A method for testing high voltage cable faults

Abstract

The present invention discloses a high-voltage cable fault testing method. The method is applied to a high-voltage cable fault testing platform, the platform includes a core of a three-phase single-core cable, a first and a second direct grounding box, and two cross-connected grounding boxes; the core of each single-core cable includes three equal sections of cable metal sheaths; each cable metal sheath includes a core intermediate joint; different sections of cable metal sheaths form three cable metal sheath loops through two cross-connected grounding boxes; the first direct grounding box includes at least three first AC mutual inductors; the second direct grounding box includes at least three second AC mutual inductors; the method includes: obtaining each first actual sheath grounding current on each cable metal sheath loop collected by each first AC mutual inductor and each second actual sheath grounding current of each cable metal sheath loop collected by each second AC mutual inductor; and determining the high-voltage cable fault according to each first actual sheath grounding current and each second actual sheath grounding current.

Description

Technical Field

[0001] The embodiment of the present invention relates to the field of high-voltage power transmission detection, and in particular to a high-voltage cable fault testing method. Background Art

[0002] With the increasing development speed of the power transmission and distribution grid, the scale of high-voltage cables in the power transmission system is getting larger and larger due to their advantages such as meeting the transmission requirements of large-capacity electric energy and protecting the urban appearance from being destroyed. Therefore, timely understanding the operation status of the cable and ensuring the normal operation of the high-voltage cable play a vital role in the safety and stability of the power system.

[0003] High-voltage cables generally refer to single-core cables operating at voltage levels of 110kV and above. The outer layer of the main insulation has a metal sheath as a shielding layer. When current flows through the cable core, due to the principle of electromagnetic induction, an induced voltage will appear at both ends of the metal sheath. The induced voltage at any point on the metal sheath shall not be greater than 50V. In engineering, the metal sheath grounding method is usually used to isolate the influence of the internal field strength of the cable on the outside world, so as to achieve the purpose of limiting the induced voltage of the metal sheath. For the transmission system of long-distance high-voltage cables with a length of more than 1500m, a cross-connected grounding method is generally used. Statistical data show that the most prone to failure in the cross-connected grounding system of high-voltage cables is the connecting parts such as the middle joints, connection boxes and terminals of the cable. At present, the existing technology is to classify and locate different faults by monitoring the changes in the current amplitude of the coaxial cable in the cross-connected box. However, the current at the coaxial cable is superimposed by the currents of different sheath loops, and relying solely on the changes in the current amplitude is not enough to locate the specific location of the fault in the same sheath loop.

[0004] Alternatively, in the prior art, the grounding current at both ends of the cable metal sheath and the amplitude of the coaxial cable current in the cross-connection box are directly measured, and the ratio analysis and imbalance analysis of the three-phase current of the grounding wire under fault and normal conditions are performed to identify the fault. However, this method measures too many currents and requires more sensors. It usually involves a large number of characteristic quantities or complex fault judgment criteria to realize cable fault identification, which often affects the rapidity of cable fault identification and is usually not conducive to engineering applications. Summary of the invention

[0005] The present invention provides a high-voltage cable fault testing method to realize rapid identification of high-voltage cable faults, and provides a new method for online monitoring of high-voltage cable line faults.

[0006] The embodiment of the present invention provides a high-voltage cable fault testing method, which is applied to a high-voltage cable fault testing platform, wherein the high-voltage cable fault testing platform comprises a core of a three-phase single-core cable, a first direct grounding box, a second direct grounding box and two cross-connected grounding boxes; the core of each single-core cable comprises three equal sections of cable metal sheaths; each of the cable metal sheaths comprises a core intermediate joint; different sections of cable metal sheaths form three cable metal sheath loops through the two cross-connected grounding boxes; the first direct grounding box comprises at least three first AC mutual inductors; the second direct grounding box comprises at least three second AC mutual inductors;

[0007] The high voltage cable fault testing method comprises:

[0008] Acquire each first actual sheath grounding current on each of the cable metal sheath loops collected by each of the first AC transformers and each second actual sheath grounding current on each of the cable metal sheath loops collected by each of the second AC transformers;

[0009] A high-voltage cable fault is determined according to each of the first actual sheath grounding currents and each of the second actual sheath grounding currents.

[0010] Optionally, determining a high-voltage cable fault according to each of the first actual sheath grounding currents and each of the second actual sheath grounding currents includes: determining a high-voltage cable fault classification according to each of the first actual sheath grounding currents and each of the second actual sheath grounding currents:

[0011] Determining a high-voltage cable fault classification according to each of the first actual sheath grounding currents and each of the second actual sheath grounding currents includes:

[0012] Determine the absolute value of the phase difference between the first actual sheath grounding current and the second actual sheath grounding current on different cable sheath loops;

[0013] Determine the phase ratio and amplitude ratio of each of the first actual sheath grounding currents and each of the second actual sheath grounding currents on the same cable sheath loop;

[0014] The high-voltage cable fault classification is determined according to the phase difference absolute value, the phase ratio value and the amplitude ratio value.

