Early fault simulation test platform and test method based on actual operation environment of cable

Abstract

The invention discloses an early fault simulation test platform and test method based on an actual operation environment of a cable, and relates to the technical field of electrical equipment. Comprising a test box, and a cable sample, an insulation support, a sprayer, a current-limiting resistor, an insulation oil tank and a cable joint are arranged in the test box. According to the method, the change of electrical quantity and non-electrical quantity characteristics in the fault is observed by performing a secondary cycle early fault simulation experiment, then the surface topography of a sample after the experiment is observed and analyzed, and the development process of the secondary cycle early fault and the mutual relation between the electrical quantity and the non-electrical quantity in the process are analyzed by integrating various observed characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical equipment, and particularly to an early fault simulation test platform and test method based on the actual operating environment of cables. Background Art

[0002] With the development of the urbanization process in China, medium-voltage cables are more widely used in cities. The power outages caused by cable faults have seriously affected the reliability of the operation of urban distribution network lines. Among them, the faults of cable joints are particularly prominent. At present, researchers have found that some cable joints have self-clearing and self-recovering discharges with a single duration within one cycle before permanent faults. This kind of discharge is also called sub-cycle early fault. The development of sub-cycle early faults will lead to permanent faults. If accurate identification of early faults can be achieved, the fault power outage losses caused by permanent faults can be prevented.

[0003] At present, researchers study early faults from two directions: one is the early fault identification method based on an external circuit equivalent model; the other is the simulation experiment of early faults under different conditions such as sandy land, rainfall, and high temperature. At present, researchers have conducted certain research on early faults, but the existing research lacks the study of the development process of early faults. Therefore, the changes in real-time electrical and non-electrical quantity characteristics during the development process of early faults are still unknown. There are problems that the known fault characteristics are isolated, and the early fault identification algorithm based on known characteristics has low verifiability and poor interpretability.

[0004] Therefore, in view of the problem of insufficient understanding of the development process of sub-cycle early faults in the existing research, an early fault simulation test platform and test method based on the actual operating environment of cables are proposed to solve the difficulties existing in the prior art. Summary of the Invention

[0005] In view of this, the present invention provides an early fault simulation test platform and test method based on the actual operating environment of cables. By conducting sub-cycle early fault simulation experiments, observing the changes in electrical and non-electrical quantity characteristics in the faults, and then observing and analyzing the surface morphology of the samples after the experiments, and comprehensively analyzing various observed characteristics, the development process of sub-cycle early faults and the mutual relationship between electrical and non-electrical quantities during this process are analyzed.

[0006] To achieve the above object, the present invention adopts the following technical solutions: An early fault simulation test platform based on the actual operating environment of cables, comprising: a test box, and the interior of the test box includes a cable sample, an insulating bracket, a sprinkler, a current-limiting resistor, an insulating oil tank, and a cable joint; wherein, The cable sample is placed on an insulating support, and a sprayer is installed directly above the insulating support. One end of the cable sample is connected to a current-limiting resistor, and the other end is immersed in an insulating oil tank. The cable sample on the side immersed in the insulating oil tank is connected to the ground point, and a cable joint with pre-drilled holes is installed on the cable sample.

[0007] Optionally, the cable joint installed on the cable sample is wrapped with a copper mesh.

[0008] Optionally, the grounding method is grounding through a small resistor at the neutral point.

[0009] Optionally, the test box also includes an oscillograph. The current probe of the oscillograph is connected in series between the cable grounding wire and the ground point to collect the current flowing through the fault point; One side of the voltage probe of the oscillograph is connected to the incoming line end of the cable sample, and the other side is connected to the cable grounding wire to collect the voltage at both ends of the cable sample.

[0010] Optionally, the oscillograph is an MR-1200 type oscillograph, with a sampling frequency of 10 kHz, an A / D resolution of 16 bits, a voltage range of 0 - 10 kV, and a current range of 0 - 1 A.

[0011] Optionally, the cable sample used in the experiment is a three-core copper conductor cable with a cross-sectional area of 50 mm 2 and the configuration of the cable joint is a silicone rubber cold shrinkable cable joint.

[0012] Optionally, before the experiment, the cable joint connects two 70-cm long cables to obtain a connecting piece cable. Subsequently, the insulation and semi-conductive layers at both ends of the connecting piece cable are removed by 5 cm each to expose the cable conductors therein as wiring poles, and then the semi-conductive layers at 10 cm from the ends of the conductors are removed to obtain the cable sample.

