Fault monitoring device for current transformer and multi-core alternating current cable

Abstract

The utility model provides a current transformer and a multi-core AC cable fault monitoring device, the current transformer comprises a first coil group, the first coil group comprises a first coil used for monitoring a first phase wire core and a second coil used for monitoring a second phase wire core, one end of the first coil forms a first electrode, and the other end forms a second electrode; a third electrode is formed at one end of the second coil, a fourth electrode is formed at the other end of the second coil, the first electrode and the third electrode are used for being electrically connected with a first load, the second electrode is connected with the fourth electrode, and the condition that if the first coil and the second coil are arranged in the same induced magnetic field, the first electrode and the third electrode have the same polarity is met. According to the technical scheme, signal interference of the conductive shielding layer can be inhibited, and fault monitoring of the multi-core AC cable is improved.

Description

Technical Field

[0001] This application relates to the field of optical fiber sensing technology, and more specifically, to a current transformer and a fault monitoring device for multi-core AC cables. Background Technology

[0002] Sampling devices and power extraction devices for three-core cables are two common types of equipment in power systems. The sampling device is mainly used to detect and collect current signals in the cable. Analyzing the current signals can be used for fault detection and location. The power extraction device is mainly used to extract electrical energy from the cable to power the monitoring equipment.

[0003] In sampling and energy harvesting devices, current transformers are used for fault monitoring of multi-core AC cables. These cables include a conductive shielding layer and the first and second phase conductors located within it. Some related technologies integrate sampling and energy harvesting devices based on current transformers. However, in practical applications, existing current transformer sampling, energy harvesting, and subsequent fault diagnosis have several problems: Firstly, because distribution cables typically use three-core cables, the magnetic fields generated by the three-phase conductors cancel each other out, affecting the current transformer's energy harvesting and sampling, hindering fault analysis and diagnosis. Secondly, due to interference from the conductive shielding layer, the accompanying magnetic field generated by the short-circuit current further affects the current transformer's fault signal sampling, making accurate online fault monitoring impossible. Utility Model Content

[0004] The purpose of this application is to provide a current transformer and a multi-core AC cable fault monitoring device to improve the interference problem of the conductive shielding layer and monitor the faults of the multi-core AC cable online.

[0005] In a first aspect, this application provides a current transformer for fault monitoring of a multi-core AC cable. The multi-core AC cable includes a conductive shielding layer and a first phase core and a second phase core located within the conductive shielding layer. The current transformer includes a first coil group, which includes a first coil for monitoring the first phase core and a second coil for monitoring the second phase core. One end of the first coil forms a first electrode, and the other end forms a second electrode. One end of the second coil forms a third electrode, and the other end forms a fourth electrode. The first electrode and the third electrode are respectively used for electrical connection with a first load. The second electrode and the fourth electrode are connected, and the first coil and the second coil satisfy the condition that if the first coil and the second coil are placed in the same induced magnetic field, the first electrode and the third electrode exhibit the same polarity, and the second electrode and the fourth electrode exhibit the same polarity.

[0006] In the above scheme, if a cable fault occurs, the current in the faulty core will increase abnormally, and a fault current will be induced in the first coil group, thereby monitoring whether there is a fault in the cable. When a changing current is generated in the cable shield, the two coils will generate induced current and induced electromotive force in the same direction. Since the two poles with the same polarity in the first and second coils are connected together, the influence of the cable shield on the two coils can be weakened, improving the sampling accuracy of the current transformer. In addition, after the interference of the conductive shield is weakened, the current transformer can be used not only for sampling and monitoring faults, but also as a power supply device.

[0007] As an optional embodiment, the multi-core AC cable is a three-phase cable that also includes a third phase conductor located within the conductive shielding layer. The current transformer further includes a second coil group, which includes a third coil for monitoring one of the first phase conductor and the second phase conductor, and a fourth coil for monitoring the third phase conductor. One end of the third coil forms a fifth electrode, and the other end forms a sixth electrode. One end of the fourth coil forms a seventh electrode, and the other end forms an eighth electrode. The fifth and seventh electrodes are connected, and the sixth and eighth electrodes are respectively used for electrical connection with a second load. The third and fourth coils satisfy the following conditions: if the third and fourth coils are placed in the same induced magnetic field, the fifth and seventh electrodes exhibit the same polarity, and the sixth and eighth electrodes exhibit the same polarity.

[0008] In the above scheme, the first coil group set on the first phase core and the second phase core can only monitor the faults of the first phase core and the second phase core. For three-core cables, the addition of the second coil group can also monitor the faults of the third phase core, realizing all-round online fault monitoring of multi-core cables.

[0009] Alternatively, the first coil and the second coil may have the same number of turns; and / or, the first coil and the second coil may have the same coil area, wherein the coil area is the area of ​​the planar figure enclosed by a single turn of the coil; and / or, the first coil and the second coil may have the same internal resistance; and / or, the third coil and the fourth coil may have the same number of turns; and / or, the third coil and the fourth coil may have the same coil area, wherein the coil area is the area of ​​the planar figure enclosed by a single turn of the coil; and / or, the third coil and the fourth coil may have the same internal resistance.

[0010] In the above scheme, when the configuration of the first coil and the second coil is the same, the conductive shielding layer will generate equal and induced current and induced electromotive force in the two coils. At this time, the weakening effect on the interference generated by the conductive shielding layer is the most obvious, thereby improving the sampling accuracy of the current transformer.

[0011] As an alternative, it also includes: a coil support, wherein the first coil group and the second coil group are fixed in the coil support, the coil support being configured to be disposed on the multi-core AC cable, and the first coil group and the second coil group are evenly arranged in a ring array around the multi-core AC cable.

[0012] As an alternative, the first coil group and the second coil group have the same structure; and / or, the current transformer further includes an iron core, with at least one of the iron cores passing through the first coil group and the second coil group; and / or, a clamping frame connected to the coil support, the clamping frame being configured to clamp and engage with a multi-core AC cable so that the first coil group and the second coil group are evenly arranged in a ring array around the multi-core AC cable.

