High-voltage cable joint insulation characteristic degradation prediction method and device and storage medium

Abstract

The invention discloses a high-voltage cable joint insulation characteristic degradation prediction method and device and a storage medium, and belongs to the technical field of high-voltage cable safety characteristics, and the method comprises the steps: obtaining the real-time temperature, cable sheath ring current and partial discharge of a cable in a running state; respectively constructing a temperature rise degradation prediction model, a sheath ring current degradation prediction model and a partial discharge degradation prediction model in a cable operation state; constructing a comprehensive degradation prediction model according to the temperature rise degradation prediction model, the sheath circulation degradation prediction model, the partial discharge degradation prediction model and the importance of each parameter in cable insulation degradation; and inputting the real-time temperature, the real-time cable sheath ring current and the real-time partial discharge into the comprehensive degradation prediction model to obtain a prediction result and send out a corresponding alarm, thereby realizing the predictability and reliability of the insulation characteristic alarm of the high-voltage cable joint. And the probability of high-voltage cable power utilization safety accidents and the economic loss caused by the accidents are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-voltage cable safety characteristics, and in particular relates to a method, device and storage medium for predicting insulation characteristic degradation of a high-voltage cable joint. Background Art

[0002] In recent years, flat aluminum sheathed cross-linked polyethylene (XLPE) power cables have been increasingly used in power systems. With the advancement of cross-linking technology for polyethylene materials, XLPE cables are playing an increasingly important role in the safe operation of urban power grids. Cable connectors are components used to connect cables to power transmission and distribution lines and related distribution devices. XLPE cable connectors are all multi-layer solid composite dielectric insulation structures. The size of the insulation dielectric loss of XLPE cables is directly related to the power transmission capacity of the cable, as well as the service life and safety of the cable. The larger the dielectric loss value, the greater the internal heat loss of the medium, the smaller the power transmission capacity of the cable, the shorter its service life, and the lower the safety of use.

[0003] At present, with the research on measuring the dielectric loss value of cables, the on-site measurement of the dielectric loss value of medium and low voltage cables has developed to the on-site measurement of the dielectric loss value of high voltage cables. Although the technology for on-site measurement of the dielectric loss value of high voltage cables has been perfected, there is no perfect method to predict the quality of cable insulation characteristics in advance, and it is still not possible to prevent the occurrence of cable power safety accidents. Summary of the invention

[0004] The present invention provides a method, device and storage medium for predicting the insulation degradation of high-voltage cable joints. By combining the importance of various insulation characteristic parameters in the degradation of cable insulation characteristics and the degradation prediction model of each insulation characteristic parameter, a comprehensive degradation prediction model is designed to predict the real-time operation of the cable and issue an alarm, thereby reducing the probability of safety accidents in the use of high-voltage cables.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] In a first aspect, the present invention provides a method for predicting insulation degradation of a high-voltage cable joint, comprising:

[0007] Obtain the real-time temperature, cable sheath circulating current and partial discharge of the cable under the operating state;

[0008] The temperature rise degradation prediction model, sheath circulation degradation prediction model and partial discharge degradation prediction model under the cable operation state are constructed respectively;

[0009] Constructing a comprehensive insulation property degradation prediction model based on the temperature rise degradation prediction model, the sheath circulation degradation prediction model, the partial discharge degradation prediction model and the importance of each parameter in cable insulation degradation;

[0010] The real-time temperature, real-time cable sheath circulating current and real-time partial discharge are input into the insulation property comprehensive degradation prediction model to obtain the prediction result and issue a corresponding alarm.

[0011] Optionally, respectively obtaining the real-time temperature, cable sheath circulating current and partial discharge under the operating state of the cable includes: using three temperature sensors to respectively collect the temperature at each phase line joint in real time; using three circulating current transformers to respectively collect the ground circulating current value at each phase line joint in real time; using a partial discharge collection system to collect the partial discharge amount and discharge frequency at each phase line joint in real time.

[0012] Optionally, the building of a temperature rise degradation prediction model under a cable operation state includes:

[0013] The cable operating temperature degradation prediction model is constructed based on the cable operating temperature and the cable operating environment temperature: ,in, is the cable temperature alarm threshold, is the ambient temperature when the cable is used, It is the temperature change of the cable corresponding to the minimum value of the cable insulation resistance;

[0014] A temperature rise prediction degradation prediction model is constructed based on the cable operation temperature degradation prediction model:

[0015] ,

[0016] in, is the rate of increase of cable temperature, , is the real-time measurement value of the cable temperature, is the time for the cable temperature to rise, .

