Monitoring Method and Monitoring System for Resistive Current of Transmission Cable Lightning Arrester

Abstract

The present invention discloses a method for monitoring the resistive current of a transmission cable lightning arrester, which includes the following steps: determining the positions of three lightning arresters to be monitored, and defining a first transmission device, a second transmission device, and a third transmission device; collecting the current signals of the cable body and the current signals on the sheath grounding wire in each transmission device; performing data processing on the collected current signals, and calculating the vector values of the fundamental waves of each current signal by using the single-point interpolation Fourier coefficient method; performing phase compensation on the obtained current vector values; calculating the three-phase leakage current of the transmission cable based on the phase-compensated current vector values; and calculating the resistive current of the three-phase lightning arrester based on the three-phase leakage current of the transmission cable. When applied, the present invention has a low safety risk, accurate monitoring results, can realize the on-line monitoring of the resistive current of the lightning arrester, and can evaluate the operating state of the lightning arrester.

Description

Technical Field

[0001] The present invention relates to the field of condition monitoring of lightning arresters, specifically a method and a monitoring system for monitoring the resistive current of transmission cable lightning arresters. Background Art

[0002] Lightning arresters are widely used in power transmission systems due to their excellent non-linear volt-ampere characteristics and current-carrying capacity. They are usually connected in parallel with the terminals of transmission cables to protect the transmission cables and their related equipment. When a normal operating voltage is applied to the lightning arrester, the lightning arrester is in a cut-off state, with a relatively large internal resistance value, and does not affect the normal operation of the transmission cable. When an overvoltage is applied to the lightning arrester, its internal resistance value drops sharply to release the energy of the overvoltage, limit the overvoltage borne by the insulation of the transmission cable, and prevent the transmission cable from being damaged by the overvoltage. Under the action of factors such as humidity, temperature, and electric field, the lightning arrester will age, and subsequent breakdown accidents of the lightning arrester are likely to occur, seriously threatening the stable operation of the power transmission system. Therefore, online monitoring of the operating state of the lightning arrester can ensure the safe and stable operation of the power system. The continuous operating current (total current) of the lightning arrester can effectively reflect the operating state of the lightning arrester. Its total current is mainly composed of resistive current and capacitive current. Usually, the proportion of the resistive current component in the total current is 5%-20%. When the lightning arrester ages, the capacitive current component remains almost unchanged, while the resistive current component increases significantly. Moreover, the active power generated by the resistive current component will cause abnormal heating of the lightning arrester, gradually damaging the insulation performance of the lightning arrester and seriously shortening the service life of the lightning arrester. Therefore, the operating state of the lightning arrester can be accurately evaluated by monitoring the resistive current of the lightning arrester.

[0003] Chinese Patent Publication No. CN117405172A published on January 16, 2024, discloses an invention patent application with the invention title "Method, System and Device for Evaluating the Operating State of Lightning Arresters Based on Multidimensional Detection". It provides a method for calculating the resistive current of a lightning arrester by using the operating voltage and total current of the lightning arrester, and cooperating with parameters such as temperature difference and partial discharge intensity to evaluate the operating state of the lightning arrester. This method requires accurate measurement of the operating voltage of the lightning arrester, which not only requires connecting voltage transformer equipment, has a large wiring difficulty, but also has a safety risk of high-voltage measurement of primary equipment.

[0004] The Chinese patent publication number CN115575856A published an invention patent application with the invention title "Online monitoring method and system for leakage current of lightning arresters in transmission cable terminals" on January 6, 2023. It provides a method for recording the instantaneous mutation vector of the total current of the lightning arrester and using the power factor of the power system and the load current of the transmission cable to judge whether the resistive current component is abnormal. This method not only does not consider the influence of factors such as power factor fluctuation and the no-load state of the transmission cable on the diagnosis result, but also the instantaneous mutation vector of the total current cannot reflect the slow aging state of the lightning arrester.

[0005] The Chinese patent publication number CN116068262A published an invention patent application with the invention title "An online monitoring method for resistive current of zinc oxide lightning arresters on overhead transmission lines" on May 5, 2023. It provides a method for directly comparing the phases of the total current of the lightning arrester and the sheath grounding current of the transmission cable to calculate the value of the resistive current in the total current of the lightning arrester. This method directly takes the sheath grounding current of the transmission cable at a single measurement point as the capacitive current of the transmission cable, without considering the influence of the sheath induced circulating current component and the sheath grounding method in the transmission cable, which is likely to cause incorrect calculation results of the resistive current of the lightning arrester.

[0006] In summary, the prior art cannot monitor the operating state of lightning arresters safely, accurately and efficiently. Summary of the Invention

[0007] The purpose of the present invention is to overcome the deficiency that the prior art cannot monitor the operating state of lightning arresters safely, accurately and efficiently, and provides a monitoring method for the resistive current of transmission cable lightning arresters. When applied, it does not need to measure the operating voltage of the lightning arrester, has a simple wiring, low safety risk, accurate monitoring results, can realize the online monitoring of the resistive current of the lightning arrester, and can evaluate the operating state of the lightning arrester.

[0008] The purpose of the present invention is mainly realized through the following technical solutions:

[0009] In the first aspect, the present application proposes a monitoring method for the resistive current of transmission cable lightning arresters, including the following steps:

[0010] Step 1: Determine three positions of lightning arresters to be monitored. The three lightning arresters to be monitored are connected to the three phases of the transmission cable one by one. Select any one of the A phase, B phase and C phase of the transmission cable and define it as the X phase. Define the first transmission device, the second transmission device and the third transmission device. Among them,

[0011] The first transmission device is configured to be the transmission cable and the lightning arrester at the lightning arrester to be monitored;

[0012] The second power transmission device is configured as the power transmission cable at the first through joint adjacent to the arrester to be monitored;

[0013] The third power transmission device is configured as the power transmission cable at the first insulating joint or cable terminal adjacent to the arrester to be monitored; wherein, the through joint, insulating joint and cable terminal are all located on the same side of the arrester to be monitored; the through joint is configured as the first power transmission cable accessory adjacent to the arrester to be monitored; the insulating joint and cable terminal are configured as the first power transmission cable accessory adjacent to the arrester to be monitored, or when the first power transmission cable accessory adjacent to the arrester to be monitored is a through joint, the second power transmission cable accessory adjacent to the arrester to be monitored;

[0014] Step 2: Collect the current signals I a1 、I b1 、I c1 on the sheath grounding wires of the A-phase, B-phase and C-phase of the power transmission cable in the first power transmission device, collect the current signal I X1 of the X-phase cable body of the power transmission cable in the first power transmission device, collect the current signals I AS1 、I BS1 、I CS1 on the base grounding wires of the A-phase, B-phase and C-phase arresters to be monitored in the first power transmission device, collect the current signals I a2 、I b2 、I c2 on the sheath grounding wires of the A-phase, B-phase and C-phase of the second power transmission device, collect the current signal I X2 of the X-phase cable body of the second power transmission device, collect the current signals I a3 、I b3 、I c3 on the sheath grounding wires of the A-phase, B-phase and C-phase of the third power transmission device, collect the current signal I X3 of the X-phase cable body of the third power transmission device;

[0015] Step 3: Perform data processing on the collected current signals, and use the single-point interpolation Fourier coefficient method to calculate the vector values of the fundamental waves of each current signal, which are defined as current vector values, including the current vector values I a_1 、I b_1 、I c_1 on the sheath grounding wires of the A-phase, B-phase and C-phase of the power transmission cable in the first power transmission device, the current vector value I X_1 of the X-phase cable body of the power transmission cable in the first power transmission device, the current vector values I AS_1 、I BS_1 、I CS_1, the current vector values \(I\) of the A-phase, B-phase, and C-phase sheath grounding wires of the second transmission device a_2 , \(I\) b_2 , \(I\) c_2 , the current vector value \(I\) of the X-phase cable body of the second transmission device X_2 , the current vector values \(I\) of the A-phase, B-phase, and C-phase sheath grounding wires of the third transmission device a_3 , \(I\) b_3 , \(I\) c_3 , the current vector value \(I\) of the X-phase cable body of the third transmission device X_3 , where the current vector value of the X-phase cable sheath grounding wire of the transmission cable in the first transmission device is defined as \(I\) x_1 , the current vector value of the X-phase cable sheath grounding wire of the second transmission device is defined as \(I\) x_2 , the current vector value of the X-phase cable sheath grounding wire of the third transmission device is defined as \(I\) x_3 ; where, when the first transmission cable accessory adjacent to the lightning arrester to be monitored is an insulating joint or a terminal, the second transmission device does not exist, and \(I\) X_2 = \(I\) X_1 ; \(I\) a_2 = 0A∠0°; \(I\) b_2 = 0A∠0°; \(I\) c_2 = 0A∠0°;