[0013] A test method for an early fault simulation test platform based on the actual operating environment of a cable. Applying an early fault simulation test platform based on the actual operating environment of a cable as described in any one of the above, includes the following steps: S1. Place the cable sample on the insulating support inside the test box and connect the power supply. Adjust the side of the cable sample with holes to face the sprayer directly above the insulating support; S2. Turn on the power supply, then turn on the sprayer. At the same time, observe through the oscillograph and high-speed camera whether there is an abnormal current amplitude during partial discharge and the flash during arc discharge. If so, record the experimental phenomena and fault characteristics, and turn off the sprayer; S3. If there is no abnormal current amplitude during partial discharge and the flash during arc discharge in S2, turn off the power supply, adjust the position of the cable sample, replace the next test sample, and then repeat S2. If no discharge occurs within the preset number of times for a certain hole or test sample, replace the test sample; S4. If abnormal current amplitude of partial discharge and flash during arc discharge occur in S2, repeat S1 - S3. If high - intensity arc discharge that lasts for several seconds or more and cannot stop on its own occurs in the cable sample, it is considered that the sample has suffered a permanent fault, stop the experiment and replace the test sample.

[0014] As can be seen from the above - mentioned technical solutions, compared with the prior art, the present invention provides an early - fault simulation test platform and test method based on the actual operating environment of cables, having the following beneficial effects: (1) The present invention summarizes the initial fault scenarios of sub - cycle early faults according to the actual operating scenarios of cables. On this basis, sub - cycle early - fault simulation experiments are carried out to observe the changes in electrical and non - electrical quantity characteristics during the faults. After that, the surface morphology of the samples after the experiments is observed and analyzed. By synthesizing various observed characteristics, the development process of sub - cycle early faults and the mutual relationship between electrical and non - electrical quantities during this process are analyzed; (2) According to the experimental phenomena, for cable joints, the voids without water accumulation still have sufficient insulation strength to prevent breakdown, but the infiltration of water reduces the length of the insulation area and lowers the breakdown difficulty. The peak current of a single early fault can reach several hundred to several thousand amperes, and the duration is about 1 / 8 - 1 / 4 cycle. During early faults, the wall insulation will generate cumulative conductive traces due to burning, reducing the environmental insulation strength. After several early faults, a permanent fault will be formed. The permanent fault is manifested as a continuous and intense arc discharge with a flat shoulder on the cycle - level scale on the macroscopic time scale, and the discharge intensity will gradually increase with time. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0016] Figure 1 It is a schematic diagram of the structure of a cable and a cable joint provided by the present invention. Among them, 1a is a schematic diagram of the cable structure, and 1b is a schematic diagram of the cable joint structure; Figure 2 It is the position of the fault point in the grid provided by the present invention; Figure 3 It is a schematic diagram of the cable sample structure provided by the present invention; Figure 4 It is a schematic diagram of the experimental circuit structure provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with 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, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] The present invention discloses an early fault simulation test platform based on the actual operating environment of a cable, including: a test box, and the interior of the test box includes a cable sample, an insulating bracket, a sprinkler, a current-limiting resistor, an insulating oil tank, and a cable joint; wherein, The cable sample is placed on the insulating bracket, a sprinkler is installed directly above the insulating bracket, one end of the cable sample is connected to the current-limiting resistor, and the other end is immersed in the insulating oil tank. The cable sample immersed on one side of the insulating oil tank is connected to the ground point, and a cable joint equipped with pre-drilled holes is installed on the cable sample.

[0019] Further, the cable joint installed on the cable sample is wrapped with a copper mesh.

[0020] Further, the grounding method is grounding through a small resistor at the neutral point.

[0021] Further, a recorder is also included inside the test box. The current probe of the recorder is connected in series between the cable grounding wire and the ground point for collecting the current flowing through the fault point; One side of the voltage probe of the recorder is connected to the incoming line end of the cable sample, and the other side is connected to the cable grounding wire for collecting the voltages at both ends of the cable sample.

[0022] Further, the recorder is an MR-1200 type recorder, the sampling frequency is 10 kHz, the A / D resolution is 16 bits, the voltage range is 0 - 10 kV, and the current range is 0 - 1 A.

[0023] Further, the cable sample used in the experiment is a three-core copper conductor cable with a cross-sectional area of 50 mm 2 and the configuration of the cable joint is a silicone rubber cold shrinkable cable joint.

