CN111736042A - XLPE cable degassing state evaluation method based on insulation resistance - Google Patents

XLPE cable degassing state evaluation method based on insulation resistance Download PDF

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Publication number
CN111736042A
CN111736042A CN202010570412.4A CN202010570412A CN111736042A CN 111736042 A CN111736042 A CN 111736042A CN 202010570412 A CN202010570412 A CN 202010570412A CN 111736042 A CN111736042 A CN 111736042A
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CN
China
Prior art keywords
degassing
cable
insulation resistance
insulation
xlpe cable
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Pending
Application number
CN202010570412.4A
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Chinese (zh)
Inventor
钟力生
李飞
陶贺香
李文鹏
王聪
陈新
张翀
李震宇
于钦学
高景晖
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State Grid Corp of China SGCC
State Grid Zhejiang Electric Power Co Ltd
Xian Jiaotong University
Global Energy Interconnection Research Institute
Original Assignee
State Grid Corp of China SGCC
State Grid Zhejiang Electric Power Co Ltd
Xian Jiaotong University
Global Energy Interconnection Research Institute
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Application filed by State Grid Corp of China SGCC, State Grid Zhejiang Electric Power Co Ltd, Xian Jiaotong University, Global Energy Interconnection Research Institute filed Critical State Grid Corp of China SGCC
Priority to CN202010570412.4A priority Critical patent/CN111736042A/en
Publication of CN111736042A publication Critical patent/CN111736042A/en
Pending legal-status Critical Current

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    • G—PHYSICS
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters

Abstract

The invention discloses an XLPE cable degassing state evaluation method based on insulation resistance, which comprises the following steps: measuring the insulation resistance value of the XLPE cable in the degassing process on line; and judging whether the XLPE cable reaches the degassing end point according to the online measurement result of the insulation resistance value. The disclosure also discloses an XLPE cable degassing state evaluation system based on the insulation resistance. According to the method, the degassing condition of the tested cable can be truly reflected through the online measurement of the insulation resistance, the change of the insulation state inside the XLPE cable can be timely found and detected, and the degassing terminal point can be judged according to the existing measurement data.

