A system and method for detecting the resistance of a high-voltage cable cross-connection loop

Abstract

The present invention relates to a system and method for detecting the resistance of a cross-connected loop of a high-voltage cable under live conditions, the system comprising: a current injection module: injecting direct current into any two-phase metal sheaths of a three-phase cable of a cross-connected loop of a high-voltage cable on one side of a cross-connected box to form a current loop; a current and voltage acquisition module: testing the magnitude of the injected current and the voltage difference between the two-phase injection points forming the current loop; a loop direct current detection module: detecting the magnitude of the direct current in the metal sheath of the three-phase cable on the other side of the cross-connected box when injecting direct current; a central processing unit: controlling the switching of the current injection module to inject into the three-phase loop, and calculating the magnitude of the loop resistance of the three-phase cable cross-connected loop before and after the direct current injection point based on the collected data. Compared with the prior art, the present invention can perform live testing and realize high-precision detection of milliohm-level resistance in a high-voltage cable cross-connected loop with an induced voltage of up to several hundred volts and a circulating current of tens or hundreds of amperes.

Description

Technical Field

[0001] The present invention relates to the technical field of live detection of cross-connected circuits of high-voltage cables, and in particular to a system and method for detecting the resistance liveness of cross-connected circuits of high-voltage cables. Background Art

[0002] With the acceleration of urbanization in my country, the demand for electricity load has increased dramatically. More and more urban overhead lines are being renovated and underground power grids are being laid. The cable lines are becoming longer and longer. In order to effectively reduce the sheath ring current, long cable lines currently use a high-voltage cable cross-interconnected grounding system.

[0003] The cross-connection circuit of high-voltage cables includes: cable metal sheath, accessory copper shell or tail pipe, intermediate joint bridge wire, ground wire, and crimping and fasteners between various parts. Any poor connection, such as unfastened bolts, cold soldering, and poor lead sealing, will cause the cross-connection circuit resistance to increase. For example: poor welding between the cable metal sheath and the copper braided wire increases the connection resistance by 0.1Ω. Under the action of a 10kA short-circuit current, the instantaneous heating power at this point is 10MW, causing local temperature rise, burning the main insulation of the cable, and causing the cable to break down near the joint or tail pipe. If the resistance is further increased, it will limit the short-circuit current value, prolong the tripping time, and cause a fire. Therefore, it is particularly important to detect grounding defects in the cross-connection circuit of high-voltage cables. At present, the commonly used methods include infrared temperature measurement, ultrasonic testing and eddy current testing. Infrared temperature measurement detects the surface temperature of the cable to determine whether a defect has occurred. Ultrasonic testing determines the occurrence of defects by detecting arc discharge. These two methods can only detect when a fault is approaching. Eddy current testing technology is a flaw detection method that uses the principle of electromagnetic induction to detect surface defects of accessories and metal connections, but it cannot detect small-sized defects inside metal connections, such as sand holes. Therefore, the existing detection methods cannot detect the cross-connection circuit resistance of high-voltage cables in a timely and accurate manner. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a system and method for detecting the resistance of a cross-connected circuit of a high-voltage cable.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A high-voltage cable cross-connection loop resistance live detection system, the system comprising:

[0007] Current injection module: used to inject DC current into any two-phase metal sheaths of the A, B, and C three-phase cables of the high-voltage cable cross-connection circuit on one side of the cross-connection box to form a current loop;

[0008] Current and voltage acquisition module: used to test the injection current size and the voltage difference between the two-phase injection points forming the current loop when injecting DC current;

[0009] Loop DC current detection module: used to detect the DC current in the metal sheath of the A, B, and C three-phase cables on the other side of the cross-connection box, which is located on the grounding side of the high-voltage cable cross-connection loop, when injecting DC current;

[0010] Central processing unit: used to control the switching of the current injection module into the three-phase circuit, and calculate the loop resistance of the A, B, C three-phase cable cross-connection circuit before and after the DC current injection point based on the data collected by the current and voltage acquisition module and the loop DC current detection module.

[0011] Preferably, the current injection module includes a current source, a three-phase switch, a three-phase access component and a protection suppression circuit. The three-phase access component is used to connect the A, B, and C three-phase copper buses of the cross-connection box to form an injection point. The current source is connected to the three-phase access component through a three-phase switch. The three-phase switch is used to connect any two phases of A, B, and C to the current source to form a current loop. The protection suppression circuit and the current and voltage acquisition module are both connected to the current loop through the three-phase switch.

