Submarine Cable Shielding Grounding Fault Judgment Method and System

Abstract

A method and system for judging the shielding grounding fault of submarine cables, which collect the shielding grounding current of submarine cables; judge the faults of abnormal phenomena of submarine cable shielding grounding: set the amplitude alarm limit M of the collected quantity, the number of times K of over-amplitude alarm and the judgment period T, and analyze the collected samples; set the calculation formula: y1(t) = x1(t)g(t), #imgabs0# set the judgment conditions: Judgment condition 1: |y1(t) - y2(t)| > M0; Judgment condition 2: y1(t) > M1; or y2(t) > M2; Set the fault judgment logic: If Judgment condition 1 is not satisfied, then judge Judgment condition 2; If Judgment condition 2 is not satisfied, then return to the sampling starting point; If Judgment condition 2 is satisfied, then store the result in the database and issue a fault abnormality warning. By adding a current transformer to the grounding lead-out wire of the submarine cable shielding layer to monitor the magnitude of the grounding current, the grounding situation of the submarine cable shielding layer lead-out can be judged online in real time, avoiding virtual connection and thermal breakdown at the joints of the submarine cable switchgear.

Description

Technical Field

[0001] The present invention belongs to the technical field of submarine cable shielding grounding fault analysis, and particularly relates to a method and system for judging submarine cable shielding grounding faults. Background Art

[0002] For submarine cables of offshore wind turbines, generally, the steel armor layer is grounded at the base tower opening, and then the three-phase submarine cables are respectively introduced into the switch cabinet. The submarine cables are connected to the switch cabinet in a T-head manner. Before the T-head, the shielding layer of the submarine cable needs to be led out and grounded, and the shielding layers at both ends of a section of submarine cable need to be grounded separately. When the wind turbine is operating normally, a circulating current is formed between the shielding layer of the submarine cable and the ground through electromagnetic induction of the main conductor. Due to reasons such as the current-carrying design of the shielding layer grounding wire, construction technology, and heat accumulation of the circulating current, thermal breakdown occurs at the grounding lead-out joint of the shielding layer of the submarine cable. As the operation years of the unit increase, the thermal breakdown at the grounding lead-out joint of the shielding layer of the submarine cable is obvious. The thermal breakdown of the submarine cable may cause the collector line to trip and the switch cabinet to be damaged. The repair time cycle of the submarine cable is relatively long, seriously affecting equipment and personal safety, resulting in significant power generation losses, and obvious decline in operating economic benefits.

[0003] In recent years, among the fault causes of offshore wind power collector lines, the proportion of heat breakdown of the shielding layer grounding wire of submarine cables is relatively large. However, the T-head of the submarine cable and the installation position of the shielding layer grounding wire are in the lower cabin of the switch cabinet, and it is impossible to carry out regular inspection and maintenance during the operation of the wind turbine. Once thermal breakdown occurs, it will cause the collector line to trip, resulting in power generation losses. At the same time, the economic cost and time cost of repairing the submarine cable are high, and there is a lack of effective monitoring means. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for judging submarine cable shielding grounding faults. By adding current transformers to the grounding lead-out wire of the shielding layer of the submarine cable to monitor the magnitude of the grounding current, the grounding situation of the shielding layer of the submarine cable can be judged in real time online, avoiding virtual connection and thermal breakdown at the joint of the submarine cable switch cabinet.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is:

[0006] A method and system for judging submarine cable shielding grounding faults, the steps are as follows:

[0007] Collect the grounding current of the submarine cable shielding;

[0008] Judge the fault of abnormal phenomena of the submarine cable shielding grounding:

[0009] Set the amplitude alarm limit M of the collected quantity, the number of alarm times K for exceeding the amplitude, and the judgment period T, and analyze the collected samples;

[0010] Set the calculation formula:

[0011] y1(t) = x1(t)g(t),

[0012]

[0013] Set judgment conditions:

[0014] Judgment condition 1: |y1(t) - y2(t)| > M0;

[0015] Judgment condition 2: y1(t) > M1; or y2(t) > M2;

[0016] Set the fault judgment logic: If judgment condition 1 is not satisfied, then judge judgment condition 2;

[0017] If judgment condition 2 is not satisfied, then return to the sampling starting point;

[0018] If judgment condition 2 is satisfied, then store the result in the database and issue a fault exception warning.

