A 10kv cable intermediate joint insulation on-line monitoring device and its early warning evaluation method

Abstract

The application discloses a kind of 10kV cable intermediate joint insulation on-line monitoring device and its early warning evaluation method, including being installed on the 10kV cable to be detected and coupling operating cable power frequency voltage signal and the high-frequency pulse voltage signal generated by cable partial discharge electric field coupling sensor, and for receiving processing and gathering cable power frequency voltage signal, the monitoring module of high-frequency pulse voltage signal of electric field coupling sensor output;The electric field coupling sensor includes shell, and the upper plate of metal material, the upper pressing plate of insulating material and the lower plate of metal material are successively stacked and installed on the outside of shell.The application can realize cable intermediate joint insulation monitoring, and the electric field coupling sensor of the application can simultaneously carry out the collection of high-frequency pulse voltage signal and cable power frequency voltage signal, process high-frequency pulse voltage signal in combination with cable power frequency voltage signal, which is beneficial to improve the accuracy of intermediate joint insulation monitoring result.

Description

Technical Field

[0001] This invention belongs to the field of power system distribution technology, and particularly relates to an online monitoring device for insulation of 10kV cable intermediate joints and its early warning assessment method. Background Technology

[0002] 10kV distribution cables, due to their three-core structure, differ from single-core cables. Three-core cables generally use a two-point grounding method, with the intermediate joint not grounded. The cables are usually directly buried, with only the intermediate joint having a vertical shaft. Affected by factors such as laying method, laying environment, and manufacturing process, the failure rate of distribution network cables remains high, with failures mostly occurring at the terminal and intermediate joint locations. Therefore, correctly assessing the cable insulation condition, detecting insulation abnormalities in advance and issuing early warnings, and promptly eliminating defects can effectively prevent failures and benefit the operation and maintenance of 10kV cables.

[0003] Existing monitoring methods for partial discharge in three-core cables mostly employ high-frequency current methods and are generally installed at the grounding point of the cable terminal. This method cannot achieve full cable coverage for long cables and makes it difficult to monitor the location of cable joints. Furthermore, due to the high cost of high-frequency current sensors, they are rarely deployed in 10kV distribution cables. Summary of the Invention

[0004] Purpose of the invention: The first purpose of this invention is to provide an online insulation monitoring device for 10kV cable joints that can realize insulation monitoring of cable joints.

[0005] The second objective of this invention is to provide an early warning assessment method for an online monitoring device for the insulation of 10kV cable joints.

[0006] Technical Solution: This invention discloses an online monitoring device for the insulation of a 10kV cable joint, comprising an electric field coupling sensor installed on the 10kV cable to be tested and coupling the power frequency voltage signal of the cable during operation with the high-frequency pulse voltage signal generated by partial discharge of the cable, and a monitoring module for receiving, processing and acquiring the power frequency voltage signal and the high-frequency pulse voltage signal output by the electric field coupling sensor; the electric field coupling sensor includes a housing, and a metal upper electrode plate, an insulating upper pressure plate and a metal lower electrode plate stacked on the outside of the housing in sequence, the lower electrode plate being configured as a U-shaped structure and installed on the 10kV cable to be monitored during use; the lower electrode plate and the 10kV cable to be monitored form a first capacitor, the upper electrode plate and the lower electrode plate form a second capacitor, and the first capacitor and the second capacitor are connected in series to form a voltage divider circuit for extracting the power frequency voltage signal and the high-frequency pulse voltage signal of the cable.

[0007] Furthermore, the monitoring module is fixedly installed inside the housing, and the lead wires of the upper electrode plate and the lower electrode plate are respectively connected to the shield wire and the core wire of one end of the coaxial cable, and the other end of the coaxial cable is connected to the monitoring module through an IPEX connector.

[0008] Furthermore, the electric field coupling sensor also includes a lower pressure plate made of insulating material that is snapped into the lower electrode plate, and the lower pressure plate is fixedly connected to the outer shell.

[0009] Furthermore, the monitoring module includes an acquisition module, a power and communication management module, and a battery pack. The acquisition module is used to condition and acquire cable power frequency voltage signals and high-frequency pulse voltage signals. The power and communication management module is used to control the power supply of the acquisition module and external information interaction. The battery pack is used for power supply.

[0010] Furthermore, the acquisition module includes a front-end conditioning circuit, an A / D sampling circuit, and a control unit. The front-end conditioning circuit receives the cable power frequency voltage signal and the high-frequency pulse voltage signal from the electric field coupling sensor, separates the cable power frequency voltage signal and the high-frequency pulse voltage signal, and conditions the separated cable power frequency voltage signal and high-frequency pulse voltage signal. The A / D sampling circuit acquires the conditioned cable power frequency voltage signal and high-frequency pulse voltage signal. The control unit is used to control the A / D sampling circuit to sample and to perform calculation processing on the sampled data.

