CN114859104A - Method and system for synchronizing offline detection time of current of cross-connection high-voltage cable sheath - Google Patents

Abstract

The invention relates to a method and a system for synchronizing the offline detection time of sheath current of a cross-connected high-voltage cable, wherein the method comprises the steps of inputting the voltage of a core of the high-voltage cable and respectively measuring the sheath current between two corresponding cross-connected grounding points; calculating the capacitance current component of each phase of sheath current according to the sheath circuit; and calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, calculating the optimal time offset of the capacitance current residual, and correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points. According to the invention, the capacitance current component and the capacitance current residual error in each phase of sheath current are calculated through the sheath current to determine the optimal time offset, so that the initial sampling time deviation of the power supply side and the load side is corrected, the time synchronization of a plurality of sheath grounding current monitoring points is realized, and the sheath current vector is accurately extracted to assist the diagnosis of the sheath grounding fault of the cross-connection high-voltage cable.

Description

Method and system for synchronizing offline detection time of current of cross-connection high-voltage cable sheath

Technical Field

The invention relates to the technical field of high-voltage cable detection, in particular to a method and a system for synchronizing offline detection time of cross-connection high-voltage cable sheath current.

Background

The sheath current phasor is a key state quantity for diagnosing the grounding fault of the sheath of the cross-connection high-voltage cable, and the time synchronization of the distributed sheath current measurement signal is a precondition for accurately extracting the sheath phasor. In the past, the distributed online monitoring of the sheath grounding current of the cross-interconnected high-voltage cable system depends on the hardware time synchronization of a GPS or a local network, and cannot be applied to offline mobile inspection due to the limitation of no signal of an underground cable channel and networking cost, so that the application of a sheath current detection technology in an offline scene is limited. When no GPS signal and local network exist, the problem of time synchronization of the distributed sheath current signal of the high-voltage cable can not be realized.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a method and a system for synchronizing the offline detection time of the current of the sheath of the cross-connected high voltage cable, aiming at the deficiencies of the prior art.

The technical scheme for solving the technical problems is as follows: a cross-connection high-voltage cable sheath current off-line detection time synchronization method comprises the following steps:

s1: inputting the voltage of a core of a high-voltage cable, and respectively measuring the sheath current between two corresponding cross interconnection grounding points by two groups of six current transformers arranged on a sheath connecting wire of the intermediate structure of each phase of the high-voltage cable;

s2: calculating the capacitance current component of each phase of sheath current according to the sheath circuit;

s3: and calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, calculating the optimal time offset of the capacitance current residual, and correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points.

The invention has the beneficial effects that: the method for synchronizing the off-line detection time of the sheath current of the cross-connection high-voltage cable measures the sheath current between two cross-connection grounding points through a current transformer, then calculates the capacitance current component in each phase of sheath current, calculates the capacitance current residual error by combining with an equivalent model of a detection circuit, and determines the optimal time offset, thereby correcting the initial sampling time deviation of a power supply side and a load side, realizing the time synchronization of a plurality of sheath grounding current monitoring points, and facilitating the accurate extraction of sheath current vectors and the aided diagnosis of the sheath grounding fault of the cross-connection high-voltage cable.

On the basis of the technical scheme, the invention can be further improved as follows:

further: the calculating of the capacitance current component of each phase of sheath current according to the sheath circuit specifically includes the following steps:

s11: dividing each phase of the three-phase high-voltage cable into three sections, sequentially marking as 1-9 sections, and defining sheath current of a power supply side detection point as I _CT1 、I _CT2 、I _CT3 The starting time of the power supply side detection point is t ₁ The sheath current at the load side detection point is denoted as I _CT4 、I _CT5 、I _CT6 The start time of the load-side detection point is t ₂ The starting time difference of the two detection points is delta t;

Δt＝t ₂ -t ₁ (1)

s12: calculating the induced current corresponding to each phase of induced current loop according to the equivalent model of the inductive coupling loop of the cross-interconnected high-voltage cable;

wherein, I _L1 、I _L5 The induced current of the induced current loop formed for the sections 1-5-9, namely the induced component of the sheath current measured by the CT1 and the CT 5; i is _L2 、I _L6 The induced current of the induced current loop formed for 2-6-7 sections, namely the sheath current induced component measured by CT2 and CT 6; i is _L3 、I _L4 The induced current of the induced current loop formed for the 3-4-8 segments, i.e. the sheath current induced component measured by CT3 and CT4, E ₁ ，E ₅ And E ₉ Induced electromotive forces, Z, on the 1 st, 5 th and 9 th sections, respectively ₁ -Z ₉ Respectively, the insulation resistance of the high-voltage cables of the 1 st to 9 th sections.

The beneficial effects of the further scheme are as follows: the induced current of the Zhu induced current loop can be accurately calculated by combining the induced electromotive force and the insulation impedance on each section of the high-voltage cable through an equivalent model of the inductive coupling loop of the cross-interconnected high-voltage cable, so that the capacitance current can be accurately calculated according to the sheath current and the induced current in the follow-up process.

Further: the method for calculating the capacitance current residual according to the capacitance current component of each phase of sheath current specifically comprises the following steps:

s21: for ideal time synchronous discrete sampling, determining the coupling relation among sheath currents measured by six current transformers according to a capacitive coupling loop equivalent model of cross-connected high-voltage cable sheath currents, specifically:

I _CT5 [t _n ]-I _CT1 [t _n ]＝I _C5 [t _n ] (5)

I _CT2 [t _n ]-I _CT6 [t _n ]＝I _C6 [t _n ] (6)

I _CT4 [t _n ]-I _CT3 [t _n ]＝I _C4 [t _n ] (7)

wherein, I _CT1 [t _n ]-I _CT6 [t _n ]Respectively representing the nth sampling point time t _n The current transformer CT1-CT6 measures the induced current;

s22: aiming at actual non-time synchronous discrete sampling, the coupling relation among sheath currents measured by six current transformers is specifically as follows:

I _CT5 [t ₁ +t _n ]-I _CT1 [t ₁ +Δt+t _n ]＝ΔI _C5 [t ₁ +t _n ] (8)

I _CT2 [t ₁ +t _n ]-I _CT6 [t ₁ +Δt+t _n ]＝ΔI _C6 [t ₁ +t _n ] (9)

I _CT4 [t ₁ +t _n ]-I _CT3 [t ₁ +Δt+t _n ]＝ΔI _C4 [t ₁ +t _n ] (10)

wherein, t ₁ +t _n Represents the start sampling time, t, of the nth sample point on the power supply side ₁ +Δt+t _n Represents the start sampling time of the nth sampling point on the load side, Δ t represents the time offset between the corresponding sampling points on the power side and the load side, Δ I _C4 、ΔI _C5 、ΔI _C6 The residual errors of the capacitance currents of the 4 th, 5 th and 6 th sections of the high-voltage cables are respectively.