[0019] Preferably, the collected amounts of the shielding ground currents of phases a, b, and c are respectively The collected amounts of the three-phase shielding grounds are Then the collection amount formula is Collect the three-phase current collection amounts, and the collection function:

[0020]

[0021] Then the output amounts are respectively y1(t) = x1(t)g(t),

[0022] Preferably, the fault judgment process is as follows:

[0023] Judge the collected output amounts y1(t) and y2(t). When the difference between the two collected output amounts is greater than a certain limit value, judge that the sampling of the sampling device is abnormal, trigger an alarm message, and issue a sampling abnormal alarm;

[0024] When |y1(t)| > M1 or |y2(t)| > M2, judge the number of times K of the over-amplitude alarm of the collected current output amount within a judgment period T after the current over-limit time t has passed. If it is greater than K, trigger an alarm message, judge that there is a problem with the grounding of the grounding lead of the submarine cable shielding layer, and issue an equipment abnormal alarm.

[0025] Preferably, if |y1(t) - y2(t)| > M0; then directly output the sampling abnormal alarm result.

[0026] Preferably, current transformers are additionally installed on the grounding lead-out wires of the shielding layers below the T-type joints of the a, b, and c phases of the submarine cable of the offshore wind turbine to collect real-time three-phase shielding currents. At the same time, a current transformer is additionally installed after the grounding lead-out wires of the shielding layers of the a, b, and c phases are aggregated to collect the three-phase unbalanced current of the shielding layer in real time;

[0027] The sampling signal of the current transformer is connected to the comprehensive protection device of the fan through a cable, converted into a digital signal through the analog channel of the comprehensive protection device, and the collected data is encrypted by using the existing longitudinal encryption device of the wind turbine. The encrypted acquisition signal is transmitted out through the fan switch, and the transmission optical fiber follows the path of the submarine cable and is connected in series to all the wind turbines on this collector line;

[0028] Preferably, the process of collecting the shielding grounding current is as follows: The grounding current acquisition amounts of each section of the submarine cable of each collector line are connected to the offshore substation switch through the submarine cable optical fiber, decrypted by the longitudinal encryption device, and stored, analyzed, and processed at the manual interaction station of the offshore substation; at the same time, it is transmitted to the onshore through the optical fiber of the offshore substation and the onshore centralized control station, and stored, analyzed, and processed at the manual interaction station of the onshore centralized control station.

[0029] A submarine cable shielding grounding current acquisition system includes a current transformer, a comprehensive protection device, a longitudinal encryption device, a communication device, a fan switch, and an optical fiber terminal. The current transformer is a current transformer, which is installed on the shielding grounding wire. The current transformer is connected to the comprehensive protection device through a sampling transmission cable. The comprehensive protection device is connected to the communication device through an optical fiber. The communication device is communicatively connected to the longitudinal encryption device and the fan switch. The fan switch is connected to the optical fiber terminal through an optical fiber. The optical fiber terminal is connected to the optical fiber terminal box of other fans through a continuous box.

[0030] A submarine cable shielding grounding fault judgment system includes a current transformer, a comprehensive protection device, a longitudinal encryption device, a communication device, a fan switch, and an optical fiber terminal. The optical fiber terminal is connected to a data processing unit. It is characterized in that: the current transformer is a current transformer, which is installed on the shielding grounding wire. The current transformer is connected to the comprehensive protection device through a sampling transmission cable. The comprehensive protection device is connected to the communication device through an optical fiber. The communication device is communicatively connected to the longitudinal encryption device and the fan switch. The fan switch is connected to the optical fiber terminal through an optical fiber. The optical fiber terminal is connected to the optical fiber terminal box of other fans through a continuous box. The data processing unit is connected to the optical fiber terminal box, and the program instructions adopted by the data processing unit are the submarine cable shielding grounding fault judgment method.

[0031] A data processing unit for submarine cable shielding grounding faults is characterized in that the program instructions adopted by the data processing unit are the submarine cable shielding grounding fault judgment method.

[0032] The present invention can achieve the following beneficial effects:

[0033] 1. By adding current transformers to the grounding lead-out wire of the submarine cable shielding layer to monitor the magnitude of the shielding grounding current, the grounding situation of the submarine cable shielding layer can be judged online in real time, avoiding virtual connection and thermal breakdown at the joints of the submarine cable switchgear.

[0034] 2. Through fault analysis and judgment, the grounding status of the submarine cable shielding layer can be effectively monitored, warned, and recorded. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below in conjunction with the drawings and embodiments:

[0036] Figure 1 It is the judgment logic diagram of the submarine cable shielding grounding fault judgment method of the present invention;

[0037] Figure 2 It is the connection diagram of a submarine cable shielding grounding current acquisition system of the present invention;

[0038] Figure 3 It is the connection system diagram of the onshore centralized control station and the offshore booster station of the present invention;

[0039] Figure 4 It is the installation schematic diagram of the current transformer of the present invention.