[0015] Optionally, the method further includes: obtaining the line voltage of the single-core cable of each phase, the core length of the single-core cable of each phase, and the core capacitance parameter of the single-core cable of each phase;

[0016] Determine the sheath leakage current on each of the cable metal sheath loops according to the line voltage of the line core, the length of the line core and the line core capacitance parameters;

[0017] Obtaining the core line current of each phase of the single-core cable and the mutual inductance parameter of the core of each phase of the single-core cable to the metal sheath of each cable;

[0018] Determine the sheath ring current on each of the cable metal sheath loops according to the core line current and the mutual inductance parameter;

[0019] The theoretical sheath grounding current on each of the cable metal sheath loops is determined according to the sheath leakage current and the sheath ring current.

[0020] Optionally, determining a high-voltage cable fault based on each of the first actual sheath grounding currents and each of the second actual sheath grounding currents also includes: determining whether a high-voltage cable fault occurs based on each of the first actual sheath grounding currents, each of the second actual sheath grounding currents and each of the theoretical sheath grounding currents on each of the cable sheath loops.

[0021] Optionally, determining whether a high-voltage cable fails according to each of the first actual sheath grounding currents, each of the second actual sheath grounding currents, and each of the theoretical sheath grounding currents on each of the cable sheath loops includes:

[0022] When the first actual sheath grounding currents or the second actual sheath grounding currents on the cable sheath loops are different from the theoretical sheath grounding currents, it is determined that a high-voltage cable fault occurs.

[0023] Optionally, the sheath leakage current on each of the cable metal sheath loops is determined according to the line voltage of the line core, the line length of the line core and the line capacitance parameters, specifically:

[0024] I A1 =jwU A L A1 C A

[0025] Among them: U A is the line core voltage vector of the A-phase single-core cable; l A1 is the length of the cable metal sheath A1; C A is the core capacitance of the A-phase single-core cable; since the lengths of the cable metal sheath A2 and the cable metal sheath A3 are the same as the length of the cable metal sheath A1, the sheath leakage currents of the cable metal sheath A2 and the cable metal sheath A3 are the same as the sheath leakage current of the cable metal sheath A1;

[0026] I B1 =jwU B L B1 C B

[0027] Among them, U Bis the line core voltage vector of the B-phase single-core cable; l B1 is the length of the cable metal sheath B1; C B is the core capacitance of the B-phase single-core cable; since the lengths of the cable metal sheath B2 and the cable metal sheath B3 are the same as the length of the cable metal sheath B1, the sheath leakage currents of the cable metal sheath B2 and the cable metal sheath B3 are the same as the sheath leakage current of the cable metal sheath B1;

[0028] I C1 =jwU C L C1 C C

[0029] Among them, U C is the line core voltage vector of the C-phase single-core cable; l C1 is the length of the cable metal sheath C1; C C is the core capacitance of the C-phase single-core cable; since the length of the cable metal sheath C2 and the cable metal sheath C3 is the same as the length of the cable metal sheath C1, the sheath leakage current of the cable metal sheath C2 and the cable metal sheath C3 is the same as the sheath leakage current of the cable metal sheath C1.

[0030] Optionally, the core capacitance parameter is specifically:

[0031]

[0032] Among them, ε r is the relative dielectric constant, D C is the diameter of the single-core cable core; δ is the thickness of the insulation.

[0033] Optionally, the sheath ring current on each of the cable metal sheath loops is determined according to the core line current and the mutual inductance parameter; specifically:

[0034]

[0035]

[0036]

[0037] Among them, U SCn (n=1, 2, 3) is the induced voltage of the metal sheath of each cable section; Z mAn , Z mBn and Z mCn (n=1, 2, 3) is the equivalent impedance of the metal sheath of each cable section; Re and Rg are the grounding resistances at both ends of the cross-connected main section; I m1 ,I m2 and I m3They are respectively the sheath circulation currents flowing through the cable metal sheath loops A1-B2-C3, B1-C2-A3 and C1-A2-B3;

[0038] Here we take the induced voltage of the metal sheath of A1 cable as an example; U SA1 =-jw(I A L AA +I B M AB +I C M AC ) A1 ; The induced voltage of the metal sheath of A1 cable includes the induced voltage of the A-phase single-phase cable on the metal sheath of A1 section plus the voltage generated by the mutual inductance of the B-phase and C-phase single-core cables on the metal sheath of A1 section cable, where: I A ,I B ,I C They refer to the core currents of cable A, cable B and cable C respectively; LAA is the mutual inductance coefficient of A-phase single-core cable to cable metal sheath A1; MAB and MAC are the mutual inductance coefficients of B-phase and C-phase single-core cables to A1 cable metal sheath respectively; the calculation method of the induced voltage of other small sections of metal sheath is similar to the induced voltage of A1 cable metal sheath.

