Ac-dc integrated cable current sensor and 10kv cable insulation aging monitoring method

Abstract

The application belongs to the technical field of power transmission and distribution, and discloses an AC-DC integrated cable current sensor and a 10KV cable insulation aging monitoring method. The sensor comprises a sensor body, a cable AC signal acquisition module for acquiring cable AC signals and a cable DC signal acquisition module for acquiring cable DC signals. The cable AC signals are used to determine the transient aging degree of cable insulation, and the cable DC signals are used to determine the steady-state aging degree of cable insulation. The two modules are independently modularized. The sensor uses AC-DC signal monitoring fusion processing, and combines the highly nonlinear relationship between the electrical signals at the two ends of the cable and the local aging parameters. The sensor can effectively extract the position information of the local aging and realize accurate prediction of various aging characteristics. The sensor is not limited by the smooth change section of the insulation electrical parameters, and can accurately locate the local aging section of the cable in real time.

Description

Technical Field

[0001] This invention belongs to the field of power system transmission and distribution technology, and particularly relates to an AC / DC integrated cable current sensor and a method for monitoring the insulation aging of 10KV cables. Background Technology

[0002] As a crucial component of urban power transmission, cables are increasingly being replaced by underground cables and internal conduit cables as urban economic levels rise. Cables possess excellent mechanical and electrical properties, and the vast majority of failures stem from insulation aging. Many factors influence aging, including the cable material itself, the external operating environment, and human or foreign object damage. Each or a combination of these factors contributes to varying degrees of cable aging. Based on the stress that promotes insulation aging, aging can be broadly categorized into thermal aging, electrical aging, water aging, chemical corrosion, and mechanical aging. However, the root cause is ultimately high-temperature heating, with sustained high temperatures being the primary inducing factor for thermal and insulation aging.

[0003] Due to the long distances and limited underground space of power distribution cables, maintenance personnel find it difficult to access the lower levels to inspect specific fault nodes. They can only rely on fault information transmitted back to the control center, using data transmission and attenuation models to calculate the relative location. However, many current fault location methods are inaccurate, making it difficult for maintenance personnel to pinpoint the exact fault location, significantly impacting fault repair. Large errors also increase maintenance costs considerably. Therefore, fault location methods for power distribution cables are worthy of further research. Based on an assessment of the overall cable insulation condition, further locating locally aged sections of the cable helps achieve targeted repairs, thereby reducing system maintenance costs. However, current research on real-time location methods for locally aged cable insulation is limited. Existing research mostly relies on traveling wave injection. However, when dealing with smoothly changing insulation electrical parameters, traveling wave injection lacks sufficient reflected signals for location due to the absence of obvious impedance discontinuities, making it impossible to locate locally aged sections of the cable with smoothly changing insulation electrical parameters in real time.

[0004] It is evident that existing monitoring methods are insufficient to generate sufficiently strong reflected signals for location analysis of smoothly changing insulation electrical parameters, thus making it impossible to locate localized aging sections of cables with smoothly changing insulation electrical parameters in real time. Summary of the Invention

[0005] This invention provides an AC / DC integrated cable current sensor and a 10KV cable insulation aging monitoring method to solve the technical problem that existing monitoring methods are unable to generate sufficiently strong reflected signals for positioning in smooth-changing segments of insulation electrical parameters, thus making it impossible to locate local aging segments of cables with smooth-changing insulation electrical parameters in real time.

[0006] To achieve the above objectives, the present invention employs the following technical content:

[0007] An integrated AC / DC cable current sensor includes a sensor body and a cable AC signal acquisition module and a cable DC signal acquisition module disposed in the sensor body;

[0008] The cable AC signal acquisition module is used to acquire cable AC signals to determine the transient aging degree of cable insulation based on the abrupt current amplitude in the cable AC signal.

[0009] The cable DC signal acquisition module is used to acquire the cable DC signal in order to determine the steady-state aging degree of the cable insulation based on the cable DC signal.

[0010] The AC signal acquisition module and the DC signal acquisition module share a common sampling input terminal, and the acquired AC signal and DC signal are output independently.

