A quick diagnosis method for poor contact of high-voltage cable grounding system

Abstract

This application provides a rapid diagnostic method for poor contact in high-voltage cable grounding systems, belonging to the field of high-voltage cable testing technology. The technical problem is that poor grounding contact poses a significant hazard, and existing testing and repair solutions have many shortcomings. The technical solution is as follows: S1: Simplify the cross-interconnection section and direct protective grounding section in the high-voltage cable grounding system, and construct the actual grounding physical circuit equivalently as a lumped-parameter resistor network; S2: Inject non-power frequency AC test voltage excitation signals at preset key nodes and measure the current response at each key node; S3: Construct a set of electrical equations for the grounding circuit based on the relationship between the voltage excitation signal and the current response; S4: Solve by inversion to obtain the equivalent resistance values ​​of each key node in the lumped-parameter resistor network; S5: Analyze the equivalent resistance values, identify equivalent resistances with abnormally increased resistance values, and determine the corresponding physical sections as poor contact fault sections; applied to high-voltage cable testing.

Description

Technical Field

[0001] This invention provides a rapid diagnostic method for poor contact in high-voltage cable grounding systems, belonging to the field of high-voltage cable testing technology. Background Technology

[0002] In power systems, the high-voltage cable grounding system is a crucial link in ensuring the safety and stability of power transmission. High-voltage cables are mainly used for long-distance power transmission in power systems, ensuring the power supply to cities and industries by transmitting large amounts of electrical energy. The grounding system of high-voltage cables ensures the safety of the cables during normal operation and in case of short circuits due to faults. Grounding is a vital part of this system, safely introducing the charge from the live parts of the cable into the earth, thereby preventing equipment damage or personal injury caused by charge accumulation. High-voltage cable grounding systems are classified into direct protective grounding systems and cross-interconnected grounding systems according to grounding type, mainly serving the functions of mechanical protection, potential clamping, charge discharge, and current return. The high-voltage cable grounding circuit mainly consists of a grounding box, grounding leads, lead seals, the aluminum sheath of the high-voltage cable, and intermediate joint bridging wires. However, any poor connection or tightness between any part, such as loose bolts, poor welding, or inadequate lead sealing, will cause an increase in grounding resistance. A defect in the grounding system with excessive circuit resistance will create a floating voltage in the cable's metal sheath and main insulation shield, discharging to nearby grounding points, burning the main insulation, and causing a fault.

[0003] To address these issues, various detection and remediation solutions have been proposed within the industry, but these methods currently have limitations in terms of efficiency and initial investment. Many detection methods are often time-consuming and labor-intensive, and cannot provide timely feedback on problems. Remediation work is similarly time-consuming and labor-intensive, and in some cases may require the replacement of expensive equipment or have uncertain overall impact on the system. Summary of the Invention

[0004] To address the technical problems existing in the background art, the present invention provides a rapid diagnostic method for poor contact in high-voltage cable grounding systems, comprising the following steps:

[0005] Step 1: For the cross-interconnection section and direct protective grounding section in the high-voltage cable grounding system, simplify the processing according to the topology and physical connection relationship of each grounding section, and construct the actual grounding physical circuit equivalently as a lumped parameter resistor network;

[0006] Step 2: Under the condition that the high-voltage cable grounding system is powered on, inject a non-power frequency AC test voltage excitation signal at the preset key nodes of the high-voltage cable grounding system, and simultaneously measure the current response at each key node.

[0007] Step 3: Based on the current response at key nodes, construct a bridge network diagram. Based on the two criteria of the upper, lower, left, and right bridge arms and the middle bridge current in the bridge network diagram, determine and accurately locate the location of the defect in the high-voltage cable grounding system.

