High-voltage cable metal sheath grounding system fault rapid diagnosis method and system based on same sheath loop phase angle difference absolute value and sheath current effective value

Abstract

The invention discloses a high-voltage cable metal sheath grounding system fault rapid diagnosis method and system based on the same sheath loop phase angle difference absolute value and the sheath current effective value, and relates to the technical field of power system fault diagnosis. The method comprises the following steps: collecting sheath current data at the head end and the tail end of a high-voltage cable metal sheath loop in real time; phase and current effective value information in the sheath current data is extracted, and the phase angle difference absolute value of the head end and the tail end of a sheath loop and the standard effective value of current are calculated; and judging whether a fault exists and the fault type according to the change of the absolute value of the phase angle difference and the standardized effective value of the current. According to the invention, various faults in the high-voltage cable metal sheath grounding system can be quickly and accurately diagnosed.

Description

Technical Field

[0001] The present invention relates to the technical field of power system fault diagnosis, and more specifically, to a fast fault diagnosis method and system for a high-voltage cable metal sheath grounding system based on the absolute value of the phase angle difference and the effective value of the sheath current in the same sheath loop. Background Art

[0002] Compared with traditional overhead lines, power cables have extremely obvious advantages in terms of space utilization rate, reliability, and protection of the urban landscape. At present, power cables have almost replaced all traditional overhead transmission lines in urban areas and have become the main channels for urban power transmission and distribution. Therefore, the safe and reliable operation of high-voltage cables plays a crucial role in the stability of the urban power grid and the normal life of residents. Therefore, the research on cable fault diagnosis is particularly important.

[0003] High-voltage cables use the method of metal sheath grounding to isolate the strong electric field inside the cable from the outside, shield electromagnetic interference, provide a fault current conduction path during cable faults, reduce the damage to the cable body during faults, and protect the safety of external equipment and personnel at the same time. The grounding methods of high-voltage cable sheaths mainly include single-end grounding, two-end grounding, midpoint grounding, cross-bonding grounding, etc. At present, cross-bonding grounding is mainly used for long-distance power transmission. This grounding method uses the method of transposing the three-phase sheaths of high-voltage cables to weaken the total induced voltage on the sheath and can effectively suppress the induced current on the sheath.

[0004] Research has found that when a cable fails, it is often accompanied by changes in characteristic signals such as an increase in the induced voltage and induced current of the metal sheath, and an increase in the temperature at the fault and joint. Compared with other signals, the cable sheath current has the advantages of obvious fault characteristics, small current, low induced voltage level, and online acquisition, which better meets the requirements for the identification and classification of various faults such as cable core faults, grounding system faults, and interconnecting box faults. Therefore, the sheath grounding current can reflect the operating state of the cable to a certain extent and can be conveniently obtained without power outage of the system. Therefore, it has become an important indicator for measuring the reliability of high-voltage cables.

[0005] Most of the existing fault diagnosis methods rely on the amplitude information of the sheath current. The diagnosis criteria are complex and the application scenarios are narrow, making it difficult to be widely applied in actual engineering. Therefore, there is an urgent need for a simple, efficient, and field-applicable fault diagnosis method. Summary of the Invention

[0006] In view of this, the present invention provides a fast fault diagnosis method and system for a high-voltage cable metal sheath grounding system based on the absolute value of the phase angle difference and the effective value of the sheath current in the same sheath loop, which can quickly and accurately diagnose various faults in the high-voltage cable metal sheath grounding system.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A rapid fault diagnosis method for a high-voltage cable metal sheath grounding system based on the absolute value of the phase angle difference and the effective value of the sheath current of the same sheath circuit, comprising the following steps:

[0009] Real-time collect the sheath current data at both ends of the head and tail of the high-voltage cable metal sheath circuit;

[0010] Extract the phase and effective current value information from the sheath current data, and calculate the absolute value of the phase angle difference and the standardized effective value of the current at both ends of the head and tail of the sheath circuit;

[0011] Judge whether there is a fault and the type of fault according to the change of the absolute value of the phase angle difference and the standardized effective value of the current.