[0012] Preferably, the three-phase access component includes a test clip, which respectively clamps the three-phase copper busbars of the cross-connected box A, B, and C to form electrical conduction. The test clips of the three phases A, B, and C respectively lead out two measuring lines, one of which is used to connect the current source through a three-phase switching circuit to form a current loop, and the other is connected to the current and voltage acquisition module through the three-phase switching circuit.

[0013] Preferably, the current and voltage acquisition module comprises a current collector and a voltage collector, the current collector is connected in series to the current loop through a three-phase switch, and the voltage collector is connected in parallel to two test clips corresponding to the current loop through a three-phase switch.

[0014] Preferably, the loop DC current detection module includes a DC current sensor.

[0015] Preferably, the current injection module, current and voltage acquisition module, loop DC current detection module and central processing unit are integrated in the test box, and the current injection module and loop DC current detection module are led out of the test box for connecting the A, B, C three-phase cable metal sheaths respectively.

[0016] Preferably, the system further comprises a mobile intelligent terminal for remote monitoring, and the mobile intelligent terminal is connected to the central processing unit via a communication module.

[0017] A method for detecting the charged resistance of a cross-connection circuit of a high-voltage cable, the method is implemented based on the above-mentioned system for detecting the charged resistance of a cross-connection circuit of a high-voltage cable, and the method comprises the following steps:

[0018] (1) The current injection module injects current into the A and B phases of the three-phase cable. The injection points of the A and B phases are denoted as m and n, respectively. A first current loop of the AB phase and a second current loop of the AB phase are formed before and after the injection points m and n, respectively.

[0019] (2) The current and voltage acquisition module obtains the injection current magnitude I1 and the voltage difference U1 between the injection points m and n. At the same time, the loop DC current detection module obtains the DC current magnitude I1 in the three-phase cables A, B, and C. A1 ,I B1 ,I C1 ;

[0020] (3) For the AB phase first current loop and the AB phase second current loop, the voltage equation is obtained according to Kirchhoff's current-voltage law;

[0021] (4) Based on steps (1) to (3), the current injection module injects current into the B and C phases and the A and C phases of the three-phase cable and obtains the corresponding voltage equation;

[0022] (5) Solve the voltage equation to find the loop resistance of the three-phase cable cross-connection loop A, B, and C before and after the DC current injection point.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The system of the present invention can realize high-precision detection of milliohm (mΩ) resistance in the cross-connection loop of high-voltage cables under the interference of power frequency induced voltage up to 300V and power frequency current of hundreds of amperes (A), and has strong anti-interference capability. It can effectively detect the state of the cross-connection loop of high-voltage cables and accurately locate the position of bad connection points without power outage when the cables are in operation, thereby reducing the cable failure rate and having good economic and social benefits;

[0025] (2) The present invention has a remote telemetry function. The system communicates with the mobile intelligent terminal to achieve remote control, measurement, and data storage, which is safer and more convenient.

[0026] (3) The system of the present invention can act quickly under external overvoltage or overcurrent to ensure the safety of the detection system, the tested cable and the detection personnel, and has high safety;

[0027] (4) The system and method of the present invention can first perform preliminary detection to determine the defect phase, and then use the loop resistance precise positioning technology to achieve accurate positioning of the defect point. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a block diagram of the composition of the high-voltage cable cross-interconnection loop resistance live detection system of the present invention;

[0029] Figure 2 The schematic diagram of the live detection of the high-voltage cable cross-connection loop resistance using the live detection system of the present invention;

[0030] Figure 3 A simplified circuit diagram of live detection using the high-voltage cable cross-connection loop resistance live detection system of the present invention;

[0031] Figure 4 This is a schematic diagram of the circuit principle when injecting DC current into the A and B phase cables;

[0032] Figure 5 This is a schematic diagram of the circuit principle when injecting DC current into the A and C phase cables;

[0033] Figure 6 This is a schematic diagram of the circuit principle when injecting DC current into the B and C phase cables;

[0034] In the figure, 1 is a current injection module, 2 is a current and voltage acquisition module, 3 is a loop DC current detection module, 4 is a central processing unit, 5 is a mobile intelligent terminal, 6 is a communication module, 7 is a copper bus on one side of the cross-connection box, 8 is a cable on the other side of the cross-connection box, 11 is a current source, 12 is a three-phase switch, 13 is a three-phase access component, and 14 is a protection suppression circuit. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Note that the following embodiments are merely illustrative in nature, and the present invention is not intended to limit its applicable objects or uses, and the present invention is not limited to the following embodiments.