[0008] Step 4: Based on the relationship between the non-power frequency AC test voltage excitation signal and the current response, construct a set of electrical equations for the grounding loop;

[0009] Step 5: Inversely solve the electrical equations of the grounding loop to obtain the equivalent resistance values ​​of each key node in the lumped parameter resistor network;

[0010] Step 6: Introduce the standard deviation statistical criterion to analyze the equivalent resistance value, identify the equivalent resistance with abnormally increased resistance value, and determine the physical section corresponding to the key node to which the equivalent resistance with abnormally increased resistance value belongs to the contact failure section.

[0011] Furthermore, in step 1, the resistance of the aluminum sheath (2) of a high-voltage cable and the lead-sealed contact resistance of the high-voltage cable connector are integrated and equivalent to a lumped equivalent resistance.

[0012] Furthermore, in step 1, each interconnection branch circuit in the cross-interconnection segment is first equivalent to an independent branch equivalent resistance. The three independent branch equivalent resistances are connected in series to form a series branch. Then, the three series branches are connected in parallel to form the equivalent circuit of the series-parallel composite resistance corresponding to the cross-interconnection segment.

[0013] Furthermore, in step 1, the multi-channel grounding loop structure in the direct protective grounding section of the high-voltage cable is equivalent to an equivalent resistance circuit consisting of three independent grounding resistors connected in parallel.

[0014] Furthermore, step 2 specifically includes the following steps:

[0015] Step 2.1: Determine whether the preset key node of the high-voltage cable grounding system is a cross-interconnection section or a direct protective grounding section; if it is a cross-interconnection section, proceed to steps 2.2 to 2.8; if it is a direct protective grounding section, proceed to steps 2.9 to 2.11.

[0016] Step 2.2: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the first time. Measure the current response at each key node;

[0017] Step 2.3: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the second time. Measure the current response at each key node;

[0018] Step 2.4: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the third time. Measure the current response at each key node;

[0019] Step 2.5: Inject a non-power frequency AC test voltage excitation signal into the cross-connection segment for the fourth time. Measure the current response at each key node;

[0020] Step 2.6: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the fifth time. Measure the current response at each key node;

[0021] Step 2.7: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the sixth time. Measure the current response at each key node;

[0022] Step 2.8: Use flexible clamps to measure the non-power frequency current on both sides of the 9 connectors in the cross-connection section, and input the 6 sets of test current results into the corresponding bridge model;

[0023] Step 2.9: Inject a non-power frequency AC test voltage excitation signal into the direct protective grounding section for the first time. Measure the current response at each key node;

[0024] Step 2.10: Inject a non-power frequency AC test voltage excitation signal into the direct protective grounding section for the second time. Measure the current response at each key node;

[0025] Step 2.11: Inject a non-power frequency AC test voltage excitation signal for the third time into the direct protective grounding section. The current response at each key node was measured.

[0026] Furthermore, step 6 specifically includes the following steps:

[0027] Step 6.1: Based on the equivalent resistance values ​​of each key node in the cross-interconnection segment of the lumped parameter resistor network obtained in Step 5. ; Calculate the equivalent resistance value Arithmetic mean:

[0028] ;

[0029] Step 6.2: Calculate the equivalent resistance value Relative to the arithmetic mean Squared deviation:

[0030] ;

[0031] Step 6.3: Adjust the equivalent resistance value The corresponding squared deviation By comparison, the physical segment corresponding to the critical node to which the i-th equivalent resistance with the largest deviation square is identified as the faulty contact segment within the cross-interconnection segment;

[0032] Step 6.4: Based on the equivalent resistance values ​​of each key node in the direct protective grounding section of the lumped parameter resistor network obtained in Step 5. ; Calculate the equivalent resistance value Arithmetic mean:

[0033] ;

[0034] Step 6.5: Calculate the equivalent resistance value Relative to the arithmetic mean Squared deviation:

[0035] ;

[0036] Step 6.6: Adjust the equivalent resistance value The corresponding squared deviation By comparison, the physical section corresponding to the critical node to which the x-th equivalent resistance with the largest deviation square is identified as the faulty contact section within the direct protective grounding section.