[0017] Optionally, the constructing of a sheath circulation degradation prediction model in a cable operation state includes:

[0018] According to the circulating current data of each phase sheath in the three-phase cable, it is judged whether the insulation characteristics of each phase have changed;

[0019] If the insulation characteristics of a phase change, calculate the change in the circulating current of the cable sheath of that phase , the calculation formula is as follows:

[0020] ,

[0021] in, It represents the average value of the i-th cable sheath circulating current value, It represents the average value of the i+1 cable sheath circulating current value;

[0022] According to the change Calculate the rate of change of the cable sheath circulating current of this phase , the calculation formula is as follows:

[0023] ,

[0024] in, Indicates the interval time of the change of the circulating current of the cable sheath of this phase;

[0025] According to the rate of change , and the maximum value of the cable sheath circulating current of this phase is obtained : ;

[0026] According to the maximum value of the cable sheath circulating current, a sheath circulating current degradation prediction model is constructed:

[0027] .

[0028] Optionally, judging whether the insulation characteristics of each phase have changed according to the circulating current data of the sheath of each phase in the three-phase cable includes:

[0029] The sheath circulating current data of each phase in the three-phase cable are obtained respectively. The calculation formula of the cable sheath circulating current data is as follows:

[0030] ,

[0031] in, It represents the average value of the circulating current of the cable sheath n times;

[0032] According to the circulating current data of each phase sheath, it is judged whether the circulating current of each phase cable increases. If it increases, the mutation value point of the cable circulating current is detected and the mutation value point is filtered out. The formula for calculating the mutation value point is as follows:

[0033] ,

[0034] in, Indicates the difference between each cable sheath circulating current value and the average value;

[0035] After the circulation increase judgment and mutation value point filtering operations are iterated n times, it is judged whether the circulation current data of each phase sheath increases. If the circulation current of a phase increases, the insulation characteristics of the phase change.

[0036] Optionally, the constructing of a partial discharge degradation prediction model in a cable operation state includes:

[0037] Constructing a partial discharge frequency degradation prediction model: ,in, is the total frequency of each small amplitude partial discharge, is the frequency of each small amplitude partial discharge, Normalize the minimum amplitude of partial discharge obtained;

[0038] Constructing a partial discharge amplitude degradation prediction model: ,in, is the maximum partial discharge amplitude, is the maximum allowable amplitude of partial discharge;

[0039] Constructing a partial discharge total energy degradation prediction model: ,in, is the frequency of partial discharge with maximum amplitude, It is the total partial discharge energy at the maximum partial discharge amplitude.

[0040] Optionally, the insulation property comprehensive degradation prediction model is constructed according to the temperature rise degradation prediction model, the sheath circulation degradation prediction model, the partial discharge degradation prediction model and the importance of each parameter in cable insulation degradation, including:

[0041] According to the correlation between the parameters of cable insulation characteristics, a comprehensive degradation prediction model is obtained:

[0042] ,

[0043] in, is the comprehensive value of cable insulation alarm, To monitor the parameters of cable operation, is the weight of the corresponding parameter, is the maximum value of the corresponding parameter. is the alarm threshold of the corresponding parameter.

[0044] In a second aspect, the present invention provides a device for predicting insulation degradation of a high-voltage cable joint, comprising:

[0045] Modules for constructing parameter degradation prediction models: used to construct temperature rise degradation prediction models, sheath circulation degradation prediction models and partial discharge degradation prediction models under cable operation conditions;

[0046] A comprehensive degradation prediction model construction module: used to construct an insulation characteristic comprehensive degradation prediction model according to the temperature rise degradation prediction model, the sheath circulation degradation prediction model and the partial discharge degradation prediction model;

[0047] Each parameter acquisition module: used to obtain the real-time temperature, cable sheath circulating current and partial discharge of the cable under the operating state;

[0048] Deterioration prediction result acquisition module: used to input the real-time temperature, real-time cable sheath circulating current and real-time partial discharge into the insulation characteristic comprehensive degradation prediction model, obtain the prediction result and issue a corresponding alarm.

[0049] In a third aspect, the present invention provides a computer storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the method for predicting degradation of insulation characteristics of a high-voltage cable joint as described in the first aspect.

