High-voltage XLPE cable buffer layer discharge simulation method

Abstract

The invention discloses a discharge simulation method for a buffer layer of a high-voltage XLPE cable. The discharge simulation method comprises the following steps: intercepting a section of corrugated aluminum sheath cable sample to be researched; step-type processing is carried out on the end part of the cable, so that the cable guide core, the outer shielding layer and the aluminum sheath are exposed; removing the cable in a lossless manner, and removing the cable conductor core, the insulating layer and the inner and outer shielding layers from the cable to expose the surface of the outer shielding layer of the cable; the surface of the outer shielding layer of the cable is processed, so that the surface of the outer shielding layer is uniformly covered with a conductive layer, the conductivity of the conductive layer is close to the range of good conductors such as aluminum and copper, and the cable is reassembled; and voltage is applied between the conductive layer on the surface of the outer shielding layer and the aluminum sheath, and a buffer layer discharge ablation experiment is carried out. According to the method, the voltage can be directly and uniformly applied to the inner and outer surfaces of the buffer layer, the discharge generation environment of the buffer layer is simulated on the real cable, and the problem that the discharge of the buffer layer cannot be simulated due to voltage drop generated by the influence of the resistance value of the semi-conductive outer shielding layer and uneven heating of the buffer layer is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of cable discharge test and state detection, and in particular relates to a high-voltage XLPE cable buffer layer discharge simulation method. Background Art

[0002] High-voltage XLPE cables are widely used in the field of urban power transmission because of their convenient laying, excellent electrical performance, and not easily affected by climate change. The increasing utilization rate of high-voltage cables has put forward higher requirements for the operation reliability and detection and maintenance technology of cables. In recent years, there have been many cable operation failures caused by discharge burning of the buffer layer, which seriously endangered the safe operation of the cable system. The discharge ablation of the buffer layer will penetrate the outer shielding layer of the cable and cause carbonization of the main insulation, accelerate the aging and damage of the insulation layer, and eventually lead to a short circuit failure of the cable. The problem that needs to be solved urgently is how to effectively realize the early detection of defects to avoid economic losses.

[0003] On the one hand, high-voltage XLPE cables are inevitably affected by some mechanical stress during manufacturing, transportation, and operation, which prevents the buffer layer from fully contacting the aluminum sheath. On the other hand, due to the influence of humid environment and inadequate sealing, moisture enters the buffer layer and is absorbed by the water-blocking powder, and reacts with the aluminum sheath to form an insulating white precipitate. This increases the volume resistivity of the cable buffer layer and the potential difference on both sides of the buffer layer, leading to the occurrence of partial discharge.

[0004] Partial discharge is the main cause of buffer layer ablation failure. At present, the discharge problem inside the cable buffer layer has attracted widespread attention in the industry. At present, most of the research on buffer layer discharge ablation relies on the construction of experimental platforms, but the current settings of such experimental platforms are relatively simple. For example, only using buffer layer samples for partial discharge experiments, etc., it is difficult to restore the actual conditions when the cable is running in actual engineering. In the experiments conducted on the real cable platform, due to the semi-conductive properties of the outer shielding layer, it is difficult to apply uniform pressure on both ends of the buffer layer alone. Conducting research on the electric field distribution of the cable buffer layer under actual complex working conditions and exploring the discharge evolution law under the defective state of the buffer layer are of great significance to cable status monitoring and operation and maintenance management.

[0005] The invention with application publication number CN 117054784 A designs a high-voltage cable buffer layer ablation simulation detection device and method with adjustable temperature, humidity and pressure. This method uses simulated electrodes to pressurize the buffer layer sample in a closed cavity, and does not conduct experiments on a real cable platform. In CN 117192019 A, a high-voltage cable buffer layer ablation simulation device and method are designed, which can simulate the situation where the cable is not laid horizontally, but it is also carried out in a test box, and only for buffer layer samples rather than real cables. CN 117092463 A discloses a real high-voltage XLPE cable discharge simulation and gas generation detection device. This invention simulates local discharge in the cable buffer layer area through a deep electrode, but this method can only simulate local defects in the buffer layer, and cannot achieve large-area uniform pressurization and discharge simulation of the entire axial direction of the cable. CN 114299798A discloses a true cable fault simulation system, which uses a sheet electrode disposed between the insulation layer and the buffer layer of the target cable to apply voltage to the buffer layer of the target cable. However, this method can only achieve uniform pressure on the buffer layer within the coverage range of the sheet electrode.