[0012] Optionally, when real-time collecting the sheath current data at both ends of the head and tail of the high-voltage cable metal sheath circuit, Rogowski coils are respectively installed at the head and tail positions of the three-phase cable, and the clocks at both ends are kept synchronized during the collection process. At the same time, start the data acquisition systems at both ends of the head and tail to record the current waveforms.

[0013] Optionally, use the synchronous clock information to align the current waveforms at both ends of the head and tail, perform Fourier transform on the current waveforms, and extract the fundamental wave components.

[0014] Optionally, perform Fourier transform on the current waveform i(t) to obtain the frequency domain representation I(f):

[0015]

[0016] The fundamental wave component corresponds to the frequency f1, and the amplitude and phase of this frequency are extracted from I(f):

[0017] I1 = I(f1);

[0018] Convert the fundamental wave component back to the time domain:

[0019]

[0020] Among them, |I1| is the fundamental wave amplitude, is the phase.

[0021] Optionally, the fault diagnosis criteria include:

[0022] Normal situation: the absolute value of the phase angle difference is less than 10°, and the standardized effective value of the sheath current is between 0.5 and 1.5;

[0023] Short circuit between the cable core and the sheath: the absolute value of the phase angle difference of the faulty sheath circuit exceeds 120°, the absolute value of the phase angle difference of the non-faulty sheath circuit is less than 10°, and the standardized effective values of the 6 sheath currents all exceed 100;

[0024] Short - circuit between sheath circuits: The absolute value of the phase - angle difference between two short - circuited faulty circuits exceeds 50°, the absolute value of the phase - angle difference of the non - faulty sheath circuit is less than 10°, and the standardized effective values of the four sheath currents of the faulty circuits all exceed 7;

[0025] Cable sheath grounding: The absolute value of the phase - angle difference of the grounding - fault circuit exceeds 50°, the absolute value of the phase - angle difference of the non - faulty sheath circuit is less than 10°, and at least one of the standardized effective values of the sheath current of the faulty circuit exceeds 2;

[0026] Water immersion in cross - bonding box: The absolute values of the phase - angle differences of the three faulty sheath circuits all exceed 120°, and the standardized effective values of the sheath currents of the three faulty circuits are all greater than 7;

[0027] Installation defect of cross - bonding box: The absolute values of the phase - angle differences of the three faulty sheath circuits all exceed 50°, and at least one exceeds 100°, and the standardized effective values of the sheath currents of the three faulty circuits are all greater than 9.

[0028] A fast fault diagnosis system for the high - voltage cable metal sheath grounding system based on the absolute value of the phase - angle difference of the same sheath circuit and the effective value of the sheath current includes:

[0029] Sheath current data acquisition module: Used to collect the sheath current data at both ends of the head and tail of the high - voltage cable metal sheath circuit in real - time;

[0030] Calculation module for the absolute value of the phase - angle difference and the standardized effective value of the current: Used to extract the phase and current effective - value information from the sheath current data, and calculate the absolute value of the phase - angle difference and the standardized effective value of the current at both ends of the sheath circuit;

[0031] Fault diagnosis module: Used to judge whether there is a fault and the type of the fault according to the change of the absolute value of the phase - angle difference and the standardized effective value of the current.