The beneficial effects of the further scheme are as follows: and determining the residual error of the capacitance current according to the sheath current coupling relation of the capacitive coupling loop equivalent model of the cross-interconnected high-voltage cable sheath current under the ideal time synchronization condition, so that the optimal time offset can be determined according to the residual error of the capacitance current, the initial sampling time is corrected, and the time detection time is synchronized.

Further: the calculating of the optimal time offset of the capacitive current residual specifically comprises the following steps:

s31: and calculating the arithmetic mean least square variance of the residual error of the capacitance current, wherein the calculation formula is as follows:

Min:avg(norm2(ΔI _C4 )+norm2(ΔI _C5 )+norm2(ΔI _C6 ))

among them, norm2(Δ I) _C4 )、norm2(ΔI _C5 )、norm2(ΔI _C6 ) 2 norms of residual errors of the high-voltage cable capacitance currents of the 4 th section, the 5 th section and the 6 th section respectively;

s32: and determining the optimal time offset delta t according to the 2 norm of the residual error of the 4 th, 5 th and 6 th sections of high-voltage cable capacitance current.

The beneficial effects of the further scheme are as follows: by setting different time offsets and adopting a recursive least square method, the amplitude, the phase deviation and the observation within one end time of two groups of sheath grounding currents with different time offsets are compared, so that the optimal time offset delta t can be accurately calculated, and the time synchronization of a plurality of sheath grounding current detection points is realized.

Further: the step of correcting the initial detection time error according to the optimal time offset specifically comprises the following steps:

s33: calculating the average value of the residual errors of the capacitance currents of the three sheath loops, judging whether the average value is smaller than a preset threshold value, if so, correcting the initial detection time error according to the optimal time offset delta t, outputting a synchronization result, and ending the processing flow, otherwise, entering S34;

s34: the optimum time offset Δ t is increased by a preset time offset amount and returns to S33.

The beneficial effects of the further scheme are as follows: the average value of the three sheath loop capacitance current residuals is compared with a preset threshold value, so that the optimal time offset can be adjusted according to the average value, and the correction of the initial detection time of a plurality of sheath grounding current detection points is realized.

The invention also provides a cross-connection high-voltage cable sheath current off-line detection time synchronization system, which comprises a sensing acquisition module, a calculation module and a correction module;

the sensing acquisition module comprises two groups of six current transformers which are arranged on a sheath connecting line of the middle structure of each phase of the high-voltage cable and are used for respectively measuring sheath currents between two corresponding cross interconnection grounding points;

the calculation module is used for calculating the capacitance current component of each phase of sheath current according to the sheath circuit; the device is also used for calculating a capacitance current residual according to the capacitance current component of each phase of sheath current and calculating the optimal time offset of the capacitance current residual;

and the correction module is used for correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points.

According to the system for off-line detection time synchronization of sheath current of the cross-interconnected high-voltage cable, the sheath current between two cross-interconnected grounding points is measured through the current transformer, then the capacitance current component in each phase of sheath current is calculated, the capacitance current residual error is calculated by combining with an equivalent model of a detection circuit, and the optimal time offset is determined, so that the initial sampling time deviation of a power supply side and a load side is corrected, the time synchronization of a plurality of sheath grounding current monitoring points is realized, the sheath current vector is accurately extracted, and the diagnosis of the sheath grounding fault of the cross-interconnected high-voltage cable is aided.

On the basis of the technical scheme, the invention can be further improved as follows:

further: the calculation module calculates the capacitance current component of each phase of sheath current according to the sheath circuit, and the calculation module comprises the following concrete implementation steps:

dividing each phase of the three-phase high-voltage cable into three sections, sequentially marking as 1-9 sections, and defining sheath current of a power supply side detection point as I _CT1 、I _CT2 、I _CT3 The starting time of the power supply side detection point is t ₁ The sheath current at the load side detection point is denoted as I _CT4 、I _CT5 、I _CT6 The start time of the load-side detection point is t ₂ The starting time difference of the two detection points is delta t;

Δt＝t ₂ -t ₁ (1)

calculating the induced current corresponding to each phase of induced current loop according to the equivalent model of the inductive coupling loop of the cross-interconnected high-voltage cable;

wherein, I _L1 、I _L5 The induced current of the induced current loop formed for the sections 1-5-9, namely the induced component of the sheath current measured by the CT1 and the CT 5; i is _L2 、I _L6 The induction currents of the induction current loop formed for 2-6-7 segments are the sheath current induction components measured by CT2 and CT 6; i is _L3 、I _L4 The induced current of the induced current loop formed for the 3-4-8 segments, i.e. the sheath current induced component measured by CT3 and CT4, E ₁ ，E ₅ And E ₉ Induced electromotive forces, Z, on the 1 st, 5 th and 9 th sections, respectively ₁ -Z ₉ Respectively representing the insulation resistance of the high-voltage cables of the 1 st to 9 th sections;

the specific implementation of the calculation module for calculating the capacitance current residual according to the capacitance current component of each phase of sheath current is as follows:

for ideal time synchronous discrete sampling, determining the coupling relation among sheath currents measured by six current transformers according to a capacitive coupling loop equivalent model of cross-connected high-voltage cable sheath currents, specifically:

I _CT5 [t _n ]-I _CT1 [t _n ]＝I _C5 [t _n ] (5)

I _CT2 [t _n ]-I _CT6 [t _n ]＝I _C6 [t _n ] (6)

I _CT4 [t _n ]-I _CT3 [t _n ]＝I _C4 [t _n ] (7)

wherein, I _CT1 [t _n ]-I _CT6 [t _n ]Respectively representing the nth sampling point time t _n The current transformer CT1-CT6 measures the induced current;

aiming at actual non-time synchronous discrete sampling, the coupling relation among sheath currents measured by six current transformers is specifically as follows:

I _CT5 [t ₁ +t _n ]-I _CT1 [t ₁ +Δt+t _n ]＝ΔI _C5 [t ₁ +t _n ] (8)

I _CT2 [t ₁ +t _n ]-I _CT6 [t ₁ +Δt+t _n ]＝ΔI _C6 [t ₁ +t _n ] (9)

I _CT4 [t ₁ +t _n ]-I _CT3 [t ₁ +Δt+t _n ]＝ΔI _C4 [t ₁ +t _n ] (10)

wherein, t ₁ +t _n Represents the start sampling time, t, of the nth sample point on the power supply side ₁ +Δt+t _n Represents the start sampling time of the nth sampling point on the load side, Δ t represents the time offset between the corresponding sampling points on the power supply side and the load side, Δ I _C4 、ΔI _C5 、ΔI _C6 Residual errors of the capacitance currents of the 4 th, 5 th and 6 th sections of high-voltage cables are respectively obtained;

the calculation module calculates the optimal time offset of the capacitance current residual error by specifically implementing:

and calculating the arithmetic mean least square variance of the residual error of the capacitance current, wherein the calculation formula is as follows:

Min:avg(norm2(ΔI _C4 )+norm2(ΔI _C5 )+norm2(ΔI _C6 ))

among them, norm2(Δ I) _C4 )、norm2(ΔI _C5 )、norm2(ΔI _C6 ) Is divided into2 norms of residual errors of the 4 th, 5 th and 6 th sections of high-voltage cable capacitance currents;

and determining the optimal time offset delta t according to the 2 norm of the residual error of the 4 th, 5 th and 6 th sections of high-voltage cable capacitance current.

The beneficial effects of the further scheme are as follows: the induced current of the Zhu induced current loop can be accurately calculated by combining the induced electromotive force and the insulation impedance on each section of the high-voltage cable through an equivalent model of the inductive coupling loop of the cross-interconnected high-voltage cable, so that the capacitance current can be accurately calculated according to the sheath current and the induced current; determining residual errors of the capacitance currents according to the equivalent model of the capacitive coupling loop of the cross-interconnected high-voltage cable sheath currents under the ideal time synchronization condition, so that the optimal time offset can be determined according to the residual errors of the capacitance currents in the follow-up process, the initial sampling time is corrected, and the time detection time is synchronized; by setting different time offsets and adopting a recursive least square method, the amplitude, the phase deviation and the observation within one end time of two groups of sheath grounding currents with different time offsets are compared, so that the optimal time offset delta t can be accurately calculated, and the time synchronization of a plurality of sheath grounding current detection points is realized.

Further: the specific implementation of the correction module for correcting the initial detection time error according to the optimal time offset is as follows:

and calculating the average value of the residual errors of the capacitance currents of the three sheath loops, judging whether the average value is smaller than a preset threshold value, if so, correcting the initial detection time error according to the optimal time offset delta t, outputting a synchronization result, and ending the processing flow, otherwise, increasing the optimal time offset delta t by a preset time offset until the average value is smaller than the preset threshold value.

The beneficial effects of the further scheme are as follows: by comparing the average value of the three sheath loop capacitance current residuals with a preset threshold value, the optimal time offset can be adjusted according to the average value, and the correction of the initial detection time of a plurality of sheath grounding current detection points is realized.

The invention also provides a computer-readable storage medium, in which a computer program is stored, which, when being executed by a processor, carries out the method steps of:

calculating the capacitance current component of each phase of sheath current according to the sheath current between two corresponding cross interconnection grounding points respectively measured by two groups of six current transformers arranged on the sheath connecting line of the middle structure of each phase of high-voltage cable;

calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, and calculating the optimal time offset of the capacitance current residual;

and correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points.

The invention also provides a device for synchronizing the offline detection time of the current of the sheath of the cross-connected high-voltage cable, which is characterized in that: comprising said storage medium and a processor, said processor implementing the following method steps when executing the computer program on said storage medium:

calculating the capacitance current component of each phase of sheath current according to the sheath current between two corresponding cross interconnection grounding points respectively measured by two groups of six current transformers arranged on the sheath connecting line of the middle structure of each phase of high-voltage cable;

calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, and calculating the optimal time offset of the capacitance current residual;

and correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points.

Drawings

FIG. 1 is a schematic flow chart of a cross-connect high voltage cable sheath current offline detection time synchronization method according to an embodiment of the present invention;

fig. 2 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 invention;

FIG. 3 is an equivalent circuit diagram of the inductive coupling between ground current detection points of the 1-5-9 sheath loop according to one embodiment of the present invention;

FIG. 4 is an equivalent circuit of the capacitive coupling loop between ground current detection points of the 1-5-9 sheath loop according to one embodiment of the present invention;

FIG. 5 is a schematic diagram of an original sheath current instantaneous value collected at a power side detection point and a load side detection point according to an embodiment of the present invention;

FIG. 6a is a waveform of current transformers CT1 and CT5 on the sheath loop before detection time synchronization of the present invention, in accordance with one embodiment;

FIG. 6b is a schematic diagram of waveforms of the current transformers CT2 and CT6 on the sheath loop 2-6-7 before detecting time synchronization according to an embodiment of the present invention;

FIG. 6c is a schematic waveform diagram of the current transformers CT3 and CT4 on the sheath loop before detecting time synchronization according to an embodiment of the present invention;

FIG. 7a is a waveform of the current transformers CT1 and CT5 on the sheath loop 1-5-9 after detecting time synchronization in accordance with one embodiment of the present invention;

FIG. 7b is a schematic diagram of waveforms of the current transformers CT2 and CT6 on the 2-6-7 sheath loop after detecting time synchronization according to an embodiment of the present invention;

FIG. 7c is a schematic waveform diagram of the current transformers CT3 and CT4 on the 3-4-8 sheath loop after detecting time synchronization according to an embodiment of the present invention;

fig. 8 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 invention.

Detailed Description

The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.

