Cable metal sheath damage detection system and method

Abstract

The invention provides a cable metal sheath damage detection system and method, and relates to the technical field of power equipment detection. The system comprises a power supply module, a voltage measurement module, a grounding controller module, a line loss compensation module and a damage analysis module. Wherein the line loss compensation module is used for determining a theoretical attenuation coefficient of a to-be-detected cable, and setting a threshold value according to the theoretical attenuation coefficient of the to-be-detected cable, the cable length, the cable type and environmental factors; and the damage analysis module is used for calculating the voltage deviation of the to-be-detected cable according to the theoretical attenuation coefficient, the head end voltage and the tail end voltage of the to-be-detected cable, comparing the voltage deviation with a threshold value, and judging whether the metal sheath of the to-be-detected cable is damaged or not. Whether the metal sheath of the cable is damaged or not can be accurately judged, and the detection precision is high.

Description

Technical Field

[0001] This invention relates to the field of power equipment testing technology, specifically to a cable metal sheath damage detection system and method. Background Technology

[0002] In power transmission systems, the metallic sheath (armor / shielding layer) of cables plays a crucial role, and its integrity directly affects the cable's service life and safety. However, existing methods for testing cable metallic sheaths have the following drawbacks: 1. While DC withstand voltage tests and insulation resistance tests can detect the insulation performance of cables, they cannot accurately reflect the true state of the cable under actual power frequency conditions. Offline testing methods, although effective, require power outages, which not only affects the continuity of power supply but may also cause inconvenience to users.

[0003] 2. Although distributed fiber optic temperature measurement technology can provide continuous temperature monitoring, its high cost and insensitivity to minor local damage limit its widespread application.

[0004] 3. Existing power frequency withstand voltage tests lack a quantitative relationship between sheath voltage and the degree of damage. Conventional power frequency withstand voltage tests primarily focus on the main insulation performance, making it difficult to effectively detect damage to the metallic sheath. Furthermore, voltage attenuation (line loss) caused by the inherent impedance of the cable can mask damage signals, further affecting detection accuracy. Summary of the Invention

[0005] The purpose of this invention is to provide a cable metal sheath damage detection system and method to solve the problems of low detection accuracy and complex operation in the prior art, and to accurately determine whether there is damage to the cable metal sheath with high detection accuracy.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a cable metal sheath damage detection system, comprising a power supply module, a voltage measurement module, a grounding controller module, a line loss compensation module, and a damage analysis module; the grounding controller module is used to ground the end of the cable under test, the power supply module is used to output an adjustable power frequency voltage to the beginning of the cable under test, the voltage measurement module is used to simultaneously measure the beginning and end voltages of the cable under test; the line loss compensation module is used to determine the theoretical attenuation coefficient of the cable under test, and set a threshold value based on the theoretical attenuation coefficient, cable length, cable type, and environmental factors; the damage analysis module is used to calculate the voltage deviation of the cable under test based on the theoretical attenuation coefficient, beginning and end voltages, and compare the voltage deviation with the threshold value to determine whether the metal sheath of the cable under test is damaged.

[0007] According to the present invention, a cable metal sheath damage detection system is provided, wherein the metal sheath of the cable under test includes an armor layer or a shielding layer.

[0008] According to the cable metal sheath damage detection system provided by the present invention, the theoretical attenuation coefficient of the cable under test is calculated as follows:

[0009] in, e The base of the natural logarithm, The length of the cable to be tested is 1. is the attenuation constant.

[0010] According to the cable metal sheath damage detection system provided by the present invention, the attenuation constant is calculated as follows:

[0011] Where R is the conductor resistance per unit length of the cable under test, and G is the insulation conductance per unit length of the cable under test.

[0012] According to the present invention, the environmental factors of a cable metal sheath damage detection system include temperature or humidity.

[0013] According to the cable metal sheath damage detection system provided by the present invention, the threshold is calculated as follows:

[0014] Where w1, w2, w3, w4, and w5 are weighting coefficients, L is the cable length of the cable under test, K is the theoretical attenuation coefficient of the cable under test, and Cable_Type is the cable type of the cable under test. Temp For temperature, Humi Let be the humidity, and b be a constant. According to the cable metal sheath damage detection system provided by the present invention, the voltage deviation is calculated using the following formula:

[0015] Among them, U in U out These are the voltage at the beginning and end of the cable under test, respectively.

