Adaptive reclosing method and device for overhead-cable hybrid line based on difference in ground mode component attenuation

Abstract

The application discloses an overhead-cable hybrid line adaptive reclosing method and device based on ground mode component attenuation difference. The method utilizes the physical characteristics that the ground mode component attenuates small in overhead lines and large in cables, generates the detectability binary flag of each end ground mode component through double-end transient current acquisition and phase mode transformation; after exchanging the flag, the fault section is preliminarily judged according to the combined criterion, and the comparison result of the energy ratio of the ground mode and the line mode and the reference threshold at the junction is used for correction; for the overhead line segment fault, the confidence is further evaluated based on the energy margin ratio; finally, the differentiated reclosing decision is executed: the overhead line segment high-confidence fault allows reclosing, and the cable segment fault or low-confidence state blocks reclosing and alarms. The application only needs 100 kHz sampling rate and 1-bit communication overhead, and realizes low-cost, high-reliable fault section discrimination and adaptive reclosing control.

Description

Technical Field

[0001] This invention relates to the field of new energy grid connection and power system relay protection technology, specifically an adaptive reclosing method and device for overhead-cable hybrid lines based on the attenuation difference of ground mode components. Background Technology

[0002] With the rapid development of urban power grid construction, the number of lines with mixed connections of overhead lines and cable lines is increasing. In urban high-voltage transmission and distribution networks, due to space constraints in urban areas, a large number of hybrid topologies of overhead line-cable-overhead line are adopted. There are fundamental differences in the fault characteristics of overhead line segments and cable segments in hybrid lines: overhead line segment faults are mainly transient, accounting for over 80%, and are suitable for rapid power restoration using automatic reclosing; while cable segment faults are almost all permanent, and erroneous reclosing will cause secondary damage to the cable insulation, exacerbating equipment damage. Therefore, accurately identifying the faulty section and implementing differentiated reclosing strategies accordingly is a key technical problem facing the protection of hybrid lines.

[0003] In existing technologies, fault location methods for hybrid lines based on the double-ended traveling wave time difference method utilize the wave impedance matching principle for fault location. However, these methods require a high sampling rate of at least 1MHz and accurate wave velocity parameters, and do not link the location results with reclosing decisions. Fault segment discrimination methods for hybrid lines based on traveling wave polarity analysis utilize the polarity variation law of traveling waves for segment discrimination, but the reliability of polarity identification decreases when the transition resistance exceeds 100Ω, and no adaptive reclosing strategy based on segment discrimination results is proposed. Adaptive fault location methods for hybrid lines based on traveling wave velocity differences propose adaptive wave velocity correction, but still rely on high sampling rate traveling wave detection, failing to address the linkage issue between segment discrimination and reclosing decisions. None of the above methods utilize the attenuation differences of traveling wave modulus components in different line media for segment discrimination, nor do they establish a complete technical solution for segment discrimination confidence assessment and reclosing decisions.

[0004] Therefore, this invention proposes a fault section identification and adaptive reclosing method for overhead-cable hybrid lines based on the attenuation difference of ground mode components. Utilizing the inherent physical characteristic that ground mode components attenuate less in overhead lines and more in cables, reliable fault section identification is achieved through a combination criterion of the detectability of ground mode components at both ends. Furthermore, confidence is assessed based on the energy margin ratio, and differentiated adaptive reclosing decisions are executed in a coordinated manner. This method requires only a 100kHz sampling rate and eliminates the need for precise traveling wave positioning, thus reducing hardware costs and algorithm complexity. Summary of the Invention

[0005] To address the shortcomings and needs of existing overhead-cable hybrid lines, such as difficulty in fault segment identification and lack of differentiated reclosing decisions, this invention provides a method and apparatus for fault segment identification and adaptive reclosing of overhead-cable hybrid lines based on the attenuation difference of ground mode components. The purpose is to utilize the attenuation difference characteristics of ground mode components in different line media to achieve reliable fault segment identification, and to conduct confidence assessment based on the energy margin ratio, thereby triggering differentiated adaptive reclosing decisions.

[0006] To achieve the above objectives, according to one aspect of the present invention, an adaptive reclosing method for overhead-cable hybrid lines based on the attenuation difference of ground mode components is provided, comprising the following steps:

[0007] Step 1: Install transient signal acquisition devices at both ends of the overhead-cable hybrid line, with a sampling frequency of not less than 100kHz. When a sudden change in current is detected at either end exceeding the preset trigger threshold, that moment is taken as the fault moment t. f The sampling clocks at both ends are synchronized via GPS or BeiDou to synchronously collect fault transient three-phase current signals.

[0008] Step 2: Perform phase-mode transformation on the fault transient three-phase current signals collected at both ends to decouple and obtain the ground mode component and the line mode component;

[0009] Step 3: Calculate the transient energy values ​​of the ground mode components and line mode components at both ends within a preset time window starting from the fault time, and obtain the transient energy value E of the ground mode at each end. 0,M E 0,N and the transient energy value E of the linear mode 1,M E 1,N Then, the energy ratio η between the ground model and the linear model at each end is calculated. M η N The transient energy values ​​of each end mode are compared with the preset detectability threshold E. th In comparison, the local mode transient energy value is greater than E. th A detectable flag 1 is generated when the condition is met, and an undetectable flag 0 is generated otherwise, forming a binary flag F for the detectability of the ground model components at each end. M F N ;

[0010] Step 4: Transmit the binary flag F of the detectability of the ground model components at both ends through the communication channel. M F N To exchange;

[0011] Step 5: Based on the swapped binary flag combination for double-ended detectability (F) M , F NThe fault location section is initially identified, and the initial identification result is corrected by comparing the energy ratio of the ground model and the line model with the threshold of the reference energy ratio at the junction. When both ends of the detectability flag are 1, the abnormal status is output.