[0040] In the figure: T-shaped joint 1, shielding wire grounding wire 2, current transformer 3, sampling and transmission cable 4, cable 5, switchgear bottom 6. DETAILED DESCRIPTION OF THE INVENTION

[0041] The preferred solution is as Figures 1 to 4 shown. A method for judging submarine cable shielding grounding faults has the following steps:

[0042] Sensor installation: Current transformers are added to the grounding lead-out wires of the shielding layers below the T-shaped joints of the a, b, and c phases of the submarine cable of the offshore wind turbine to collect the real-time three-phase shielding currents. At the same time, a current transformer is added after the grounding lead-out wires of the shielding layers of the a, b, and c phases are aggregated to collect the real-time three-phase unbalanced current of the shielding layer.

[0043] Specifically, current transformers with high precision, low power consumption, and wide frequency band are selected to ensure accurate measurement of tiny shielding current changes under various sea conditions. During installation, it is necessary to ensure that the transformers are closely attached to the grounding lead-out wires of the shielding layer to reduce measurement errors, and they are wrapped with anti-corrosion materials to improve durability in the marine environment. A special submarine cable resistant to salt spray and corrosion is used to connect the transformers to the comprehensive protection device, and the wiring path should avoid high-risk areas as much as possible, such as areas with frequent submarine geological activities, to reduce the risk of external damage.

[0044] The sampling signal of the current transformer is connected to the comprehensive protection device of the fan through a cable, converted into a digital signal through the analog channel of the comprehensive protection device, and the collected data is encrypted by using the existing longitudinal encryption device of the wind turbine. The encrypted acquisition signal is sent out through the fan switch, and the transmission optical fiber follows the path of the submarine cable, connecting all the wind turbines on this collector line in series;

[0045] Specifically, a high-resolution ADC (analog-to-digital converter) is integrated inside the comprehensive protection device to improve the accuracy of the collected signal. A filtering algorithm is added in the preprocessing stage to remove signal noise and improve the accuracy of subsequent analysis. The latest AES-256-bit encryption standard is adopted, combined with dynamic key management technology, to ensure that the data is not stolen or tampered with during transmission. At the same time, the key distribution center (KDC) mechanism is used to ensure the secure exchange and regular update of keys.

[0046] The collected amount of the shielding grounding current of each section of the submarine cable of each collector line is connected to the offshore substation switch through the submarine cable optical fiber, decrypted by the longitudinal encryption device, and stored, analyzed, and processed at the manual interaction station of the offshore substation; at the same time, it is transmitted to the onshore through the optical fiber of the offshore substation and the onshore centralized control station, and stored, analyzed, and processed at the manual interaction station of the onshore centralized control station.

[0047] The fault judgment process is as follows:

[0048] S1. Collect the shielding grounding current of the submarine cable;

[0049] The collected amounts of the shielding grounding currents of phases a, b, and c are respectively The collected amounts of the three-phase shielding grounding currents are Then the collection amount formula is The three-phase current collection amounts are pooled, and the pooling function:

[0050]

[0051] Then the output amounts are y1(t) = x1(t)g(t),

[0052] S2. Judge the fault of the abnormal phenomenon of the shielding grounding of the submarine cable:

[0053] S2.1. Set the alarm limit M of the collection amount amplitude, the number of times K of over-amplitude alarm, and the judgment period T, and analyze the collected samples;

[0054] S2.2. Set the calculation formula:

[0055] y1(t) = x1(t)g(t),

[0056]

[0057] S2.3. Set the judgment conditions:

[0058] Judgment condition 1: |y1(t) - y2(t)| > M0;

[0059] Judgment condition 2: y1(t) > M1; or y2(t) > M2;

[0060] S2.4. Set the fault judgment logic: If judgment condition 1 is not satisfied, then judge judgment condition 2;

[0061] If judgment condition 2 is not satisfied, then return to the sampling starting point;

[0062] If judgment condition 2 is satisfied, then store the result in the database and issue a fault exception warning.

[0063] Furthermore, the fault judgment process is as follows:

[0064] Judge the acquisition output quantities y1(t) and y2(t). When the difference between the two acquisition output quantities is greater than a certain limit value, judge that the sampling device has abnormal sampling, trigger an alarm message, and send a sampling abnormal alarm;

[0065] When |y1(t)| > M1 or |y2(t)| > M2, judge the number of times K of the over-amplitude alarm of the collected current output quantity within a judgment period T in the current over-limit time t. If it is greater than K, trigger an alarm message, judge that there is a problem with the grounding of the grounding lead of the submarine cable shielding layer, and send an equipment abnormal alarm.