[0050] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the present invention proposes a temperature rise degradation prediction model, a sheath circulation degradation prediction model and a local discharge degradation prediction model for cable joints under operating conditions, and combines the different importance of the temperature value, sheath circulation value and local discharge value at the cable joint in the degradation of the cable insulation characteristics, sets the proportion of the temperature value, ground circulation value and local discharge value at the cable joint in the degradation of the cable insulation characteristics, and proposes a comprehensive degradation prediction model for the insulation characteristics of the cable joint. The collected real-time cable joint temperature, sheath circulation and local discharge data are analyzed and predicted, and the corresponding level of alarm information is issued to achieve the predictability and reliability of the insulation characteristic alarm of the high-voltage cable joint, thereby reducing the probability of high-voltage cable power safety accidents and the economic losses caused thereby. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The figure is a flow chart of a method for predicting insulation property degradation of a high-voltage cable joint in one embodiment of the present invention;

[0052] Figure 2 The figure shows a schematic diagram of a CT power supply module in an embodiment of the present invention;

[0053] Figure 3 The figure shows a structural block diagram of a temperature acquisition module in an embodiment of the present invention;

[0054] Figure 4 Shown is a schematic diagram of the installation of a PT100 temperature sensor and a cable connector in an embodiment of the present invention;

[0055] Figure 5 The figure shows a structural block diagram of a sheath circulation current acquisition module in an embodiment of the present invention;

[0056] Figure 6 Shown is a structural block diagram of a partial discharge acquisition module in an embodiment of the present invention;

[0057] Figure 7 The figure shows a schematic diagram of the structure of a high-level pulse current sensor in one embodiment of the present invention;

[0058] Figure 8 Shown is a schematic structural diagram of an industrial frequency phase transformer in an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0060] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0061] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0062] Example 1

[0063] This embodiment provides a method for predicting insulation property degradation of a high-voltage cable joint, including:

[0064] Obtain the real-time temperature, cable sheath circulating current and partial discharge of the cable under the operating state;

[0065] The temperature rise degradation prediction model, sheath circulation degradation prediction model and partial discharge degradation prediction model under the cable operation state are constructed respectively;

[0066] Constructing a comprehensive insulation property degradation prediction model based on the temperature rise degradation prediction model, the sheath circulation degradation prediction model, the partial discharge degradation prediction model and the importance of each parameter in cable insulation degradation;

[0067] The real-time temperature, real-time cable sheath circulating current and real-time partial discharge are input into the insulation property comprehensive degradation prediction model to obtain the prediction result and issue a corresponding alarm.

[0068] Example 2

[0069] Based on Example 1, this example also makes the following design.

[0070] The method for predicting the degradation of insulation characteristics of high-voltage cable joints is divided into the following steps:

[0071] S1. Obtain the insulation characteristic parameters of each cable. In this embodiment, the host computer management system receives the real-time parameters sent by each parameter acquisition module through the RS485 / 5G communication module, wherein each parameter acquisition module includes a CT power acquisition module, a temperature acquisition module, a sheath circulating current acquisition module and a partial discharge module.

[0072] 1. CT power supply module

[0073] In the power system, the current transformer CT (Current Transformer) measures the size of the AC current in the cable. In practical applications, its secondary output current can also be used for conversion to achieve the purpose of current sensing power supply. In this system, the data acquisition module at the cable joint uses CT to obtain power. The principle of CT power supply is as follows: Figure 2 shown.

[0074] 2. Temperature acquisition module

[0075] The cable temperature acquisition module uses the STM32F103RET6 microcontroller as the system main control chip, and the temperature sensor uses PT100. The design block diagram of the temperature acquisition module at the cable joint is as follows: Figure 3 As shown, A, B, and C are the three phase wires of the three-phase cable.

[0076] The PT100 temperature sensor collects the temperature of the cable connector and is installed as follows: Figure 4 As shown in the figure. After the PT100 collects the temperature change signal and passes through the signal processing circuit, it is connected to the 12-bit ADC conversion channel of the STM32F103RET6 microcontroller. The three temperature sensors measure the temperature of the three phase line connectors of the three-phase cable respectively. The STM32F103RET6 microcontroller converts the filtered and amplified temperature signal into a digital quantity, and then sends it to the host computer management system through the RS485 (5G) communication line.

[0077] 3. Sheath circulation collection module

[0078] Cable sheath circulation is an important parameter for monitoring the changes in cable insulation characteristics during cable operation. Cable sheath circulation will not only cause circulation loss, resulting in a reduction in cable current carrying capacity and affecting the insulation performance of the cable, but will even burn the ground wire when it is severely heated. This kind of accident has occurred repeatedly in existing cable lines. Therefore, a cable sheath circulation monitoring system needs to be designed for cable safety monitoring. The design block diagram of the cable sheath circulation acquisition module is shown in the figure below: Figure 5 shown.

[0079] The circulating current transformer collects the cable circulating current change signal and then connects it to the 12-bit ADC conversion channel of the STM32F103RET6 microcontroller after the signal processing circuit. The three circulating current transformers measure the circulating current values ​​of the three phase line connectors of the three-phase cable to the ground respectively. The STM32F103RET6 microcontroller converts the filtered and amplified circulating current signal into a digital quantity, and then sends it to the host computer management system through the RS485 (5G) communication line.