[0012] Step Six: When the final judgment result of Step Five is an overhead line segment fault, calculate the maximum energy value E of the ground model components at both ends. max = max(E 0,M E 0,N ), and calculate the energy margin ratio R=E max E th R is compared with the preset confidence margin coefficient K. r Comparison: If R > K r Then it is judged as high confidence level, if 1 <R≤ K r If the final determination is a cable segment fault, then it is judged as low confidence; no confidence assessment is performed when the final determination is a cable segment fault.

[0013] Step 7: Based on the final judgment result of Step 5 and the confidence assessment result of Step 6, execute differentiated adaptive reclosing decisions: when the final judgment result is an overhead line segment fault and the confidence level is high, automatic reclosing is allowed; when the final judgment result is a cable segment fault, reclosing is blocked; when the confidence level is low, reclosing is blocked and a maintenance alarm is issued; when Step 5 determines an abnormal state, reclosing is blocked and an abnormal alarm is issued.

[0014] Furthermore, the detectability threshold E in step three... th An adaptive tuning method is adopted: during normal line operation, the mean μ of the background noise energy of the ground mode component is continuously calculated using a sliding window. noise Take E th = k·μ noise , where k is the threshold multiplier coefficient, ranging from 3 to 5, the sliding window width is an integer multiple of one power frequency cycle, and the update cycle does not exceed 1 second.

[0015] Furthermore, the confidence margin coefficient K in step six... r The buffer width d is determined using the following physical method. buffer For the distance range near the overhead line-cable junction that requires conservative handling, then K r = exp(2·α 0,OHL ·d buffer ), where α 0,OHL K is the attenuation coefficient of the overhead line ground modulus component, exp is the natural exponential function; r The value range is 2 to 10.

[0016] Furthermore, the reference energy ratio η at the boundary in step five... thresholdCalculate using the following method:

[0017] First, calculate the theoretical energy ratio when the fault occurs exactly at the overhead line-cable junction:

[0018] η boundary =exp(-2α 0,OHL · L OHL )exp(-2α 1,OHL · L OHL )=exp[-2(α 0,OHL -α 1,OHL )· L OHL ];

[0019] Where α 0,OHL Attenuation coefficient of overhead line ground mode component, α 1,OHL L is the attenuation coefficient of the overhead line modulus component. OHL This refers to the length of the near-end overhead line segment;

[0020] Then introduce the reliability factor K s Take η threshold =η boundary × K s K s The value range is 1.1 to 1.5.

[0021] Furthermore, step five involves combining the swapped two-end detectability binary flags (F... M , F N The initial identification of the fault location section includes: when (1,0), it is initially identified as a fault in the M-end overhead line segment; when (0,1), it is initially identified as a fault in the N-end overhead line segment; when (0,0), it is initially identified as a cable segment fault; and when (1,1), it is identified as an abnormal state. The correction of the initial identification result using the comparison result of the ground-to-line-mode energy ratio η and the reference energy ratio threshold at the junction includes: when the initial identification result is an overhead line segment fault, further taking the ground-to-line-mode energy ratio η at the detectable end and the preset reference energy ratio threshold η at the junction. threshold Compare, if η < η threshold If the condition is met, the judgment result will be corrected to a cable segment fault; otherwise, the overhead line segment fault will be maintained.

[0022] An adaptive reclosing device for overhead-cable hybrid lines based on the attenuation difference of ground mode components includes:

[0023] The transient signal acquisition module is installed at both ends of the hybrid line to synchronously acquire the transient three-phase current signal of the fault. Its sampling frequency is not less than 100kHz, and the sampling clock at both ends is synchronized through GPS or Beidou.

[0024] The modulus conversion module is used to perform phase-mode conversion on the fault transient three-phase current signal to decouple and obtain the ground mode component and the line mode component;

[0025] The energy calculation and detectability discrimination module is used to calculate the transient energy values ​​of the ground mode component and the line mode component within a preset time window after the fault. The energy ratio between the ground model and the line model is calculated, and the transient energy value of the ground model component is compared with the detectability threshold to generate a binary flag for the detectability of the ground model component at each end.

[0026] A communication switching module is used to exchange the detectability binary flags of the ground mode components between the two ends of the hybrid line;

[0027] The section discrimination module is used to initially discriminate fault sections based on the combination of the swapped dual-end detectability binary flags, and to correct the initial discrimination results by comparing the energy ratio of the ground model and the line model with the threshold of the reference energy ratio at the junction. When both dual-end detectability flags are 1, an abnormal status is output.

[0028] The confidence assessment module is used to calculate the energy margin ratio R and compare it with the confidence margin coefficient when the section identification result is an overhead line section fault, and output a high confidence or low confidence flag.

[0029] The adaptive reclosing decision module is used to execute differentiated reclosing strategies based on the section identification results and confidence level flags: when the final identification result is an overhead line section fault and the confidence level is high, automatic reclosing is allowed; when the final identification result is a cable section fault, reclosing is blocked; when the confidence level is low, reclosing is blocked and a maintenance alarm is issued; when the identification is an abnormal state, reclosing is blocked and an abnormal alarm is issued.

[0030] Furthermore, in the energy calculation and detectability discrimination module, the detectability threshold adopts an adaptive tuning method, which continuously calculates the average value of the background noise energy of the ground mode component using a sliding window, takes 3 to 5 times the average value as the detectability threshold, and automatically updates it according to the operating mode.

[0031] Furthermore, in the confidence assessment module, the confidence margin coefficient is tuned to K according to the buffer width. r =exp(2·α 0,OHL ·d buffer ),

[0032] Where d buffer For the distance range near the overhead line-cable junction that requires conservative handling, α 0,OHL Let be the attenuation coefficient of the overhead line ground mode component, and exp be the natural exponential function.

