CN116298716A - Bypass flexible high-voltage power cable insulation residual life assessment method and experimental platform - Google Patents
Bypass flexible high-voltage power cable insulation residual life assessment method and experimental platform Download PDFInfo
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- 238000002474 experimental method Methods 0.000 claims abstract description 33
- 238000011156 evaluation Methods 0.000 claims abstract description 23
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- 238000012360 testing method Methods 0.000 claims description 38
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 12
- 239000011889 copper foil Substances 0.000 claims description 12
- 229910001369 Brass Inorganic materials 0.000 claims description 10
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- 238000005070 sampling Methods 0.000 claims description 6
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- 238000005520 cutting process Methods 0.000 claims description 4
- 239000004696 Poly ether ether ketone Substances 0.000 claims description 3
- 230000005684 electric field Effects 0.000 claims description 3
- 229920002530 polyetherether ketone Polymers 0.000 claims description 3
- 229920002379 silicone rubber Polymers 0.000 claims description 3
- 239000004945 silicone rubber Substances 0.000 claims description 3
- 238000004804 winding Methods 0.000 claims description 3
- 238000003556 assay Methods 0.000 claims 4
- 210000001217 buttock Anatomy 0.000 abstract 1
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- 238000010586 diagram Methods 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 238000012544 monitoring process Methods 0.000 description 4
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- 229920000181 Ethylene propylene rubber Polymers 0.000 description 2
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- 241001391944 Commicarpus scandens Species 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
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- 230000001276 controlling effect Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
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- HQQADJVZYDDRJT-UHFFFAOYSA-N ethene;prop-1-ene Chemical group C=C.CC=C HQQADJVZYDDRJT-UHFFFAOYSA-N 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
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- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
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Abstract
The invention relates to a bypass flexible high-voltage power cable insulation residual life assessment method and an experimental platform, which solve the problem that the bypass flexible high-voltage power cable insulation residual life assessment cannot be realized in the prior art. The buttocks prescription method comprises the following steps: and (3) preparing a cable sample, performing an accelerated aging experiment on the sheet sample and the short cable sample, determining an evaluation equation of the residual service life of the cable insulation, and evaluating the residual service life of the bypass flexible high-voltage power cable in use. The experimental platform comprises an accelerated aging experimental platform and a measurement experimental platform. The cable insulation life is sampled and accelerated to age, the relation between the cable insulation life and aging temperature and conductance current is determined, an evaluation equation is obtained, the cable load current, the conductance current and the surrounding environment temperature are measured on the site, the cable insulation residual life is calculated, the cable insulation state is mastered, hidden dangers are avoided, the reliability of a power supply channel in the uninterrupted operation on site is ensured, and the method has important engineering application value.
Description
Technical Field
The invention relates to the field of evaluation of insulation residual life of high-voltage power cables, in particular to an evaluation method and an experimental platform for insulation residual life of a bypass flexible high-voltage power cable.
Background
The bypass flexible high-voltage power cable is an important component for supplying power to bypass operation equipment and ensuring uninterrupted operation of the power distribution network. The cable adopts quick plug-in connection, has small bending radius of the body and can be repeatedly used. Along with the wide popularization of uninterrupted operation of the distribution network in China, the bypass flexible high-voltage power cable is increasingly popularized. However, in the actual use process, the bypass flexible high-voltage power cable needs to cope with maintenance work of various sudden power failure accidents, and the cable is easy to cause insulation problems due to repeated use and moving. Therefore, the service life of the bypass flexible high-voltage power cable is evaluated, the state of the cable is mastered, and unnecessary faults before the maintenance work of the power distribution network is carried out can be avoided.
Current research on bypass cables is mainly focused on bypass cable monitoring and cable joints. A fast networking and fault early warning device for bypass cable monitoring and an early warning method thereof are disclosed, which are applied by Guangdong power grid limited responsibility company, and relate to a fast networking and fault early warning device for bypass cable monitoring and an early warning method thereof, which are used for monitoring the temperature and the environmental temperature of a bypass cable joint and diagnosing whether the cable joint has an insulation fault or a poor contact fault by combining temperature rise and load current, but do not illustrate a specific implementation process of fault diagnosis and also provide an insulation residual life assessment method. The utility model provides a measuring method of bypass system load circuit of a bypass current real-time monitoring device of the intelligent equipment limited company of Wuhan Hua Yi, which reduces the potential safety hazard of manual detection, but does not explain whether the measuring method is suitable for bypass cable load current measurement or not, and does not evaluate the bypass equipment, particularly the insulation residual life of the bypass cable according to the current.
Therefore, aiming at the problems, the technical problem that the insulation life of the bypass flexible high-voltage power cable cannot be evaluated is urgently needed.
Disclosure of Invention
The invention aims to solve the technical problem of providing a bypass flexible high-voltage power cable insulation residual life assessment method and an experimental platform, which are used for realizing bypass flexible high-voltage power cable insulation residual life assessment, so as to ensure the reliability of uninterrupted operation of a power distribution network.
To solve the above technical problems, according to an aspect of the present invention, there is provided a bypass flexible high voltage power cable insulation remaining life assessment method including the steps of:
step one, preparing cable samples, including preparing sheet samples and short cable samples; taking a brand new same type of cable of the bypass flexible high-voltage power cable to be evaluated, stripping an outer sheath and a shielding layer of the cable, and reserving a wire core and an insulating layer to respectively prepare the sheet-shaped sample and the short cable sample;
step two, performing an accelerated aging test on the sheet sample;
1. determining the accelerated aging temperature T and the accelerated aging voltage of the sheet sampleU a ；
The accelerated aging temperature T of the sheet sample is based on a heat exposure temperature T0 of the cable insulation layer material (the heat exposure temperature T0 is the highest temperature at which the cable insulation layer material can run for a long time and is not damaged), at least four temperature values are obtained by increasing the temperature increase delta T as the accelerated aging temperature T of the sheet sample, namely T0+Delta T, T0+2Delta T, T0 +3Delta T, T0 +4DeltaT, wherein the temperature increase delta T is less than or equal to 10 ℃ and less than or equal to 30 ℃, and the accelerated aging temperature T of the sheet sample is less than or equal to 50% of the initial temperature of thermal decomposition of the cable insulation layer material (the initial temperature of thermal decomposition is the lowest temperature at which macromolecular chains of the cable insulation material can decompose); in specific implementation, the maximum value of the accelerated aging temperature T of the sheet sample is as close as possible to 50% of the thermal decomposition starting temperature of the cable insulating layer material;
Accelerated aging voltage of sheet sampleU a Voltage for power frequency voltage test of bypass flexible high-voltage power cable to be evaluatedU t Maximum electric field strength borne by short cable sample under actionE max Thickness of sheet sampledThe product of (a), i.e
Wherein:R 1 is the inner radius of the insulating layer of the cable,R 2 is the outer radius of the cable insulation layer;
2. the accelerated aging temperature T and the accelerated aging voltage of the sheet sample determined according to the previous stepU a The method comprises the steps of performing accelerated aging on a sheet sample, setting basic time length L0 of accelerated aging before aging, enabling an accelerated aging temperature T of the sheet sample to be realized by a temperature control box, placing a plurality of sheet samples in the temperature control box, and applying an accelerated aging voltage of the sheet sample to the sheet samples in the temperature control box at the accelerated aging temperature T of the sheet sampleU a Timing to reach the ageing time length L, taking out the corresponding sheet sample for subsequent experiments, and continuing ageing of the rest sheet samples; the aging time length L is an integer multiple of the basic time length L0; before the accelerated aging of the sheet sample, the temperature control box needs to be preheated in advance to reach the accelerated aging temperature T of the sheet sample; in order to meet the requirement of the subsequent experiment, taking out the aged sheet sample each time, simultaneously putting a new sheet sample, and re-marking and recording the ageing time; if the sheet sample breaks down in the accelerated aging process, short circuit can be caused, current is increased, overcurrent protection of the alternating-current high-voltage power supply automatically cuts off the power supply, timing is stopped, the aging of the sheet sample at the temperature is stopped, and the actual aging time length is recorded as the service life of the cable insulation layer at the accelerated aging temperature T of the corresponding sheet sample L T The method comprises the steps of carrying out a first treatment on the surface of the After the sample is taken out, a puncture black hole is seen on the sample; meanwhile, the flaky sample in the temperature control box is replaced integrally, and the flaky sample with a temperature value below the flaky sample accelerated aging temperature T is subjected to accelerated aging; how to apply a voltage to the sheet-like sample in the temperature control box can be accomplished using a variety of well-known structures to those skilled in the art.