[0011] Furthermore, the sensor body includes a coil and a conditioning module; the receiving ends of the cable AC signal acquisition module and the cable DC signal acquisition module are respectively connected to the coil, and the output ends are respectively connected to the conditioning module; the conditioning module is used to condition and output the acquired cable AC signal and cable DC signal.

[0012] Furthermore, the coil adopts a double-layer structure; wherein, the inner coil is connected to the cable AC signal acquisition module and is responsible for acquiring the cable AC signal generated by the cable joint; the outer coil is connected to the cable DC signal acquisition module and is responsible for acquiring the cable DC signal generated by the cable injection signal; the coil is made of iron-based microcrystalline alloy or permalloy material.

[0013] Furthermore, the AC signal acquisition module for the cable uses a Hall sensor and sampling chip, which is located at the top of the inner coil; the DC signal acquisition module for the cable uses a TMR chip, which is electrically connected to the outer coil.

[0014] Furthermore, the Hall sensing and sampling chip uses GaAs material and is a THS119 chip;

[0015] The TMR chip uses the MAGIC2001 electromagnetic chip.

[0016] Furthermore, the conditioning module includes a temperature compensation circuit, a signal conditioning circuit, and an amplification and zeroing circuit;

[0017] The temperature compensation circuit is used to adjust the operational amplifier parameters according to the ambient temperature to compensate for the sensitivity of the TMR chip.

[0018] The signal conditioning circuit includes an AC component conditioning circuit connected to the Hall sensing and sampling chip and a DC component conditioning circuit connected to the TMR chip, used to improve the spread spectrum communication distance.

[0019] The amplification and zeroing circuit is used to amplify the signals acquired by the Hall sensor and sampling chip and the TMR chip, and to zero the TMR chip.

[0020] Furthermore, the sensor employs an open-loop mode to monitor cable insulation; the acquisition principle of the cable AC signal acquisition module is based on the following formula:

[0021]

[0022] In the formula, R is the output voltage signal; I is the Hall coefficient; B is the driving current of the Hall element; and B is the magnetic field strength of the air gap in the magnetic ring.

[0023] A method for monitoring the insulation aging of 10kV cables, based on the aforementioned AC / DC integrated cable current sensor, includes:

[0024] Collect AC signals from the cable insulation and determine the transient aging degree of the cable insulation based on the abrupt current amplitude in the current signal.

[0025] The DC signal of the cable insulation is collected synchronously, and the steady-state aging degree of the cable insulation is determined based on the DC signal.

[0026] Furthermore, by injecting a common-mode DC current signal source, the DC signal of the cable insulation is acquired using the TMR electromagnetic detection method.

[0027] Furthermore, it also includes: plotting leakage current variation trend curves based on the output cable insulation DC signal, so as to compare and analyze the steady-state aging degree of cable insulation corresponding to different cable insulations according to the leakage current variation trend curves.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention provides an integrated AC / DC cable current sensor. The sensor includes a sensor body containing an AC signal acquisition module for acquiring AC signals and a DC signal acquisition module for acquiring DC signals. It determines the transient aging degree of cable insulation based on the AC signal and the steady-state aging degree based on the DC signal. The two modules are designed as independent modules. This sensor utilizes AC / DC signal monitoring and fusion processing, taking into account the highly nonlinear relationship between the electrical signals at both ends of the cable and local aging parameters. This effectively extracts the location information of local aging and achieves accurate prediction of various aging characteristics. This sensor is not limited by the smooth change segment of insulation electrical parameters and can accurately locate local aging segments of the cable in real time. The sensor has a simple structure and principle, high monitoring efficiency and accuracy, and has good application value.

[0030] Preferably, in this invention, the sensor body includes a coil and a conditioning circuit, making the signal acquisition and conditioning process clearer; the direct connection between the coil and the acquisition module, as well as the further processing of the signal by the conditioning circuit, improves the efficiency and accuracy of signal acquisition.

[0031] More preferably, in this invention, the coil adopts a double-layer structure, which is optimized for AC signals and DC signals respectively, thereby improving the targeting and sensitivity of signal acquisition; the outer shielding layer can shield and cancel large AC currents through the inner coil, thereby improving the measurement accuracy of small currents in the outer layer.

