complexity of existing cable insulation monitoring. Attached Figure Description

[0030] Appendix Figure 1 This is a schematic diagram of the method flow of the present invention.

[0031] Appendix Figure 2 This is a schematic diagram of the monitoring connection of the present invention.

[0032] Appendix Figure 3 This is a schematic diagram of the method for obtaining the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end in this invention.

[0033] Appendix Figure 4 This is a schematic diagram of the method for obtaining the equivalent impedance of the monitored cable in this invention.

[0034] Appendix Figure 5 This is a schematic diagram of the cable impedance model in this invention.

[0035] Appendix Figure 6 This is a schematic diagram of the two-end equivalence model in this invention. Detailed Implementation

[0036] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0037] The present invention will be further described below with reference to embodiments and accompanying drawings:

[0038] Example 1: As shown in the attached document Figure 1 , 2 As shown in the figure, an embodiment of the present invention discloses a cable insulation monitoring method based on power quality monitoring data, including:

[0039] Step S101: Using the voltage value at each end of the monitored cable, obtain the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end;

[0040] Step S102: Calculate the equivalent impedance of the monitored cable by using the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end.

[0041] Step S103: The equivalent impedance of the monitored cable is compared with the impedance threshold. If the equivalent impedance is less than the impedance threshold, the insulation condition of the monitored cable is abnormal.

[0042] This invention discloses a cable insulation monitoring method based on power quality monitoring data. It only requires the use of existing devices to collect the voltage values ​​at each end of the monitored cable, which is low-cost. By using the voltage values ​​at each end of the monitored cable, the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end are obtained, and the equivalent impedance of the monitored cable is calculated. Based on the equivalent impedance, it is determined whether the insulation state of the monitored cable is abnormal. This enables real-time insulation monitoring, has low requirements for the monitoring environment, can adapt to cable insulation monitoring in various environments, and can effectively avoid the limitations of partial discharge online monitoring methods, sheath current monitoring methods, and temperature monitoring methods, reducing the complexity of existing cable insulation monitoring.

[0043] Example 2: As shown in the attached document Figure 1 , 3 As shown in Figure 4, this embodiment of the invention discloses a cable insulation monitoring method based on power quality monitoring data, including:

[0044] Step S201: Using the voltage value at each end of the monitored cable, obtain the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end, including:

[0045] Step S2011: Use two high-voltage transformers to convert the voltage value at each end of the monitored cable into the corresponding secondary voltage.

[0046] Here, the high-voltage sides of two high-voltage transformers are connected to both ends of the monitored cable, respectively. The voltage value of each end of the monitored cable is collected and converted into a secondary voltage, which is then output from the low-voltage side to other equipment. The high-voltage transformers here are commonly used devices, so the application cost of this embodiment is low.

[0047] Step S2012: Obtain the amplitude and phase of the harmonic voltage output from the secondary side of the two high-voltage transformers using the secondary voltage;

[0048] In this embodiment, the voltage amplitude and phase of each harmonic can be output through the Fourier calculation function via the power quality monitoring terminal.

[0049] Step S2013: The harmonic voltage amplitude and phase output from the secondary side of the two high-voltage transformers are restored to the high-voltage side harmonic voltage amplitude and phase corresponding to each end of the cable to be monitored.

[0050] In this embodiment, a suitable voltage and current ratio can be set in the power quality monitoring terminal to restore the harmonic voltage amplitude and phase output from the secondary side of the high-voltage transformer to the harmonic voltage amplitude and phase corresponding to the high-voltage side at the cable end (here, the harmonic voltage amplitude and phase corresponding to the high-voltage side at the cable end are the same as the wth harmonic voltage amplitude and phase corresponding to the high-voltage side at the cable end).

[0051] Step S202: Using the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end, calculate the equivalent impedance of the monitored cable, including:

[0052] Step S2021: Input the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end of the monitored cable into the cable impedance model to obtain the capacitance value of the monitored cable.

[0053] The cable impedance model is attached here. Figure 5 As shown in the figure, C a0 The capacitance of phase a cable to ground. Cb0 C is the capacitance to ground of phase b cable. c0 This refers to the capacitance to ground of phase C cable. ab C is the mutual capacitance between phase a cable and phase b cable. ac C is the mutual capacitance between phase b and phase c cables. bc This refers to the mutual capacitance between phase b and phase c cables.