3. Measuring elongation at break of the sheet sample obtained in the aging process without sample breakdown in the last step, stopping the aging process of the sheet sample at the corresponding sheet sample accelerated aging temperature T if the measured elongation at break is less than or equal to half of the elongation at break of the unaged sheet sample, and recording the aging time L of the sheet sample as the service life of the cable insulation layer at the corresponding sheet sample accelerated aging temperature TL T The method comprises the steps of carrying out a first treatment on the surface of the Otherwise, continuing to accelerate aging temperature T of subsequent corresponding sheet sampleThe aged sheet sample is subjected to elongation at break measurement until the life corresponding to the accelerated aging temperature T of the sheet sample is obtainedL T The method comprises the steps of carrying out a first treatment on the surface of the According to the steps 2 and 3, aging, breakdown, sampling, elongation at break measurement and judgment, the service lives of the cable insulating layers corresponding to all temperature values of the accelerated aging temperature T of the sheet sample are finally obtained; wherein the elongation at break is the ratio of the elongation after stretching to the length before stretching of the sheet sample, and how to measure the elongation at break of the cable insulation layer material belongs to the prior known technology for the person skilled in the art.
4. Service life of cable insulating layer obtained in last stepL T Fitting with the corresponding accelerated aging temperature T of the sheet sample according to the following formula:
Wherein:Lthe service life of the cable insulating layer is in hours;AandBis a temperature dependent coefficient;Tthe accelerated aging temperature of the sheet sample is K;
how to fit in this step on the basis of the measured data is common knowledge to the person skilled in the art;
step three, performing an accelerated aging test on the short cable sample;
1. determining the accelerated aging temperature of the short cable sample according to the aging experimental data of the sheet sampleT D Duration of ageingL D And accelerated aging voltage of short cable sampleU t ；
Wherein, the short cable sample accelerates the aging temperatureT D The accelerated aging temperature T of the sheet sample is the accelerated aging temperature T of the sheet sample during the accelerated aging test of the sheet sample; aging durationL D Service life of cable insulation layer corresponding to accelerated aging temperature T of sheet sampleL T The aging voltage is the voltage for the power frequency voltage test of the bypass flexible high-voltage power cable to be evaluatedU t ；
2. Short cable test sample determined according to the previous stepAccelerated aging temperatureT D Duration of ageingL D And accelerated aging voltage of short cable sampleU t Accelerated aging of short cable sample and accelerated aging temperature of short cable sample T D Still realized by a temperature control box, namely, the short cable sample is placed in the temperature control box, and the aging temperature of the short cable sample is acceleratedT D Applying a voltage for power frequency voltage test to the test boardU t Simultaneously carrying out aging timing, when the aging time reaches the aging temperatureT D Corresponding aging time periodL D When the aging is stopped, carrying out subsequent parameter measurement on the short cable sample after the aging; how to apply a voltage to a short cable sample in a temperature controlled box is readily accomplished by one skilled in the art.
3. Measuring the conductivity current of short cable samples after accelerated agingI D The method comprises the steps of carrying out a first treatment on the surface of the Applying a DC voltage to the aged short cable samples one by one, and measuring the conductance current passing through the grounding electrode of the short cable sampleI D The method comprises the steps of carrying out a first treatment on the surface of the Finally, the accelerated aging temperature of the short cable sample is obtainedT D Conductive current corresponding to each temperature valueI D The method comprises the steps of carrying out a first treatment on the surface of the It is common knowledge to a person skilled in the art how to measure the conductance current of a short cable sample in particular.
4. Conducting current of the short cable sample obtained in the step 2 and the step 3I D And the corresponding aging time lengthL D Fitting was performed according to the following formula:
Wherein:Lthe service life of the cable insulating layer is in hours;Cconstant coefficients greater than zero;Iis a conductive current, and the unit is A; nIs an ageing index;
determining an evaluation equation of the insulation residual life of the bypass flexible high-voltage power cable (namely, the duration of time that the bypass flexible high-voltage power cable can still be used continuously); the bypass flexible high-voltage power cable insulation residual life evaluation equation is obtained according to the formula (2) and the formula (3) as follows:
Wherein:Lthe service life of the cable insulating layer is in hours;AandBis a temperature dependent coefficient;Cconstant coefficients greater than zero;Iis a conductive current, and the unit is A;nis an ageing index;T s the temperature of a wire core is K when the bypass flexible high-voltage power cable operates;
wherein,,
(5)
Wherein:ρthe resistivity of the wire core in the standard state;ρ T is an insulating thermal coefficient in a standard state;ρ 0 is the thermal coefficient of the surrounding environment in a standard state;I s is the load current at run time;T a is ambient temperature;
step five, evaluating the insulation residual life of the bypass flexible high-voltage power cable in use; according to the bypass flexible high-voltage power cable insulation residual life evaluation equation obtained in the previous step, performing insulation residual life evaluation on the bypass flexible high-voltage power cable to be evaluated;
according to formulas (4) and (5), directly measuring the load current of the bypass flexible high-voltage power cable to be evaluated on the application site of the bypass flexible high-voltage power cable to be evaluated I s Conductive currentIAnd ambient temperatureT a The insulation residual life of the bypass flexible high-voltage power cable to be evaluated can be calculatedL，I.e. the remaining lifetime of the bypass flexible high voltage power cable to be evaluated.