[0032] Meanwhile, the use of iron-based microcrystalline alloys or permalloy materials enhances the magnetic properties and stability of the coil.

[0033] More preferably, in this invention, the AC signal acquisition module for the cable uses a Hall sensor and sampling chip, and the DC signal acquisition module for the cable uses a TMR chip, which improves the accuracy and reliability of signal acquisition.

[0034] More preferably, in this invention, the Hall sensing and sampling chip uses the THS119 chip made of GaAs material; the TMR chip uses the MAGIC2001 electromagnetic chip, which ensures the stable performance of the signal acquisition module and may bring additional technical advantages, such as low power consumption and high sensitivity.

[0035] More preferably, in this invention, the conditioning module includes a temperature compensation circuit, a signal conditioning circuit, and an amplification and zeroing circuit, which further improves the accuracy and stability of signal processing; in particular, the temperature compensation circuit effectively reduces the impact of temperature on the sensitivity of the TMR chip.

[0036] Preferably, in this invention, the AC signal acquisition module of the sensor is based on the Hall effect to achieve signal acquisition, which has the advantages of non-contact and high precision.

[0037] This invention also provides a method for monitoring the aging of 10KV cable insulation. By synchronously acquiring AC and DC signals of the cable, it achieves comprehensive monitoring of the transient and steady-state aging degree of the cable insulation. The AC and DC component detection adopts an independent modular design. This method is designed with two output lines, sampling two analog signals respectively as the basis for platform fault judgment. The two line signals are isolated, modularized, and shielded, which greatly reduces sampling interference. This method improves the real-time performance and accuracy of monitoring.

[0038] Preferably, in this invention, by injecting a common-mode DC current signal source and using TMR electromagnetic detection, the acquisition accuracy and reliability of the cable DC signal are improved; by measuring the cable insulation leakage current, the cable insulation capacitance and resistance can be monitored, enabling the function of accurately monitoring the DC leakage current signal of a 10kV cable online.

[0039] Preferably, the present invention also includes a step of comparing and analyzing the steady-state aging degree of cable insulation based on the leakage current change trend curve, which provides strong support for long-term monitoring and evaluation of cable insulation status; this helps to identify potential problems in a timely manner and take corresponding maintenance measures. Attached Figure Description

[0040] Figure 1 A structural block diagram of an integrated AC / DC cable current sensor provided in an embodiment of the present invention;

[0041] Figure 2 This is a trend diagram of capacitive leakage current variation corresponding to the aging degree of a 10kV cable provided in an embodiment of the present invention.

[0042] Figure 3 The resistive leakage current variation trend diagram corresponding to the aging degree of a 10kV cable is provided for the embodiments of the present invention.

[0043] Figure label: Detailed Implementation

[0044] To make the technical problems solved by the present invention, the technical solutions, and the beneficial effects clearer, the following specific embodiments provide a further detailed description of the present invention. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0046] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0047] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0048] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0049] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0050] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0051] Example 1

[0052] As mentioned in the background section, there is currently little research on real-time location methods for localized aging of cable insulation. Most existing studies rely on traveling wave injection. However, when dealing with smoothly changing sections of insulation electrical parameters, traveling wave injection is insufficient to generate a sufficiently strong reflected signal for location because there are no obvious impedance discontinuities. This makes it impossible to locate locally aged sections of cables with smoothly changing insulation electrical parameters in real time.

[0053] To address the aforementioned issues, this embodiment provides an integrated AC / DC cable current sensor and a method for monitoring the aging of 10KV cable insulation. Unlike traditional traveling wave-based methods, this method utilizes AC / DC signal monitoring and fusion processing. It leverages the highly nonlinear relationship between the electrical signals at both ends of the cable and local aging parameters, effectively extracting the location information of local aging and solving the problem of accurately predicting various aging characteristics. Furthermore, this monitoring method improves the accuracy of online monitoring and positioning of distribution cable insulation, reducing the level of intelligence and maintenance costs of intelligent inspection of distribution cables.