[0011] Furthermore, the front-end conditioning circuit consists of an RF measurement circuit for conditioning high-frequency pulse voltage signals and a power frequency synchronization circuit for conditioning power frequency voltage signals of cables. The RF measurement circuit includes a 100kHz~100MHz bandpass filter, an RF amplifier, a detector circuit, and a broadening circuit connected to the electric field coupling sensor. The power frequency synchronization circuit includes a 1kHz low-pass filter and a power frequency amplifier connected to the electric field coupling sensor.

[0012] Based on the same inventive concept, this invention also discloses an early warning assessment method for an online monitoring device for the insulation of a 10kV cable joint, comprising the following steps:

[0013] The acquisition module is set to acquire signals at a frequency that is equal to the frequency of the signal acquisition per day. The acquisition module continuously acquires n samples in a single sampling. The acquisition module acquires a single sample in the following way: starting from the zero point of the cable power frequency voltage signal, it acquires the target data within the period of S cable power frequency voltage signals. The target data includes the amplitude of the high-frequency pulse voltage signal, the number of pulses of the high-frequency pulse voltage signal, and the phase of the high-frequency pulse voltage signal within the cable power frequency synchronous voltage signal.

[0014] For n samples obtained by the acquisition module in a single sampling, if the total number of pulses in the n samples falls within a preset range, partial discharge is considered to exist, and the partial discharge count is incremented by 1; otherwise, partial discharge is not considered to exist, and the partial discharge count remains unchanged. The maximum amplitude of the high-frequency pulse voltage signal in the n samples is taken as the reference value. The maximum value of all reference values ​​collected within the day is taken as the historical maximum value.

[0015] The duration of partial discharge on a given day is calculated based on the statistical count of partial discharge.

[0016] The intensity index of partial discharge is calculated based on the historical maximum value to describe the intensity of partial discharge.

[0017] Calculate the product of the daily partial radiation duration index and the partial radiation intensity index, and record this product as the evaluation index. If the evaluation index is 0, the trend index is set to 0. If the evaluation index is greater than 0, take the evaluation index m days prior to the current day, fit a linear equation between the evaluation index and time, and calculate the trend index based on the slope of the linear equation. If there are less than m days prior to the current day, the trend index is set to 0.

[0018] A score is calculated based on evaluation indicators and trend indicators to assess the insulation status of the intermediate joint of the cable to be monitored.

[0019] Based on scoring and preset criteria, the current insulation status of the intermediate joints of the monitored cable is classified and an early warning is issued.

[0020] Furthermore, the method for calculating the duration index of partial discharge on a given day is: partial discharge statistics divided by the number of monitoring sessions per day;

[0021] The partial radiative intensity index is calculated as follows: set threshold one and threshold two, with threshold two being greater than threshold one. If the historical maximum value is less than threshold one, the partial radiative intensity index is 0; if the historical maximum value is greater than or equal to threshold one and less than or equal to threshold two, the partial radiative intensity index is 0.5; if the historical maximum value is greater than threshold two, the partial radiative intensity index is 1.

[0022] The method for calculating the trend index based on the slope of the linear equation is as follows: set thresholds three, four, and five, with threshold five being greater than threshold four and threshold four being greater than threshold three. If the slope is less than threshold three, the trend index is 0; if the slope is greater than or equal to threshold three and less than or equal to threshold four, the trend index is 0.5; if the slope is greater than threshold four and less than or equal to threshold five, the trend index is 0.8; and if the slope is greater than threshold five, the trend index is 1.

[0023] Furthermore, the scoring method is as follows: set the weight values ​​of the evaluation index and the trend index respectively, calculate the product of the evaluation index and the trend index with the corresponding weight value respectively, and the difference between 1 and the sum of the two products is recorded as the score.

[0024] The preset criteria are as follows: set thresholds six, seven, and eight, with threshold six greater than threshold seven and threshold seven greater than threshold eight. If the score equals threshold six, the insulation status of the intermediate joint is judged as normal, and no warning is needed; if the score is greater than or equal to threshold seven and less than threshold six, the insulation status of the intermediate joint is judged as a warning state, and a warning is issued; if the score is greater than or equal to threshold eight and less than threshold seven, the insulation status of the intermediate joint is judged as a severe state, and a warning is issued; if the score is less than threshold eight, the insulation status of the intermediate joint is judged as a critical state, and a warning is issued.

[0025] Furthermore, when the insulation status of the intermediate joint is judged to be a warning state, a severe state, or a crisis state, the amplitude of all high-frequency pulse voltage signals and the phase of the high-frequency pulse voltage signals within the cable power frequency synchronous voltage signal are extracted from the n sample data currently collected by the acquisition module, and statistically formed into PRPD statistical spectrum and PRPS statistical spectrum.