[0016] According to the present invention, a cable metal sheath damage detection system compares voltage deviation with a threshold to determine whether the metal sheath of the cable under test is damaged, including: if If the metal sheath of the cable under test is damaged, it is determined that the cable's metal sheath is damaged; if If the test result is positive, the metal sheath of the cable under test is deemed to be intact.

[0017] The cable metal sheath damage detection system provided by the present invention further includes an early warning module; the early warning module is used to issue an audible and visual alarm when the damage analysis module determines that the metal sheath of the cable under test is damaged.

[0018] In a second aspect, the present invention provides a method for detecting cable metal sheath damage, employing the cable metal sheath damage detection system of the first aspect, the method comprising: The end of the cable under test is grounded through the grounding controller module; The power module inputs a high-voltage power frequency to the beginning of the cable under test; The voltage measurement module measures the voltage at the beginning and end of the cable under test; The line loss compensation module determines the theoretical attenuation coefficient of the cable under test and sets a threshold based on the theoretical attenuation coefficient, cable length, cable type and environmental factors. The damage analysis module calculates the voltage deviation of the cable under test based on the theoretical attenuation coefficient, the voltage at the beginning and the voltage at the end of the cable, and compares the voltage deviation with a threshold to determine whether there is damage to the metal sheath of the cable under test.

[0019] This invention has at least the following technical effects: 1. High Detection Accuracy. Accuracy of measurement results is ensured through dynamic line loss compensation and the use of high-precision measuring devices. First, by introducing dynamic line loss compensation to set a threshold, the interference of voltage attenuation (line loss) caused by the inherent impedance of the cable on the measurement results is effectively eliminated. Furthermore, by establishing an equivalent circuit model of "voltage application end - damage point - grounding point," the voltage attenuation characteristics caused by damage are quantified, thereby improving the detection capability for minute damages. Second, the voltage measurement module achieves an accuracy of ±0.1%, accurately capturing minute voltage changes and ensuring the reliability of the detection results. Simultaneously, the use of dual-end synchronous measurement technology ensures the consistency of measurement time between the first and last voltage ends, avoiding errors caused by time differences.

[0020] 2. High sensitivity. In terms of damage detection capability, it can detect damage larger than 5cm. 2 The metal sheathing damage was detected, compared to traditional methods which can only detect damage larger than 50cm. 2 The sensitivity to damage has been increased tenfold. Furthermore, it exhibits high detection sensitivity for minor, localized damage to cables, enabling timely identification of potential faults. In terms of real-time monitoring, it can acquire voltage data in real time and process it through the damage analysis module, thereby promptly detecting and addressing damage to the cable's metallic sheath.

[0021] 3. Strong anti-interference capability. In power frequency voltage applications, testing is conducted using 50Hz or 60Hz power frequency voltage, effectively eliminating the interference of capacitive current in the cable on the measurement results and improving the accuracy of the test. Simultaneously, the system possesses good electromagnetic compatibility, enabling it to operate normally in complex electromagnetic environments without being affected by external electromagnetic interference. Regarding the current-limiting resistor design, a current-limiting resistor Rg (Rg≤10Ω) limits the grounding current, preventing excessive grounding current from affecting the measurement results or damaging the cable.

[0022] 4. Strong Engineering Applicability. This system excels in adapting to various cable types, suitable for different types and specifications of cables, including cross-linked polyethylene (XLPE) cables and polyvinyl chloride (PVC) cables, demonstrating broad applicability. Furthermore, the system supports segmented testing of long cables, with a test point every 2 kilometers, enabling segmented testing of long-distance cables and improving the comprehensiveness of the inspection. Regarding ease of integration and maintenance, the system adopts a modular design, with each functional module operating independently, facilitating integration and maintenance. Simultaneously, all modules can be integrated into a portable chassis, simplifying on-site operation and transportation.

[0023] 5. High safety. Regarding safety measures, the power module capable of outputting high-voltage power at industrial frequency has overvoltage and overcurrent protection functions to ensure the safety of the testing process. In addition, the grounding controller module has a quick disconnection function, which can quickly disconnect the grounding in an emergency to ensure the safety of operators.