In the step (I), when a sheet sample is prepared, a cable slicer is used for longitudinally sampling a cable insulating layer, and the sheet sample is obtained by flat cutting; when a short cable sample is prepared, a short cable with a certain length is cut, an insulating layer at one end of the short cable is stripped, an exposed wire core is a high-voltage wire terminal in an experiment, and the other end of the short cable is encapsulated by silicone rubber; winding a copper foil on the surface of the short cable insulating layer to form a grounding electrode and two protection electrodes positioned on two sides of the grounding electrode; the copper foil coverage width of the ground electrode is at least 10 times the copper foil coverage width of the guard electrode.
According to another aspect of the invention, in order to efficiently and accurately realize the bypass flexible high-voltage power cable insulation residual life assessment method, the invention also provides an experimental platform for bypass flexible high-voltage power cable insulation residual life assessment, which comprises an accelerated aging experimental platform and a measurement experimental platform;
the accelerated aging experiment table comprises an alternating-current high-voltage power supply, a temperature control box and a fixing component for fixing a high-voltage power cable sample; the fixed component is arranged in the temperature control box; the fixing assembly comprises a clamp for fixing the sheet-shaped sample and a placing frame for placing the short cable sample; the fixture comprises a lower aluminum plate and an upper aluminum plate which is fixed right above the lower aluminum plate through an insulating support, wherein the insulating support is a polyether-ether-ketone round bar, a plurality of round holes are uniformly distributed in the upper aluminum plate, an aluminum bar which can move up and down along the round holes and is in electrical contact with the upper aluminum plate is inserted into the round holes, and a brass electrode positioned between the upper aluminum plate and the lower aluminum plate is fixed at the bottom end of the aluminum bar; the placing rack is an insulating supporting rack; a high-voltage sleeve is fixed on the temperature control box, one end of the high-voltage sleeve is connected with a high-voltage output end of an alternating-current high-voltage power supply through a protection resistor, and the other end of the high-voltage sleeve is connected with an upper aluminum plate of the clamp and is connected with a short cable sample when the short cable sample is aged rapidly; grounding of the alternating-current high-voltage power supply is grounded; a grounding end is arranged in the temperature control box; the lower aluminum plate of the clamp is grounded through a grounding electrode;
The measuring experiment table comprises a direct-current power supply, a shielding box, a placing rack for placing a short cable sample and a bypass flexible high-voltage power cable to be evaluated, and an ammeter which is arranged outside the shielding box and used for measuring conductance current; the placement frame is arranged in the shielding box; the placing rack is an insulating supporting rack; a high-voltage sleeve is fixed on the shielding box, one end of the high-voltage sleeve is connected with a high-voltage output end of a direct-current power supply through a protection resistor, and the other end of the high-voltage sleeve is a measurement connecting end A connected with a short cable sample and a bypass flexible high-voltage power cable to be evaluated; the grounding end of the direct current power supply is grounded; the shielding box is internally provided with a protection grounding end B and a measurement grounding end C, the protection grounding end B is directly grounded, the measurement grounding end C is grounded through an ammeter, and the ammeter is connected with a protection switch in parallel.
Further, the brass electrode of the fixture is square, the side length is 30mm, and the thickness is 5mm.
Further, the aluminum bar is connected with the round hole of the upper aluminum plate by threads.
Further, the temperature control box and the shielding box adopt an electrothermal blowing drying box.
Further, the sheet-like test piece was square, 50mm in width and 0.5mm in thickness.
Further, the short cable test piece was 320mm long and the high voltage terminal thereof was 20mm long.
The accelerated aging test bed of the test platform is used for completing artificial accelerated aging of the sheet-shaped test sample and the short cable test sample; when the sheet sample is aged, fixing the sheet sample by using a clamp, and clamping the sheet sample between a brass electrode and a lower aluminum plate of the clamp; placing the clamp with the clamped sample into a temperature control box; the accelerated aging temperature T and the accelerated aging voltage of the sheet sample determined by the evaluation method of the inventionU a Time period of agingLThe accelerated aging test bed ages the sheet sample, and provides the sheet sample after aging according to the requirement for determining the relationship between the insulation life of the cable and the aging temperature after the evaluation method; when the aging of the short cable sample is realized, the short cable sample is placed on a placing rack in a temperature control box, a wire core of the short cable sample is connected with a high-voltage sleeve fixed on the temperature control box, and a grounding electrode and a protection electrode of the short cable sample are grounded through a grounding electrode arranged in the temperature control box; accelerated aging temperature of short cable sample determined by the evaluation method of the inventionT D Accelerated aging voltage of short cable sampleU t Time period of agingL D Aging the short cable sample by an accelerated aging test bed; determining the relationship between the insulation life of a cable and the conductance current for the evaluation method Short cable samples aged as required are provided.
The measuring experiment table of the experiment platform is used for measuring the conductance current of the short cable sample and the bypass flexible high-voltage power cable to be evaluated; when the conductance current of the short cable sample is measured, the short cable sample aged by the accelerated aging experiment table is placed on a placing frame in a shielding box, and a wire core of the short cable sample is connected with a measurement connecting end A of a high-voltage sleeve; the protective electrode is grounded through a protective grounding end B; the grounding electrode is connected with the ammeter through a measuring grounding end C. Then, applying direct-current voltage to the test sample, switching off the protection switch, and starting to measure the conductance current of the short cable test sample after accelerated aging by the ammeter to provide accurate conductance current measurement data for determining the relationship between the cable insulation life and the conductance current in the subsequent evaluation method; when the conductance current of the bypass flexible high-voltage power cable to be evaluated is measured, the bypass flexible high-voltage power cable to be evaluated is placed on a placing frame in a shielding box, and a conductor exposed out of the cable is connected with a measuring connection end A of a high-voltage sleeve, and the conductor at the other end is suspended; the cable shield is connected to the measurement ground C. Then, applying direct-current voltage to the bypass flexible high-voltage power cable to be evaluated, switching off the protection switch, and starting measurement by the ammeter to obtain the conductance current of the bypass flexible high-voltage power cable to be evaluated; and further obtaining the insulation residual life of the bypass flexible high-voltage power cable to be evaluated according to the insulation residual life evaluation equation of the bypass flexible high-voltage power cable.
According to the invention, through sampling and artificially accelerating aging of a brand new same type of cable of the bypass flexible high-voltage power cable to be evaluated, the relation between the insulation life of the cable and the aging temperature and the relation between the insulation life of the cable and the conductance current are gradually determined, and finally, the evaluation equation of the insulation residual life of the bypass flexible high-voltage power cable is obtained, so that before the bypass flexible high-voltage power cable to be evaluated is used on site, the residual life of the cable can be calculated by measuring the load current, the conductance current and the ambient temperature of the cable, the insulation state of the cable is mastered, hidden danger is avoided, the reliability of a power supply channel in the uninterrupted operation on site is ensured, and the bypass flexible high-voltage power cable has important engineering application value.
Drawings
FIG. 1 is a schematic diagram of the structure of an accelerated aging test bench according to the present invention;
FIG. 2 is a schematic structural view of the fixture in the accelerated aging test bench;
FIG. 3 is a top view of FIG. 2;
FIG. 4 is a state diagram of the rack when a short cable sample is placed;
FIG. 5 is a schematic diagram of the structure of a short cable sample;
fig. 6 is a schematic diagram of a measurement experiment table according to the present invention.