[0080] 4. Partial discharge acquisition module

[0081] In the partial discharge monitoring of high-voltage cables, the partial discharge pulse current signal in the cable body is coupled by a high-frequency pulse current sensor installed on the grounding wire of the cable joint. The partial discharge pulse signal coupled to the high-frequency pulse current sensor is transmitted to the partial discharge collector through a coaxial cable. The partial discharge collector amplifies the high-frequency analog signal and converts it into a digital signal after analog-to-digital conversion and then transmits it to the monitoring host. The power frequency phase transformer uses a Rogowski coil to couple the power frequency signal of the cable body for synchronization of the collector. The system can send data to the background server via RS485 communication and can support ModBUS RTU communication protocol.

[0082] The structure diagram of the partial discharge monitoring system is as follows: Figure 6 As shown, Figure 6 The high-voltage cable partial discharge monitoring system shown is suitable for online monitoring of partial discharge of cables with a grade of 6kV to 500kV. It can display the partial discharge amplitude and frequency of each monitoring point and each section of the cable in real time, determine the relative position of the discharge point, give an alarm when necessary, and store the test spectrum and discharge trend, so as to timely discover the insulation defects of the cable and the joints, and provide a criterion for evaluating the insulation level and aging degree, and provide a basis for the maintenance of the cable. The embedded high-performance processor is used in the high-voltage cable partial discharge detection system, which greatly reduces the power consumption of the device while ensuring high-speed sampling. Each data acquisition device is networked through the 485 bus and MODBUS-RTU protocol for remote communication. Each partial discharge collector can be connected in series with a multi-core cable that integrates power supply and communication, which greatly simplifies the on-site wiring.

[0083] The minimum measured discharge amplitude of the online monitoring system for partial discharge of high-voltage cables is 2pC, and the frequency range of the pulse current sensor is 1M-100MHz. This system adopts comprehensive anti-interference measures such as analog filtering, pulse grouping, periodic pulse elimination, setting dynamic thresholds, and opening phase windows to make the test data true and reliable. The partial discharge monitoring technology based on the pulse current method (IEC60270 standard) can detect partial discharge signals above 2pC. The combined use of bandpass filtering technology and noise identification and elimination algorithms can effectively identify partial discharge signals. The measurement system can monitor the discharge amplitude, phase, number and other parameters of the cable; it can display discharge trend charts, set alarms, and perform historical inquiries. The power frequency phase transformer couples the power frequency signal of the cable body to synchronize the acquisition. The open and close clamp sensor is compact and easy to disassemble and install, which can easily monitor key stations, key equipment, and abnormal equipment for a long time.

[0084] The high-frequency pulse current sensor is mainly used for cable joints with grounding wires, such as terminal joints and intermediate joints of three-phase split cables with grounding wires. It adopts a clamp-type structure design, the shell is made of aluminum alloy, the surface is treated with oxidation insulation technology, and the interface is a waterproof connector. Using the principle of Rogowski coil, it can sense the signal of 1M-100MHz frequency band in real time to achieve the coupling of cable partial discharge signal. Figure 7 shown.

[0085] The power frequency phase transformer in partial discharge monitoring uses the Rogowski coil to couple the power frequency signal of the cable body, so that the acquisition signal is synchronized with the high-frequency acquisition signal. Its installation method is snap-on installation, which is easy to operate. Figure 8 shown.

[0086] The partial discharge acquisition system collects the partial discharge amount and discharge frequency at the three-phase connector of the three-phase cable and transmits this value to the upper computer management system.

[0087] S2. Construct a prediction model for the degradation of various insulation characteristic parameters under cable operation conditions

[0088] 1. Cable insulation characteristics temperature rise degradation prediction model

[0089] Power cables are composed of two parts: one is the conductor and the other is the insulator. The function of the conductor is to conduct current, so it will generate heat, and the greater the current, the greater the heat. The insulator itself does not generate heat, but the insulator is wrapped outside the conductor, and the heat of the conductor will be transferred to the insulator, causing the insulator temperature to rise. In order to ensure that the insulation of the cable will not be damaged by high temperature and cause hidden dangers, it is necessary to limit the heat generated by the conductor, that is, to limit the temperature of the conductor. The maximum allowable temperature is the highest temperature that the cable can withstand. Different cables have different temperature requirements. Take the commonly used cross-linked polyethylene insulated cable as an example.

[0090] (1) Operating temperature: The maximum rated operating temperature of the cable conductor is 90°C.

[0091] (2) Overload temperature: The maximum short-term overload temperature of the cable shall not exceed 130°C.