[0033] Furthermore, in the segment discrimination module, the reference energy ratio threshold η at the boundary is... thresholdCalculate using the following method: First, calculate the theoretical energy ratio when the fault occurs precisely at the overhead line-cable junction:

[0034] η boundary =exp(-2α 0,OHL · L OHL )exp(-2α 1,OHL · L OHL )=exp[-2(α 0,OHL -α 1,OHL )· L OHL ];

[0035] Where α 0,OHL Attenuation coefficient of overhead line ground mode component, α 1,OHL L is the attenuation coefficient of the overhead line modulus component. OHL The length of the near-end overhead line segment is given; then a reliability factor K is introduced. s Take η threshold =η boundary × K s K s The value range is 1.1 to 1.5.

[0036] Furthermore, the sampling frequency of the transient signal acquisition module is 100kHz, and the amount of the ground mode component detectability binary flag data transmitted by the communication exchange module is 1 bit.

[0037] In summary, this invention addresses the difficulties in fault segment identification and the lack of differentiation in reclosing decisions in overhead-cable hybrid lines. It utilizes the inherent physical characteristic that ground modulus components attenuate less in overhead lines but more in cables, using this attenuation difference as a natural criterion for segment identification. By combining binary flags indicating the detectability of the ground modulus components at both ends, only one bit of communication information needs to be exchanged for preliminary fault segment identification. Furthermore, by comparing the energy ratio of the ground modulus to the line modulus with a threshold energy ratio calculated based on the known length of the overhead line segment at the junction, faults at the cable entry point are effectively identified, and the preliminary identification result is corrected, solving the problem of misidentification of faults near the junction. A confidence assessment mechanism is established based on the energy margin ratio, automatically blocking reclosing and issuing a maintenance alarm for weak, low-confidence faults. This method requires only a 100kHz sampling rate, does not require precise traveling wave positioning, and correctly identifies segments under all test conditions verified in simulations. Simultaneously, the linked adaptive reclosing decision effectively prevents false reclosing of permanent cable segment faults. This invention is applicable to the formulation and application of reclosing control strategies for overhead-cable hybrid lines in urban high-voltage transmission and distribution networks. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the overhead-cable hybrid line system of the present invention.

[0039] Figure 2 This is a flowchart of the fault section identification and adaptive reclosing method based on the attenuation difference of ground mode components in this invention.

[0040] Figure 3 This is a schematic diagram comparing the attenuation characteristics of the ground mode component of the present invention in overhead line segments and cable segments.

[0041] Figure 4 This is a simulation result diagram of the energy distribution of the dual-end ground mode components under different fault locations according to the present invention.

[0042] Figure 5 This is a simulation result diagram of the energy components of the double-end ground mode when the overhead line section is faulted according to the present invention.

[0043] Figure 6 This is a simulation result diagram of the energy components of the double-end ground mode during a cable section fault according to the present invention.

[0044] Figure 7 This is a simulation result of the energy of the dual-end ground mode components when there is a fault near the boundary of the invention.

[0045] Figure 8 This is a summary diagram of the results of the multi-fault location comprehensive judgment and reclosing decision of the present invention. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Please see Figure 1 and Figure 2 This invention provides a method for fault section identification and adaptive reclosing of overhead-cable hybrid lines based on the attenuation difference of ground mode components. It is applicable to hybrid topologies such as overhead line-cable-overhead line and cable-overhead line, and includes the following steps:

[0048] Step 1: Acquire and synchronize the two-end transient signals.

[0049] Transient signal acquisition devices are installed at both the M and N ends of the overhead-cable hybrid line, with a sampling frequency of no less than 100kHz. The acquisition devices at both ends achieve clock synchronization via satellite timing services such as BeiDou / GPS, with a synchronization accuracy better than 10μs. When either end detects a fault-initiating element's activation signal, activation occurs if the current surge exceeds a preset initiation threshold. The moment when the current surge exceeds the initiation threshold is taken as the fault time t. fSimultaneously record the transient three-phase current signals i at both ends 10ms before and after the fault. a (t), i b (t), i c (t).

[0050] This method only requires the transient energy of the ground mode component for segment discrimination, without the need to extract the traveling wave front. Therefore, a sampling rate of 100kHz is sufficient, which reduces the hardware requirements of the acquisition device.

[0051] Step 2: Perform phase-mode transformation on the fault transient three-phase current signal to extract the ground mode component and the line mode component.

[0052] The fault transient three-phase current signals acquired at both ends are subjected to Karrenbauer transform to decouple the three-phase coupled signals into line-mode components and ground-mode components (i.e., zero-sequence components). The formula for extracting the ground-mode component is as follows:

[0053] i0=(i a +i b +i c ) / 3 (1)

[0054] Where i0 is the ground mode current component; i a i b i c This represents the instantaneous value of the three-phase current. The ground mode component i0 is generated only during ground faults, and its propagation characteristics are closely related to the line medium. In overhead lines, it propagates through the earth as a loop, resulting in relatively small attenuation; in cables, due to the low impedance loop provided by the metal shielding layer, the attenuation is extremely large.

[0055] Taking line model 1 as an example, the formula for extracting line model components is:

[0056] i1=(2i a -i b -i c ) / 3 (2)

[0057] Where i1 represents the line-mode current component. In both overhead lines and cables, the line-mode component propagates through loops between conductors, and its attenuation coefficient is relatively small, typically around 0.02 Np / km for overhead lines and around 0.05 Np / km for cables, which contrasts sharply with the high attenuation of the ground-mode component in cables.