[0016] Step 4: Perform phase compensation on the obtained current vector values to obtain the compensated current vector values \(I'\) a_1 , \(I'\) b_1 , \(I'\) c_1 , \(I'\) X_1 , \(I'\) AS_1 , \(I'\) BS_1 , \(I'\) CS_1 , \(I'\) a_3 , \(I'\) b_3 , \(I'\) c_3 , \(I'\) X_3 ;

[0017] Step 5: Based on the compensated current vector values, calculate the three-phase leakage currents \(i\) of the transmission cable a , \(i\) b , \(i\) c ;

[0018] Step 6: Based on the three-phase leakage currents of the transmission cable, calculate the resistive currents of the A-phase, B-phase, and C-phase lightning arresters.

[0019] Further, the specific method for calculating the vector value of the fundamental wave of the collected current signal by using the single-point interpolation Fourier coefficient method in step 3 is:

[0020] Let any collected current signal be y(n), and determine the interpolation point value k:

[0021] k = T N f J / f s

[0022] Where, T N is the number of sampling points, f J is the fundamental frequency of the power system, f s is the sampling frequency;

[0023] Calculate the Fourier coefficient Y of the fundamental wave according to the interpolation point value k:

[0024]

[0025] Where, j is the imaginary unit, and the Fourier coefficient Y is defined as the current vector value of the current signal y(n).

[0026] Furthermore, the specific content of step 4 is as follows:

[0027] Step 4.1: According to the KCL law, determine the phase compensation reference channel: Select the second transmission device as the phase compensation reference device:

[0028] For the first transmission device, select the current vector value I X_1 of the X-phase cable body of the transmission cable in the first transmission device as the first reference channel, and select the current vector value I X_2 of the X-phase cable body of the second transmission device as the second reference channel;

[0029] For the third transmission device, select the current vector value I X_3 of the X-phase cable body of the third transmission device as the third reference channel, and select the difference I X_2 between the current vector value I x_2 of the X-phase cable body of the second transmission device and the current vector value I X_2 -I x_2 of the current vector value on the X-phase cable sheath grounding wire of the second transmission device as the fourth reference channel;

[0030] Step 4.2: Calculate the phase error:

[0031] For the first transmission device, define the phase difference between the first reference channel I X_1 and the second reference channel I X_2 as the first phase error ΔP1:

[0032] ΔP1 = angle(I X_1 ) - angle(I X_2 )

[0033] For the third power transmission equipment, define the third reference channel I X_3 and the fourth reference channel I X_2 -I x_2 The phase difference of is the second phase error ΔP2:

[0034] ΔP2 = angle(I X_3 ) - angle(I X_2 -I x_2 )

[0035] where angel() represents obtaining the phase of the vector;

[0036] Step 4.3: Perform phase compensation:

[0037] Keep all the current vector values of the phase compensation reference equipment unchanged. For the first power transmission equipment, subtract the first phase error ΔP1 from the phases of all the current vector values to obtain the compensated current vector values I' a_1 、I' b_1 、I' c_1 、I' X_1 、I' AS_1 、I' BS_1 、I' CS_1 ; For the third power transmission equipment, subtract the second phase error ΔP2 from the phases of all the current vector values to obtain the compensated current vector values I' a_3 、I' b_3 、I' c_3 、I' X_3 .

[0038] Furthermore, the specific step 5 is as follows:

[0039] When the power transmission cable accessory at the third power transmission equipment is a cable terminal, the three-phase leakage currents of the power transmission cable connected to the three surge arresters to be monitored are respectively:

[0040] i a = I' a_1 + I a_2 + I' a_3

[0041] i b = I' b_1 + I b_2 + I' b_3

[0042] i c = I' c_1 + I c_2 + I' c_3

[0043] When the power transmission cable accessory at the third power transmission device is an insulating joint, where

[0044] When the cable sheaths on both sides of the insulating joint are connected to the sheath grounding box through a single-core cable sheath grounding wire, the three-phase leakage currents of the power transmission cable connected to the three surge arresters to be monitored are respectively:

[0045] i a = I’ a_1 + I a_2 + I’ a_3

[0046] i b = I’ b_1 + I b_2 + I’ b_3

[0047] i c = I’ c_1 + I c_2 + I’ c_3

[0048] When the cable sheaths on both sides of the insulating joint are connected to the sheath grounding box through a coaxial cable sheath grounding wire, where

[0049] When the cable sheaths on both sides of the insulating joint are in a cross-connected A / B connection mode, the three-phase leakage currents of the power transmission cable connected to the three surge arresters to be monitored are respectively:

[0050] i ac = I’ a_1 - I’ c_1 + I a_2 - I c_2 + I’ a_3

[0051] i ba = I’ b_1 - I’ a_1 + I b_2 - I a_2 + I’ b_3

[0052] i cb = I’ c_1 - I’ b_1 + I c_2 - I b_2 + I’ c_3

[0053] i a = (i ac - i ba ) / 3

[0054] i b = (iba -i cb ) / 3

[0055] i c =(i cb -i ac ) / 3

[0056] When the cable sheaths on both sides of the insulating joint are cross-connected in an A / C connection mode, the three-phase leakage currents of the power transmission cable connected to the three surge arresters to be monitored are respectively:

[0057] i ab =I’ a_1 -I’ b_1 +I a_2 -I b_2 +I’ a_3

[0058] i bc =I’ b_1 -I’ c_1 +I b_2 -I c_2 +I’ b_3

[0059] i ca =I’ c_1 -I’ a_1 +I c_2 -I a_2 +I’ c_3

[0060] i a =(i ab -i ca ) / 3

[0061] i b =(i bc -i ab ) / 3

[0062] i c =(i ca -i bc ) / 3

[0063] Among them, i ac 、i ba 、i cb 、i ab 、i bc 、i ca are the line leakage currents of the cables of phases AC, BA, CB, AB, BC, and CA respectively.

[0064] Furthermore, step 6 is specifically as follows:

[0065] Step 6.1: Determine the phase of the main core voltage of the power transmission cable:

[0066]

[0067] Among them, U A , U B , U C respectively represent the three-phase voltages of the main cores of the power transmission cables, and angle() represents obtaining the phase of the vector value;

[0068] Step 6.2: Calculate the resistive current of the arrester:

[0069] Resistive current of the arrester in phase A: I ASZ_1 = F(I’ AS_1 ){cos[angle(I’ AS_1 ) - angle(U A )]}

[0070] Resistive current of the arrester in phase B: I BSZ_1 = F(I’ BS_1 ){cos[angle(I’ BS_1 ) - angle(U B )]}

[0071] Resistive current of the arrester in phase C: I CSZ_1 = F(I’ CS_1 ){cos[angle(I’ CS_1 ) - angle(U C )]}

[0072] Step 6.3: Substitute the formula obtained in Step 6.1 into the formula obtained in Step 6.2 to obtain:

[0073] Resistive current of the arrester in phase A: I ASZ_1 = F(I’ AS_1 ){sin[angle(i a ) - angle(I’ AS_1 )]}

[0074] Resistive current of the arrester in phase B: I BSZ_1 = F(I’ BS_1 ){sin[angle(i b ) - angle(I’ BS_1 )]}

[0075] Resistive current of the arrester in phase C: I CSZ_1 = F(I’ CS_1 ){sin[angle(i c ) - angle(I’ CS_1 )]}

[0076] Among them, F() represents obtaining the amplitude of a vector.