[0092] (3) Short-circuit temperature: When the cable is short-circuited, the maximum temperature shall not exceed 250°C (the maximum duration shall not exceed 5 seconds).

[0093] (4) Laying temperature: The laying temperature of the cable shall not be lower than 0°C. If the laying temperature is lower than 0°C, it shall be preheated.

[0094] The normal operating temperature of cross-linked polyethylene insulated cables does not exceed 90°C. As the load current increases, the cable temperature rises. Experiments show that when lightly loaded, the normal operating temperature of the cable varies slightly in different seasons and time periods. At the same time, as the operating load of the cable changes, the operating temperature of the cable is slightly higher than the ambient temperature. When heavily loaded, the temperature of the cable rises significantly, and the heavier the load, the faster the temperature rises. As the heavy-load operating time of the cable increases, the temperature rise rate of the cable tends to gradually increase. Therefore, during cable operation, if the temperature of the cable is slightly higher than the ambient temperature and fluctuates within a small range, it means that the cable is in normal operating condition and the insulation characteristics of the cable are good. If the cable temperature rises too quickly and there is a large difference with the ambient temperature, it can be judged that the cable at this collection point is abnormal. The cable operating temperature alarm threshold setting model is:

[0095] (1)

[0096] In formula (1), is the cable temperature alarm threshold, is the ambient temperature when the cable is used, It is the temperature change of the cable corresponding to the minimum value when the cable insulation resistance drops to the minimum value. In order to improve the scientificity and foresight of the alarm, the model can be modified into a temperature rise predictable model:

[0097] (2)

[0098] In formula (2), is the cable temperature alarm threshold, is the ambient temperature when the cable is used, is the rate of increase of cable temperature, is the time for the cable temperature to rise. Calculated by the cable temperature monitoring system, the calculation formula is:

[0099] (3)

[0100] is the measured value of the cable temperature. The temperature increase time of the cable is calculated using formula (3) for the temperature at this point in time.

[0101] (4)

[0102] Formula (4) can be used to estimate the time it takes for the cable temperature to rise to the cable temperature alarm threshold, and the system will issue a predicted alarm message.

[0103] In formula (3), the cable temperature rise rate As the cable insulation characteristics vary, It also varies with the insulation characteristics of the cable, which makes it possible to achieve predictability of cable temperature alarms.

[0104] 2. Prediction model of sheath circulation degradation

[0105] Cables of 110 kV and above use a general single-core structure. The alternating magnetic field generated by the working current will generate an induced potential on the metal sheath. If the sheath forms a path through the earth, a ground loop will be generated on the metal sheath. Excessive ground loop current (the loop current value is greater than 50A or exceeds 20% of the load current or the ratio of the maximum / minimum value between phases is greater than 3) will affect the cable current carrying capacity and cable insulation characteristics. At the same time, the severe heating caused by the cable loop current will burn the ground wire or ground box, causing serious power accidents.

[0106] There are three conditions for circulating current alarm: (1) greater than 50A; (2) greater than 20% of the load current; (3) the ratio of maximum circulating current to minimum circulating current is greater than 3.

[0107] The cable sheath circulation data has certain regularity, but does not have a completely linear relationship. Conditions (1) and (2) are relatively intuitive. As long as the ground circulation reaches this threshold, the system will issue an alarm. However, in the actual operation of the cable, conditions (1) and (2) have not been reached, and the insulation characteristics of the cable have been destroyed. Therefore, using condition (3) to alarm the cable circulation has more practical application significance. When using condition (3) to alarm the cable circulation, it is often caused by a sudden change or inaccurate detection, which causes false triggering and unnecessary waste. The present invention uses an incremental change method to collect cable sheath circulation data by current variance.

[0108] (5)

[0109] (6)

[0110] In formula (5), the current value of the cable-to-ground loop current is calculated 10 times, and the average value is obtained and recorded in the system. Formula (6) traverses and obtains the difference between each loop current and the average value and records it in the system.

[0111] When the power cable is laid and used, the insulation characteristics of the cable are basically symmetrical, that is, the difference in the ground circulation data between the three phases A, B, and C is very small. During use, the insulation characteristics of one or two phases of the cable will change, thus breaking the symmetry of the insulation characteristics between the three phases. Once the insulation characteristics of a phase cable change, the sheath circulation of this phase will increase.

[0112] By formula (5), the system calculates the ground circulation of the three phases A, B, and C of the cable. When the circulation of a phase increases, the system detects the sudden change value point of the cable circulation by formula (6), filters it out, and iterates. After 10 iterations, the circulation calculated by formula (5) becomes larger, which means that the insulation characteristics of the phase have changed. The method of iteratively filtering the sudden change value point can reduce the false triggering caused by a sudden change of the circulation.

