CN115201716A - Sheath protector fault online diagnosis method based on sheath current difference amplitude-frequency characteristic - Google Patents

Abstract

Translated fromChinese

本发明提供基于护层电流差幅频特性的护层保护器故障在线诊断方法，所述方法包括以下步骤：判断电缆末端与首端的电流差是否等于电缆内部各分段电缆流入的泄漏电流之和，若等于则电缆回路中未发生接地短路故障；反之则判断异常电流差是否含有谐波，若不含有则电缆回路中未发生其它类型的接地短路故障；若含有则电缆回路中发生接地短路故障。本发明给出了工频下电流差以及故障护层保护器泄漏电流的计算方法并建立了护层保护器故障后谐波分量的等效电路模型，设计了以电缆护层电流差的幅频特性为依据的护层保护器故障诊断方法，提高了现阶段护层保护器检修的效率。

The invention provides an on-line fault diagnosis method for a sheath protector based on the amplitude-frequency characteristic of sheath current difference. The method includes the following steps: judging whether the current difference between the end of the cable and the head end is equal to the sum of the leakage currents flowing into each segmented cable inside the cable , if it is equal to the grounding short-circuit fault in the cable circuit; otherwise, it is judged whether the abnormal current difference contains harmonics, if not, other types of grounding short-circuit faults have not occurred in the cable circuit; . The invention provides the calculation method of the current difference and the leakage current of the fault sheath protector under the power frequency, establishes the equivalent circuit model of the harmonic component after the sheath protector fails, and designs the amplitude frequency of the cable sheath current difference. The fault diagnosis method of the sheath protector based on the characteristics improves the maintenance efficiency of the sheath protector at the current stage.

Description

Translated fromChinese

基于护层电流差幅频特性的护层保护器故障在线诊断方法On-line fault diagnosis method of sheath protector based on sheath current difference amplitude and frequency characteristics

技术领域technical field

本发明涉及高压电缆线路的技术领域，更具体地，涉及一种基于护层电流差幅频特性的护层保护器故障在线诊断方法。The invention relates to the technical field of high-voltage cable lines, and more particularly, to an on-line fault diagnosis method for sheath protectors based on sheath current difference amplitude-frequency characteristics.

背景技术Background technique

目前已有的护层保护器故障监测方法主要依靠人工巡检，并且护层保护器故障和电缆外护套破损等故障引起的工频护层电流变化相近，依靠护层电流幅值、护层电流相对值和护层电流与护层电流差相角等方法难以区分两者。针对护层保护器内部氧化锌阀片的非线性电阻特性，本发明以护层电流差的幅频特性提高护层保护器故障诊断的准确性。At present, the existing sheath protector fault monitoring methods mainly rely on manual inspection, and the power frequency sheath current changes caused by faults such as sheath protector fault and cable outer sheath damage are similar. Methods such as the relative value of the current and the difference between the sheath current and the sheath current are difficult to distinguish between the two. Aiming at the nonlinear resistance characteristics of the zinc oxide valve plate inside the sheath protector, the present invention improves the accuracy of fault diagnosis of the sheath protector by using the amplitude-frequency characteristics of the sheath current difference.

发明内容SUMMARY OF THE INVENTION

本发明针对现有技术中存在的技术问题，给出了工频下电流差以及故障护层保护器泄漏电流的计算方法并建立了护层保护器故障后谐波分量的等效电路模型，设计了以电缆护层电流差的幅频特性为依据的护层保护器故障诊断方法，提高了现阶段护层保护器检修的效率。Aiming at the technical problems existing in the prior art, the present invention provides a calculation method for the current difference under the power frequency and the leakage current of the fault protective layer protector, and establishes an equivalent circuit model of the harmonic components after the protective layer protector fails. The fault diagnosis method of the sheath protector based on the amplitude-frequency characteristic of the cable sheath current difference is presented, which improves the maintenance efficiency of the sheath protector at the present stage.

本发明提供了基于护层电流差幅频特性的护层保护器故障在线诊断方法，包括：The invention provides an on-line fault diagnosis method for a sheath protector based on the differential amplitude-frequency characteristics of sheath current, including:

获取电缆末端与首端的电流差，判断电流差是否等于电缆内部各分段电缆流入的泄漏电流之和，若等于则电缆回路中未发生接地短路故障；反之则线路发生接地短路故障。Obtain the current difference between the end of the cable and the head end, and determine whether the current difference is equal to the sum of the leakage currents flowing into each segmented cable inside the cable. If it is equal, there is no grounding short-circuit fault in the cable loop;

在上述技术方案的基础上，本发明还可以作出如下改进。On the basis of the above technical solutions, the present invention can also make the following improvements.

优选地，所述线路发生接地短路故障之后还包括：判断电流差是否含有谐波，若不含有则电缆回路中未发生其它类型的接地短路故障；若含有则根据预设判据和诊断结果进行护层保护器故障诊断和定位。Preferably, after the ground short-circuit fault occurs in the line, it further includes: judging whether the current difference contains harmonics, if not, no other types of grounding short-circuit faults have occurred in the cable loop; Sheath protector fault diagnosis and location.

优选地，所述根据预设判据和诊断结果进行护层保护器故障诊断和定位包括，通过建立的工频下护层保护器故障后护层电路的电流差和护层保护器故障后谐波分量的等效电路模型，依据护层保护器故障引起护层电流的幅频特性制定故障诊断判据，并判断护层保护器故障所在的回路。Preferably, performing the fault diagnosis and location of the sheath protector according to the preset criteria and the diagnosis results includes: by establishing the current difference of the sheath circuit after the sheath protector fails under the power frequency and the harmonic after the sheath protector failure The equivalent circuit model of the wave component is used to formulate the fault diagnosis criterion according to the amplitude-frequency characteristics of the sheath current caused by the fault of the sheath protector, and determine the circuit where the sheath protector is faulty.

优选地，依据护层保护器故障引起护层电流的幅频特性制定故障诊断判据包括：将故障护层保护器中泄漏电流各次分量等效为谐波源，由故障护层保护器位置注入金属护层回路中，经电缆护层的滤波作用，电缆首末两端的护层电流中的谐波含量因护层保护器故障位置发生改变，并以此制定故障护层保护器中泄漏电流各次谐波含量图作为故障诊断判据。Preferably, formulating the fault diagnosis criterion according to the amplitude-frequency characteristic of the sheath current caused by the fault of the sheath protector includes: equivalently using each component of the leakage current in the sheath protector as a harmonic source, and the position of the sheath protector is determined by the position of the sheath protector. Injected into the metal sheath circuit, through the filtering effect of the cable sheath, the harmonic content of the sheath current at the beginning and end of the cable changes due to the fault position of the sheath protector, and the leakage current in the fault sheath protector is determined accordingly. The harmonic content diagram of each order is used as the fault diagnosis criterion.