[0066] Furthermore, if |y1(t) - y2(t)| > M0; then directly output the sampling abnormal alarm result.

[0067] Example 1:

[0068] Assume that there are 100 wind turbines in a certain offshore wind farm, which are connected to the offshore substation through three collector lines, and each collector line serves about 33 wind turbines. The submarine cable type is 3×220kV AC submarine cable, and the length of each phase of the submarine cable is about 30 kilometers. Use specific numerical values to show how to use the above technical solution to judge and warn the grounding fault of the submarine cable shielding layer.

[0069] 1. Sensor installation and configuration:

[0070] Current transformer specifications: Select a current transformer with a rated current of 1A and an accuracy class of 0.5, which can accurately measure the shielding current from microamps to several hundred milliamps.

[0071] Sampling frequency: The comprehensive protection device sets the sampling frequency to 1kHz to ensure that high-frequency transient current changes can be captured

[0072] 2. Data acquisition and processing:

[0073] Encryption algorithm: The AES-256-GCM encryption algorithm is adopted to ensure the security of data during transmission.

[0074] Sampling and analysis period: The data sampling period is set to 1 second, and the analysis period is 5 minutes, that is, the fault judgment logic operation is performed every 5 minutes.

[0075] Threshold setting: Based on historical data analysis and on-site testing, the alarm limits are set as follows:

[0076] The amplitude alarm limit M = 50 mA to prevent false alarms and ensure sensitivity;

[0077] The number of times of over-amplitude alarm K = 3. Within a judgment period T = 5 minutes, if the current of a certain phase exceeds the value of M three times, an alarm is triggered; the unbalanced current threshold M0 = 200 mA is used to judge the three-phase unbalanced situation; the single-phase current threshold M1 = 100 mA, and the total threshold of three-phase unbalanced current M2 = 300 mA.

[0078] In a certain data acquisition, the average value of the current of the shielding layer of phase a is 80 mA, that of phase b is 70 mA, that of phase c is 60 mA, and the three-phase unbalanced current is 50 mA. In the next 5 minutes, the sampling value of phase a exceeds 100 mA four times, and the rest of the time is normal.

[0079] Judgment process:

[0080] 1) Calculate that the maximum difference between the zero-sequence current and the sampled zero-sequence current is 20 mA, which is less than the set unbalanced current threshold M0 = 200 mA, so the sampling anomaly alarm is not triggered.

[0081] 2) Analyze the current of phase a and find that the sampling value exceeds the single-phase current threshold M1 = 100 mA four times, and these four over-amplitude occurrences are within the judgment period, meeting the condition y1(t)>M1 in condition two.

[0082] Therefore, the system judges that there may be a grounding problem in the shielding layer of phase a, immediately sends an equipment anomaly alarm to the maintenance team, and records it in the database for subsequent analysis and maintenance plan formulation.

[0083] A submarine cable shielding grounding current acquisition system includes a current transformer, a comprehensive protection device, a longitudinal encryption device, a communication device, a fan switch, and an optical fiber terminal. The current transformer is an electromagnetic current transformer, which is installed on the shielding grounding wire. The current transformer is connected to the comprehensive protection device through a sampling transmission cable. The comprehensive protection device is connected to the communication device through an optical fiber. The communication device communicates with the longitudinal encryption device and the fan switch. The fan switch is connected to the optical fiber terminal through an optical fiber. The optical fiber terminal is connected to the optical fiber terminal boxes of other fans through a continuous box.

[0084] A submarine cable shielding grounding fault judgment system includes a mutual inductor, a comprehensive protection device, a longitudinal encryption device, a communication device, a fan switch, and an optical fiber terminal. The optical fiber terminal is connected to a data processing unit. The mutual inductor is a current mutual inductor, which is installed on the shielding grounding wire. The current mutual inductor is connected to the comprehensive protection device through a sampling transmission cable. The comprehensive protection device is connected to the communication device through an optical fiber. The communication device is communicatively connected to the longitudinal encryption device and the fan switch. The fan switch is connected to the optical fiber terminal through an optical fiber. The optical fiber terminal is connected to the optical fiber terminal boxes of other fans through a continuous box. The data processing unit is connected to the optical fiber terminal box. The program instructions adopted by the data processing unit are the submarine cable shielding grounding fault judgment method.

[0085] A data processing unit for submarine cable shielding grounding faults, characterized in that the program instructions adopted by the data processing unit are the submarine cable shielding grounding fault judgment method.