[0058] It should be noted that this method is applicable to fault types that generate zero-sequence components, such as single-phase grounding faults and two-phase grounding faults. For phase-to-phase short-circuit faults that do not generate zero-sequence components, the ground mode component energy is zero, and both ends are undetectable. In this case, other criteria must be used for segment discrimination, which is not within the scope of this invention.

[0059] Step 3: Calculate the transient energy and detectability of the ground mode and line mode components.

[0060] Calculate the ground mode current components at terminals M and N within the post-fault time window [t]. f , t f +T w Transient energy value within:

[0061] E 0,M = ∫[t f , t f +T w i 0,M 2 (t) dt (3)

[0062] E 0,N = ∫[t f , t f +T w i 0,N 2 (t) dt (4)

[0063] Simultaneously, calculate the transient energy values ​​of the line-mode current components at both ends within the same time window:

[0064] E 1,M = ∫[t f , t f +T w i 1,M 2 (t) dt (5)

[0065] E 1,N = ∫[t f , t f +T w i 1,N 2 (t) dt (6)

[0066] Among them, E 0,M and E 0,N These are the transient energy values ​​of the ground mode components at the M and N ends, respectively; E 1,M and E 1,N These are the transient energy values ​​of the line mode components at the M and N ends, respectively; t f The fault moment is determined by the moment when the sudden change in current exceeds the start-up threshold in step one; T w The width of the energy calculation time window is set to 1ms to 2ms after the fault.

[0067] Furthermore, the energy ratio η between the ground mode and the linear mode at each end is calculated:

[0068] η M =E 0,ME 1,M (7)

[0069] η N =E 0,N E 1,N (8)

[0070] Where, η M and η N These represent the energy ratios of the ground mode and the line mode at the M and N ends, respectively. The physical meaning of this energy ratio is as follows: since the ground mode and line mode components originate from the same fault event, their ratio η eliminates the influence of the fault source energy, meaning it is only affected by the fault type and transition resistance, reflecting the degree of attenuation of the ground mode component relative to the line mode component. When the fault is in an overhead line segment, both the ground mode and line mode propagate only through the overhead line, resulting in a larger η. When the fault is at the cable entry point, the ground mode component experiences additional attenuation through the short cable segment and interface, while the line mode component is almost unaffected, resulting in a significantly smaller η.

[0071] The transient energy values ​​of each end model component are compared with the detectability threshold E. th Compare and generate a binary label:

[0072] F M = (9)

[0073] F N = (10)

[0074] Among them, F M and F N These are binary indicators of the detectability of the ground model components at the M and N ends, respectively; E th The threshold is the detectability threshold. The threshold tuning method is as follows: During normal operation of the line, a sliding window with a window width that is an integer multiple of one power frequency cycle is used, with an update cycle of no more than 1 second, to continuously calculate the mean μ of the background noise energy of the ground mode component. noise Take E th = k·μ noise Where k is the threshold multiplier coefficient, which takes a value of 3 to 5.

[0075] Step 4: Exchange detectability flags via two-way communication.

[0076] The M-end and N-end exchange their respective ground mode component detectability binary flag F via communication channels such as optical fiber. M and F N Since each end only needs to transmit 1 bit of information, 0 or 1, the amount of communication data is extremely small, and the requirements for communication bandwidth and latency are extremely low. Even under the condition that the communication latency reaches 10ms, it does not affect the accuracy of segment identification.

[0077] Step 5: Identify faulty sections based on combined criteria.

[0078] Based on the combination of binary indicators for the detectability of dual-end ground model components (F) M , F N Identify the section where the fault is located.

[0079] Taking a hybrid overhead-cable-overhead line as an example, the fault section identification rules are as follows, where S is the section identification result: 1) When (F M , F N When ) = (1, 0), S = M-end overhead line segment fault; 2) When (F M , F N When ) = (0, 1), S = N-end overhead line segment fault; 3) When (F M , F N When (F) = (0, 0), S = cable segment fault; 4) When (F) = (0, 0), S = cable segment fault. M , F N When ) = (1, 1), S = abnormal state.

[0080] For an overhead line-cable-overhead line topology, the ground modulus component cannot traverse long cable sections (when the cable section length is ≥1km, the energy of the ground modulus component attenuates to an undetectable level after passing through the cable section). Therefore, when the fault is at the M-end overhead line section, the ground modulus component can only be detected at the M-end; when the fault is at the N-end overhead line section, the ground modulus component can only be detected at the N-end; and when the fault is at the cable section, it is undetectable at both ends. When an abnormal combination occurs where both ends can be detected (F... M , F N When )=(1,1), it indicates that the cable section is too short (does not meet the applicable condition of ≥1km) or the data acquisition equipment is abnormal. At this time, the reclosing is blocked and an alarm signal is issued, which is then checked and handled by the operation and maintenance personnel.

[0081] Step Six: Correct the criteria for faults at the junction based on the energy ratio of the ground model and the linear model.

[0082] The above is based on (F) M , F N The initial discrimination rule of the combination is reliable in most cases, but there is a boundary blind zone: when the fault occurs inside the cable segment but very close to the overhead line-cable junction (such as 10m to hundreds of meters on the cable side), the ground modulus component enters the overhead line and reaches the near-end measuring device after only a short cable segment. The attenuation is not large enough, and the ground modulus component can still be detected at the near end, resulting in the initial discrimination result being an overhead line segment fault, which leads to a misjudgment.