优选地，所述获取电缆末端与首端的电流差包括以下步骤：Preferably, the obtaining the current difference between the cable end and the head end includes the following steps:

将6个工频电流互感器安装于交叉互联高压电缆线路两端的接地箱中，同步获取电缆两端护层电流信号；Install 6 power frequency current transformers in the grounding boxes at both ends of the cross-connected high-voltage cable lines, and obtain the current signals of the sheathing at both ends of the cables simultaneously;

将所采集护层电流信号按护层回路分组，分别计算相应分组护层电流差；The collected sheath current signals are grouped according to sheath circuits, and the sheath current differences of the corresponding groups are calculated respectively;

对护层电流差波形做傅里叶变换，得出泄露电流中谐波的含量。The Fourier transform is performed on the current difference waveform of the sheath, and the content of harmonics in the leakage current is obtained.

优选地，所述判断电流差是否等于电缆内部各分段电缆流入的泄漏电流之和包括：Preferably, the judging whether the current difference is equal to the sum of the leakage currents flowing into each segmented cable inside the cable includes:

获取护层保护器等效阻抗；Obtain the equivalent impedance of the sheath protector;

分别建立容性耦合分量和感性耦合分量的等效电路，根据等效电路得到护层故障保护器故障引起的护层电流相量差；The equivalent circuits of the capacitive coupling component and the inductive coupling component are established respectively, and the sheath current phasor difference caused by the fault of the sheath fault protector is obtained according to the equivalent circuit;

根据护层电流相量差计算故障护层保护器含谐波分量的泄漏电流，根据泄漏电流得到基波电流差相角含谐波分量的电流差。Calculate the leakage current of the fault sheath protector with harmonic components according to the phasor difference of the sheath current, and obtain the current difference of the fundamental current with the harmonic components according to the leakage current.

优选地，所述获取护层保护器等效阻抗，包括以下步骤：Preferably, the obtaining the equivalent impedance of the sheath protector includes the following steps:

获取护层保护器的并联等效电阻和并联等效电容；Obtain the parallel equivalent resistance and parallel equivalent capacitance of the sheath protector;

建立等效阻抗计算模型；Establish an equivalent impedance calculation model;

将并联等效电阻和并联等效电容，代入等效阻抗计算模型，得到等效阻抗。Substitute the parallel equivalent resistance and parallel equivalent capacitance into the equivalent impedance calculation model to obtain the equivalent impedance.

优选地，所述等效阻抗计算模型表示为：Preferably, the equivalent impedance calculation model is expressed as:

式中，Z_L表示等效阻抗，j表示虚数因子，ω表示工频角速度；Rsvl表示并联等效电阻，Csvl表示并联等效电容。In the formula, Z_L represents the equivalent impedance, j represents the imaginary factor, and ω represents the power frequency angular velocity; Rsvl represents the parallel equivalent resistance, and Csvl represents the parallel equivalent capacitance.

优选地，所述根据泄漏电流得到基波电流差相角含谐波分量的电流差包括:Preferably, obtaining the current difference of the fundamental wave current difference phase angle containing harmonic components according to the leakage current includes:

在对护层保护器故障后电缆线路的仿真中，分别建立工频和谐波频率下的护层电路模型,护层保护器故障后谐波分量的等效电路模型中，将故障护层保护器视作谐波源，电缆护层电路等效为串联R-L电路，并且假设电缆首端和末端的地阻抗相等,回路总长度为l的线路中，护层电流差对故障护层保护器泄漏电流的谐波分量的传递函数定义为两者的比值。In the simulation of the cable line after the fault of the sheath protector, the sheath circuit models under the power frequency and the harmonic frequency are established respectively. In the equivalent circuit model of the harmonic component after the sheath protector fault, the fault sheath protection The cable sheath circuit is equivalent to a series R-L circuit, and it is assumed that the ground impedance at the head end and the end of the cable are equal, and in a line with a total loop length of l, the sheath current difference leaks to the fault sheath protector. The transfer function of the harmonic components of the current is defined as the ratio of the two.

本发明的技术效果和优点：Technical effects and advantages of the present invention:

本发明依据护层保护器内部结构中氧化锌阀片的非线性电阻特性，依据电流差谐波含量监测护层保护器故障；建立交叉互联高压电缆等效电路模型，提出以电流差谐波含量为护层保护器故障特征量的检测方法，并给出故障时电流差的计算方法，制定三相九段交叉互联高压电缆系统中护层保护器的故障诊断流程，提高了现阶段护层保护器检修的效率。The invention monitors the fault of the sheath protector according to the non-linear resistance characteristics of the zinc oxide valve sheet in the internal structure of the sheath protector and the harmonic content of the current difference; establishes an equivalent circuit model of a cross-connected high-voltage cable, and proposes to use the harmonic content of the current difference to monitor the fault of the sheath protector. In order to detect the fault characteristic quantity of the sheath protector, and give the calculation method of the current difference when the fault occurs, the fault diagnosis process of the sheath protector in the three-phase nine-segment cross-connected high-voltage cable system is formulated, which improves the current stage of the sheath protector. overhaul efficiency.

本发明的其它特征和优点将在随后的说明书中阐述，并且，部分地从说明书中变得显而易见，或者通过实施本发明而了解。本发明的目的和其他优点可通过在说明书、权利要求书以及附图中所指出的结构来实现和获得。Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure pointed out in the description, claims and drawings.

附图说明Description of drawings

图1为本发明故障诊断方法流程图；Fig. 1 is the flow chart of the fault diagnosis method of the present invention;

图2为本发明护层保护器故障判据制定流程图；Fig. 2 is the flow chart of the fault criterion formulation of the sheath protector of the present invention;

图3为本发明故障护层保护器中泄漏电流各次谐波含量；Fig. 3 is each harmonic content of leakage current in the fault protective layer protector of the present invention;

图4为本发明三相九段式交叉互联高压护层保护器结构图；4 is a structural diagram of a three-phase nine-section cross-connected high-voltage sheath protector according to the present invention;

图5为本发明回路1护层电流示意图；Fig. 5 is the schematic diagram of the sheath current ofcircuit 1 of the present invention;

图6为本发明回路1护层电路容性耦合分量等效电路图；FIG. 6 is an equivalent circuit diagram of the capacitive coupling component of the sheath circuit of theloop 1 of the present invention;

图7为本发明回路1护层电路感性耦合分量等效电路图；Fig. 7 is the equivalent circuit diagram of the inductive coupling component of the sheath circuit of theloop 1 of the present invention;

图8为本发明回路1护层保护器故障后谐波分量的等效电路模型；Fig. 8 is the equivalent circuit model of the harmonic component after the fault of thecircuit 1 sheath protector of the present invention;

图9为本发明回路1护层保护器故障后谐波分量的电流含量图。FIG. 9 is a current content diagram of harmonic components after the fault of the sheath protector ofcircuit 1 of the present invention.