In the figure: 1-alternating-current high-voltage power supply, 2-protection resistor, 3-high-voltage sleeve, 4-temperature control box, 5-fixture, 6-sheet sample, 7-rack, 8-short cable sample, 9-direct-current power supply, 10-holding switch, 11-ammeter, 12-protection resistor, 13-high-voltage sleeve, 14-shielding box, 51-insulation pillar, 52-brass electrode, 53-aluminum bar, 54-upper aluminum plate, 55-lower aluminum plate, 82-grounding electrode, 81-protection electrode, 83-protection electrode and 84-wire core.
Detailed Description
The technical scheme of the invention is further described below with reference to the accompanying drawings.
In the embodiment, the method and the experimental platform disclosed by the invention are adopted to evaluate the service life of the insulation of the 8.7/15kV bypass flexible high-voltage power cable, wherein the insulation of the cable is ethylene propylene rubber.
The specific method comprises the following steps:
preparing cable samples, including preparing a sheet-shaped sample 6 and a short cable sample 8; taking a brand new 8.7/15kV bypass flexible high-voltage power cable, stripping an outer sheath and a shielding layer of the bypass flexible high-voltage power cable, and reserving a wire core and an insulating layer;
1. preparing a sheet sample 6, longitudinally sampling a cable insulating layer by using a cable slicer, and flatly cutting to obtain a square sheet sample with the width of 50mm and the thickness of 0.5 mm; the preparation quantity of the sheet-shaped samples meets the requirement of subsequent experiments;
2. preparing a short cable sample 8, as shown in fig. 5, cutting a short cable with the length of 320mm, stripping an insulating layer with the length of 20mm at one end of the short cable, wherein an exposed wire core 84 is a high-voltage wire terminal in an experiment, and the other end of the short cable is encapsulated by silicone rubber; forming a grounding electrode 82 and two protection electrodes 81 and 83 positioned on two sides of the grounding electrode 82 by winding copper foil on the surface of the short cable insulating layer; in specific implementation, the copper foil coverage width of the grounding electrode 82 is 200mm, the copper foil coverage width of the protecting electrodes 81 and 83 is 5mm, the ratio of the copper foil coverage width of the grounding electrode 82 to the copper foil coverage width of the protecting electrodes 81 and 83 is far greater than 10, the thicknesses of the grounding electrode 82 and the protecting electrodes 81 and 83 are 0.1mm, the distance between the protecting electrodes 81 and 83 and the grounding electrode 82 is 3mm, and the distance between the two end sections of the short cable sample 8 is 30mm; before the copper foil is wound, absolute ethyl alcohol is used for cleaning the insulating surface of the cable, and impurities are removed so as not to influence the subsequent experimental result of the short cable sample; the number of the short cable samples 8 should meet the requirement of the subsequent experiment;
Secondly, performing an accelerated aging test on the sheet sample;
1. determining the accelerated aging temperature T and the accelerated aging voltage of the sheet sampleU a ；
The thermal exposure temperature T0 of ethylene propylene rubber of the 8.7/15kV bypass flexible high-voltage power cable insulating layer material is 90 ℃, and the thermal decomposition starting temperature is 340 ℃, so that the temperature increase delta T takes 20 ℃ to obtain four temperature values of the accelerated aging temperature T of the sheet sample: 110 ℃, 130 ℃, 150 ℃ and 170 ℃;
8.7/15kV bypass flexible high-voltage power cable voltage for power frequency voltage testU t 35kV, the thickness of the insulating layer is 5mm, and the sectional area is 95mm 2 Inner radius of insulationR 1 About 5.5mm, outer radiusR 2 About 10.5mm; according to the accelerated aging voltage of the sheet sampleU a Is the voltage for power frequency voltage testU t Maximum electric field strength borne by short cable sample under actionE max Thickness of sheet sampledThe product of (a), i.e
Wherein:R 1 is the inner radius of the insulating layer of the cable,R 2 is an insulating layer of a cableIs a radius of the outer surface of the steel sheet;
obtaining the accelerated aging voltage of the sheet sampleU a 4.9kV;
2. the accelerated aging temperature T and the accelerated aging voltage of the sheet sample determined according to the previous stepU a The method comprises the steps of carrying out accelerated aging on a sheet-shaped sample 6, wherein the step is completed by an accelerated aging experiment table of the experiment platform, and as shown in fig. 1, the accelerated aging experiment table comprises an alternating-current high-voltage power supply 1, a temperature control box 4 and a fixing component for fixing a high-voltage power cable sample; the fixed component is arranged in the temperature control box 4; the fixing assembly comprises a clamp 5 for fixing a sheet-shaped sample 6 and a placing frame 7 for placing a short cable sample 8; as shown in fig. 2 and 3, the fixture 5 comprises a lower aluminum plate 55 and an upper aluminum plate 54 fixed right above the lower aluminum plate 55 through an insulating support column 51, 9 round holes are uniformly distributed on the upper aluminum plate 54, aluminum bars 53 capable of moving up and down along the round holes and electrically contacting the upper aluminum plate 54 are respectively inserted into each round hole, and brass electrodes 52 positioned between the upper aluminum plate 54 and the lower aluminum plate 55 are fixed at the bottom ends of the aluminum bars 53; the placing frame 7 is an insulating supporting frame; a high-voltage sleeve 3 is fixed on the temperature control box 4, one end of the high-voltage sleeve 3 is connected with a high-voltage output end of the alternating-current high-voltage power supply 1 through a protection resistor 2, and the other end of the high-voltage sleeve 3 is connected with an upper aluminum plate 54 of the clamp 5 and is connected with the short cable sample 8 when the short cable sample 8 is aged at an accelerated speed; the grounding end of the alternating-current high-voltage power supply 1 is grounded; a grounding end is arranged in the temperature control box 4; the lower aluminum plate 55 of the jig 5 is grounded via a ground.
The alternating-current high-voltage power supply 1 provides sample accelerated aging voltage, the output voltage range is 0-100 kV, the frequency is 50Hz, and the current is not less than 0.5mA; the protection resistor 2 is a water resistor of 100kV, and the resistance value is 10kΩ; the high-voltage sleeve 3 is a high-voltage sleeve of a 100kV porcelain bottle; the temperature control box 4 adopts the existing electrothermal blowing drying box on the market and is used for controlling the ageing temperature of the sheet-shaped sample and the short cable sample, and the temperature adjustment range is from room temperature to 250 ℃.