[0039] Optionally, determining the theoretical sheath grounding current on each of the cable metal sheath loops according to the sheath leakage current and the sheath ring current includes:

[0040] The theoretical sheath grounding current on each cable metal sheath loop is the vector sum of the sheath leakage current and the sheath ring current.

[0041] Optionally, the theoretical sheath grounding current on each of the cable metal sheath loops is determined according to the sheath leakage current and the sheath ring current, specifically:

[0042] I 1a =(I LA1 +I LB2 +I LC3 )-(I LR1 +I RB2 +I RC3 )-I m1

[0043] I 1b =(I LB1 +I LC2 +I LA3 )-(I RB1 +I RC2 +I RA3 )-I m2

[0044] I 1c =(ILC1 +I LA2 +I LB3 )-(I RC1 +I RA2 +I RB3 )-I m3

[0045] I 2a =(I RB1 +I RC2 +I RA3 )-(I LB1 +I LC2 +I LA3 )+I m2

[0046] I 2b =(I RC1 +I RA2 +I RB3 )-(I LC1 +I LA2 +I LB3 )+I m3

[0047] I 1a =(I RA1 +I RB2 +I RC3 )-(I LA1 +I LB2 +I LC3 )+I m1

[0048] Where: I 1a and I 2c Together they reflect the theoretical sheath grounding current on the cable metal sheath loop A1-B2-C3; I 1b and I 2a Together they reflect the theoretical sheath grounding current on the cable metal sheath loop B1-C2-A3; I 1c and I 2b Together they reflect the theoretical sheath grounding current on the cable metal sheath loop C1-A2-B3; I m1 ,I m2 and I m3 The sheath circulation currents flowing through the cable metal sheath loops A1-B2-C3, B1-C2-A3 and C1-A2-B3 respectively; I LAn ,I LBn ,I LCn I is the current component of the leakage current flowing to the left on the metal sheath of each cable section; RAn ,I RBn and I RCnis the component of leakage current flowing to the right on the metal sheath of each cable section; here we take the component flowing to the right on the metal sheath of A1 cable as an example;

[0049]

[0050]

[0051] Among them, ZmLA1 and ZmRA1 are the equivalent impedances of the left and right sides of the metal sheath of A1 cable respectively; ZmLA1 and ZmRA1 constitute Z mA1 , which is the overall impedance of the metal sheath of cable A1; the corresponding components flowing to the right on the metal sheath of other cable segments are similar.

[0052] The embodiment of the present invention is based on a high-voltage cable fault testing platform, by obtaining each first actual sheath grounding current on each cable metal sheath loop collected by each first AC transformer and each second actual sheath grounding current of each cable metal sheath loop collected by each second AC transformer; and determining the high-voltage cable fault according to each first actual sheath grounding current and each second actual sheath grounding current, thereby realizing rapid identification of high-voltage cable faults and providing a new method for online monitoring of high-voltage cable line faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a flow chart of a high-voltage cable fault testing method provided by an embodiment of the present invention;

[0054] Figure 2 It is a structural schematic diagram of a high-voltage cable fault testing platform provided by an embodiment of the present invention;

[0055] Figure 3 is a flow chart of another high-voltage cable fault testing method provided by an embodiment of the present invention;

[0056] Figure 4 is a flow chart of another high-voltage cable fault testing method provided by an embodiment of the present invention;

[0057] Figure 5 is an equivalent circuit diagram of a high-voltage cable fault test provided by an embodiment of the present invention;

[0058] Figure 6 It is a schematic diagram of the flow direction of the sheath leakage current of the cable metal sheath A1 section provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0060] Figure 1 : is a flow chart of a high voltage cable fault testing method provided by an embodiment of the present invention; Figure 1 As shown, the method specifically comprises the following steps:

[0061] S110, obtaining each first actual sheath grounding current on each cable metal sheath loop collected by each first AC transformer and each second actual sheath grounding current on each cable metal sheath loop collected by each second AC transformer.