具体实施方式Detailed ways

下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

当护层保护器被击穿，将出现一条由上电极经氧化锌阀片至下电极的碳化通道，此时护层保护器的等效阻抗等物理特性将发生改变，本发明依据氧护层保护器主要组成部分氧化锌阀片的特点。利用护层保护器故障发生时，护层电流的差幅频特性变化实现护层保护器故障在线诊断和定位。When the protective layer protector is broken down, a carbonization channel will appear from the upper electrode to the lower electrode through the zinc oxide valve plate. At this time, the physical characteristics such as the equivalent impedance of the protective layer protector will change. The main components of the protector are the characteristics of the zinc oxide valve plate. When the fault of the sheath protector occurs, the difference amplitude and frequency characteristics of the sheath current are used to realize the on-line diagnosis and location of the sheath protector fault.

为解决现有技术的不足，本发明中提出一种基于护层电流差幅频特性的护层保护器故障在线诊断方法，具体如图1所示，所述方法包含如下步骤：In order to solve the deficiencies of the prior art, the present invention proposes an on-line fault diagnosis method for a sheath protector based on the differential amplitude-frequency characteristics of sheath current, as shown in FIG. 1 , the method includes the following steps:

将6个工频电流互感器安装于交叉互联高压电缆线路的两端的接地箱中，同步获取电缆两端护层电流信号；Install 6 power frequency current transformers in the grounding boxes at both ends of the cross-connected high-voltage cable line, and obtain the current signal of the sheath at both ends of the cable simultaneously;

具体地，在获取电缆末端与首端的电流差后，判断电缆末端与首端电流差的是否等于三小段电缆流入的泄漏电流之和，若等于则电缆回路中未发生接地短路故障，反之则线路发生接地短路故障。Specifically, after obtaining the current difference between the cable end and the head end, determine whether the current difference between the cable end and the head end is equal to the sum of the leakage currents flowing into the three small sections of the cable. A short to ground fault has occurred.

将所采集电流信号按护层回路分组，分别计算相应护层电流差；The collected current signals are grouped according to sheath loops, and the corresponding sheath current differences are calculated respectively;

具体地，计算相应护层电流差步骤包括对护层保护器参数进行测量、建立电缆线路模型、护层保护器故障诊断、故障护层保护器泄漏电流与电流差的计算和故障分类与检测。计算相应护层电流差步骤将在后续进行着重描述，再次不做累述。如图2所示为护层保护器故障判据制定流程图，图中，当判断线路发生接地短路故障之后，还包括判断电流差是否含有谐波，若不含有则电缆回路中未发生其它类型的接地短路故障；若含有则电缆回路中发生接地短路故障。Specifically, the steps of calculating the corresponding sheath current difference include measuring sheath protector parameters, establishing a cable line model, sheath protector fault diagnosis, calculation of the leakage current and current difference of the fault sheath protector, and fault classification and detection. The steps of calculating the corresponding sheath current difference will be described emphatically in the follow-up, and will not be repeated again. Figure 2 shows the flow chart of the fault criterion formulation of the sheath protector. In the figure, after judging that the line has a ground short-circuit fault, it also includes judging whether the current difference contains harmonics. If it does not, no other types have occurred in the cable circuit A short-to-ground fault occurs in the cable loop; if present, a short-to-ground fault occurs in the cable loop.

对护层电流差波形做快速傅里叶变换，得出3、5、7、9次谐波的含量。The fast Fourier transform is performed on the current difference waveform of the sheath, and the content of the 3rd, 5th, 7th and 9th harmonics is obtained.

具体地，根据得出的3、5、7、9次谐波的含量，作为故障诊断的诊断结果。Specifically, according to the content of the obtained 3rd, 5th, 7th, and 9th harmonics, it is used as the diagnosis result of fault diagnosis.

根据预设判据和诊断结果进行护层保护器故障诊断和定位。Carry out fault diagnosis and location of sheath protector according to preset criteria and diagnosis results.

具体地，根据预设判据和诊断结果进行护层保护器故障诊断和定位是通过建立的工频下护层保护器故障后护层电路的电流差和护层保护器故障后谐波分量的等效电路模型，依据护层保护器故障引起护层电流的幅频特性制定故障诊断判据，并判断护层保护器故障所在的回路。Specifically, the fault diagnosis and location of the sheath protector according to the preset criteria and the diagnosis results is based on the established current difference of the sheath circuit after the sheath protector fails at the power frequency and the harmonic components after the sheath protector fails. The equivalent circuit model is used to formulate fault diagnosis criteria according to the amplitude-frequency characteristics of the sheath current caused by the fault of the sheath protector, and determine the circuit where the sheath protector is faulty.

依据护层保护器故障引起护层电流的幅频特性制定故障诊断判据为将故障护层保护器中泄漏电流各次分量等效为谐波源，由故障护层保护器位置注入金属护层回路中，经电缆护层的滤波作用，电缆首末两端的护层电流中的谐波含量因护层保护器故障位置发生改变，并以此制定故障护层保护器中泄漏电流各次谐波含量图作为故障诊断的预设判据。According to the amplitude-frequency characteristics of the sheath current caused by the fault of the sheath protector, the fault diagnosis criterion is formulated as follows: the leakage current in the fault sheath protector is equivalent to a harmonic source, and the metal sheath is injected from the position of the fault sheath protector. In the loop, through the filtering effect of the cable sheath, the harmonic content of the sheath current at the beginning and end of the cable changes due to the fault position of the sheath protector, and based on this, each harmonic of the leakage current in the fault sheath protector is determined. The content map is used as the preset criterion for fault diagnosis.

在本实施例中，故障护层保护器中泄漏电流各次谐波含量根据实验测试，在线路发生接地短路故障的情况下，护层保护器内部的氧化锌阀片在工频100V电压下，泄漏电流中谐波主要为3、5、7、9次谐波，如图3所示为故障护层保护器中泄漏电流各次谐波含量，以基波电流为参考，谐波含量分别为65.4％、27.5％、5.9％和3.4％。本发明制定了三个回路中护层保护器故障诊断的标准，护层保护器故障电流差幅频特性见下表1所示：In this embodiment, the harmonic content of the leakage current in the fault protective layer protector is tested according to the experimental test. In the case of a grounding short-circuit fault on the line, the zinc oxide valve plate inside the protective layer protector is under the power frequency of 100V. The harmonics in the leakage current are mainly the 3rd, 5th, 7th, and 9th harmonics. As shown in Figure 3, the harmonic contents of the leakage current in the fault protective layer protector are shown in Figure 3. Taking the fundamental current as a reference, the harmonic contents are 65.4%, 27.5%, 5.9% and 3.4%. The present invention formulates the standards for fault diagnosis of sheath protectors in three circuits, and the fault current difference amplitude-frequency characteristics of sheath protectors are shown in Table 1 below:

回路1loop 1回路2loop 2回路3loop 3电流差3次谐波含量(％)Current difference 3rd harmonic content (%)1.88～21.311.88～21.311.30～23.711.30～23.711.53～16.151.53～16.15电流差5次谐波含量(％)Current difference 5th harmonic content (%)0.79～8.980.79～8.980.55～9.990.55～9.990.65～6.810.65～6.81电流差7次谐波含量(％)Current difference 7th harmonic content (%)0.17～1.940.17～1.940.12～2.160.12～2.160.14～1.470.14～1.47电流差9次谐波含量(％)Current difference 9th harmonic content (%)0.11～1.100.11～1.100.07～1.220.07～1.220.08～0.830.08～0.83

需要说明的是，本发明通过检测高压电缆护层电流，计算电流相位差进行诊断的方法诊断和定位护层保护器故障。应用本发明技术方案，可以在高压电缆护层电流巡检中，有效利用检测电流数据，及时发现并定位护层保护器的故障，以便于后续对故障保护器进行更换，从而有效保护高压电缆护层及绝缘的安全，保障电缆线路的安全运行。It should be noted that the present invention diagnoses and locates the fault of the sheath protector by detecting the sheath current of the high-voltage cable and calculating the current phase difference for diagnosis. By applying the technical solution of the present invention, the detection current data can be effectively used in the current inspection of the high-voltage cable sheath, and the fault of the sheath protector can be found and located in time, so as to facilitate the subsequent replacement of the fault protector, thereby effectively protecting the high-voltage cable protection. Layer and insulation safety, to ensure the safe operation of cable lines.

