Cross-connected high-voltage cable sheath current offline detection time synchronization method and system

Abstract

The present invention relates to a method and system for offline detection time synchronization of sheath current of cross-connected high-voltage cables. The method comprises inputting a high-voltage cable core voltage and measuring the sheath current between two corresponding cross-connected grounding points; calculating the capacitive current component of each phase sheath current according to the sheath circuit; calculating the capacitive current residual according to the capacitive current component of each phase sheath current, and calculating the optimal time offset of the capacitive current residual, and correcting the initial detection time error according to the optimal time offset to complete the time synchronization of multiple sheath grounding current detection points. The present invention calculates the capacitive current component and the capacitive current residual in each phase sheath current through the sheath current to determine the optimal time offset, thereby correcting the initial time deviation of the power supply side and the load side sampling, and achieving time synchronization of multiple sheath grounding current monitoring points, so as to facilitate accurate extraction of the sheath current vector and assist in the diagnosis of sheath grounding faults of cross-connected high-voltage cables.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage cable detection, and in particular to a method and system for offline detection time synchronization of sheath current of cross-connected high-voltage cables. Background Art

[0002] The sheath current phasor is a key state variable for diagnosing sheath grounding faults in cross-connected high-voltage cables. Time synchronization of distributed sheath current measurement signals is a prerequisite for accurate sheath phasor extraction. Traditionally, distributed online monitoring of sheath grounding current in cross-connected high-voltage cable systems relied on hardware synchronization using GPS or local networks. This limitation, due to the lack of signal in underground cable tunnels and network costs, made it impractical for offline mobile inspections, limiting the application of sheath current detection technology in offline scenarios. In the absence of GPS signals and local networks, time synchronization of distributed sheath current signals in high-voltage cables cannot be achieved. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and to provide a method and system for offline detection time synchronization of sheath current of cross-connected high-voltage cables.

[0004] The present invention solves the above-mentioned technical problem with the following technical solution: A method for offline detection time synchronization of cross-connected high-voltage cable sheath current, comprising the following steps:

[0005] S1: Input the high-voltage cable core voltage. Two groups of six current transformers installed on the sheath connection wires of the middle structure of each phase high-voltage cable respectively measure the sheath current between the corresponding two cross-connected grounding points.

[0006] S2: Calculating the capacitive current component of each phase sheath current according to the sheath circuit;

[0007] S3: Calculate the capacitive current residual according to the capacitive current component of each phase sheath current, calculate the optimal time offset of the capacitive current residual, and correct the initial detection time error according to the optimal time offset to complete the time synchronization of multiple sheath grounding current detection points.

[0008] The beneficial effects of the present invention are as follows: the off-line detection time synchronization method of the cross-interconnected high-voltage cable sheath current of the present invention measures the sheath current between two cross-interconnected grounding points through a current transformer, and then calculates the capacitive current component in the sheath current of each phase, calculates the capacitive current residual in combination with the equivalent model of the detection circuit, and determines the optimal time offset, thereby correcting the initial time deviation of the power supply side and the load side sampling, and realizing the time synchronization of multiple sheath grounding current monitoring points, so as to accurately extract the sheath current vector and assist in the diagnosis of the sheath grounding fault of the cross-interconnected high-voltage cable.

[0009] On the basis of the above technical solution, the present invention can also be improved as follows:

[0010] Further: the calculation of the capacitive current component of each phase sheath current according to the sheath circuit specifically includes the following steps:

[0011] S11: Divide each phase of the three-phase high-voltage cable into three sections, and record them as sections 1-9 in sequence. Define the sheath current of the detection point on the power supply side as I CT1 , I CT2 , I CT3 The starting time of the detection point on the power supply side is t1, and the sheath current of the detection point on the load side is recorded as I CT4 , I CT5 , I CT6 , the start time of the load side detection point is t2, and the start time difference between the two detection points is Δt;

[0012] Δt=t2-t1 (1)

[0013] S12: Calculating the induced current corresponding to each phase induced current loop according to an equivalent model of the inductive coupling loop of the cross-connected high-voltage cable;

[0014]

[0015]

[0016]

[0017] Among them, I L1 , I L5 The induced current of the induced current loop formed by the 1-5-9 segment, that is, the sheath current induced component measured by CT1 and CT5; I L2 , I L6 The induced current of the induced current loop formed by the 2-6-7 segment, that is, the sheath current induced component measured by CT2 and CT6; I L3 , I L4 It is the induced current of the induced current loop formed by sections 3-4-8, that is, the sheath current induced component measured by CT3 and CT4. E1, E5 and E9 are the induced electromotive force on sections 1, 5 and 9 respectively. Z1-Z9 represent the insulation impedance of high-voltage cables in sections 1 to 9 respectively.

[0018] The beneficial effect of the above further scheme is: through the equivalent model of the inductive coupling loop of the cross-connected high-voltage cables, combined with the induced electromotive force and insulation impedance on each section of the high-voltage cable, the induced current of the inductive current loop can be accurately calculated, which makes it easier to accurately calculate the capacitive current based on the sheath current and the induced current.

[0019] Further: the calculation of the capacitive current residual according to the capacitive current component of each phase sheath current specifically includes the following steps:

[0020] S21: For ideal time-synchronized discrete sampling, the coupling relationship between the sheath currents measured by the six current transformers is determined based on the equivalent model of the capacitive coupling loop of the cross-connected high-voltage cable sheath current, specifically:

[0021] I CT5 [t n ]-I CT1 [t n ]=I C5 [t n ] (5)

[0022] I CT2 [t n ]-I CT6 [t n ]=I C6 [t n ] (6)

[0023] I CT4 [t n ]-I CT3 [t n ]=I C4 [t n ] (7)

[0024] Among them, I CT1 [t n ]-I CT6 [t n ] represent the nth sampling point at time t n The induced current measured by current transformers CT1-CT6;

[0025] S22: For non-time-synchronous discrete sampling in practice, the coupling relationship between the sheath currents measured by the six current transformers is as follows:

[0026] I CT5 [t1+t n ]-I CT1 [t1+Δt+t n ]=ΔI C5 [t1+t n ] (8)

[0027] I CT2 [t1+t n ]-I CT6 [t1+Δt+t n ]=ΔI C6 [t1+t n ] (9)

[0028] I CT4 [t1+t n ]-I CT3 [t1+Δt+t n ]=ΔI C4 [t1+t n ] (10)

[0029] Among them, t1+t n Indicates the start sampling time of the nth sampling point on the power supply side, t1+Δt+t n Indicates the start sampling time of the nth sampling point on the load side, Δt indicates the time offset between the corresponding sampling points on the power side and the load side, ΔI C4 , ΔI C5 , ΔI C6 They are the residuals of the capacitance current of the 4th, 5th and 6th sections of high-voltage cables respectively.