[0026] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: This invention enables insulation monitoring of cable joints, solving the problem that partial discharge measurement cannot be performed using the high-frequency current method on 10kV cable joints due to the lack of a grounding wire. The electric field coupling sensor and monitoring module of this invention, working together, can simultaneously acquire high-frequency pulse voltage signals and cable power frequency voltage signals, providing a built-in power frequency synchronization signal source based on real-time grid signals for partial discharge measurement. Furthermore, this invention can determine whether the high-frequency pulse voltage signal is generated by partial discharge by observing the phase position of the high-frequency pulse voltage signal appearing in the cable power frequency voltage signal, which helps improve the accuracy of joint insulation monitoring results. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the present invention;

[0028] Figure 2 For the present invention Figure 1 Exploded view;

[0029] Figure 3 The equivalent circuit diagram of coupling capacitor C1 and coupling capacitor C2 of the present invention is shown below.

[0030] Figure 4 This is a schematic diagram of the monitoring module of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0032] Example 1

[0033] This invention discloses an online insulation monitoring device for 10kV cable joints, such as... Figure 1 and Figure 2 As shown, it includes an electric field coupling sensor and a monitoring module. The electric field coupling sensor is installed on the 10kV cable to be tested and couples the cable's power frequency voltage signal and the high-frequency pulse voltage signal generated by the cable's partial discharge during operation. The monitoring module is used to receive and process the cable's power frequency voltage signal and high-frequency pulse voltage signal output by the electric field coupling sensor, and to collect the processed cable power frequency voltage signal and high-frequency pulse voltage signal.

[0034] The electric field coupling sensor includes a housing 1, an upper electrode plate 2, an upper pressure plate 3, a lower electrode plate 4, a lower pressure plate 5, and a mounting bracket 6. A mounting groove is provided on the outer side of the housing 1, and the upper electrode plate 2, upper pressure plate 3, lower electrode plate 4, and lower pressure plate 5 are stacked and installed in the mounting groove in sequence. The upper electrode plate 2 is fitted into the mounting groove and is made of metal, with a rectangular plate structure. The upper pressure plate 3 is in contact with the side of the upper electrode plate 2 away from the housing 1, and is made of insulating material, with a rectangular plate structure. The lower electrode plate 4 is in contact with the side of the upper pressure plate 3 away from the housing 1, and is made of metal, with a U-shaped structure. The insulating upper pressure plate 3 is positioned between the conductive upper electrode plate 2 and the lower electrode plate 4, and the three components constitute a second capacitor C2. The lower electrode plate 4 is U-shaped, facilitating the snap-fit ​​installation of the online monitoring device onto the cable to be monitored during use. The lower pressure plate 5 is snapped into the lower electrode plate 4, and the lower pressure plate 5 is fixedly connected to the outer casing 1. Preferably, the connection between the lower pressure plate 5 and the outer casing 1 is a bolt connection. Preferably, the lower pressure plate 5 is configured as a flat bridge structure, located inside the U-shape of the lower electrode plate 4, and both sides of the lower pressure plate 5 are snapped into the arc-shaped portion of the lower electrode plate 4. The mounting bracket 6 is fixedly installed on the outer casing 1, and both sides of the mounting bracket 6 are provided with hook structures for fixing the tethering rope. In use, the mounting bracket 6 is placed near the intermediate joint of the cable to be monitored, and the mounting bracket 6 is fixed to the cable by the tethering rope. The U-shaped lower pressure plate 5 and mounting bracket 6 allow the insulation online monitoring device of the present invention to be directly snapped into and fixed to the cable, making installation convenient. Furthermore, the mounting bracket 6 allows the insulation online monitoring device to be applied to cables of different diameters, and with the cooperation of the tethering rope and the mounting bracket 6, the insulation online monitoring device can better fit the cable.

[0035] The leads of the upper electrode 2 and the lower electrode 4 are respectively connected to the shield wire and core wire of one end of the coaxial cable, and the other end of the coaxial cable is connected to the monitoring module through an IPEX connector. The lower electrode 4 and the 10kV cable to be monitored form a first capacitor C1, and the upper electrode 2 and the lower electrode 4 form a second capacitor C2. The first capacitor C1 and the second capacitor C2 are connected in series to form a voltage divider circuit for extracting the power frequency voltage signal and high frequency pulse voltage signal of the cable. The voltage division ratio of the first capacitor C1 and the second capacitor C2 is preferably 2:1, and the equivalent circuit diagram of the voltage divider circuit is shown below. Figure 3 As shown, the voltage signal output after voltage division by the first capacitor C1 and the second capacitor C2 is v0, which includes the cable power frequency voltage signal and the high-frequency pulse voltage signal. When the online monitoring device of the present invention is started, the voltage signal processed and collected by the monitoring module is v0, and the first capacitor C1 and the second capacitor C2 couple the cable power frequency voltage signal and the high-frequency pulse voltage signal generated by cable partial discharge during operation.