同时，在上述计算相应护层电流差包括以下部分：At the same time, the corresponding sheath current difference in the above calculation includes the following parts:

01)对护层保护器参数进行测量01) Measure the parameters of the sheath protector

在本实施例中，电缆由外向内依次包括外护层、金属护层、绝缘层和电缆线芯，其中，护层保护器安装于交叉互联电缆线路中两个金属护层分段之间的交叉互联接地箱中，通常35kV大截面电力电缆和66kV、110kV及以上电压等级的电力电缆均为单芯电缆，电缆金属护层一端三相互联并接地，另一端不接地，当雷电波或内部过电压沿电缆线芯流动时，电缆金属护层不接地端会出现较高的冲击过电压，或当系统短路事故电流流经电缆线芯时，其护层不接地端也会出现很高的工频感应过电压。上述过电压可能击穿电缆外护层绝缘，造成电缆金属护层多点接地故障，严重影响电力电缆正常运行甚至大幅减少电缆使用寿命。因此，为限制电力电缆金属护层上的感应电压和故障过电压，并避免在护层中形成环流，电缆护层一端直接接地，另一端则须通过护层保护器接地。如果线路较长，可以将电缆护层分三段或三的倍数段相互绝缘，分段处的护层交叉互联后通过护层保护器接地。护层保护器采用ZnO压敏电阻或ZnO阀片作为保护元件，ZnO阀片无串联间隙，具有优良的电压-电流特性曲线。护层保护器用绝缘材料作为外绝缘，较传统的放电间隙保护、带间隙碳化硅电阻片保护等方式，其伏安特性更显优越。In this embodiment, the cable sequentially includes an outer sheath, a metal sheath, an insulating layer and a cable core from the outside to the inside, wherein the sheath protector is installed between two metal sheath segments in the cross-connected cable line In the cross-connected grounding box, usually 35kV large-section power cables and power cables with voltage levels of 66kV, 110kV and above are single-core cables. One end of the cable metal sheath is three-phase interconnected and grounded, and the other end is not grounded. When the overvoltage flows along the cable core, the ungrounded end of the metal sheath of the cable will have a high impulse overvoltage, or when the system short-circuit accident current flows through the cable core, the ungrounded end of the sheath will also have a high impact. Power frequency induced overvoltage. The above-mentioned overvoltage may break down the insulation of the outer sheath of the cable, causing multi-point grounding faults in the metal sheath of the cable, which seriously affects the normal operation of the power cable and even greatly reduces the service life of the cable. Therefore, in order to limit the induced voltage and fault overvoltage on the metal sheath of the power cable and avoid the formation of circulating current in the sheath, one end of the cable sheath is directly grounded, and the other end must be grounded through the sheath protector. If the line is long, the cable sheath can be insulated from each other in three sections or multiples of three, and the sheaths at the sections are cross-connected and grounded through the sheath protector. The protective layer protector uses ZnO varistor or ZnO valve plate as the protection element. The ZnO valve plate has no series gap and has excellent voltage-current characteristic curve. The sheath protector uses insulating material as the outer insulation, and its volt-ampere characteristics are more superior than the traditional discharge gap protection and silicon carbide resistance chip protection with gaps.

在实际应用中，若护层保护器被击穿，将出现一条由上电极经氧化锌阀片至下电极的碳化通道，此时护层保护器的等效阻抗等物理特性将发生改变，依据氧护层保护器主要组成部分氧化锌阀片的特点，建立护层保护器的等效电路模型，其中，建立护层保护器的等效电路模型，包括以下步骤：获取故障护层保护器的并联等效电阻R_svl和并联等效电容C_svl；建立等效阻抗计算模型，将并联等效电阻R_svl和并联等效电容C_svl代入等效阻抗计算模型，得到等效阻抗Z_L。在本实施例中，利用交流电桥可测得故障护层保护器的并联等效电阻R_svl和并联等效电容C_svl，等效电阻R_svl和等效电容C_svl之间并联连接，计算等效阻抗Z_L包括将并联等效电阻R_svl和并联等效电容C_svl代入下式1的等效阻抗计算模型中求出等效阻抗Z_L，In practical applications, if the sheath protector is broken down, a carbonization channel will appear from the upper electrode through the zinc oxide valve plate to the lower electrode. At this time, the physical characteristics such as the equivalent impedance of the sheath protector will change. According to The characteristics of the zinc oxide valve plate, the main component of the oxygen sheath protector, establish the equivalent circuit model of the sheath protector, wherein, establishing the equivalent circuit model of the sheath protector includes the following steps: obtaining the fault sheath protector Parallel equivalent resistance R_svl and parallel equivalent capacitance C_svl ; establish an equivalent impedance calculation model, and substitute the parallel equivalent resistance R_svl and parallel equivalent capacitance C_svl into the equivalent impedance calculation model to obtain the equivalent impedance Z_L . In this embodiment, the parallel equivalent resistance R_svl and the parallel equivalent capacitance C_svl of the fault protective layer protector can be measured by using an AC bridge, and the parallel connection between the equivalent resistance R_svl and the equivalent capacitance C_svl can be calculated, etc. The effective impedance Z_L consists of substituting the parallel equivalent resistance R_svl and the parallel equivalent capacitance C_svl into the equivalent impedance calculation model of the followingformula 1 to obtain the equivalent impedance Z_L ,

式中，j表示虚数因子，ω表示工频角速度；R_svl表示并联等效电阻，C_svl表示并联等效电容。In the formula, j represents the imaginary factor, ω represents the power frequency angular velocity; R_svl represents the parallel equivalent resistance, and C_svl represents the parallel equivalent capacitance.