[0032] Through the above - mentioned technical solutions, compared with the prior art, the present invention provides a fast fault diagnosis method and system for the high - voltage cable metal sheath grounding system based on the absolute value of the phase - angle difference of the same sheath circuit and the effective value of the sheath current. This fault diagnosis method is simple and efficient, and is suitable for engineering - site applications. By combining the phase - angle difference and the effective value of the sheath current, various faults in the high - voltage cable metal sheath grounding system can be diagnosed quickly and accurately. The required data is easy to obtain, and the data processing is not complex, which is suitable for popularization and application in actual engineering. Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0034] Figure 1 is a schematic diagram of the installation of the high-voltage cable cross-bonding grounding system and its measuring instrument provided by the present invention;

[0035] Figure 2 is a schematic diagram of the simulation modeling provided by the present invention;

[0036] Figure 3 is a schematic diagram of setting the water immersion fault of the cross-bonding box provided by the present invention;

[0037] Figure 4 is a current waveform diagram before and after the water immersion fault of the cross-bonding box provided by the present invention. Specific Embodiments

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0039] Embodiment 1

[0040] This embodiment discloses a fast fault diagnosis method for the high-voltage cable metal sheath grounding system based on the absolute value of the phase angle difference and the effective value of the sheath current in the same sheath circuit, including the following steps:

[0041] Real-time collect the sheath current data at both ends of the head and tail of the high-voltage cable metal sheath circuit;

[0042] Extract the phase and effective value information of the sheath current data, and calculate the absolute value of the phase angle difference and the standardized effective value of the current at both ends of the sheath circuit;

[0043] Judge whether there is a fault and the type of the fault according to the change of the absolute value of the phase angle difference and the standardized effective value of the current.

[0044] Specifically, a method for rapid fault diagnosis of the grounding system of the metal sheath of high-voltage cables is to measure the grounding current of the cable sheath and extract the required characteristic quantities from it. The required characteristic quantities include: the absolute value of the phase angle difference of the same sheath loop and the standardized effective value of the sheath current. Among them, the calculation method of the standardized effective value: Let I0 be the selected base value, which is the integer value of the average of the three sheath currents during the normal operation of the cable under a certain setting. The value obtained by dividing the measured value by I0 is the standardized effective value. The phase angle difference of the same sheath loop refers to the phase angle measured at the end of a sheath loop minus the phase angle measured at its head end. The fault diagnosis criteria are extracted from a large number of simulation results.

[0045] Fault diagnosis method: By measuring the sheath currents at the head and end of the metal sheath loop of the high-voltage cable, calculate the absolute value of the phase angle difference and the standardized effective value of the sheath current. Determine whether there is a fault based on the change in the absolute value of the phase angle difference. If the absolute value of the phase angle difference increases significantly, it is determined that there is a fault in this sheath loop. Combining with the change in the standardized effective value of the sheath current, further determine the type of fault.

[0046] Before conducting on-line sheath current monitoring and data acquisition, it is necessary to clarify the required facilities: 6 Rogowski coils of model EX100RD, a high-precision GPS synchronous clock, and a high-speed data acquisition system. When installing the equipment, install the six Rogowski coils at the head and end positions of the three-phase cable respectively. When conducting measurement and acquisition work, it is necessary to ensure the clock synchronization at the head and end, start the data acquisition systems at the head and end simultaneously, record the current waveforms for 0.1 s, and then save the current waveform data at the head and end to the same computer. To prevent data loss, upload it to the cloud at the same time.

[0047] During the process of data processing and obtaining characteristic quantities, four steps need to be carried out: waveform alignment, fundamental component extraction, phase extraction and phase difference calculation, standardized effective value extraction and standardized effective value calculation.

[0048] Furthermore, waveform alignment is to align the current waveforms at the head and end using the synchronous clock information.

[0049] Furthermore, perform Fourier transform on the current waveform to extract the fundamental component.

[0050] Specifically, perform Fourier transform on the current waveform i(t) to obtain the frequency-domain representation I(f):

[0051]

[0052] The fundamental component corresponds to the frequency f1, and extract the amplitude and phase of this frequency from I(f):

[0053] I1 = I(f1);

[0054] Convert the fundamental wave component back to the time domain:

[0055]

[0056] where |I1| is the fundamental wave amplitude, is the phase.