[0113] When the insulation characteristics of a phase of the cable change, the ground circulating current of that phase gradually increases.

[0114] (7)

[0115] The change of the ground circulation can be calculated by equation (7), and the change rate of the circulation can be calculated by equation (8).

[0116] (8)

[0117] (9)

[0118] (10)

[0119] is the maximum value of the circulating current. According to formula (10), the time of cable circulating current alarm under this insulation characteristic can be calculated, providing a mathematical prediction model for predicting circulating current alarm.

[0120] 3. Partial discharge degradation prediction model

[0121] When the cable is in operation, the total partial discharge energy is related to the frequency of partial discharge and the energy of each partial discharge. The total partial discharge energy of the cable in operation is:

[0122] (11)

[0123] in is the total discharge energy, is the discharge amplitude, in units of PC (picocoulomb), is the discharge frequency. When local discharge occurs during cable operation, the local discharge with small energy has little effect on the insulation characteristics of the cable, but when the local discharge with small energy is too frequent, it will also have a certain impact on the insulation characteristics of the cable. Local discharge with an amplitude exceeding 200PC has a greater impact on the insulation characteristics of the cable (the 200PC discharge amplitude is related to the cable material and wire diameter). When the frequency of local discharge with an amplitude exceeding 200PC exceeds 100 times, that is, the total energy of the local discharge with an amplitude of 200PC exceeds 20000PC, the insulation characteristics of the cable will deteriorate, and the system must issue a corresponding alarm. When the local discharge monitoring system is monitoring, the system monitors the local discharge energy and the discharge frequency of the local discharge with this amplitude. In order to improve the reliability of the local discharge monitoring and alarm system, the upper computer management system method in this embodiment monitors both the frequency and discharge amplitude of local discharge and issues corresponding alarm information. The local discharge alarm is divided into three categories: frequency alarm, amplitude alarm and total energy alarm.

[0124] (12)

[0125] In formula (12), is the total frequency of each small amplitude partial discharge, is the frequency of each small amplitude partial discharge, is the normalized minimum amplitude of the monitored partial discharge. When it is large, it means that the cable has frequent small-amplitude partial discharges during operation, which has a certain impact on the insulation characteristics of the cable. The host computer management system issues a corresponding warning of excessive partial discharge frequency, and the insulation characteristics of the cable should be inspected.

[0126] (13)

[0127] Formula (13) monitors the maximum amplitude of partial discharge in cable operation. When it is greater than the maximum allowable amplitude of partial discharge, it has a greater impact on the insulation characteristics of the cable. The host computer management system issues a corresponding warning of excessive partial discharge amplitude, and the insulation characteristics of the cable should be inspected.

[0128] (14)

[0129] In formula (14), is the maximum partial discharge amplitude, is the frequency of partial discharge with maximum amplitude, is the total partial discharge energy at the maximum partial discharge amplitude. When the total partial discharge energy exceeds the maximum allowable value during cable operation, the insulation characteristics of the cable have deteriorated, and the upper computer management system issues an alarm for cable insulation degradation.

[0130] S3. Construct a comprehensive insulation property degradation prediction model

[0131] The insulation characteristic parameters of cables will change under different loads. The cable temperature growth rate increases with the increase of load, the cable circulating current also increases with the increase of cable load, and the circulation growth also increases with it. The frequency of partial discharge of cables increases with the increase of load, and the discharge amplitude also increases to varying degrees.

[0132] At the same time, the three phases of the cable are symmetrical when they start running, and the insulation characteristic parameters between the phases are roughly equal. In actual engineering applications, due to different environments and construction processes, it is impossible to achieve absolute symmetry between the three phases of the cable, but there is little difference during normal operation. When the insulation characteristics of the sheath of one phase of the cable deteriorate, the symmetry of the insulation characteristics of the three-phase cable is broken. A large circulating current will be generated at the deteriorated metal sheath, causing local overheating. Therefore, comparing the balance between the temperature and sheath circulating current between the three phases of the power cable can reflect the abnormal state of the cable insulation characteristics. Due to different causes of formation, partial discharge is often inconsistent between the three phases. If similar partial discharge occurs in the three phases of the cable, it is often caused by spatial interference discharge from the same source. Therefore, when making a cable operation status alarm, the load change factor must be considered to avoid false alarms.

[0133] This embodiment provides a predictable alarm model for temperature, circulating current, and partial discharge. The online operation of cables is a complex process. The alarm and prediction of a single parameter is not comprehensive and reliable enough, and often results in a situation where one thing is neglected while another is neglected. Therefore, the present invention comprehensively considers the correlation between the various parameters of cable insulation characteristics and provides a comprehensive degradation prediction model.