[0036] The monitoring module is fixedly installed inside the housing 1, which is then waterproofed and sealed. The monitoring module includes an acquisition module, a power and communication management module, and a battery pack. The acquisition module is used to condition and acquire cable power frequency voltage signals and high-frequency pulse voltage signals. The power and communication management module is used to control the power supply to the acquisition module and external information exchange. The battery pack supplies power to the acquisition module, the power and communication management module, and the electric field coupling sensor, and is controlled by the power and communication management module. The battery pack is preferably a high-capacity lithium-ion battery. The power and communication management module includes a power management submodule and a communication management submodule. The power management module is responsible for managing the power supply to the device and starting, stopping, and putting the online monitoring device into sleep mode according to a set time. The communication module is responsible for communication with the acquisition module and with the external upper-level platform. Preferably, the communication management submodule uses wireless communication for upward communication, and can adopt the following two communication configuration schemes: Scheme 1: Configure a LoRa module, and equip each ring network node or cable shaft with one LoRa-4G data acquisition unit. The data acquisition unit needs to be powered by a power supply or battery pack. It receives and calculates data from the downstream receiving device and transmits it to the upper-level device or system via 4G. For overhead-to-ground cable joints, a 4G module is equipped to directly transmit the data to the system. Scheme 2: Configure a 4G module, and the device directly transmits the data collected and calculated to the upper-level device or system.

[0037] like Figure 4As shown, the acquisition module includes a front-end conditioning circuit, an A / D sampling circuit, and a control unit. The front-end conditioning circuit receives the cable power frequency voltage signal and high-frequency pulse voltage signal from the electric field coupling sensor, separates these signals, and conditions them. The front-end conditioning circuit sequentially filters, amplifies, detects, and broadens the separated high-frequency pulse voltage signal. Simultaneously, it sequentially filters and amplifies the separated cable power frequency voltage signal. The A / D sampling circuit acquires the conditioned cable power frequency voltage signal and high-frequency pulse voltage signal. The control unit controls the A / D sampling circuit to sample and processes the sampled data.

[0038] The module's front-end conditioning circuit consists of an RF measurement circuit and a power frequency synchronization circuit. The RF measurement circuit is used to condition the high-frequency pulse voltage signal and includes a 100kHz~100MHz bandpass filter connected to the electric field coupling sensor, an RF amplifier, a detector circuit, and a bandwidth extension circuit. The 100kHz~100MHz bandpass filter filters the signal output from the electric field coupling sensor, separating the high-frequency pulse voltage signal. The RF amplifier amplifies the filtered high-frequency pulse voltage signal. The detector circuit envelops the amplified high-frequency pulse voltage signal from the RF amplifier. The bandwidth extension circuit adjusts the output signal width of the detector circuit.

[0039] The power frequency synchronization circuit is used to condition the power frequency voltage signal of the cable. The power frequency synchronization circuit consists of a 1KHz low-pass filter connected to the electric field coupling sensor and a power frequency amplifier. The 1KHz low-pass filter filters the signal output by the electric field coupling sensor and separates the cable power frequency voltage signal. The power frequency amplifier amplifies the cable power frequency voltage signal.

[0040] In use, the online monitoring device of the present invention is installed and fixed near the intermediate joint of the cable to be monitored by using the mounting bracket 6 and the tether. The online monitoring device of the present invention adopts a timed start-up mode. The device is normally in a dormant state. After the set time is reached, the power and communication management module starts the acquisition module. After completing the data acquisition work, the device enters a dormant state. When the online monitoring device of the present invention is started, the first capacitor C1 and the second capacitor C2 are connected in series to form a voltage divider circuit. The voltage divider circuit formed by the first capacitor C1 and the second capacitor C2 is used to extract the cable power frequency voltage signal and the high frequency pulse voltage signal. The cable power frequency voltage signal and the high frequency pulse voltage signal are transmitted to the acquisition module in the form of voltage signal v0. The front-end conditioning circuit receives the voltage signal v0 from the electric field coupling sensor and separates the voltage signal v0 into the cable power frequency voltage signal and the high frequency pulse voltage signal. The cable power frequency voltage signal and the high frequency pulse voltage signal separated by the front-end conditioning circuit are conditioned. The A / D sampling circuit acquires the conditioned cable power frequency voltage signal and the high frequency pulse voltage signal. The acquired cable power frequency voltage signal and the high frequency pulse voltage signal are transmitted to the control unit. Finally, the control unit calculates and processes the cable power frequency voltage signal and the high frequency pulse voltage signal and outputs the insulation status at the intermediate joint of the cable to be monitored.