[0057] Furthermore, extract the phase angles at the beginning and end of the fundamental wave component, calculate the difference between the phase angles at the beginning and end, and take the absolute value to obtain the absolute value of the phase angle difference.

[0058] Furthermore, extract the root mean square (RMS) values of the current waveforms at the beginning and end and divide by I0 to obtain the standardized RMS value of the sheath current.

[0059] Considering that classifying cable faults based on circuit topology can effectively reflect the characteristics of grounding current and avoid being unable to distinguish faults with different causes but similar circuit topologies, common grounding system faults are classified based on topology here.

[0060] Furthermore, according to the circuit topology, common faults are divided into 4 categories, including: open circuit of the cable sheath circuit, new branch in the cable, new ground branch in the cable sheath circuit, and failure of cross-bonding in the cable sheath circuit. Among them, the new fault branch in the cable includes two specific faults: short circuit between the conductor core and the sheath and short circuit between sheath circuits; the new ground branch in the cable sheath circuit includes three specific faults: grounding of the cable body sheath, breakdown and grounding of the protector in the cross-bonding box, and water ingress in the cross-bonding box.

[0061] The fault diagnosis criteria are summarized based on a large number of simulation results. Use simulation software to establish a simulation model of the high-voltage cable metal sheath grounding system to simulate the changes in sheath current and phase angle difference under different fault types.

[0062] Furthermore, use simulation software (such as PSCAD / EMTDC) to establish a simulation model of the high-voltage cable metal sheath grounding system. The simulation model is as Figure 2 shown, and simulate the changes in sheath current and phase angle difference under different fault conditions.

[0063] Through simulation analysis, summarize the characteristic quantities (absolute value of phase angle difference and standardized RMS value of sheath current) of various faults, and establish the following fault diagnosis criteria.

[0064] Furthermore, normal condition: the absolute value of the phase angle difference is less than 10°, and the standardized RMS value of the sheath current is between 0.5 and 1.5;

[0065] Furthermore, short circuit between the cable conductor core and the sheath: the absolute value of the phase angle difference of the faulty sheath circuit exceeds 120°, the absolute value of the phase angle difference of the non-faulty sheath circuit is less than 10°, and the standardized RMS values of the 6 sheath currents all exceed 100;

[0066] Furthermore, short - circuit between sheath circuits: The absolute value of the phase - angle difference between two short - circuited faulty circuits exceeds 50°, the absolute value of the phase - angle difference of the non - faulty sheath circuit is less than 10°, and the standardized effective values of the sheath currents of the four faulty circuits all exceed 7;

[0067] Furthermore, cable sheath grounding: The absolute value of the phase - angle difference of the grounded faulty circuit exceeds 50°, the absolute value of the phase - angle difference of the non - faulty sheath circuit is less than 10°, and at least one of the standardized effective values of the sheath current of the faulty circuit exceeds 2;

[0068] Furthermore, the cross - bonding box is flooded: The absolute value of the phase - angle difference of the three faulty sheath circuits all exceeds 120°, and the standardized effective values of the sheath currents of the three faulty circuits are all greater than 7;

[0069] Furthermore, installation defects of the cross - bonding box: The absolute value of the phase - angle difference of the three faulty sheath circuits all exceeds 50°, and at least one exceeds 100°, and the standardized effective values of the sheath currents of the three faulty circuits are all greater than 9.

[0070] This embodiment also discloses a high - voltage cable metal sheath grounding system fault rapid diagnosis system based on the absolute value of the phase - angle difference of the same sheath circuit and the effective value of the sheath current, including:

[0071] Sheath current data acquisition module: It is used to collect the sheath current data at both ends of the head and the end of the high - voltage cable metal sheath circuit in real time;

[0072] Calculation module of the absolute value of the phase - angle difference and the standardized effective value of the current: It is used to extract the phase and current effective value information in the sheath current data, and calculate the absolute value of the phase - angle difference and the standardized effective value of the current at both ends of the sheath circuit;

[0073] Fault diagnosis module: It is used to judge whether there is a fault and the type of the fault according to the change of the absolute value of the phase - angle difference and the standardized effective value of the current.