[0036] Example

[0037] like Figure 1 As shown, a high-voltage cable cross-connection loop resistance live detection system, the system comprises:

[0038] Current injection module 1: used to inject direct current into any two-phase metal sheaths of the A, B, and C three-phase cables of the high-voltage cable cross-connection loop on one side of the cross-connection box to form a current loop;

[0039] Current and voltage acquisition module 2: used to test the injection current size and the voltage difference between the two-phase injection points forming the current loop when injecting DC current;

[0040] Loop DC current detection module 3: used to detect the DC current in the metal sheath of the A, B, and C three-phase cables on the other side of the cross-connection box located on the ground side of the high-voltage cable cross-connection loop when injecting DC current;

[0041] Central processing unit 4: used to control the switching of the current injection module 1 into the three-phase circuit, and calculate the loop resistance of the A, B, C three-phase cable cross-connection circuit before and after the DC current injection point based on the data collected by the current and voltage acquisition module 2 and the loop DC current detection module 3.

[0042] The current injection module 1 includes a current source 11, a three-phase switch 12, a three-phase access component 13 and a protection suppression circuit 14. The three-phase access component 13 is used to connect the A, B, and C three-phase copper busbars on one side of the cross-connection box to form an injection point. The current source 11 is connected to the three-phase access component 13 through the three-phase switch 12. The three-phase switch 12 is used to connect any two phases of the three phases A, B, and C to the current source 11 to form a current loop. The protection suppression circuit 14 and the current and voltage acquisition module 2 are both connected to the current loop through the three-phase switch 12.

[0043] The three-phase access component 13 includes a test clamp, which clamps the three-phase cables A, B, and C respectively to form electrical conduction. Specifically, the test clamps are clamped on the copper bus 7 on one side of the cross-connection box. The test clamps of the three phases A, B, and C respectively lead out two measuring lines, one of which is used to connect the current source 11 through the three-phase switching circuit to form a current loop, and the other is connected to the current and voltage acquisition module 2 through the three-phase switching circuit.

[0044] The current and voltage acquisition module 2 includes a current collector and a voltage collector. The current collector is connected in series to the current loop through a three-phase switch 12 , and the voltage collector is connected in parallel to two test clips corresponding to the current loop through the three-phase switch 12 .

[0045] The loop DC current detection module 3 includes a DC current sensor with an accuracy of 1%. Three DC current sensors are provided, which are respectively clamped on the cable 8 at the other side of the cross-connection box to measure the DC current in the cable.

[0046] The current injection module 1, the current and voltage acquisition module 2, the loop DC current detection module 3 and the central processing unit 4 are integrated in the test box. The current injection module 1 and the loop DC current detection module 3 are led out of the test box to connect the metal sheaths of the A, B and C three-phase cables respectively.

[0047] The system also includes a mobile intelligent terminal 5 for remote monitoring. The mobile intelligent terminal 5 is connected to the central processing unit 4 via a communication module 6. In this embodiment, the communication module 6 can use a wireless communication module 6 to realize wireless communication.

[0048] In this embodiment, the central processing unit 4 can adopt a microprocessor similar to a single-chip computer or a DSP, the three-phase switch 12 in the current injection module 1 can adopt a relay, and a four-wire connection method is adopted. The current collector of the current and voltage acquisition module 2 includes a sampling resistor and a first voltmeter. The sampling resistor is connected in series between two injection points of any two phases of the three phases A, B, and C through the three-phase switch 12. The voltage of the sampling resistor is measured between any two phases of the three phases A, B, and C to obtain the current in the current loop. The voltage collector includes a second voltmeter, which is connected in parallel to the two injection points corresponding to the current loop through the three-phase switch 12. The protection suppression circuit 14 includes a common over-current and over-voltage protection circuit and a filtering circuit, etc., so as to suppress the influence of the power frequency induced voltage of up to 300V and the ground current of hundreds of amperes (A) in the measurement signal on the detection system.