[0054] According to the appendix Figure 5 The capacitance matrix C of the cable can be obtained as shown below;

[0055]

[0056] In this embodiment, the expression for the admittance matrix is ​​defined as follows:

[0057] Y=jωC

[0058] Similarly, the impedance matrix of the cable can be calculated using the Karl von Kahn formula, and the corresponding expression is shown below:

[0059]

[0060] Where Z is the impedance of the cable, Z aa For phase a, the self-impedance, Z ab Z represents the mutual impedance between phase a and phase b. bb For phase b's self-impedance, Z cc For the self-impedance of phase c, Z bc Z represents the mutual impedance between phase b and phase c. ac Let A and C be the mutual impedances.

[0061] In this embodiment, the characteristic admittance matrix is ​​defined, and the corresponding expression is shown below:

[0062]

[0063] In step S2022, the capacitance value of the cable to be monitored is input into the equivalent model at both ends of the cable to calculate the equivalent impedance of the cable to be monitored.

[0064] The equivalent models of the two ends of the cable are attached. Figure 6 As shown in the diagram, the cable model at both ends is divided into end m and end n. The voltage at end m is V. m The current at terminal m is I m The voltage at terminal n is Vn, and the current at terminal n is I. n .

[0065] According to the appendix Figure 6 As shown, the expression for the relationship between the voltage and current at both ends of the cable can be derived as follows:

[0066]

[0067] By collecting voltage and current values ​​at cable ends m and n times at multiple time points, the above can be extended to:

[0068] Y m =KX

[0069] in:

[0070] Y m =[I m (1)LI m (k) LI m (q)]

[0071]

[0072]

[0073] Where: q is the total number of sampling points, and k is any positive integer from 1 to q.

[0074] Applying the least squares method to the above equation, the corresponding expression is as follows:

[0075] K = (X T X) -1 X T Y m

[0076] After obtaining the coefficient matrix K based on the identification, the estimated value of Yc can be calculated according to the above formula.

[0077]

[0078] in: Let Yc be the estimated value, and K(1,1) be the elements of the first three rows and first three columns of the K matrix.

[0079] Similarly, it can be calculated using the above formula. The estimated value.

[0080]

[0081] in: for The estimated value is K(1,2), which is the element of the first three rows and the fourth to sixth columns of the K matrix.

[0082] Based on the characteristic admittance matrix, the estimated value of Yc, The estimated value can be used to derive the estimated value of the Y matrix:

[0083]

[0084] in: This is an estimate of Y.

[0085] Based on the above, take The elements in the first row and second column, and the elements in the second row and first column, are used as the basis for impedance determination. The specific expression is as follows:

[0086]

[0087] Step S203: The equivalent impedance of the monitored cable is compared with the impedance threshold. If the equivalent impedance is less than the impedance threshold, the insulation condition of the monitored cable is abnormal.

[0088] The impedance threshold can be set according to the actual situation, and can be set to 0.5MΩ. When the equivalent impedance Zp of the monitored cable is greater than 0.5MΩ, the insulation condition of the cable is normal; when the equivalent impedance Zp of the monitored cable is less than 0.5MΩ, the insulation condition of the cable is abnormal.

[0089] Example 3: This embodiment of the invention discloses a storage medium storing a computer program that can be read by a computer. The computer program is configured to execute a cable insulation monitoring method based on power quality monitoring data during runtime.

[0090] The aforementioned storage media may include, but are not limited to, USB flash drives, read-only memory, portable hard drives, magnetic disks, optical disks, and other media capable of storing computer programs.

[0091] Example 4: This embodiment of the invention discloses an electronic device, including a processor and a memory. The memory stores a computer program, which is loaded and executed by the processor to implement a cable insulation monitoring method based on power quality monitoring data.

[0092] The aforementioned electronic device also includes transmission devices and input / output devices, wherein both the transmission devices and the input / output devices are connected to the processor.

[0093] The aforementioned processor can be a central processing unit (CPU), a general-purpose processor, a digital signal processor (DSP), an ASIC, an FPGA, or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. It can implement or execute the various exemplary logic blocks, modules, and circuits described in conjunction with the disclosure of this application. It can also be a combination that implements computational functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, etc.