[0024] Further, before the experiment, the cable joint connects two 70-cm long cables to obtain a connecting piece cable. Subsequently, the insulation and semi-conductive layers at both ends of the connecting piece cable are each removed by 5 cm to expose the cable conductors therein as the wiring poles, and then the semi-conductive layers at 10 cm from the ends of the conductors are removed, thereby obtaining the cable sample.

[0025] In a specific embodiment, it includes the following: The simulation test platform for the actual operating environment of the cable includes a test box, and the interior of the test box includes a cable sample, an insulating bracket, a sprinkler, a current-limiting resistor, an insulating oil tank, and a cable joint.

[0026] The cable used in the experiment is a three-core copper conductor cable with a cross-sectional area of 50 mm 2 . This configuration of cable line is commonly used in the end line of the distribution network. In the experiment, actual devices were used as experimental samples, namely cable samples. The configuration of the cable joint is a silicone rubber cold shrinkable cable joint, and its structure is as shown in Figure 1 . Figure 1a is a schematic diagram of the cable structure, and Figure 1b is a schematic diagram of the cable joint structure.

[0027] For the cable joint with a single-phase grounding fault, the line structure at the fault point is as shown in Figure 2 . Since the fault grounding circuit is in parallel with the load and they do not affect each other, the circuit connecting the load after the fault point can be ignored in the experiment.

[0028] Before the experiment, two 70-cm-long cables can be connected with a sound cable joint. Subsequently, the insulation and semi-conductive layers at both ends of the connector are removed by 5 cm each to expose the cable conductors therein as the wiring poles. Then, 10 cm of the semi-conductive layer is removed from the end of the conductor to prevent unexpected discharge between the end of the conductor and the semi-conductive layer during the pressurization process. The sample parameters are shown in Table 1.

[0029] Table 1 Cable sample parameters

[0030] Among them, the cable insulation material HDPE is high-density polyethylene; the cable conductor material Copper is pure copper, and both the main insulation material and the semi-conductive layer material of the joint are a kind of silicone rubber.

[0031] Two groups of control experiments were set up in the experiment. First, for the defects at different positions of the cable joint caused by external force damage or defects such as sharp corners in the semi-conductive layer, in the experiment, holes with the same diameter and different depths were simulated at different parts of the cable joint in the same state. The processed samples are as shown in Figure 3 . The depths of the holes at different positions of the cable sample are shown in Table 2. In addition, to study the damage of the development of early faults to the insulation performance of the cable joint, the experiment also compared the same sample after different numbers of discharges.

[0032] Table 2 Depths of holes at different positions of the cable sample

[0033] Figure 4This is an early failure experiment circuit. The frequency of the experimental power supply is 50Hz, which is connected to the experimental circuit after passing through an isolation transformer. The effective value of the voltage on the primary side of the isolation transformer is 35kV, and the secondary side is 10kV. The grounding method is that the neutral point is grounded through a small resistor with a resistance value of 20Ω. A current-limiting resistor with a resistance value of 1000Ω is connected in series in the secondary circuit to prevent the impact of high current on the power grid at the moment of metal ground fault. When calculating, the current-limiting resistor with a resistance value of 1000Ω is removed. In addition, an external circuit structure in which a 5km overhead line equivalent to an RLC combination is connected in series with a 5km cable line is also connected in series in the line to simulate the scenario of mixed use of overhead lines and cable lines in urban distribution networks.

[0034] The internal structure of the test box is as Figure 4 shown. The cable sample is placed on an insulating bracket. One end of the exposed conductor of the cable sample is connected to the current-limiting resistor. Since the load circuit can be ignored, the other end of the exposed conductor can be immersed in an insulating oil tank. The semiconductive layer of the cable on the side immersed in the insulating oil tank is connected to the ground point. A cable joint with pre-drilled holes is installed on the connected cable and wrapped with a copper mesh with good contact and no dirt to restore the grounding condition of the cable joint in the normal environment.

[0035] The insulating bracket and the cable sample on it are placed in a constant temperature and humidity test box. The environmental conditions in the test box are set to 20°C and the relative humidity is 90%.

[0036] A sprinkler is installed directly above the insulating bracket, and its flow rate is set to 2mL / s to simulate the influence in the cable well. The sprinkler is facing the side of the cable joint with holes, and the droplet coverage area covers the hole area. The water used in the experiment is tap water from the local area of the experiment. After measurement, the conductivity is about 0.05 S / m.