[0077] In a second aspect, the present application also proposes a monitoring system for the resistive current of a transmission cable lightning arrester to implement the monitoring method for the resistive current of a transmission cable lightning arrester as described above, including a first current monitoring device, a second current monitoring device, and a third current monitoring device, where:

[0078] The first current monitoring device is used to monitor and collect the current signals I a1 、I b1 、I c1 on the sheath grounding wires of the A-phase, B-phase, and C-phase of the transmission cable in the first transmission equipment, and is used to monitor and collect the current signal I X1 of the X-phase cable body in the first transmission equipment, and is used to monitor and collect the current signals I AS1 、I BS1 、I CS1 on the grounding wires of the bases of the A-phase, B-phase, and C-phase arresters to be monitored in the first transmission equipment;

[0079] The second current monitoring device is used to monitor and collect the current signals I a2 、I b2 、I c2 on the sheath grounding wires of the A-phase, B-phase, and C-phase of the second transmission equipment, and is used to monitor and collect the current signal I X2 of the X-phase cable body in the second transmission equipment;

[0080] The third current monitoring device is used to monitor and collect the current signals I a3 、I b3 、I c3 on the sheath grounding wires of the A-phase, B-phase, and C-phase of the third transmission equipment, and is used to monitor and collect the current signal I X3 of the X-phase cable body in the third transmission equipment.

[0081] Furthermore, the monitoring system for the resistive current of a transmission cable lightning arrester further includes a data processing unit, and the data processing unit is used to receive and process the current signals of the first current monitoring device, the second current monitoring device, and the third current monitoring device.

[0082] Furthermore, the data processing unit is a computer.

[0083] In summary, the present invention has the following beneficial effects compared with the prior art:

[0084] (1) The present invention monitors and collects the full current of the lightning arrester, the sheath current of the power transmission cable, and the body current of the power transmission cable, obtains the phase of the operating voltage through the vector relationship between the currents, and realizes the monitoring of the resistive current of the lightning arrester without connecting a voltage transformer device, simplifies the wiring, and avoids the safety risks of high-voltage measurement of primary equipment;

[0085] (2) The present invention takes the type of power transmission cable accessories as a variable, collects the full current of the lightning arrester, the sheath current of the power transmission cable, and the body current of the power transmission cable under different power transmission cable accessories conditions through current sensors, and calculates the resistive current of the lightning arrester therefrom, which can be applied to various common grounding methods of the power transmission cable sheath and has high versatility;

[0086] (3) The present invention calculates the fundamental wave vector values of the collected currents through the single-point interpolation Fourier coefficient method, can reduce the negative impact of non-integer-cycle truncated sampling of the signal, and realizes the accurate estimation of the vector values of the current signals;

[0087] (4) The present invention eliminates the phase error of the collected currents through phase compensation, and improves the accuracy of the test results;

[0088] (5) The present invention fully considers the influence of factors such as the induced current of the cable sheath and the grounding method of the power transmission cable sheath, proposes a calculation method for the leakage current of the power transmission cable, and uses the phase relationship between the leakage current of the power transmission cable, the operating voltage of the lightning arrester, the resistive current of the lightning arrester, and the full current of the lightning arrester to accurately calculate the resistive current of the lightning arrester to evaluate the operating state of the lightning arrester. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0090] Figure 1 It is a schematic installation diagram of the first current monitoring device when the A phase is used as the X phase in the embodiment of the present invention;

[0091] Figure 2 It is a schematic installation diagram of the second current monitoring device when the A phase is used as the X phase in the embodiment of the present invention;

[0092] Figure 3 It is a schematic installation diagram of the third current monitoring device when the A phase is used as the X phase in the embodiment of the present invention;

[0093] Figure 4 It is another schematic installation diagram of the third current monitoring device when the A phase is used as the X phase in the embodiment of the present invention;

[0094] Figure 5 It is another schematic installation diagram of the third current monitoring device when the A phase is used as the X phase in the embodiment of the present invention;

[0095] Figure 6 This is another installation schematic diagram of the third current monitoring device when the A phase is used as the X phase in the embodiment of the present invention;

[0096] Figure 7 This is the flow chart of the embodiment of the present invention;

[0097] Figure 8 This is a schematic diagram of a certain discrete current sampling result of the current signal y = 20cos(100t + 60°);

[0098] Figure 9 This is the schematic diagram of the current loop of the A-phase cable sheath in the embodiment of the present invention;

[0099] Figure 10 This is the schematic diagram of the cable sheath current loop corresponding to the insulating joint (coaxial cable sheath grounding wire - cross-connected A / B) in the embodiment of the present invention. Detailed implementation manners

[0100] In order to make the purpose, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments and drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and do not limit the present invention.

[0101] Embodiment:

[0102] The monitoring system for the resistive current of the transmission cable lightning arrester includes a first current monitoring device, a second current monitoring device and a third current monitoring device. Among them, the first current monitoring device is used to monitor and collect the current signals I a1 、I b1 、I c1 on the sheath grounding wires of the A-phase, B-phase and C-phase transmission cables in the first transmission equipment, and is used to monitor and collect the current signal I X1 of the X-phase cable body in the first transmission equipment, and is used to monitor and collect the current signals I AS1 、I BS1 、I CS1 on the grounding wires of the A-phase, B-phase and C-phase lightning arrester bases to be monitored in the first transmission equipment; the second current monitoring device is used to monitor and collect the current signals I a2 、I b2 、I c2 on the sheath grounding wires of the A-phase, B-phase and C-phase in the second transmission equipment, and is used to monitor and collect the current signal I X2 of the X-phase cable body in the second transmission equipment; the third current monitoring device is used to monitor and collect the current signals I a3 、Ib3 and I c3 , for monitoring and collecting the current signal I of the X-phase cable body of the third power transmission device X3 . In this embodiment, three lightning arresters are provided, which are respectively connected to the three phases of the power transmission cable. Any one of the A-phase, B-phase, and C-phase of the power transmission cable is defined as the X-phase, and the first power transmission device, the second power transmission device, and the third power transmission device are defined. The first power transmission device is configured to be the power transmission cable and the lightning arrester to be monitored at the lightning arrester to be monitored; the second power transmission device is configured to be the power transmission cable at the first through joint adjacent to the lightning arrester to be monitored; the third power transmission device is configured to be the power transmission cable at the first insulating joint or cable terminal adjacent to the lightning arrester to be monitored; wherein, the through joint, the insulating joint, and the cable terminal are all on the same side of the lightning arrester to be monitored; the through joint is configured to be the first power transmission cable accessory adjacent to the lightning arrester to be monitored; the insulating joint and the cable terminal are configured to be the first power transmission cable accessory adjacent to the lightning arrester to be monitored, or when the first power transmission cable accessory adjacent to the lightning arrester to be monitored is a through joint, the second power transmission cable accessory adjacent to the lightning arrester to be monitored.

[0103] More specifically, the first current monitoring device includes seven current sensors, and the seven current sensors are respectively used for monitoring and collecting the current signals I on the sheath grounding wires of the A-phase, B-phase, and C-phase of the power transmission cable in the first power transmission device a1 and I b1 and I c1 , the current signal I of the X-phase cable body of the power transmission cable in the first power transmission device X1 and the current signals I on the grounding wires of the bases of the A-phase, B-phase, and C-phase arresters to be monitored in the first power transmission device AS1 and I BS1 and I CS1 ; the second current monitoring device includes four current sensors, and the four current sensors are respectively used for monitoring and collecting the current signals I on the sheath grounding wires of the A-phase, B-phase, and C-phase of the second power transmission device a2 and I b2 and I c2 and the current signal I of the X-phase cable body of the second power transmission device X2 ; the third current monitoring device includes four current sensors, and the four current sensors are respectively used for monitoring and collecting the current signals I on the sheath grounding wires of the A-phase, B-phase, and C-phase of the third power transmission device a3 and I b3 and I c3 and the current signal I of the X-phase cable body of the third power transmission device X3 .