[0024] 6. Significant Economic Benefits. Regarding reduced testing costs, the system can perform tests without power outages, avoiding economic losses caused by power outages. Furthermore, by promptly detecting and addressing damage to the cable's metallic sheath, it extends the cable's lifespan and reduces replacement costs. In terms of improved power supply reliability, the system's regular inspections promptly detect damage to the cable's metallic sheath, preventing cable faults and thus improving power supply reliability. Simultaneously, early detection and handling of potential faults reduce the cost of cable repair and replacement. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] In the attached diagram: Figure 1 This is a structural block diagram of the cable metal sheath damage detection system of the present invention; Figure 2This is a graph showing the relationship between cable length and threshold in scenario 1 of the present invention; Figure 3 This is a graph showing the relationship between temperature and threshold in scenario 2 of the present invention; Figure 4 This is a graph showing the relationship between the K value and the threshold in scenario 3 of the present invention; Figure 5 A graph showing the relationship between cable length and threshold values ​​obtained by setting threshold values ​​for existing methods and the weighted method of this invention; Figure 6 This is an equivalent circuit diagram when the metal sheath of the cable of the present invention is damaged. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] The following detailed description of some embodiments of the present invention will be provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0029] Please see Figure 1 This invention provides a cable metal sheath damage detection system based on power frequency withstand voltage and line loss compensation, comprising a power supply module, a voltage measurement module, a grounding controller module, a line loss compensation module, and a damage analysis module. The grounding controller module, power supply module, voltage measurement module, damage analysis module, and line loss compensation module are electrically connected in sequence.

[0030] The power supply module can be a power frequency high-voltage source, used to output an adjustable power frequency voltage to the beginning of the cable under test. The voltage range is 0.5kV to 5kV, and the frequency is 50Hz or 60Hz (depending on the local power grid frequency). The output voltage accuracy is ±0.5%. It also has overvoltage and overcurrent protection functions to ensure the safety of the testing process, and can be remotely controlled and transmit data through the control interface.

[0031] The voltage measurement module is used to simultaneously measure the voltage U at the beginning of the cable under test. in and terminal voltage U out It features a measurement accuracy of ±0.1% and a sampling rate of ≥10kHz, ensuring accurate capture of instantaneous voltage waveforms. Simultaneously, it possesses electromagnetic interference resistance, enabling it to adapt to complex electromagnetic environments on-site.

[0032] The grounding controller module is used to ground the end of the cable under test. It can control the grounding status of the cable end, achieve rapid disconnection, and has a grounding resistance of ≤10Ω to ensure grounding reliability. Its response time is less than 1ms to ensure rapid switching, and it has a status monitoring function to provide real-time feedback on the grounding status.

[0033] The line loss compensation module is used to determine the theoretical attenuation coefficient K of the cable under test, and to set a threshold based on the theoretical attenuation coefficient K, cable length L, cable type (Cable_Type), and environmental factors (including temperature, humidity, etc.) (Env). It can compensate for voltage attenuation caused by the inherent impedance Z of the cable under test, with a calculation accuracy of ≥99%.

[0034] It should be noted that the voltage attenuation caused by the inherent impedance Z of the cable under test can be described by the theoretical attenuation coefficient K: ; in, e The base of the natural logarithm, This refers to the cable length. The attenuation constant is related to the conductor resistance R per unit length of the cable under test (unit: ) and insulation conductivity per unit length G (unit: )related,

[0035] Attenuation constant This indicates the rate at which an electrical signal weakens as it travels through a cable; the farther the signal travels, the greater the attenuation. Cable losses mainly have the following two aspects: 1. Conductor loss: When current passes through the metal conductor of a cable, some energy is lost due to the resistance of the metal conductor. The resistance per unit length of the metal conductor is represented by R.

[0036] 2. Dielectric loss: Current also loses energy in the insulation layer of the cable. This depends on the characteristics of the insulation material and is expressed as insulation conductance G per unit length.

[0037] However, the theoretical attenuation coefficient K is merely intended to provide the most accurate initial estimate possible when direct measurement is not possible (such as during initial system use or after drastic changes in operating conditions), thereby improving the system's applicability and response speed. This is because the conductor resistance R and insulation conductance G per unit length of cable are not only difficult to obtain precisely, but also dynamically change with factors such as ambient temperature, humidity, cable aging, and laying method. For example, increased temperature leads to an increase in conductor resistance R per unit length, and insulation conductance G also changes. Therefore, the theoretical attenuation coefficient K calculated purely from theoretical formulas and cable manual parameters inevitably contains significant errors. Directly setting a threshold based on the theoretical attenuation coefficient K for damage assessment is highly prone to false alarms or missed alarms, and setting the threshold is also quite difficult.