[0013] Secondly, this application provides a multi-core AC cable fault monitoring device, comprising: a current transformer as described in the first aspect; a first load electrically connected to a first electrode and a third electrode, wherein the first load is at least used to monitor the multi-core AC cable for faults by means of a first induced current.

[0014] In the above scheme, the fault current sampled by the first coil group can also be sent to the first load connected to the first coil group for analysis to further determine the fault type, thereby achieving more detailed fault monitoring.

[0015] As an optional approach, it also includes: a second load electrically connected to the sixth and eighth electrodes, the second load being used at least for fault monitoring of the multi-core AC cable by means of the acquired second induced current.

[0016] In the above scheme, the first load connected to the first coil group can only monitor the faults of the first phase core and the second phase core. For three-core cables, the addition of the second coil group can also monitor the faults of the third phase core, realizing all-round online fault monitoring of multi-core cables.

[0017] As an optional configuration, the first load includes a first duplex switching circuit, a first polarity detection circuit, a first power extraction module, and a first processor. The first duplex switching circuit, electrically connected to the second and fourth electrodes, receives the first induced current and separates it into two electrical signals: one is a power frequency current, and the other is a high-frequency fault signal. The first polarity detection circuit, connected to the first duplex switching circuit, receives the high-frequency fault signal and transmits it to the processor. The first power extraction module, connected to the first duplex switching circuit, receives the power frequency current and converts it into electrical energy usable by the first processor. The first processor, connected to both the first polarity detection circuit and the first power extraction module, receives the high-frequency fault signal for multi-core AC cable fault monitoring.

[0018] In the above scheme, the first duplex switching circuit and the first polarity detection circuit perform preliminary processing on the sampled current. The processed sampled current is sent to the first processor to facilitate the analysis of the fault type. The first power supply module, as a power supply device, can provide power to the circuit parts involved in sampling and fault analysis.

[0019] As an optional approach, the first duplex switching circuit is a duplex filter circuit or an antenna switch; and / or, the first polarity detection circuit includes a first positive polarity detection circuit and a first negative polarity detection circuit, wherein both the first positive and negative polarity detection circuits include a capacitor-adjustable RC integral circuit and a Schmitt trigger circuit; and / or, the first power extraction module further includes an energy storage battery, which is used to store the electrical energy converted by the first power extraction module.

[0020] In the above scheme, the second load and the first load have the same function: to process the sampled current in the corresponding coil group and analyze the fault type.

[0021] Alternatively, the second load may have the same structure as the first load.

[0022] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing embodiments of this application. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is an assembly diagram of the first type of current transformer provided in the embodiments of this application;

[0025] Figure 2 This is an assembly diagram of the second type of current transformer provided in an embodiment of this application;

[0026] Figure 3 A three-dimensional schematic diagram of a current transformer and cable installation provided in this application embodiment;

[0027] Figure 4 A schematic diagram of the structure of the first type of multi-core AC cable fault monitoring device provided in the embodiments of this application;

[0028] Figure 5 A schematic diagram of the electrical connections of a first type of multi-core AC cable fault monitoring device provided in the embodiments of this application;

[0029] Figure 6 This is a schematic diagram of the electrical connections of a second type of multi-core AC cable fault monitoring device provided in an embodiment of this application;

[0030] Figure 7 A schematic diagram of the electrical connections of a third type of multi-core AC cable fault monitoring device provided in this application embodiment. Detailed Implementation

[0031] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0032] It should be noted that all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0033] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0034] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0035] Reference Figure 1 , Figure 1 This is a schematic diagram of the assembly of a first type of current transformer provided in an embodiment of this application. The current transformer is used for fault monitoring of a multi-core AC cable. The multi-core AC cable includes a conductive shielding layer and a first phase core and a second phase core located within the conductive shielding layer. The current transformer includes a first coil group, which includes a first coil for monitoring the first phase core and a second coil for monitoring the second phase core. One end of the first coil forms a first electrode 01, and the other end forms a second electrode 02. One end of the second coil forms a third electrode 03, and the other end forms a fourth electrode 04. The first electrode 01 and the third electrode 03 are respectively used for electrical connection with a first load. The second electrode 02 and the fourth electrode 04 are connected, and the first coil and the second coil satisfy the condition that if the first coil and the second coil are placed in the same induced magnetic field, the first electrode 01 and the third electrode 03 exhibit the same polarity, and the second electrode 02 and the fourth electrode 04 exhibit the same polarity.

[0036] The conductive shielding layer of a multi-core AC cable is an important structural component used to reduce electromagnetic interference, uniformly distribute the electric field, provide grounding protection, and improve mechanical strength. The conductive shielding layer is typically made of materials such as metal foil, braided metal wire mesh, or conductive coating, and is wrapped around the insulation layer.

[0037] The first coil group is used to monitor faults in the first phase conductor and the second phase conductor. Figure 1 In this example, taking phase A as the first phase core and phase B as the second phase core, the first coil is denoted as A1 and the second coil as B1. When the same magnetic flux passes through both coils simultaneously, the first electrode 01 of the first coil and the third electrode 03 of the second coil exhibit the same polarity—either both are positive or both are negative. This means that in the same induced magnetic field, the induced electromotive force of the first electrode 01 and the third electrode 03 is also the same. Connecting the first electrode 01 and the third electrode 03 can cancel or partially cancel the interference of the changing current in the conductive shielding layer on the two coils. The first and second coils are arranged circumferentially along the multi-core AC cable and are located on the same cross-section.

[0038] The current transformer is configured such that, in use, a first coil and a second coil are arranged circumferentially around the axis of a multi-core AC cable, the distance from the first coil to the axis is equal to the distance from the second coil to the axis, the first coil is configured to be closer to the first phase conductor, and the second coil is configured to be closer to the second phase conductor.

[0039] In one implementation, the first coil is located at a certain magnetic field extreme point of the first phase conductor, and the second coil is located at a certain magnetic field extreme point of the second phase conductor. The magnetic field extreme points of the first coil and the second coil are located on the same cross-section of the multi-core AC cable.