[0104] Taking the A phase of the transmission cable as the X phase as an example, as Figure 1 shown, install the first current monitoring device at the location of the first transmission equipment, that is, install three current sensors at three places: the A-phase cable body, the A-phase cable sheath grounding wire, and the A-phase arrester base grounding wire. The remaining four current sensors are installed on the B-phase cable sheath grounding wire, the B-phase arrester base grounding wire, the C-phase cable sheath grounding wire, and the C-phase arrester base grounding wire. Attached Figure 1 The names corresponding to the reference numerals in the figure are: 101, the A-phase cable terminal of the first transmission equipment; 102, the A-phase cable body of the first transmission equipment; 103, the A-phase cable body current sensor of the first current monitoring device; 104, the direction of the A-phase cable body current sensor of the first current monitoring device; 105, the A-phase cable sheath grounding wire of the first transmission equipment; 106, the A-phase cable sheath current sensor of the first current monitoring device; 107, the direction of the A-phase cable sheath current sensor of the first current monitoring device; 108, the sheath grounding box of the first transmission equipment; 109, the A-phase arrester of the first transmission equipment; 110, the A-phase arrester base grounding wire of the first transmission equipment; 111, the direction of the A-phase arrester full current sensor of the first current monitoring device; 112, the A-phase arrester full current sensor of the first current monitoring device.

[0105] To facilitate the description of the installation positions of the second current monitoring device and the third current monitoring device, define the side of the transmission cable accessory adjacent to the arrester to be monitored as the head end side, and the other side as the tail end side. As Figure 2 shown, when the first transmission cable accessory adjacent to the arrester to be monitored is a straight-through joint, the cable sheaths on both sides of the straight-through joint are connected to the sheath grounding box through a single-core cable sheath grounding wire. One current sensor in the second current monitoring device is installed on the A-phase cable body on the head end side of the straight-through joint, and the remaining three current sensors are installed on the A-phase, B-phase, and C-phase single-core cable sheath grounding wires. Attached Figure 2 The names corresponding to the reference numerals in the figure are: 201, the direction of the A-phase cable body current sensor of the second current monitoring device; 202, the A-phase cable body current sensor of the second current monitoring device; 203, the direction of the A-phase cable body current sensor of the second current monitoring device; 204, the A-phase cable sheath current sensor of the second current monitoring device; 205, the direction of the C-phase cable sheath current sensor of the second current monitoring device; 206, the C-phase cable sheath current sensor of the second current monitoring device; 207, the direction of the B-phase cable sheath current sensor of the second current monitoring device; 208, the B-phase cable sheath current sensor of the second current monitoring device; 209, the sheath grounding box of the second transmission equipment.

[0106] As Figure 3As shown, when the first power transmission cable accessory adjacent to the arrester to be monitored is an insulating joint, and the cable sheath on the first-end side of the insulating joint is connected to the sheath grounding box through a single-core cable sheath grounding wire, one current sensor in the third current monitoring device is installed on the A-phase cable body on the first-end side of the insulating joint, and the other three current sensors are respectively installed on the single-core cable sheath grounding wires of phases A, B, and C.

[0107] As Figure 4 and Figure 5 shown, when the first power transmission cable accessory adjacent to the arrester to be monitored is an insulating joint, and the connection mode of the power transmission cables on both sides of the insulating joint is cross-connected, the cable sheaths on both sides of the insulating joint are connected to the sheath grounding box through coaxial cable sheath grounding wires. One current sensor in the third current monitoring device is installed on the A-phase cable body on the first-end side of the insulating joint, and the other three current sensors are respectively installed on the coaxial cable sheath grounding wires of phases A, B, and C. Attached Figures 3 - 5 The names corresponding to the reference numerals in the figure are: 301, the direction of the A-phase cable body current sensor of the third current monitoring device; 302, the A-phase cable body current sensor of the third current monitoring device; 303, the direction of the A-phase cable body current sensor of the third current monitoring device; 304, the A-phase cable sheath current sensor of the third current monitoring device; 305, the direction of the C-phase cable sheath current sensor of the third current monitoring device; 306, the C-phase cable sheath current sensor of the third current monitoring device; 307, the direction of the B-phase cable sheath current sensor of the third current monitoring device; 308, the B-phase cable sheath current sensor of the third current monitoring device; 309, the sheath grounding box of the third power transmission equipment.

[0108] As Figure 6 shown, when the first power transmission cable accessory adjacent to the arrester to be monitored is a terminal, at the A-phase cable terminal, one current sensor in the third current monitoring device is installed on the A-phase cable body, one current sensor is installed on the A-phase cable sheath grounding wire, and the other two current sensors are respectively installed on the B-phase cable sheath grounding wire and the C-phase cable sheath grounding wire. Attached Figure 6 The names corresponding to the reference numerals in the figure are: 301, the direction of the A-phase cable body current sensor of the third current monitoring device; 302, the A-phase cable body current sensor of the third current monitoring device; 303, the direction of the A-phase cable body current sensor of the third current monitoring device; 304, the A-phase cable sheath current sensor of the third current monitoring device; 309, the sheath grounding box of the third power transmission equipment; 401, the A-phase cable terminal of the third power transmission equipment; 402, the A-phase cable body of the third power transmission equipment; 403, the A-phase cable sheath grounding wire of the third power transmission equipment.

[0109] More specifically, for the case where the first power transmission cable accessory adjacent to the arrester to be monitored is a straight-through joint, since the cable sheaths on both sides of the straight-through joint are electrically connected inside the joint, therefore, at the first power transmission cable accessory adjacent to the end side of the straight-through joint, that is, at the second power transmission cable accessory adjacent to the arrester to be monitored, a third current monitoring device is installed, and its installation position is as Figures 2 - 6 shown. It should be noted that for the second power transmission cable accessory adjacent to the arrester to be monitored, under normal circumstances, it will only be the following four types: insulating joint, the cable sheath is connected to the sheath grounding box through a single-core cable sheath grounding wire; insulating joint, the cable sheath is connected to the sheath grounding box through a coaxial cable sheath grounding wire (the connection method of the power transmission cable is A / B cross-interconnection method); insulating joint, the cable sheath is connected to the sheath grounding box through a coaxial cable sheath grounding wire (the connection method of the power transmission cable is A / C cross-interconnection method); terminal.

[0110] In this embodiment, the monitoring system for the resistive current of the power transmission cable arrester further includes a data processing unit, and the data processing unit is used to receive and process the current signals of the first current monitoring device, the second current monitoring device, and the third current monitoring device. Preferably, the data processing unit is a computer.