[0038] Based on this, in addition to considering the theoretical attenuation coefficient K, this invention also considers the effects of cable length L, cable type (Cable_Type), and environmental factors (Env). The longer the cable, the more the signal naturally attenuates during transmission, resulting in a larger normal fluctuation range for longer cables, thus requiring a larger threshold. The theoretical attenuation coefficient K represents the theoretical degree of signal attenuation; a smaller K indicates greater signal attenuation, necessitating a larger threshold to avoid misjudgments. Different types of cables (e.g., different materials) have different electrical characteristics. For example, XLPE cables and PVC cables have different normal fluctuation ranges, therefore requiring different thresholds. Environmental conditions such as temperature and humidity affect the electrical characteristics of cables; under different environments, the normal fluctuation range of cables varies, necessitating corresponding adjustments to the threshold settings.

[0039] In some embodiments, threshold It can be viewed as a function of multiple variables:

[0040] The present invention uses the controlled variable method to analyze the weights of each influencing factor as follows.

[0041] Change the cable length (L): Select undamaged cables of the same type with lengths of 100m, 200m, 500m, 1000m, and 2000m. Under the same environmental conditions (e.g., 20℃, 50% humidity) and K value, measure the voltage deviation of each cable and record its maximum value or standard deviation.

[0042] Change cable type (Cable_Type): Select intact cables of the same length (e.g., 500m) but different cable types (XLPE, PVC, etc.), measure their voltage deviations under the same conditions, and record their maximum values ​​or standard deviations.

[0043] Changing the cable's environment (Env): Place the same intact cable in an environmental test chamber and change the temperature (e.g., -10℃, 0℃, 20℃, 40℃) and humidity (30%, 50%, 80%), measure the voltage deviation of each cable, and record the maximum value or standard deviation.

[0044] Changing the theoretical attenuation coefficient K of a cable: For the same intact cable, the change in the value of K can be simulated by adding external impedance, etc., and the voltage deviation of each cable can be measured and its maximum value or standard deviation recorded.

[0045] A series of datasets were finally obtained, some of which are shown in Table 1.

[0046]

[0047] Specifically, based on the above dataset, the weights are determined using a multivariate statistical regression model:

[0048] Where w1, w2, w3, w4, and w5 are weighting coefficients, respectively. Temp For temperature, Humi Let be the humidity, and b be a constant.

[0049] Based on extensive experimental data fitting and practical engineering experience, the weights of each influencing factor in a specific embodiment of this invention can be determined as follows: The weight of cable length L (w1) is 40%, having the greatest direct impact because line loss is exponentially related to length. The weight of the theoretical attenuation coefficient K (w2) is 30%. The value of K directly determines the compensation benchmark; the smaller the K value, the greater the inherent attenuation and the wider the normal fluctuation range. The weight of cable type (w3) is 20%. Different armor materials (such as steel tape, steel wire, copper tape) and different insulation materials (XLPE, PVC) have different resistances and insulation conductivities, directly affecting inherent attenuation. In the cable's environment (Env), temperature has a weight of 5%, and humidity has a weight of 5%. As temperature increases, metal resistance increases, leading to greater attenuation; simultaneously, insulation conductivity also changes. Increased humidity may lead to increased surface conductivity of the insulation, resulting in a slight increase in attenuation.

[0050] The following are the simulation experimental data results of this invention.

[0051] Scenario 1: With fixed environmental conditions and K value, observe the effects of cable length and cable type.

[0052] The cable's environmental conditions are set to standard (20℃, 50% humidity). The K value is 0.88. Calculate the threshold values ​​for XLPE and PVC cables at different lengths. Plot the relationship between cable length and the threshold value as shown below. Figure 2 As shown.

[0053] Scenario 2: With fixed cable length, K value, and humidity, observe the effects of ambient temperature and cable type.

[0054] Set the cable length to 500 meters, K value to 0.88, and humidity to 50%. Calculate the threshold values ​​for XLPE and PVC cables at different temperatures and plot the relationship between temperature and threshold values ​​as follows: Figure 3 As shown.

[0055] Scenario 3: With fixed length and environment, observe the effects of K value and cable type.

[0056] The cable length is set to 500 meters, and the environmental conditions are 20℃ and 50% humidity. Calculate the threshold values ​​for XLPE and PVC cables at different K values, and plot the relationship between K values ​​and threshold values ​​as follows: Figure 4 As shown.

