A partial discharge detection device for high voltage cable joint

Abstract

The application provides a partial discharge detection device for high-voltage cable intermediate joint, which comprises a first partial discharge sensor directly installed on a straight-through intermediate joint of a high-voltage cable, a second partial discharge sensor directly installed on an insulation-type intermediate joint of the high-voltage cable, and a partial amplification signal processing circuit connected with the first partial discharge sensor and the second partial discharge sensor respectively. The application designs a partial discharge sensor and a detection circuit directly installed on the intermediate joint of the high-voltage cable, and proposes a defect joint identification method for the insulation-type intermediate joint of the high-voltage cable. Since the partial discharge sensor is directly installed on the intermediate joint of the cable, the detection sensitivity is much higher than that of the cable, and the defect joint identification method for the insulation-type intermediate joint of the high-voltage cable based on energy distribution is proposed, so that the insulation state monitoring effect of the cable accessory can be improved.

Description

Technical Field

[0001] This invention belongs to the technical field of partial discharge detection devices for cable joints, and in particular relates to a partial discharge detection device for intermediate joints of high-voltage cables. Background Technology

[0002] High-voltage cross-linked polyethylene insulated power cables are widely used in urban power grids due to their good electrical performance and ease of installation. When high-voltage power cable lines are long, intermediate joints are often required. There are two types of intermediate joints: 1. Straight-through intermediate joints are required for cable splicing; 2. Insulated intermediate joints are required for cross-interconnection and grounding. Since the service life of cables is 30 years, cables and accessories are highly susceptible to failure during long-term operation. According to statistics from the State Grid Corporation of China, accessory failures account for more than 70% of cable line failures.

[0003] Partial discharge faults are both a major cause of cable accessory failures and a key characteristic of cable accessory status. Therefore, monitoring partial discharge in cable accessories to determine their health status is of paramount importance in the operation and maintenance of power transmission and transformation equipment by the State Grid Corporation of China.

[0004] Currently, the partial discharge detection of cable accessories often adopts the high-frequency current method, which detects the partial discharge current pulse signal on the grounding wire through the high-frequency current transformer inside the cable joint. This method has the following disadvantages: (1) When the high-frequency current transformer is not installed in a suitable position, it cannot effectively monitor the partial discharge signal of the cable joint; (2) It requires local modification of the cable joint structure, which destroys the original compact insulation structure and may have an adverse effect on electrical and mechanical performance.

[0005] Xi'an Jiaotong University has proposed an indirect method for detecting partial discharge in cable accessories. This method is based on the principle of capacitive coupling, where a metal strip is wound around the semiconductive layer of the cable near the intermediate joint. This metal strip and the cable core form a high-voltage capacitor, while the metal strip and the grounding copper mesh form a low-voltage capacitor. The partial discharge signal is measured using the principle of capacitive voltage division. However, this method has a drawback: it indirectly reflects the partial discharge situation at the intermediate joint using a cable sensor installed near the joint, rather than directly detecting the partial discharge signal at the joint. This means the detected signal may be one or a combination of cable partial discharge, cable accessory partial discharge, ground potential interference, or a combination of all three, resulting in poor monitoring of the insulation condition of cable accessories in practical applications. Summary of the Invention

[0006] In view of this, the present invention aims to overcome the shortcomings of the above-mentioned problems in the prior art and proposes a partial discharge detection device for high-voltage cable intermediate joints.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0008] A partial discharge detection device for a high-voltage cable intermediate joint includes a first partial discharge sensor directly installed on a straight-through intermediate joint of a high-voltage cable, a second partial discharge sensor directly installed on an insulated intermediate joint of a high-voltage cable, and a partial amplification signal processing circuit connected to the first partial discharge sensor and the second partial discharge sensor respectively.

[0009] The first partial discharge sensor includes a first wire core, a first outer semiconductive layer and a grounding copper mesh, a first high-voltage electrode, a first 50Ω resistor, a first BNC waterproof connector, and a first coaxial signal cable. The grounding copper mesh with the outer semiconductor layer removed is coated with 2mm of epoxy resin. A circular copper electrode with a length less than the cut length of the epoxy resin and a thickness of 1mm is attached to the epoxy resin. The copper electrode is soldered with signal leads. The circular copper electrode and the first wire core form a high-voltage capacitor. The circular copper electrode, the first outer semiconductor layer and the grounding copper mesh form a low-voltage capacitor. The partial discharge signal detected on the circular copper electrode is sent to the partial discharge signal processing circuit through the first 50Ω resistor, the first BNC waterproof connector and the first coaxial signal cable.