[0037] The advantages of this invention over the prior art are as follows:

[0038] 1. A lumped-parameter equivalent resistance network model for a high-voltage cable cross-interconnection grounding system was established. Physical connection units such as the cable aluminum sheath, lead seal, and joint lead seal are uniformly represented as resistive elements, and the entire cross-interconnection section is simplified into a series-parallel network consisting of nine resistors, laying a theoretical foundation for further bridge model transformation. This modeling method is characterized by strong versatility, clear physical meaning, and ease of engineering application.

[0039] 2. A defect-sensitive circuit model based on bridge topology was constructed. By sequentially applying non-power frequency AC constant current excitation to the three-phase copper busbars (ab, bc, ca) in the cross-connection box, the original series-parallel network was transformed into a bridge circuit consisting of four bridge arm branches and one bridge branch. When any one of the six contact resistances in the four bridge arm branches becomes defective, the circuit immediately changes its balance state, with the cable in the middle bridge branch jumping from zero to the order of magnitude of the defect resistance increase. When the defect resistance is transferred to the middle bridge branch, the bridge circuit will regain balance, and the unbalanced current in the middle bridge branch will drop back to zero. Based on the highly sensitive detection index of the unbalanced current in the middle bridge branch, it is determined whether there is a contact resistance defect in the overall circuit. When there is a contact defect in the outer bridge arm branch, the shunt current of the faulty bridge arm branch will decrease accordingly with the increase in contact resistance. By comparing the current distribution ratios of the four outer bridge arm branches (upper, lower, left, and right), the target outer bridge arm branch with the contact defect can be quickly located. Among them, the "arm current extreme value ratio" is the most sensitive fault index. By using two criteria—the change in zero value of the intermediate bridge branch and the current ratio of the bridge arm branch—the defect diagnosis problem is transformed into a comparative analysis of the currents of five branches, which significantly improves the sensitivity and accuracy of defect identification. Attached Figure Description

[0040] The present invention will be further described below with reference to the accompanying drawings:

[0041] Figure 1 This is a schematic diagram of the high-voltage cable grounding system in this invention;

[0042] Figure 2 This is an equivalent schematic diagram of the aluminum sheath of the cable and the lead seal of the connecting joint in this invention;

[0043] Figure 3 This is an equivalent schematic diagram of the interconnection branch loop in the cross-interconnection segment of the present invention;

[0044] Figure 4 This is an equivalent schematic diagram of the multi-channel grounding loop structure in the direct protection grounding section of the present invention;

[0045] Figure 5 This invention provides the first injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. The equivalent circuit diagram;

[0046] Figure 6 The second injection of non-power frequency AC test voltage excitation signal into the cross-connection segment in this invention. The equivalent circuit diagram;

[0047] Figure 7 This invention provides the third injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. The equivalent circuit diagram;

[0048] Figure 8 This invention provides the fourth injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. The equivalent circuit diagram;

[0049] Figure 9 This invention provides the fifth injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. The equivalent circuit diagram;

[0050] Figure 10 This invention provides the sixth injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. The equivalent circuit diagram;

[0051] Figure 11 This invention provides the first injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. Circuit diagram;

[0052] Figure 12 The second injection of non-power frequency AC test voltage excitation signal into the cross-connection segment in this invention. Circuit diagram;

[0053] Figure 13 This invention provides the third injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. Circuit diagram;

[0054] Figure 14 This invention provides the fourth injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. Circuit diagram;

[0055] Figure 15 This invention provides the fifth injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. Circuit diagram;

[0056] Figure 16 This invention provides the sixth injection of a non-power frequency AC test voltage excitation signal into the cross-connection segment. Circuit diagram;

[0057] Figure 17 This invention provides the first injection of a non-power frequency AC test voltage excitation signal into the directly protected grounding section. Circuit diagram;

[0058] Figure 18 This invention provides the first injection of a non-power frequency AC test voltage excitation signal into the directly protected grounding section. Circuit diagram;