[0040] For the first coil group, the definition is... Figure 1 and Figure 2 The induced current of the first coil group flows from the first electrode 01 through the first load to the third electrode 03, which is the first polarity (positive polarity) direction; the induced current of the first coil group flows from the third electrode 03 through the first load to the first electrode 01, which is the second polarity (negative polarity) direction.

[0041] Furthermore, such as Figure 1 and Figure 4 As shown, coils A1 and B1 are in close contact with the cores of phases A and B, therefore, coils A1 and B1 mainly induce the current in the cores of phases A and B. Since the first electrode 01 and the third electrode 03 of coils A1 and B1, which have the same polarity, are connected through the first load 20, and the current increases sharply when a cable fault occurs, the following explanation, using the example of the first coil group located between the power supply and the fault point, illustrates how to perform fault analysis and define polarity based on the induced current induced by the first coil group, from a theoretical perspective:

[0042] If a phase-to-ground short circuit occurs in phase A conductor, the current in phase A conductor increases sharply. Since the distance between coil A1 and phase A conductor is less than the distance between coil B1 and phase A conductor, the induced current generated by coil A1 is greater than the induced current generated by coil B1. The induced current of the first coil group flows from the first electrode 01 through the first load 20 to the third electrode 03. In summary, the polarity of the induced current generated by the first coil group is positive, i.e., the first polarity.

[0043] If a phase-to-ground short circuit occurs in phase B, the current in phase B increases sharply. Since the distance between coil B1 and phase B is less than the distance between coil A1 and phase B, the induced current generated by coil B1 is greater than the induced current generated by coil A1. Therefore, the induced current generated by the first coil group is negative, i.e., the second polarity. At this time, the induced current of the first coil group flows from the third electrode 03 through the first load 20 to the first electrode 01, exhibiting the second polarity (negative polarity), and its magnitude is I. B1 -I A1 .

[0044] If a phase-to-phase short circuit occurs between phases A and B, the two phases form a loop, and the current within it increases sharply and becomes equal. The current direction can be either A→B or B→A. When the current direction is A→B, that is, the induced current of the first coil group flows from the first electrode 01 through the first load 20 to the third electrode 03, the polarity of the induced current generated by the first coil group is positive, and the magnitude is 2A1. When the current direction is B→A, that is, the induced current of the first coil group flows from the third electrode 03 through the first load 20 to the first electrode 01, the polarity of the induced current generated by the first coil group is negative, and the magnitude is -2A1.

[0045] Similarly, definition Figure 2 The induced current of the second coil group flows from the sixth electrode 06 through the second load 30 to the eighth electrode 08 in the first polarity (positive polarity) direction; the induced current of the second coil group flows from the eighth electrode 08 through the second load 30 to the sixth electrode 06 in the second polarity (negative polarity) direction.

[0046] In the second coil group, when located between the power supply and the fault point, when the current direction is B (current B), the induced current of the second coil group flows from the sixth electrode 06 through the second load to the eighth electrode 08, and the polarity of the induced current generated by the second coil group is the first polarity (positive polarity). When the current direction is C (current C), the induced current of the second coil group flows from the eighth electrode 08 through the second load to the sixth electrode 06, and the polarity of the induced current generated by the second coil group is the second polarity (negative polarity). Specifically, the definition of the polarity of the induced current of the second coil group is the same as that of the first coil group, and will not be elaborated further.

[0047] In the above scheme, if a cable fault occurs, the current in the faulty core will increase abnormally, and a fault current will be induced in the first coil group, thereby monitoring whether there is a fault in the cable. When a changing current is generated in the cable shield, the two coils will generate induced current and induced electromotive force in the same direction. Since the two poles with the same polarity in the first and second coils are connected together, the influence of the cable shield on the two coils can be weakened, improving the sampling accuracy of the current transformer. In addition, after the interference of the conductive shield is weakened, the current transformer can be used not only for sampling and monitoring faults, but also as a power supply device.

[0048] In some embodiments, refer to Figure 2 , Figure 2This is a schematic diagram of the assembly of a second type of current transformer provided in an embodiment of this application. The multi-core AC cable is a three-phase cable that also includes a third phase conductor located within a conductive shielding layer. The current transformer also includes a second coil group, which includes a third coil for monitoring one of the first and second phase conductors and a fourth coil for monitoring the third phase conductor. One end of the third coil forms a fifth electrode 05, and the other end forms a sixth electrode 06. One end of the fourth coil forms a seventh electrode 07, and the other end forms an eighth electrode 08. The fifth electrode 05 and the seventh electrode 07 are connected. The sixth electrode 06 and the eighth electrode 08 are respectively used for electrical connection with a second load. The third coil and the fourth coil satisfy the condition that if the third coil and the fourth coil are placed in the same induced magnetic field, the fifth electrode 05 and the seventh electrode 07 exhibit the same polarity, and the sixth electrode 06 and the eighth electrode 08 exhibit the same polarity.

[0049] The current transformer is configured such that, in use, the third and fourth coils are arranged circumferentially around the axis of the multi-core AC cable, with the distance from the third coil to the axis being equal to the distance from the fourth coil to the axis. The third coil is configured to be closer to the first or second phase conductor, and the fourth coil is configured to be closer to the third phase conductor.

[0050] When a multi-core AC cable is a three-core cable, including three phase cores, if only the first coil group (e.g., A1B1) is used, it can only monitor faults in phases A and B. When a phase-to-ground short circuit occurs in phase C, the distance between phase C and coils A1 and B1 is the same, and the induced current generated by the first coil group is zero, which can easily be confused with normal alternating induced current. To monitor faults in the third phase core, a second coil group needs to be added on top of the first coil group. One of the two coils in the second coil group is configured to be closer to the third phase core. The design concept and connection method of the second coil group are the same as those of the first coil group.

[0051] If the other coil of the second coil group is configured to be close to the side of the first phase conductor, the second coil group is used to monitor faults in the first phase conductor and the third phase conductor; if the other coil of the second coil group is configured to be close to the side of the second phase conductor, the second coil group is used to monitor faults in the second phase conductor and the third phase conductor.