[0062] Among them, the high-voltage cable fault testing method is applied to the high-voltage cable fault testing platform. Figure 2 Schematic diagram of a high voltage cable fault testing platform provided by an embodiment of the present invention; Figure 2 As shown, the high-voltage cable fault test platform includes a core of a three-phase single-core cable (phase A, phase B, phase C), a first direct grounding box G1, a second direct grounding box G2 and two cross-connected grounding boxes J1 and J2; the core of each single-core cable (phase A, phase B, phase C) includes three equal sections of cable metal sheaths (A1, A2, A3, B1, B2, B3, C1, C2, C3); the metal sheaths of each cable include core intermediate joints (JA1, JA2, JB1, JC1, JC2) and JA0, JB0, JC0, JA3, JB3, JC3 terminal joints; different sections of cable metal sheaths are connected through two cross-connected grounding boxes J1, J1 to form three cable metal sheath loops A1-B2-C3; B1-C2-A3C1-A2-B3; the first direct grounding box G1 includes at least three first AC mutual inductors; the second direct grounding box G2 includes at least three second AC mutual inductors; this embodiment obtains each first actual sheath grounding current I on each cable metal sheath loop collected by each first AC mutual inductor 1a I 1b I 1c and each second actual sheath grounding current I of each cable metal sheath loop collected by each second AC transformer 2a I 2b I 2c ; Among them, I 1a and I 2c It can reflect the operation status of the cable metal sheath loop A1-B2-C3; 1b and I 2a It can reflect the operation status of the cable metal sheath loop B1-C2-A3;1c and I 2b It can jointly reflect the operating conditions of the cable metal sheath loop C1-A2-B3.

[0063] S120. Determine a high-voltage cable fault according to each first actual sheath grounding current and each second actual sheath grounding current.

[0064] In this embodiment, each first actual sheath grounding current I 1a I 1b I 1c And the second actual sheath grounding current I 2a I 2b I 2c It can be determined that the high voltage cable has a fault. It is understandable that if I 1a and I 2c Not the same, or when I 1a and I 2c Respectively with the theoretical sheath grounding current I 1a’ and I 2c’ If they are different, it means that a fault has occurred on the cable metal sheath loop A1-B2-C3; if I 1b and I 2a Not the same, or when I 1b and I 2a Respectively with the theoretical sheath grounding current I 1b’ and I 2a’ If the cable metal sheath loop B1-C2-A3 is different, a fault occurs; if I 1c and I 2b Not the same, or when I 1c and I 2b Respectively with the theoretical sheath grounding current I 1c’ and I 2b’ If they are different, a fault occurs on the cable metal sheath loop C1-A2-B3; further, through each first actual sheath grounding current I 1a I 1b I 1c And the second actual sheath grounding current I 2a I 2b I 2c Different fault types of high-voltage cables can be determined. For example, the fault classification includes: short circuit or open circuit of the middle joints (JA1, JA2, JB1, JC1, JC2) of the core and the end joints (JA0, JB0, JC0, JA3, JB3, JC3), or short circuit of the cross-connected grounding box due to water ingress, etc., so that the actual grounding current I 1a I 1b I 1c And the second actual sheath grounding current I 2a I2b I 2c It realizes the rapid identification of high-voltage cable faults, provides a new method for online monitoring of high-voltage cable line faults, and solves the problem that the existing technology uses complex fault judgment criteria to realize cable fault identification, which often affects the rapidity of cable fault identification.

[0065] Optionally, based on the above embodiment, the determination of high voltage cable fault is further refined. Figure 3 FIG. 1 is a flow chart of another high voltage cable fault testing method provided by an embodiment of the present invention. Figure 3 As shown, the method includes:

[0066] S210, obtaining each first actual sheath grounding current on each cable metal sheath loop collected by each first AC transformer and each second actual sheath grounding current of each cable metal sheath loop collected by each second AC transformer.

[0067] S220. Determine the absolute value of the phase difference between each first actual sheath grounding current and each second actual sheath grounding current on different cable sheath loops.

[0068] Among them, each first actual sheath grounding current I 1a I 1b I 1c And the second actual sheath grounding current I 2a I 2b I 2c According to the amplitude and phase, it can be expressed as: I 1a =x1∠y1;I 1b =x2∠y2;I 1c =x3∠y3;I 2c =x4∠y4;I 2a =x5∠y5;I 2b =x6∠y6; due to I 1a and I 2c It can reflect the operation status of the cable metal sheath loop A1-B2-C3; 1b and I 2a It can reflect the operation status of the cable metal sheath loop B1-C2-A3; 1c and I 2b It can jointly reflect the operating conditions of the cable metal sheath loop C1-A2-B3, thereby determining the phase difference between the cable metal sheath loops A1-B2-C3 and B1-C2-A3 to be t1=|y1-y2|; determining the phase difference between the cable metal sheath loops B1-C2-A3 and C1-A2-B3 to be t2=|y2-y3|; determining the phase difference between the cable metal sheath loops A1-B2-C3 and C1-A2-B3 to be t3=|y1-y3|.