[0010] The second partial discharge sensor includes a second wire core, a second outer semiconductive layer and a grounding copper mesh, a second high-voltage electrode, a second 50Ω resistor, a second BNC waterproof connector, a second coaxial signal cable, and an insulating flange. The grounding copper mesh of the outer semiconductive layer is removed. A ring-shaped copper electrode, shorter than the cut-off grounding copper mesh length and 1mm thick, is attached to the outer semiconductive layer. Signal leads are soldered to the copper electrode. Epoxy resin is applied to the copper electrode with a thickness of 2mm. The grounding copper mesh is then connected to the outer surface of the epoxy resin using two semi-circular flanges. The ring-shaped copper electrode and the second wire core form a high-voltage capacitor. The ring-shaped copper electrode and the second outer shell of the intermediate connector form a low-voltage capacitor. The partial discharge signal detected on the ring-shaped copper electrode is sent to the partial discharge signal processing circuit through the second 50Ω resistor, the second BNC waterproof connector, and the second coaxial signal cable.

[0011] Furthermore, the first 50Ω resistor is made of 0.02mm constantan wire twin-wound, the first BNC connector is a waterproof IP65 BNC connector, and waterproof sealant is applied to the threaded part of the first BNC connector and the first housing. The signal is transmitted using an RF coaxial signal cable with a characteristic impedance of 50Ω.

[0012] Furthermore, the second 50Ω resistor is made of 0.02mm constantan wire twin-wound, the second BNC connector is a waterproof IP65 BNC connector, and waterproof sealant is applied to the threaded part of the second BNC connector and the second housing. The signal is transmitted using an RF coaxial signal cable with a characteristic impedance of 50Ω.

[0013] Furthermore, the partial discharge signal processing circuit includes a DC blocking capacitor and an active low-pass filter, wherein the amplifier is powered by a regulated power supply.

[0014] Furthermore, the cutoff frequency of the low-pass filter is 300MHz.

[0015] Furthermore, for high-voltage cable straight-through joints, the health status of the straight-through joint is determined based on the first partial discharge sensor installed in each phase.

[0016] Furthermore, for three-phase cable systems containing insulated joints, the criterion for defective insulated joints is:

[0017] (1) The phase with the smallest signal amplitude detected by the second partial discharge sensor installed on the insulating joint is phase X;

[0018] (2) Determine that the cross-connection of the X-phase insulation joint is the X-phase and the Y-phase;

[0019] (3) The defective phase is the Z phase, which is the only phase other than the X and Y phases.

[0020] Compared with existing technologies, the partial discharge detection device for high-voltage cable intermediate joints described in this invention has the following advantages:

[0021] (1) The partial discharge detection device for high voltage cable intermediate joints designed in this invention has higher sensitivity than the current sensor currently in use and higher accuracy than the capacitive sensor currently installed on the cable.

[0022] (2) Partial discharge sensors were designed for the different structures of straight-through joints and insulated joints of high-voltage cables. The partial discharge sensor installed on the straight-through joint did not change the structural requirement of the grounding copper grid connectivity of the straight-through joint, and the partial discharge sensor installed on the insulated joint did not change the structural requirement of the segmented insulation of the insulated joint.

[0023] (3) In response to the dustproof and waterproof requirements of high-voltage cable straight-through joints and insulated joints, BNC joints were used to ensure that the introduction of partial discharge sensors would not reduce the dustproof and waterproof rating of intermediate joints.

[0024] (4) In order to meet the requirements of high-frequency partial discharge signal transmission, non-inductive resistors and radio frequency coaxial cables are used for signal transmission to ensure that the high-frequency partial discharge signal is transmitted without distortion.

[0025] (5) Based on simulation analysis and partial discharge test results, a partial discharge signal processing circuit was designed. This circuit consists of a DC blocking capacitor C0 and an active low-pass filter with a cutoff frequency of 300MHz. The amplifier is powered by a regulated power supply. This ensures that all partial discharge signals can pass through the signal processing circuit and filters out higher frequency interference signals.