[0052] In the above scheme, the first coil group set on the first phase core and the second phase core can only monitor the faults of the first phase core and the second phase core. For three-core cables, the addition of the second coil group can also monitor the faults of the third phase core, realizing all-round online fault monitoring of multi-core cables.

[0053] In some embodiments, the first coil and the second coil have the same number of turns; and / or, the first coil and the second coil have the same coil area, which is the area of ​​the planar figure enclosed by a single turn of the coil; and / or, the first coil and the second coil have the same internal resistance; and / or, the third coil and the fourth coil have the same number of turns; and / or, the third coil and the fourth coil have the same coil area, which is the area of ​​the planar figure enclosed by a single turn of the coil; and / or, the third coil and the fourth coil have the same internal resistance.

[0054] In some embodiments, the first coil group and the second coil group have the same structure.

[0055] In the above scheme, when the configuration of the first coil and the second coil is the same, the conductive shielding layer will generate equal and induced current and induced electromotive force in the two coils. At this time, the weakening effect on the interference generated by the conductive shielding layer is the most obvious, thereby improving the sampling accuracy of the current transformer.

[0056] In some embodiments, refer to Figure 3 , Figure 3 This is a perspective view of a current transformer and cable installation according to an embodiment of this application. The current transformer also includes a coil support 100, on which a first coil group and a second coil group are fixed. The coil support 100 is configured to be disposed on a multi-core AC cable, and the first coil group and the second coil group are evenly arranged in a ring array around the multi-core AC cable. In some embodiments, the current transformer also includes a clamping frame 200, which is connected to the coil support 100 and configured to clamp the multi-core AC cable, so that the first coil group and the second coil group are evenly arranged in a ring array around the multi-core AC cable.

[0057] Explanatory Figure 1-2 The middle coil, winding around all the phase conductors, is a conductive shielding layer. Take a current transformer with two coil groups as an example. (Reference) Figure 1-3 The current transformers in the various schemes of this application also include a coil support 100 and a clamping frame 200. The coil support 100 and clamping frame 200 can use existing structures, and will not be described in detail here. The first coil group and the second coil group are fixed to the coil support 100 and arranged in a ring array around the multiphase AC cable. The first and second coils of the first coil group, and the third and fourth coils of the second coil group are referenced. Figure 2 The arrangement of the coils corresponds spatially to the corresponding phase conductors. For example, the first coil might correspond to the first phase conductor; the second coil to the second phase conductor; the third coil to either the second or first phase conductor; and the fourth coil to all three phase conductors, for fault monitoring.

[0058] In some embodiments, the current transformer further includes an iron core, with at least one iron core passing through the first coil group and the second coil group.

[0059] Reference Figure 4 , Figure 4 This is a schematic diagram of the structure of a first type of multi-core AC cable fault monitoring device provided in the embodiments of this application. The multi-core AC cable fault monitoring device includes a first load 20 and a current transformer 10 in any of the aforementioned embodiments. The first load 20 is electrically connected to the first electrode 01 and the third electrode 03. The first load 20 is at least used to monitor the fault of the multi-core AC cable by collecting the first induced current.

[0060] In the above scheme, the fault current sampled by the first coil group can also be sent to the first load 20 connected to the first coil group for analysis to further determine the fault type, thereby achieving more detailed fault monitoring.

[0061] In some embodiments, the multi-core AC cable fault monitoring device further includes a second load 30, which is electrically connected to the sixth electrode 06 and the eighth electrode 08. The second load 30 is used at least to monitor the multi-core AC cable for faults by means of the second induced current collected.

[0062] In the above scheme, the first load 20 connected to the first coil group can only monitor the faults of the first phase core and the second phase core. For three-core cables, the addition of the second coil group can also monitor the faults of the third phase core, realizing all-round online fault monitoring of multi-core cables.

[0063] In some embodiments, refer to Figure 5 , Figure 5 This is a schematic diagram of the electrical connections of a first type of multi-core AC cable fault monitoring device provided in an embodiment of this application. The first load 20 includes a first duplex switching circuit 201, a first polarity detection circuit 202, a first power extraction module 203, and a first processor 204. The first duplex switching circuit 201 is electrically connected to the second electrode 02 and the fourth electrode 04, and is used to receive a first induced current and separate it into two electrical signals: one is a power frequency current, and the other is a high-frequency fault signal. The first polarity detection circuit 202 is connected to the first duplex switching circuit 201 and is used to receive the high-frequency fault signal and transmit it to the processor. The first power extraction module 203 is connected to the first duplex switching circuit 201 and is used to receive the power frequency current and convert it into electrical energy usable by the first processor 204. The first processor 204 is connected to both the first polarity detection circuit 202 and the first power extraction module 203, and is used to receive the high-frequency fault signal for multi-core AC cable fault monitoring.

[0064] When the multi-core AC cable is working normally, the alternating current inside the cable will generate a power frequency current in the coil. The power frequency current flows to the first power supply module 203 through the first duplex switching circuit 201, which can be used to power the first processor 204.

[0065] When a grounding or short-circuit fault occurs in a multi-core AC cable, a high-frequency current is generated in the core. The fault current induced in the current transformer 10 by the high-frequency current is separated by the first duplex switching circuit 201 and then wakes up the first processor 204 through the first polarity detection circuit 202.

[0066] In the above scheme, the first duplex switching circuit 201 and the first polarity detection circuit 202 perform preliminary processing on the sampled current. The processed sampled current is sent to the first processor 204 to facilitate the analysis of the fault type. The first power supply module 203, as a power supply device, can provide power to the circuit parts involved in sampling and fault analysis.

[0067] In some embodiments, refer to Figure 6 , Figure 6 This is a schematic diagram of the electrical connections for a second type of multi-core AC cable fault monitoring device provided in this application embodiment. The first duplex switching circuit 201 is a duplex filter circuit or an antenna switch; and / or, the first polarity detection circuit 202 includes a first positive polarity detection circuit 2021 and a first negative polarity detection circuit 2022, wherein the first positive and negative polarity detection circuits 2021 and 2022 both include a capacitor-adjustable RC integral circuit and a Schmitt trigger circuit; and / or, the first power extraction module 203 further includes an energy storage battery, which is used to store the electrical energy converted by the first power extraction module 203.