[0057] In practical applications, multivariate nonlinear regression or machine learning algorithms (such as random forests and gradient boosting trees) can be used to fit the data and ultimately determine the threshold. Additionally, as... Figure 5 As shown, with XLPE cable, temperature 20℃, humidity 50%, and K=0.88, the relationship between cable length and threshold is illustrated using the existing method (a multiplier model that multiplies various influencing parameters) and the weighted method of this invention (an additive model) when setting the threshold. It is evident that the weighted method of this invention sets the threshold closer to the true value, and the set threshold is more accurate.

[0058] The damage analysis module is used to analyze the theoretical attenuation coefficient K and the first-end voltage U of the cable under test. in and terminal voltage U out Calculate the voltage deviation ΔU of the cable under test, and compare the voltage deviation ΔU with the threshold value. By comparison, it can be determined whether the metal sheath of the cable under test is damaged.

[0059] Voltage deviation The formula for calculation is: .

[0060] When the metallic sheath of the cable under test is damaged, the shunting effect at the point of damage will lead to... Decrease, thus making Increase.

[0061] The damage analysis module's judgment logic is based on ΔU and The comparison results, if If the metal sheath of the cable under test is damaged, it is determined that the cable's metal sheath is damaged; if If the damage analysis module detects damage to the metal sheath, the system is determined to be intact. Furthermore, the system includes an early warning module; when the damage analysis module determines that the metal sheath is damaged, the early warning module can issue an audible and visual alarm, thus providing an alarm function.

[0062] Based on the same inventive concept, another embodiment of the present invention provides a method for detecting cable metal sheath damage, employing the cable metal sheath damage detection device of the aforementioned embodiment, the method comprising: Step 1: Ground the end of the cable under test through the grounding controller module; Step 2: The power module inputs a high-frequency power voltage to the beginning of the cable under test; Step 3: The voltage measurement module measures the voltage U at the beginning of the cable under test. in and terminal voltage U out ; Step 4: The line loss compensation module determines the theoretical attenuation coefficient K of the cable under test, and sets a threshold based on the theoretical attenuation coefficient K, cable length L, cable type (Cable_Type), and environmental factors (including temperature, humidity, etc.) (Env). ; Step 5: The damage analysis module analyzes the theoretical attenuation coefficient K and the starting voltage U of the cable under test. in and terminal voltage U out Calculate the voltage deviation ΔU of the cable under test and compare it with the threshold. By comparison, it can be determined whether the metal sheath of the cable under test is damaged.

[0063] like Figure 6 The diagram shown is an equivalent circuit diagram when the metallic sheath of a cable is damaged. Among them, The voltage applied to the beginning of the cable under test by the power module. Z is the voltage at the end of the cable under test; Z is the inherent impedance of the cable under test; Rg is the current-limiting resistor, a protective resistor with a known resistance provided by the grounding controller module, whose main function is to limit the current in the grounding loop and ensure the safety of the system and operators. Rp is the equivalent resistance at the point of damage in the cable under test.

[0064] Specifically, a high-frequency voltage (typically 1-2kV) can be applied to the armored end of the cable under test, through a current-limiting resistor. ( (≤10Ω) Ground the armored end of the cable under test, and simultaneously measure the voltage at the beginning of the cable using a voltage measurement module. With the voltage at the end .if If the metal sheath of the cable under test is damaged, it is determined that the cable's metal sheath is damaged; if If the test result is positive, the metal sheath of the cable under test is deemed to be intact.

[0065] Furthermore, when the damage analysis module detects damage to the metal sheath of the cable under test, it triggers an audible and visual alarm via the early warning module. It can also record data such as the location of the damage, time, and voltage deviation, which allows staff to manually verify the damage based on the alarm information.

[0066] The following are specific embodiments of the present invention.

[0067] Example 1: Inspection of the metallic sheath of a 10kV YJV22 cable.

[0068] The cable is 500m long.

[0069] Disconnect the cable end and ground it, apply a 1.5kV power frequency voltage, and then apply the voltage through the current-limiting resistor R. g =10Ω, ground the armored end of the cable. Measure U in =1.5kV, U out =0.97kV, the calculated K=0.88, set =0.2kV. Calculate ΔU = 0.88 × 1.5 - 0.97 = 0.35kV. Compare ΔU with... : 0.35kV>0.2kV.

[0070] Judgment result: Alarm triggered, the metal sheath of the cable is damaged.

[0071] The test results were manually verified: the cable was manually inspected, confirming a 5cm gap approximately 200m from the beginning of the cable. 2 Damage.