[0030] The beneficial effect of the above further scheme is: according to the capacitive coupling loop equivalent model of the cross-connected high-voltage cable sheath current, the sheath current coupling relationship is determined under ideal time synchronization, thereby facilitating the subsequent determination of the optimal time offset based on the residual of the capacitive current, and then correcting the initial sampling time and achieving time detection time synchronization.

[0031] Further: the calculating of the optimal time offset of the capacitor current residual specifically includes the following steps:

[0032] S31: Calculate the arithmetic mean least squares error of the capacitor current residual, using the following formula:

[0033] Min:avg(norm2(ΔI C4 )+norm2(ΔI C5 )+norm2(ΔI C6 ))

[0034] Among them, norm2(ΔI C4 )、norm2(ΔI C5 )、norm2(ΔI C6 ) are the 2 norms of the residuals of the capacitance currents of the 4th, 5th and 6th high-voltage cable sections respectively;

[0035] S32: Determine the optimal time offset Δt according to the 2-norm of the residual of the capacitance current of the fourth, fifth, and sixth sections of the high-voltage cable.

[0036] The beneficial effect of the above further scheme is: by setting different time offsets and using the recursive least squares method to compare the amplitudes, phase deviations and observations within one end time of two groups of sheath grounding currents with different time offsets, the optimal time offset Δt can be accurately calculated, thereby achieving time synchronization of multiple sheath grounding current detection points.

[0037] Further: the correcting of the initial detection time error according to the optimal time offset specifically includes the following steps:

[0038] S33: Calculate the mean of the capacitance current residuals of the three sheath loops and determine whether the mean is less than a preset threshold. If so, correct the initial detection time error according to the optimal time offset Δt, output the synchronization result, and terminate the processing flow. Otherwise, proceed to S34.

[0039] S34: Increase the optimal time offset Δt by a preset time offset amount, and return to S33.

[0040] The beneficial effect of the above further scheme is: by comparing the mean of the three sheath loop capacitance current residuals with the preset threshold, the optimal time offset can be adjusted according to the size of the mean, thereby realizing the correction of the initial detection time of multiple sheath grounding current detection points.

[0041] The present invention also provides a cross-connected high-voltage cable sheath current offline detection time synchronization system, comprising a sensing acquisition module, a calculation module and a correction module;

[0042] The sensing acquisition module includes two groups of six current transformers installed on the sheath connection wires of the middle structure of each phase high-voltage cable, and is used to measure the sheath current between the corresponding two cross-connected grounding points respectively;

[0043] The calculation module is used to calculate the capacitive current component of each phase of the sheath current according to the sheath circuit; and is also used to calculate the capacitive current residual according to the capacitive current component of each phase of the sheath current, and calculate the optimal time offset of the capacitive current residual;

[0044] The correction module is used to correct the initial detection time error according to the optimal time offset to achieve time synchronization of multiple sheath grounding current detection points.

[0045] The cross-connected high-voltage cable sheath current offline detection time synchronization system of the present invention measures the sheath current between two cross-connected grounding points through a current transformer, then calculates the capacitive current component in the sheath current of each phase, calculates the capacitive current residual in combination with the equivalent model of the detection circuit, and determines the optimal time offset, thereby correcting the initial time deviation of the power supply side and the load side sampling, achieving time synchronization of multiple sheath grounding current monitoring points, so as to accurately extract the sheath current vector and assist in the diagnosis of cross-connected high-voltage cable sheath grounding faults.

[0046] On the basis of the above technical solution, the present invention can also be improved as follows:

[0047] Further: the specific implementation of the calculation module calculating the capacitive current component of each phase sheath current according to the sheath circuit is:

[0048] Each phase of the three-phase high-voltage cable is divided into three sections, which are marked as sections 1-9 in sequence. The sheath current of the detection point on the power supply side is defined as I CT1 , I CT2 , I CT3 The starting time of the detection point on the power supply side is t1, and the sheath current of the detection point on the load side is recorded as I CT4 , I CT5 , I CT6 , the start time of the load side detection point is t2, and the start time difference between the two detection points is Δt;

[0049] Δt=t2-t1 (1)

[0050] Calculate the induced current corresponding to each phase induced current loop based on the equivalent model of the inductive coupling loop of the cross-connected high-voltage cable;

[0051]

[0052]

[0053]

[0054] Among them, I L1 , I L5 The induced current of the induced current loop formed by the 1-5-9 segment, that is, the sheath current induced component measured by CT1 and CT5; I L2 , I L6 The induced current of the induced current loop formed by the 2-6-7 segment, that is, the sheath current induced component measured by CT2 and CT6; I L3 , I L4is the induced current of the induced current loop formed by sections 3-4-8, that is, the sheath current induced component measured by CT3 and CT4, E1, E5 and E9 are the induced electromotive force on sections 1, 5 and 9 respectively, and Z1-Z9 represent the insulation impedance of sections 1-9 of the high-voltage cable respectively;

[0055] The specific implementation of the calculation module calculating the capacitive current residual according to the capacitive current component of each phase sheath current is:

[0056] For ideal time-synchronized discrete sampling, the coupling relationship between the sheath currents measured by the six current transformers is determined based on the equivalent model of the capacitive coupling loop of the cross-connected high-voltage cable sheath current, specifically:

[0057] I CT5 [t n ]-I CT1 [t n ]=I C5 [t n ] (5)

[0058] I CT2 [t n ]-I CT6 [t n ]=I C6 [t n ] (6)

[0059] I CT4 [t n ]-I CT3 [t n ]=I C4 [t n ] (7)

[0060] Among them, I CT1 [t n ]-I CT6 [t n ] represent the nth sampling point at time t n The induced current measured by current transformers CT1-CT6;

[0061] For non-time-synchronous discrete sampling in practice, the coupling relationship between the sheath currents measured by the six current transformers is as follows:

[0062] I CT5 [t1+t n ]-I CT1 [t1+Δt+t n ]=ΔI C5 [t1+t n ] (8)

[0063] I CT2 [t1+tn ]-I CT6 [t1+Δt+t n ]=ΔI C6 [t1+t n ] (9)

[0064] I CT4 [t1+t n ]-I CT3 [t1+Δt+t n ]=ΔI C4 [t1+t n ] (10)

[0065] Among them, t1+t n Indicates the start sampling time of the nth sampling point on the power supply side, t1+Δt+t n Indicates the start sampling time of the nth sampling point on the load side, Δt indicates the time offset between the corresponding sampling points on the power side and the load side, ΔI C4 , ΔI C5 , ΔI C6 are the residuals of the capacitance current of the 4th, 5th and 6th sections of high-voltage cables respectively;

[0066] The specific implementation of the calculation module calculating the optimal time offset of the capacitor current residual is:

[0067] The arithmetic mean least squares error of the capacitor current residual is calculated using the following formula:

[0068] Min:avg(norm2(ΔI C4 )+norm2(ΔI C5 )+norm2(ΔI C6 ))

[0069] Among them, norm2(ΔI C4 )、norm2(ΔI C5 )、norm2(ΔI C6 ) are the 2 norms of the residuals of the capacitance currents of the 4th, 5th and 6th high-voltage cable sections respectively;

[0070] The optimal time offset Δt is determined according to the 2-norm of the residual of the capacitance current of the fourth, fifth and sixth sections of the high-voltage cable.

[0071] The beneficial effects of the above further scheme are: through the equivalent model of the inductive coupling loop of the cross-connected high-voltage cable, combined with the induced electromotive force and insulation impedance on each section of the high-voltage cable, the induced current of the inductive current loop can be accurately calculated, so that the capacitive current can be accurately calculated based on the sheath current and the induced current; according to the equivalent model of the capacitive coupling loop of the sheath current of the cross-connected high-voltage cable, the sheath current coupling relationship is used to determine the residual of the capacitive current under ideal time synchronization, so as to facilitate the subsequent determination of the optimal time offset based on the residual of the capacitive current, and then to correct the initial sampling time and synchronize the time detection time; by setting different time offsets and using the recursive least squares method, the amplitude, phase deviation and observation of two groups of sheath grounding currents with different time offsets are compared, so that the optimal time offset Δt can be accurately calculated, thereby realizing time synchronization of multiple sheath grounding current detection points.

[0072] Further: the specific implementation of the correction module correcting the initial detection time error according to the optimal time offset is:

[0073] Calculate the mean of the three sheath loop capacitance current residuals and determine whether the mean is less than a preset threshold. If so, correct the initial detection time error according to the optimal time offset Δt, output the synchronization result, and end the processing flow. Otherwise, increase the optimal time offset Δt by the preset time offset amount until the mean is less than the preset threshold.

[0074] The beneficial effect of the above further scheme is: by comparing the mean of the three sheath loop capacitance current residuals with the preset threshold, the optimal time offset can be adjusted according to the size of the mean, thereby realizing the correction of the initial detection time of multiple sheath grounding current detection points.

[0075] The present invention further provides a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the following method steps are implemented:

[0076] The capacitive current component of each phase sheath current is calculated based on the sheath current between the corresponding two cross-connected grounding points measured by two groups of six current transformers installed on the sheath connection line of the middle structure of each phase high-voltage cable;

[0077] Calculating a capacitive current residual according to the capacitive current component of each phase sheath current, and calculating an optimal time offset of the capacitive current residual;

[0078] The initial detection time error is corrected according to the optimal time offset to complete the time synchronization of multiple sheath grounding current detection points.

[0079] The present invention also provides a cross-connected high-voltage cable sheath current offline detection time synchronization device, characterized in that it includes the above-mentioned storage medium and a processor, and the processor implements the following method steps when executing the computer program on the storage medium:

[0080] The capacitive current component of each phase sheath current is calculated based on the sheath current between the corresponding two cross-connected grounding points measured by two groups of six current transformers installed on the sheath connection line of the middle structure of each phase high-voltage cable;

[0081] Calculating a capacitive current residual according to the capacitive current component of each phase sheath current, and calculating an optimal time offset of the capacitive current residual;

[0082] The initial detection time error is corrected according to the optimal time offset to complete the time synchronization of multiple sheath grounding current detection points. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 A schematic flow chart of a method for offline detection of time synchronization of sheath current in cross-connected high-voltage cables according to an embodiment of the present invention;

[0084] Figure 2 This is a schematic diagram of a distributed sheath current detection structure of a three-phase cross-connected high-voltage cable according to an embodiment of the present invention;

[0085] Figure 3 An equivalent circuit diagram of the inductive coupling between the ground current detection points of the 1-5-9 sheath loop according to one embodiment of the present invention;

[0086] Figure 4 The equivalent circuit of the capacitive coupling circuit between the ground current detection points of the 1-5-9 sheath loop of one embodiment of the present invention;

[0087] Figure 5 A schematic diagram of the instantaneous value of the original sheath current collected by the power supply side detection point and the load side detection point according to an embodiment of the present invention;

[0088] Figure 6 a is the waveform of the current transformers CT1 and CT5 on the 1-5-9 sheath loop before detection time synchronization according to an embodiment of the present invention;