[0049] In addition, the system also includes a human-computer interaction interface for displaying the measurement results, and the human-computer interaction interface is connected to the central processing unit 4. The human-computer interaction interface can adopt an LCD interactive interface for real-time display of measurement data, detection and diagnosis conclusions; and according to relevant national standards, corresponding processing suggestions are put forward. At the same time, the system also includes a memory for storing historical data of the detected cross-connected loop resistance, and the memory is connected to the central processing unit 4. The memory completes the storage of current measurement data and the review of historical data. The central processing unit 4 automatically generates a time-resistance change trend chart based on the detection data of the same loop cable at different times, and displays it through the human-computer interaction interface and the mobile intelligent terminal 5. In addition, a power module for powering the system is configured in the test box of this system.

[0050] A method for detecting the charged resistance of a cross-connection circuit of a high-voltage cable, the method is implemented based on the above-mentioned system for detecting the charged resistance of a cross-connection circuit of a high-voltage cable, and the method comprises the following steps:

[0051] (1) The current injection module 1 injects current into the A and B phases of the three-phase cable, the injection points of the A and B phases are denoted as m and n respectively, and the AB phase first current loop and the AB phase first current loop are formed before and after the injection points m and n respectively;

[0052] (2) The current and voltage acquisition module 2 obtains the injection current magnitude I1 and the voltage difference U1 between the injection points m and n. At the same time, the loop DC current detection module 3 obtains the DC current magnitude I1 in the three-phase cables A, B, and C. A1 ,I B1 ,I C1 ;

[0053] (3) For the AB phase first current loop and the AB phase second current loop, the voltage equation is obtained according to Kirchhoff's current-voltage law;

[0054] (4) Based on steps (1) to (3), the current injection module 1 injects current into the B and C phases and the A and C phases of the three-phase cable and obtains the corresponding voltage equation;

[0055] (5) Solve the voltage equation to find the loop resistance of the three-phase cable cross-connection loop A, B, and C before and after the DC current injection point.

[0056] The specific instructions are as follows:

[0057] The principle of live detection using a cross-connected circuit resistance live detection system is as follows Figure 2 As shown:

[0058] First, the current source 11 three-phase measurement fixture of the high-voltage cable cross-connection circuit resistance live detection system is connected to the A, B, and C phase copper bars inside the cross-connection box respectively, marked as points k, m, and n, to ensure good contact;

[0059] Then, the grounding points at both ends of the cross-connected loop are marked as x and y respectively, and the probe of the first DC current sensor is stuck between the xm points to measure the DC current of phase A; the probe of the second DC current sensor is stuck between the xn points to measure the DC current of phase B; the probe of the third DC current sensor is stuck between the xk points to measure the DC current of phase C;

[0060] Finally, the current source 11 and the three-way current and voltage measurement module are automatically switched between AB, AC, and BC by the internal control current source 11 and the three-way current and voltage measurement module of the high-voltage cable cross-connection circuit resistance live detection system to change the current injection circuit. The current value measured by the current probe and the data measured by the three-way current and voltage measurement module are used to establish the equation group and solve R xm , R xn , R xk , R ym , R yn , R yk The value is calculated and compared with the theoretical value to determine whether there is a fault in the high-voltage cable cross-connection circuit. The specific calculation method is as follows:

[0061] First, to make the diagram clear, the cross-connection diagram is simplified. Figure 3 The simplified diagram shown is based on Figure 3 , note R xm For R A1 , note R xn For R B1 , note R xk For R C1 , note R ym For R A2 , note R yn For R B2 , note R yk For RC2 , the DC value measured by the first DC current sensor is recorded as I A , direction to the right; the DC value measured by the second DC current sensor is recorded as I B , direction to the right; the DC value measured by the third DC current sensor is recorded as I C , direction is to the right. It should be noted that the current direction is marked as right. If the current direction is actually to the left, the read value is negative. The three test clamps of current source 11 are still clamped at the m, n, and k positions.

[0062] ① When the current source 11 injects current between m and n, the schematic diagram is as follows Figure 4 As shown:

[0063] The output current of the current source 11 is recorded as I1, and the voltage is recorded as U1. At this time, the current measured by the DC current sensor is recorded as I A1 , I B1 , I C1 The x potential at this point is U x , the potential at point y is U y , the potential at point m is U m , the potential at point n is U n .