[0083] To address this issue, a correction criterion based on the energy ratio η between the ground mode and the line mode is introduced. When the initial judgment result S indicates a fault in the overhead line segment (i.e., (F...)... M , F N= (1,0) or (0,1)), take the energy ratio η of the ground mode and the line mode at the detectable end, and the reference energy ratio threshold η at the junction. threshold Compare them. Where, if (F M , F N If ) = (1,0), then take η. M If (0,1), then take η. N。

[0084] The reference energy ratio η at the boundary boundary The calculation method is as follows: Assuming the fault occurs precisely at the overhead line-cable junction, both the ground modulus component and the line modulus component propagate only along the entire length of the near-end overhead line segment to reach the measurement end. In this case, the theoretical value of η is:

[0085] η boundary =exp(-2α 0,OHL · L OHL )exp(-2α 1,OHL · L OHL )=exp[-2(α 0,OHL -α 1,OHL )· L OHL (11)

[0086] Where, α 0,OHL α is the attenuation coefficient of the overhead line ground modulus component, typically taken as 0.2 Np / km; 1,OHL L is the attenuation coefficient of the overhead line modulus component, typically taken as 0.02 Np / km; OHL This refers to the length of the near-end overhead line segment.

[0087] Considering factors such as errors in the attenuation coefficient and impedance mismatch at the interface in practical engineering, a reliability coefficient K is introduced. s Its value can range from 1.1 to 1.5, with a recommended value of 1.3. The baseline energy ratio threshold at the boundary is obtained as follows:

[0088] η threshold =η boundary × K s (12)

[0089] When the initial assessment is that the fault is in the overhead line segment S, if the near-end η < η threshold Then, S = cable segment fault is corrected. This correction criterion indicates that if the measured η is lower than the reference value η at the junction... threshold This indicates that the ground mode component experienced additional attenuation beyond that of pure overhead line propagation, meaning the ground mode component crossed the interface and entered the cable segment. This suggests that the fault may actually be inside the cable segment, near the interface. Reliability factor K sA value greater than 1 makes the threshold higher than the theoretical benchmark value, and the fault on a small section of the overhead line near the junction is also included in the conservative handling scope, that is, the reclosing is blocked to ensure the safety of the cable section protection.

[0090] Taking the parameters in this embodiment as an example: α 0,OHL =0.2 Np / km, α 1,OHL =0.02 Np / km, L OHL,M =5 km, K s =1.3, then η boundary = exp[-2×(0.2-0.02)×5] = exp(-1.8) ≈ 0.165; η threshold = 0.165 × 1.3 ≈ 0.215. That is, when the ground model component (F) is detected at the M end... M =1) and η M When the value is less than 0.215, the preliminary judgment result is corrected from "M-end overhead line segment fault" to "cable segment fault", and reclosing is blocked.

[0091] Step 7: Conduct a confidence assessment based on the energy margin ratio.

[0092] When the section identification result S indicates an overhead line section fault, i.e., F M =1 or F N =1. To evaluate the reliability of the segment discrimination results, the energy margin ratio R is defined as:

[0093] E max = max(E 0,M E 0,N (13)

[0094] R=E max E th (14)

[0095] Among them, E max E represents the maximum energy of the two end modulus components. th R represents the detectability threshold in step three. R reflects the margin of the detected ground mode component energy relative to the noise threshold.

[0096] When the segment identification result S indicates a cable segment fault, i.e., F M =0 and F N =0. The energy at both ends is lower than the detectability threshold. At this time, R<1, no confidence assessment is performed, and the process directly proceeds to step seven to perform the blocking reclosing.

[0097] Furthermore, a confidence margin coefficient K is introduced. r Its value can range from 2 to 10, with a recommended value of K. r Take 5. Assess the confidence level based on the energy margin ratio R:

[0098] (9)

[0099] Where C represents the confidence level. When C=1, the energy of the ground mode component is much higher than the noise threshold, and the margin ratio exceeds K. r A ratio of 1:1 indicates that the fault generated a strong ground mode component signal, the section identification result is reliable, and reclosing can be performed accordingly; when C=0, the ground mode component energy is only slightly higher than the noise threshold, and the margin ratio does not exceed K. r A value of 1 times indicates a weak fault signal, which may be caused by a high transition resistance fault or a fault point close to the boundary. There is uncertainty in the section identification, and a conservative reclosing strategy should be adopted.

[0100] Confidence margin coefficient K r The physical tuning method is as follows: Define the buffer width d buffer For the distance range near the overhead line-cable junction that requires conservative handling, a value of 2 to 5 kilometers is recommended, then K r = exp(2·α 0,OHL ·d buffer ), where α 0,OHL Let be the attenuation coefficient of the ground modulus component of the overhead line, and exp be the natural exponential function. This formula represents the propagation d of the ground modulus component from the fault point. buffer The energy decay factor after distance is exp(2·α) 0,OHL ·d buffer Using this attenuation factor as the confidence margin coefficient, the energy margin ratio R is naturally lower than K when the fault point is located within the buffer zone. r Therefore, it is judged as having low confidence. Using α... 0,OHL =0.2Np / km, d buffer Taking 4 km as an example, K r = exp(2×0.2×4) = exp(1.6) ≈ 4.95, rounded to 5.

[0101] Typical scenarios with low confidence include: (1) high transition resistance faults (e.g., 200 to 500 ohms), where the fault source energy is small and the ground mode component signal is weak; (2) fault points near the overhead line-cable junction, where the ground mode component attenuates significantly after propagating through a long overhead line; and (3) when the above two factors are superimposed, the ground mode component energy is closer to the noise threshold. Confidence assessment can further improve the safety of reclosing.

[0102] Step 8: Execute the adaptive reclosing strategy.

[0103] Based on the segment discrimination result S from step five and the confidence level C from step six, a differentiated adaptive reclosing strategy is executed:

[0104] 1) When S = overhead line segment fault and C = 1, A = reclosing is allowed;

[0105] 2) When S = cable section fault, A = reclosing is blocked;

[0106] 3) When C=0, A=reclosing is blocked and maintenance alarm is triggered;

[0107] 4) When S is in an abnormal state, A is blocked from reclosing and an abnormal alarm is triggered.