[0026] (6) Based on the modulus analysis of multi-conductor transmission lines, it was found that the signal amplitude monitored by the three-phase insulation joint exhibited a "two large and one small" characteristic, and a defect criterion for high-voltage cable insulation joints was proposed accordingly. This criterion is simple and effective, and can be conveniently applied to the evaluation of the insulation status of cross-connection insulation joints of three-phase high-voltage cables. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 This is a schematic diagram of the installation of the first partial discharge sensor of the present invention;

[0029] Figure 2 This is a schematic diagram of the installation of the second partial discharge sensor of the present invention;

[0030] Figure 3 This is a schematic diagram of the partial discharge signal processing circuit of the present invention;

[0031] Figure 4 This is a schematic diagram illustrating the relationship between the detection impedance current and the axial length of the present invention;

[0032] Figure 5 This is a schematic diagram illustrating the relationship between the detection impedance current and the radial distance according to the present invention;

[0033] Figure 6 This is a schematic diagram of the cross-interconnection of three-phase cables according to the present invention;

[0034] Figure 7 This is a schematic diagram of the signal amplitude of the three-phase insulated connector sensor of the present invention.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1-First conductor core, 2-First conductor crimping tube, 3-First cross-linked polyethylene insulation, 4-First stress cone, 5-First silicone rubber insulation, 6-First outer semiconducting layer and grounding copper mesh, 7-First outer shell, 8-First high-voltage electrode, 9-First 50Ω resistor, 10-First BNC waterproof connector, 11-First coaxial signal cable, 12-Second conductor core, 13-Second conductor crimping tube, 14-Second cross-linked polyethylene insulation, 15-Second stress cone, 16-Second silicone rubber insulation, 17-Second outer semiconducting layer and grounding copper mesh, 18-Second outer shell, 19-Second high-voltage electrode, 20-Second 50Ω resistor, 21-Second BNC waterproof connector, 22-Second coaxial signal cable, 23-Second insulating flange. Detailed Implementation

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0038] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the 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 invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" 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 will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0040] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] like Figure 1-2As shown, the present invention discloses a partial discharge detection device for a high-voltage cable intermediate joint, including a first partial discharge sensor directly installed on a straight-through intermediate joint of a high-voltage cable, a second partial discharge sensor directly installed on an insulated intermediate joint of a high-voltage cable, and a partial amplification signal processing circuit connected to the first partial discharge sensor and the second partial discharge sensor respectively.

[0042] The first partial discharge sensor includes a first wire core 1, a first outer semiconductive layer and a grounding copper mesh 6, a first high-voltage electrode 8, a first 50Ω resistor 9, a first BNC waterproof connector 10, and a first coaxial signal cable 11. The grounding copper mesh with the outer semiconductive layer removed is coated with 2mm of epoxy resin. A circular copper electrode with a length less than the cut length of the epoxy resin and a thickness of 1mm is attached to the epoxy resin. The copper electrode is soldered with signal leads. The circular copper electrode and the first wire core 11 form a high-voltage capacitor, and the circular copper electrode, the first outer semiconductive layer, and the grounding copper mesh 6 form a low-voltage capacitor. The partial discharge signal detected on the circular copper electrode is sent to the partial discharge signal processing circuit through the first 50Ω resistor 9, the first BNC waterproof connector 10, and the first coaxial signal cable 11. During installation, the first partial discharge sensor is connected to the intermediate connector via the first outer shell 7, the first conductor crimping tube 2, the first cross-linked polyethylene insulation 3, the first stress cone 4, and the first silicone rubber insulation 5.

[0043] Specifically, the first 50Ω resistor 9 is made of 0.02mm constantan wire twin-wound, the first BNC waterproof connector 10 is a BNC connector with a waterproof rating of IP65, and waterproof sealant is applied to the threaded part of the first BNC waterproof connector 10 and the first housing 7. The signal is transmitted using a radio frequency coaxial signal cable with a characteristic impedance of 50Ω.

[0044] The second partial discharge sensor includes a second wire core 12, a second outer semiconductive layer and a grounding copper mesh 17, a second high-voltage electrode 19, a second 50Ω resistor 20, a second BNC waterproof connector 21, a second coaxial signal cable 22, and an insulating flange 23. The grounding copper mesh of the outer semiconductive layer is removed, and a ring-shaped copper electrode with a length less than the cut grounding copper mesh and a thickness of 1mm is attached to the outer semiconductive layer. The signal lead is soldered to the copper electrode, and a 2mm layer of epoxy resin is applied to the copper electrode. The grounding copper mesh is then connected to the outer surface of the epoxy resin using two semi-circular flanges. The ring-shaped copper electrode and the second wire core 12 form a high-voltage capacitor, and the ring-shaped copper electrode and the second outer shell 18 of the intermediate connector form a low-voltage capacitor. The partial discharge signal detected on the ring-shaped copper electrode is sent to the partial discharge signal processing circuit through the second 50Ω resistor, the second BNC waterproof connector, and the second coaxial signal cable. During installation, the second partial discharge sensor is connected to the intermediate joint via the second housing 18, the second conductor crimping tube 13, the second cross-linked polyethylene insulation 14, the second stress cone 15, and the second silicone rubber insulation 16.