In the concrete implementation, the brass electrode 52 of the fixture 5 is square, the side length is 30mm, and the thickness is 5mm; the insulating support column 51 adopts a polyether-ether-ketone round rod which is a novel high-molecular polymer material and has the characteristics of high temperature resistance and corrosion resistance; in addition, the aluminum bar 53 is connected with the round hole of the upper aluminum plate 54 by adopting threads, and the sheet sample 6 is clamped between the brass electrode 52 and the lower aluminum plate 54 by adjusting the screwing depth of the aluminum bar 53;
setting a basic time length L0 for accelerated aging before aging, wherein the value is 100 hours, and the subsequent aging time length L is an integer multiple of the basic time length L0; fixing 9 sheet-shaped samples by using a clamp 5, namely respectively clamping the 9 sheet-shaped samples between 9 brass electrodes 52 and a lower aluminum plate 55 of the clamp 5; simultaneously, 9 sheet-like samples were encoded: s01, S02, S03, S04, S05, S06, S07, S08, S09; placing the clamp 5 with the clamped sample into an electrothermal blowing drying oven; the temperature of the electrothermal blowing drying oven is regulated to be a first temperature value of the accelerated aging temperature T of the sheet sample: 110 ℃; after preheating for 30 minutes (under the condition of no voltage application, even if the sheet sample is preheated at high temperature in the temperature control box, the aging speed is very slow, and considering that the preheating time is not long and the influence caused by the preheating step can be ignored), the alternating current high-voltage power supply 1 is turned on, and the output voltage is regulated to be the accelerated aging voltage of the sheet sample U a Turning on a high-voltage output button of the alternating-current high-voltage power supply 1, applying voltage to 9 sheet-shaped samples 6, and starting timing; after aging for 100 hours, taking out the S01 sheet sample for subsequent experiments, and continuing aging the rest sheet samples; after aging for 200 hours, taking out the S02 sheet sample for subsequent experiments, and continuing aging of the rest sheet samples; after aging for 300 hours, taking out the S03 sheet sample for subsequent experiments, and continuing aging of the rest sheet samples; until the aging of the sheet-like sample at that temperature was stopped according to the results of the subsequent experiments. A new sheet specimen is placed while each sheet specimen is taken out, and the aging time thereof is re-labeled and recorded, for example: the new sample S11 replaces the sample S01, and the new sample S12 replaces the sample S02. If any sheet sample breaks down in the accelerated aging process of the sheet sample at the accelerated aging temperature Ttemperature value of 110 ℃, stopping timing, stopping aging the sheet sample at the temperature, and recording that the actual aging time is the service life of the cable insulation layer at the accelerated aging temperature Ttemperature value of 110 DEG of the sheet sampleL 110 ；Meanwhile, the flaky sample in the temperature control box is replaced integrally, and the flaky sample is subjected to accelerated aging at the temperature value of 130 ℃ below the accelerated aging temperature T of the flaky sample;
3. And (3) measuring elongation at break of the sheet-shaped sample obtained in the aging process without sample breakdown in the last step, and taking 3 dumbbell-shaped samples on the S01 sheet-shaped sample, measuring the elongation at break and taking an average value of 3 times of measurement. If the average value of the elongation at break obtained by measurement is less than or equal to half of the elongation at break of the unaged sheet sample, stopping the aging process of the sheet sample at the accelerated aging temperature Ttemperature value of 110 ℃, and recording the service life of the cable insulation layer at 110 DEG CL 110 100 hours; and otherwise, continuously measuring elongation at break of the sheet-shaped sample aged at the temperature of 110 ℃ of the accelerated aging temperature T of the subsequent sheet-shaped sample, taking 3 dumbbell-shaped samples from the S02 sheet-shaped sample aged for 200 hours, measuring the elongation at break of the dumbbell-shaped sample, and taking the average value of 3 times of measurement. If the average value of the elongation at break obtained by measurement is less than or equal to half of the elongation at break of the unaged sheet sample, stopping the aging process of the sheet sample at the accelerated aging temperature Ttemperature value of 110 ℃, and recording the service life of the cable insulation layer at 110 DEG CL 110 200 hours; otherwise, continuously measuring elongation at break of the sheet sample aged at 110 ℃ of the accelerated aging temperature Ttemperature value of the subsequent sheet sample until the service life of the cable insulating layer at 110 ℃ of the accelerated aging temperature Ttemperature value of the sheet sample is obtained L 110 。
Aging according to steps 2 and 3, determining whether breakdown, sampling, measuring elongation at break and judging, and finally obtaining the service lives of the cable insulating layers corresponding to the other three temperature values 130 ℃, 150 ℃ and 170 ℃ of the accelerated aging temperature T of the sheet sampleL 130 、L 150 AndL 170 the unit is hours.
In the specific practical process, the breaking elongation of the sheet-shaped sample which is broken down is not less than or equal to half of the breaking elongation of the unaged sheet-shaped sample in the aging process, namely, the breaking elongation of the sheet-shaped sample in the aging process is broken down before half of the breaking elongation of the unaged sheet-shaped sample is reached, and the breaking down is easy to occur when the aging temperature is close to the thermal decomposition starting temperature; but for an aging process with an aging temperature close to the thermal exposure temperature T0 of the insulating material,the sheet sample is not easy to break down, and the time for ending the aging process is required to be judged according to the elongation at break; the measured cable insulation lifetime is zero and is complete. In this example, the life data of the cable insulation layer corresponding to the four temperature values 110 ℃, 130 ℃, 150 ℃ and 170 ℃ of the 8.7/15kV bypass flexible high-voltage power cable and the accelerated aging temperature T of the sheet sample are actually measured as follows:L 110 for a time of =3400 hours,L 130 the time period of time is =1000 hours,L 150 =173 hours sum L 170 =66 hours;
4. service life of cable insulating layer obtained in last stepL T Fitting with the corresponding accelerated aging temperature T of the sheet sample according to the following formula:
Wherein:Lthe service life of the cable insulating layer is in hours;AandBis a temperature dependent coefficient;Tthe accelerated aging temperature of the sheet sample is K;
in specific implementation, the service life of the cable insulation layer of the 8.7/15kV bypass flexible high-voltage power cableLAnd aging temperatureTThe relation of (2) is as follows:
Wherein:Lthe service life of the cable insulating layer is in hours;Tthe ageing temperature is given in K;
thirdly, performing an accelerated aging test on the short cable sample;
1. determining the accelerated aging temperature of the short cable sample according to the aging experimental data of the sheet sampleT D Duration of ageingL D And accelerated aging voltage of short cable sampleU t ；
Wherein, the short cable sample accelerates the aging temperatureT D Sheet test for accelerated aging test of sheet samplesSample accelerated aging temperature T, namely 110 ℃, 130 ℃, 150 ℃ and 170 ℃; aging durationL D Service life of cable insulation layer corresponding to accelerated aging temperature T of sheet sampleL 110 、L 130 、L 150 AndL 170 accelerated aging voltage of short cable sampleU t 35kV is used for the power frequency voltage test of the 8.7/15kV bypass flexible high-voltage power cable;