[0059] Figure 19 This invention provides the first injection of a non-power frequency AC test voltage excitation signal into the directly protected grounding section. Circuit diagram;

[0060] In the diagram: 1 is a lead seal, 2 is an aluminum sheath, 3 is a direct grounding box, and 4 is a cross-connection box. Detailed Implementation

[0061] like Figures 1 to 13 As shown, the present invention provides a rapid diagnostic method for poor contact in a high-voltage cable grounding system, comprising the following steps:

[0062] Step 1: As Figure 1 As shown, in a high-voltage cable grounding system, from left to right, there are "direct protective grounding section, cross-interconnection section, and direct protective grounding section". For the cross-interconnection section and direct protective grounding section in the high-voltage cable grounding system, a simplified approach is taken based on the topology and physical connection relationship of each grounding section, and the actual grounding physical circuit is equivalently constructed as a lumped-parameter resistor network; the specific equivalent relationship is as follows: Figure 2 As shown, the resistance of the aluminum sheath 2 of a high-voltage cable and the lead-sealing contact resistance of the high-voltage cable connector are integrated and equivalently combined into a single lumped equivalent resistance; for example... Figure 3 As shown, each interconnection branch loop in the cross-connection segment is equivalent to an independent branch equivalent resistance. The three independent branch equivalent resistances are connected in series to form a series branch. Then, the three series branches are connected in parallel to form the equivalent circuit of the series-parallel composite resistance corresponding to the cross-connection segment; as shown. Figure 4 As shown in the figure, the multi-channel grounding loop structure in the direct protective grounding section of the high-voltage cable is equivalent to an equivalent resistance circuit consisting of three independent grounding resistors connected in parallel. Let K be the equivalent resistance of the kth segment of phase x, i.e. The equivalent resistance of the first segment of phase a is This is the equivalent resistance of the first segment of phase b, and so on.

[0063] Define the key nodes in the original circuit as follows: positive power supply connection point U, negative power supply connection point D, left common line L (voltage VL), and right common line R (voltage VR); equivalent parallel branch: upper left arm (connected to U and L). Left forearm (connected to L and D) Right upper arm (connected to U and R) Right forearm (connected to R and D) Intermediate bridge (connecting L and R) .

[0064] Step 2: Under the condition of uninterrupted power supply to the high-voltage cable grounding system, inject a non-power frequency AC test voltage excitation signal at the preset key nodes of the high-voltage cable grounding system, and simultaneously measure the current response at each key node; specifically including the following steps:

[0065] Step 2.1: Determine whether the preset key node of the high-voltage cable grounding system is a cross-interconnection section or a direct protective grounding section; if it is a cross-interconnection section, proceed to steps 2.2 to 2.8; if it is a direct protective grounding section, proceed to steps 2.9 to 2.11.

[0066] Step 2.2: As Figure 5 , Figure 11 As shown, a non-power frequency AC test voltage excitation signal is injected for the first time into the cross-connection section. Measure the current response at each key node. The sheath current during the nth injection of a non-power frequency AC test voltage excitation signal into the k-th segment of phase x, such as... The sheath current is the current when the non-power frequency AC test voltage excitation signal is injected for the first time in the first segment of phase a, and so on;

[0067] Step 2.3: As Figure 6 , Figure 12 As shown, a non-power frequency AC test voltage excitation signal is injected for the second time into the cross-connection section. Measure the current response at each key node;

[0068] Step 2.4: As Figure 7 , Figure 13 As shown, a non-power frequency AC test voltage excitation signal is injected for the third time into the cross-connection segment. Measure the current response at each key node;

[0069] Step 2.5: As Figure 8 , Figure 14 As shown, a non-power frequency AC test voltage excitation signal is injected for the fourth time into the cross-connection segment. Measure the current response at each key node;

[0070] Step 2.6: As Figure 9 , Figure 15 As shown, a non-power frequency AC test voltage excitation signal was injected for the fifth time into the cross-connection segment. Measure the current response at each key node;

[0071] Step 2.7: As Figure 10 , Figure 16 As shown, a non-power frequency AC test voltage excitation signal was injected for the sixth time into the cross-connection segment. Measure the current response at each key node;

[0072] Step 2.8: Use flexible clamps to measure the non-power frequency current on both sides of the 9 connectors in the cross-interconnection section, and input the 6 sets of test current results into Table 1;

[0073] Table 1. Test record of current in four bridge arms under six excitations.