[0069] S230, determining the phase ratio and amplitude ratio of each first actual sheath grounding current and each second actual sheath grounding current on the same cable sheath loop.

[0070] Among them, the amplitude ratio a1 and phase ratio b1 on the same cable metal sheath loop A1-B2-C3 are: The amplitude ratio a2 and phase ratio b2 on the same metal cable sheath loop B1-C2-A3 are: The amplitude ratio a3 and phase ratio b3 on the same metal cable sheath loop B1-C2-A3 are:

[0071] S240. Determine the high-voltage cable fault classification according to the absolute value of the phase difference, the phase ratio and the amplitude ratio.

[0072] As shown in Table 1 below, Table 1 illustrates different high-voltage cable fault classifications determined according to the absolute value of the phase difference, the phase ratio, and the amplitude ratio;

[0073] Table 1: Fault classification table:

[0074]

[0075] Based on the above embodiments, this embodiment further determines different high-voltage cable fault classifications according to the absolute value of the phase difference, the phase ratio and the amplitude ratio, and achieves accurate positioning of the fault type on the basis of rapid fault identification.

[0076] Optionally, based on the above embodiment, further refinement is performed: Figure 4 FIG. 1 is a flow chart of another high voltage cable fault testing method provided by an embodiment of the present invention. Figure 4 As shown, the method comprises the following steps:

[0077] S310, obtaining each first actual sheath grounding current on each cable metal sheath loop collected by each first AC transformer and each second actual sheath grounding current on each cable metal sheath loop collected by each second AC transformer.

[0078] S320, obtaining the line voltage of each phase single-core cable, the line length of each phase single-core cable, and the line capacitance parameters of each phase single-core cable.

[0079] S330, determining the sheath leakage current on each cable metal sheath loop according to the line core voltage, line core length and line core capacitance parameters.

[0080] Specifically, Figure 5 : is an equivalent circuit diagram of a high voltage cable fault test provided by an embodiment of the present invention; Figure 5As shown, the fault test equivalent circuit diagram includes three metal sheath loops after cross-interconnection: A1-B2-C3, B1-C2-A3 and C1-A2-B3; Figure 6 Schematic diagram of the flow direction of the sheath leakage current of the cable metal sheath A1 section provided by the embodiment of the present invention; Figure 5 and 6 As shown, the sheath leakage current I of the cable metal sheath A1 section A1 for:

[0081] I A1 =jwU A L A1 C A

[0082] Among them: U A is the line core voltage vector of the A-phase single-core cable; l A1 is the length of the cable metal sheath A1; C A is the core capacitance of the A-phase single-core cable; the sheath leakage current I flowing through the insulation impedance Zi A1 It will flow to the left and right on the cable metal sheath A1, and its component is I LA1 with I RA1 ; Satisfy I A1 =I LA1 +I RA1 ; ZmLA1 and ZmRA1 are the equivalent impedances on the left and right sides of the cable metal sheath A1 respectively, and the sum of ZmLA1 and ZmRA1 is the overall impedance of the cable metal sheath A1.

[0083] Since the lengths of the cable metal sheath A2 and the cable metal sheath A3 are the same as the length of the cable metal sheath A1, the sheath leakage currents of the cable metal sheath A2 and the cable metal sheath A3 are the same as the sheath leakage current of the cable metal sheath A1.

[0084] Similarly, the leakage current flow direction of other cable metal sheath sections is similar to that of sheath A1; the sheath leakage current I B1 for

[0085] I B1 =jwU B L B1 C B

[0086] Among them, U B is the line core voltage vector of the B-phase single-core cable; l B1 is the length of the cable metal sheath B1; C Bis the core capacitance of the B-phase single-core cable; since the lengths of the cable metal sheath B2 and the cable metal sheath B3 are the same as the length of the cable metal sheath B1, the sheath leakage currents of the cable metal sheath B2 and the cable metal sheath B3 are the same as the sheath leakage current of the cable metal sheath B1;

[0087] Similarly, the sheath leakage current I C1 for:

[0088] I C1 =jwU C L C1 C C

[0089] Among them, U C is the line core voltage vector of the C-phase single-core cable; l C1 is the length of the cable metal sheath C1; C C is the core capacitance of the C-phase single-core cable; since the length of the cable metal sheath C2 and the cable metal sheath C3 is the same as the length of the cable metal sheath C1, the sheath leakage current of the cable metal sheath C2 and the cable metal sheath C3 is the same as the sheath leakage current of the cable metal sheath C1.