[0041] The first capacitor C1 and the second capacitor C2 are connected in series to form a voltage divider circuit, which can extract the cable power frequency voltage signal and the high-frequency pulse voltage signal. After receiving the cable power frequency voltage signal and the high-frequency pulse voltage signal, the front-end conditioning circuit not only separates the cable power frequency voltage signal and the high-frequency pulse voltage signal, but also conditions the separated cable power frequency voltage signal and the high-frequency pulse voltage signal. In summary, the electric field coupling sensing and monitoring module can not only measure the partial discharge signal, but also extract the cable power frequency voltage signal to determine the insulation status of the cable intermediate joint while measuring the partial discharge signal, without the need for a separate power frequency voltage signal measuring device that provides a synchronous signal source.

[0042] Example 2

[0043] This invention discloses an early warning assessment method for an online monitoring device for insulation of 10kV cable joints, comprising the following steps:

[0044] S1: Set the frequency of signal acquisition by the acquisition module per day. The acquisition module continuously acquires n samples in a single sampling. The acquisition module acquires a single sample in the following way: starting from the zero point of the cable power frequency voltage signal, it acquires the target data within the period of S cable power frequency voltage signals. The target data includes the amplitude Ai of the high-frequency pulse voltage signal, the number of pulses Np of the high-frequency pulse voltage signal, and the phase of the high-frequency pulse voltage signal within the cable power frequency synchronous voltage signal.

[0045] Preferably, n is 10. Where S is the rated frequency of the power system, and its value is 50 or 60.

[0046] S2: For n samples obtained by the acquisition module in a single sampling, if the total number of pulses Np in the n samples belongs to the preset interval, then partial discharge is considered to exist, and the partial discharge statistical count Npd is incremented by 1; otherwise, partial discharge is not considered to exist, and the partial discharge statistical count Npd remains unchanged; take the maximum value of the amplitude Ai of the high-frequency pulse voltage signal in the n samples as the reference value; take the maximum value of all reference values ​​collected within the day as the historical maximum value Apdmax;

[0047] The preferred preset interval is [50, 500], that is, 50 ≤ Np ≤ 500.

[0048] S3: Calculate the local discharge persistence index W1 for the day based on the local discharge statistics. The method for calculating the local discharge persistence index for the day is: local discharge statistics Npd divided by the number of monitoring times per day; if the monitoring frequency is set to once per hour, and a total of 24 monitoring times are conducted per day, then W1 = Npd / 24.

[0049] S4: Calculate the partial discharge intensity index A based on the historical maximum value to describe the intensity of partial discharge.

[0050] The partial radiation intensity index is calculated as follows: Threshold 1 and Threshold 2 are set, with Threshold 2 being greater than Threshold 1. If the historical maximum value Apdmax is less than Threshold 1, the partial radiation intensity index A is 0; if the historical maximum value Apdmax is greater than or equal to Threshold 1 and less than or equal to Threshold 2, the partial radiation intensity index A is 0.5; if the historical maximum value Apdmax is greater than Threshold 2, the partial radiation intensity index A is 1. Preferably, Threshold 1 is 20 and Threshold 2 is 30. The formula for calculating the partial radiation intensity index A is as follows:

[0051] .

[0052] S5: Calculate the product of the daily partial radiation duration index W1 and the partial radiation intensity index A, and record this product as the evaluation index W1*A. If the evaluation index W1*A is 0, then the trend index Q is recorded as 0. If the evaluation index W1*A is greater than 0, then take the evaluation index W1*A for m days prior to the current day as the starting point, and fit the linear equation of the evaluation index W1*A with time, and calculate the trend index Q based on the slope b1 of the linear equation. If there are less than m days prior to the current day, then the trend index Q is recorded as 0.

[0053] The method for calculating the trend index Q based on the slope b1 of the linear equation is as follows: set thresholds three, four, and five, where threshold five is greater than threshold four, and threshold four is greater than threshold three. If the slope b1 is less than threshold three, the trend index Q is 0; if the slope b1 is greater than or equal to threshold three and less than or equal to threshold four, the trend index Q is 0.5; if the slope b1 is greater than threshold four and less than or equal to threshold five, the trend index Q is 0.8; and if the slope b1 is greater than threshold five, the trend index Q is 1.

[0054] Preferably, if threshold three is set to 0.1, threshold four to 0.2, and threshold five to 0.4, then the formula for calculating the trend indicator Q is as follows:

[0055] .

[0056] S6: Calculate the score Wz for evaluating the insulation status of the intermediate joint of the cable to be monitored based on the evaluation index W1*A and the trend index Q.

[0057] The scoring method is as follows: Set weight values ​​for the evaluation indicator W1*A and the trend indicator Q, respectively. Calculate the product of each indicator W1*A and the trend indicator Q with its corresponding weight value. Sum the two products, and the difference between 1 and this sum is recorded as the score Wz. Let the weight value of the evaluation indicator W1*A be... The weight value of the trend indicator Q is ,and and If the sum of is 1, then the formula for calculating the score Wz is: .