As shown in fig. 1, a method for synchronizing current offline detection time of a sheath of a cross-connected high-voltage cable includes the following steps:

s1: inputting the voltage of a core of a high-voltage cable, and respectively measuring the sheath current between two corresponding cross interconnection grounding points by two groups of six current transformers arranged on a sheath connecting wire of the intermediate structure of each phase of the high-voltage cable;

s2: calculating the capacitance current component of each phase of sheath current according to the sheath circuit;

s3: and calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, calculating the optimal time offset of the capacitance current residual, and correcting the initial detection time error according to the optimal time offset so as to finish the detection time synchronization of a plurality of sheath grounding current detection points.

The method for synchronizing the off-line detection time of the sheath current of the cross-connection high-voltage cable measures the sheath current between two cross-connection grounding points through a current transformer, then calculates the capacitance current component in each phase of sheath current, calculates the capacitance current residual error by combining with an equivalent model of a detection circuit, and determines the optimal time offset, thereby correcting the initial sampling time deviation of a power supply side and a load side, realizing the time synchronization of a plurality of sheath grounding current monitoring points, and facilitating the accurate extraction of sheath current vectors and the aided diagnosis of the sheath grounding fault of the cross-connection high-voltage cable.

As shown in fig. 2, the present invention adopts two sets of six sheath current transformers (CT1-CT6) respectively installed on the sheath connecting wires of the high voltage cable intermediate connector, respectively measures the sheath currents between two cross-connection grounding points, and realizes off-line time synchronization by using the coupling relationship of the sheath currents at different detection points.

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

s11: dividing each phase of the three-phase high-voltage cable into three sections, sequentially recording the three sections as 1-9 sections, appointing initial starting detection time at detection points on two sides before measurement starts, starting a program to record distributed sheath current data, and recording sheath current of the detection points on the power supply side as I _CT1 、I _CT2 、I _CT3 The starting time of the power supply side detection point is t ₁ The sheath current at the load side detection point is denoted as I _CT4 、I _CT5 、I _CT6 The start time of the load-side detection point is t ₂ Then, the difference in the start times of the two detection points is Δ t;

Δt＝t ₂ -t ₁ (1)

s12: the sheath current of the cross-connection high-voltage cable is vector superposition of induced current and capacitance current, and due to the symmetry of the three-phase nine-section cross-connection high-voltage cable circuit, taking sheath loops 1-5-9 as an example, according to an equivalent model of an inductive coupling loop of the cross-connection high-voltage cable, the sheath protector normally has an earth impedance of 10 ¹² Above ohm, it can be equivalent to open circuit to ground, on the 1 st, 5 th and 9 th sections of cable sheath, the induced electromotive force between the high-voltage cable core loop and the sheath loop is respectively E ₁ ，E ₅ And E ₉ The 1 st, 5 th and 9 th sections of cable sheath and grounding resistor R _e And R _g The induction current loops are formed together, so that the induction current corresponding to each phase of induction current loop can be calculated according to the ohm circuit;

wherein, I _L1 、I _L5 The induced current of the induced current loop formed for the sections 1-5-9, namely the induced component of the sheath current measured by the CT1 and the CT 5; i is _L2 、I _L6 The induced current of the induced current loop formed for 2-6-7 sections, namely the sheath current induced component measured by CT2 and CT 6; I.C. A _L3 、I _L4 The induced current of the induced current loop formed for the 3-4-8 segments, i.e. the sheath current induced component measured by CT3 and CT4, E ₁ ，E ₅ And E ₉ Induced electromotive forces, Z, on the 1 st, 5 th and 9 th sections, respectively ₁ -Z ₉ Respectively, the insulation resistance of the high-voltage cables of the 1 st to 9 th sections. The other sheath loops are analogically repeated and will not be described one by one here. As shown in FIG. 3, is a crossEquivalent circuit schematic of the inductively coupled loops interconnecting the high voltage cables.

The induced current of the Zhu induced current loop can be accurately calculated by combining the induced electromotive force and the insulation impedance on each section of the high-voltage cable through an equivalent model of the inductive coupling loop of the cross-interconnected high-voltage cable, so that the capacitance current can be accurately calculated according to the sheath current and the induced current in the follow-up process.

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 shown in fig. 4. Wherein, the core voltage of ABC three phases uses U respectively _A 、U _B 、U _C Expressed as insulation resistance Z _i1 、Z _i5 、Z _i9 The capacitance currents are respectively represented by I _C1 、I _C5 、I _C9 And (4) showing.

In one or more embodiments of the present invention, the calculating the capacitance current residual according to the capacitance current component of each sheath current specifically includes the following steps:

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 capacitance current of each phase respectively flows to the direct grounding points at two ends, and the insulation impedance is 10 ¹⁵ Ohmic order far greater than 10 of the sheath impedance ^-2 ～10 ¹ Magnitude of force, the capacitance current that flows to the direct ground point in both ends is half respectively, and then the capacitance current size of the adjacent monitoring point in same sheath return circuit equals, and the opposite direction, again because of the induced current size in same sheath return circuit equals, consequently, the coupling relation between the sheath current of six current transformer measurements specifically is:

I _CT5 [t _n ]-I _CT1 [t _n ]＝I _C5 [t _n ] (5)

I _CT2 [t _n ]-I _CT6 [t _n ]＝I _C6 [t _n ] (6)

I _CT4 [t _n ]-I _CT3 [t _n ]＝I _C4 [t _n ] (7)

wherein, I _CT1 [t _n ]-I _CT6 [t _n ]Respectively representing the nth sampling point time t _n The current transformer CT1-CT6 measures the induced current;

s22: in the embodiment of the invention, during actual sampling, because the detection points of the current transformers CT1, CT2 and CT3 are separated from the detection points of the current transformers CT4, CT5 and CT6 by 500m, before entering an underground cable channel, a worker needs to agree on sampling start time, however, the actual sampling start time of the two detection points and the agreed sampling time inevitably have errors, the time agreed by a formula 1 is adopted, the whole measurement process can be regarded as non-time-synchronous discrete sampling, and the coupling relationship among sheath currents measured by six current transformers is specifically as follows:

I _CT5 [t ₁ +t _n ]-I _CT1 [t ₁ +Δt+t _n ]＝ΔI _C5 [t ₁ +t _n ] (8)

I _CT2 [t ₁ +t _n ]-I _CT6 [t ₁ +Δt+t _n ]＝ΔI _C6 [t ₁ +t _n ] (9)

I _CT4 [t ₁ +t _n ]-I _CT3 [t ₁ +Δt+t _n ]＝ΔI _C4 [t ₁ +t _n ] (10)

wherein, t ₁ +t _n Represents the start sampling time, t, of the nth sample point on the power supply side ₁ +Δt+t _n Represents the start sampling time of the nth sampling point on the load side, Δ t represents the time offset between the corresponding sampling points on the power supply side and the load side, Δ I _C4 、ΔI _C5 、ΔI _C6 The residual errors of the capacitance currents of the 4 th, 5 th and 6 th sections of the high-voltage cables are respectively.