[0064] According to Kirchhoff's current-voltage law, the equation can be listed:

[0065] For loop 1, the potential difference between points m and n can be expressed as follows:

[0066] U1=U mn =U m -U n =(U x -R A1 *I A1 )-(U x -R B1 *I B1 )

[0067] Right now:

[0068] U1=-R A1 *I A1 +R B1 *I B1 (1)

[0069] For loop 2, the potential difference between points m and n can be expressed as follows:

[0070] U1=U mn =U m -U n =[U y +R A2 *(I A1+I1)]-[U y +R B2 *(I B1 -I1)]

[0071] Right now:

[0072] U1=R A2 *(I A1 +I1)+R B2 *(I1-I B1 ) (2)

[0073] ② When the current source 11 injects current between m and k, the schematic diagram is as follows Figure 5 As shown:

[0074] The output current of the current source 11 is recorded as I2, and the voltage is recorded as U2. At this time, the current measured by the DC current sensor is recorded as I A2 , I B2 , I C2 The x potential at this point is U x , the potential at point y is U y , the potential at point m is U m , the potential at point k is U k .

[0075] According to Kirchhoff's current-voltage law, the equation can be listed:

[0076] For loop 3, the potential difference between points m and k can be listed as follows:

[0077] U2=U mn =U m -U n =(U x -R A1 *I A1 )-(U x -R B1 *I B1 )

[0078] Right now:

[0079] U2=-R A1 *I A2 +R C1 *I C2 (3)

[0080] For loop 4, the potential difference between points m and k can be expressed as follows:

[0081] U2=U mk =U m -U k =[U y +R A2 *(I A2+I2)]-[U y +R C2 *(I C2 -I2)]

[0082] Right now:

[0083] U2=R A2 *(I A2 +I2)+R C2 *(I2-I C2 ) (4)

[0084] ③ When the current source 11 injects current between n and k, the schematic diagram is as follows Figure 6 As shown:

[0085] The output current of the current source 11 is recorded as I3, and the voltage is recorded as U3. At this time, the current measured by the DC current sensor is recorded as I A3 , I B3 , I C3 The x potential at this point is U x , the potential at point y is U y , the potential at point n is U n , the potential at point k is U k .

[0086] According to Kirchhoff's current-voltage law, the equation can be listed:

[0087] For loop 5, the potential difference between points n and k can be expressed as follows:

[0088] U3=U nk =U n -U k =(U x -R B1 *I B3 )-(U x -R C1 *I C3 )Right now:

[0089] U3=-R B1 *I B3 +R C1 *I C3 (5)

[0090] For loop 6, the potential difference between points n and k can be expressed as follows:

[0091] U3=U nk =U n -U k =[U y +R B2 *(I B3 +I3)]-[U y +RC2 *(I C3 -I3)]

[0092] Right now:

[0093] U3=R B2 *(I B3 +I3)+R C2 *(I3-I C3 ) (6)

[0094] ④ Combining equations (1) to (6), we can obtain:

[0095] U1=-R A1 *I A1 +R B1 *I B1

[0096] U1=R A2 *(I A1 +I1)+R B2 *(I1-I B1 )

[0097] U2=-R A1 *I A2 +R C1 *I C2

[0098] U2=R A2 *(I A2 +I2)+R C2 *(I2-I C2 )

[0099] U3=-R B1 *I B3 +R C1 *I C3

[0100] U3=R B2 *(I B3 +I3)+R C2 *(I3-I C3 )

[0101] There are six unknowns in these six equations. A1 , R B1 ,R C1 , R A2 ,R B2 ,R C2 , theoretically a unique solution can be obtained.

[0102] Therefore, by constructing the matrix, solving the equation, and solving R A1 , R B1 ,R C1 , RA2 ,R B2 ,R C2 After obtaining the value, it is compared with the theoretical value to determine whether the cross-connection circuit resistance of the high-voltage cable under test is normal.

[0103] If the resistance of each section measured in the first cross-connection grounding box is normal, it means that the resistance of the high-voltage cable cross-connection circuit is normal; otherwise, it means that the tested high-voltage cable cross-connection circuit is abnormal: if R A1 , R B1 ,R C1 If it is abnormal, you can directly determine which circuit is faulty: A2 ,R B2 ,R C2 If it is abnormal, you should go to the second cross-connection grounding box for further inspection, measure the resistance of each loop section, and determine the point or loop section with large resistance. If necessary, you can accurately locate the potential defect position of the defective phase (such as whether it is at the lead sealing point of the tail pipe, etc.).

[0104] Finally, it should be noted that the system and method are applied to live detection of resistance of cross-connection loops of high-voltage cables. Of course, the application is not limited to live detection, but can also be used for power outage detection.