[0037] In the experiment, an MR-1200 type oscillograph is used. Its sampling frequency is 10kHz, the A / D resolution is 16 bits, the voltage range is 0~10kV, and the current range is 0~1A; the current probe of the oscillograph is connected in series between the cable grounding wire and the ground point to collect the current flowing through the fault point ; one side of the voltage probe is connected to the incoming line end of the experimental sample, and the other side is connected to the cable grounding wire to collect the voltage across the device .

[0038] Analysis of experimental phenomena: After the power supply is turned on and before the sprinkler is turned on, no arc discharge phenomenon occurs in the holes at different depths of the cable joint. This phenomenon indicates that even if voids are generated inside the main insulation of the cable joint due to external force damage, internal stress concentration points, etc., since the voids still have a certain length, the overall cable joint will not be broken down.

[0039] When the sprinkler is turned on, there is still no arc discharge in the holes that do not penetrate the main insulation of the cable joint and in the holes that have penetrated the main insulation of the cable joint but have not yet damaged the cable body. However, for the holes that have penetrated the cable joint insulation and damaged the cable insulation by 3 - 5 mm, breakdown will occur after being immersed in external moisture. That is, there is no discharge in holes (1) and (2) in Table 2, while there is discharge in holes (3) and (4). This phenomenon indicates that when the cable's own insulation is not damaged, even if the cable joint has been damaged by external force, it can still prevent arc discharge from occurring.

[0040] For holes (3) and (4), before breakdown occurs, as the amount of water accumulated on the surface and inside the holes of the cable joint increases, continuous corona discharge appears in the holes with the possibility of discharge. However, the discharge at this time is still relatively weak and no obvious arc is formed. As the amount of water further increases, the intensity of the corona discharge gradually rises, and finally obvious arc discharge occurs. When breakdown occurs, a momentary spark can be observed between the copper shield of the cable joint and the surface of the cable joint from the outside, along with water vapor escaping from the holes. The discharge at this time can stop by itself without external interference, which is an early fault.

[0041] After the discharge ends, on the macroscopic scale, compared with the insulation without early fault, the surface of the insulation in contact with the arc shows a gray - white and black rough surface, and the diameter of the hole increases compared with that before discharge. After the discharge ends, the temperature of the insulation surface rises significantly compared with that before the fault, and the accumulated water in the hole is completely evaporated.

[0042] After the arc extinguishes, under the influence of precipitation and condensation, water will seep into the holes formed by the previous damage again. Thus, the conditions for triggering the sub - cycle early fault are formed again. In the experiment, when the sub - cycle early fault is triggered several times, the subsequent discharge will not stop by itself, that is, a permanent fault occurs. The arc flame during the permanent fault, at this time the discharge intensity far exceeds that in the early fault period, and the discharge - induced flame penetrates the cable joint grounding grid, reaching more than ten centimeters. The tip of the flame shows green, and it can be known from the flame color reaction that there are copper particles in the tip of the flame. During the discharge, from time to time, sparks containing solid particles break away from the tip of the flame, accompanied by continuous thick smoke. This phenomenon indicates that the temperature of the arc root at this time is higher than the melting point of copper, and the cable copper conductor is vaporized during the discharge and transported to the tip of the flame by the arc gas flow. Since the duration and intensity of the discharge are higher than those in the early fault, the damage to the insulation caused by the permanent fault is also greater than that of the early fault.

[0043] Corresponding to the above - mentioned experimental platform, the embodiment of the present invention also provides a test method for an early - fault simulation test platform based on the actual operating environment of the cable, including the following steps: S1. Place the cable sample on the insulation support inside the test chamber and connect the power supply. Adjust the side of the cable sample with holes to face directly below the sprayer above the insulation support. S2. Turn on the power supply, then turn on the sprayer. At the same time, observe through the oscillograph and high-speed camera whether there is an abnormal current amplitude of partial discharge and the flash during arc discharge. If so, record the experimental phenomena and fault characteristics, and turn off the sprayer. S3. If there is no abnormal current amplitude of partial discharge and the flash during arc discharge in S2, turn off the power supply, adjust the position of the cable sample, replace the next test sample, and then repeat S2. If no discharge occurs within the preset number of times for a certain hole or test sample, replace the test sample. S4. If there is an abnormal current amplitude of partial discharge and the flash during arc discharge in S2, repeat S1 - S3. If the cable sample shows a high-intensity arc discharge that lasts for several seconds or more and cannot stop on its own, it is considered that the sample has suffered a permanent fault. Stop the experiment and replace the test sample.