And determining the residual error of the capacitance current according to the sheath current coupling relation of the capacitive coupling loop equivalent model of the cross-interconnected high-voltage cable sheath current under the ideal time synchronization condition, so that the optimal time offset can be determined according to the residual error of the capacitance current, the initial sampling time is corrected, and the time detection time is synchronized.

The physical essence of the whole time correction process is that the sheath current waveforms measured by the current transformers CT1 and CT5, the current transformers CT2 and CT6 and the current transformers CT3 and CT4 are continuously shifted along with time until the two differences approach the cable capacitance current waveforms of the 5 th section, the 6 th section and the 4 th section. Therefore, the time synchronization problem of the distributed sheath current detection data of the cross-interconnected high-voltage cables is converted into the optimization problem of least square: the optimal time offset Δ t is found to minimize the arithmetic mean least squares variance of the capacitive current residuals in equations 8, 9, 10, i.e. the mean of norm2 norm.

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:

s31: and calculating the arithmetic mean least square variance of the residual error of the capacitance current, wherein the calculation formula is as follows:

Min:avg(norm2(ΔI _C4 )+norm2(ΔI _C5 )+norm2(ΔI _C6 ))

among them, norm2(Δ I) _C4 )、norm2(ΔI _C5 )、norm2(ΔI _C6 ) 2 norms of residual errors of the 4 th, 5 th and 6 th sections of high-voltage cable capacitance currents respectively;

s32: and determining the optimal time offset delta t according to the 2 norm of the residual error of the 4 th, 5 th and 6 th sections of high-voltage cable capacitance current.

By setting different time offsets and adopting a recursive least square method, the amplitude, the phase deviation and the observation within one end time of two groups of sheath grounding currents with different time offsets are compared, so that the optimal time offset delta t can be accurately calculated, and the time synchronization of a plurality of sheath grounding current detection points is realized.

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

s33: calculating the average value of the residual errors of the capacitance currents of the three sheath loops, judging whether the average value is smaller than a preset threshold value, if so, correcting the initial detection time error according to the optimal time offset delta t, outputting a synchronization result, and ending the processing flow, otherwise, entering S34;

s34: the optimum time offset Δ t is increased by a preset time offset amount and returns to S33.

The average value of the three sheath loop capacitance current residuals is compared with a preset threshold value, so that the optimal time offset can be adjusted according to the average value, and the correction of the initial detection time of a plurality of sheath grounding current detection points is realized.

The method for synchronizing the current offline detection time of the sheath of the cross-interconnected high-voltage cable realizes the synchronization of the current distributed offline detection data of the sheath of the cross-interconnected high-voltage cable, as shown in fig. 5, the method is applied to a 220kV cable system powered by a certain high-speed rail traction station, before the detection starts, a worker 1 acquires the sheath currents of current transformers CT1, CT2 and CT3, three current transformers are connected to the same data acquisition card 1, a worker 2 acquires the sheath currents of the current transformers CT4, CT5 and CT6, and three current transformers are connected to the 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 instantaneous value of the original sheath current obtained by the operator 1 is shown in fig. 5(a), and the instantaneous value of the original sheath current obtained by the operator 2 is shown in fig. 5 (b).

To further illustrate the effect of the present invention, the sheath current waveforms are taken within a short time of 0.1 second, the waveforms of CT1 and CT5 on loop 1 are shown in fig. 6(a), the waveforms of CT2 and CT6 on loop 2 are shown in fig. 6(b), and the waveforms of CT3 and CT4 on loop 3 are shown in fig. 6 (c). Similar to FIG. 5, the sheath currents at two probing points on three sheath loops are all biased.

By adopting the offline detection time synchronization method for the current of the cross-connected high-voltage cable sheath, the pair of the difference waveform and the capacitance current waveform of the current transformers CT1 and CT5 on the loop 1 is shown in fig. 7(a), the pair of the difference waveform and the capacitance current waveform of the current transformers CT2 and CT6 on the loop 2 is shown in fig. 7(b), and the pair of the difference waveform and the capacitance current waveform of the current transformers CT3 and CT4 on the loop 3 is shown in fig. 7 (c). As can be seen from fig. 7, after the present invention is applied, the difference waveforms of the current transformers CT1 and CT5 approach to the measured capacitance current waveform of the 5 th segment, the difference waveforms of the current transformers CT2 and CT6 approach to the measured capacitance current waveform of the 6 th segment, and the difference waveforms of the current transformers CT3 and CT4 approach to the measured capacitance current waveform of the 4 th segment.

As shown in fig. 8, the present invention further provides a cross-connected high voltage cable sheath current offline detection time synchronization system, which comprises a sensing acquisition module, a calculation module and a correction module;

the sensing acquisition module comprises two groups of six current transformers which are arranged on a sheath connecting line of the middle structure of each phase of the high-voltage cable and are used for respectively measuring sheath currents between two corresponding cross interconnection grounding points;

the calculation module is used for calculating the capacitance current component of each phase of sheath current according to the sheath circuit; the device is also used for calculating a capacitance current residual error according to the capacitance current component of each phase of sheath current and calculating the optimal time offset of the capacitance current residual error;

and the correction module is used for correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points.

According to the system for off-line detection time synchronization of sheath current of the cross-interconnected high-voltage cable, the sheath current between two cross-interconnected grounding points is measured through the current transformer, then the capacitance current component in each phase of sheath current is calculated, the capacitance current residual error is calculated by combining with an equivalent model of a detection circuit, and the optimal time offset is determined, so that the initial sampling time deviation of a power supply side and a load side is corrected, the time synchronization of a plurality of sheath grounding current monitoring points is realized, the sheath current vector is accurately extracted, and the diagnosis of the sheath grounding fault of the cross-interconnected high-voltage cable is aided.