[0074] .

[0075] Step 2.8 specifically includes the following steps:

[0076] Based on the equivalent circuit, write the equations for node L:

[0077] ;

[0078] ;

[0079] Under normal conditions (reference, all resistors are r), substitute the values:

[0080] Solving for .

[0081] This yields the reference current and the normalization factor (1.00):

[0082] ;

[0083] ;

[0084] ;

[0085] ;

[0086] ;

[0087] The results include the current of each arm after the fault (expressed as a multiple of the reference value) and the extreme ratio of the currents of the newly added four arms (i.e., , , , The ratio of the maximum to the minimum current value directly reflects the degree of current imbalance caused by the fault.

[0088] Table 2. Ratio of extreme values ​​of current in each arm after the fault and the current in the newly added four arms.

[0089] .

[0090] In summary, due to the symmetry of the circuit structure, the circuit is in equilibrium under normal conditions, with equal voltages at the two common nodes L and R, and zero current in the intermediate bridge branch. After applying a non-power frequency AC constant current excitation between the two phases of the cross-connection section, the three-phase sheath grounding loop is equivalent to a five-branch parallel bridge circuit model containing four outer bridge arm branches and one intermediate bridge branch. When any one of the six contact resistances in the four bridge arm branches becomes defective, the circuit immediately changes its equilibrium state, jumping from zero to the order of magnitude of the defective resistance increase. When the defective resistance is transferred to the intermediate bridge branch, the bridge will regain equilibrium, and the unbalanced current in the intermediate bridge branch will drop back to zero. Based on this highly sensitive detection indicator of the unbalanced current in the intermediate bridge branch, it can be determined whether there is a contact resistance defect in the overall circuit.

[0091] When a contact defect exists in an outer arm branch, the shunt current in that faulty arm branch will decrease accordingly with the increase in contact resistance. By comparing the current distribution ratios of the upper, lower, left, and right outer arm branches, the target outer arm branch with the contact defect can be quickly located. Among these, the "arm current extreme value ratio" is the most sensitive fault indicator.

[0092] Under normal conditions, the current in the left arm is twice that of the right arm, and the extreme value ratio is 2.0. When the upper left or lower left arm fails, the current in that arm drops sharply, and the extreme value ratio soars to 33.6, indicating a serious current imbalance. When the upper right or lower right arm fails, the extreme value ratio soars to 68.0, and the imbalance is even more serious. This is because the fault point is located in the branch with a smaller current, which has a greater impact on the overall current distribution.

[0093] Faults can be accurately located by comparing the multipliers:

[0094] Left upper arm malfunction ( ): Minimum (0.018), Maximum (1.196);

[0095] Left lower arm malfunction ( ): Minimum (0.018), Maximum (1.196);

[0096] Right upper arm malfunction ( ): Minimum (0.032), Maximum (1.088);

[0097] Right lower arm malfunction ( ): Minimum (0.032), Maximum (1.088).

[0098] In practical applications, if any resistance in one of the four bridge arm branches is defective, the bridge branch current becomes extremely sensitive, jumping from zero in equilibrium to an order of magnitude increase due to the defective resistance. Conversely, when the defective resistance is located within the bridge branch, the bridge current returns to equilibrium and drops to zero, indicating the presence of a defect. The current in the defective bridge arm branch will shrink to an order of magnitude corresponding to the resistance increase. By analyzing the ratio of the currents in the four bridge arm branches (upper, lower, left, and right), the defective bridge arm branch can be quickly located. Through six excitations and analysis of 30 branch currents, the defect is reproduced four times and verified twice, ultimately allowing for the precise output of a unique defective connector number and indicating whether the defect is located on the left or right contact surface of that connector.