[0108] Among them, A is the reclosing action strategy. The engineering significance of this strategy is: (1) For high-confidence overhead line segment faults, since the proportion of transient faults in overhead lines is as high as 80%, automatic reclosing is allowed to quickly restore power supply; (2) For cable segment faults, since cable faults are almost all permanent faults, reclosing is blocked to prevent secondary damage to cable insulation; (3) For low-confidence faults near the junction, although the section identification result points to the overhead line segment, the fault point may actually be located at the junction or even the cable segment entrance. For safety considerations, reclosing is blocked and a maintenance alarm is issued, sacrificing a small number of reclosing success rates to ensure the safety of cable segment protection; (4) For abnormal conditions, reclosing is blocked and an abnormal alarm is issued, and maintenance personnel are asked to investigate the cause.

[0109] To verify the effectiveness of the method of this invention, a simulation model of a 110kV overhead-cable hybrid line was built on the PSCAD / EMTDC simulation platform. The line topology is overhead section (5km) - cable section (10km) - overhead section (5km), with a total length of 20km. The simulation parameters are set as follows: system rated voltage 110kV, overhead line section length L... OHL,M The cable section is 5km long, with a length L. cable The length of the overhead line segment is 10km. OHL,N For a distance of 5km, the attenuation coefficient α of the overhead line ground modulus component is... 0,OHL The attenuation coefficient α of the cable ground mode component is 0.2 Np / km. 0,cable The sampling frequency is 2.0 Np / km. s The energy calculation time window is 100kHz. w The time limit is 2ms, the noise threshold factor k=4, and the confidence margin factor K. r =5.

[0110] This invention also provides an adaptive reclosing device for overhead-cable hybrid lines based on the attenuation difference of ground mode components, corresponding to the above method, including:

[0111] The transient signal acquisition module is installed at both ends of the hybrid line to synchronously acquire the transient three-phase current signal of the fault. Its sampling frequency is not less than 100kHz, and the sampling clock at both ends is synchronized through GPS or Beidou.

[0112] The modulus conversion module is used to perform phase-mode conversion on the fault transient three-phase current signal to decouple and obtain the ground mode component and the line mode component;

[0113] The energy calculation and detectability discrimination module is used to calculate the transient energy values ​​of the ground mode component and the line mode component within a preset time window after the fault. The energy ratio between the ground model and the line model is calculated, and the transient energy value of the ground model component is compared with the detectability threshold to generate a binary flag for the detectability of the ground model component at each end.

[0114] A communication switching module is used to exchange the detectability binary flags of the ground mode components between the two ends of the hybrid line;

[0115] The section discrimination module is used to initially discriminate fault sections based on the combination of the swapped dual-end detectability binary flags, and to correct the initial discrimination results by comparing the energy ratio of the ground model and the line model with the threshold of the reference energy ratio at the junction. When both dual-end detectability flags are 1, an abnormal status is output.

[0116] The confidence assessment module is used to calculate the energy margin ratio R and compare it with the confidence margin coefficient when the section identification result is an overhead line section fault, and output a high confidence or low confidence flag.

[0117] The adaptive reclosing decision module is used to execute differentiated reclosing strategies based on the section identification result and confidence level: when the final identification result is an overhead line section fault and the confidence level is high, automatic reclosing is allowed; when the final identification result is a cable section fault, reclosing is blocked; when the confidence level is low, reclosing is blocked and a maintenance alarm is issued; when the identification is an abnormal state, reclosing is blocked and an abnormal alarm is issued.

[0118] Faults were set at different locations on the line to verify the effectiveness of the reclosing strategy proposed in this invention for cable section faults, overhead section faults, high resistance faults at junctions, faults near junctions in cables, and faults near junctions in overhead lines, as shown in Table 2. Figure 3 This is a schematic diagram comparing the attenuation characteristics of the ground mode component in overhead line segments and cable segments according to the present invention. Figure 4 These are simulation results of the energy distribution of the dual-end ground mode components at different fault locations according to the present invention. Figure 5 This is a simulation result diagram of the energy components of the double-ended ground mode during an overhead line segment fault according to the present invention. Figure 6 This is a simulation result diagram of the energy components of the double-ended ground mode during a cable segment fault according to the present invention. Figure 7 This is a simulation result diagram of the dual-end ground mode component energy when a fault occurs near the boundary of the invention. Figure 8 This is a summary diagram of the results of the multi-fault location comprehensive judgment and reclosing decision of the present invention.

[0119] Table 1 Simulation Parameters

[0120]

[0121] Table 2. Results of Multi-Fault Location Comprehensive Judgment and Reclosing Decision

[0122]

[0123] As shown in Table 2, under all 23 test conditions in the simulation verification, the final section discrimination results were all correct and the reclosing decisions were all reasonable. Among them: (1) For the metallic faults of the overhead line section far from the boundary, the η value was higher than η when the distance from the M end was 1 to 4 km. threshold =0.215, no η correction is triggered, and the energy margin ratio R is greater than K. r =5, confidence level is high, automatic reclosing is allowed; (2) For overhead line sections and cable entry points that are close to the junction, the η value is lower than η at 4.5 to 5.5 km from the M end. threshold =0.215, triggering the η correction criterion, and finally determined to be a cable segment fault, and blocking reclosing; (3) The fault in the middle of the cable segment is 6 to 14 km away from the M end. The energy of the ground mode components at both ends is lower than the detectability threshold, and it is directly determined to be a cable segment fault, and blocking reclosing. The η correction criterion effectively eliminates the blind spot of the judgment near the junction, and correctly corrects the cable entry fault that may have been misjudged as an overhead line segment fault to a cable segment fault.