In one or more embodiments of the present invention, the calculation module calculates the capacitance current component of each phase of sheath current according to the sheath circuit by:

dividing each phase of the three-phase high-voltage cable into three sections, sequentially marking as 1-9 sections, and defining sheath current of a power supply side detection point as I _CT1 、I _CT2 、I _CT3 The starting time of the power supply side detection point is t ₁ The sheath current at the load side detection point is denoted as I _CT4 、I _CT5 、I _CT6 The start time of the load-side detection point is t ₂ The starting time difference of the two detection points is delta t;

Δt＝t ₂ -t ₁ (1)

calculating the induced current corresponding to each phase of induced current loop according to the equivalent model of the inductive coupling loop of the cross-interconnected high-voltage cable;

wherein, I _L1 、I _L5 The induced current of the induced current loop formed for the sections 1-5-9, namely the induced component of the sheath current measured by the CT1 and the CT 5; i is _L2 、I _L6 The induced current of the induced current loop formed for 2-6-7 sections, namely the sheath current induced component measured by CT2 and CT 6; i is _L3 、I _L4 The induced current of the induced current loop formed for the 3-4-8 segments, i.e. the sheath current induced component measured by CT3 and CT4, E ₁ ，E ₅ And E ₉ Induced electromotive forces, Z, on the 1 st, 5 th and 9 th sections, respectively ₁ -Z ₉ Respectively, the insulation resistance of the high-voltage cables of the 1 st to 9 th sections.

The induced current of the Zhu induced current loop can be accurately calculated by combining the induced electromotive force and the insulation impedance on each section of the high-voltage cable through an equivalent model of the inductive coupling loop of the cross-interconnected high-voltage cable, so that the capacitance current can be accurately calculated according to the sheath current and the induced current.

In one or more embodiments of the present invention, the calculation module calculates the capacitance current residual according to the capacitance current component of each sheath current by:

for ideal time synchronous discrete sampling, determining the coupling relation among sheath currents measured by six current transformers according to a capacitive coupling loop equivalent model of cross-connected high-voltage cable sheath currents, specifically:

I _CT5 [t _n ]-I _CT1 [t _n ]＝I _C5 [t _n ] (5)

I _CT2 [t _n ]-I _CT6 [t _n ]＝I _C6 [t _n ] (6)

I _CT4 [t _n ]-I _CT3 [t _n ]＝I _C4 [t _n ] (7)

wherein, I _CT1 [t _n ]-I _CT6 [t _n ]Respectively representing the nth sampling point time t _n The current transformer CT1-CT6 measures the induced current;

aiming at actual non-time synchronous discrete sampling, the coupling relation among sheath currents measured by six current transformers is specifically as follows:

I _CT5 [t ₁ +t _n ]-I _CT1 [t ₁ +Δt+t _n ]＝ΔI _C5 [t ₁ +t _n ] (8)

I _CT2 [t ₁ +t _n ]-I _CT6 [t ₁ +Δt+t _n ]＝ΔI _C6 [t ₁ +t _n ] (9)

I _CT4 [t ₁ +t _n ]-I _CT3 [t ₁ +Δt+t _n ]＝ΔI _C4 [t ₁ +t _n ] (10)

wherein, t ₁ +t _n Represents the start sampling time, t, of the nth sample point on the power supply side ₁ +Δt+t _n Represents the start sampling time of the nth sampling point on the load side, Δ t represents the time offset between the corresponding sampling points on the power supply side and the load side, Δ I _C4 、ΔI _C5 、ΔI _C6 The residual errors of the capacitance currents of the 4 th, 5 th and 6 th sections of the high-voltage cables are respectively.

And determining the residual error of the capacitance current according to the sheath current coupling relation of the capacitive coupling loop equivalent model of the cross-interconnected high-voltage cable sheath current under the ideal time synchronization condition, so that the optimal time offset can be determined according to the residual error of the capacitance current, the initial sampling time is corrected, and the time detection time is synchronized.

In one or more embodiments of the present invention, the calculation module calculates the optimal time offset of the capacitance current residual by:

and calculating the arithmetic mean least square variance of the residual error of the capacitance current, wherein the calculation formula is as follows:

Min:avg(norm2(ΔI _C4 )+norm2(ΔI _C5 )+norm2(ΔI _C6 ))

among them, norm2(Δ I) _C4 )、norm2(ΔI _C5 )、norm2(ΔI _C6 ) 2 norms of residual errors of the high-voltage cable capacitance currents of the 4 th section, the 5 th section and the 6 th section respectively;

and determining the optimal time offset delta t according to the 2 norm of the residual error of the 4 th, 5 th and 6 th sections of high-voltage cable capacitance current.

By setting different time offsets and adopting a recursive least square method, the amplitude, the phase deviation and the observation within one end time of two groups of sheath grounding currents with different time offsets are compared, so that the optimal time offset delta t can be accurately calculated, and the time synchronization of a plurality of sheath grounding current detection points is realized.

In one or more embodiments of the present invention, the implementation of the correcting module for correcting the initial detection time error according to the optimal time offset is as follows:

and calculating the average value of the residual errors of the capacitance currents of the three sheath loops, judging whether the average value is smaller than a preset threshold value, if so, correcting the initial detection time error according to the optimal time offset delta t, outputting a synchronization result, and ending the processing flow, otherwise, increasing the optimal time offset delta t by a preset time offset until the average value is smaller than the preset threshold value.

The average value of the three sheath loop capacitance current residuals is compared with a preset threshold value, so that the optimal time offset can be adjusted according to the average value, and the correction of the initial detection time of a plurality of sheath grounding current detection points is realized.

The invention also provides a computer-readable storage medium, in which a computer program is stored, which, when being executed by a processor, carries out the method steps of:

calculating the capacitance current component of each phase of sheath current according to the sheath current between two corresponding cross interconnection grounding points respectively measured by two groups of six current transformers arranged on the sheath connecting line of the middle structure of each phase of high-voltage cable;

calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, and calculating the optimal time offset of the capacitance current residual;

and correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points.