02)建立电缆线路模型02) Establish a cable line model

本发明采用三相九段式交叉互联高压护层保护器，具体如图4所示，电缆护层分三段相互绝缘，在图4中电缆护层的9个金属护套分段将由第一段金属护套S1、第二段金属护套S2、第三段金属护套S3、第四段金属护套S4、第五段金属护套S5、第六金属段护套S6、第七金属段护套S7、第八段金属护套S8和第九段金属护套S9组成。其中，第一段金属护套S1、第五段金属护套S5和第九段金属护套S9组成护层回路1；第四段金属护套S4、第八段金属护套S8和第三段金属护套S3组成护层回路2；第七段金属护套S7、第二段金属护套S2和第六段金属护套S6组成护层回路3。第一护层保护器Z_SVL1、第二护层保护器Z_SVL2、第三护层保护器Z_SVL3、第四护层保护器Z_SVL4、第五护层保护器Z_SVL5、第六护层保护器Z_SVL6分别安装于电缆线路首端的第一电流传感器cs₁、第二电流传感器cs₂和第三电流传感器cs₃上，和安装于电缆线路尾端的第四电流传感器cs₄、第五电流传感器cs₅、第六电流传感器cs₆上。其中，

为电缆三相的线芯电流。The present invention adopts a three-phase nine-section cross-connected high-voltage sheath protector. Specifically, as shown in Figure 4, the cable sheath is insulated from each other in three sections. In Figure 4, the nine metal sheath sections of the cable sheath will be divided by the first section. Metal sheath S1, second metal sheath S2, third metal sheath S3, fourth metal sheath S4, fifth metal sheath S5, sixth metal sheath S6, seventh metal sheath The sleeve S7, the eighth-section metal sheath S8 and the ninth-section metal sheath S9 are composed. Among them, the first metal sheath S1, the fifth metal sheath S5 and the ninth metal sheath S9 constitute thesheath circuit 1; the fourth metal sheath S4, the eighth metal sheath S8 and the third The metal sheath S3 constitutes thesheath circuit 2 ; the seventh metal sheath S7 , the second metal sheath S2 and the sixth metal sheath S6 constitute the sheath circuit 3 . The first sheath protector Z_SVL1 , the second sheath protector Z_SVL2 , the third sheath protector Z_SVL3 , the fourth sheath protector Z_SVL4 , the fifth sheath protector Z_SVL5 , the sixth sheath protector The device Z_{SVL6 is} respectively installed on the first current sensor cs₁ , the second current sensor cs₂ and the third current sensor cs₃ at the head end of the cable line, and the fourth current sensor cs₄ and the fifth current sensor installed at the tail end of the cable line cs₅ and the sixth current sensor cs₆ . in,

It is the core current of the three-phase cable.

3)护层保护器故障诊断3) fault diagnosis of sheath protector

本发明以回路1为例进行重点说明，回路2和回路3与回路1类似，在此不在赘述。具体如图5所示为回路1护层电流示意图，第一段金属护套S1、第五段金属护套S5和第九段金属护套S9之间串联连接，I_cs1、I_cs5分别为电流传感器cs1、cs5处测量得到的护层对地电流；I_LS1、I_LS5和I_LS9分别表示由电缆线芯流入第一段金属护套S1、第五段金属护套S5和第九段金属护套S9的泄漏电流，在正常无故障情况下，由基尔霍夫电流定律在金属护层中电流差等于第一段金属护套S1上流入的泄漏电流：The present invention takes theloop 1 as an example for key description. Theloop 2 and the loop 3 are similar to theloop 1, and are not repeated here. Specifically, Fig. 5 is a schematic diagram of the sheath current ofcircuit 1. The first metal sheath S1, the fifth metal sheath S5 and the ninth metal sheath S9 are connected in series, and I_cs1 and I_cs5 are the currents respectively. The sheath-to-ground currents measured at the sensors cs1 and cs5; I_LS1 , I_LS5 and I_LS9 indicate that the cable core flows into the first metal sheath S1, the fifth metal sheath S5 and the ninth metal sheath, respectively The leakage current of the sleeve S9, under the normal and no fault condition, the current difference in the metal sheath is equal to the leakage current flowing in the first metal sheath S1 according to Kirchhoff's current law:

在互层保护器发生故障情况下，此时护层保护器的等效阻抗等物理特性将发生改变，依据氧护层保护器主要组成部分氧化锌阀片的特点。利用护层保护器故障发生时，护层电流的差幅频特性变化实现护层保护器故障在线诊断和定位。本发明考虑到故障护层保护器的非线性电阻特性，以异常电流差是否含有谐波区分出护层保护器故障和其他类型的接地短路故障；通过建立的工频下护层保护器故障后护层电路的电流差和护层保护器故障后谐波分量的等效电路模型，依据护层保护器故障引起护层电流的幅频特性制定故障诊断判据，并判断护层保护器故障所在的回路。In the event of failure of the interlayer protector, the physical characteristics such as the equivalent impedance of the sheath protector will change, according to the characteristics of the zinc oxide valve plate, which is the main component of the oxygen sheath protector. When the fault of the sheath protector occurs, the difference amplitude and frequency characteristics of the sheath current are used to realize the on-line diagnosis and location of the sheath protector fault. The invention takes into account the nonlinear resistance characteristics of the fault protective layer protector, and distinguishes the protective layer protector fault from other types of grounding short-circuit faults according to whether the abnormal current difference contains harmonics; The current difference of the sheath circuit and the equivalent circuit model of the harmonic components after the sheath protector fails, the fault diagnosis criterion is formulated according to the amplitude-frequency characteristics of the sheath current caused by the sheath protector fault, and the fault of the sheath protector is determined. circuit.

3)故障护层保护器泄漏电流与电流差的计算3) Calculation of leakage current and current difference of fault sheath protector

为分析故障阻抗与检测护层电流的关系，本发明给出了工频下电流差以及故障护层保护器泄漏电流的计算方法。相较于绝缘阻抗，护层保护器对地阻抗可以忽略，因此假设护层保护器接地故障时，泄漏电流与正常时相等。相较于故障点，同一回路中另一个正常护层保护器阻抗很大，对地视为开路。为便于计算，假设电缆线路末端与首端的地阻抗近似相等，即R_e1＝R_e2＝R。In order to analyze the relationship between the fault impedance and the detection sheath current, the present invention provides a calculation method for the current difference under the power frequency and the leakage current of the fault sheath protector. Compared with the insulation resistance, the impedance of the sheath protector to ground can be ignored, so it is assumed that when the sheath protector is grounded, the leakage current is equal to that of normal. Compared with the fault point, another normal sheath protector in the same circuit has a large impedance and is regarded as an open circuit to the ground. For the convenience of calculation, it is assumed that the ground impedances at the end of the cable line and the head end are approximately equal, that is,_Re1 =R_e2 =R.