[0099] Step 2.9: As Figure 17 As shown, a non-power frequency AC test voltage excitation signal is injected for the first time into the directly protective grounding section. Measure the current response at each key node. The sheath current during the nth injection of a non-power frequency AC test voltage excitation signal into phase x, such as... The sheath current is the current when the non-power frequency AC test voltage excitation signal is injected for the first time in phase a, and so on;

[0100] Step 2.10: As Figure 18 As shown, a non-power frequency AC test voltage excitation signal is injected for the second time into the directly protected grounding section. Measure the current response at each key node;

[0101] Step 2.11: As Figure 19 As shown, a non-power frequency AC test voltage excitation signal is injected for the third time into the directly protected grounding section. The current response at each key node was measured.

[0102] Step 3: Based on the current response at key nodes, construct a bridge network diagram. Based on the two criteria of the upper, lower, left, and right bridge arms and the middle bridge current in the bridge network diagram, determine and accurately locate the location of the defect in the high-voltage cable grounding system.

[0103] Step 4: Based on the relationship between the non-power frequency AC test voltage excitation signal and the current response, construct a set of electrical equations for the grounding loop;

[0104] Step 5: Inversely solve the electrical equations of the grounding loop to obtain the equivalent resistance values ​​of each key node in the lumped parameter resistive network; specifically including the following steps:

[0105] Step 5.1: Combine the non-power frequency AC test voltage excitation signal and current response of the cross-connection section in Steps 2.1 to 2.6 with... Figures 5 to 10 Based on the displayed circuit structure, establish the first voltage-current constraint equation set under the corresponding operating conditions:

[0106] ;

[0107] Step 5.2: Inversely solve the voltage-current constraint equations of the first loop to obtain the equivalent resistance values ​​of each key node in the cross-interconnection section. ;

[0108] Step 5.3: Combine the non-power frequency AC test voltage excitation signal and current response of the directly protected grounding section in steps 2.7 to 2.9 with... Figures 11 to 13 Based on the displayed circuit structure, establish the second voltage-current constraint equation set under the corresponding operating conditions:

[0109] ;

[0110] Step 5.4: Inversely solve the voltage-current constraint equations of the second loop to obtain the equivalent resistance values ​​of each key node in the direct protective grounding section. .

[0111] Step 6: Introduce the root mean square error statistical criterion to analyze the equivalent resistance value, identify the equivalent resistance with abnormally increased resistance, and determine the physical section corresponding to the key node to which the equivalent resistance with abnormally increased resistance belongs to the contact failure section; specifically including the following steps:

[0112] Step 6.1: Based on the equivalent resistance values ​​of each key node in the cross-interconnection segment of the lumped parameter resistor network obtained in Step 5. ; Calculate the equivalent resistance value Arithmetic mean:

[0113] ;

[0114] Step 6.2: Calculate the equivalent resistance value Relative to the arithmetic mean Squared deviation:

[0115] ;

[0116] Step 6.3: Adjust the equivalent resistance value The corresponding squared deviation By comparison, the physical segment corresponding to the critical node to which the i-th equivalent resistance with the largest deviation square is identified as the faulty contact segment within the cross-interconnection segment;

[0117] Step 6.4: Based on the equivalent resistance values ​​of each key node in the direct protective grounding section of the lumped parameter resistor network obtained in Step 5. ; Calculate the equivalent resistance value Arithmetic mean:

[0118] ;

[0119] Step 6.5: Calculate the equivalent resistance value Relative to the arithmetic mean Squared deviation:

[0120] ;

[0121] Step 6.6: Adjust the equivalent resistance value The corresponding squared deviation By comparison, the physical section corresponding to the critical node to which the x-th equivalent resistance with the largest deviation square is identified as the faulty contact section within the direct protective grounding section.