[0124] This invention addresses the difficulties in fault segment identification and the lack of differentiation in reclosing decisions in overhead-cable hybrid lines. Utilizing the attenuation differences of ground mode components in different line media, it proposes a fault segment identification method based on a combined criterion of detectability of double-ended ground mode components and a modified criterion of the energy ratio η between ground mode and line mode, and integrates adaptive reclosing decisions. As simulation results show, in a typical 110kV overhead-cable-overhead hybrid line, the fault segment identification was correct for all 23 test fault points, and the reclosing decisions were all reasonable.

[0125] Table 3 Comparison of the present invention with the prior art

[0126]

[0127] Table 3 shows a comparison between the present invention and existing technologies, and the advantages of the present invention are summarized as follows:

[0128] 1. The section discrimination principle is reliable. It utilizes the inherent physical characteristic that the ground mode component attenuates very quickly in cables, with an attenuation coefficient of approximately 2.0 Np / km, while the attenuation in overhead lines is relatively small, typically around 0.2 Np / km. The attenuation coefficient ratio is 10:1, and it has the ability to withstand transition resistances from 0 to 300 Ω under ground fault conditions.

[0129] 2. Low sampling rate requirement. Only a 100kHz sampling rate is needed to complete segment discrimination, eliminating the need for the high sampling rate of over 1MHz required for precise traveling wave positioning. The sampling rate is reduced to one-tenth of that of existing methods, thus reducing the hardware cost of the acquisition device.

[0130] 3. Extremely low communication requirements. Only 1 bit of ground mode component detectability flag needs to be exchanged at both ends, with extremely low requirements for communication bandwidth and latency, and is compatible with existing fiber optic communication channels.

[0131] 4. Confidence assessment mechanism. A confidence assessment system is established based on the energy margin ratio. The system automatically blocks reclosing for low-confidence faults with weak signals, effectively preventing false reclosing caused by uncertainties in section discrimination.

[0132] 5. Linked reclosing decision. Based on the section identification results and confidence level, the system automatically executes differentiated reclosing strategies. Overhead line section faults allow reclosing to restore power supply, cable section faults block reclosing to prevent secondary damage, faults near junctions block reclosing and issue alarms, and abnormal conditions block reclosing and issue abnormal alarms.

[0133] Compared with existing technologies, the technical solution of this invention is not a simple replacement of signal processing methods or parameter adjustment. Instead, it overcomes the technical bias of treating high attenuation of ground mode components as a disadvantage by reversely utilizing the high attenuation characteristics of ground mode components in cables. Existing technologies generally attempt to overcome signal loss caused by attenuation by increasing the sampling rate and algorithm complexity, while this invention transforms the phenomenon of "undetectable" ground mode components in cables into a natural physical criterion for segment discrimination. Compared with the existing traveling wave time difference method, this invention reduces the sampling rate to one-tenth, from 1MHz to 100kHz, and the communication data volume to 1 bit, while adding confidence assessment and reclosing decision linkage functions.

[0134] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An adaptive reclosing method for overhead-cable hybrid lines based on the attenuation difference of ground mode components, characterized in that, Includes the following steps: Step 1: Install transient signal acquisition devices at both ends of the overhead-cable hybrid line, with a sampling frequency of not less than 100kHz. When a sudden change in current is detected at either end exceeding the preset trigger threshold, that moment is taken as the fault moment t. f The sampling clocks at both ends are synchronized via GPS or BeiDou to synchronously collect fault transient three-phase current signals. Step 2: Perform phase-mode transformation on the fault transient three-phase current signals collected at both ends to decouple and obtain the ground mode component and the line mode component; Step 3: Calculate the transient energy values ​​of the ground mode components and line mode components at both ends within a preset time window starting from the fault time, and obtain the transient energy value E of the ground mode at each end. 0,M E 0,N and the transient energy value E of the linear mode 1,M E 1,N Then, the energy ratio η between the ground model and the linear model at each end is calculated. M η N The transient energy values ​​of each end mode are compared with the preset detectability threshold E. th In comparison, the local mode transient energy value is greater than E. th A detectable flag 1 is generated when the condition is met, and an undetectable flag 0 is generated otherwise, forming a binary flag F for the detectability of the ground model components at each end. M F N ; Step 4: Transmit the binary flag F of the detectability of the ground model components at both ends through the communication channel. M F N To exchange; Step 5: Based on the swapped binary flag combination for double-ended detectability (F) M , F N The fault location section is initially identified, and the initial identification result is corrected by comparing the energy ratio of the ground model and the line model with the threshold of the reference energy ratio at the junction. When both ends of the detectability flag are 1, the abnormal status is output. Step Six: When the final judgment result of Step Five is an overhead line segment fault, calculate the maximum energy value E of the ground model components at both ends. max = max(E 0,M E 0,N ), and calculate the energy margin ratio R=E max E th R is compared with the preset confidence margin coefficient K. r Comparison: If R > K r Then it is judged as high confidence level, if 1 <R≤ K r If the final determination is a cable segment fault, then it is judged as low confidence; no confidence assessment is performed when the final determination is a cable segment fault. Step 7: Based on the final judgment result of Step 5 and the confidence assessment result of Step 6, execute differentiated adaptive reclosing decisions: when the final judgment result is an overhead line segment fault and the confidence level is high, automatic reclosing is allowed; when the final judgment result is a cable segment fault, reclosing is blocked; when the confidence level is low, reclosing is blocked and a maintenance alarm is issued; when Step 5 determines an abnormal state, reclosing is blocked and an abnormal alarm is issued.