[0089] Figure 6 b is a waveform diagram of the current transformers CT2 and CT6 on the 2-6-7 sheath loop before detection time synchronization according to an embodiment of the present invention;

[0090] Figure 6 c is a waveform diagram of the current transformers CT3 and CT4 on the 3-4-8 sheath loop before detection time synchronization according to an embodiment of the present invention;

[0091] Figure 7 a is the waveform of the current transformers CT1 and CT5 on the 1-5-9 sheath loop after detection time synchronization according to an embodiment of the present invention;

[0092] Figure 7 b is a waveform diagram of the current transformers CT2 and CT6 on the 2-6-7 sheath loop after detection time synchronization according to an embodiment of the present invention;

[0093] Figure 7 c is a waveform diagram of the current transformers CT3 and CT4 on the 3-4-8 sheath loop after detection time synchronization according to an embodiment of the present invention;

[0094] Figure 8 The present invention is a schematic structural diagram of a cross-connected high-voltage cable sheath current offline detection time synchronization system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0095] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0096] like Figure 1 As shown, a method for offline detection time synchronization of cross-connected high-voltage cable sheath current includes the following steps:

[0097] S1: Input the high-voltage cable core voltage. Two groups of six current transformers installed on the sheath connection wires of the middle structure of each phase high-voltage cable respectively measure the sheath current between the corresponding two cross-connected grounding points.

[0098] S2: Calculating the capacitive current component of each phase sheath current according to the sheath circuit;

[0099] S3: Calculate the capacitive current residual according to the capacitive current component of each phase sheath current, calculate the optimal time offset of the capacitive current residual, and correct the initial detection time error according to the optimal time offset to complete the detection time synchronization of multiple sheath grounding current detection points.

[0100] The present invention provides a method for offline detection time synchronization of cross-connected high-voltage cable sheath current. The method measures the sheath current between two cross-connected grounding points through a current transformer, calculates the capacitive current component in each phase sheath current, calculates the capacitive current residual in combination with an equivalent model of the detection circuit, and determines the optimal time offset, thereby correcting the initial time deviation of power supply side and load side sampling, achieving time synchronization of multiple sheath grounding current monitoring points, and facilitating accurate extraction of the sheath current vector, thereby assisting in the diagnosis of cross-connected high-voltage cable sheath grounding faults.

[0101] like Figure 2As shown, the present invention uses two groups of six sheath current transformers (CT1-CT6) installed respectively on the sheath connection lines of the middle joint of the high-voltage cable to measure the sheath current between two cross-connected grounding points respectively, and uses the coupling relationship of the sheath currents at different detection points to realize offline timing.

[0102] In one or more embodiments of the present invention, the step of calculating the capacitive current component of each phase sheath current according to the sheath circuit specifically includes the following steps:

[0103] S11: Divide each phase of the three-phase high-voltage cable into three sections and record them as sections 1-9 in sequence. Before the measurement begins, the detection points on both sides agree on the initial detection time. The program starts recording the distributed sheath current data. The sheath current at the power supply side detection point is recorded as I CT1 , I CT2 , I CT3 The starting time of the detection point on the power supply side is t1, and the sheath current of the detection point on the load side is recorded as I CT4 , I CT5 , I CT6 , the start time of the load side detection point is t2, so the start time difference between the two detection points is Δt;

[0104] Δt=t2-t1 (1)

[0105] S12: The sheath current of the cross-connected high-voltage cable is the vector superposition of the inductive current and the capacitive current. Due to the symmetry of the three-phase nine-section cross-connected high-voltage cable circuit, taking the sheath loop 1-5-9 as an example, according to the equivalent model of the inductive coupling loop of the cross-connected high-voltage cable, the sheath protector has a normal impedance to ground of 10 12 Ohm or above, which is equivalent to an open circuit to the ground. On the 1st, 5th and 9th cable sheaths, the induced electromotive force between the high-voltage cable core loop and the sheath loop is E1, E5 and E9 respectively. The 1st, 5th and 9th cable sheaths and the grounding resistance R e and R g Together they form an induced current loop. Therefore, the induced current corresponding to each phase induced current loop can be calculated according to the Ohm-Ding circuit.

[0106]

[0107]

[0108]

[0109] Among them, I L1 , I L5 The induced current of the induced current loop formed by the 1-5-9 segment, that is, the sheath current induced component measured by CT1 and CT5; I L2 , I L6The induced current of the induced current loop formed by the 2-6-7 segment, that is, the sheath current induced component measured by CT2 and CT6; I L3 , I L4 The induced current of the induced current loop formed by sections 3-4-8 is the inductive component of the sheath current measured by CT3 and CT4. E1, E5 and E9 are the induced electromotive force on sections 1, 5 and 9 respectively. Z1-Z9 represent the insulation impedance of the high-voltage cable sections 1-9 respectively. The other sheath loops are similar and will not be explained here one by one. Figure 3 As shown, it is a schematic diagram of the equivalent circuit of the inductive coupling loop of the cross-connected high-voltage cables.

[0110] By using the equivalent model of the inductive coupling loop of the cross-connected high-voltage cables and combining the induced electromotive force and insulation impedance on each section of the high-voltage cable, the induced current in the inductive current loop can be accurately calculated. This makes it easier to accurately calculate the capacitive current based on the sheath current and the induced current.

[0111] Due to the symmetry of the three-phase nine-section cross-connected high-voltage cable circuit, taking the sheath loop 1-5-9 as an example, the equivalent circuit of the capacitive coupling loop is as follows: Figure 4 As shown. Among them, the line core voltages of the three phases ABC are represented by U A 、U B 、U C Insulation resistance is represented by Z i1 、Z i5 、Z i9 The capacitor current is represented by I C1 , I C5 , I C9 express.