[0045] Specifically, the second 50Ω resistor 20 is made of 0.02mm constantan wire twin-wound, the second BNC waterproof connector 21 is a BNC connector with a waterproof rating of IP65, and waterproof sealant is applied to the threaded part of the second BNC waterproof connector 21 and the second housing 18. The signal is transmitted using a radio frequency coaxial signal cable with a characteristic impedance of 50Ω.

[0046] like Figure 3 As shown, the partial discharge signal processing circuit consists of a DC blocking capacitor C0 and an active low-pass filter, with the amplifier powered by a regulated power supply. Simulation analysis and partial discharge testing revealed that the spectrum of the high-voltage cable joint is mainly distributed within 600MHz, with two peaks at 50MHz and 230MHz respectively. The main energy of the partial discharge signal from the joint is concentrated between 10MHz and 300MHz. Preferably, the cutoff frequency of the low-pass filter is designed to be 300MHz.

[0047] When the radial radius of the annular copper electrode is 18 mm, the detection impedance Z L The relationship between the current at both ends and the axial length is as follows: Figure 4 As shown. By Figure 4 It can be seen that as the axial length increases, the detection impedance Z... L The current at both ends gradually increases. While maintaining an axial length of 20mm, changing the radial distance of the annular copper electrode results in a detection impedance Z... L The relationship between the current at both ends and the radial distance is as follows: Figure 5 As shown. By Figure 5 It can be seen that as the radial distance increases, the detection impedance Z... LThe current at both ends gradually decreases. While ensuring the signal is not distorted, the axial length of the capacitive sensor can be appropriately increased, while the radial distance can be decreased. Preferably, an axial length of 20mm and a radial distance of 18mm are selected as the optimal design parameters for the annular copper electrode.

[0048] For high-voltage cable straight-through joints, the health status of the joint can be determined by partial discharge sensors installed on each phase. For high-voltage cable insulated joints, since they are three-phase cable cross-connection joints, their grounding copper mesh is isolated by insulating flanges and connected by medium-voltage cross-linked polyethylene cables. The core of the medium-voltage cross-linked polyethylene cable and the grounding copper mesh are respectively connected to the grounding copper mesh leads at both ends of the high-voltage cable, and then interconnected and transposed in the cross-connection box. Therefore, the partial discharge signal detected by the partial discharge sensor of the insulated joint installed at the cross-connection transposition point is affected not only by the partial discharge of the insulated joint of this phase, but also by the partial discharge of the insulated joints of the other two phases. For three-phase cable systems containing insulated joints, mode analysis can be performed using the multi-conductor transmission line modulus transformation theory. Assume that the characteristic admittance of the three-phase cable on the side where partial discharge occurs is Y. C1 The characteristic admittance of the three-phase cable away from the partial discharge side is Y. C2 Based on the cross-transposition order, we get:

[0049] Y c2 =M T Y c M (1)

[0050] Where Y C Let M be the characteristic admittance when arranged in the normal order, and M be the cross-transposition matrix. Taking the cross-transposition order AB, BC, CA as an example, M is:

[0051]

[0052] The refractive index at the intersection is derived as follows:

[0053] α=E+(M T Y c MY c (M) T Y c M+Y c ) -1 (3)

[0054] Equation (3) can be used to derive the ratio of sensor signals on the cross-connected insulation joints. Assuming partial discharge occurs at the A-phase insulation joint, the ratio of sensor signals on the three-phase insulation joints is 1+2x:1:1+2x, where x is the ratio of the external characteristic admittance to the internal characteristic admittance of the three-phase cable. That is, partial discharge occurs at the A-phase insulation joint, and the three-phase transposition sequence is as follows: Figure 6As shown, when the three-phase transposition sequence is AB, BC, CA, the signal amplitude of the three-phase insulation joint sensor is as follows: Figure 7 As shown, the partial discharge signal amplitudes of phase A and phase C insulation joints are greater than those of phase B insulation joints, exhibiting a "two large and one small" amplitude characteristic. The criterion for defective insulation joints is:

[0055] (1) The phase with the smallest signal amplitude detected by the partial discharge sensor installed on the insulating joint is phase X;

[0056] (2) Determine that the cross-connection of the X-phase insulation joint is the X-phase and the Y-phase;

[0057] (3) The defective phase is the Z phase, which is the only phase other than the X and Y phases.