[0105] The above embodiments are merely examples and do not limit the scope of the present invention. These embodiments can also be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the technical concept of the present invention.

Claims

1. A high-voltage cable cross-connection loop resistance live detection system, characterized in that: The system includes: A current injection module (1): used to inject a direct current into any two-phase metal sheaths of the A, B, and C three-phase cables of the high-voltage cable cross-connection loop at one side of the cross-connection box to form a current loop; A current and voltage acquisition module (2): used to test the magnitude of the injected current and the voltage difference between the two-phase injection points forming the current loop when injecting direct current; A loop DC current detection module (3): used to detect the magnitude of the DC current in the metal sheaths of the A, B and C three-phase cables located on the ground side of the high-voltage cable cross-connection loop at the other side of the cross-connection box when the DC current is injected; The central processing unit (4) is used to control the switching of the current injection module (1) into the three-phase circuit, and calculate the circuit resistance of the A, B, C three-phase cable cross-connection circuit before and after the DC current injection point based on the data collected by the current and voltage acquisition module (2) and the circuit DC current detection module (3).

2. A high-voltage cable cross-connection loop resistance live detection system according to claim 1, characterized in that: The current injection module (1) comprises a current source (11), a three-phase switch (12), a three-phase access component (13) and a protection suppression circuit (14); the three-phase access component (13) is used to connect the three-phase copper busbars of the cross-connection box A, B and C to form an injection point; the current source (11) is connected to the three-phase access component (13) via the three-phase switch (12); the three-phase switch (12) is used to connect any two phases of the three phases A, B and C to the current source (11) to form a current loop; the protection suppression circuit (14) and the current and voltage acquisition module (2) are both connected to the current loop via the three-phase switch (12).

3. A high-voltage cable cross-connection loop resistance live detection system according to claim 2, characterized in that: The three-phase access component (13) comprises a test clamp, which respectively clamps the A, B, and C phase copper bars of the cross-connection box to form electrical conduction. The A, B, and C three-phase test clamps respectively lead out two measuring lines, one of which is used to connect to the current source (11) through a three-phase switching circuit to form a current loop, and the other is connected to the current and voltage acquisition module (2) through the three-phase switching circuit.

4. A high-voltage cable cross-connection loop resistance live detection system according to claim 3, characterized in that: The current and voltage acquisition module (2) comprises a current collector and a voltage collector, wherein the current collector is connected in series to the current loop via a three-phase switch (12), and the voltage collector is connected in parallel to two test clamps corresponding to the current loop via the three-phase switch (12).

5. A high-voltage cable cross-connection loop resistance live detection system according to claim 1, characterized in that: The loop DC current detection module (3) comprises a DC current sensor.

6. A high-voltage cable cross-connection loop resistance live detection system according to claim 1, characterized in that: The current injection module (1), the current and voltage acquisition module (2), the loop DC current detection module (3) and the central processing unit (4) are integrated in a test box; the current injection module (1) and the loop DC current detection module (3) are led out of the test box for respectively connecting to the metal sheaths of the A, B and C three-phase cables.

7. A high-voltage cable cross-connection loop resistance live detection system according to claim 1, characterized in that: The system also includes a mobile intelligent terminal (5) for remote monitoring, wherein the mobile intelligent terminal (5) is connected to the central processing unit (4) via a communication module (6).

8. A method for detecting the resistance of a high-voltage cable cross-connection loop, characterized in that: The method is implemented based on the system described in any one of claims 1 to 7, and the method comprises the following steps: (1) The current injection module injects current into the A and B phases of the three-phase cable. The injection points of the A and B phases are denoted as m and n, respectively. A first current loop of the AB phase and a second current loop of the AB phase are formed before and after the injection points m and n, respectively. (2) The current and voltage acquisition module obtains the injection current magnitude I1 and the voltage difference U1 between the injection points m and n. At the same time, the loop DC current detection module obtains the DC current magnitude I1 in the metal sheath of the three-phase cable A, B, and C. A1 ,I B1 ,I C1 ; (3) For the AB phase first current loop and the AB phase second current loop, the voltage equation is obtained according to Kirchhoff's current-voltage law; (4) Based on steps (1) to (3), the current injection module injects current into the B and C phases and the A and C phases of the three-phase cable and obtains the corresponding voltage equation; (5) Solve the voltage equation to find the loop resistance of the three-phase cable cross-connection loop A, B, and C before and after the DC current injection point.

Images