[0086] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations to the present invention. The protection scope of the present invention should be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. Method for judging submarine cable shielding grounding fault, characterized by the following steps: Collect the submarine cable shielding grounding current; Judge the fault of abnormal phenomena of submarine cable shielding grounding: Set the amplitude alarm limit M of the collected quantity, the number of over-amplitude alarms K and the judgment period T, and analyze the collected samples; Set the calculation formula: y1(t) = x1(t)g(t), y1(t): calculated zero-sequence current; y2(t): sampled zero-sequence current; x1(t): collected quantity of shielding grounding current of phases a, b, and c; g(t): calculated zero-sequence current aggregation matrix; Set the judgment conditions: Judgment condition 1: |y1(t) - y2(t)| > M0; Judgment condition 2: y1(t) > M1; or y2(t) > M2; M0: unbalanced current threshold; M1: single-phase current threshold; M2: total threshold of three-phase unbalanced current; Set the fault judgment logic: If judgment condition 1 is not satisfied, then judge judgment condition 2; If judgment condition 2 is not satisfied, return to the sampling starting point; If judgment condition 2 is satisfied, store the result in the database and issue a fault anomaly warning; The collected shielding grounding currents of phases a, b, and c are The three-phase shield grounding current collection quantity is: The collection volume formula is Aggregate the three-phase current collection data, aggregation function: Then the output quantities are y1(t)=x1(t)g(t), 2. The method for determining a submarine cable shielding grounding fault according to claim 1, characterized in that: The processing process of the collected samples is as follows: The fault judgment process is as follows: Judge the collected output quantities y1(t) and y2(t). When the difference between the two collected output quantities is greater than a certain limit value, judge that the sampling device has abnormal sampling, trigger an alarm message, and issue a sampling anomaly alarm; When |y1(t)| > M1 or |y2(t)| > M2, judge the number of over-amplitude alarms K of the collected current output quantity within a judgment period T when the current over-limit time t has passed. If it is greater than K, trigger an alarm message and judge that there is a problem with the grounding of the grounding lead of the submarine cable shielding layer, and issue an equipment anomaly alarm.

3. The method for determining a submarine cable shielding grounding fault according to claim 2, characterized in that: If |y1(t) - y2(t)| > M0; then directly output the sampling anomaly alarm result.

4. The method for determining a submarine cable shielding grounding fault according to claim 1, characterized in that: Add current transformers to the shielding grounding leads of phases a, b, and c of the submarine cable T-joints under the offshore wind turbine to collect real-time three-phase shielding currents. At the same time, add current transformers after the shielding grounding leads of phases a, b, and c are aggregated to collect the three-phase unbalanced current of the shielding layer in real time; The sampling signal of the current transformer is connected to the comprehensive protection device of the fan through a cable, converted into a digital signal through the analog channel of the comprehensive protection device, encrypt the collected data by using the existing longitudinal encryption device of the wind turbine, and transmit the encrypted collected signal through the fan switch. The transmission optical fiber follows the submarine cable path and is connected in series to all wind turbines on the collector line.

5. The method for determining a submarine cable shielding grounding fault according to claim 4, characterized in that: The grounding current collection process is as follows: The collected quantity of the grounding current of each section of the submarine cable of each collector line is connected to the offshore substation switch through the submarine cable optical fiber, decrypted by the longitudinal encryption device, and stored, analyzed, and processed at the manual interaction station of the offshore substation; at the same time, it is transmitted to the onshore through the optical fiber of the offshore substation and the onshore centralized control station, and stored, analyzed, and processed at the manual interaction station of the onshore centralized control station.

6. A submarine cable shielding grounding fault judgment system, comprising a mutual inductor, a comprehensive protection device, a longitudinal encryption device, a communication device, a fan switch and an optical fiber terminal, wherein the optical fiber terminal is connected to a data processing unit, and is characterized in that: The mutual inductor is a current mutual inductor, which is installed on the shielded grounding wire. The current mutual inductor is connected to the comprehensive protection device through a sampling transmission cable, and the comprehensive protection device is connected to the communication equipment through optical fiber. The communication equipment is connected to the longitudinal encryption equipment and the fan switch through optical fiber. The fan switch is connected to the optical fiber terminal through optical fiber, and the optical fiber terminal is connected to the optical fiber terminal box of other fans through a continuous box. The data processing unit is connected to the optical fiber terminal box. The program instructions used by the data processing unit are the submarine cable shielding grounding fault judgment method according to any one of claims 1 to 5.

7. A data processing unit for submarine cable shielding grounding fault, characterized in that: The program instructions used by the data processing unit are the method for determining a submarine cable shielding grounding fault according to claim 1.

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