[0044] Specifically, S1. Place the cable sample on the support of the temperature and humidity control chamber and connect the power supply. Adjust the side with holes to face directly upward, and through adjustment, make the hole to be tested face directly below the sprayer above, and the water sprayed by the sprayer will not affect the holes not being tested in this experiment. S2. Turn on the power supply, then turn on the sprayer so that it covers a circular area with a radius of about 2 cm at a flow rate of 3 mL / s. At the same time, pay attention to the oscillograph and high-speed camera to observe whether there is a current amplitude and flash during arc discharge that are significantly different from partial discharge. If the above situations occur, record the experimental phenomena and fault characteristics, and turn off the sprayer. S3. If there is no arc discharge in S2, turn off the power supply, adjust the position of the experimental sample, replace the next test sample, and then repeat S2. If a certain hole or sample fails to discharge continuously five times, also replace it with the next test sample. S4. For the sample with discharge phenomena in S2, repeat S1 - S3. If the sample shows a high-intensity arc discharge that lasts for several seconds or more and cannot stop on its own, it is considered that the sample has suffered a permanent fault. Stop the experiment and replace the test sample.

[0045] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other.

[0046] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An early fault simulation test platform based on the actual operating environment of cables, characterized in that Including: A test chamber, inside which there are a cable sample, an insulating bracket, a sprayer, a current-limiting resistor, an insulating oil tank and a cable joint; among which, The cable sample is placed on the insulating bracket, a sprayer is installed directly above the insulating bracket, one end of the cable sample is connected to the current-limiting resistor, the other end is immersed in the insulating oil tank, the cable sample immersed on one side of the insulating oil tank is connected to the ground point, and a cable joint equipped with pre-drilled holes is installed on the cable sample.

2. The early fault simulation test platform based on the actual operating environment of the cable according to claim 1, characterized in that The cable joint installed on the cable sample is wrapped with a copper mesh.

3. The early fault simulation test platform based on the actual operating environment of the cable according to claim 1, characterized in that The grounding method is that the neutral point is grounded through a small resistor.

4. The early fault simulation test platform based on the actual operating environment of the cable according to claim 1, characterized in that The test chamber also includes a recorder, and the current probe of the recorder is connected in series between the cable grounding wire and the ground point for collecting the current flowing through the fault point; One side of the voltage probe of the recorder is connected to the cable sample inlet end, and the other side is connected to the cable grounding wire for collecting the voltages at both ends of the cable sample.

5. The early fault simulation test platform based on the actual operating environment of the cable according to claim 4, characterized in that The recorder is an MR-1200 type recorder, the sampling frequency is 10 kHz, the A / D resolution is 16 bits, the voltage range is 0~10 kV, and the current range is 0~1 A.

6. The early fault simulation test platform based on the actual operating environment of the cable according to claim 1, characterized in that The cable sample used in the experiment is a three-core copper conductor cable with a cross-sectional area of 50 mm 2 , and the configuration of the cable joint is a silicone rubber cold-shrinkable cable joint.

7. The early fault simulation test platform based on the actual operating environment of the cable according to claim 6, characterized in that Before the experiment, the cable joint connects two 70-cm-long cables to obtain a connecting piece cable, and then removes the insulation and semi-conductive layers at both ends of the connecting piece cable by 5 cm each to expose the cable conductors therein as the wiring poles, and then removes the semi-conductive layers at 10 cm each from the ends of the conductors, so as to obtain the cable sample.

8. A test method for an early fault simulation test platform based on the actual operating environment of a cable, characterized in that, Applying the early fault simulation test platform based on the actual operating environment of the cable according to any one of claims 1-7, includes the following steps: S1. Place the cable sample on the insulating bracket in the test chamber and connect the power supply, and adjust the side of the cable sample with holes to face the sprayer directly above the insulating bracket; S2. Turn on the power supply, then turn on the sprayer, and at the same time observe through the recorder and the high-speed camera whether there is an abnormal current amplitude during partial discharge and the flash during arc discharge. If so, record the experimental phenomena and fault characteristics, and turn off the sprayer; S3. If there is no abnormal current amplitude during partial discharge and the flash during arc discharge in S2, turn off the power supply, adjust the position of the cable sample, replace the next test sample, and then repeat S2. If no discharge occurs within the preset number of times for a certain hole or test sample, replace the test sample; S4. If abnormal current amplitudes of partial discharge and flashes during arc discharge occur in S2, then repeat S1 - S3. If the cable sample experiences a high-intensity arc discharge that lasts for several seconds or more and cannot stop on its own, it is considered that the sample has suffered a permanent fault, and the experiment is stopped and the test sample is replaced.

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