A method for identifying interference of harmonic components of ground current

Abstract

The application relates to a ground current harmonic component interference identification method, which comprises the following steps: a differential circuit is designed based on a cable without defects; the differential circuit is used for defect detection of a cable sample loop; and an output signal of the differential circuit is a harmonic component signal caused by defects after elimination of power supply side harmonic interference. The application constructs a power distribution cable sample loop defect harmonic component detection loop suitable for elimination of power supply side harmonics in a laboratory, can eliminate the influence of power supply side harmonics introduced by a power supply and a through core transformer loop on the power distribution cable sample defect harmonic component detection in the laboratory, and improves the analysis efficiency of test detection data.

Description

Technical Field

[0001] This invention relates to the field of harmonic component live detection technology, and specifically to a method for identifying grounding current harmonic component interference. Background Technology

[0002] Currently, the insulation condition assessment of power distribution cables mainly relies on oscillating wave partial discharge and ultra-low frequency dielectric loss detection. Offline high-voltage testing suffers from limitations such as power outage planning and high risks of insulation damage. Therefore, new live-line testing technologies for power distribution cables are receiving increasing attention. In the research of live-line harmonic component detection technology, distinguishing between power supply-side harmonics and defect-generated harmonics is crucial for developing live-line testing technologies and identification algorithms. However, current methods generally assess power supply-side power quality by monitoring cable line voltage and current-carrying harmonics using an added power quality analysis device. Existing research methods primarily employ a through-type transformer circuit to conduct current-increasing tests on cable ring samples. Experiments show that inserting the power quality analysis device into the circuit causes new circuit shunting, resulting in the loss of measurable harmonic components. Furthermore, the electromagnetic field model of conductor harmonic voltage and current coupling to the cable's metal shield is complex, making it difficult to compare the device's output data with grounding current harmonic components in real time, significantly hindering data analysis. Therefore, designing and constructing a defect harmonic component detection circuit for power distribution cable samples suitable for power supply-side harmonic elimination in a laboratory setting is extremely important. Summary of the Invention

[0003] The purpose of this invention is to propose a method for identifying ground current harmonic component interference, so as to improve the efficiency of experimental data analysis.

[0004] To achieve the above objectives, embodiments of the present invention propose a method for identifying grounding current harmonic component interference, comprising:

[0005] The outer sheath, armor layer, and metal shield of the cable are circumferentially cut.

[0006] At the circumferential cut, the three-phase cable cores are wound with soft copper tape to form a three-core integrated electrode. The electrode is at least 1 cm away from the metal shield of other sections of the cable on both sides.

[0007] Signal leads are soldered onto the electrodes, and the solder joints are wrapped with insulating tape.

[0008] The electrode insulating tape is covered with copper mesh, and the two ends of the copper mesh are pressed with the metal shielding layer of the cable on both sides by constant force springs, and the outside is wrapped with water-blocking armor tape.

[0009] The detection signals of the grounding wire and the signal lead wire of the cable sample circuit are respectively connected to an oscilloscope for data observation. The 2nd to 20th harmonic voltage and current are injected between the conductor and the grounding wire of the unenergized cable sample circuit. The specific harmonic voltage and current ratio detected by the grounding wire and the signal lead wire of the cable sample circuit is observed. The amplification factor of the differential circuit is determined according to the specific harmonic voltage and current ratio.

[0010] A differential circuit is set up according to the amplification factor, and the detection signals of the cable sample circuit grounding wire and the signal lead wire are respectively introduced into the differential circuit set up according to the amplification factor to detect the output signal of the differential circuit. Among them, when the cable is free of defects, when the power frequency and the 2nd to 20th harmonic voltage and current are applied, the output of the differential circuit is 0. If it is not 0, the amplification factor of the differential circuit is further adjusted until the output of the differential circuit is 0, thus obtaining the target differential circuit.

[0011] The target differential circuit is used to detect defects in the cable sample circuit. The output signal of the target differential circuit is the harmonic component signal generated by the defect after eliminating the harmonic interference from the power supply side.

[0012] Optionally, the circumferential cut width is greater than or equal to 12-15 cm.

[0013] Optionally, the width of the soft copper strip is 10cm.

[0014] Optionally, the thickness of the insulating tape after wrapping is 3-5 mm.

[0015] Implementing the embodiments of the present invention has at least the following beneficial effects:

[0016] The embodiments of the present invention construct a detection circuit for the defect harmonic components of power distribution cable sample circuits suitable for power supply side harmonic elimination in the laboratory. It can eliminate the influence of power supply side harmonics introduced by the power supply and the through transformer circuit on the detection of defect harmonic components of power distribution cable samples, and improve the analysis efficiency of test data.

[0017] Other features and advantages of embodiments of the present invention will be set forth in the following description. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1This is a flowchart of a grounding current harmonic component interference identification method according to an embodiment of the present invention. Detailed Implementation

[0020] Various exemplary embodiments, features, and aspects of the present invention will now be described in detail with reference to the accompanying drawings. Furthermore, numerous specific details are set forth in the following detailed embodiments to better illustrate the invention. Those skilled in the art will understand that the invention can be practiced without certain specific details. In some instances, means well-known to those skilled in the art have not been described in detail in order to highlight the spirit of the invention.