2. Accelerated aging temperature of short cable sample determined according to the previous stepT D Duration of ageingL D And accelerated aging voltage of short cable sampleU t The method comprises the steps of carrying out accelerated aging on short cable samples, wherein the step is still completed by an accelerated aging experiment table of the experiment platform, as shown in fig. 4, three short cable samples 8 are placed on a placing frame 7 and are placed in a temperature control box 4 together, the placing frame 7 is an insulating supporting frame, and in the concrete implementation, the insulating supporting frame adopts a bakelite plate box body to realize the function of supporting and placing the short cable samples and cables to be evaluated; the wire cores 84 of the three short cable samples 8 are connected with the high-voltage sleeve 3 fixed on the temperature control box 4, and the grounding electrode 82 and the protection electrodes 81 and 83 of the short cable samples 8 are grounded through the grounding electrodes arranged in the temperature control box 4; after the temperature of the temperature control box 4 is regulated to 110 ℃ and preheated for 30 minutes, the alternating-current high-voltage power supply 1 is turned on, the output voltage of the alternating-current high-voltage power supply 1 is regulated to be 35kV for power frequency voltage test of the bypass flexible high-voltage power cable with the voltage of 8.7/15kV, a high-voltage output button of the alternating-current high-voltage power supply 1 is turned on, voltage is applied to 3 short cable samples, timing is started, and the aging time length is prolongedL D Reach toL 110 Then, taking out three short cable samples 8 and encoding for subsequent parameter measurement; three short cable samples 8 are put in again, the temperature of the temperature control box 4 is regulated to 130 ℃, after the temperature control box is preheated for 30 minutes, an alternating current high-voltage power supply 1 is turned on, the output voltage of the alternating current high-voltage power supply 1 is regulated to be 35kV for power frequency voltage test of an 8.7/15kV bypass flexible high-voltage power cable, a high-voltage output button of the alternating current high-voltage power supply 1 is turned on, voltage is applied to 3 short cable samples, timing is started, and the aging time length is long L D Reach toL 130 Then, taking out three short cable samples 8 and encoding for subsequent parameter measurement; continuing to take according to the above processObtaining the accelerated aging temperature 150 ℃ and aging time of the short cable sampleL 150 Three short cable samples 8 aged under the condition of short cable sample accelerated aging voltage of 35kV, and short cable sample accelerated aging temperature of 170 ℃ and aging time periodL 170 Three short cable samples 8 aged under the condition of the accelerated aging voltage of 35 kV; a total of 12 aged short cable samples;
3. measuring the conductivity current of short cable samples after accelerated agingI D The method comprises the steps of carrying out a first treatment on the surface of the As shown in fig. 6, this step is completed by a measurement experiment table of the experiment platform of the present invention, which comprises a direct current power supply 9, a shielding case 14, a placement frame for placing a short cable sample and a bypass flexible high-voltage power cable to be evaluated, and an ammeter 11 arranged outside the shielding case for measuring a conductance current; the placement rack is arranged in the shielding box 14; the placing rack is an insulating supporting rack; a high-voltage sleeve 13 is fixed on the shielding box 14, one end of the high-voltage sleeve 13 is connected with the high-voltage output end of the direct-current power supply 9 through a protection resistor 12, and the other end is a measurement connecting end A connected with a short cable sample and a bypass flexible high-voltage power cable to be evaluated; the grounding end of the direct current power supply 9 is grounded; the shielding box 14 is internally provided with a protection grounding end B and a measurement grounding end C, the protection grounding end B is directly grounded, the measurement grounding end C is grounded through an ammeter 11, and the ammeter 11 is connected with a protection switch 10 in parallel. Wherein, the insulating support frame adopts the bakelite board box to realize supporting the function of placing short cable sample and waiting to evaluate the cable.
In the specific implementation, the output voltage of the direct-current power supply 9 is +5kV, and the current is not lower than 20mA; connecting the wire core 84 of the short cable sample 8 subjected to accelerated aging with the measurement connecting end A of the high-voltage sleeve 13; the protective electrodes 81 and 83 are grounded through a protective grounding end B; the ground electrode 82 is connected to the measurement ground C; then, keeping the protection switch 10 in a closed state, opening a switch of the direct current power supply 9, and outputting +5kV direct current voltage; after 10s, the protection switch 10 is disconnected, and the ammeter 11 starts to measure the conductance current of the short cable sample after accelerated aging and counts time; after 10 minutes, the current value displayed by the ammeter is recorded, the recording interval is 5 seconds, 10 points are recorded, and then the average value of the current values of the 10 points is taken as the sample of the short cable after agingIs a conducting current of (a); measuring the conduction current of 12 aged short cable samples one by one, and accelerating the aging temperature of the same short cable sampleT D The conductivity current of the 3 short cable samples aged below was averaged and recorded as the accelerated aging temperature with the short cable samplesT D Corresponding electric conduction currentI D Finally, the accelerated aging temperature of the short cable sample is obtainedT D Conduction current corresponding to four temperature valuesI 110 、I 130 、I 150 AndI 170 ；
in specific implementation, the conductance current value of the short cable sample after the aging of the 8.7/15kV bypass flexible high-voltage power cable is actually measured at +5kV is as follows: I 110 =0.27nA、I 130 =3.26nA、I 150 =1.04mA、I 170 =7.17mA；
4. Conducting current of the short cable sample obtained in the step 2 and the step 3I D And the corresponding aging time lengthL D Fitting was performed according to the following formula:
Wherein:Lthe service life of the cable insulating layer is in hours;Cconstant coefficients greater than zero;Iis a conductive current, and the unit is A;nis an ageing index;
in specific implementation, the service life of the cable insulation of the 8.7/15kV bypass flexible high-voltage power cableLAnd electric conduction currentIThe relation of (2) is as follows:
Wherein:Lthe service life of the cable insulating layer is in hours;Iis a conductive current, and the unit is A;
fourthly, determining an evaluation equation of the insulation residual life of the bypass flexible high-voltage power cable; the bypass flexible high-voltage power cable insulation residual life evaluation equation is obtained according to the formula (2) and the formula (3) as follows:
Wherein:Lthe insulation life of the cable is in hours;AandBis a temperature dependent coefficient;Cconstant coefficients greater than zero;Iis a conductive current, and the unit is A;nis an ageing index;T s the temperature of a wire core is K when the bypass flexible high-voltage power cable operates;
wherein,,
(5)
Wherein:ρthe resistivity of the wire core in the standard state;ρ T is an insulating thermal coefficient in a standard state; ρ 0 Is the thermal coefficient of the surrounding environment in a standard state;I s load current when the flexible high-voltage power cable is bypassed;T a is ambient temperature;
in specific implementation, the relationship between the conduction current and the service life of the 8.7/15kV bypass flexible high-voltage power cable can be obtained according to the formula (6) and the formula (8) as follows:
Wherein:T s the temperature of a wire core is K when the bypass flexible high-voltage power cable operates;Iis a conductive current, and the unit is A;
fifthly, evaluating the insulation residual life of the bypass flexible high-voltage power cable in use; according to the bypass flexible high-voltage power cable insulation residual life evaluation equation obtained in the previous step, performing insulation residual life evaluation on the bypass flexible high-voltage power cable to be evaluated;
according to formulas (4) and (5), directly measuring the load current of the bypass flexible high-voltage power cable to be evaluated on the application site of the bypass flexible high-voltage power cable to be evaluatedI s Conductive currentIAnd ambient temperatureT a The insulation residual life of the bypass flexible high-voltage power cable to be evaluated can be calculatedL，I.e. the remaining lifetime of the bypass flexible high voltage power cable to be evaluated.