[0058] Preferred, 0.7 The value is 0.3. The evaluation index W1*A includes the combined changes in the duration and amplitude of partial discharge; the trend index Q represents the rate of increase of the measured amplitude, and the faster the rate of increase, the faster the insulation deteriorates. Considering both the evaluation index W1*A and the trend index Q, the importance of partial discharge intensity should be greater than the rate of increase, because the initial increase of partial discharge starts from a small value, and the intensity is constantly increasing. When the discharge is continuous and the amplitude rises to above 30 dB ( Even if the rate of increase is small or even zero, timely action is still required. A=1, therefore the score is 1-0.7=0.3 points. At this point, Wz=0.3, and the joint insulation condition is critical. If an upward rate of increase exists, Wz will be less than 0.3 points, and the joint insulation condition will be endangered.

[0059] S7: Based on the score Wz and preset criteria, classify and warn about the current insulation status of the intermediate joint of the cable to be monitored.

[0060] The preset criteria are as follows: set thresholds six, seven, and eight, with threshold six greater than threshold seven and threshold seven greater than threshold eight. If the score Wz equals threshold six, the insulation status of the intermediate joint is judged as normal, and no warning is needed; if the score Wz is greater than or equal to threshold seven and less than threshold six, the insulation status of the intermediate joint is judged as a warning status, and a warning is issued; if the score Wz is greater than or equal to threshold eight and less than threshold seven, the insulation status of the intermediate joint is judged as a severe status, and a warning is issued; if the score Wz is less than threshold eight, the insulation status of the intermediate joint is judged as a critical status, and a warning is issued.

[0061] Preferably, if threshold six is ​​set to 1, threshold seven to 0.5, and threshold eight to 0.3, then the rules for classifying the insulation status of intermediate joints are as follows:

[0062] .

[0063] S8: When the insulation status of the intermediate joint is judged to be a warning state, a serious state, or a crisis state, extract the amplitude Ai of all high-frequency pulse voltage signals and the phase of the high-frequency pulse voltage signals within the cable power frequency synchronous voltage signal from the n sample data currently collected by the acquisition module, and statistically form PRPD statistical spectrum and PRPS statistical spectrum.

[0064] When the insulation condition of the intermediate joint is judged to be in a warning state, a serious state, or a crisis state, in practical applications, the partial discharge type can be further judged based on the PRPD and PRPS statistical charts. At the same time, the insulation condition score Wz of the intermediate joint can be combined to provide further guidance for maintenance decisions.

[0065] Example 3

[0066] Using the early warning assessment method of a 10kV cable intermediate joint insulation online monitoring device disclosed in this invention, an abnormal insulation condition was found in one intermediate joint of a cable. The method includes the following steps.

[0067] S1: Execute step S1 in Example 2. The acquisition module acquires signals at a frequency of once per hour, where n is 10 and S is 50.

[0068] S2: Execute step S2 in Example 2. In this example, partial discharge exists during the first sampling. The partial discharge statistical count Npd is 1, and the historical maximum value Apdmax is less than 20.

[0069] S3: Perform step S3 in Example 2, W1=1 / 24.

[0070] S4: Execute step S4 in Example 2, with threshold 1 being 20, threshold 2 being 30, and the historical maximum value Apdmax being less than 20, therefore the partial discharge intensity index A is 0.

[0071] S5: Execute step S5 in Example 2, wherein threshold three is set to 0.1, threshold four is set to 0.2, threshold five is set to 0.4; evaluation index W1*A is 0, and trend index Q is 0.

[0072] S6: Perform step S6 in Example 2, wherein 0.7 It is 0.3; .

[0073] S7: Execute step S7 in Example 2, where threshold six is ​​set to 1, threshold seven is set to 0.5, and threshold eight is set to 0.3; the insulation status of the cable intermediate joint is normal during the first sampling.

[0074] The acquisition module samples the cable every hour and repeats steps S2-S7 above. Step S7 represents the initial sampling result, and the insulation condition of the cable joint is normal.

[0075] Considering the long time required to monitor the cable and the large amount of data collected, this embodiment only lists some of the test data and corresponding monitoring results.

[0076] During a monitoring session in the fourth month, the historical maximum value Apdmax obtained from the data acquisition module was less than 20, and the partial radiation intensity index A was 0; the measured b1 was greater than 0.1 and less than 0.2, and Q was 0.5. During this sampling, the insulation condition of the cable joint was in a warning state. Comparison with the initial sampling results showed that the partial discharge amplitude of the cable was increasing at a certain rate, therefore monitoring continued.