[0111] As Figure 7 shown, when the monitoring system described in this embodiment is applied, it includes the following steps: Step 1: Determine the positions of three arresters to be monitored; Step 2: Collect the current signals I a1 、I b1 、I c1 on the sheath grounding wires of phases A, B, and C of the power transmission cable in the first power transmission equipment, collect the current signal I X1 of the cable body of phase X of the power transmission cable in the first power transmission equipment, collect the current signals I AS1 、I BS1 、I CS1 on the base grounding wires of arresters of phases A, B, and C to be monitored in the first power transmission equipment, collect the current signals I a2 、I b2 、I c2 on the sheath grounding wires of phases A, B, and C of the second power transmission equipment, collect the current signal I X2 of the cable body of phase X of the second power transmission equipment, collect the current signals I a3 、I b3 、I c3 on the sheath grounding wires of phases A, B, and C of the third power transmission equipment, collect the current signal I X3; Step 3: Process the collected current signals, and calculate the vector values of the fundamental waves of each current signal by using the single-point interpolation Fourier coefficient method, which are defined as current vector values, including the current vector values \(I\) a_1 、\(I\) b_1 、\(I\) c_1 on the sheath grounding wires of phases A, B, and C of the power transmission cable in the first power transmission device, the current vector value \(I\) X_1 of the cable body of phase X of the power transmission cable in the first power transmission device, the current vector values \(I\) AS_1 、\(I\) BS_1 、\(I\) CS_1 on the sheath grounding wires of the arresters of phases A, B, and C to be monitored in the first power transmission device, the current vector values \(I\) a_2 、\(I\) b_2 、\(I\) c_2 on the sheath grounding wires of phases A, B, and C of the second power transmission device, the current vector value \(I\) X_2 of the cable body of phase X of the second power transmission device, the current vector values \(I\) a_3 、\(I\) b_3 、\(I\) c_3 on the sheath grounding wires of phases A, B, and C of the third power transmission device, the current vector value \(I\) X_3 of the cable body of phase X of the third power transmission device, where the current vector value on the sheath grounding wire of the cable of phase X in the first power transmission device is defined as \(I\) x_1 , the current vector value on the sheath grounding wire of the cable of phase X in the second power transmission device is defined as \(I\) x_2 , and the current vector value on the sheath grounding wire of the cable of phase X in the third power transmission device is defined as \(I\) x_3 ; where, when the first power transmission cable accessory adjacent to the arrester to be monitored is an insulating joint or a terminal, the second power transmission device does not exist, and \(I\) X_2 is assigned \(I\) X_1 ; \(I\) a_2 = 0 A∠0°; \(I\) b_2 = 0 A∠0°; \(I\) c_2 = 0 A∠0°; Step 4: Perform phase compensation on the obtained current vector values to obtain the compensated current vector values \(I'\) a_1 、\(I'\) b_1 、\(I'\) c_1 、\(I'\) X_1 、\(I'\) AS_1 、\(I'\) BS_1 、\(I'\) CS_1 、\(I'\) a_3 、\(I'\) b_3 、\(I'\) c_3 、\(I'\) X_3; Step 5: Based on the phase-compensated current vector value, calculate the three-phase leakage current \(i\) of the transmission cable a of the transmission cable, \(i\) b of the transmission cable, \(i\) c of the transmission cable; Step 6: Based on the three-phase leakage current of the transmission cable, calculate the resistive currents of the arresters in phases A, B, and C.

[0112] Further, the specific method for calculating the vector value of the fundamental wave of the collected current signal by using the single-point interpolation Fourier coefficient method in Step 3 is as follows:

[0113] Let any collected current signal be \(y(n)\), and determine the interpolation point value \(k\):

[0114] \(k = T\) N \(f\) J / \(f\) s

[0115] where, \(T\) N is the number of sampling points, \(f\) J is the fundamental wave frequency of the power system, \(f\) s is the sampling frequency;

[0116] Calculate the Fourier coefficient \(Y\) of the fundamental wave according to the interpolation point value \(k\):

[0117]

[0118] where, \(j\) is the imaginary unit, and the Fourier coefficient \(Y\) is defined as the current vector value of the current signal \(y(n)\).

[0119] In this embodiment, the method for calculating the fundamental wave vector value in the current signal is preferably the single-point interpolation Fourier coefficient method. Assume that a certain current signal is \(y = 20\cos(100t + 60°)\), where \(t\) is the time variable, and the true vector value of this current signal is \(20A∠60°\). When the sampling frequency is \(1kHz\), the number of sampling points is 313, and the fundamental wave frequency of the power system is \(50Hz\), the discrete current sampling results are as Figure 8 shown. For Figure 8 the discrete sampling results of the current signal in, using the single-point interpolation Fourier coefficient method to calculate its current vector value is \(19.85A∠59.8°\), and using the traditional Fourier transform method to calculate its current vector value is \(16.04A∠356.9°\). By comparing the calculated values of the single-point interpolation Fourier coefficient method, the calculated values of the traditional Fourier transform method, and the true value, it can be seen that the single-point interpolation Fourier coefficient method can effectively estimate the vector value of the current signal sampling result compared with the traditional Fourier transform method, and the estimation error is small. In the traditional Fourier transform method, when the signal is not sampled by truncating the whole period, the fence effect and spectral leakage will cause calculation errors in amplitude and phase, thus affecting the final vector estimation result.

[0120] Since the first current monitoring device, the second current monitoring device, and the third current monitoring device are distributed systems, there are differences in the timing rates between the devices, so time deviations will be formed between the devices, resulting in phase errors. Traditional optical fiber wired clock synchronization and GPS network clock synchronization are difficult to be applied to long-distance and signal-free power transmission cable channels. In order to eliminate the phase errors caused by time deviations between the devices and compensate for the phase errors, further, step 4 is specifically as follows:

[0121] Step 4.1: According to Kirchhoff's current law (KCL), determine the phase compensation reference channels: Select the second power transmission device as the phase compensation reference device:

[0122] For the first power transmission device, select the current vector value I of the X-phase cable body of the power transmission cable in the first power transmission device X_1 as the first reference channel, and select the current vector value I of the X-phase cable body of the second power transmission device X_2 as the second reference channel;

[0123] For the third power transmission device, select the current vector value I of the X-phase cable body of the third power transmission device X_3 as the third reference channel, and select the difference I between the current vector value I of the X-phase cable body of the second power transmission device X_2 and the current vector value I on the grounding wire of the X-phase cable sheath of the second power transmission device x_2 as the fourth reference channel; X_2 -I x_2 as the fourth reference channel;

[0124] Step 4.2: Calculate the phase error:

[0125] For the first power transmission device, define the phase difference between the first reference channel I X_1 and the second reference channel I X_2 as the first phase error ΔP1:

[0126] ΔP1 = angle(I X_1 ) - angle(I X_2 )

[0127] For the third power transmission device, define the phase difference between the third reference channel I X_3 and the fourth reference channel I X_2 -I x_2 as the second phase error ΔP2:

[0128] ΔP2 = angle(I X_3 ) - angle(I X_2 -I x_2 )

[0129] Among them, angel() represents obtaining the phase of a vector value;

[0130] Step 4.3: Perform phase compensation:

[0131] Keep all current vector values of the phase compensation reference device unchanged. For the first power transmission device, subtract the first phase error ΔP1 from the phase of all current vector values to obtain the compensated current vector values I’ a_1 、I’ b_1 、I’ c_1 、I’ X_1 、I’ AS_1 、I’ BS_1 、I’ CS_1 ; For the third power transmission device, subtract the second phase error ΔP2 from the phase of all current vector values to obtain the compensated current vector values I’ a_3 、I’ b_3 、I’ c_3 、I’ X_3 .

[0132] It should be noted that in this embodiment, when the first power transmission cable accessory adjacent to the lightning arrester to be monitored is not a straight-through joint, only the first current monitoring device and the third current monitoring device are installed. For the convenience of calculation, when the first power transmission cable accessory adjacent to the lightning arrester to be monitored is not a straight-through joint, assign I X_2 =I X_1 ; I a_2 =0A∠0°; I b_2 =0A∠0°; I c_2 =0A∠0°.

[0133] Furthermore, the specific steps of step 5 are as follows:

[0134] When the power transmission cable accessory at the third power transmission device is a cable terminal, the three-phase leakage currents of the power transmission cables connected to the three lightning arresters to be monitored are respectively:

[0135] i a =I’ a_1 +I a_2 +I’ a_3

[0136] i b =I’ b_1 +I b_2 +I’ b_3

[0137] i c =I’ c_1 +I c_2 +I’ c_3

[0138] When the transmission cable accessory at the third transmission device is an insulating joint, where

[0139] When the cable sheaths on both sides of the insulating joint are connected to the sheath grounding box through a single-core cable sheath grounding wire, the three-phase leakage currents of the transmission cable connected to the three surge arresters to be monitored are respectively:

[0140] i a = I’ a_1 + I a_2 + I’ a_3

[0141] i b = I’ b_1 + I b_2 + I’ b_3

[0142] i c = I’ c_1 + I c_2 + I’ c_3

[0143] When the cable sheaths on both sides of the insulating joint are connected to the sheath grounding box through a coaxial cable sheath grounding wire, where

[0144] When the cable sheaths on both sides of the insulating joint are in a cross-connected A / B connection mode, the three-phase leakage currents of the transmission cable connected to the three surge arresters to be monitored are respectively:

[0145] i ac = I’ a_1 - I’ c_1 + I a_2 - I c_2 + I’ a_3

[0146] i ba = I’ b_1 - I’ a_1 + I b_2 - I a_2 + I’ b_3

[0147] i cb = I’ c_1 - I’ b_1 + I c_2 - I b_2 + I’ c_3

[0148] i a =(i ac - i ba ) / 3

[0149] i b=(i ba -i cb ) / 3

[0150] i c =(i cb -i ac ) / 3

[0151] When the cable sheaths on both sides of the insulating joint are cross-connected in an A / C connection mode, the three-phase leakage currents of the power transmission cable connected to the three surge arresters to be monitored are respectively:

[0152] i ab =I’ a_1 -I’ b_1 +I a_2 -I b_2 +I’ a_3

[0153] i bc =I’ b_1 -I’ c_1 +I b_2 -I c_2 +I’ b_3

[0154] i ca =I’ c_1 -I’ a_1 +I c_2 -I a_2 +I’ c_3

[0155] i a =(i ab -i ca ) / 3

[0156] i b =(i bc -i ab ) / 3

[0157] i c =(i ca -i bc ) / 3

[0158] Among them, i ac , i ba , i cb , i ab , i bc , i ca are the line leakage currents of the cables of phases AC, BA, CB, AB, BC, and CA respectively.