[0112] In one or more embodiments of the present invention, calculating the capacitive current residual according to the capacitive current component of each phase sheath current specifically includes the following steps:

[0113] S21: For ideal time synchronous discrete sampling, according to the equivalent model of capacitive coupling loop of cross-connected high-voltage cable sheath current, the capacitive current of each phase flows to the direct grounding points at both ends. 15 Ohm level, much greater than 10 of the sheath impedance -2 ~10 1 The capacitive currents flowing to the direct grounding points at both ends are half each, so the capacitive currents at adjacent monitoring points of the same sheath loop are equal in magnitude but opposite in direction. Since the induced currents in the same sheath loop are equal in magnitude, the coupling relationship between the sheath currents measured by the six current transformers is specifically:

[0114] I CT5 [t n ]-I CT1[t n ]=I C5 [t n ] (5)

[0115] I CT2 [t n ]-I CT6 [t n ]=I C6 [t n ] (6)

[0116] I CT4 [t n ]-I CT3 [t n ]=I C4 [t n ] (7)

[0117] Among them, I CT1 [t n ]-I CT6 [t n ] represent the nth sampling point at time t n The induced current measured by current transformers CT1-CT6;

[0118] S22: For actual non-time-synchronous discrete sampling, sampling time differences are inevitably present at the sheath current detection points on both sides due to agreed time differences, hardware delays, software delays, and other reasons. In the embodiment of the present invention, during actual sampling, because the detection points of current transformers CT1, CT2, and CT3 are 500 m apart from the detection points of current transformers CT4, CT5, and CT6, workers are required to agree on a sampling start time before entering the underground cable channel. However, there is inevitably an error between the actual sampling start time and the agreed sampling time at the two detection points. Using the agreed time in Formula 1, the entire measurement process can be regarded as a non-time-synchronous discrete sampling. The coupling relationship between the sheath currents measured by the six current transformers is specifically:

[0119] I CT5 [t1+t n ]-I CT1 [t1+Δt+t n ]=ΔI C5 [t1+t n ] (8)

[0120] I CT2 [t1+t n ]-I CT6 [t1+Δt+t n ]=ΔI C6 [t1+t n ] (9)

[0121] ICT4 [t1+t n ]-I CT3 [t1+Δt+t n ]=ΔI C4 [t1+t n ] (10)

[0122] Among them, t1+t n Indicates the start sampling time of the nth sampling point on the power supply side, t1+Δt+t n Indicates the start sampling time of the nth sampling point on the load side, Δt indicates the time offset between the corresponding sampling points on the power side and the load side, ΔI C4 , ΔI C5 , ΔI C6 They are the residuals of the capacitance current of the 4th, 5th and 6th sections of high-voltage cables respectively.

[0123] According to the capacitive coupling loop equivalent model of the sheath current of the cross-connected high-voltage cable under ideal time synchronization, the sheath current coupling relationship is determined to determine the residual of the capacitive current, so as to facilitate the subsequent determination of the optimal time offset based on the residual of the capacitive current, and then to correct the initial sampling time and synchronize the time detection time.

[0124] The physical essence of the entire time correction process is to continuously shift the sheath current waveforms measured by current transformers CT1 and CT5, current transformers CT2 and CT6, and current transformers CT3 and CT4 over time until their pairwise differences approach the cable capacitance current waveforms of sections 5, 6, and 4. Therefore, the time synchronization problem of distributed sheath current detection data for cross-connected high-voltage cables is transformed into a least-squares optimization problem: finding the optimal time offset Δt that minimizes the arithmetic mean and squares variance of the capacitance current residuals in Equations 8, 9, and 10, i.e., the mean of the norm2 norm.

[0125] In one or more embodiments of the present invention, the calculating the optimal time offset of the capacitor current residual specifically includes the following steps:

[0126] S31: Calculate the arithmetic mean least squares error of the capacitor current residual, using the following formula:

[0127] Min:avg(norm2(ΔI C4 )+norm2(ΔI C5 )+norm2(ΔI C6 ))

[0128] Among them, norm2(ΔI C4 )、norm2(ΔI C5 )、norm2(ΔI C6) are the 2 norms of the residuals of the capacitance currents of the 4th, 5th and 6th high-voltage cable sections respectively;

[0129] S32: Determine the optimal time offset Δt according to the 2-norm of the residual of the capacitance current of the fourth, fifth, and sixth sections of the high-voltage cable.

[0130] By setting different time offsets and using the recursive least squares method to compare the amplitudes, phase deviations, and observations within one end of the time of two groups of sheath grounding currents with different time offsets, the optimal time offset Δt can be accurately calculated, thereby achieving time synchronization of multiple sheath grounding current detection points.

[0131] In one or more embodiments of the present invention, correcting the initial detection time error according to the optimal time offset specifically includes the following steps:

[0132] S33: Calculate the mean of the capacitance current residuals of the three sheath loops and determine whether the mean is less than a preset threshold. If so, correct the initial detection time error according to the optimal time offset Δt, output the synchronization result, and terminate the processing flow. Otherwise, proceed to S34.

[0133] S34: Increase the optimal time offset Δt by a preset time offset amount, and return to S33.

[0134] By comparing the mean of the three sheath loop capacitance current residuals with a preset threshold, the optimal time offset can be adjusted according to the size of the mean, thereby realizing the correction of the initial detection time of multiple sheath grounding current detection points.

[0135] The cross-connected high-voltage cable sheath current offline detection time synchronization method of the present invention realizes the synchronization of the cross-connected high-voltage cable sheath current distributed offline detection data. Figure 5 As shown, the present invention is applied to a 220kV cable system for power supply of a high-speed railway traction station. Before the detection begins, worker 1 collects the sheath current of current transformers CT1, CT2, and CT3. The three current transformers are connected to the same data acquisition card 1. Worker 2 collects the sheath current of current transformers CT4, CT5, and CT6. The three current transformers are connected to current transformer 2. The two workers agree on the starting time and then enter the underground cable channel to collect the sheath current. Before time synchronization, the original sheath current instantaneous value obtained by worker 1 is as follows: Figure 5 As shown in (a), the instantaneous value of the original sheath current obtained by worker 2 is as follows Figure 5 (b) shown.