[0058] This invention designs a partial discharge sensor and detection circuit that can be directly installed on the intermediate joint of a high-voltage cable, and proposes a method for identifying defective joints in high-voltage cable insulation intermediate joints. Because the partial discharge sensor is directly installed on the cable intermediate joint, its detection sensitivity is much higher than that installed on the cable itself. Furthermore, a method for identifying defective joints in high-voltage cable insulation intermediate joints based on energy distribution is proposed, which can improve the monitoring effect of the insulation condition of cable accessories.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A partial discharge detection device for a high-voltage cable intermediate joint, characterized in that: It includes a first partial discharge sensor directly installed on a straight-through intermediate joint of a high-voltage cable, a second partial discharge sensor directly installed on an insulated intermediate joint of a high-voltage cable, and a partial amplification signal processing circuit connected to the first partial discharge sensor and the second partial discharge sensor respectively. The first partial discharge sensor includes a first wire core, a first outer semiconductive layer and a grounding copper mesh, a first high-voltage electrode, a first 50Ω resistor, a first BNC waterproof connector, and a first coaxial signal cable. The grounding copper mesh with the outer semiconductor layer removed is coated with 2mm of epoxy resin. A circular copper electrode with a length less than the cut length of the epoxy resin and a thickness of 1mm is attached to the epoxy resin. The copper electrode is soldered with signal leads. The circular copper electrode and the first wire core form a high-voltage capacitor. The circular copper electrode, the first outer semiconductor layer and the grounding copper mesh form a low-voltage capacitor. The partial discharge signal detected on the circular copper electrode is sent to the partial discharge signal processing circuit through the first 50Ω resistor, the first BNC waterproof connector and the first coaxial signal cable. The second partial discharge sensor includes a second wire core, a second outer semiconductive layer and a grounding copper mesh, a second high-voltage electrode, a second 50Ω resistor, a second BNC waterproof connector, a second coaxial signal cable, and an insulating flange. The grounding copper mesh of the outer semiconductive layer is removed. A ring-shaped copper electrode, shorter than the cut-off grounding copper mesh length and 1mm thick, is attached to the outer semiconductive layer. Signal leads are soldered to the copper electrode. Epoxy resin is applied to the copper electrode with a thickness of 2mm. The grounding copper mesh is then connected to the outer surface of the epoxy resin using two semi-circular flanges. The ring-shaped copper electrode and the second wire core form a high-voltage capacitor. The ring-shaped copper electrode and the second outer shell of the intermediate connector form a low-voltage capacitor. The partial discharge signal detected on the ring-shaped copper electrode is sent to the partial discharge signal processing circuit through the second 50Ω resistor, the second BNC waterproof connector, and the second coaxial signal cable.

2. The partial discharge detection device for a high-voltage cable intermediate joint according to claim 1, characterized in that: The first 50Ω resistor is made of 0.02mm constantan wire twin-wound, the first BNC waterproof connector is a BNC connector with a waterproof rating of IP65, and waterproof sealant is applied to the thread of the first BNC waterproof connector and the first housing. The signal is transmitted using a radio frequency coaxial signal cable with a characteristic impedance of 50Ω.

3. The partial discharge detection device for a high-voltage cable intermediate joint according to claim 1, characterized in that: The second 50Ω resistor is made of 0.02mm constantan wire twin-wound, the second BNC waterproof connector is a BNC connector with a waterproof rating of IP65, and waterproof sealant is applied to the threads of the second BNC waterproof connector and the second housing. The signal is transmitted using a radio frequency coaxial signal cable with a characteristic impedance of 50Ω.

4. The partial discharge detection device for a high-voltage cable intermediate joint according to claim 1, characterized in that: The partial discharge signal processing circuit includes a DC blocking capacitor and an active low-pass filter, wherein the amplifier is powered by a regulated power supply.

5. The partial discharge detection device for a high-voltage cable intermediate joint according to claim 4, characterized in that: The cutoff frequency of the low-pass filter is 300MHz.

6. The partial discharge detection device for a high-voltage cable intermediate joint according to claim 1, characterized in that: For high-voltage cable straight-through joints, the health status of the straight-through joint is determined based on the first partial discharge sensor installed in each phase.

7. The partial discharge detection device for a high-voltage cable intermediate joint according to claim 1, characterized in that: For a three-phase cable system containing insulated joints, the criterion for defective insulated joints is: (1) The phase with the smallest signal amplitude detected by the second partial discharge sensor installed on the insulating joint is phase X; (2) Determine that the cross-connection of the X-phase insulation joint is the X-phase and the Y-phase; (3) The defective phase is the Z phase, which is the only phase other than the X and Y phases.

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