[0159] The sheath current of the power transmission cable is composed of the cable sheath induced current and the cable leakage current. Taking the phase A power transmission cable as an example, Figure 9The figure shows a schematic diagram of the current loop of the sheath of phase A cable, where U A is the voltage of the main core of phase A cable; i a is the leakage current of phase A cable; U am is the induced voltage of the sheath of phase A cable; I am is the induced current of the sheath of phase A cable; I ag_1 is the grounding current of the sheath of phase A cable at the first current monitoring device; I ag_2 is the grounding current of the sheath of phase A cable at the second current monitoring device; I ag_3 is the grounding current of the sheath of phase A cable at the third current monitoring device.

[0160] In the invention patent application with the invention title of "An On-line Monitoring Method for Resistive Current of Zinc Oxide Arresters on Overhead Transmission Lines" and the Chinese patent publication number CN116068262A, which was published on May 5, 2023, I ag_1 is directly used as the leakage current of the phase A transmission cable. In fact, I ag_1 =-I am +i a_1 , where i a_1 represents the shunt current of the leakage current of phase A cable at the first current monitoring device. Due to various factors such as manufacturing process, laying process, and service environment, which will affect the sheath impedance and sheath induced voltage of the transmission cable, resulting in uncertainties in the sheath impedance and sheath induced voltage, so both I am and i a_1 are uncertain variables, and it is difficult to calculate the leakage current of the transmission cable only through I ag_1 .

[0161] In this embodiment, from Figure 9 it can be obtained that I ag_1 =-I am +i a_1 , I ag_2 =I am_2 +i a_2 , I ag_3 =I am_3 +i a_3 . In the formula, I am_2 is the shunt of I am at the second current monitoring device, I am_3 is the shunt of I am at the third current monitoring device, i a_2 represents the shunt current of the leakage current of phase A cable at the second current monitoring device, and i a_3 represents the shunt current of the leakage current of phase A cable at the third current monitoring device. According to I am_2 , I am_3 , i a_1 , i a_2 , ia_3 According to the definition, I am = I am_2 + I am_3 , i a = i a_1 + i a_2 + i a_3 , so it can be obtained that I ag_1 + I ag_2 + I ag_3 = -I am + I am_2 + I am_3 + i a_1 + i a_2 + i a_3 = i a . Similarly, it can be obtained that i b = I bg_1 + I bg_2 + I bg_3 , i c = I cg_1 + I cg_2 + I cg_3 . Among them, I bg_1 is the grounding current of the B-phase cable sheath at the first current monitoring device; I bg_2 is the grounding current of the B-phase cable sheath at the second current monitoring device; I bg_3 is the grounding current of the B-phase cable sheath at the third current monitoring device; I cg_1 is the grounding current of the C-phase cable sheath at the first current monitoring device; I cg_2 is the grounding current of the C-phase cable sheath at the second current monitoring device; I cg_3 is the grounding current of the C-phase cable sheath at the third current monitoring device.

[0162] It should be noted that in actual application of this embodiment, when the transmission cable accessories at the third transmission equipment are insulating joints (single-core cable sheath ground wires) or cable terminals, I ag_1 , I ag_2 and I ag_3 are all measured currents, that is, I ag_1 = I’ a_1 , I ag_2 = I a_2 , I ag_3 = I’ a_3 , thus obtaining i a = I’ a_1 + I a_2 + I’ a_3 , similarly, i b = I’ b_1 + I b_2 + I’ b_3 , i c = I’c_1 +I c_2 +I’ c_3 。

[0163] Taking the leakage current of phase BA corresponding to the insulating joint (coaxial cable sheath ground wire - cross - connection A / B) at the third power transmission equipment as an example, Figure 10 The following figure shows the schematic diagram of the cable sheath current loop corresponding to the insulating joint (coaxial cable sheath ground wire - cross - connection A / B). From Figure 10 it can be obtained that I’ b_3 = I bg_3 - I ag_3 ,I ag_1 = I’ a_1 ,I ag_2 = I a_2 ,I bg_1 = I’ b_1 ,I bg_2 = I b_2 。According to the cable sheath current loops of phases A and B, it can be obtained that i ba = i b - i a = I bg_1 + I bg_2 + I bg_3 - I ag_1 - I ag_2 - I ag_3 = I’ b_1 - I’ a_1 + I b_2 - I a_2 + I’ b_3 。Similarly, it can be obtained that i ac = I’ a_1 - I’ c_1 + I a_2 - I c_2 + I’ a_3 ,i cb = I’ c_1 - I’ b_1 + I c_2 - I b_2 + I’ c_3 。

[0164] Under normal circumstances, i a 、i b 、i c show a vector relationship with equal amplitudes and a phase difference of 120° from each other, and at the same time satisfy i a + i b + i c = 0. Thus, it can be obtained that i a = 3i a / 3 = (2i a + 0 - i c-i b ) / 3 = (i a -i c -i b +i a ) / 3 = (i ac -i ba ) / 3, similarly, i b =(i ba -i cb ) / 3, i c =(i cb -i ac ) / 3.

[0165] Similarly, when the transmission cable accessories at the third transmission equipment are insulating joints (coaxial cable sheath ground wire - cross - bonding A / C), the three - phase leakage currents of the transmission cable are respectively i ab =I’ a_1 -I’ b_1 +I a_2 -I b_2 +I’ a_3 , i bc =I’ b_1 -I’ c_1 +I b_2 -I c_2 +I’ b_3 , i ca =I’ c_1 -I’ a_1 +I c_2 -I a_2 +I’ c_3 , i a =(i ab -i ca ) / 3, i b =(i bc -i ab ) / 3, i c =(i ca -i bc ) / 3.

[0166] Furthermore, step 6 is specifically as follows:

[0167] Step 6.1: Determine the phase of the main core voltage of the transmission cable:

[0168]

[0169] Among them, U A , U B , U C respectively represent the three - phase voltages of the main core of the transmission cable, and angle() represents obtaining the phase of the vector value;

[0170] Step 6.2: Calculate the resistive current of the arrester:

[0171] Resistive current of the arrester in phase A: I ASZ_1 = F(I’ AS_1 ){cos[angle(I’ AS_1 ) - angle(U A )]}

[0172] Resistive current of the arrester in phase B: I BSZ_1 = F(I’ BS_1 ){cos[angle(I’ BS_1 ) - angle(U B )]}

[0173] Resistive current of the arrester in phase C: I CSZ_1 = F(I’ CS_1 ){cos[angle(I’ CS_1 ) - angle(U C )]}

[0174] Step 6.3: Substitute the formula obtained in Step 6.1 into the formula obtained in Step 6.2 to obtain:

[0175] Resistive current of the arrester in phase A: I ASZ_1 = F(I’ AS_1 ){sin[angle(i a ) - angle(I’ AS_1 )]}

[0176] Resistive current of the arrester in phase B: I BSZ_1 = F(I’ BS_1 ){sin[angle(i b ) - angle(I’ BS_1 )]}

[0177] Resistive current of the arrester in phase C: I CSZ_1 = F(I’ CS_1 ){sin[angle(i c ) - angle(I’ CS_1 )]}

[0178] Among them, F() represents obtaining the amplitude of the vector.