[0077] The historical maximum value Apdmax obtained during a monitoring session in the seventh month of the acquisition module was less than 20, and the partial discharge intensity index A was 0; the measured b1 was greater than 0.2 and less than 0.4, and Q was 0.8. During this sampling, the insulation condition of the cable joint was still in a warning state. Comparison with the previous two sampling results showed that the partial discharge amplitude of the cable was still increasing at a certain rate, therefore monitoring continued.

[0078] During a monitoring session in the ninth month, the partial discharge statistics Npd obtained from the data acquisition module were 12, the historical maximum value Apdmax was greater than 20 and less than 30, W1=1 / 2, the partial discharge intensity index A was 0.5, and the evaluation index W1*A was 0.25; the measured b1 was greater than 0.2 and less than 0.4, and Q was 0.8. During this sampling, the insulation condition of the cable joint was still in a warning state. Comparison with the previous three sampling results showed that the partial discharge amplitude of the cable was still increasing at a certain rate, therefore monitoring continued.

[0079] During a monitoring session in the tenth month, the partial discharge statistics Npd obtained from the data acquisition module were 24, the historical maximum value Apdmax was greater than 20 and less than 30, W1=1, the partial discharge intensity index A was 0.5, and the evaluation index W1*A was 0.5; the measured b1 was greater than 0.2 and less than 0.4, and Q was 0.8. The insulation condition of the cable joint was critical at the time of sampling. Disassembly of the joint revealed traces of electrical discharge.

[0080] In this embodiment, the cable with insulation defects is being tested, therefore no corresponding PRPD and PRPS statistical maps are generated. In practical applications, when the insulation status of the intermediate joint is judged to be in a warning state, a severe state, or a crisis state, step S8 in embodiment 2 can be implemented to extract the amplitude Ai of the corresponding high-frequency pulse voltage signal and the phase of the high-frequency pulse voltage signal within the cable's power frequency synchronization voltage signal, respectively. Corresponding statistical maps of PRPD and PRPS are then generated, and combined with the insulation status score Wz of the corresponding intermediate joint, further guidance is provided for the cable's maintenance decision.

Claims

1. An online monitoring device for insulation of a 10kV cable joint, characterized in that: The system includes an electric field coupling sensor installed on the 10kV cable to be tested and coupled with the power frequency voltage signal of the cable and the high-frequency pulse voltage signal generated by the partial discharge of the cable, and a monitoring module for receiving, processing and acquiring the power frequency voltage signal and the high-frequency pulse voltage signal output by the electric field coupling sensor; the electric field coupling sensor includes a housing (1), and a metal upper electrode plate (2), an insulating upper pressure plate (3) and a metal lower electrode plate (4) stacked on the outside of the housing (1) in sequence. The lower electrode plate (4) is configured as a U-shaped structure and is installed on the 10kV cable to be tested when in use; the lower electrode plate (4) and the 10kV cable to be tested form a first capacitor, the upper electrode plate (2) and the lower electrode plate (4) form a second capacitor, and the first capacitor and the second capacitor are connected in series to form a voltage divider circuit for extracting the power frequency voltage signal and the high-frequency pulse voltage signal of the cable.

2. The 10kV cable joint insulation online monitoring device according to claim 1, characterized in that: The monitoring module is fixedly installed inside the housing (1). The lead wires of the upper electrode plate (2) and the lead wires of the lower electrode plate (4) are respectively connected to the shield wire and the core wire of one end of the coaxial cable, and the other end of the coaxial cable is connected to the monitoring module through the IPEX connector.

3. The 10kV cable joint insulation online monitoring device according to claim 1, characterized in that: The electric field coupling sensor also includes a lower pressure plate (5) made of insulating material that is snapped into the lower electrode plate (4), and the lower pressure plate (5) is fixedly connected to the outer shell (1).

4. The 10kV cable joint insulation online monitoring device according to claim 1, characterized in that: The monitoring module includes an acquisition module, a power and communication management module, and a battery pack. The acquisition module is used to condition and acquire cable power frequency voltage signals and high-frequency pulse voltage signals. The power and communication management module is used to control the power supply of the acquisition module and external information interaction. The battery pack is used for power supply.

5. The 10kV cable joint insulation online monitoring device according to claim 4, characterized in that: The acquisition module includes a front-end conditioning circuit, an A / D sampling circuit, and a control unit. The front-end conditioning circuit receives the cable power frequency voltage signal and the high-frequency pulse voltage signal from the electric field coupling sensor, separates the cable power frequency voltage signal and the high-frequency pulse voltage signal, and conditions the separated cable power frequency voltage signal and high-frequency pulse voltage signal. The A / D sampling circuit acquires the conditioned cable power frequency voltage signal and high-frequency pulse voltage signal. The control unit is used to control the A / D sampling circuit to sample and to perform calculations and processing on the sampled data.