[0074] Embodiment 2

[0075] The difference between this embodiment and Embodiment 1 is only as follows:

[0076] Taking the normal operation of the high - voltage cable and the cross - bonding box flooding fault in the simulation as examples for illustration.

[0077] The voltage level of the main cable section selected for modeling is 220 kV, the total length is 1500 m, the length of each cable section is 500 m, the direct - burial depth of the cable is 1 m, the phase - spacing is 0.425 m, the cable laying method is defaulted to flat laying, the grounding resistance is 0.5 Ω, and the fault resistance is 0.1 Ω. The simulation duration is set to 0.3 s, and the load current of the established simulation measured by the ammeter in the simulation circuit is 1200 A, and the cable laying method is flat laying.

[0078] Under normal conditions, the simulation model is modeled according to Figure 1 At this time, the value of I0 is calculated to be 10A through calculation. The standardized effective values of the currents in the three sheath circuits are 1.02, 1.09, and 0.88 respectively through calculation. The absolute values of the phase angle differences between the first and last phases of the three sheath circuits are 0.24, 0.13, and 0.85 respectively, all of which are close to 0. This meets the range of fault characteristic values for normal operation proposed in the previous fault diagnosis.

[0079] The cross-bonding box flooding fault is set as Figure 3 shown. The fault is set as the cross-bonding box J1 being flooded. When the cross-bonding box is not tightly sealed, during the rainy season, rainwater is likely to seep into the cross-bonding box, resulting in the sheath protector being flooded and short-circuited, which is equivalent to the three-phase grounding of the metal sheath. After the fault appears at 0.1s, the absolute values of the phase angle differences of the three sheath circuits measured are 179.18°, 168.03°, and 177.5° respectively. When the cross-bonding box flooding fault occurs, the three-phase current waveforms at the head and end are respectively as Figure 3 、 Figure 4 shown, and the fault occurs at 0.1s.

[0080] Based on the measured results to reverse the fault, the data shows that the absolute values of the phase angle differences of the three sheath circuits have all changed drastically, indicating that faults have occurred in all three sheath circuits. Looking at the previously proposed fault diagnosis criteria, this characteristic meets the condition that the absolute values of the phase angle differences of the three sheath circuits all exceed 120°. Therefore, the most likely situation is that there is a cross-bonding box flooding fault. Staff should be arranged to check the cross-bonding boxes on the line in time, and after finding the fault, carry out repairs to reduce losses.

[0081] Specifically in engineering applications, the general steps are summarized as follows:

[0082] Data acquisition: Rogowski coils are installed at both the head and end of the metal sheath circuit of the high-voltage cable to collect sheath current data in real time.

[0083] Characteristic value calculation: Extract the phase and current effective value information from the collected data, and then calculate the absolute value of the phase angle difference and the standardized effective value of the current at both the head and end of the sheath circuit.

[0084] Fault judgment: According to the change in the absolute value of the phase angle difference, judge whether there is a fault. If the absolute value of the phase angle difference increases significantly, it is determined that there is a fault in the sheath circuit.

[0085] Fault type determination: Based on the absolute value of the phase angle difference and, if necessary, supplemented by the standardized effective value of the sheath current, further determine the fault type.

[0086] Fault diagnosis result output: Output the diagnosis result to the monitoring system for reference by the operation and maintenance personnel.

[0087] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For related parts, reference can be made to the description in the method section.

[0088] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A rapid fault diagnosis method for the grounding system of the metal sheath of high-voltage cables based on the absolute value of the phase angle difference of the same sheath circuit and the effective value of the sheath current, characterized in that, It includes the following steps: Collect the sheath current data at both the beginning and the end of the high-voltage cable metal sheath loop in real time; Extract the phase and current effective value information from the sheath current data, and calculate the absolute value of the phase angle difference and the standardized effective value of the current at both the beginning and the end of the sheath loop; Judge whether there is a fault and the type of the fault according to the change of the absolute value of the phase angle difference and the standardized effective value of the current.