[0134] (15)

[0135] In formula (15), is the comprehensive value of cable insulation alarm, To monitor the parameters of cable operation, is the weight of the corresponding parameter, as shown in Table 1. is the maximum value of the corresponding parameter. is the alarm threshold of the corresponding parameter.

[0136] Table 1 Cable operation monitoring parameters

[0137] Cable monitoring parameter name <![CDATA[ w i ]]> 1 Cable operating temperature 1 2 Cable temperature rise rate 2 3 Cable circulation 1 4 Maximum circulation / minimum circulation 2 5 Partial discharge frequency 1 6 Partial discharge amplitude 1 7 Total partial discharge energy 1

[0138] During cable operation, the possibility of simultaneous deterioration of the insulation characteristics of the three-phase cable is small. Generally, one phase changes first. When one phase changes, it will cause an imbalance between the three phases. Therefore, when setting the parameter alarm weight in formula (15), the upper computer management system will set the unbalanced parameter weight At the same time, when the cable is in operation, when the cable is overloaded or partially deteriorated, it will cause the cable temperature to rise rapidly. Therefore, the system sets the cable temperature rise rate weight Also set it heavier.

[0139] In order to facilitate the alarm logic setting, is the floor rounding function, that is, when:

[0140] When the value is 0, The value is 1, and the rest are similarly taken.

[0141] The larger the value, the higher the alarm level. The comprehensive alarm logic of cable online monitoring is shown in Table 2.

[0142] Table 2 Cable online comprehensive alarm logic

[0143] F Alarm logic 1 General alarm 2 Call the police 3 Serious alarm 4 Extremely serious alarm

[0144] S4, substitute the parameters collected in step S1 into equation (15) in step S4, and set the parameter weights according to the values ​​in Table 1, and obtain value, and then corresponding to the alarm logic in Table 2, a degradation prediction is issued to the outside world.

[0145] Example 3

[0146] This embodiment provides a device for predicting insulation degradation of a high-voltage cable joint, including:

[0147] Modules for constructing parameter degradation prediction models: used to construct temperature rise degradation prediction models, sheath circulation degradation prediction models and partial discharge degradation prediction models under cable operation conditions;

[0148] A comprehensive degradation prediction model construction module: used to construct an insulation characteristic comprehensive degradation prediction model according to the temperature rise degradation prediction model, the sheath circulation degradation prediction model and the partial discharge degradation prediction model;

[0149] Each parameter acquisition module: used to obtain the real-time temperature, cable sheath circulating current and partial discharge of the cable under the operating state;

[0150] Deterioration prediction result acquisition module: used to input the real-time temperature, real-time cable sheath circulating current and real-time partial discharge into the insulation characteristic comprehensive degradation prediction model, obtain the prediction result and issue a corresponding alarm.

[0151] Example 4

[0152] This embodiment provides a computer storage medium on which a computer program is stored. When the computer program is executed by a processor, the method for predicting the degradation of insulation characteristics of a high-voltage cable joint described in Embodiment 2 is implemented.

[0153] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0154] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0155] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0156] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0157] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. A method for predicting insulation degradation of a high-voltage cable joint, characterized in that: include: Obtain the real-time temperature, cable sheath circulating current and partial discharge of the cable under the operating state; The temperature rise degradation prediction model, sheath circulation degradation prediction model and partial discharge degradation prediction model under the cable operation state are constructed respectively; Constructing a comprehensive insulation property degradation prediction model based on the temperature rise degradation prediction model, the sheath circulation degradation prediction model, the partial discharge degradation prediction model and the importance of each parameter in cable insulation degradation; The real-time temperature, real-time cable sheath circulating current and real-time partial discharge are input into the insulation property comprehensive degradation prediction model to obtain the prediction result and issue a corresponding alarm.

2. The method for predicting the degradation of insulation characteristics of a high-voltage cable joint according to claim 1, characterized in that: The real-time temperature, cable sheath circulating current and partial discharge of the cable under the operating state are respectively obtained, including: using three temperature sensors to respectively collect the temperature at each phase line joint in real time; using three circulating current mutual inductors to respectively collect the ground circulating current value at each phase line joint in real time; using a partial discharge collection system to collect the partial discharge amount and discharge frequency at each phase line joint in real time.