[0021] See Figure 1 The present invention provides a method for identifying ground current harmonic component interference, comprising the following steps:

[0022] Step S1: Perform circumferential cutting on the cable outer sheath, armor layer, and metal shield;

[0023] Specifically, the circumferential cut width is greater than or equal to 12-15 cm;

[0024] Step S2: At the circumferential cut, use soft copper tape to wrap the three-phase cable cores to form a three-core integrated electrode. The electrode is at least 1 cm away from the metal shield of other sections of the cable on both sides.

[0025] Specifically, the width of the soft copper strip is 10cm;

[0026] Step S3: Solder signal leads onto the electrodes and wrap the solder joint with insulating tape.

[0027] Specifically, the thickness of the insulating tape after wrapping is 3-5mm;

[0028] Step S4: Copper mesh is used to cover the electrode insulating tape. The two ends of the copper mesh are pressed with the metal shielding layer of the cable on both sides by constant force springs, and water-blocking armor tape is wrapped around the outside.

[0029] Specifically, the copper mesh is a metal copper mesh used for cable joints, and the water-blocking armor tape is used to protect the electrodes and restore the metal shielding layer structure. The operation requirements are the same as those for restoring the metal shielding layer of general cable joints.

[0030] Step S5: Connect the detection signals of the cable sample circuit grounding wire and the signal lead wire to an oscilloscope for data observation. Inject 2 to 20th harmonic voltage and current between the conductor of the unenergized cable sample circuit and the grounding wire. Observe the ratio of specific harmonic voltage and current detected by the cable sample circuit grounding wire and the signal lead wire. Determine the amplification factor of the differential circuit based on the ratio of specific harmonic voltage and current.

[0031] Step S6: Set up a differential circuit according to the amplification factor, and introduce the detection signals of the cable sample circuit grounding wire and the signal lead wire into the differential circuit set according to the amplification factor, respectively, and detect the output signal of the differential circuit; wherein, when the cable is free of defects, when the power frequency and the 2nd to 20th harmonic voltage and current are applied, the output of the differential circuit is 0. If it is not 0, further adjust the amplification factor of the differential circuit until the output of the differential circuit is 0, and obtain the target differential circuit;

[0032] Step S7: Use the target differential circuit to perform defect detection on the cable sample circuit. The output signal of the target differential circuit is the harmonic component signal generated by the defect after eliminating the harmonic interference from the power supply side.

[0033] The embodiments of the present invention construct a detection circuit for the defect harmonic components of power distribution cable sample circuits suitable for power supply side harmonic elimination in the laboratory. It can eliminate the influence of power supply side harmonics introduced by the power supply and the through transformer circuit on the detection of defect harmonic components of power distribution cable samples, and improve the analysis efficiency of test data.

[0034] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and substitutions will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical applications, or technological improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for identifying grounding current harmonic component interference, characterized in that, include: The outer sheath, armor layer, and metal shield of the cable are circumferentially cut. At the circumferential cut, the three-phase cable cores are wound with soft copper tape to form a three-core integrated electrode. The electrode is at least 1 cm away from the metal shield of other sections of the cable on both sides. Signal leads are soldered onto the electrodes, and the solder joints are wrapped with insulating tape. The electrode insulating tape is covered with copper mesh, and the two ends of the copper mesh are pressed with the metal shielding layer of the cable on both sides by constant force springs, and the outside is wrapped with water-blocking armor tape. The detection signals of the grounding wire and the signal lead wire of the cable sample circuit are respectively connected to an oscilloscope for data observation. The 2nd to 20th harmonic voltage and current are injected between the conductor and the grounding wire of the unenergized cable sample circuit. The specific harmonic voltage and current ratio detected by the grounding wire and the signal lead wire of the cable sample circuit is observed. The amplification factor of the differential circuit is determined according to the specific harmonic voltage and current ratio. A differential circuit is set up according to the amplification factor, and the detection signals of the cable sample circuit grounding wire and the signal lead wire are respectively introduced into the differential circuit set up according to the amplification factor to detect the output signal of the differential circuit. Among them, when the cable is free of defects, when the power frequency and the 2nd to 20th harmonic voltage and current are applied, the output of the differential circuit is 0. If it is not 0, the amplification factor of the differential circuit is further adjusted until the output of the differential circuit is 0, thus obtaining the target differential circuit. The target differential circuit is used to detect defects in the cable sample circuit. The output signal of the target differential circuit is the harmonic component signal generated by the defect after eliminating the harmonic interference from the power supply side.

2. The grounding current harmonic component interference identification method according to claim 1, characterized in that, The circumferential cut width is greater than or equal to 12-15 cm.

3. The grounding current harmonic component interference identification method according to claim 1, characterized in that, The width of the soft copper strip is 10cm.

4. The grounding current harmonic component interference identification method according to claim 1, characterized in that, The thickness of the insulating tape after wrapping is 3-5mm.

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