[0068] If the first duplex switching circuit 201 is a duplex filter circuit, the duplex filter circuit includes a capacitor high-pass coupling part and an inductor low-pass coupling part. The sampling current in the current transformer 10 can be separated into a fault high-frequency signal through the capacitor high-pass coupling part and into a power frequency current for power supply through the inductor low-pass coupling part.

[0069] Reference Figure 7 , Figure 7 This is a schematic diagram of the electrical connections for a third type of multi-core AC cable fault monitoring device provided in this application. The first load 20 and the second load 30 can each have independent load circuits, or they can be configured as follows: Figure 7 The two circuits share a common power supply module and processor, but each has its own separate duplex switching circuit and polarity detection circuit.

[0070] In the above scheme, the second load 30 and the first load 20 have the same function: to process the sampling current in the corresponding coil group and analyze the fault type.

[0071] In some embodiments, reference Figure 6-7 The second load 30 and the first load 20 have the same structure. Identical structure means that the functional modules operate on the same principle. The second load 30 and the first load 20 can be two independent loads, or they can share the first processor 204 and the first power supply module 203. It is important to emphasize that the second load 30 and the first load 20 need to have separate polarity detection functions to process the corresponding high-frequency fault signals respectively.

[0072] Based on the above-mentioned multi-core AC cable fault monitoring device, this application also provides a variety of multi-core AC cable fault monitoring methods, which are described in detail below.

[0073] First, the first method for fault monitoring of multi-core AC cables provided in the embodiments of this application is introduced. The method includes:

[0074] Step S10: Obtain a first induced current, the first induced current comes from at least one multi-core AC cable fault monitoring device according to at least one embodiment of this application; wherein, when there are multiple multi-core AC cable fault monitoring devices, the multiple multi-core AC cable fault monitoring devices are arranged side by side at intervals along the multi-core AC cable, the multi-core AC cable fault monitoring devices are configured such that, when in use, the first coil and the second coil are arranged at intervals in the circumferential direction around the axis of the multi-core AC cable, the distance from the first coil to the axis is equal to the distance from the second coil to the axis, the first coil is configured to be close to the side of the first phase core, and the second coil is configured to be close to the side of the second phase core.

[0075] Step S20: Based on the fault high-frequency signal separated from the first induced current, perform fault monitoring on the multi-core AC cable.

[0076] The first induced current is the induced current in the first coil group of the multi-core AC cable fault monitoring device.

[0077] In the above scheme, when a current transformer is installed along the multi-core AC cable, it can be used to monitor faults. When multiple current transformers are installed along the multi-core AC cable, they can be used to locate the fault range and determine the fault type.

[0078] In some implementations, step S20 includes:

[0079] If two adjacent current transformers exist, and a high-frequency fault signal cannot be obtained based on the first induced current of one current transformer, but a high-frequency fault signal can be obtained based on the first induced current of the other current transformer, then the fault point is determined to be located between the two adjacent current transformers, and the fault type is a phase-to-phase short circuit. And / or,

[0080] If there are two adjacent current transformers, and a high-frequency fault signal with the first polarity is obtained based on the first induced current of one current transformer, and a high-frequency fault signal with the second polarity opposite to the first polarity is obtained based on the first induced current of the other current transformer, then the fault point is determined to be located between the two adjacent current transformers, and the fault type is a phase-to-ground short circuit.

[0081] This application does not specifically limit the direction of the first polarity. Those skilled in the art can adjust it according to the actual situation. For example, the induced current flowing from the first electrode 0101 to the third electrode 0303 in the first coil group can be defined as the first polarity. Correspondingly, the second polarity is the current flowing from the third electrode 0303 to the first electrode 0101 through the first load 20.

[0082] The polarity of the first induced current induced by the current transformer is affected by the direction of current flow in the corresponding phase conductor. Under different fault conditions—phase-to-ground short circuit and phase-to-phase short circuit—the direction of the corresponding current flow in the conductor will differ. Specifically, the current direction in the corresponding phase conductor between the fault point and the substation, and between the fault point and the electrical appliance, will differ significantly, thus the polarity of the corresponding first induced current will also differ. Based on this, the cause and fault range of the fault can be located using the above characteristics, and the judgment criteria are as follows:

[0083] One end of a multi-core AC cable is connected to a substation, and the other end is connected to an electricity user; the fault point is located in the multi-core AC cable between the substation and the electricity user.

[0084] When a phase-to-ground short circuit occurs, the large current generated by the fault in the faulty conductor of the multi-core AC cable flows from the substation to the fault point, and finally flows to the ground at the fault point. Between the fault point and the user, the current flowing to the user's electrical appliances decreases sharply, and the appliances induce a large current from the appliances to the fault point, which eventually flows to the ground at the fault point. Therefore, the directions of the large current generated by the fault between the substation and the fault point are opposite to those between the fault point and the user.

[0085] When a phase-to-phase short circuit occurs, between the substation and the fault point, the direction of the current generated by the fault in the multi-core AC cable is from one phase core to another, and the current directions of the two are opposite. Between the fault point and the power user, the direction of the fault current generated by the fault core is the same, and both flow towards the fault point.

[0086] Based on the analysis of the above phenomena, when a current transformer is installed on a multi-core AC cable, it can generate an induced current. Furthermore, depending on the type of fault and the location of the current transformer relative to the fault point and substation, the high-frequency fault signal corresponding to the captured induced current will differ in its presence, magnitude, and polarity. Therefore, if multiple current transformers are deployed in a cable line, the specific fault range and fault type of the multi-core AC cable can be deduced from the presence, magnitude, and polarity of the high-frequency fault signal.