3. The method for predicting the degradation of insulation characteristics of a high-voltage cable joint according to claim 1 or 2, characterized in that: The construction of the temperature rise degradation prediction model under the cable operation state includes: The cable operating temperature degradation prediction model is constructed based on the cable operating temperature and the cable operating environment temperature: ,in, is the cable temperature alarm threshold, is the ambient temperature when the cable is used, It is the temperature change of the cable corresponding to the minimum value of the cable insulation resistance; A temperature rise prediction degradation prediction model is constructed based on the cable operation temperature degradation prediction model: ， in, is the rate of increase of cable temperature, , is the real-time measurement value of the cable temperature, is the time for the cable temperature to rise, .

4. The method for predicting the degradation of insulation characteristics of a high-voltage cable joint according to claim 3, characterized in that: The construction of the sheath circulation degradation prediction model under the cable operation state includes: According to the circulating current data of each phase sheath in the three-phase cable, it is judged whether the insulation characteristics of each phase have changed; If the insulation characteristics of a phase change, calculate the change in the circulating current of the cable sheath of that phase , the calculation formula is as follows: ， in, It represents the average value of the i-th cable sheath circulating current value, It represents the average value of the i+1 cable sheath circulating current value; According to the change Calculate the rate of change of the cable sheath circulating current of this phase , the calculation formula is as follows: ， in, Indicates the interval time of the change of the circulating current of the cable sheath of this phase; According to the rate of change , and the maximum value of the cable sheath circulating current of this phase is obtained : ; According to the maximum value of the cable sheath circulating current, a sheath circulating current degradation prediction model is constructed: 。 5. The method for predicting the degradation of insulation characteristics of a high-voltage cable joint according to claim 4, characterized in that: The method of judging whether the insulation characteristics of each phase have changed according to the circulating current data of each phase sheath in the three-phase cable comprises: The sheath circulating current data of each phase in the three-phase cable are obtained respectively. The calculation formula of the cable sheath circulating current data is as follows: ， in, It represents the average value of the circulating current of the cable sheath n times; According to the circulating current data of each phase sheath, it is judged whether the circulating current of each phase cable increases. If it increases, the mutation value point of the cable circulating current is detected and the mutation value point is filtered out. The formula for calculating the mutation value point is as follows: ， in, Indicates the difference between each cable sheath circulating current value and the average value; After the circulation increase judgment and mutation value point filtering operations are iterated n times, it is judged whether the circulation current data of each phase sheath increases. If the circulation current of a phase increases, the insulation characteristics of the phase change.

6. The method for predicting the degradation of insulation characteristics of a high-voltage cable joint according to claim 5, characterized in that: The construction of the partial discharge degradation prediction model under the cable operation state includes: Constructing a partial discharge frequency degradation prediction model: ,in, is the total frequency of each small amplitude partial discharge, is the frequency of each small amplitude partial discharge, Normalize the minimum amplitude of partial discharge obtained; Constructing a partial discharge amplitude degradation prediction model: ,in, is the maximum partial discharge amplitude, is the maximum allowable amplitude of partial discharge; Constructing a partial discharge total energy degradation prediction model: ,in, is the frequency of partial discharge with maximum amplitude, It is the total partial discharge energy at the maximum partial discharge amplitude.

7. The method for predicting the degradation of insulation characteristics of a high-voltage cable joint according to claim 6, characterized in that: The insulation property comprehensive degradation prediction model is constructed according to the temperature rise degradation prediction model, the sheath circulation degradation prediction model, the partial discharge degradation prediction model and the importance of each parameter in the cable insulation degradation, including: According to the correlation between the parameters of cable insulation characteristics, a comprehensive degradation prediction model is obtained: ， in, is the comprehensive value of cable insulation alarm, To monitor the parameters of cable operation, is the weight of the corresponding parameter, is the maximum value of the corresponding parameter. is the alarm threshold of the corresponding parameter.

8. A device for predicting insulation degradation of a high-voltage cable joint, characterized in that: include: Modules for constructing parameter degradation prediction models: used to construct temperature rise degradation prediction models, sheath circulation degradation prediction models and partial discharge degradation prediction models under cable operation conditions; A comprehensive degradation prediction model construction module is used to construct an insulation characteristic comprehensive degradation prediction model according to the temperature rise degradation prediction model, the sheath circulation degradation prediction model and the partial discharge degradation prediction model; Each parameter acquisition module: used to obtain the real-time temperature, cable sheath circulating current and partial discharge of the cable under the operating state; Deterioration prediction result acquisition module: used to input the real-time temperature, real-time cable sheath circulating current and real-time partial discharge into the insulation characteristic comprehensive degradation prediction model, obtain the prediction result and issue a corresponding alarm.

9. A computer storage medium, characterized in that A computer program is stored thereon, and when the computer program is executed by a processor, the method for predicting the degradation of insulation characteristics of a high-voltage cable joint as claimed in any one of claims 1 to 7 is implemented.

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