[0006] At present, the experimental platform for the study of discharge ablation of the buffer layer is relatively simple and cannot truly reflect the cable structure. There are two main methods proposed for pressurizing the cable buffer layer. The first is to use electrodes to apply voltage at both ends of the buffer layer sample, change the electrode shape and contact pressure to simulate different defect states of the buffer layer; the second is to conduct a discharge ablation experiment on the buffer layer of a real cable.

[0007] The main problem faced by the first research method is that it is difficult to completely restore the operating conditions of the buffer layer in the actual project, and there are deviations in the experimental results; the second research method usually applies voltage to the buffer layer by applying pressure between the conductor and the aluminum sheath or between the cable outer shielding layer and the aluminum sheath. The main problem faced by the former is that due to the existence of the cable insulation layer, a very high voltage needs to be applied to obtain the expected voltage in the buffer layer. However, when the cable is not terminally protected, due to the surface discharge at the cable end, a high voltage cannot be applied, so the discharge simulation of the cable buffer layer cannot be achieved; due to the semi-conductive characteristics of the cable outer shielding layer, when the outer shielding layer is directly pressurized through a small electrode, it is impossible to achieve uniform pressure on both sides of the buffer layer, which is quite different from the actual conditions of the project, and the current cannot flow evenly through the shielding layer when pressurizing, which leads to ablation at the current concentration even at a lower voltage, and the buffer layer cannot have local discharge or breakdown at this voltage, so the buffer layer discharge experiment cannot be carried out. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a high-voltage XLPE cable buffer layer discharge simulation method, the specific technical solution is:

[0009] The steps include:

[0010] (1) Cutting the real high-voltage XLPE cable sample;

[0011] (2) Perform step-by-step processing on the cable end to expose the cable core, outer shielding layer and corrugated aluminum sheath;

[0012] (3) Extract the cable without loss, remove the cable core, insulation layer, inner and outer shielding layers from the cable, and expose the surface of the outer shielding layer;

[0013] (4) Treat the surface of the outer shielding layer so that it is evenly covered with a conductive layer whose conductivity is close to that of aluminum and copper, and reassemble the cable;

[0014] (5) A voltage is applied between the conductive layer on the surface of the outer shielding layer and the aluminum sheath to carry out a buffer layer discharge ablation experiment.

[0015] The present invention has the following beneficial effects:

[0016] The present invention provides a method for simulating the discharge of a buffer layer using a real high-voltage XLPE cable, and provides a method for uniformly pressurizing the buffer layer area on a real cable platform. By treating the surface of the outer shielding layer, the influence of the semi-conductive characteristics of the shielding layer on the uneven pressure on the buffer layer and the current concentration is avoided, and the electric field conditions of the buffer layer area under the cable operation conditions are more realistically simulated. Different voltage types and amplitudes can be applied according to different research needs, and different development stages such as local discharge and breakdown ablation of the buffer layer can be continuously recorded. Problems such as the formation of buffer layer defects, discharge ablation, and discharge products can be studied. In addition, because this method involves the lossless extraction process of the cable, defects can be artificially introduced into the buffer layer and the outer shielding layer during the operation, solving the problem that the sealing of the real cable is difficult to handle. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart of a method for simulating buffer layer discharge using a high voltage XLPE cable;

[0018] Figure 2 This is a schematic diagram of the structure of the simulated sample of discharge ablation of the buffer layer of a real cable;

[0019] Figure 3 This is the circuit diagram for simulating discharge ablation of the buffer layer;

[0020] Figure 4 is the buffer layer partial discharge current waveform;

[0021] Figure 5 is the buffer layer breakdown current waveform.

[0022] The figures are marked as: true high-voltage XLPE cable sample 1, first part 2, second part 3, third part 4, true cable buffer layer discharge ablation simulation sample 5, copper foil electrode 401, core guide 501, inner shielding layer 502, insulating layer 503, outer shielding layer 504, conductive layer 505, buffer layer 506, corrugated aluminum sheath 507, outer sheath 508, high-voltage power supply 6, voltage measurement module 7, current measurement module 8. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above-mentioned purpose, the present invention adopts the following technical scheme.