2. The method according to claim 1, characterized in that, The detectability threshold E in step three th An adaptive tuning method is adopted: during normal line operation, the mean μ of the background noise energy of the ground mode component is continuously calculated using a sliding window. noise Take E th = k·μ noise , where k is the threshold multiplier coefficient, ranging from 3 to 5, the sliding window width is an integer multiple of one power frequency cycle, and the update cycle does not exceed 1 second.

3. The method according to claim 1, characterized in that, The confidence margin coefficient K in step six r The buffer width d is determined using the following physical method. buffer For the distance range near the overhead line-cable junction that requires conservative handling, then K r = exp(2·α 0,OHL ·d buffer ), where α 0,OHL K is the attenuation coefficient of the overhead line ground modulus component, exp is the natural exponential function; r The value range is 2 to 10.

4. The method according to claim 1, characterized in that, The threshold energy ratio η at the boundary in step five threshold Calculate using the following method: First, calculate the theoretical energy ratio when the fault occurs exactly at the overhead line-cable junction: or boundary =exp(-2a 0,OHL · L OHL )exp(-2a 1,OHL · L OHL )=exp[-2(a 0,OHL -a 1,OHL )· L OHL ]; Where α 0,OHL Attenuation coefficient of overhead line ground mode component, α 1,OHL L is the attenuation coefficient of the overhead line modulus component. OHL This refers to the length of the near-end overhead line segment; Then introduce the reliability factor K s Take η threshold =η boundary × K s K s The value range is 1.1 to 1.

5.

5. The method according to claim 1, characterized in that, Step 5: Based on the swapped binary flag combination for double-ended detectability (F) M , F N The initial identification of the fault location section includes: when (1,0), it is initially identified as a fault in the M-end overhead line segment; when (0,1), it is initially identified as a fault in the N-end overhead line segment; when (0,0), it is initially identified as a cable segment fault; and when (1,1), it is identified as an abnormal state. The correction of the initial identification result using the comparison result of the ground-to-line-mode energy ratio η and the reference energy ratio threshold at the junction includes: when the initial identification result is an overhead line segment fault, further taking the ground-to-line-mode energy ratio η at the detectable end and the preset reference energy ratio threshold η at the junction. threshold Compare, if η < η threshold If the condition is met, the judgment result will be corrected to a cable segment fault; otherwise, the overhead line segment fault will be maintained.

6. An adaptive reclosing device for overhead-cable hybrid lines based on the attenuation difference of ground mode components, characterized in that, include: The transient signal acquisition module is installed at both ends of the hybrid line to synchronously acquire the transient three-phase current signal of the fault. Its sampling frequency is not less than 100kHz, and the sampling clock at both ends is synchronized through GPS or Beidou. The modulus conversion module is used to perform phase-mode conversion on the fault transient three-phase current signal to decouple and obtain the ground mode component and the line mode component; The energy calculation and detectability discrimination module is used to calculate the transient energy values ​​of the ground mode component and the line mode component within a preset time window after the fault, calculate the energy ratio of the ground mode and the line mode, compare the transient energy value of the ground mode component with the detectability threshold, and generate a binary flag for the detectability of the ground mode component at each end. A communication switching module is used to exchange the detectability binary flags of the ground mode components between the two ends of the hybrid line; The section discrimination module is used to initially discriminate fault sections based on the combination of the swapped dual-end detectability binary flags, and to correct the initial discrimination results by comparing the energy ratio of the ground model and the line model with the threshold of the reference energy ratio at the junction. When both dual-end detectability flags are 1, an abnormal status is output. The confidence assessment module is used to calculate the energy margin ratio R and compare it with the confidence margin coefficient when the section identification result is an overhead line section fault, and output a high confidence or low confidence flag. The adaptive reclosing decision module is used to execute differentiated reclosing strategies based on the section identification results and confidence level: when the final identification result is an overhead line section fault and the confidence level is high, automatic reclosing is allowed. When the final determination is a cable section fault, reclosing is blocked; when the confidence level is low, reclosing is blocked and a maintenance alarm is issued; when the condition is determined to be abnormal, reclosing is blocked and an abnormal alarm is issued.

7. The apparatus according to claim 6, characterized in that, In the energy calculation and detectability discrimination module, the detectability threshold adopts an adaptive tuning method. The average value of the background noise energy of the ground mode component is continuously counted by a sliding window, and 3 to 5 times the average value is taken as the detectability threshold, which is automatically updated according to the operating mode.

8. The apparatus according to claim 6, characterized in that, In the confidence assessment module, the confidence margin coefficient is tuned to K according to the buffer width. r = exp(2·α 0,OHL ·d buffer ), Where d buffer For the distance range near the overhead line-cable junction that requires conservative handling, α 0,OHL is the attenuation coefficient of the overhead line ground modulus component, and exp is the natural exponential function.

9. The apparatus according to claim 6, characterized in that, In the segment discrimination module, the reference energy ratio threshold η at the boundary is... threshold Calculate using the following method: First, calculate the theoretical energy ratio when the fault occurs precisely at the overhead line-cable junction: or boundary =exp(-2a 0,OHL · L OHL )exp(-2a 1,OHL · L OHL )=exp[-2(a 0,OHL -a 1,OHL )· L OHL ]; Where α 0,OHL Attenuation coefficient of overhead line ground mode component, α 1,OHL L is the attenuation coefficient of the overhead line modulus component. OHL The length of the near-end overhead line segment is given; then a reliability factor K is introduced. s Take η threshold =η boundary × K s K s The value range is 1.1 to 1.

5.

10. The apparatus according to claim 6, characterized in that, The sampling frequency of the transient signal acquisition module is 100kHz, and the amount of the ground mode component detectability binary flag data transmitted by the communication exchange module is 1 bit.

Images