判断电流差是否等于电缆内部各分段电缆流入的泄漏电流之和包括计算护层保护器泄漏电流与电流差，其具体为分别建立容性耦合分量和感性耦合分量的等效电路，根据等效电路得到护层故障保护器故障引起的护层电流相量差；根据护层电流相量差计算故障护层保护器含谐波分量的泄漏电流，根据泄漏电流得到基波电流差相角含谐波分量的电流差。在本实施例中，交叉互联高压电缆护层电流为容性耦合电流分量和感性耦合电流分量叠加，因此需分别建立容性耦合分量和感性耦合分量的等效电路模型。Determining whether the current difference is equal to the sum of the leakage currents flowing into each segment of the cable includes calculating the leakage current and current difference of the sheath protector. The circuit obtains the sheath current phasor difference caused by the fault of the sheath fault protector; according to the sheath current phasor difference, the leakage current of the fault sheath protector containing harmonic components is calculated, and the fundamental wave current difference phase angle containing harmonic components is obtained according to the leakage current. The current difference of the wave component. In this embodiment, the sheath current of the cross-connected high-voltage cable is the superposition of the capacitive coupling current component and the inductive coupling current component, so it is necessary to establish equivalent circuit models of the capacitive coupling component and the inductive coupling component respectively.

①容性耦合电流分量计算①Calculation of capacitive coupling current component

图6为回路1护层电路容性耦合分量等效电路图，图中，EA1为第一段金属护套S1处的感应电压，E_B2为第五段金属护套S5处的感应电压，E_C3为第九段金属护套S9处的感应电压；Z_SA1为第一段金属护套S1处的护层阻抗，Z_SB2为第五段金属护套S5处的护层阻抗，Z_SC3为第九段金属护套S9处的护层阻抗。I_cs1m和I_cs2m分别为第一电流传感器cs1和第五电流传感器cs1处测得的感性耦合电流。Figure 6 is the equivalent circuit diagram of the capacitive coupling component of the sheath circuit ofloop 1. In the figure, EA1 is the induced voltage at the first metal sheath S1, E_B2 is the induced voltage at the fifth metal sheath S5, E_C3 is the induced voltage at the metal sheath S9 of the ninth segment; Z_SA1 is the sheath impedance at the first metal sheath S1, Z_SB2 is the sheath impedance at the fifth metal sheath S5, and Z_SC3 is the ninth Sheath impedance at segment metal sheath S9. I_cs1m and I_cs2m are the inductive coupling currents measured at the first current sensor cs1 and the fifth current sensor cs1 , respectively.

电缆金属护套阻抗Z_S计算过程见式(3)，The calculation process of cable metal sheath impedance Z_S is shown in formula (3),

式中l为电缆长度；R_S为金属护套单位长度电阻；D_S为护套平均直径；f为系统运行的工频频率，ω表示工频角速度。In the formula, l is the cable length; R_S is the resistance per unit length of the metal sheath; D_S is the average diameter of the sheath; f is the power frequency frequency of the system operation, and ω represents the power frequency angular velocity.

M_X,Sn为x相电缆线芯与电缆第Sn段护层间的互感：M_{X, Sn} is the mutual inductance between the x-phase cable core and the sheath of the Sn section of the cable:

式中，d_x,Sy为x相电缆线芯与Sn段电缆护层间的平均几何距离，μ₀为真空磁导率,l_n为各小段电缆的长度。In the formula, dx_{, Sy} is the average geometric distance between the x-phase cable core and the Sn-section cable sheath, μ₀ is the vacuum permeability, and_ln is the length of each small section of the cable.

护层第一段金属护套S1、第五段金属护套S5和第九段金属护套S9上护层感应电压计算公式如下：The calculation formula of the induced voltage on the upper sheath of the first metal sheath S1, the fifth metal sheath S5 and the ninth metal sheath S9 of the sheath is as follows:

式中,E_S1、E_S5、E_S9分别为护套S1、S5和S9段上产生的护层感应电压；M_A,S1、M_B,S1、M_C,S1分别为A、B、C三相电缆对第一段金属护套S1的互感；M_A,S5、M_B,S5、M_C,S5分别为A、B、C三相电缆对第一段金属护套S5的互感；M_A,S9、M_B,S9、M_C,S9分别为A、B、C三相电缆对第一段金属护套S9的互感；I_A、I_B、I_C分别为电缆A、B、C三相的负载电流。In the formula, E_S1 , E_S5 , and E_S9 are the sheath induced voltages generated on the sheath S1, S5 and S9 segments, respectively; M_{A, S1} , M_{B, S1} , M_{C, S1} are A, B, C, respectively Mutual inductance of the three-phase cable to the first section of the metal sheath S1; M_{A, S5} , M_{B, S5} , M_{C, S5} are the mutual inductance of the A, B, C three-phase cables to the first section of the metal sheath S5; M_{A, S9} , M_{B, S9} , M_{C, S9} are the mutual inductances of the A, B, C three-phase cables to the first metal sheath S9; I_A , I_B , I_C are the cables A, B, C, respectively Three-phase load current.

②感性耦合电流分量计算②Calculation of inductive coupling current component

图7为回路1护层电路感性耦合分量等效电路图，图中，ES1为第一段金属护套S1处的感应电压，ES5为第五段金属护套S5处的感应电压，E_S9为第九段金属护套S9处的感应电压；Z_S1为第一段金属护套S1处的护层阻抗，Z_S5为第五段金属护套S5处的护层阻抗，Z_S9为第九段金属护套S9处的护层阻抗。I_cs1m和I_cs2m分别为第一电流传感器cs1和第五电流传感器cs1处测得的感性耦合电流。Figure 7 is the equivalent circuit diagram of the inductive coupling component of the sheath circuit ofloop 1. In the figure, ES1 is the induced voltage at the first metal sheath S1, ES5 is the induced voltage at the fifth metal sheath_S5 , and ES9 is the first The induced voltage at the nine-segment metal sheath S9; Z_S1 is the sheath impedance at the first metal sheath S1, Z_S5 is the sheath impedance at the fifth metal sheath S5, and Z_S9 is the ninth metal sheath. Sheath impedance at sheath S9. I_cs1m and I_cs2m are the inductive coupling currents measured at the first current sensor cs1 and the fifth current sensor cs1 , respectively.

③互层电流向量差的计算③Calculation of the current vector difference between layers

具体地，根据等效电路得到护层故障保护器故障引起的护层电流相量差包括：在工频f₁＝50Hz下，对回路1护层保护器故障S1-S2-S3电路分析；Specifically, obtaining the sheath current phasor difference caused by the fault of the sheath fault protector according to the equivalent circuit includes: at the power frequency f₁ =50Hz, the circuit analysis of the fault S1-S2-S3 of the sheath protector ofcircuit 1;

计算电缆绝缘电容C_i：Calculate the cable insulation capacitance C_i :

其中，ε为绝缘层相对介电常数；ε₀为真空中介电常数；D_C为线芯导体直径；D_S为电缆金属护层的平均几何直径。Among them, ε is the relative dielectric constant of the insulating layer; ε₀ is the dielectric constant in vacuum; D_C is the diameter of the core conductor; D_S is the average geometric diameter of the metal sheath of the cable.

在第一回路中，I_LS1为第一段金属护套S1处的容性耦合分量电流，I_LS5为第五段金属护套S5处的容性耦合分量电流，I_LS9为第九段金属护套S9处的容性耦合分量电流，其中ω₁为工频对应的角速度。In the first loop, I_LS1 is the capacitive coupling component current at the first metal sheath S1, I_LS5 is the capacitive coupling component current at the fifth metal sheath S5, and I_LS9 is the ninth metal sheath Capacitive coupling component current at sleeve S9, where ω₁ is the angular velocity corresponding to the power frequency.