Description

XLPE cable degassing state evaluation method based on insulation resistance
Technical Field
The disclosure relates to an evaluation method for a degassing state of an XLPE cable, in particular to an evaluation method for a degassing state of an XLPE cable based on insulation resistance.
Background
Crosslinked polyethylene (XLPE) has found wide application in ac and dc power cables due to its excellent electrical, thermal and mechanical properties. XLPE is obtained by crosslinking and modifying Polyethylene (PE), and currently, XLPE cables are widely produced by a peroxide crosslinking mode by using dicumyl peroxide (DCP) as a crosslinking agent. In the thermal decomposition process of DCP, a plurality of crosslinking byproducts such as cumyl alcohol, acetophenone, styrene, methane, water and the like can be generated, the performance of XLPE is affected, and the operation safety of the cable is seriously threatened. In order to reduce the effect of crosslinking by-products, in the actual cable production, the power cable is degassed after crosslinking. In the degassing process, the crosslinking by-product volatilizes, thereby ensuring the insulating property of the XLPE cable. At present, the degassing time and the degassing temperature of cables in the production process are determined by experience, and with the continuous improvement of cable production formulas and processes, the degassing conditions required by different batches of cables are different, so that the degassing end point cannot be accurately evaluated, and the degassing effect is not ideal. Therefore, it is important to develop an economical and efficient online monitoring method for monitoring the degassing state of the cable.
The conductivity of XLPE cable insulation is mainly affected by the content of impurities, including cross-linking agents, antioxidants, plasticizers, etc. introduced in the cable production. In the degassing process, the content of the by-products in the insulation is changed, so that the insulation resistance is changed, the degassing effect can be effectively reflected by the online monitoring of the insulation resistance, and the online monitoring method has guiding significance for improving the manufacturing quality and the production efficiency of the cable.
Disclosure of Invention
Aiming at the defects in the prior art, the purpose of the present disclosure is to provide an insulation resistance-based method for evaluating the degassing state of an XLPE cable, which can reflect the degassing state of a tested cable by measuring the insulation resistance of the XLPE cable on line.
In order to achieve the above purpose, the present disclosure provides the following technical solutions:
an XLPE cable degassing state evaluation method based on insulation resistance comprises the following steps:
s100: measuring the insulation resistance value of the XLPE cable in the degassing process on line;
s200: and judging whether the XLPE cable reaches the degassing end point according to the online measurement result of the insulation resistance value.
Preferably, if the online measurement result of the insulation resistance value gradually increases and becomes stable, the XLPE cable is judged to reach the degassing end point.
Preferably, determining whether the XLPE cable reaches the end point of degassing further comprises measuring the insulation absorption ratio and the insulation polarization index of the XLPE cable during degassing on-line.
Preferably, the present disclosure further provides an XLPE cable degassing state evaluation system based on insulation resistance, including: megohmmets and first to third electrode leads; one end of the first electrode lead is connected to a high-voltage electrode of the megohmmeter, and the other end of the first electrode lead is connected to a copper conductor at the end part of the cable to be tested; one end of the second electrode lead is connected to a measuring electrode of the megohmmeter, and the other end of the second electrode lead is connected to a copper strip wound on an outer shielding layer at the end part of the cable to be measured; one end of the third electrode lead is connected to a shielding pole of the megohmmeter, and the other end of the third electrode lead is connected to an outer shielding layer at the end part of the cable to be tested; the outer shielding layers connected with the second electrode and the third electrode are separated by a certain distance.
Compared with the prior art, the beneficial effect that this disclosure brought does:
1. the degassing condition of the tested cable can be truly reflected through the online measurement of the insulation resistance, the change of the insulation state in the XLPE cable can be timely found and detected, and the degassing terminal point can be judged according to the existing measurement data;
2. by researching the change rule of the insulation resistance value along with the degassing time, theoretical guidance and experimental basis can be provided for the degassing process of the large-size XLPE insulated cable.
Drawings
Fig. 1 is a flowchart of a method for evaluating a degassing state of an XLPE cable based on online measurement of insulation resistance according to an embodiment of the present disclosure;
fig. 2 is a schematic structural diagram of an XLPE cable degassing state evaluation system based on online insulation resistance measurement according to another embodiment of the present disclosure;
FIG. 3 shows the variation of insulation resistance, insulation absorption ratio (DAR), and insulation Polarization Index (PI) with degassing time in a 500kV HVDC XLPE cable according to another embodiment of the present disclosure;
FIG. 4 is a graph showing the content of three by-products in a 500kV HVDC XLPE cable according to the degassing time according to another embodiment of the present disclosure;
fig. 5 is a schematic diagram of the variation of dc resistivity, insulation absorption ratio (DAR) and insulation Polarization Index (PI) of 500kV hvdc XLPE cable coupon at different degassing states measured in the laboratory according to another embodiment of the present disclosure.
Detailed Description
Specific embodiments of the present disclosure will be described in detail below with reference to fig. 1 to 5. While specific embodiments of the disclosure are shown in the drawings, it should be understood that the disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
It should be noted that certain terms are used throughout the description and claims to refer to particular components. As one skilled in the art will appreciate, various names may be used to refer to a component. This specification and claims do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. The description which follows is a preferred embodiment of the invention, but is made for the purpose of illustrating the general principles of the invention and not for the purpose of limiting the scope of the invention. The scope of the present disclosure is to be determined by the terms of the appended claims.
To facilitate an understanding of the embodiments of the present disclosure, the following detailed description is to be considered in conjunction with the accompanying drawings, and the drawings are not to be construed as limiting the embodiments of the present disclosure.
In one embodiment, as shown in fig. 1, a method for evaluating a degassing state of an XLPE cable based on insulation resistance includes the following steps:
s100: measuring the insulation resistance value of the XLPE cable in the degassing process on line;
s200: and judging whether the XLPE cable reaches the degassing end point according to the online measurement result of the insulation resistance value.
In this embodiment, a large amount of crosslinking byproducts including a crosslinking agent, an antioxidant, a plasticizer and the like are introduced into an XLPE cable in a production process, and the electrical conductivity of the XLPE cable is mainly affected by the content of the crosslinking byproducts, and in a cable degassing process, the content of the byproducts contained in the XLPE cable is gradually reduced, so that the insulation resistance value is gradually increased, and tends to be stable when the insulation resistance value is increased to a certain extent.