6. The 10kV cable joint insulation online monitoring device according to claim 5, characterized in that: The front-end conditioning circuit consists of an RF measurement circuit for conditioning high-frequency pulse voltage signals and a power frequency synchronization circuit for conditioning power frequency voltage signals of cables. The RF measurement circuit includes a 100kHz~100MHz bandpass filter, an RF amplifier, a detector circuit, and a broadening circuit connected to the electric field coupling sensor. The power frequency synchronization circuit includes a 1kHz low-pass filter and a power frequency amplifier connected to the electric field coupling sensor.

7. A method for early warning assessment of an online monitoring device for insulation of a 10kV cable joint as described in any one of claims 1 to 6, characterized in that: Includes the following steps, The acquisition module is set to acquire signals at a frequency that is equal to the frequency of the signal acquisition per day. The acquisition module continuously acquires n samples in a single sampling. The acquisition module acquires a single sample in the following way: starting from the zero point of the cable power frequency voltage signal, it acquires the target data within the period of S cable power frequency voltage signals. The target data includes the amplitude of the high-frequency pulse voltage signal, the number of pulses of the high-frequency pulse voltage signal, and the phase of the high-frequency pulse voltage signal within the cable power frequency synchronous voltage signal. For n samples obtained by the acquisition module in a single sampling, if the total number of pulses in the n samples falls within a preset range, partial discharge is considered to exist, and the partial discharge count is incremented by 1; otherwise, partial discharge is not considered to exist, and the partial discharge count remains unchanged. The maximum amplitude of the high-frequency pulse voltage signal in the n samples is taken as the reference value. The maximum value of all reference values ​​collected within the day is taken as the historical maximum value. The duration of partial discharge on a given day is calculated based on the statistical count of partial discharge. The intensity index of partial discharge is calculated based on the historical maximum value to describe the intensity of partial discharge. Calculate the product of the daily partial radiation duration index and the partial radiation intensity index, and record this product as the evaluation index. If the evaluation index is 0, the trend index is set to 0. If the evaluation index is greater than 0, take the evaluation index m days prior to the current day, fit a linear equation between the evaluation index and time, and calculate the trend index based on the slope of the linear equation. If there are less than m days prior to the current day, the trend index is set to 0. A score is calculated based on evaluation indicators and trend indicators to assess the insulation status of the intermediate joint of the cable to be monitored. Based on scoring and preset criteria, the current insulation status of the intermediate joints of the monitored cable is classified and an early warning is issued.

8. The early warning assessment method for the 10kV cable intermediate joint insulation online monitoring device according to claim 7, characterized in that: The method for calculating the duration of partial discharge on a given day is: the partial discharge count divided by the number of monitoring sessions per day; The partial radiative intensity index is calculated as follows: set threshold one and threshold two, with threshold two being greater than threshold one. If the historical maximum value is less than threshold one, the partial radiative intensity index is 0; if the historical maximum value is greater than or equal to threshold one and less than or equal to threshold two, the partial radiative intensity index is 0.5; if the historical maximum value is greater than threshold two, the partial radiative intensity index is 1. The method for calculating the trend index based on the slope of the linear equation is as follows: set threshold three, threshold four and threshold five, with threshold five being greater than threshold four and threshold four being greater than threshold three. If the slope is less than threshold three, the trend index is 0; if the slope is greater than or equal to threshold three and less than or equal to threshold four, the trend index is 0.

5. If the slope is greater than threshold four and less than or equal to threshold five, the trend indicator is 0.8; if the slope is greater than threshold five, the trend indicator is 1.

9. The early warning assessment method for the 10kV cable intermediate joint insulation online monitoring device according to claim 7, characterized in that: The scoring method is as follows: set the weight values ​​of the evaluation index and the trend index respectively, calculate the product of the evaluation index and the trend index with the corresponding weight value respectively, and the difference between 1 and the sum of the two products is recorded as the score. The preset criteria are as follows: set thresholds six, seven, and eight, with threshold six being greater than threshold seven and threshold seven being greater than threshold eight. If the score equals threshold six, the insulation status of the intermediate joint is judged as normal, and no warning is required. If the score is greater than or equal to threshold seven and less than threshold six, the insulation status of the intermediate joint is judged as a warning state, and a warning is issued. If the score is greater than or equal to threshold eight and less than threshold seven, the insulation status of the intermediate joint is judged as a severe state, and a warning is issued. If the score is less than the threshold of eight, the insulation status of the intermediate joint will be judged as a critical state, and an early warning will be issued.

10. The early warning assessment method for the 10kV cable intermediate joint insulation online monitoring device according to claim 9, characterized in that: When the insulation status of the intermediate joint is judged to be a warning state, a serious state, or a crisis state, the amplitude of all high-frequency pulse voltage signals and the phase of the high-frequency pulse voltage signals within the cable power frequency synchronous voltage signal are extracted from the n sample data currently collected by the acquisition module, and statistically formed into PRPD statistical spectrum and PRPS statistical spectrum.

Images