第一回路中工作电压向量为U_loop1，其中U_A、U_B、U_C分别为A、B、C相的工作电压；负载电流向量为I_loop1，其中I_A、I_B、I_C分别为A、B、C相的负载电流；电缆绝缘层等效电容向量为C_i，其中C_S1、C_S5、C_S9分别为第一段金属护套S1、第五段金属护套S5和第九段金属护套S9的等效电容；M_loop1为回路1中电缆护层与线芯的互感矩阵，其中x相线芯与护层Sn段互阻抗定义为Z_x,Sn：The working voltage vector in the first loop is U_loop1 , where_UA , UB , and UC are the working voltages of phases_A ,_B , and_C , respectively; the load current vector is I_loop1 , where IA ,_IB , and_IC are respectively The load current of phase A, B and C; the equivalent capacitance vector of the cable insulation layer is C_i , where C_S1 , C_S5 , and C_S9 are the first metal sheath S1 , the fifth metal sheath S5 and the ninth metal sheath respectively The equivalent capacitance of segment metal sheath S9; M_loop1 is the mutual inductance matrix between the cable sheath and the core inloop 1, where the mutual impedance between the x-phase core and the sheath Sn segment is defined as Z_x,Sn :

U_loop1＝[U_A U_B U_C] (8)U_loop1 = [U_A U_B U_C ] (8)

I_loop1＝[I_A I_B I_C]^T (9)I_loop1 = [I_A I_B I_C ]^T (9)

C_i＝[C_S1 C_S5 C_S9] (10)C_i = [C_S1 C_S5 C_S9 ] (10)

回路1中护层保护器svl1故障引起的护层电流相量差I_loop1,svl1为：The sheath current phasor difference I_{loop1, svl1} caused by the fault of the sheath protector svl1 inloop 1 is:

同理可得护层保护器svl5故障引起的护层电流相量差I_loop1,svl5为：Similarly, the sheath current phasor difference I_{loop1, svl5} caused by the fault of the sheath protector svl5 can be obtained as:

④故障护层保护器含谐波分量的泄漏电流的计算④Calculation of leakage current of fault protective layer protector with harmonic components

根据护层电流相量差I_loop1,svl5计算故障护层保护器含谐波分量的泄漏电流包括：According to the sheath current phasor difference I_{loop1, svl5,} calculating the leakage current of the fault sheath protector with harmonic components includes:

工频下护层保护器svl1、svl5分别故障后通过故障护层保护器的泄漏电流计算公式如下：The formula for calculating the leakage current through the fault protective layer protector after the protective layer protectors svl1 and svl5 respectively fail under the power frequency is as follows:

由于谐波相角的随机性，设各次谐波电流的相角等于基波电流的相角φ_svl(1)，谐波次数为h以护层保护器svl1故障为例，故障护层保护器含谐波分量的泄漏电流为：Due to the randomness of the harmonic phase angle, the phase angle of each harmonic current is set equal to the phase angle of the fundamental current φ_svl(1) , and the harmonic order is h. Taking the fault of the sheath protector svl1 as an example, the fault sheath protection The leakage current of the device with harmonic components is:

在对护层保护器故障后电缆线路的仿真中，将分别建立工频和谐波频率下的护层电路模型。将故障护层保护器视作谐波源，电缆护层电路等效为串联R-L电路，护层保护器故障后谐波分量的等效电路模型如图8所示，图中，R_S1、L_s1、R_S5、L_s5、R_S9、L_s9之间串联，I_cs1m和I_cs2m分别为第一电流传感器cs1和第五电流传感器cs1处测得的感性耦合电流；在串联R-L电路中，单位长度电感L_S(单位为H/m)，单位长度电阻R_S(单位为Ω/m)，并且假设电缆首端和末端的地阻抗相等。回路1总长度为l的线路中，护层电流差对故障护层保护器泄漏电流的谐波分量的传递函数定义为两者的比值G(ω)。In the simulation of the cable line after the fault of the sheath protector, the sheath circuit model under the power frequency and the harmonic frequency will be established respectively. Considering the fault protector as a harmonic source, the cable sheath circuit is equivalent to a series RL circuit, and the equivalent circuit model of the harmonic components after the fault of the sheath protector is shown in Figure 8. In the figure, R_S1 , L_s1 , R_S5 , L_s5 , R_S9 , and L_s9 are connected in series, and I_cs1m and I_cs2m are the inductive coupling currents measured at the first current sensor cs1 and the fifth current sensor cs1 respectively; in the series RL circuit, the unit Length inductance, L_S (in H/m), resistance per unit length, R_S (in Ω/m), and assumes equal ground impedance at the beginning and end of the cable. In the line with the total length ofloop 1 being l, the transfer function of the difference between the sheath current and the harmonic component of the leakage current of the fault sheath protector is defined as the ratio G(ω).

⑤基波电流差相角含谐波分量的电流差的计算；⑤Calculation of the current difference of the fundamental wave current difference phase angle including harmonic components;

根据泄漏电流得到基波电流差相角含谐波分量的电流差包括：According to the leakage current, the current difference including the harmonic component of the fundamental wave current difference phase angle includes:

护层保护器svl1故障时，基波电流差相角φ₍₁₎含谐波分量的电流差计算公式为：When the sheath protector svl1 fails, the fundamental wave current difference phase angle φ₍₁₎ The calculation formula of the current difference with harmonic components is:

5)故障分类与检测5) Fault classification and detection

以收集到的故障护层保护器为例等效电阻R_svl＝216Ω，图9为护层保护器svl1～svl6分别故障时对应护层回路中电流差的幅频特性。在本实施例中，电缆参数如下表2所示，Taking the collected fault protective layer protector as an example, the equivalent resistance R_svl = 216Ω, and Fig. 9 shows the amplitude-frequency characteristics of the current difference in the corresponding protective layer circuit when the protective layer protectors svl1 to svl6 fail respectively. In this embodiment, the cable parameters are shown in Table 2 below,

参数/单位Parameters/Units数值Numerical value参数/单位Parameters/Units数值Numerical valueAB相间距/mAB phase spacing/m0.270.27工作电压/kVWorking voltage/kV110110BC相间距/mBC phase spacing/m0.270.27护套单位长度电阻/Ω·m^-1Sheath resistance per unit length/Ω·m^-14.26×10^-54.26×10^-5AC相间距/mAC phase spacing/m0.540.54绝缘层体积电阻率/Ω·mVolume resistivity of insulating layer/Ω·m10¹⁵10¹⁵地电阻/ΩGround resistance/Ω0.500.50第一段长度/mLength of the first section/m425425金属导体外径/mmMetal conductor outer diameter/mm35.9035.90第二段长度/mLength of the second section/m477477绝缘层厚度/mmInsulation layer thickness/mm17.3017.30第三段长度/mLength of the third section/m536536金属护层厚度/mmMetal sheath thickness/mm22自由空间介电常数Free space permittivity8.85×10^-128.85×10^-12频率/Hzfrequency/Hz5050相对介电常数Relative permittivity2.302.30