2. A rapid fault diagnosis method for the grounding system of the metal sheath of a high-voltage cable based on the absolute value of the phase angle difference and the effective value of the sheath current of the same sheath circuit, characterized in that, When collecting the sheath current data at both the beginning and the end of the high-voltage cable metal sheath loop in real time, Rogowski coils are respectively installed at the beginning and the end positions of the three-phase cable. During the collection process, keep the clocks at both the beginning and the end synchronized, and start the data collection systems at both the beginning and the end to record the current waveforms.

3. A method for rapid fault diagnosis of a high-voltage cable metal sheath grounding system based on the absolute value of the phase angle difference and the effective value of the sheath current of the same sheath circuit, characterized in that, Use the synchronous clock information to align the current waveforms at both the beginning and the end, perform Fourier transform on the current waveforms, and extract the fundamental wave components.

4. A rapid fault diagnosis method for the grounding system of the metal sheath of a high-voltage cable based on the absolute value of the phase angle difference and the effective value of the sheath current of the same sheath circuit, characterized in that, Perform Fourier transform on the current waveform i(t) to obtain the frequency-domain representation I(f): The fundamental wave component corresponds to the frequency f1. Extract the amplitude and phase of this frequency from I(f): I1 = I(f1); Convert the fundamental wave component back to the time domain: where, |I1| is the fundamental wave amplitude, is the phase.

5. A rapid fault diagnosis method for the grounding system of the metal sheath of a high-voltage cable based on the absolute value of the phase angle difference and the effective value of the sheath current of the same sheath circuit, characterized in that, The fault diagnosis criteria include: Normal condition: The absolute value of the phase angle difference is less than 10°, and the standardized effective value of the sheath current is between 0.5 and 1.5; Short circuit between the cable core and the sheath: The absolute value of the phase angle difference of the faulty sheath loop exceeds 120°, the absolute value of the phase angle difference of the non-faulty sheath loop is less than 10°, and the standardized effective values of the 6 sheath currents all exceed 100; Short circuit between sheath loops: The absolute value of the phase angle difference between the two short-circuited faulty loops exceeds 50°, the absolute value of the phase angle difference of the non-faulty sheath loop is less than 10°, and the standardized effective values of the 4 sheath currents of the faulty loop all exceed 7; Grounding of the cable sheath: The absolute value of the phase angle difference of the grounding fault loop exceeds 50°, the absolute value of the phase angle difference of the non-faulty sheath loop is less than 10°, and at least one of the standardized effective values of the sheath current of the faulty loop exceeds 2; Water ingress into the cross-bonding box: The absolute values of the phase angle differences of the three faulty sheath loops all exceed 120°, and the standardized effective values of the sheath currents of the three faulty loops are all greater than 7; Installation defect of the cross-bonding box: The absolute values of the phase angle differences of the three faulty sheath loops all exceed 50°, and at least one exceeds 100°, and the standardized effective values of the sheath currents of the three faulty loops are all greater than 9.

6. A high-voltage cable metal sheath grounding system fault rapid diagnosis system based on the absolute value of the phase angle difference of the same sheath circuit and the effective value of the sheath current, characterized in that, It includes: Sheath current data collection module: used to collect the sheath current data at both the beginning and the end of the high-voltage cable metal sheath loop in real time; Absolute value of phase angle difference and standardized effective value of current calculation module: used to extract the phase and current effective value information from the sheath current data, and calculate the absolute value of the phase angle difference and the standardized effective value of the current at both the beginning and the end of the sheath loop; Fault diagnosis module: used to judge whether there is a fault and the type of the fault according to the change of the absolute value of the phase angle difference and the standardized effective value of the current.

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