[0054] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0055] like Figure 1 As shown, this embodiment provides an integrated AC / DC cable current sensor, including a sensor body, a cable AC signal acquisition module, and a cable DC signal acquisition module. The cable AC signal acquisition module and the cable DC signal acquisition module share a single sampling input terminal, and the acquired cable AC signal and cable DC signal are output independently, effectively avoiding interference between signals and ensuring monitoring accuracy.

[0056] The AC signal acquisition module and the DC signal acquisition module for the cable are housed within the sensor body's casing.

[0057] The sensor body includes a coil and a conditioning module; the receiving ends of the cable AC signal acquisition module and the cable DC signal acquisition module are respectively connected to the coil, and the output ends are respectively connected to the conditioning circuit; the conditioning module is used to condition and output the acquired cable AC signal and cable DC signal.

[0058] The coil adopts a double-layer structure. The inner coil is connected to the cable AC signal acquisition module and is responsible for acquiring the cable AC signal generated by the cable joint. The outer coil is connected to the cable DC signal acquisition module and is responsible for acquiring the cable DC signal generated by the cable injection signal. This coil uses iron-based microcrystalline alloy or permalloy coil.

[0059] The cable AC signal acquisition module uses a Hall sensor and sampling chip, which is located at the top of the inner coil to acquire the cable AC signal. The transient aging degree of the cable insulation is determined based on the sudden change in the current amplitude in the cable AC signal.

[0060] The cable DC signal acquisition module uses a TMR chip, which is electrically connected to the outer coil, to acquire the cable DC signal and determine the steady-state aging degree of the cable insulation based on the cable DC signal.

[0061] In this embodiment, the conditioning module includes a temperature compensation circuit, a signal conditioning circuit, and an amplification and zeroing circuit, which are used to adjust the operational amplifier parameters according to the ambient temperature to compensate the sensitivity of the TMR chip, improve the spread spectrum communication distance, and zero the TMR chip.

[0062] Therefore, this sensor integrates both AC and DC signal acquisition modules within the same sensor body, achieving synchronous acquisition of AC and DC signals and improving the comprehensiveness and accuracy of cable insulation aging monitoring. Simultaneously, the shared sampling input but independent output ensures the flexibility and independence of signal processing, thereby reducing interference and improving monitoring accuracy. Furthermore, this sensor is not limited by the smooth changes in insulation electrical parameters; by utilizing AC and DC signal monitoring and fusion processing, it can achieve real-time location of locally aging sections in the cable.

[0063] Example 2

[0064] This embodiment provides an integrated AC / DC cable current sensor and a method for monitoring the aging of 10kV cable insulation. Specifically, it is applied to the monitoring and analysis of the aging degree of 10kV cable insulation. The method is based on the following ideas: First, under normal circumstances, the aging characteristics of cable insulation can be manifested as transient and steady-state changes. Transient aging is generally caused by sudden changes in load current (such as ground fault short circuits), which will generate sudden changes in current amplitude in the cable's AC signal, indicating that a transient ground fault has occurred. Second, during long-term operation, cables gradually age due to factors such as the cable structure itself, the influence of the tunnel environment, and load changes. This aging process is an accumulated process, showing gradual changes. This is addressed by injecting a common-mode DC current signal source. The first method utilizes TMR electromagnetic current detection to detect weak DC signals, thereby determining parameters of the cable's steady-state aging process. By combining two AC / DC monitoring parameters as the basis for judging the cable insulation aging process, a comprehensive understanding of the cable insulation's operating status can be achieved, providing strong on-site data support for cable team operation management. Secondly, it proposes AC current Hall effect monitoring, a non-contact measurement method where the output voltage is proportional to the magnetic field strength and independent of the magnetic field change rate. Structurally, Hall current sensors are divided into closed-loop and open-loop types. Given the current operating status of 10kV cable monitoring, most of the cables with added current sensors are already laid; therefore, only open-loop mode can be used for subsequent installations, with the inner diameter of the magnetic coil customizable later. Open-loop Hall sensors have a simple peripheral circuit and relatively low cost, but due to their poor accuracy and linearity, slow response time, and large temperature drift, they are more suitable for detecting transient AC fault currents. To avoid some of the shortcomings of Hall sensors, this embodiment makes precise judgments in the selection of Hall element materials and magnetic materials, mainly to improve the performance of magnetic focusing and measurement linearity. More specifically, this embodiment applies the Hall effect to realize the monitoring of alternating current. The Hall effect is a type of magnetoelectric effect. Components, circuits, and systems based on the Hall effect are called train sensors, which are non-contact measurement sensors. The output voltage is proportional to the magnetic field strength and is independent of the rate of change of the magnetic field. Structurally, Hall current sensors are divided into closed-loop and open-loop types. Considering the current operation of 10kV cable monitoring, most of the current sensors installed are on already laid cables. Therefore, the subsequent installation method can only adopt the open-loop mode, and the inner diameter of the magnetic coil can be customized later. The open-loop Hall current sensor has a single closed magnetic circuit core with an inner diameter of d. The Hall chip is placed in the open air gap of the core with a gap length of L. The element can directly detect the magnetic field signal and output a voltage signal Vout. The proportional relationship between the output voltage and the magnetic field B is as follows:

[0065]

[0066] I represents the driving current of the Hall element, B represents the magnetic field strength of the air gap in the magnetic ring, and R represents the Hall coefficient, which is often determined by the material of the Hall element. The Hall current sensor converts the magnetic field generated around a current-carrying conductor through a magnetic ring into a voltage signal on the order of mV. Open-loop Hall sensors have simple external circuitry and relatively low cost, but due to their poor accuracy and linearity, slow response time, and large temperature drift, they are more suitable for detecting transient AC fault currents. To avoid these shortcomings of Hall sensors, this embodiment makes precise judgments in the selection of Hall element materials and magnetic materials, with the main purpose of improving magnetic focusing and measurement linearity performance.

[0067] Third, the TMR DC micro-current monitoring method proposed in this embodiment assesses the cable insulation characteristics by monitoring leakage current, thus evaluating the cable's operational health from another perspective. Cable insulation aging is often accompanied by changes in relative permittivity. During cable operation, the number of voids in the insulation continues to increase, and moisture and impurities in the environment can easily enter these voids, further increasing the relative permittivity of the cable insulation. This embodiment studies the types of insulation aging that involve changes in the relative permittivity of the cable insulation. Extensive experimental results show that by measuring the cable insulation leakage current, the insulation capacitance and resistance of the cable can be monitored, thereby estimating the degree of insulation aging. As the degree of aging increases, the upward trend of insulation capacitance remains consistent across a wide frequency band, providing significant flexibility for monitoring. Furthermore, at power frequency or higher frequencies, the capacitive portion of the insulation leakage current is much larger than its resistive portion, resulting in higher accuracy and sensitivity in monitoring insulation capacitance. Fourth, based on the above ideas, this embodiment also provides an integrated AC / DC cable current sensor. Adopting design concepts and goals such as compactness, low power consumption, and miniaturization, it forms an integrated sensor with one sampling input and two independent signal outputs. This enables simultaneous monitoring of transient and steady-state fault currents, providing a more comprehensive real-time understanding of the cable's operating status. The hardware structure of the integrated AC / DC cable current sensor mainly consists of three main parts: coil, chip, and conditioning circuit. The integrated AC / DC cable current sensor can simultaneously achieve real-time monitoring of both AC and DC currents. Based on the above principles, this embodiment provides the following prototype device.

[0068] In this embodiment, the AC current Hall effect monitoring method adopts an open-loop mode, which enables the monitoring of various types of cables by customizing the inner diameter of the magnetic coil. It also makes accurate judgments on the selection of Hall element materials and magnetic materials, thereby improving the magnetic focusing and measurement linearity performance, so as to solve the problem of measurement accuracy being affected by poor linearity.

[0069] In this embodiment, the TMR DC micro-current monitoring method mentioned can monitor the insulation capacitance and resistance of the cable by measuring the leakage current of the cable insulation, thereby estimating the degree of insulation aging and enabling the function of online monitoring of DC leakage current signals for 10kV cables.