The invention also provides a device for synchronizing the offline detection time of the current of the sheath of the cross-connected high-voltage cable, which is characterized in that: comprising said storage medium and a processor, said processor implementing the following method steps when executing the computer program on said storage medium:

calculating the capacitance current component of each phase of sheath current according to the sheath current between two corresponding cross interconnection grounding points respectively measured by two groups of six current transformers arranged on the sheath connecting line of the middle structure of each phase of high-voltage cable;

calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, and calculating the optimal time offset of the capacitance current residual;

and correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (10)

1. A cross-connection high-voltage cable sheath current off-line detection time synchronization method is characterized by comprising the following steps:

s1: inputting the voltage of a core of a high-voltage cable, and respectively measuring the sheath current between two corresponding cross interconnection grounding points by two groups of six current transformers arranged on a sheath connecting wire of the intermediate structure of each phase of the high-voltage cable;

s2: calculating the capacitance current component of each phase of sheath current according to the sheath circuit;

s3: and calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, calculating the optimal time offset of the capacitance current residual, and correcting the initial detection time error according to the optimal time offset so as to finish the detection time synchronization of a plurality of sheath grounding current detection points.

2. The method for off-line detection time synchronization of sheath current of cross-connected high voltage cables of claim 1, wherein said calculating the capacitive current component of each phase of sheath current according to said sheath circuit comprises the steps of:

s11: dividing each phase of the three-phase high-voltage cable into three sections, sequentially marking as 1-9 sections, and defining sheath current of a power supply side detection point as I _CT1 、I _CT2 、I _CT3 The starting time of the power supply side detection point is t ₁ The sheath current at the load side detection point is denoted as I _CT4 、I _CT5 、I _CT6 The start time of the load-side detection point is t ₂ The starting time difference of the two detection points is delta t;

Δt＝t ₂ -t ₁ (1)

s12: calculating the induced current corresponding to each phase of induced current loop according to the equivalent model of the inductive coupling loop of the cross-interconnected high-voltage cable;

wherein, I _L1 、I _L5 The induced current of the induced current loop formed for the sections 1-5-9, namely the induced component of the sheath current measured by the CT1 and the CT 5; i is _L2 、I _L6 The induced current of the induced current loop formed for 2-6-7 sections, namely the sheath current induced component measured by CT2 and CT 6; i is _L3 、I _L4 The induced current of the induced current loop formed for the 3-4-8 segments, i.e. the sheath current induced component measured by CT3 and CT4, E ₁ ，E ₅ And E ₉ Induced electromotive forces, Z, on the 1 st, 5 th and 9 th sections, respectively ₁ -Z ₉ Respectively, the insulation resistance of the high-voltage cables of the 1 st to 9 th sections.

3. The method for off-line detection time synchronization of sheath currents of cross-connected high-voltage cables according to claim 2, wherein said calculating a capacitive current residual according to a capacitive current component of each sheath current phase comprises the steps of:

s21: for ideal time synchronous discrete sampling, determining the coupling relation among sheath currents measured by six current transformers according to a capacitive coupling loop equivalent model of cross-connected high-voltage cable sheath currents, specifically:

I _CT5 [t _n ]-I _CT1 [t _n ]＝I _C5 [t _n ] (5)

I _CT2 [t _n ]-I _CT6 [t _n ]＝I _C6 [t _n ] (6)

I _CT4 [t _n ]-I _CT3 [t _n ]＝I _C4 [t _n ] (7)

wherein, I _CT1 [t _n ]-I _CT6 [t _n ]Respectively representing the nth sampling point time t _n The current transformer CT1-CT6 measures the induced current;

s22: aiming at actual non-time synchronous discrete sampling, the coupling relation among sheath currents measured by six current transformers is specifically as follows:

I _CT5 [t ₁ +t _n ]-I _CT1 [t ₁ +Δt+t _n ]＝ΔI _C5 [t ₁ +t _n ] (8)

I _CT2 [t ₁ +t _n ]-I _CT6 [t ₁ +Δt+t _n ]＝ΔI _C6 [t ₁ +t _n ] (9)

I _CT4 [t ₁ +t _n ]-I _CT3 [t ₁ +Δt+t _n ]＝ΔI _C4 [t ₁ +t _n ] (10)

wherein, t ₁ +t _n Represents the start sampling time, t, of the nth sample point on the power supply side ₁ +Δt+t _n Represents the start sampling time of the nth sampling point on the load side, Δ t represents the time offset between the corresponding sampling points on the power supply side and the load side, Δ I _C4 、ΔI _C5 、ΔI _C6 The residual errors of the capacitance currents of the 4 th, 5 th and 6 th sections of the high-voltage cables are respectively.

4. The method for off-line current detection time synchronization of the sheath of the cross-interconnected high-voltage cables as claimed in claim 3, wherein said calculating the optimal time offset of the residual error of the capacitive current specifically comprises the steps of:

s31: and calculating the arithmetic mean least square variance of the residual error of the capacitance current, wherein the calculation formula is as follows:

Min:avg(norm2(ΔI _C4 )+norm2(ΔI _C5 )+norm2(ΔI _C6 ))

among them, norm2(Δ I) _C4 )、norm2(ΔI _C5 )、norm2(ΔI _C6 ) 2 norms of residual errors of the 4 th, 5 th and 6 th sections of high-voltage cable capacitance currents respectively;

s32: and determining the optimal time offset delta t according to the 2 norm of the residual error of the 4 th, 5 th and 6 th sections of high-voltage cable capacitance current.

5. The method for synchronizing offline detection of sheath current in a cross-interconnected high-voltage cable according to claim 3, wherein said step of correcting the initial detection time error according to said optimal time offset comprises the steps of:

s33: calculating the average value of the residual errors of the capacitance currents of the three sheath loops, judging whether the average value is smaller than a preset threshold value, if so, correcting the initial detection time error according to the optimal time offset delta t, outputting a synchronization result, and ending the processing flow, otherwise, entering S34;

s34: the optimum time offset Δ t is increased by a preset time offset amount and returns to S33.