在已知线路参数表2和护层保护器故障阻抗的情况下，可通过上述方法计算故障所在护层回路的电流差。并判断电流差是否等于电缆内部各分段电缆流入的泄漏电流之和，若等于则电缆回路中未发生接地短路故障；反之则线路发生接地短路故障，当线路发生接地短路故障时，还要判断电流差是否含有谐波，若不含有则电缆回路中未发生其它类型的接地短路故障；若含有则电缆回路中发生接地短路故障，并将谐波与图9中的泄漏电流中谐波进行比对，判断护层保护器故障所在的回路。When the line parameter table 2 and the fault impedance of the sheath protector are known, the current difference of the sheath circuit where the fault is located can be calculated by the above method. And judge whether the current difference is equal to the sum of the leakage currents flowing into each segment of the cable. If it is equal, there is no grounding short-circuit fault in the cable loop; otherwise, the line has a grounding short-circuit fault. Whether the current difference contains harmonics, if not, no other types of grounding short-circuit faults have occurred in the cable loop; if so, grounding short-circuit faults have occurred in the cable loop, and the harmonics are compared with the harmonics in the leakage current in Figure 9 Yes, determine the circuit where the sheath protector is faulty.

在本实施例中，在制定判据时需考虑现场电缆参数、电缆线芯电流、三小段电缆长度、地阻抗以及线芯电压等影响因素的影响。In this embodiment, the influence of factors such as on-site cable parameters, cable core current, length of three small cables, ground impedance, and core voltage need to be considered when formulating the criterion.

综上所示，本发明建立了三相九段式交叉互联高压电缆等效模型，提出护层保护器故障时，工频下护层保护器中泄漏电流以及电流差的计算方法。将故障护层保护器等效产生的各次谐波电流等效为谐波源注入电缆护层电路中，并建立对应的谐波电路模型。本发明以电流差谐波含量作为特征量，辨别线路中故障是否为护层保护器故障并确定护层保护器故障所在回路。In summary, the present invention establishes an equivalent model of a three-phase nine-section cross-connected high-voltage cable, and proposes a calculation method for the leakage current and current difference in the sheath protector under power frequency when the sheath protector fails. Each harmonic current equivalently generated by the fault sheath protector is equivalently injected into the cable sheath circuit as a harmonic source, and the corresponding harmonic circuit model is established. The present invention uses the harmonic content of the current difference as the characteristic quantity to identify whether the fault in the line is the fault of the sheath protector and to determine the circuit where the sheath protector is faulty.

最后应说明的是：以上所述仅为本发明的优选实施例而已，并不用于限制本发明，尽管参照前述实施例对本发明进行了详细的说明，对于本领域的技术人员来说，其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换，凡在本发明的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。Finally, it should be noted that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, the The technical solutions described in the foregoing embodiments can be modified, or some technical features thereof can be equivalently replaced, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included. within the protection scope of the present invention.

Claims (9)

1. The sheath protector fault on-line diagnosis method based on the sheath current difference amplitude-frequency characteristic is characterized by comprising the following steps of:

acquiring current difference between the tail end and the head end of the cable, judging whether the current difference is equal to the sum of leakage currents flowing into each segmented cable in the cable, and if the current difference is equal to the sum, not generating a ground short circuit fault in a cable loop; otherwise, the circuit has a short-circuit fault.

2. The method of claim 1, wherein: after the line has a short-circuit to ground fault, the method further comprises the following steps: judging whether the current difference contains harmonic waves, if not, not generating other types of grounding short circuit faults in the cable loop; if the fault is contained, fault diagnosis and positioning of the protective layer protector are carried out according to preset criteria and diagnosis results.

3. The method of claim 2, wherein: the step of diagnosing and positioning the faults of the protective layer protector according to the preset criterion and the diagnosis result comprises the steps of,

establishing an equivalent circuit model of current difference of a protective layer circuit after the protective layer protector fails and harmonic component after the protective layer protector fails under power frequency, formulating a fault diagnosis criterion according to amplitude-frequency characteristics of the protective layer current caused by the protective layer protector failure, and judging a loop where the protective layer protector fails.

4. The method of claim 3, wherein: the fault diagnosis criterion is formulated according to the amplitude-frequency characteristic of the sheath current caused by the sheath protector fault, and comprises the following steps:

the harmonic content in the sheath current at the first and the last ends of the cable is changed due to the fault position of the sheath protector under the filtering action of the cable sheath, and the harmonic content in the leakage current in the fault sheath protector is used as a fault diagnosis criterion.

5. The method of claim 1, wherein: said obtaining a current difference between the cable end and the head end comprises the steps of:

installing 6 power frequency current transformers in grounding boxes at two ends of a cross-connection high-voltage cable line, and synchronously acquiring sheath current signals at two ends of the cable;

grouping the collected sheath current signals according to sheath loops, and respectively calculating corresponding grouped sheath current differences;

and performing Fourier transform on the sheath current difference waveform to obtain the content of harmonic waves in the leakage current.

6. The method of claim 1, wherein: the judging whether the current difference is equal to the sum of the leakage currents flowing into each segmented cable in the cable comprises the following steps:

obtaining equivalent impedance of the protective layer protector;

respectively establishing equivalent circuits of the capacitive coupling component and the inductive coupling component, and obtaining a sheath current phase difference caused by the fault of the sheath fault protector according to the equivalent circuits;

and calculating leakage current containing harmonic components of the fault sheath protector according to the sheath current phase difference, and obtaining current difference containing harmonic components of a fundamental current difference phase angle according to the leakage current.

7. The method of claim 6, wherein: the method for acquiring the equivalent impedance of the sheath protector comprises the following steps:

acquiring a parallel equivalent resistance and a parallel equivalent capacitance of the sheath protector;

establishing an equivalent impedance calculation model;

and substituting the parallel equivalent resistance and the parallel equivalent capacitance into an equivalent impedance calculation model to obtain equivalent impedance.

8. The method of claim 7, wherein: the equivalent impedance calculation model is expressed as:

in the formula, Z_L Representing the equivalent impedance, j represents the imaginary factor,omega represents the power frequency angular velocity; rsvl represents the parallel equivalent resistance, and Csvl represents the parallel equivalent capacitance.

9. The method of claim 6, wherein: the obtaining of the current difference including the harmonic component of the fundamental current difference phase angle according to the leakage current includes:

in the simulation of a cable line with the protective layer protector after the fault, protective layer circuit models under power frequency and harmonic frequency are respectively established, in an equivalent circuit model of harmonic component after the fault of the protective layer protector, the fault protective layer protector is regarded as a harmonic source, the cable protective layer circuit is equivalent to a series R-L circuit, and in the line with the total length of the loop being L, the transfer function of the protective layer current difference to the harmonic component of leakage current of the fault protective layer protector is defined as the ratio of the two in the assumption that the ground impedances of the head end and the tail end of the cable are equal.

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