[0087] In the above scheme, cable faults are determined based on the first induced current in the current transformer. Cable faults include phase-to-phase short circuits and phase-to-ground short circuits. When a phase-to-phase short circuit or a phase-to-ground short circuit occurs, the polarity and magnitude of the induced current induced in the current transformer have their own characteristics. The fault type can be determined based on these characteristics. Furthermore, the induced currents induced by the current transformer located between the power supply and the fault point, and between the fault point and the electrical appliance, are also different. Therefore, by arranging multiple current transformers along the multi-core AC cable, the fault range can be located.

[0088] Next, we introduce a second method for fault monitoring of multi-core AC cables provided in the embodiments of this application. The method includes:

[0089] A first induced current and a second induced current are obtained. The first induced current and the second induced current are from the multi-core AC cable fault monitoring device described in the embodiments of this application. The multi-core AC cable fault monitoring device is configured such that, in use, a first coil and a second coil are arranged at intervals in the circumferential direction around the axis of the multi-core AC cable, the distance from the first coil to the axis is equal to the distance from the second coil to the axis, the first coil is arranged closer to the first phase core, and the second coil is arranged closer to the second phase core; a third coil and a fourth coil are arranged at intervals in the circumferential direction around the axis of the multi-core AC cable, the distance from the third coil to the axis is equal to the distance from the fourth coil to the axis, the third coil is arranged closer to the first phase core or the second phase core, and the fourth coil is arranged closer to the third phase core.

[0090] Based on the inductive parameters of the high-frequency fault signals separated from the first and second induced currents, fault monitoring is performed on the multi-core AC cable. The fault monitoring includes:

[0091] If the high-frequency fault signal cannot be obtained by filtering based on the first induced current, but the high-frequency fault signal is obtained based on the second induced current, then it is determined that the third phase conductor has a phase-to-ground short circuit, or the first and second phase conductors have a phase-to-phase short circuit, or both the first and second phase conductors have a phase-to-ground short circuit.

[0092] And / or,

[0093] If a high-frequency fault signal is obtained based on the first induced current, but not based on the second induced current, and if the third coil is configured to be close to the side of the first phase core, then it is determined that the second phase core has a phase-to-ground short circuit, or the first and third phase cores have a phase-to-phase short circuit, or both phases of the first and third phase cores have a phase-to-ground short circuit; if the third coil is configured to be close to the side of the second phase core, then it is determined that the first phase core has a phase-to-ground short circuit, or the second and third phase cores have a phase-to-phase short circuit, or both phases of the second and third phase cores have a phase-to-ground short circuit.

[0094] In the above scheme, cable faults are determined based on the first and second induced currents in a current transformer. Cable faults include phase-to-phase short circuits and phase-to-ground short circuits. When a phase-to-phase short circuit or a phase-to-ground short circuit occurs, the polarity and magnitude of the induced current induced in the current transformer have their own characteristics, and the fault type can be determined based on these characteristics.

[0095] The following describes a third method for fault monitoring of multi-core AC cables provided in the embodiments of this application. The method includes:

[0096] A first induced current and a second induced current are acquired, wherein the first induced current and the second induced current respectively come from multiple multi-core AC cable fault monitoring devices described in the embodiments of this application. Each multi-core AC cable fault monitoring device is arranged side by side at intervals along the multi-core AC cable. The multi-core AC cable fault monitoring device is configured such that, in use, a first coil and a second coil are arranged at intervals in the circumferential direction around the axis of the multi-core AC cable, the distance from the first coil to the axis is equal to the distance from the second coil to the axis, the first coil is arranged closer to the first phase core, the second coil is arranged closer to the second phase core, a third coil and a fourth coil are arranged at intervals in the circumferential direction around the axis of the multi-core AC cable, the distance from the third coil to the axis is equal to the distance from the fourth coil to the axis, the third coil is arranged closer to the first phase core or the second phase core, and the fourth coil is arranged closer to the third phase core.

[0097] If two adjacent current transformers satisfy the following conditions respectively, then the fault point is determined to be located between the two adjacent current transformers, wherein the first induced currents and / or the second induced currents of the two current transformers are different, and the difference includes at least one of magnitude and polarity, including the following conditions:

[0098] Based on the first induced current and the second induced current of the two current transformers, a first fault high-frequency signal is obtained. If the polarity of the first fault high-frequency signal of one current transformer is opposite and the polarity of the first fault high-frequency signal of the other current transformer is also opposite, then the fault type is determined to be a phase-to-ground short circuit in the common phase conductor of the first coil group and the second coil group, or a phase-to-ground short circuit in the non-common phase conductors of the corresponding phase conductors of the first coil group and the second coil group.

[0099] And / or,

[0100] If the first fault high-frequency signal is obtained from the first induced current and the second induced current of the two current transformers, and the polarity of the first fault high-frequency signal of one and only one current transformer is the same, then the fault type is determined to be a phase-to-phase short circuit between two non-common phase cores in the phase cores corresponding to the first coil group and the second coil group.

[0101] And / or,

[0102] If the first induced current of both current transformers fails to obtain a high-frequency fault signal, and the second induced current of both current transformers obtains a high-frequency fault signal, then the fault type is determined to be either a phase-to-ground short circuit in the third phase conductor or a phase-to-ground short circuit in both the first and second phase conductors.

[0103] And / or,

[0104] If the first fault high-frequency signal is obtained from the first induced current of both current transformers, and the fault high-frequency signal cannot be obtained from the second induced current of both current transformers, then the fault type is determined to be either a phase-to-ground short circuit in the first phase conductor or a phase-to-ground short circuit in both the second and third phase conductors.

[0105] And / or,

[0106] If a second fault high-frequency signal is obtained based on the first induced current of one of the current transformers, the fault type is determined to be a phase-to-phase short circuit between the first phase conductor and the second phase conductor. The second fault high-frequency signal is a fault high-frequency signal that is larger than the first fault high-frequency signal by a preset threshold.

[0107] And / or,

[0108] If the second fault high-frequency signal is obtained based on the second induced current of one of the current transformers, the fault type is determined to be a phase-to-phase short circuit between the two phase conductors of the transformer with the second coil group.