[0070] In this embodiment, a highly integrated current sensor is provided, which adopts a dual-channel parallel acquisition mode and can simultaneously measure transient and steady-state fault information. Through anti-interference process design, the interference between the two signals and the bypass circuit is reduced, thereby improving the accuracy of small current acquisition.

[0071] like Figure 1 As shown in the figure, this embodiment provides an integrated AC / DC cable current sensor, and the specific design concept is as follows:

[0072] The AC / DC integrated cable current sensor provided in this embodiment adopts an independent modular design for DC component detection and has two output lines, sampling two analog signals respectively as the basis for platform fault judgment. The two signal lines utilize isolation, modularity, and shielding ring design to significantly reduce sampling interference and ensure signal acquisition accuracy. The specific component design is as follows:

[0073] First, coil selection is crucial, as the current value it collects also serves as the signal source for AC / DC signal analysis. The coil material should possess characteristics such as high permeability, low temperature coefficient, and high hysteresis coefficient. Magnetic materials with high initial permeability and good linearity can improve the sensitivity and accuracy of the current sensor. Materials with good magnetic focusing effects generally include silicon steel sheets, iron-nickel soft magnetic alloys, amorphous alloys, iron-based microcrystalline alloys, and permalloy. Microcrystalline and permalloy are two magnetic materials with significant application value. Microcrystalline is an amorphous magnetic material with grain sizes on the nanometer scale; permalloy is a strongly magnetic crystalline alloy. They differ in magnetic properties, physical characteristics, and applications. The magnetic properties of microcrystalline and permalloy are one of their most fundamental differences. First, microcrystalline has a higher saturation magnetic induction intensity than permalloy. Second, microcrystalline has lower hysteresis loss than permalloy, exhibiting better high-frequency characteristics. On the other hand, permalloy has lower iron loss and higher permeability than microcrystalline. In this embodiment, iron-based permalloy was selected as the magnetic coil material after comprehensive consideration.

[0074] This coil adopts a double-layer structure design. The first layer (inner layer) collects the AC current value generated by the cable joint, and the second layer (outer layer) collects the leakage current generated by the cable injection signal. The ingenious design of the two layers enables the acquisition of current values ​​with different performance parameters. On the other hand, the outer shielding layer can shield and cancel large AC currents through the inner coil, thereby improving the measurement accuracy of small currents in the outer layer.

[0075] Second, chip selection and design: GaAs (gallium arsenide) material was used for the Hall current device. GaAs has the best output linearity and can withstand temperatures up to 200℃. A double-ended lead-out package Hall element was designed and deployed at the top of a coil layer, where the top magnetic concentration effect is best. The THS119 chip was selected, and the thickness of the Hall element is generally no more than 2mm. The MAGIC2001 electromagnetic chip from Duochuang Technology Co., Ltd. was selected for TMR, which can still ensure high measurement accuracy even in the presence of DC and harmonic components.

[0076] Third, Modulation Module Design: The core of the modulation circuit includes a temperature compensation circuit, a signal conditioning circuit, and an amplification and zero-adjustment circuit. The temperature compensation circuit adjusts the operational amplifier parameters according to the ambient temperature to compensate for the sensitivity of the internal TMR component. A temperature-sensitive voltage source is designed to power the TMR component to compensate for temperature drift errors. Given that the TMR component's output voltage is on the order of mV, a signal amplification circuit is designed to amplify the signal to the order of V. A pre-amplifier circuit and a secondary signal amplification circuit are designed. The chip component uses a bridge structure; the initial values ​​of the four internal resistors cannot be guaranteed to be completely consistent due to process limitations. Furthermore, influenced by stray magnetic fields, the TMR component has a fixed output bias voltage; therefore, a bias zero-adjustment circuit is designed. The SX1278 communication transceiver chip is selected, which integrates a modem to achieve long-distance spread spectrum communication. It has good anti-interference capabilities, low current consumption, and uses relatively low-cost materials such as crystal oscillators, achieving a relatively high sensitivity of -148dBm.

[0077] This embodiment also provides a method for monitoring the aging of 10KV cable insulation, which can be implemented using the AC / DC integrated cable current sensor provided in this embodiment. The specific steps include:

[0078] Collect AC signals from the cable insulation and determine the transient aging degree of the cable insulation based on the abrupt current amplitude in the current signal.