[0136] To further illustrate the effect of the present invention, take a short period of time within 0.1 seconds of the sheath current waveform, the waveform of CT1 and CT5 on loop 1 is as follows: Figure 6As shown in (a), the waveforms of CT2 and CT6 on loop 2 are as follows Figure 6 As shown in (b), the waveforms of CT3 and CT4 on loop 3 are as follows Figure 6 (c) is shown. Figure 5 Similarly, the sheath currents at the two detection points on the three sheath loops all have deviations.

[0137] By adopting the cross-connected high-voltage cable sheath current offline detection time synchronization method of the present invention, the difference waveform of the current transformer CT1 and CT5 on loop 1 is compared with the capacitor current waveform. Figure 7 As shown in (a), the difference waveform of the current transformer CT2 and CT6 on loop 2 is compared with the capacitor current waveform. Figure 7 As shown in (b), the difference waveform of the current transformers CT3 and CT4 on loop 3 is compared with the capacitor current waveform. Figure 7 (c) is shown. Figure 7 It can be seen that after applying the present invention, the difference waveform of the current transformers CT1 and CT5 approaches the measured capacitor current waveform of the fifth segment, the difference waveform of the current transformers CT2 and CT6 approaches the measured capacitor current waveform of the sixth segment, and the difference waveform of the current transformers CT3 and CT4 approaches the measured capacitor current waveform of the fourth segment.

[0138] like Figure 8 As shown, the present invention also provides a cross-connected high-voltage cable sheath current offline detection time synchronization system, including a sensing acquisition module, a calculation module and a correction module;

[0139] The sensing acquisition module includes two groups of six current transformers installed on the sheath connection wires of the middle structure of each phase high-voltage cable, and is used to measure the sheath current between the corresponding two cross-connected grounding points respectively;

[0140] The calculation module is used to calculate the capacitive current component of each phase of the sheath current according to the sheath circuit; and is also used to calculate the capacitive current residual according to the capacitive current component of each phase of the sheath current, and calculate the optimal time offset of the capacitive current residual;

[0141] The correction module is used to correct the initial detection time error according to the optimal time offset to achieve time synchronization of multiple sheath grounding current detection points.

[0142] The cross-connected high-voltage cable sheath current offline detection time synchronization system of the present invention measures the sheath current between two cross-connected grounding points through a current transformer, then calculates the capacitive current component in the sheath current of each phase, calculates the capacitive current residual in combination with the equivalent model of the detection circuit, and determines the optimal time offset, thereby correcting the initial time deviation of the power supply side and the load side sampling, achieving time synchronization of multiple sheath grounding current monitoring points, so as to accurately extract the sheath current vector and assist in the diagnosis of cross-connected high-voltage cable sheath grounding faults.

[0143] In one or more embodiments of the present invention, the calculation module calculates the capacitive current component of each phase sheath current according to the sheath circuit in a specific implementation as follows:

[0144] Each phase of the three-phase high-voltage cable is divided into three sections, which are marked as sections 1-9 in sequence. The sheath current of the detection point on the power supply side is defined as I CT1 , I CT2 , I CT3 The starting time of the detection point on the power supply side is t1, and the sheath current of the detection point on the load side is recorded as I CT4 , I CT5 , I CT6 , the start time of the load side detection point is t2, and the start time difference between the two detection points is Δt;

[0145] Δt=t2-t1 (1)

[0146] Calculate the induced current corresponding to each phase induced current loop based on the equivalent model of the inductive coupling loop of the cross-connected high-voltage cable;

[0147]

[0148]

[0149]

[0150] Among them, I L1 , I L5 The induced current of the induced current loop formed by the 1-5-9 segment, that is, the sheath current induced component measured by CT1 and CT5; I L2 , I L6 The induced current of the induced current loop formed by the 2-6-7 segment, that is, the sheath current induced component measured by CT2 and CT6; I L3 , I L4 It is the induced current of the induced current loop formed by sections 3-4-8, that is, the sheath current induced component measured by CT3 and CT4. E1, E5 and E9 are the induced electromotive force on sections 1, 5 and 9 respectively. Z1-Z9 represent the insulation impedance of high-voltage cables in sections 1 to 9 respectively.

[0151] By using the equivalent model of the inductive coupling loop of the cross-connected high-voltage cables, combined with the induced electromotive force and insulation impedance on each section of the high-voltage cable, the induced current in the inductive current loop can be accurately calculated. This makes it easier to accurately calculate the capacitive current based on the sheath current and the induced current.

[0152] In one or more embodiments of the present invention, the calculation module calculates the capacitive current residual according to the capacitive current component of each phase sheath current as follows:

[0153] For ideal time-synchronized discrete sampling, the coupling relationship between the sheath currents measured by the six current transformers is determined based on the equivalent model of the capacitive coupling loop of the cross-connected high-voltage cable sheath current, specifically:

[0154] I CT5 [t n ]-I CT1 [t n ]=I C5 [t n ] (5)

[0155] I CT2 [t n ]-I CT6 [t n ]=I C6 [t n ] (6)

[0156] I CT4 [t n ]-I CT3 [t n ]=I C4 [t n ] (7)

[0157] Among them, I CT1 [t n ]-I CT6 [t n ] represent the nth sampling point at time t n The induced current measured by current transformers CT1-CT6;

[0158] For non-time-synchronous discrete sampling in practice, the coupling relationship between the sheath currents measured by the six current transformers is as follows:

[0159] I CT5 [t1+t n ]-I CT1 [t1+Δt+t n ]=ΔI C5 [t1+t n ] (8)

[0160] I CT2 [t1+t n ]-I CT6 [t1+Δt+t n ]=ΔI C6 [t1+t n ] (9)

[0161] I CT4 [t1+t n ]-I CT3 [t1+Δt+t n ]=ΔI C4 [t1+t n ] (10)

[0162] Among them, t1+t n Indicates the start sampling time of the nth sampling point on the power supply side, t1+Δt+t n Indicates the start sampling time of the nth sampling point on the load side, Δt indicates the time offset between the corresponding sampling points on the power side and the load side, ΔI C4 , ΔI C5 , ΔI C6 They are the residuals of the capacitance current of the 4th, 5th and 6th sections of high-voltage cables respectively.