[0109] As one implementation method, the following example illustrates a three-phase cable with a first coil group configured on the AB phase cores and a second coil group configured on the BC phase cores. The first polarity is denoted as positive polarity. In the first coil group, the direction of the first polarity is that the induced current of the first coil group flows from the first electrode 0101 through the first load 20 to the third electrode 0303. In the second coil group, the direction of the first polarity is that the induced current of the second coil group flows from the sixth electrode 0606 through the second load 30 to the eighth electrode 0808. Table 1 below shows the correspondence between cable faults and high-frequency fault signals when the current transformer is located at different positions. Different positions include two cases: located between the fault point and the power source, and located outside the fault point and the power source. Here, 0 represents no fault high-frequency signal, + represents the first polarity, i.e., positive polarity, - represents the second polarity, i.e., negative polarity, 1 represents the first fault high-frequency signal, and 2 represents the second fault high-frequency signal. In the first column, AB and BC represent the first coil group and the second coil group, respectively. Under the phase-to-ground short circuit list, A, B, C, AB, BC, and AC represent phase-to-ground short circuit faults occurring when phase A, phase B, phase C, AB and BC are the same, and AC is the same, respectively. Under the phase-to-phase short circuit list, AB represents a phase-to-phase short circuit in phase AB with current flowing from A to B, and BA represents a phase-to-phase short circuit in phase AB with current flowing from B to A. The same applies to BC, CB, AC, and CA, which will not be elaborated further here.

[0110]

[0111] Table 1. Correspondence between cable faults and high-frequency fault signals

[0112] It should be noted that 1 and 2 only represent the magnitude relationship between the high-frequency signals of the first and second faults. It can mean that the integrated energy value of the second fault's high-frequency signal is greater than that of the first fault's high-frequency signal, but not an absolute doubling relationship. Since a phase-to-phase short circuit directly forms a loop between the two phase conductors, the current in a phase-to-phase short circuit is greater than that in a phase-to-ground short circuit where the current flows directly from the conductors to the ground. Therefore, the induced current corresponding to a phase-to-phase short circuit is also greater than that of a phase-to-ground short circuit. Thus, the preset threshold can be adjusted according to the actual situation, ensuring that the preset threshold is sufficient to distinguish between the two different fault types.

[0113] Optionally, in the above embodiments, the high-frequency fault signals of the first and second coil groups can be combined for comprehensive judgment, and Table 2 is obtained by summarizing Table 1. Table 2 also shows the correspondence between the cable faults and the high-frequency fault signals:

[0114]

[0115]

[0116] Table 2. Correspondence between cable faults and high-frequency fault signals

[0117] In Table 2, AB indicates that the high-frequency fault signals of the first coil group and the second coil group are combined. For example, the first number -1 in -10 represents the high-frequency fault signal of the first coil group, and the second number 0 represents that the second coil group did not receive a high-frequency fault signal.

[0118] The two merged numbers in Table 2 above are encoded according to the following rules:

[0119] 10==0,-11==1,0-1==2,01==3,-10==4,1-1==5,2-1==6,-21==7,-12==8,1-2==9,11==10,-1-1==11。

[0120] The coding process yielded Table 3 below, which shows the correspondence between cable faults and their codes:

[0121]

[0122] Table 3. Correspondence between cable faults and their codes

[0123] After organizing Table 3 above, we get Table 4 below. Table 4 also shows the correspondence between cable faults and their codes:

[0124] Located between the fault point and the power supply Located outside the fault point and power supply Single-phase phase-to-ground short circuit 0、1、2 3、4、5 Two-phase phase-to-ground short circuit 3、4、5 0、1、2 Phase-to-phase short circuit 6、7、8、9、10、11 0、1、2

[0125] Table 4. Correspondence between cable faults and their codes

[0126] As shown in Table 4, when {3, 4, 5} appears, it can be determined that a phase-to-ground short circuit has occurred, and the fault range of the phase-to-ground short circuit is between {0, 1, 2} and {3, 4, 5}. When {6, 7, 8, 9, 10, 11} appears, it can be determined that a phase-to-phase short circuit has occurred, and the fault range is between {6, 7, 8, 9, 10, 11} and {0, 1, 2}.

[0127] In the above scheme, cable faults are determined based on the first and second induced currents in multiple current transformers. Cable faults include phase-to-phase short circuits and phase-to-ground short circuits. When a phase-to-phase short circuit or a phase-to-ground short circuit occurs, the polarity and magnitude of the induced current induced in the current transformers have their own characteristics. The fault type can be determined based on these characteristics. Furthermore, the induced currents induced by the current transformers located between the power supply and the fault point, and between the fault point and the electrical appliance, are also different, thereby allowing the fault range to be located.

[0128] Furthermore, by summarizing and analyzing the patterns in Table 4 above, the following new implementation method for fault diagnosis can be derived.

[0129] This application also provides a method for fault monitoring of multi-core AC cables, the method comprising:

[0130] A first induced current and a second induced current are obtained. The first induced current and the second induced current are respectively from multiple multi-core AC cable fault monitoring devices provided in the above embodiments. Each of the multi-core AC cable fault monitoring devices is arranged side by side at intervals along the multi-core AC cable.

[0131] If two adjacent current transformers satisfy the following conditions respectively, then the fault point is determined to be located between the two adjacent current transformers, wherein the first induced currents and / or the second induced currents of the two current transformers are different, and the difference includes at least one of magnitude and polarity, and the following conditions include:

[0132] When a first monitoring result is obtained based on one of the current transformers, and a second monitoring result is obtained based on the other current transformer, it is determined that a phase-to-ground short circuit exists between the two current transformers; wherein, the first monitoring result includes a first fault high-frequency signal of the first polarity obtained based on the first induced current but not based on the second induced current, or a first fault high-frequency signal of the second polarity obtained based on the first induced current but not based on the second induced current, or a first fault high-frequency signal of the first polarity obtained based on the first induced current and a first fault high-frequency signal of the second polarity obtained based on the second induced current; and / or,

[0133] If a third monitoring result is obtained based on one of the current transformers and a second monitoring result is obtained based on the other current transformer, then it is determined that there is a phase-to-phase short circuit between the two current transformers. The second monitoring result includes obtaining a first fault high-frequency signal of a first polarity based on a first induced current and not obtaining a fault high-frequency signal based on a second induced current; or obtaining a first fault high-frequency signal of a second polarity based on a first induced current and also obtaining a first fault high-frequency signal of a first polarity based on a second induced current; or not obtaining a fault high-frequency signal based on a first induced current and obtaining a first fault high-frequency signal of a second polarity based on a second induced current. The third monitoring result includes obtaining a first fault high-frequency signal based on one of the first and second induced currents and obtaining a second fault high-frequency signal based on the other of the first and second induced currents; or obtaining first fault high-frequency signals of the same polarity based on both the first and second induced currents.