[0079] Synchronously acquire the DC signal of the cable insulation, and determine the steady-state aging degree of the cable insulation based on the DC signal;

[0080] Based on the output cable insulation DC signal, a leakage current variation trend curve is plotted to compare and analyze the steady-state aging degree of different cable insulations.

[0081] Specifically, the DC signal of the cable insulation is acquired by injecting a common-mode DC current signal source and using TMR electromagnetic detection.

[0082] As can be seen, this method achieves comprehensive monitoring of the transient and steady-state aging of cable insulation by synchronously acquiring AC and DC signals of the cable. The AC and DC component detection adopts an independent modular design. This method is designed with two output lines to sample two analog signals as the basis for platform fault judgment. The two line signals are isolated, modularized, and shielded, which greatly reduces sampling interference. This method improves the real-time performance and accuracy of monitoring.

[0083] In this embodiment, an experimental study was conducted on the aforementioned integrated cable current sensor and 10KV cable insulation aging monitoring method. The specific implementation process is as follows:

[0084] An AC / DC integrated cable current sensor is installed at a 10kV cable joint to simultaneously measure grounding current and common-mode leakage current. It is used to monitor the DC leakage current of the high-voltage feeder and the AC current of the cable sheath in real time. Both current components exist simultaneously in the high-voltage feeder.

[0085] The first step is to simulate the injection of a 12kV / 50Hz high voltage signal in the AC current measurement experiment. The AC output terminal of the integrated current sensor is connected to the computer to read the AC current output amplitude signal. Generally, when an overvoltage occurs, the cable will have a short circuit breakdown. The transient aging degree of the cable insulation can be judged based on the AC current output amplitude signal.

[0086] The second step involves measuring the common-mode leakage current of the cable. A 380V / 433V three-phase voltage regulator supplies power to a Y-connected load resistor via a three-phase test cable segment, generating a differential-mode load current (IDM). Changing the output voltage of the three-phase voltage regulator alters the magnitude of the differential load current. Simultaneously, a 220V / 250V single-phase voltage regulator is connected to a common-mode current regulating resistor via a common-mode current conductor, generating a simulated common-mode leakage current. Changing the output voltage of the single-phase voltage regulator alters the magnitude of the common-mode leakage current. The common-mode current conductor is placed close to the surface of the three-phase cable segment, and both conductors pass through the sensor prototype with the above-described structure. The DC output of the AC / DC integrated cable current sensor is connected to a computer to read the current amplitude signal. The capacitive and resistive leakage current amplitudes of the cable under different insulation aging conditions at power frequency are shown below. Figure 2 and Figure 3 As shown: Figure 2 This indicates that the capacitive leakage current of the insulation gradually increases with the increase of cable aging. Figure 3This indicates that resistive leakage current gradually increases with the degree of cable aging; and throughout the entire aging process, capacitive leakage current is significantly greater than resistive leakage current. In the early stages of cable aging, capacitive leakage current increases markedly, while resistive leakage current changes relatively little. When aging is severe, although resistive leakage current increases rapidly, it still differs from capacitive leakage current by an order of magnitude. Therefore, at power frequency, capacitive leakage current accounts for the vast majority of insulation leakage current, and measuring insulation leakage current allows for effective monitoring of insulation capacitance.

[0087] In summary, this invention provides an integrated AC / DC cable current sensor and a method for monitoring the insulation aging of 10KV cables, which has the following advantages compared to existing cable monitoring technologies:

[0088] First, this invention proposes a method for monitoring the short-circuit current of a 10kV cable using an alternating current Hall effect sensor. It adopts an open-loop mode and enables the monitoring of various types of cables by customizing the inner diameter of the magnetic coil. It also makes precise judgments on the selection of Hall effect sensor materials and magnetic materials, improving the magnetic focusing and measurement linearity performance, and solving the problem of measurement accuracy being affected by poor linearity.