Wherein the conductance current of the bypass flexible high-voltage power cable to be evaluated IWhen the measuring experiment table of the experiment platform is adopted for measurement, and referring to fig. 6, in the concrete implementation, the conductor exposed out of the 8.7/15kV bypass flexible high-voltage power cable to be evaluated is connected with the measuring connection end A of the high-voltage sleeve 13, and the conductor at the other end is suspended; the cable shielding layer of the 8.7/15kV bypass flexible high-voltage power cable to be evaluated is connected with the measurement grounding end C; then, keeping the protection switch 10 in a closed state, opening a switch of the direct current power supply 9, and outputting +5kV direct current voltage; after 10s, the protection switch 10 is opened, and the ammeter 11 starts to measure the conductance current of the bypass flexible high-voltage power cable to be evaluated and counts time; after 10 minutes, starting to record the current value displayed by the ammeter, recording 10 points at intervals of 5 seconds, and taking the average value of the current values of the 10 points to obtain the conductance current 1.2nA of the 8.7/15kV bypass flexible high-voltage power cable to be evaluated;
operating voltage of 8.7/15kV bypass flexible high-voltage power cable to be evaluated in application fieldU 0 For 8.7kV, the thermal resistivity of the insulating ethylene propylene rubberρ T Resistivity of the cable core of 4TΩ & mρ1.7X10 -4 Omega-m, thermal coefficient of thermal resistance of surrounding environmentρ 0 1.01T Ω & m, run-time currentI s 180A, the operating environment temperature is 30 ℃, and the core temperature of the 8.7/15kV bypass flexible high-voltage power cable to be evaluated in operation can be calculated according to the formula (5) is 
。
Electrical conduction of 8.7/15kV bypass flexible high-voltage power cable to be evaluatedFlow ofIAnd core temperatureT s Finally, the residual service life of the 8.7/15kV bypass flexible high-voltage power cable at the load current of 180A and the running environment temperature of 30 ℃ can be obtained by a formula (7)
Hours.
In addition, in the specific implementation, the temperature control box 4 and the shielding box 14 can be realized by adopting the same electrothermal blowing drying box, namely, when the ageing experiment is carried out, the electrothermal blowing drying box is used as the temperature control box, and when the measurement experiment is carried out, the electrothermal blowing drying box is used as the shielding box.
Claims (8)
1. The bypass flexible high-voltage power cable insulation residual life assessment method is characterized by comprising the following steps of:
step one, preparing cable samples, including preparing sheet samples and short cable samples; taking a brand new same type of cable of the bypass flexible high-voltage power cable to be evaluated, stripping an outer sheath and a shielding layer of the cable, and reserving a wire core and an insulating layer to respectively prepare the sheet-shaped sample and the short cable sample;
step two, performing an accelerated aging test on the sheet sample;
1. determining the accelerated aging temperature T and the accelerated aging voltage of the sheet sampleU a ；
The accelerated aging temperature T of the sheet sample is based on the heat exposure temperature T0 of the cable insulation layer material, at least four temperature values are obtained by increasing the temperature increase delta T, namely T0+Delta T, T0 +2Delta T, T +3Delta T, T0 +4DeltaT, wherein the temperature increase delta T is less than or equal to 30 ℃ and the accelerated aging temperature T of the sheet sample is less than or equal to 50% of the thermal decomposition initial temperature of the cable insulation layer material;
Accelerated aging voltage of sheet sampleU a Voltage for power frequency voltage test of bypass flexible high-voltage power cable to be evaluatedU t Maximum electric field strength borne by short cable sample under actionE max Thickness of sheet sampledThe product of (a), i.e
Wherein:R 1 is the inner radius of the insulating layer of the cable,R 2 is the outer radius of the cable insulation layer;
2. the accelerated aging temperature T and the accelerated aging voltage of the sheet sample determined according to the previous stepU a The method comprises the steps of performing accelerated aging on a sheet sample, setting basic time length L0 of accelerated aging before aging, enabling an accelerated aging temperature T of the sheet sample to be realized by a temperature control box, placing a plurality of sheet samples in the temperature control box, and applying an accelerated aging voltage of the sheet sample to the sheet samples in the temperature control box at the accelerated aging temperature T of the sheet sampleU a Timing to reach the ageing time length L, taking out the corresponding sheet sample for subsequent experiments, and continuing ageing of the rest sheet samples; the aging time length L is an integer multiple of the basic time length L0; before the accelerated aging of the sheet sample, the temperature control box needs to be preheated in advance to reach the accelerated aging temperature T of the sheet sample; in order to meet the requirement of the subsequent experiment, taking out the aged sheet sample each time, simultaneously putting a new sheet sample, and re-marking and recording the ageing time; if the sheet sample breaks down in the accelerated aging process, short circuit can be caused, current is increased, overcurrent protection of the alternating-current high-voltage power supply automatically cuts off the power supply, timing is stopped, the aging of the sheet sample at the temperature is stopped, and the actual aging time length is recorded as the service life of the cable insulation layer at the accelerated aging temperature T of the corresponding sheet sample L T The method comprises the steps of carrying out a first treatment on the surface of the Meanwhile, the flaky sample in the temperature control box is replaced integrally, and the flaky sample with a temperature value below the flaky sample accelerated aging temperature T is subjected to accelerated aging;
3. measuring elongation at break of the sheet sample obtained in the aging process without sample breakdown in the last step, stopping the aging process of the sheet sample at the corresponding sheet sample accelerated aging temperature T if the measured elongation at break is less than or equal to half of the elongation at break of the unaged sheet sample, and recording that the aging time L of the sheet sample is the cable insulation layer at the corresponding sheet sample accelerated aging temperature TLife spanL T The method comprises the steps of carrying out a first treatment on the surface of the Otherwise, continuously measuring the elongation at break of the sheet sample aged at the subsequent corresponding accelerated aging temperature T until the service life corresponding to the accelerated aging temperature T of the sheet sample is obtainedL T The method comprises the steps of carrying out a first treatment on the surface of the According to the steps 2 and 3, aging, breakdown, sampling, elongation at break measurement and judgment, the service lives of the cable insulating layers corresponding to all temperature values of the accelerated aging temperature T of the sheet sample are finally obtained;
4. service life of cable insulating layer obtained in last stepL T Fitting with the corresponding accelerated aging temperature T of the sheet sample according to the following formula:
Wherein:Lthe service life of the cable insulating layer is in hours; AAndBis a temperature dependent coefficient;Tthe accelerated aging temperature of the sheet sample is K;
step three, performing an accelerated aging test on the short cable sample;
1. determining the accelerated aging temperature of the short cable sample according to the aging experimental data of the sheet sampleT D Duration of ageingL D And accelerated aging voltage of short cable sampleU t ；
Wherein, the short cable sample accelerates the aging temperatureT D The accelerated aging temperature T of the sheet sample is the accelerated aging temperature T of the sheet sample during the accelerated aging test of the sheet sample; aging durationL D Service life of cable insulation layer corresponding to accelerated aging temperature T of sheet sampleL T The aging voltage is the voltage for the power frequency voltage test of the bypass flexible high-voltage power cable to be evaluatedU t ；