[0134] The advantage of the above scheme is that when using multiple current transformers for fault monitoring, it is not necessary to strictly correspond the first and second coil groups of each current transformer to the phase conductors of the three-phase cable. That is, the first coil of the first coil group of different current transformers can correspond to different phase conductors, not necessarily the same phase conductors. This can greatly reduce the installation difficulty of each current transformer and significantly reduce the installation workload. Furthermore, the above-mentioned logical judgment method can be used to locate the fault range and determine the fault type, such as phase-to-phase short circuit or phase-to-ground short circuit.

[0135] In the embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and there may be other division methods in actual implementation. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the coupling or direct coupling or communication connection shown or discussed may be through some communication interface; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0136] Furthermore, the units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0137] Furthermore, the functional modules in the various embodiments of this application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0138] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A current transformer for fault monitoring of a multi-core AC cable, the multi-core AC cable comprising a conductive shielding layer and a first phase conductor and a second phase conductor located within the conductive shielding layer, characterized in that, The current transformer includes: The first coil group includes a first coil for monitoring a first phase conductor and a second coil for monitoring a second phase conductor. One end of the first coil forms a first electrode and the other end forms a second electrode. One end of the second coil forms a third electrode and the other end forms a fourth electrode. The first electrode and the third electrode are respectively used for electrical connection with a first load. The second electrode and the fourth electrode are connected, and the first coil and the second coil satisfy the condition that if the first coil and the second coil are placed in the same induced magnetic field, the first electrode and the third electrode exhibit the same polarity, and the second electrode and the fourth electrode exhibit the same polarity.

2. The current transformer according to claim 1, characterized in that, The multi-core AC cable is a three-phase cable that also includes a third phase core located within the conductive shielding layer, and the current transformer further includes: The second coil group includes a third coil for monitoring one of the first phase conductor and the second phase conductor, and a fourth coil for monitoring the third phase conductor. One end of the third coil forms a fifth electrode and the other end forms a sixth electrode. One end of the fourth coil forms a seventh electrode and the other end forms an eighth electrode. The fifth and seventh electrodes are connected. The sixth and eighth electrodes are respectively used for electrical connection with a second load. The third and fourth coils satisfy the following conditions: if the third and fourth coils are placed in the same induced magnetic field, the fifth and seventh electrodes exhibit the same polarity, and the sixth and eighth electrodes exhibit the same polarity.

3. The current transformer according to claim 2, characterized in that, The first coil and the second coil have the same number of turns; and / or, The first coil and the second coil have the same coil area, where the coil area is the area of ​​the planar figure enclosed by a single turn of the coil; and / or, The first coil and the second coil have the same internal resistance; and / or, The third coil and the fourth coil have the same number of turns; and / or, The third coil and the fourth coil have the same coil area, which is the area of ​​the planar figure enclosed by a single turn of the coil; and / or, The third coil and the fourth coil have the same internal resistance.

4. The current transformer according to claim 2, characterized in that, Also includes: A coil support is provided, wherein the first coil group and the second coil group are fixed to the coil support, and the coil support is configured to be disposed on a multi-core AC cable, and the first coil group and the second coil group are evenly arranged in a ring array around the multi-core AC cable.

5. The apparatus according to claim 4, characterized in that, The first coil group has the same structure as the second coil group; and / or, The current transformer also includes an iron core, at least one of the iron cores being inserted into the first coil group and the second coil group, and / or a clamping frame connected to the coil support, the clamping frame being configured to clamp into a multi-core AC cable so that the first coil group and the second coil group are evenly arranged in a ring array around the multi-core AC cable.

6. A fault monitoring device for multi-core AC cables, characterized in that, include: The current transformer as described in any one of claims 1-5; The first load is electrically connected to the first electrode and the third electrode. The first load is used at least for fault monitoring of the multi-core AC cable by means of the first induced current collected.

7. The apparatus according to claim 6, characterized in that, Also includes: The second load is electrically connected to the sixth and eighth electrodes, and the second load is used at least for fault monitoring of the multi-core AC cable by means of the second induced current collected.

8. The apparatus according to claim 7, characterized in that, The first load includes a first duplex switching circuit, a first polarity detection circuit, a first power supply module, and a first processor; The first duplex switching circuit is electrically connected to the second electrode and the fourth electrode, and is used to receive the first induced current and separate the first induced current into two electrical signals, one of which is the power frequency current and the other is the fault high frequency signal. The first polarity detection circuit is connected to the first duplex switching circuit and is used to receive the fault high-frequency signal and transmit the fault high-frequency signal to the processor. The first power acquisition module is connected to the first duplex switching circuit and is used to receive the power frequency current and convert the power frequency current into electrical energy that can be used by the first processor. The first processor is connected to the first polarity detection circuit and the first power supply module, respectively, and is used to receive the fault high-frequency signal for multi-core AC cable fault monitoring.

9. The apparatus according to claim 8, characterized in that, The first polarity detection circuit includes a first positive polarity detection circuit and a first negative polarity detection circuit, wherein both the first positive and negative polarity detection circuits include a capacitor-adjustable RC integrator circuit and a Schmitt trigger circuit.

10. The apparatus according to claim 7 or 8, characterized in that, The first duplex switching circuit is a duplex filter circuit or an antenna switch; and / or, the first power-taking module further includes an energy storage battery, which is used to store the electrical energy converted by the first power-taking module.

11. The apparatus according to claim 10, characterized in that, The second load has the same structure as the first load.

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