[0072] Conclusion: The system of the present invention can accurately detect damage to the metal sheath of cables, verifying the reliability of the method.

[0073] Example 2: Detection of the metallic sheath of a 1kV PVC insulated cable.

[0074] The cable is 200m long.

[0075] Disconnect the cable end and ground it, apply a 1kV power frequency voltage, and then apply the voltage through the current-limiting resistor R. g =10Ω, ground the armored end of the cable. Measure U in =1kV, U out =0.92kV, the calculated K=0.95, set =0.1kV. Calculate ΔU = 0.95 × 1 - 0.92 = 0.03kV. Compare ΔU with... : 0.03kV>0.1kV.

[0076] Judgment result: The cable's metal sheath is intact.

[0077] The test results were manually verified: the cable was manually inspected and no damage was found.

[0078] Conclusion: No damage was detected in the system of the present invention, verifying the accuracy of the method.

[0079] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. It should be understood that the invention is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A cable metallic sheath breakage detection system, characterized in that, The system comprises a power module, a voltage measurement module, a grounding controller module, a line loss compensation module and a damage analysis module; the grounding controller module is used for grounding the end of the cable to be tested, the power module is used for outputting adjustable power frequency voltage to the head of the cable to be tested, and the voltage measurement module is used for synchronously measuring the head voltage and the end voltage of the cable to be tested; the line loss compensation module is used for determining the theoretical attenuation coefficient of the cable to be tested, and setting a threshold value according to the theoretical attenuation coefficient of the cable to be tested, the cable length, the cable type and the environmental factors; The damage analysis module is used for calculating the voltage deviation of the cable to be tested according to the theoretical attenuation coefficient, the head voltage and the end voltage of the cable to be tested, and comparing the voltage deviation with the threshold value to determine whether the metal sheath of the cable to be tested is damaged.

2. The cable metal shield breach detection system of claim 1, wherein, The metal sheath of the cable to be tested comprises an armor layer or a shielding layer.

3. The cable metal shield breach detection system of claim 1, wherein, The calculation formula of the theoretical attenuation coefficient of the cable to be tested is: wherein, e is the base of the natural logarithm, is the cable length of the cable to be measured, is the attenuation constant.

4. The cable metal shield breach detection system of claim 3, wherein, The calculation formula of the attenuation constant is: Wherein, R is the unit length conductor resistance of the cable to be tested, and G is the unit length insulation conductance of the cable to be tested.

5. The cable metal shield breach detection system of claim 1, wherein, The environmental factors include temperature or humidity.

6. The cable metal shield breach detection system of claim 5, wherein, The calculation formula of the threshold value is: Wherein, w1, w2, w3, w4, w5 are weight coefficients respectively, L is the cable length of the cable to be measured, K is the theoretical attenuation coefficient of the cable to be measured, Cable_Type is the cable type of the cable to be measured, Temp is the temperature, Humi is the humidity, and b is a constant.

7. The cable metal shield breach detection system of claim 6, wherein, The calculation formula of the voltage deviation is: Wherein, U in , U out are the head voltage and the tail voltage of the cable to be measured, respectively.

8. The cable metal shield breach detection system of claim 1, wherein, The comparison of the voltage deviation with the threshold value to determine whether the metal sheath of the cable to be tested is damaged comprises: If , it is determined that the metal sheath of the cable under test is damaged; if , it is determined that the metal sheath of the cable under test is intact.

9. The cable metal shield breach detection system of claim 8, wherein, Further comprising a pre-warning module; the pre-warning module is used for performing sound and light alarm when the damage analysis module determines that the metal sheath of the cable to be tested is damaged.

10. A method of detecting a break in a cable metallic sheath, characterized in that, The method comprises: Grounding the end of the cable to be tested through the grounding controller module; The power module inputs power frequency high voltage to the head of the cable to be tested; The voltage measurement module measures the head voltage and the end voltage of the cable to be tested; The line loss compensation module determines the theoretical attenuation coefficient of the cable to be tested, and sets a threshold value according to the theoretical attenuation coefficient of the cable to be tested, the cable length, the cable type and the environmental factors; The damage analysis module calculates the voltage deviation of the cable to be tested according to the theoretical attenuation coefficient, the head voltage and the end voltage of the cable to be tested, and compares the voltage deviation with the threshold value to determine whether the metal sheath of the cable to be tested is damaged.

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