[0090] Optional, core capacitance parameters, specifically:

[0091]

[0092] Among them, ε r is the relative dielectric constant, D C is the diameter of the single-core cable core; δ is the thickness of the insulation layer. It should be noted that each single-core cable also includes an insulation layer between the single-core cable core and the cable metal sheath ( Figure 6 The complete structure of the A-phase single-core cable is also shown).

[0093] S340, obtaining the line core current of each phase single-core cable and the mutual inductance parameter of the line core of each phase single-core cable to the metal sheath of each cable.

[0094] S350, determining the sheath ring current on each cable metal sheath loop according to the core line current and mutual inductance parameters.

[0095] Among them, the sheath ring current is the current generated in the metal sheath by the induced voltage of each sheath through the principle of electromagnetic induction; continue to refer to Figure 5 ;

[0096] The sheath ring current on each cable metal sheath loop; specifically:

[0097]

[0098]

[0099]

[0100] Among them, U SCn (n=1, 2, 3) is the induced voltage of the metal sheath of each cable section; Z mAn , Z mBn and Z mCn (n=1, 2, 3) is the equivalent impedance of the metal sheath of each cable section; Re and Rg are the grounding resistances at both ends of the cross-connected main section; I m1 ,I m2 and I m3 They are respectively the sheath circulation currents flowing through the cable metal sheath loops A1-B2-C3, B1-C2-A3 and C1-A2-B3;

[0101] Here we take the induced voltage of the metal sheath of A1 cable as an example; U SA1 =-jw(I A L AA +I B M AB +I C M AC ) A1 ; The induced voltage of the metal sheath of A1 cable includes the induced voltage of the A-phase single-phase cable on the metal sheath of A1 section plus the voltage generated by the mutual inductance of the B-phase and C-phase single-core cables on the metal sheath of A1 section cable, where: I A ,I B ,I C They refer to the core currents of cable A, cable B and cable C respectively; LAA is the mutual inductance coefficient of A-phase single-core cable to cable metal sheath A1; MAB and MAC are the mutual inductance coefficients of B-phase and C-phase single-core cables to A1 cable metal sheath respectively; the calculation method of the induced voltage of other small sections of metal sheath is similar to the induced voltage of A1 cable metal sheath.

[0102] S360. Determine the theoretical sheath grounding current on each cable metal sheath loop based on the sheath leakage current and the sheath ring current.

[0103] The theoretical sheath grounding current is the current flowing through the metal sheath loop; the theoretical sheath grounding current on each cable metal sheath loop is the vector sum of the sheath leakage current and the sheath ring current, and flows into the earth through the direct grounding boxes at both ends.

[0104] I 1a =(I LA1 +I LB2 +I LC3 )-(I LR1 +I RB2 +I RC3 )-I m1

[0105] I 1b =(I LB1 +I LC2 +I LA3 )-(I RB1 +I RC2 +I RA3 )-I m2

[0106] I 1c =(I LC1 +I LA2 +I LB3 )-(I RC1 +I RA2 +I RB3 )-I m3

[0107] I 2a =(I RB1 +I RC2 +I RA3 )-(I LB1 +I LC2 +I LA3 )+I m2

[0108] I 2b =(I RC1 +I RA2 +I RB3 )-(I LC1 +I LA2 +I LB3 )+I m3

[0109] I 1a =(I RA1 +I RB2 +I RC3 )-(I LA1 +I LB2 +I LC3 )+I m1

[0110] Where: I 1a and I 2c Together they reflect the theoretical sheath grounding current on the cable metal sheath loop A1-B2-C3; I 1b and I 2a Together they reflect the theoretical sheath grounding current on the cable metal sheath loop B1-C2-A3; I 1c and I 2b Together they reflect the theoretical sheath grounding current on the cable metal sheath loop C1-A2-B3; I m1 ,I m2 and I m3The sheath circulation currents flowing through the cable metal sheath loops A1-B2-C3, B1-C2-A3 and C1-A2-B3 respectively; I LAn ,I LBn ,I LCn I is the current component of the leakage current flowing to the left on the metal sheath of each cable section; RAn ,I RBn and I RCn is the component of leakage current flowing to the right on the metal sheath of each section of the cable; here, the component flowing to the right on the metal sheath A1 of the cable is taken as an example;

[0111]

[0112]

[0113] Among them, ZmLA1 and ZmRA1 are the equivalent impedances of the left and right sides of the metal sheath of A1 cable respectively; ZmLA1 and ZmRA1 constitute Z mA1， That is, the overall impedance of the metal sheath of the A1 cable; the corresponding components flowing to the right on the metal sheaths of other cable segments are similar. In this way, this embodiment determines the theoretical sheath grounding current I through various parameters. 1a’ I 1b’ I 1c’ I 2a’ I 2b’ I 2c’ .