[0179] To verify the monitoring effect of this monitoring system and monitoring method, the following uses a more specific embodiment to illustrate this solution.

[0180] In this embodiment, condition monitoring is carried out on the lightning arrester of the 110 kV cross-linked polyethylene power transmission cable. The first power transmission cable accessory adjacent to the position of the lightning arrester is an insulating joint. The cable sheath is connected to the sheath grounding box through a coaxial cable sheath grounding wire (the connection method of the power transmission cable is the A / C cross-interconnection method). Therefore, in this embodiment, the monitoring system for the resistive current of the power transmission cable lightning arrester includes a first current monitoring device and a third current monitoring device. The A phase of the power transmission cable is selected as the X phase, and the sampled current data of each device at a certain moment is selected, and the current vector values in the first current monitoring device and the third current monitoring device are obtained by using the single-point interpolation Fourier coefficient method, as shown in Table 1. It should be noted that since the second current monitoring device is not installed, the current vector value in the second current monitoring device is assigned as I X_2 = I’ X_1 ; I a_2 = 0 A∠0°; I b_2 = 0 A∠0°; I c_2 = 0 A∠0°.

[0181] Table 1 Current vector values in each device

[0182] First current monitoring device Second current monitoring device Third current monitoring device A-phase cable sheath current sensor 16.57A∠275.8° 0A∠0° 5.03A∠301.9° B-phase cable sheath current sensor 8.76A∠264.5° 0A∠0° 2.32A∠215.2° C-phase cable sheath current sensor 10.71A∠291.3° 0A∠0° 5.54A∠99.1° X-phase cable body current sensor 12.68A∠128.9° 12.68A∠128.9° 12.39A∠293.8° A-phase arrester total current sensor 0.35 mA ∠47.2° B-phase arrester total current sensor 0.34 mA ∠286.4° C-phase arrester total current sensor 0.38 mA ∠165.3°

[0183] According to the current vector values in each device in Table 1, the phase errors between the first current monitoring device and the second current monitoring device, and between the third current monitoring device and the second current monitoring device are respectively:

[0184] ΔP1 = angle(I X_1 ) - angle(I X_2 ) = 0°

[0185] ΔP2 = angle(I X_3 ) - angle(I X_2 - I x_2 ) = 164.9°

[0186] According to ΔP1 and ΔP2, the phases of the current vector values in the first current monitoring device and the third current monitoring device are compensated, and the current vector values of each device after compensation are shown in Table 2.

[0187] Table 2 Current vector values in each device (after compensation)

[0188] First current monitoring device Second current monitoring device Third current monitoring device A-phase cable sheath current sensor 16.57A∠275.8° 0A∠0° 5.03A∠137.0° B-phase cable sheath current sensor 8.76A∠264.5° 0A∠0° 2.32A∠50.3° C-phase cable sheath current sensor 10.71A∠291.3° 0A∠0° 5.54A∠294.2° X-phase cable body current sensor 12.68A∠128.9° 12.68A∠128.9° 12.39A∠128.9° A-phase arrester total current sensor 0.35 mA ∠220.2° B-phase arrester total current sensor 0.34 mA ∠101.4° C-phase arrester total current sensor 0.38 mA ∠345.3°

[0189] According to the current vector values of each device after compensation in Table 2, the leakage currents of the power transmission cable are calculated to be i a = 2.70 A∠225.7°, i b = 2.56 A∠105.8°, i c= 2.63 A ∠348.4°. Further calculations yield the resistive currents of the arresters in phases A, B, and C as I ASZ_1 = 0.0335 mA, I BSZ_1 = 0.0261 mA, I CSZ_1 = 0.0205 mA. At the same time, the proportions of the resistive currents of the arresters in phases A, B, and C are obtained as 9.58%, 7.67%, and 5.41% respectively, all within the normal range, indicating that the arresters in phases A, B, and C are operating normally.

[0190] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for monitoring the resistive current of a transmission cable lightning arrester, characterized in that, Including the following steps: Step 1: Determine the positions of three arresters to be monitored. The three arresters to be monitored are connected to the three phases of the transmission cable one by one. Select any one of the A-phase, B-phase, and C-phase of the transmission cable and define it as the X-phase. Define the first transmission device, the second transmission device, and the third transmission device. Among them, The first transmission device is configured for the transmission cable and the arrester at the position of the arrester to be monitored; The second transmission device is configured for the transmission cable at the first through joint adjacent to the arrester to be monitored; The third transmission device is configured for the transmission cable at the first insulating joint or cable terminal adjacent to the arrester to be monitored; among them, the through joint, the insulating joint, and the cable terminal are all on the same side of the arrester to be monitored; the through joint is configured as the first transmission cable accessory adjacent to the arrester to be monitored; the insulating joint and the cable terminal are configured as the first transmission cable accessory adjacent to the arrester to be monitored, or when the first transmission cable accessory adjacent to the arrester to be monitored is a through joint, the second transmission cable accessory adjacent to the arrester to be monitored; Step 2: Collect the current signals I a1 、I b1 、I c1 on the ground wires of the A-phase, B-phase, and C-phase sheaths of the power transmission cable in the first power transmission device, collect the current signal I X1 of the X-phase cable body in the first power transmission device, collect the current signals I AS1 、I BS1 、I CS1 on the ground wires of the A-phase, B-phase, and C-phase lightning arrester bases to be monitored in the first power transmission device, collect the current signals I a2 、I b2 、I c2 on the ground wires of the A-phase, B-phase, and C-phase sheaths of the second power transmission device, collect the current signal I X2 of the X-phase cable body in the second power transmission device, collect the current signals I a3 、I b3 、I c3 on the ground wires of the A-phase, B-phase, and C-phase sheaths of the third power transmission device, collect the current signal I X3 ; Step 3: Process the collected current signals, and use the single-point interpolation Fourier coefficient method to calculate the vector value of each current signal fundamental wave, which is defined as the current vector value, including the current vector value I on the A-phase, B-phase and C-phase sheath grounding wires of the transmission cable in the first transmission device. a_1 ,I b_1 ,I c_1 , the current vector value I of the X-phase cable body of the transmission cable in the first transmission equipment X_1 , the current vector value I on the grounding wire of the A-phase, B-phase and C-phase lightning arrester base to be monitored in the first power transmission equipment AS_1 ,I BS_1 ,I CS_1 , the current vector value I on the A-phase, B-phase and C-phase sheath grounding wires of the second power transmission equipment a_2 ,I b_2 ,I c_2 , the current vector value I of the X-phase cable body of the second power transmission equipment X_2 , the current vector value I on the A-phase, B-phase and C-phase sheath grounding wires of the third power transmission equipment a_3 ,I b_3 ,I c_3 , the current vector value I of the X-phase cable body of the third power transmission equipment X_3 , wherein the current vector value on the X-phase cable sheath grounding wire of the transmission cable in the first transmission equipment is defined as I x_1 , define the current vector value of the X-phase cable sheath grounding wire of the second power transmission equipment as I x_2 , define the current vector value on the X-phase cable sheath grounding wire of the third power transmission equipment as I x_3 Wherein, when the first transmission cable accessory adjacent to the arrester to be monitored is an insulating joint or terminal, the second transmission device does not exist and is assigned a value of I X_2 =I X_1 ;I a_2 =0A∠0°; I b_2 =0A∠0°; I c_2 =0A∠0°; Step 4: Perform phase compensation on the obtained current vector values to obtain the compensated current vector values I’ a_1 、I’ b_1 、I’ c_1 、I’ X_1 、I’ AS_1 、I’ BS_1 、I’ CS_1 、I’ a_3 、I’ b_3 、I’ c_3 、I’ X_3 ; Step 5: Calculate the three-phase leakage currents i a 、i b 、i c of the power transmission cable based on the current vector value after phase compensation; Step 6: Based on the leakage currents of the three phases of the transmission cable, calculate the resistive currents of the arresters in the A-phase, B-phase, and C-phase; Among them, the specific method for calculating the vector value of the fundamental wave of the collected current signal by using the single-point interpolation Fourier coefficient method in the step 3 is as follows: Let any collected current signal be y(n), and determine the interpolation point value k: k = T N f J / f s Among them, T N is the number of sampling points, f J is the fundamental frequency of the power system, and f s is the sampling frequency; Calculate the Fourier coefficient Y of the fundamental wave according to the interpolation point value k: Among them, j is the imaginary unit, and the Fourier coefficient Y is defined as the current vector value of the current signal y(n).