[0122] Step 7: Based on the above equivalent resistance calculation algorithm and poor contact fault identification logic, further build an input-output closed-loop automatic calculation model; specifically including the following steps:

[0123] Step 7.1: Combining long-term operation and maintenance test data of high-voltage cable grounding systems with industry safety standards, establish segmented threshold judgment functions for two grounding types: single-end direct protective grounding and cross-interconnection. This enables automated hierarchical analysis of resistance data. The specific segmentation criteria are as follows:

[0124] (1) Function for determining single-ended direct protective grounding section:

[0125] When the equivalent resistance is ≤80mΩ, the grounding status is determined to be normal, and the routine operation and maintenance strategy is executed.

[0126] When 80mΩ < equivalent resistance ≤ 200mΩ, the grounding status is determined to be a warning status, indicating a potential risk of poor contact.

[0127] When the equivalent resistance is greater than 200mΩ, the grounding condition is determined to be a defective fault condition, indicating a serious poor contact problem.

[0128] (2) Cross-connection segment determination function:

[0129] When the equivalent resistance is ≤300mΩ, the grounding status is determined to be normal, and the routine operation and maintenance strategy is executed.

[0130] When 300mΩ < equivalent resistance ≤ 600mΩ, the grounding status is determined to be a warning status, indicating a potential risk of poor contact.

[0131] When the equivalent resistance is greater than 600mΩ, the grounding condition is determined to be a defective fault condition, indicating a serious poor contact problem.

[0132] Step 7.2: Based on the above piecewise function determination results, the model automatically matches the corresponding operation and maintenance handling plan, forming a standardized operation and maintenance guidance system:

[0133] 1. Normal condition: The grounding resistance meets the standard limit, the grounding system has good contact performance, there are no potential faults, and it can be operated normally and periodically tested according to the equipment's regular inspection cycle.

[0134] 2. Pay attention to the early warning status: When the grounding resistance is in the critical abnormal range, there may be potential contact problems such as slight oxidation or loosening at the grounding joint and sheath connection. It is necessary to increase the frequency of online monitoring of the equipment, shorten the routine testing cycle, track the trend of resistance data changes, and prevent the potential problems from worsening.

[0135] 3. Defect / Fault Status: The grounding resistance is seriously excessive, and there is obvious poor contact in the grounding circuit. This can easily cause cable overheating, tripping, or even fire and explosion accidents. The defect must be reported immediately, and a power outage maintenance should be arranged. The grounding connection parts in the faulty section should be inspected, tightened, and replaced to eliminate safety hazards.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A rapid diagnostic method for poor contact in a high-voltage cable grounding system, characterized in that, Includes the following steps: Step 1: For the cross-interconnection section and direct protective grounding section in the high-voltage cable grounding system, simplify the processing according to the topology and physical connection relationship of each grounding section, and construct the actual grounding physical circuit equivalently as a lumped parameter resistor network; Step 2: Under the condition that the high-voltage cable grounding system is powered on, inject a non-power frequency AC test voltage excitation signal at the preset key nodes of the high-voltage cable grounding system, and simultaneously measure the current response at each key node. Step 3: Based on the current response at key nodes, construct a bridge network diagram. Based on the two criteria of the upper, lower, left, and right bridge arms and the middle bridge current in the bridge network diagram, determine and accurately locate the location of the defect in the high-voltage cable grounding system. Step 4: Based on the relationship between the non-power frequency AC test voltage excitation signal and the current response, construct a set of electrical equations for the grounding loop; Step 5: Inversely solve the electrical equations of the grounding loop to obtain the equivalent resistance values ​​of each key node in the lumped parameter resistor network; Step 6: Introduce the standard deviation statistical criterion to analyze the equivalent resistance value, identify the equivalent resistance with abnormally increased resistance value, and determine the physical section corresponding to the key node to which the equivalent resistance with abnormally increased resistance value belongs to the contact failure section.