[0114] S370. Determine whether a high-voltage cable fails based on each first actual sheath grounding current, each second actual sheath grounding current, and each theoretical sheath grounding current on each cable sheath loop.

[0115] When each first actual sheath grounding current or each second actual sheath grounding current on each cable sheath loop is different from each corresponding theoretical sheath grounding current, it can be determined that a high-voltage cable fault occurs.

[0116] This embodiment determines the theoretical sheath grounding currents based on various parameters, and determines that a high-voltage cable fault occurs when the first actual sheath grounding currents and the second actual sheath grounding currents on each cable sheath loop are different from the one-to-one corresponding theoretical sheath grounding currents, thereby providing a new testing method for high-voltage cable faults.

Claims

1. A high voltage cable fault testing method, characterized in that: Applied to a high-voltage cable fault test platform, the high-voltage cable fault test platform comprises a core of a three-phase single-core cable, a first direct grounding box, a second direct grounding box and two cross-connected grounding boxes; the core of each single-core cable comprises three equal sections of cable metal sheaths; each cable metal sheath comprises a core intermediate joint; different sections of cable metal sheaths form three cable metal sheath loops through the two cross-connected grounding boxes; the first direct grounding box comprises at least three first AC mutual inductors; the second direct grounding box comprises at least three second AC mutual inductors; The high voltage cable fault testing method comprises: Acquire each first actual sheath grounding current on each of the cable metal sheath loops collected by each of the first AC transformers and each second actual sheath grounding current on each of the cable metal sheath loops collected by each of the second AC transformers; Determine a high-voltage cable fault according to each of the first actual sheath grounding currents and each of the second actual sheath grounding currents; The method also includes: obtaining the line voltage of the single-core cable of each phase, the line length of the single-core cable of each phase, and the line capacitance parameter of the single-core cable of each phase; Determine the sheath leakage current on each of the cable metal sheath loops according to the line voltage of the line core, the length of the line core and the line core capacitance parameters; The sheath leakage current on each of the cable metal sheath loops is determined according to the line voltage of the line core, the line length of the line core and the line capacitance parameters, specifically: I A1 =jwU A L A1 C A Among them: U A is the line core voltage vector of the A-phase single-core cable; l A1 is the length of the cable metal sheath A1; C A is the core capacitance of the A-phase single-core cable; since the lengths of the cable metal sheath A2 and the cable metal sheath A3 are the same as the length of the cable metal sheath A1, the sheath leakage currents of the cable metal sheath A2 and the cable metal sheath A3 are the same as the sheath leakage current of the cable metal sheath A1; I B1 =jwU B L B1 C B Among them, U B is the line core voltage vector of the B-phase single-core cable; l B1 is the length of the cable metal sheath B1; C B is the core capacitance of the B-phase single-core cable; since the lengths of the cable metal sheath B2 and the cable metal sheath B3 are the same as the length of the cable metal sheath B1, the sheath leakage currents of the cable metal sheath B2 and the cable metal sheath B3 are the same as the sheath leakage current of the cable metal sheath B1; I C1 =jwU C L C1 C C Among them, U C is the line core voltage vector of the C-phase single-core cable; l C1 is the length of the cable metal sheath C1; C C is the core capacitance of the C-phase single-core cable; since the lengths of the cable metal sheath C2 and the cable metal sheath C3 are the same as the length of the cable metal sheath C1, the sheath leakage currents of the cable metal sheath C2 and the cable metal sheath C3 are the same as the sheath leakage current of the cable metal sheath C1; The core capacitance parameter is specifically: Among them, ε r is the relative dielectric constant, D C is the diameter of the single-core cable core; δ is the thickness of the insulation; Obtaining the core line current of each phase of the single-core cable and the mutual inductance parameter of the core of each phase of the single-core cable to the metal sheath of each cable; Determine the sheath ring current on each of the cable metal sheath loops according to the core line current and the mutual inductance parameter; Wherein, the sheath ring current on each of the cable metal sheath loops is determined according to the core line current and the mutual inductance parameter; specifically: Among them, U SCn (n=1, 2, 3) is the induced voltage of the metal sheath of each cable section; Z mAn , Z mBn and Z mCn (n=1, 2, 3) is the equivalent impedance of the metal sheath of each cable section; Re and Rg are the grounding resistances at both ends of the cross-connected main section; I m1 ,I m2 and I m3 They are respectively the sheath circulation currents flowing through the cable metal sheath loops A1-B2-C3, B1-C2-A3 and C1-A2-B3; Here we take the induced voltage of the metal sheath of A1 cable as an example; U SA1 =-jw(I A L AA +I B M AB +I C M AC ) A1 ; The induced voltage of the metal sheath of A1 cable includes the induced voltage of the A-phase single-phase cable on the metal sheath of A1 section plus the voltage generated by the mutual inductance of the B-phase and C-phase single-core cables on the metal sheath of A1 section cable, where: I B ,I B ,I C They refer to the core currents of cable A, cable B and cable C respectively; LAA is the mutual inductance coefficient of the A-phase single-core cable to the cable metal sheath A1; MAB and MAC are the mutual inductance coefficients of the B-phase and C-phase single-core cables to the A1 cable metal sheath respectively; the calculation method of the induced voltage of other small sections of the metal sheath is the same as the induced voltage of the A1 cable metal sheath; The theoretical sheath grounding current on each of the cable metal sheath loops is determined according to the sheath leakage current and the sheath ring current.