[0094] The aforementioned storage module can be a memory, including but not limited to: USB flash drive, read-only memory, portable hard drive, magnetic disk or optical disk, and other media that can store computer programs.

[0095] The above technical features constitute the preferred embodiment of the present invention, which has strong adaptability and optimal implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the requirements of different situations.

Claims

1. A cable insulation monitoring method based on power quality monitoring data, characterized in that, include: By using the voltage value at each end of the monitored cable, the amplitude and phase of the high-voltage side harmonic voltage at each end are obtained; The equivalent impedance of the monitored cable is obtained by using the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end. The equivalent impedance of the monitored cable is compared with an impedance threshold. If the equivalent impedance is less than the impedance threshold, the insulation condition of the monitored cable is abnormal. Specifically, the equivalent impedance of the monitored cable is calculated by using the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end, including: The amplitude and phase of the high-voltage side harmonic voltage corresponding to each end of the monitored cable are input into the cable impedance model to obtain the capacitance value of the monitored cable. The capacitance value of the cable to be monitored is input into the equivalent model at both ends of the cable, and the equivalent impedance of the cable to be monitored is obtained by calculation, including: Based on the capacitance value of the monitored cable, the capacitance matrix C of the cable is obtained, and the admittance matrix Y is defined. Y=jωC Define the characteristic admittance matrix Y C The corresponding expression is shown below: Where Z is the impedance matrix of the cable; Based on the equivalent model of both ends of the cable, the expressions for the voltage and current at both ends of the cable are derived as follows: Among them, V m Let I be the voltage at terminal m. m Let V be the current at terminal m. n Let I be the voltage at terminal n. n The current at terminal n; By collecting voltage and current values ​​at cable ends m and n times at multiple time points, the above can be extended to: Y m KX in, Y m =[I m (1) … I m (k) … I m (q)] Where q is the total number of sampling points, and k is any positive integer from 1 to q; Applying the least squares method to the above equation yields the coefficient matrix K, as shown in the following expression: K=(X T X) -1 X T Y m Substitute the coefficient matrix K into Get Y c The estimated value and The estimated value Where K(1,1) are the elements of the first three rows and the first three columns of matrix K, and K(1,2) are the elements of the first three rows and the fourth to sixth columns of matrix K; Based on the characteristic admittance matrix Y c Estimated value estimated value The estimated value of the admittance matrix Y is obtained. Pick The element in the first row and second column The element in the second row and first column The equivalent impedance of the monitored cable is obtained by the following expression:

2. The cable insulation monitoring method based on power quality monitoring data according to claim 1, characterized in that, The method of obtaining the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end of the monitored cable by utilizing the voltage value at each end includes: Two high-voltage transformers are used to convert the voltage value at each end of the monitored cable into the corresponding secondary voltage. The amplitude and phase of the harmonic voltage output from the secondary side of the two high-voltage transformers are obtained using the secondary voltage. The harmonic voltage amplitude and phase output from the secondary side of the two high-voltage transformers are restored to the high-voltage side harmonic voltage amplitude and phase corresponding to each end of the cable being monitored.

3. A cable insulation monitoring device based on power quality monitoring data, wherein the cable insulation monitoring device based on power quality monitoring data uses the cable insulation monitoring method based on power quality monitoring data as described in any one of claims 1 to 2, characterized in that, include: The first monitoring and execution unit uses the voltage value at each end of the monitored cable to obtain the amplitude and phase of the high-voltage side harmonic voltage at each end. The second monitoring and execution unit uses the amplitude and phase of the high-voltage side harmonic voltage corresponding to each end to calculate the equivalent impedance of the monitored cable. The anomaly detection unit compares the equivalent impedance of the monitored cable with an impedance threshold. If the equivalent impedance is less than the impedance threshold, the insulation condition of the monitored cable is abnormal.

4. A storage medium, characterized in that, The storage medium stores a computer program that can be read by a computer, and the computer program is configured to execute the cable insulation monitoring method based on power quality monitoring data as described in any one of claims 1 to 2 when it runs.

5. An electronic device, characterized in that, It includes a processor and a memory, wherein the memory stores a computer program, which is loaded and executed by the processor to implement the cable insulation monitoring method based on power quality monitoring data as described in any one of claims 1 to 2.

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