2. A rapid diagnostic method for poor contact in a high-voltage cable grounding system according to claim 1, characterized in that: In step 1, the resistance of the aluminum sheath (2) of a high-voltage cable and the lead-sealed contact resistance of the high-voltage cable connector are integrated and equivalent to a lumped equivalent resistance.

3. A rapid diagnostic method for poor contact in a high-voltage cable grounding system according to claim 1, characterized in that: In step 1, each interconnection branch circuit in the cross-interconnection segment is first equivalent to an independent branch equivalent resistance. The three independent branch equivalent resistances are connected in series to form a series branch. Then, the three series branches are connected in parallel to form the equivalent circuit of the series-parallel composite resistance corresponding to the cross-interconnection segment.

4. A rapid diagnostic method for poor contact in a high-voltage cable grounding system according to claim 1, characterized in that: In step 1, the multi-channel grounding loop structure in the direct protective grounding section of the high-voltage cable is equivalent to an equivalent resistance circuit consisting of three independent grounding resistors connected in parallel.

5. A rapid diagnostic method for poor contact in a high-voltage cable grounding system according to any one of claims 2-4, characterized in that, Step 2 specifically includes the following steps: Step 2.1: Determine whether the preset key node of the high-voltage cable grounding system is a cross-interconnection section or a direct protective grounding section; if it is a cross-interconnection section, proceed to steps 2.2 to 2.8; if it is a direct protective grounding section, proceed to steps 2.9 to 2.

11. Step 2.2: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the first time. Measure the current response at each key node; Step 2.3: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the second time. Measure the current response at each key node; Step 2.4: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the third time. Measure the current response at each key node; Step 2.5: Inject a non-power frequency AC test voltage excitation signal into the cross-connection segment for the fourth time. Measure the current response at each key node; Step 2.6: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the fifth time. Measure the current response at each key node; Step 2.7: Inject a non-power frequency AC test voltage excitation signal into the cross-connection section for the sixth time. Measure the current response at each key node; Step 2.8: Use flexible clamps to measure the non-power frequency current on both sides of the 9 connectors in the cross-connection section, and input the 6 sets of test current results into the corresponding bridge model; Step 2.9: Inject a non-power frequency AC test voltage excitation signal into the direct protective grounding section for the first time. Measure the current response at each key node; Step 2.10: Inject a non-power frequency AC test voltage excitation signal into the direct protective grounding section for the second time. Measure the current response at each key node; Step 2.11: Inject a non-power frequency AC test voltage excitation signal for the third time into the direct protective grounding section. The current response at each key node was measured.

6. A rapid diagnostic method for poor contact in a high-voltage cable grounding system according to claim 5, characterized in that, Step 6 specifically includes the following steps: Step 6.1: Based on the equivalent resistance values ​​of each key node in the cross-interconnection segment of the lumped parameter resistor network obtained in Step 5. ; Calculate the equivalent resistance value Arithmetic mean: ； Step 6.2: Calculate the equivalent resistance value Relative to the arithmetic mean Squared deviation: ； Step 6.3: Adjust the equivalent resistance value The corresponding squared deviation By comparison, the physical segment corresponding to the critical node to which the i-th equivalent resistance with the largest deviation square is identified as the faulty contact segment within the cross-interconnection segment; Step 6.4: Based on the equivalent resistance values ​​of each key node in the direct protective grounding section of the lumped parameter resistor network obtained in Step 5. ; Calculate the equivalent resistance value Arithmetic mean: ； Step 6.5: Calculate the equivalent resistance value Relative to the arithmetic mean Squared deviation: ； Step 6.6: Adjust the equivalent resistance value The corresponding squared deviation By comparison, the physical section corresponding to the critical node to which the x-th equivalent resistance with the largest deviation square is identified as the faulty contact section within the direct protective grounding section.

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