6. A cross-connection high-voltage cable sheath current off-line detection time synchronization system is characterized by comprising a sensing acquisition module, a calculation module and a correction module;

the sensing acquisition module comprises two groups of six current transformers which are arranged on a sheath connecting line of the middle structure of each phase of the high-voltage cable and are used for respectively measuring sheath currents between two corresponding cross interconnection grounding points;

the calculation module is used for calculating the capacitance current component of each phase of sheath current according to the sheath circuit; the device is also used for calculating a capacitance current residual according to the capacitance current component of each phase of sheath current and calculating the optimal time offset of the capacitance current residual;

and the correction module is used for correcting the initial detection time error according to the optimal time offset so as to finish the detection time synchronization of a plurality of sheath grounding current detection points.

7. The system for off-line detection of sheath current in a cross-connected high-voltage cable according to claim 6, wherein the calculation module calculates the capacitance current component of each phase of sheath current according to the sheath circuit by:

dividing each phase of the three-phase high-voltage cable into three sections, sequentially marking as 1-9 sections, and defining sheath current of a power supply side detection point as I _CT1 、I _CT2 、I _CT3 The starting time of the power supply side detection point is t ₁ The sheath current at the load side detection point is denoted as I _CT4 、I _CT5 、I _CT6 The start time of the load-side detection point is t ₂ The starting time difference of the two detection points is delta t;

Δt＝t ₂ -t ₁ (1)

calculating the induced current corresponding to each phase of induced current loop according to the equivalent model of the inductive coupling loop of the cross-interconnected high-voltage cable;

wherein, I _L1 、I _L5 The induction current of the induction current loop formed for the segments 1-5-9 is the sheath current induction component measured by CT1 and CT 5; I.C. A _L2 、I _L6 The induced current of the induced current loop formed for 2-6-7 sections, namely the sheath current induced component measured by CT2 and CT 6; i is _L3 、I _L4 The induced current of the induced current loop formed for the 3-4-8 segments, i.e. the sheath current induced component measured by CT3 and CT4, E ₁ ，E ₅ And E ₉ Induced electromotive forces, Z, on the 1 st, 5 th and 9 th sections, respectively ₁ -Z ₉ Respectively representing the insulation resistance of the high-voltage cables of the 1 st to 9 th sections;

the specific implementation of the calculation module for calculating the capacitance current residual according to the capacitance current component of each phase of sheath current is as follows:

for ideal time synchronous discrete sampling, determining the coupling relation among sheath currents measured by six current transformers according to a capacitive coupling loop equivalent model of cross-connected high-voltage cable sheath currents, specifically:

I _CT5 [t _n ]-I _CT1 [t _n ]＝I _C5 [t _n ] (5)

I _CT2 [t _n ]-I _CT6 [t _n ]＝I _C6 [t _n ] (6)

I _CT4 [t _n ]-I _CT3 [t _n ]＝I _C4 [t _n ] (7)

wherein, I _CT1 [t _n ]-I _CT6 [t _n ]Respectively representing the nth sampling point time t _n The current transformer CT1-CT6 measures the induced current;

aiming at actual non-time synchronous discrete sampling, the coupling relation among sheath currents measured by six current transformers is specifically as follows:

I _CT5 [t ₁ +t _n ]-I _CT1 [t ₁ +Δt+t _n ]＝ΔI _C5 [t ₁ +t _n ] (8)

I _CT2 [t ₁ +t _n ]-I _CT6 [t ₁ +Δt+t _n ]＝ΔI _C6 [t ₁ +t _n ] (9)

I _CT4 [t ₁ +t _n ]-I _CT3 [t ₁ +Δt+t _n ]＝ΔI _C4 [t ₁ +t _n ] (10)

wherein, t ₁ +t _n Represents the start sampling time, t, of the nth sample point on the power supply side ₁ +Δt+t _n Represents the start sampling time of the nth sampling point on the load side, Δ t represents the time offset between the corresponding sampling points on the power supply side and the load side, Δ I _C4 、ΔI _C5 、ΔI _C6 Residual errors of the capacitance currents of the 4 th, 5 th and 6 th sections of high-voltage cables are respectively obtained;

the calculation module calculates the optimal time offset of the capacitance current residual error by specifically implementing:

and calculating the arithmetic mean least square variance of the residual error of the capacitance current, wherein the calculation formula is as follows:

Min:avg(norm2(ΔI _C4 )+norm2(ΔI _C5 )+norm2(ΔI _C6 ))

among them, norm2(Δ I) _C4 )、norm2(ΔI _C5 )、norm2(ΔI _C6 ) 2 norms of residual errors of the high-voltage cable capacitance currents of the 4 th section, the 5 th section and the 6 th section respectively;

and determining the optimal time offset delta t according to the 2 norm of the residual error of the 4 th, 5 th and 6 th sections of high-voltage cable capacitance current.

8. The system for off-line detection time synchronization of current of sheath of cross-interconnected high-voltage cable according to claim 6, wherein the correction module corrects the initial detection time error according to the optimal time offset by:

and calculating the average value of the residual errors of the capacitance currents of the three sheath loops, judging whether the average value is smaller than a preset threshold value, if so, correcting the initial detection time error according to the optimal time offset delta t, outputting a synchronization result, and ending the processing flow, otherwise, increasing the optimal time offset delta t by a preset time offset until the average value is smaller than the preset threshold value.

9. A computer-readable storage medium storing a computer program, characterized in that: when being executed by a processor, the computer program realizes the following method steps:

calculating the capacitance current component of each phase of sheath current according to the sheath current between two corresponding cross interconnection grounding points respectively measured by two groups of six current transformers arranged on the sheath connecting line of the middle structure of each phase of high-voltage cable;

calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, and calculating the optimal time offset of the capacitance current residual;

and correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points.

10. The utility model provides a cross interconnection high tension cable sheath electric current off-line detection time synchronization equipment which characterized in that: comprising a storage medium according to claim 9 and a processor, which when executing the computer program on the storage medium performs the method steps of:

calculating the capacitance current component of each phase of sheath current according to the sheath current between two corresponding cross interconnection grounding points respectively measured by two groups of six current transformers arranged on the sheath connecting line of the middle structure of each phase of high-voltage cable;

calculating a capacitance current residual according to the capacitance current component of each phase of sheath current, and calculating the optimal time offset of the capacitance current residual;

and correcting the initial detection time error according to the optimal time offset so as to complete the time synchronization of a plurality of sheath grounding current detection points.

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