[0089] Secondly, this invention proposes a TMR DC micro-current monitoring method, which can monitor the insulation capacitance and resistance of cables by measuring the leakage current of cable insulation, and can realize the function of accurate online monitoring of DC leakage current signals of 10kV cables.

[0090] Third, this invention proposes an integrated AC / DC cable current sensor, which simultaneously acquires transient and steady-state fault information of 10kV cables. The AC / DC component detection is internally designed with independent modularity and two output lines, which sample two analog signals as the basis for platform fault judgment. The two line signals are isolated, modularized, and shielded by a shielding design mode, which greatly reduces sampling interference.

[0091] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. An AC / DC integrated cable current sensor, characterized in that, Includes the sensor body, as well as the AC signal acquisition module and DC signal acquisition module of the cable installed in the sensor body; The cable AC signal acquisition module is used to acquire cable AC signals to determine the transient aging degree of cable insulation based on the abrupt current amplitude in the cable AC signal. The cable DC signal acquisition module is used to acquire the cable DC signal in order to determine the steady-state aging degree of the cable insulation based on the cable DC signal. The cable AC signal acquisition module and the cable DC signal acquisition module share a common sampling input terminal, and the acquired cable AC signal and cable DC signal are output independently. The sensor body includes a coil and a conditioning module; the receiving ends of the cable AC signal acquisition module and the cable DC signal acquisition module are respectively connected to the coil, and their output ends are respectively connected to the conditioning module; the conditioning module is used to condition and output the acquired cable AC signal and cable DC signal. The coil adopts a double-layer structure; the inner coil is connected to the cable AC signal acquisition module and is responsible for acquiring the cable AC signal generated by the cable joint; the outer coil is connected to the cable DC signal acquisition module and is responsible for acquiring the cable DC signal generated by the cable injection signal; the coil is made of iron-based microcrystalline alloy or permalloy material. The AC signal acquisition module for the cable uses a Hall sensor and sampling chip, which is located at the top of the inner coil; the DC signal acquisition module for the cable uses a TMR chip, which is electrically connected to the outer coil.

2. The AC / DC integrated cable current sensor according to claim 1, characterized in that, The Hall sensing and sampling chip uses GaAs material and is a THS119 chip. The TMR chip uses the MAGIC2001 electromagnetic chip.

3. The AC / DC integrated cable current sensor according to claim 1, characterized in that, The conditioning module includes a temperature compensation circuit, a signal conditioning circuit, and an amplification and zeroing circuit. The temperature compensation circuit is used to adjust the operational amplifier parameters according to the ambient temperature to compensate for the sensitivity of the TMR chip. The signal conditioning circuit includes an AC component conditioning circuit connected to the Hall sensing and sampling chip and a DC component conditioning circuit connected to the TMR chip, used to improve the spread spectrum communication distance. The amplification and zeroing circuit is used to amplify the signals acquired by the Hall sensor and sampling chip and the TMR chip, and to zero the TMR chip.

4. The AC / DC integrated cable current sensor according to claim 1, characterized in that, The sensor uses an open-loop mode to monitor cable insulation; the acquisition principle of the cable AC signal acquisition module is based on the following formula: In the formula, R is the output voltage signal; I is the Hall coefficient; B is the driving current of the Hall element; and B is the magnetic field strength of the air gap in the magnetic ring. It is the inner diameter of the iron core.

5. A method for monitoring the aging of 10KV cable insulation, characterized in that, Based on the AC / DC integrated cable current sensor according to any one of claims 1-4, it includes: Collect AC signals from cable insulation and determine the transient aging degree of cable insulation based on the abrupt current amplitude in the AC signals. The DC signal of the cable insulation is collected synchronously, and the steady-state aging degree of the cable insulation is determined based on the DC signal.

6. The method for monitoring the aging of 10kV cable insulation according to claim 5, characterized in that, The DC signal of the cable insulation is acquired by injecting a common-mode DC current signal source and using TMR electromagnetic detection.

7. The method for monitoring the aging of 10kV cable insulation according to claim 5, characterized in that, Also includes: Based on the output cable insulation DC signal, a leakage current variation trend curve is plotted to compare and analyze the steady-state aging degree of different cable insulations.

Images