[0163] According to the capacitive coupling loop equivalent model of the sheath current of the cross-connected high-voltage cable under ideal time synchronization, the sheath current coupling relationship is determined to determine the residual of the capacitive current, so as to facilitate the subsequent determination of the optimal time offset based on the residual of the capacitive current, and then to correct the initial sampling time and synchronize the time detection time.

[0164] In one or more embodiments of the present invention, the calculation module calculates the optimal time offset of the capacitor current residual as follows:

[0165] The arithmetic mean least squares error of the capacitor current residual is calculated using the following formula:

[0166] Min:avg(norm2(ΔI C4 )+norm2(ΔI C5 )+norm2(ΔI C6 ))

[0167] Among them, norm2(ΔI C4 )、norm2(ΔI C5 )、norm2(ΔI C6 ) are the 2 norms of the residuals of the capacitance currents of the 4th, 5th and 6th high-voltage cable sections respectively;

[0168] The optimal time offset Δt is determined according to the 2-norm of the residual of the capacitance current of the fourth, fifth and sixth sections of the high-voltage cable.

[0169] By setting different time offsets and using the recursive least squares method to compare the amplitudes, phase deviations, and observations within one end of the time of two groups of sheath grounding currents with different time offsets, the optimal time offset Δt can be accurately calculated, thereby achieving time synchronization of multiple sheath grounding current detection points.

[0170] In one or more embodiments of the present invention, the correction module corrects the initial detection time error according to the optimal time offset in the following specific implementations:

[0171] Calculate the mean of the three sheath loop capacitance current residuals and determine whether the mean is less than a preset threshold. If so, correct the initial detection time error according to the optimal time offset Δt, output the synchronization result, and end the processing flow. Otherwise, increase the optimal time offset Δt by the preset time offset amount until the mean is less than the preset threshold.

[0172] By comparing the mean of the three sheath loop capacitance current residuals with a preset threshold, the optimal time offset can be adjusted according to the size of the mean, thereby realizing the correction of the initial detection time of multiple sheath grounding current detection points.

[0173] The present invention further provides a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the following method steps are implemented:

[0174] The capacitive current component of each phase sheath current is calculated based on the sheath current between the corresponding two cross-connected grounding points measured by two groups of six current transformers installed on the sheath connection line of the middle structure of each phase high-voltage cable;

[0175] Calculating a capacitive current residual according to the capacitive current component of each phase sheath current, and calculating an optimal time offset of the capacitive current residual;

[0176] The initial detection time error is corrected according to the optimal time offset to complete the time synchronization of multiple sheath grounding current detection points.

[0177] The present invention also provides a cross-connected high-voltage cable sheath current offline detection time synchronization device, characterized in that it includes the above-mentioned storage medium and a processor, and the processor implements the following method steps when executing the computer program on the storage medium:

[0178] The capacitive current component of each phase sheath current is calculated based on the sheath current between the corresponding two cross-connected grounding points measured by two groups of six current transformers installed on the sheath connection line of the middle structure of each phase high-voltage cable;

[0179] Calculating a capacitive current residual according to the capacitive current component of each phase sheath current, and calculating an optimal time offset of the capacitive current residual;

[0180] The initial detection time error is corrected according to the optimal time offset to complete the time synchronization of multiple sheath grounding current detection points.

[0181] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for offline detection time synchronization of sheath current of cross-connected high-voltage cables, characterized in that: The process includes the following steps: S1: Input the high-voltage cable core voltage. Two groups of six current transformers installed on the sheath connection wires of the middle structure of each phase high-voltage cable respectively measure the sheath current between the corresponding two cross-connected grounding points. S2: Calculate the capacitive current component of each phase sheath current according to the sheath circuit; S3: Calculating a capacitive current residual based on the capacitive current component of each phase sheath current, calculating an optimal time offset of the capacitive current residual, and correcting an initial detection time error based on the optimal time offset to achieve detection time synchronization of multiple sheath grounding current detection points; The calculation of the capacitive current residual according to the capacitive current component of each phase sheath current specifically includes the following steps: S21: For ideal time-synchronized discrete sampling, the coupling relationship between the sheath currents measured by the six current transformers is determined based on the equivalent model of the capacitive coupling loop of the cross-connected high-voltage cable sheath currents. Specifically, (5) (6) (7) in, - Represents the nth sampling point moment The induced current measured by current transformers CT1-CT6; S22: For non-time-synchronous discrete sampling in practice, the coupling relationship between the sheath currents measured by the six current transformers is as follows: (8) (9) (10) Among them, t1+t n Indicates the start sampling time of the nth sampling point on the power supply side, t1+Δt+t n Indicates the start sampling time of the nth sampling point on the load side, Indicates the time offset between the corresponding sampling points on the power supply side and the load side, ΔI C4 , ΔI C5 , ΔI C6 The residuals of the capacitance current of the 4th, 5th and 6th high-voltage cable sections are The step of calculating the optimal time offset of the capacitor current residual specifically includes the following steps: S31: Calculate the arithmetic mean least squares error of the capacitor current residual, using the following formula: ； in, 、 、 are the 2 norms of the residuals of the capacitance currents of the 4th, 5th and 6th sections of the high-voltage cable respectively; S32: Determine the optimal time offset according to the 2 norm of the residual of the capacitance current of the 4th, 5th and 6th sections of the high-voltage cable .