[0024] The present invention provides a high-voltage XLPE cable buffer layer discharge simulation method, wherein a voltage applying unit applies voltage to a real cable sample, and a voltage and current detection unit detects voltage and current. The real cable sample needs to be pre-processed, and the process is as follows: Figure 1 , Figure 2 As shown. The true high-voltage XLPE cable sample 1 includes a core conductor 501, an inner shielding layer 502, an insulating layer 503, an outer shielding layer 504, a buffer layer 506, a corrugated aluminum sheath 507 and an outer sheath 508 from the inside to the outside. The outer sheath 508 is removed to expose about 5 cm of the corrugated aluminum sheath 507, and the outer sheath 508, the corrugated aluminum sheath 507, and the buffer layer 506 are removed to expose about 5 cm of the outer shielding layer 504. The outer sheath 508, the corrugated aluminum sheath 507, the buffer layer 506, the outer shielding layer 504, the insulating layer 503, and the inner shielding layer 502 are removed to expose about 5 cm of the core conductor 501. The pre-treated true high-voltage XLPE cable 1 is non-destructively extracted, and the core conductor 501, the inner shielding layer 502, the insulating layer 503, and the outer shielding layer 504 are extracted to be divided into two parts: the first part 2 and the second part 3. The first part 2 includes a conductor core 501, an inner shielding layer 502, an insulating layer 503 and an outer shielding layer 504 from the inside to the outside. The second part 3 includes a buffer layer 506, a corrugated aluminum sheath 507 and an outer sheath 508 from the inside to the outside. The outer shielding layer 504 of the first part 2 is wrapped with a copper foil electrode 401 as a conductive layer 505, and the third part 4 is obtained after the treatment. The third part 4 is assembled with the second part 3 to obtain a real cable buffer layer discharge ablation simulation sample 5, whose cross section is Figure 2 As shown, from inside to outside, they are respectively a conductor core 501, an inner shielding layer 502, an insulating layer 503, an outer shielding layer 504, a conductive layer 505, a buffer layer 506, a corrugated aluminum sheath 507 and an outer sheath 508.

[0025] Figure 3 The schematic diagram of the buffer layer discharge ablation simulation is shown in FIG. The voltage application unit includes a high voltage power supply 6, and the voltage and current detection unit includes a voltage measurement module 7 and a current measurement module 8. The two ends of the high voltage power supply 6 are respectively applied to the corrugated aluminum sheath 507 and the copper foil electrode 401 of the real cable buffer layer discharge ablation simulation sample 5. The high voltage power supply 6 adopts one of a DC, AC or pulse power supply. The voltage measurement module 7 adopts one of a voltmeter, a voltage divider or a high voltage probe. The current measurement module 8 adopts one of an ammeter or a Rogowski coil.

[0026] The treatment of the outer shielding layer in the third part 4 can be other conductive materials in addition to winding copper foil.

[0027] During the extraction process, the buffer layer 506 can be retained in the second part 3 or in the first part 2, and the processing flow remains substantially unchanged.

[0028] The real cable buffer layer discharge ablation simulation sample 5 can also be further processed, such as drilling a hole in the outer sheath to the buffer layer area and sealing both ends to collect characteristic gases generated during the buffer layer discharge process.

[0029] Defects may be artificially introduced into the first part 2 and the second part 3, such as performing moisture treatment on the buffer layer 506 area, performing local treatment on the buffer layer 506, simulating defects on the external shielding layer 504, etc.

[0030] The high voltage power supply 6 can also be applied between the conductor core 501 and the conductive layer 505 of the real cable buffer layer discharge ablation simulation sample 5 to analyze the discharge and state characteristics of the cable insulation layer 503. Specific embodiments

[0032] 1) Processing of real cable samples

[0033] A 110 kV cable sample with a length of 1.2 m was selected. The end of the cable sample was processed, the cable outer sheath 508 was removed, and the corrugated aluminum sheath 507 of about 5 cm was exposed. The cable outer sheath 508, the corrugated aluminum sheath 507, and the buffer layer 506 were removed, and the outer shielding layer 504 of about 5 cm was exposed. The cable outer sheath 508, the corrugated aluminum sheath 507, the buffer layer 506, the inner and outer shielding layers 502, 504, and the insulating layer 503 were removed, and the cable core 501 of about 5 cm was exposed. The core 501, the inner shielding layer 502, the insulating layer 503, and the outer shielding layer 504 were pulled out from the cable together, and the copper foil electrode 401 was wrapped around the outer shielding layer 504 and reassembled.