2. The high voltage cable fault testing method according to claim 1, characterized in that: Determining a high-voltage cable fault according to each of the first actual sheath grounding currents and each of the second actual sheath grounding currents includes: determining a high-voltage cable fault classification according to each of the first actual sheath grounding currents and each of the second actual sheath grounding currents: Determining a high-voltage cable fault classification according to each of the first actual sheath grounding currents and each of the second actual sheath grounding currents includes: Determine the absolute value of the phase difference between the first actual sheath grounding currents and the second actual sheath grounding currents on different cable sheath loops; Determine the phase ratio and amplitude ratio of each of the first actual sheath grounding currents and each of the second actual sheath grounding currents on the same cable sheath loop; The high-voltage cable fault classification is determined according to the phase difference absolute value, the phase ratio value and the amplitude ratio value.

3. The high voltage cable fault testing method according to claim 2, characterized in that: Determining a high-voltage cable fault based on each of the first actual sheath grounding currents and each of the second actual sheath grounding currents also includes: determining whether a high-voltage cable fault occurs based on each of the first actual sheath grounding currents, each of the second actual sheath grounding currents and each of the theoretical sheath grounding currents on each of the cable sheath loops.

4. The high voltage cable fault testing method according to claim 3, characterized in that: Determining whether a high-voltage cable fails according to the first actual sheath grounding currents, the second actual sheath grounding currents and the theoretical sheath grounding currents on the cable sheath loops includes: When the first actual sheath grounding currents or the second actual sheath grounding currents on the cable sheath loops are different from the theoretical sheath grounding currents, it is determined that a high-voltage cable fault occurs.

5. The high voltage cable fault testing method according to claim 1, characterized in that: Determining the theoretical sheath grounding current on each of the cable metal sheath loops according to the sheath leakage current and the sheath ring current includes: The theoretical sheath grounding current on each cable metal sheath loop is the vector sum of the sheath leakage current and the sheath ring current.

6. The high voltage cable fault testing method according to claim 5, characterized in that: The theoretical sheath grounding current on each of the cable metal sheath loops is determined according to the sheath leakage current and the sheath ring current, specifically: I 1a =(I LA1 +I LB2 +I LC3 )-(I LR1 +I RB2 +I RC3 )-I m1 I 1b =(I LB1 +I LC2 +I LA3 )-(I RB1 +I RC2 +I RA3 )-I m2 I 1c =(I LC1 +I LA2 +I LB3 )-(I RC1 +I RA2 +I RB3 )-I m3 I 2a =(I RB1 +I RC2 +I RA3 )-(I LB1 +I LC2 +I LA3 )+I m2 I 2b =(I RC1 +I RA2 +I RB3 )-(I LC1 +I LA2 +I LB3 )+I m3 I 1a =(I RA1 +I RB2 +I RC3 )-(I LA1 +I LB2 +I LC3 )+I m1 Where: I 1a and I 2c Together they reflect the theoretical sheath grounding current on the cable metal sheath loop A1-B2-C3; I 1b and I 2a Together they reflect the theoretical sheath grounding current on the cable metal sheath loop B1-C2-A3; I 1c and I 2b Together they reflect the theoretical sheath grounding current on the cable metal sheath loop C1-A2-B3; I m1 ,I m2 and I m3 The sheath circulation currents flowing through the cable metal sheath loops A1-B2-C3, B1-C2-A3 and C1-A2-B3 respectively; I LAn ,I LBn ,I LCn I is the current component of the leakage current flowing to the left on the metal sheath of each cable section; RAn ,I RBn and I RCn is the component of leakage current flowing to the right on the metal sheath of each cable section; here we take the component flowing to the right on the metal sheath of A1 cable as an example; Among them, ZmLA1 and ZmRA1 are the equivalent impedances of the left and right sides of the metal sheath of A1 cable respectively; ZmLA1 and ZmRA1 constitute Z mA1， That is the overall impedance of the metal sheath of cable A1; the corresponding components flowing to the right on the metal sheaths of other cable segments are also the same.

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