2. The method for offline detection time synchronization of cross-connected high-voltage cable sheath current according to claim 1, characterized in that: The calculation of the capacitive current component of each phase sheath current according to the sheath circuit specifically comprises the following steps: S11: Divide each phase of the three-phase high-voltage cable into three sections, and record them as sections 1-9 in sequence. Define the sheath current of the detection point on the power supply side as I CT1 , I CT2 , I CT3 The starting time of the detection point on the power supply side is t1, and the sheath current of the detection point on the load side is recorded as I CT4 , I CT5 , I CT6 , the start time of the load side detection point is t2, and the start time difference between the two detection points is Δt; （1） S12: Calculating the induced current corresponding to each phase induced current loop according to an equivalent model of the inductive coupling loop of the cross-connected high-voltage cable; (2) (3) (4) Among them, I L1 , I L5 The induced current of the induced current loop formed by the 1-5-9 segment, that is, the sheath current induced component measured by CT1 and CT5; I L2 , I L6 The induced current of the induced current loop formed by the 2-6-7 segment, that is, the sheath current induced component measured by CT2 and CT6; I L3 , I L4 It is the induced current of the induced current loop formed by sections 3-4-8, that is, the sheath current induced component measured by CT3 and CT4. E1, E5 and E9 are the induced electromotive force on sections 1, 5 and 9 respectively. Z1-Z9 represent the insulation impedance of sections 1-9 of the high-voltage cable respectively. The same applies to other sheath loops.

3. The method for offline detection time synchronization of cross-connected high-voltage cable sheath current according to claim 1, characterized in that: The correcting of the initial detection time error according to the optimal time offset specifically comprises the following steps: S33: Calculate the mean of the three sheath loop capacitance current residuals and determine whether the mean is less than a preset threshold. If so, adjust the time offset according to the optimal time. Correct the initial detection time error, output the synchronization result, and end the processing flow. Otherwise, enter S34; S34: offset the optimal time The preset time offset is increased, and the process returns to S33.

4. A cross-connected high-voltage cable sheath current offline detection time synchronization system, characterized in that : Includes sensing acquisition module, calculation module and correction module; The sensing acquisition module includes two groups of six current transformers installed on the sheath connection line of the middle structure of each phase high-voltage cable, which are used to measure the sheath current between the corresponding two cross-connected grounding points; The calculation module is used to calculate the capacitive current component of each phase of the sheath current according to the sheath circuit; and is also used to calculate the capacitive current residual according to the capacitive current component of each phase of the sheath current, and calculate the optimal time offset of the capacitive current residual; The correction module is used to correct the initial detection time error according to the optimal time offset to achieve detection time synchronization of multiple sheath grounding current detection points; The specific implementation of the calculation module calculating the capacitive current residual according to the capacitive current component of each phase sheath current is: For ideal time-synchronized discrete sampling, the coupling relationship between the sheath currents measured by the six current transformers is determined based on the equivalent model of the capacitive coupling loop of the cross-connected high-voltage cable sheath current, specifically: (5) (6) (7) in, - Represents the nth sampling point moment The induced current measured by current transformers CT1-CT6; For non-time-synchronous discrete sampling in practice, the coupling relationship between the sheath currents measured by the six current transformers is as follows: (8) (9) (10) Among them, t1+t n Indicates the start sampling time of the nth sampling point on the power supply side, t1+Δt+t n Indicates the start sampling time of the nth sampling point on the load side, Indicates the time offset between the corresponding sampling points on the power supply side and the load side, ΔI C4 , ΔI C5 , ΔI C6 are the residuals of the capacitance current of the 4th, 5th and 6th sections of high-voltage cables respectively; The specific implementation of the calculation module calculating the optimal time offset of the capacitor current residual is: The arithmetic mean least squares error of the capacitor current residual is calculated using the following formula: ； in, 、 、 are the 2 norms of the residuals of the capacitance currents of the 4th, 5th and 6th sections of the high-voltage cable respectively; The optimal time offset is determined based on the 2 norm of the residual of the capacitance current of the 4th, 5th and 6th sections of the high-voltage cable. .

5. The cross-connected high-voltage cable sheath current offline detection time synchronization system according to claim 4 is characterized in that The specific implementation of the calculation module calculating the capacitive current component of each phase sheath current according to the sheath circuit is as follows: Each phase of the three-phase high-voltage cable is divided into three sections, which are marked as sections 1-9 in sequence. The sheath current of the detection point on the power supply side is defined as I CT1 , I CT2 , I CT3 The starting time of the detection point on the power supply side is t1, and the sheath current of the detection point on the load side is recorded as I CT4 , I CT5 , I CT6 , the start time of the load side detection point is t2, and the start time difference between the two detection points is Δt; （1） Calculate the induced current corresponding to each phase induced current loop based on the equivalent model of the inductive coupling loop of the cross-connected high-voltage cable; (2) (3) (4) Among them, I L1 , I L5 The induced current of the induced current loop formed by the 1-5-9 segment, that is, the sheath current induced component measured by CT1 and CT5; I L2 , I L6 The induced current of the induced current loop formed by the 2-6-7 segment, that is, the sheath current induced component measured by CT2 and CT6; I L3 , I L4 It is the induced current of the induced current loop formed by sections 3-4-8, that is, the sheath current induced component measured by CT3 and CT4. E1, E5 and E9 are the induced electromotive force on sections 1, 5 and 9 respectively. Z1-Z9 represent the insulation impedance of sections 1-9 of the high-voltage cable respectively. The same applies to other sheath loops.

6. The cross-connected high-voltage cable sheath current offline detection time synchronization system according to claim 4 is characterized in that The specific implementation of the correction module correcting the initial detection time error according to the optimal time offset is as follows: Calculate the mean of the three sheath loop capacitance current residuals and determine whether the mean is less than a preset threshold. If so, adjust the time offset according to the optimal time. Correct the initial detection time error, output the synchronization result, and end the processing flow. Otherwise, the optimal time offset The preset time offset is increased until the mean value is less than a preset threshold value.

7. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method steps described in any one of claims 1 to 3 are implemented.

8. A cross-connected high-voltage cable sheath current offline detection time synchronization device, characterized by: The method comprises the storage medium according to claim 7 and a processor, wherein the processor implements the method steps according to any one of claims 1 to 3 when executing the computer program on the storage medium.

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