[0034] 2) Discharge ablation experiment

[0035] An AC power supply is used to apply voltage across the buffer layer 506, a protective resistor with a resistance of 100 Ω is connected in series, and an oscilloscope and a voltage and current probe are used to detect the partial discharge signal of the buffer layer. The applied voltage starts from 55 V and gradually increases by 5 V, and each voltage level stays for 10 minutes.

[0036] The partial discharge signal is detected from 80 V. Figure 4 is the partial discharge current signal of the buffer layer. When the voltage is increased to 105V, the buffer layer breaks down. Figure 5 It is the current signal when the buffer layer breaks down.

Claims

1. A high voltage XLPE cable buffer layer discharge simulation method, characterized in that: The steps include: (1) Cutting the real high-voltage XLPE cable sample; (2) Perform step-by-step processing on the cable end to expose the cable core, outer shielding layer and corrugated aluminum sheath; (3) Extract the cable without loss, remove the cable core, insulation layer, inner and outer shielding layers from the cable, and expose the surface of the outer shielding layer; (4) Treat the surface of the outer shielding layer so that it is evenly covered with a conductive layer whose conductivity is close to that of aluminum and copper, and reassemble the cable; (5) A voltage is applied between the conductive layer on the surface of the outer shielding layer and the aluminum sheath to simulate the buffer layer discharge.

2. The high-voltage XLPE cable buffer layer discharge simulation method according to claim 1, characterized in that: The voltage applying unit is used to apply voltage to the cable sample, and the voltage and current detecting unit detects the current voltage. The voltage and current detecting unit includes a voltage measuring module and a current measuring module.

3. The high-voltage XLPE cable buffer layer discharge simulation method according to claim 1, characterized in that: The true high-voltage XLPE cable includes a core conductor, an inner shielding layer, an insulating layer, an outer shielding layer, a buffer layer, a corrugated aluminum sheath, and an outer sheath from the inside to the outside.

4. The high-voltage XLPE cable buffer layer discharge simulation method according to claim 3, characterized in that: Step (2) is specifically as follows: removing the outer protective layer to expose about 5 cm of the corrugated aluminum sheath, removing the outer protective layer, the corrugated aluminum sheath, and the buffer layer to expose about 5 cm of the outer shielding layer, and removing the outer protective layer, the corrugated aluminum sheath, the buffer layer, the inner and outer shielding layers, and the insulating layer to expose about 5 cm of the conductor.

5. The high-voltage XLPE cable buffer layer discharge simulation method according to claim 4, characterized in that: The lossless extraction specifically includes pulling out the conductor core, inner shielding layer, insulating layer, and outer shielding layer. The circuit is divided into a first part and a second part. The first part includes the conductor core, inner shielding layer, insulating layer, and outer shielding layer from the inside to the outside, and the second part includes a buffer layer, a corrugated aluminum sheath, and an outer sheath from the inside to the outside.

6. The high-voltage XLPE cable buffer layer discharge simulation method according to claim 5, characterized in that: Step (4) includes: uniformly wrapping a copper foil electrode around the outer shielding layer of the first part as a conductive layer, obtaining a third part after the processing, and assembling the third part with the second part to obtain a real cable buffer layer discharge ablation simulation sample.

7. The high-voltage XLPE cable buffer layer discharge simulation method according to claim 6, characterized in that: The real cable buffer layer discharge ablation simulation sample is composed of the conductor core, inner shielding layer, insulating layer, outer shielding layer, conductive layer, i.e. copper foil electrode, buffer layer, corrugated aluminum sheath and outer sheath from inside to outside.

8. The high-voltage XLPE cable buffer layer discharge simulation method according to claim 2, characterized in that: The voltage applying unit comprises a high voltage power supply, and two ends of the high voltage power supply are respectively applied to the corrugated aluminum sheath and the copper foil electrode of the real cable buffer layer discharge ablation simulation sample.

9. The high-voltage XLPE cable buffer layer discharge simulation method according to claim 2, characterized in that: The high voltage power supply adopts one of direct current, alternating current or pulse power supply.

10. The high-voltage XLPE cable buffer layer discharge simulation method according to claim 2, characterized in that: The voltage measurement module adopts one of a voltmeter, a voltage divider or a high-voltage probe; the current measurement module adopts one of an ammeter or a Rogowski coil.

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