2. The monitoring method of the resistive current of the transmission cable lightning arrester according to claim 1, characterized in that The specific content of the step 4 is as follows: Step 4.1: According to the KCL law, determine the phase compensation reference channel: Select the second transmission device as the phase compensation reference device: For the first power transmission device, select the current vector value I of the X-phase cable body of the power transmission cable in the first power transmission device X_1 as the first reference channel, and select the current vector value I of the X-phase cable body of the second power transmission device X_2 as the second reference channel; For the third power transmission device, select the current vector value I of the X-phase cable body of the third power transmission device X_3 as the third reference channel, and select the current vector value I of the X-phase cable body of the second power transmission device X_2 and the difference I x_2 between the current vector value I on the grounding wire of the X-phase cable sheath of the second power transmission device X_2 -I x_2 as the fourth reference channel; Step 4.2: Calculate the phase error: For the first power transmission device, define the first reference channel I X_1 and the second reference channel I X_2 The phase difference of is the first phase error ΔP1: ΔP1 = angle(I X_1 ) - angle(I X_2 ) For the third power transmission device, define the third reference channel I X_3 and the fourth reference channel I X_2 -I x_2 The phase difference of is the second phase error ΔP2: ΔP2 = angle(I X_3 ) - angle(I X_2 -I x_2 ) Among them, angel() represents obtaining the phase of the vector; Step 4.3: Perform phase compensation: Keeping all current vector values of the phase compensation reference device unchanged, for the first power transmission device, the phase of all current vector values is subtracted by the first phase error ΔP1 to obtain the compensated current vector values I’ a_1 、I’ b_1 、I’ c_1 、I’ X_1 、I’ AS_1 、I’ BS_1 、I’ CS_1 ; for the third power transmission device, the phase of all current vector values is subtracted by the second phase error ΔP2 to obtain the compensated current vector values I’ a_3 、I’ b_3 、I’ c_3 、I’ X_3 .

3. The monitoring method of resistive current of a transmission cable lightning arrester according to claim 1, characterized in that The specific content of the step 5 is as follows: When the transmission cable accessory at the third transmission device is a cable terminal, the leakage currents of the three phases of the transmission cable connected to the three arresters to be monitored are respectively: i a = I’ a_1 + I a_2 + I’ a_3 i b = I’ b_1 + I b_2 + I’ b_3 i c = I’ c_1 + I c_2 + I’ c_3 When the transmission cable accessory at the third transmission device is an insulating joint, among them, When the cable sheaths on both sides of the insulating joint are connected to the sheath grounding box through a single-core cable sheath grounding wire, the leakage currents of the three phases of the transmission cable connected to the three arresters to be monitored are respectively: i a = I’ a_1 + I a_2 + I’ a_3 i b = I’ b_1 + I b_2 + I’ b_3 i c = I’ c_1 + I c_2 + I’ c_3 When the cable sheaths on both sides of the insulating joint are connected to the sheath grounding box through a coaxial cable sheath grounding wire, among them, When the cable sheaths on both sides of the insulating joint are in a cross-connected A / B connection mode, the leakage currents of the three phases of the transmission cable connected to the three arresters to be monitored are respectively: i ac = I’ a_1 - I’ c_1 + I a_2 - I c_2 + I’ a_3 i ba = I’ b_1 - I’ a_1 + I b_2 - I a_2 + I’ b_3 i cb = I’ c_1 - I’ b_1 + I c_2 - I b_2 + I’ c_3 i a = (i ac - i ba ) / 3 i b = (i ba - i cb ) / 3 i c = (i cb - i ac ) / 3 When the cable sheaths on both sides of the insulating joint are in a cross-connected A / C connection mode, the leakage currents of the three phases of the transmission cable connected to the three arresters to be monitored are respectively: i ab = I’ a_1 - I’ b_1 + I a_2 - I b_2 + I’ a_3 i bc = I’ b_1 - I’ c_1 + I b_2 - I c_2 + I’ b_3 i ca = I’ c_1 - I’ a_1 + I c_2 - I a_2 + I’ c_3 i a = (i ab - i ca ) / 3 i b = (i bc - i ab ) / 3 i c = (i ca - i bc ) / 3 Among them, i ac , i ba , i cb , i ab , i bc , i ca are the line leakage currents of the cables of the AC phase, BA phase, CB phase, AB phase, BC phase, and CA phase respectively.

4. The monitoring method of the resistive current of the transmission cable lightning arrester according to claim 1, characterized in that, The specific content of the step 6 is as follows: Step 6.1: Determine the phase of the cable main core voltage of the transmission cable: Among them, U A , U B , U C respectively represent the three-phase voltages of the main cores of the power transmission cables, and angle() represents obtaining the phase of the vector value; Step 6.2: Calculate the resistive current of the arrester: Resistive current of the lightning arrester for phase A: I ASZ_1 = F(I’ AS_1 ){cos[angle(I’ AS_1 ) - angle(U A )]} Resistive current of the B-phase lightning arrester: I BSZ_1 = F(I’ BS_1 ){cos[angle(I’ BS_1 ) - angle(U B )]} Resistive current of the lightning arrester for phase C: I CSZ_1 = F(I’ CS_1 ){cos[angle(I’ CS_1 ) - angle(U C )]} Step 6.3: Substitute the formula obtained in Step 6.1 into the formula obtained in Step 6.2, and obtain: Resistive current of the lightning arrester for phase A: I ASZ_1 = F(I’ AS_1 ){sin[angle(i a ) - angle(I’ AS_1 )]} Resistive current of the B-phase lightning arrester: I BSZ_1 = F(I’ BS_1 ){sin[angle(i b ) - angle(I’ BS_1 )]} Resistive current of the C-phase lightning arrester: I CSZ_1 = F(I’ CS_1 ){sin[angle(i c ) - angle(I’ CS_1 )]} wherein, F() represents obtaining the amplitude of a vector.

5. Monitoring system for resistive current of transmission cable lightning arrester, which implements the monitoring method for resistive current of transmission cable lightning arrester according to any one of claims 1 to 4, characterized in that, including a first current monitoring device, a second current monitoring device, and a third current monitoring device, wherein: The first current monitoring device is used to monitor and collect the current signals IA, IB, and IC on the sheath grounding wires of the A-phase, B-phase, and C-phase of the power transmission cable in the first power transmission equipment a1 , IA b1 , IB c1 , IC, and is used to monitor and collect the current signal IX of the cable body of the X-phase of the power transmission cable in the first power transmission equipment X1 , and is used to monitor and collect the current signals IA, IB, and IC on the grounding wires of the bases of the A-phase, B-phase, and C-phase lightning arresters to be monitored in the first power transmission equipment AS1 , IA BS1 , IB CS1 ; The second current monitoring device is used to monitor and collect the current signals I a2 on the sheath grounding wires of phase A, phase B, and phase C of the second power transmission equipment b2 , I c2 , and is used to monitor and collect the current signal I X2 of the cable body of phase X of the second power transmission equipment; The third current monitoring device is used to monitor and collect the current signal I on the A-phase, B-phase and C-phase sheath grounding wires of the third power transmission equipment. a3 ,I b3 ,I c3 , used to monitor and collect the current signal I of the X-phase cable body of the third power transmission equipment X3 .

6. The monitoring system for resistive current of a transmission cable lightning arrester according to claim 5, characterized in that, further including a data processing unit, which is configured to receive and process the current signals of the first current monitoring device, the second current monitoring device, and the third current monitoring device.

7. The monitoring system for resistive current of a transmission cable lightning arrester according to claim 6, characterized in that The data processing unit is a computer.

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