2. Accelerated aging temperature of short cable sample determined according to the previous stepT D Duration of ageingL D And accelerated aging voltage of short cable sampleU t Accelerated aging of short cable sample and accelerated aging temperature of short cable sampleT D Still by control by temperature change caseThe realization is that the short cable sample is placed in a temperature control box, and the aging temperature of the short cable sample is acceleratedT D Applying a voltage for power frequency voltage test to the test boardU t Simultaneously carrying out aging timing, when the aging time reaches the aging temperatureT D Corresponding aging time periodL D When the aging is stopped, carrying out subsequent parameter measurement on the short cable sample after the aging;
3. Measuring the conductivity current of short cable samples after accelerated agingI D The method comprises the steps of carrying out a first treatment on the surface of the Applying a DC voltage to the aged short cable samples one by one, and measuring the conductance current passing through the grounding electrode of the short cable sampleI D The method comprises the steps of carrying out a first treatment on the surface of the Finally, the accelerated aging temperature of the short cable sample is obtainedT D Conductive current corresponding to each temperature valueI D ；
4. Conducting current of the short cable sample obtained in the step 2 and the step 3I D And the corresponding aging time lengthL D Fitting was performed according to the following formula:
Wherein:Lthe service life of the cable insulating layer is in hours;Cconstant coefficients greater than zero;Iis a conductive current, and the unit is A;nis an ageing index;
determining an evaluation equation of the insulation residual life of the bypass flexible high-voltage power cable; the bypass flexible high-voltage power cable insulation residual life evaluation equation is obtained according to the formula (2) and the formula (3) as follows:
Wherein:Lthe service life of the cable insulating layer is in hours;AandBis a temperature dependent coefficient;Cconstant coefficients greater than zero;Iis a conductive current, the unit is A；nIs an ageing index;T s the temperature of a wire core is K when the bypass flexible high-voltage power cable operates;
wherein,,
(5)
Wherein:ρthe resistivity of the wire core in the standard state; ρ T Is an insulating thermal coefficient in a standard state;ρ 0 is the thermal coefficient of the surrounding environment in a standard state;I s is the load current at run time;T a is ambient temperature;
step five, evaluating the insulation residual life of the bypass flexible high-voltage power cable in use; according to the bypass flexible high-voltage power cable insulation residual life evaluation equation obtained in the previous step, performing insulation residual life evaluation on the bypass flexible high-voltage power cable to be evaluated;
according to formulas (4) and (5), directly measuring the load current of the bypass flexible high-voltage power cable to be evaluated on the application site of the bypass flexible high-voltage power cable to be evaluatedI s Conductive currentIAnd ambient temperatureT a The insulation residual life of the bypass flexible high-voltage power cable to be evaluated can be calculatedL，I.e. the remaining lifetime of the bypass flexible high voltage power cable to be evaluated.
2. The bypass flexible high voltage power cable insulation remaining life assessment method according to claim 1, wherein: in the first step, when preparing a sheet sample, using a cable slicer to longitudinally sample a cable insulating layer, and performing flat cutting to obtain the sheet sample; when a short cable sample is prepared, a short cable with a certain length is cut, an insulating layer at one end of the short cable is stripped, an exposed wire core is a high-voltage wire terminal in an experiment, and the other end of the short cable is encapsulated by silicone rubber; winding a copper foil on the surface of the short cable insulating layer to form a grounding electrode and two protection electrodes positioned on two sides of the grounding electrode; the copper foil coverage width of the ground electrode is at least 10 times the copper foil coverage width of the guard electrode.
3. An experimental platform for the bypass flexible high voltage power cable insulation remaining life assessment method according to claim 1 or 2, characterized in that: the device comprises an accelerated aging test bed and a measurement test bed;
the accelerated aging experiment table comprises an alternating-current high-voltage power supply (1), a temperature control box (4) and a fixing component for fixing a high-voltage power cable sample; the fixed component is arranged in the temperature control box (4); the fixing assembly comprises a clamp (5) for fixing the sheet-shaped sample (6) and a placing frame (7) for placing the short cable sample; the fixture (5) comprises a lower aluminum plate (55) which is grounded and an upper aluminum plate (54) which is fixed right above the lower aluminum plate (55) through an insulating support column (51), wherein the insulating support column (51) adopts a polyether-ether-ketone round bar, a plurality of round holes are uniformly distributed in the upper aluminum plate (54), an aluminum bar (53) which can move up and down along the round holes and is in electrical contact with the upper aluminum plate (54) is inserted into the round holes, and a brass electrode (52) positioned between the upper aluminum plate (54) and the lower aluminum plate (55) is fixed at the bottom end of the aluminum bar (53); the placing rack (7) is an insulating supporting rack; a high-voltage sleeve (3) is fixed on the temperature control box (4), one end of the high-voltage sleeve (3) is connected with the high-voltage output end of the alternating-current high-voltage power supply (1) through a protection resistor (2), and the other end of the high-voltage sleeve is connected with an upper aluminum plate (54) of the clamp (5) and is connected with a short cable sample (8) when the short cable sample is aged at an accelerated speed; the grounding end of the alternating-current high-voltage power supply (1) is grounded; a grounding end is arranged in the temperature control box; the lower aluminum plate (55) of the clamp (5) is grounded through a grounding terminal;
The measuring experiment table comprises a direct-current power supply (9), a shielding box (14), a placing rack for placing short cable samples and bypass flexible high-voltage power cables to be evaluated, and an ammeter (11) arranged outside the shielding box and used for measuring conductance current; the placement frame is arranged in the shielding box (14); a high-voltage sleeve (13) is fixed on the shielding box (14), one end of the high-voltage sleeve (13) is connected with the high-voltage output end of the direct-current power supply (9) through a protection resistor (12), and the other end of the high-voltage sleeve is a measurement connecting end A connected with a short cable sample and a bypass flexible high-voltage power cable to be evaluated; the grounding end of the direct current power supply (9) is grounded; the shielding box (14) is internally provided with a protection grounding end B and a measurement grounding end C, the protection grounding end B is directly grounded, the measurement grounding end C is grounded through an ammeter (11), and the ammeter (11) is connected with a protection switch (10) in parallel.
4. An experimental platform according to claim 3, characterized in that: the brass electrode (52) of the fixture (5) is square, has a side length of 30mm and a thickness of 5mm.
5. The assay platform of claim 3 or 4, wherein: the aluminum bar (53) is connected with the round hole of the upper aluminum plate (54) by screw threads.
6. The assay platform of claim 5, wherein: the temperature control box (4) and the shielding box (14) adopt electrothermal blowing drying boxes.
7. The assay platform of claim 3 or 6, wherein: the sheet sample was square, 50mm wide and 0.5mm thick.
8. The assay platform of claim 7, wherein: the short cable sample is 320mm long and the high voltage cable terminal is 20mm long.
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