In another embodiment, determining whether the XLPE cable reaches the end of the degassing further comprises measuring the insulation absorption ratio and the insulation polarization index of the XLPE cable during the degassing process on-line.
In this embodiment, the insulation performance of the cable cannot be fully reflected only by measuring the insulation resistance value at a certain time because of the following two reasons: 1. if the cable only has local defects and partial good insulation is still kept between the two poles, the variation of the insulation resistance value is small or unchanged; 2. under the action of direct-current voltage, the cable can generate various polarization phenomena. The current is high at the start of polarization, and as the pressing time increases, the current value decreases and the insulation resistance increases accordingly, a phenomenon called absorption. In good insulation, the absorbed current decreases rapidly along with the pressurization time, and finally the stable current is also very small; however, the absorption current of the defective insulator changes slowly, and the stable current value is also large, so the insulation performance of the cable needs to be further judged by measuring the insulation absorption ratio DAR which is the insulation resistance value ratio at 1min and 15s after pressurization.
Furthermore, for cables with large capacity and long absorption process, sometimes the absorption ratio is not enough to reflect the whole absorption process, so that the insulation performance of the cable needs to be judged by adopting a long-time insulation resistance ratio, namely, by measuring the insulation resistance ratio between 10min and 1min, namely the insulation polarization index PI.
In another embodiment, the present disclosure provides an XLPE cable degassing state evaluation system based on insulation resistance, including: megohmmets and first to third electrode leads; one end of the first electrode lead is connected to a high-voltage electrode of the megohmmeter, and the other end of the first electrode lead is connected to a copper conductor at the end part of the cable to be tested; one end of the second electrode lead is connected to a measuring electrode of the megohmmeter, and the other end of the second electrode lead is connected to a copper strip wound on an outer shielding layer at the end part of the cable to be measured; one end of the third electrode lead is connected to a shielding pole of the megohmmeter, and the other end of the third electrode lead is connected to an outer shielding layer at the end part of the cable to be tested; the outer shielding layers connected with the second electrode and the third electrode are separated by a certain distance.
In this embodiment, as shown in fig. 2, an insulation shield, an XLPE insulation and a conductor shield part with a length of 30cm are stripped from an end of a 500kV hvdc XLPE cable, so that a copper conductor is exposed and connected to a high-voltage pole of a megohmmeter; winding a circle of copper strip on the outer side of the insulation shield at the end part of the cable to be connected with a measuring electrode of the megger; the outer shield was stripped off by a width of 10cm both near the end of the high voltage pole and 70cm from the end of the cable, resulting in a length of shield pole spaced from the measurement pole and connected to the megger. In the system, the copper conductor and the outer shielding layer are equipotential bodies, so that the measuring circuit can measure the resistance of the whole cable.
As shown in fig. 3, 20 days before degassing, more byproducts exist inside the XLPE cable, which results in lower insulation resistance value, insulation absorption ratio and insulation polarization index, reflecting low insulation quality of the cable; along with the increase of the degassing time, the insulation resistance value, the insulation absorption ratio and the insulation polarization index are gradually increased, and the increasing trend is gradually slowed down, which indicates that the byproducts are continuously volatilized; after 55 days of degassing, the insulation resistance value, the insulation absorption ratio and the insulation polarization index gradually tend to be stable, which shows that the residual byproducts in the XLPE insulation are less, the cable electrical performance is not obviously influenced, and the cable reaches the degassing end point.
As shown in FIG. 4, XLPE insulation of 500kV high voltage DC cable with degassing time of 0 day, 15 days, 45 days and 75 days is cut circularly to obtain insulation flat plate sample with thickness of 0.2mm, infrared spectrum test (FTIR) is adopted to determine the content of crosslinking by-products in XLPE insulation, α -functional groups of methyl styrene, acetophenone and cumyl alcohol are respectively C-C, -C-O and-OH, and the corresponding infrared spectrum absorption peaks are respectively 1600cm-1、1690cm-1、3370cm-1The higher the content of the by-product, the greater the absorbance at the position of the absorption peak corresponding to the characteristic functional group. To eliminate minor differences in the thickness of the lathe ring cut samples, the results were normalized by methylene (-CH)2-) the peak value of the infrared characteristic absorption peak is only related to the thickness of the sample, the peak value is selected as a reference peak, the ratio of the peak value of the absorption peaks of the three byproducts in the sample to the methylene absorption peak in the sample is calculated, and the ratio is usedReferring to the relative amounts of α -methylstyrene, acetophenone and cumyl alcohol in the sample, as shown in FIG. 4, the amount of by-products decreased with the increase of the degassing time, but a large amount of by-products remained after 75 days of degassing and the degassing end point was not reached.
As shown in fig. 5, when the same insulation flat plate sample as that in fig. 4 is measured by using the technical solution of the present disclosure, when the cable is not degassed at all, the content of the by-product is higher, the insulation resistance value, the insulation absorption ratio, and the insulation polarization index are lower, and as the degassing time increases, the content of the by-product decreases, and the insulation resistivity increases by one order of magnitude, which indicates that the insulation resistance measurement result can reflect the content of the by-product.
As can be seen from a comparison of fig. 4 and 5, the degassing state of the XLPE cable can be accurately determined by measuring the insulation resistance on-line.
The foregoing describes the general principles of the present disclosure in conjunction with specific embodiments, however, it is noted that the advantages, effects, etc. mentioned in the present disclosure are merely examples and are not limiting, and they should not be considered essential to the various embodiments of the present disclosure. Furthermore, the foregoing disclosure of specific details is for the purpose of illustration and description and is not intended to be limiting, since the foregoing disclosure is not intended to be exhaustive or to limit the disclosure to the precise details disclosed.

Claims (4)

1. An XLPE cable degassing state evaluation method based on insulation resistance comprises the following steps:
s100: measuring the insulation resistance value of the XLPE cable in the degassing process on line;
s200: and judging whether the XLPE cable reaches the degassing end point according to the online measurement result of the insulation resistance value.
2. Method according to claim 1, wherein preferably, if the on-line measurement of the insulation resistance value increases and becomes stable, it is determined that the XLPE cable reaches the degassing end point.
3. The method of claim 1, wherein determining whether the XLPE cable reaches a degassing endpoint further comprises measuring an insulation absorption ratio and an insulation polarization index on-line during a degassing of the XLPE cable.
4. An insulation resistance-based XLPE cable degassing state evaluation system comprises:
megohmmets and first to third electrode leads; one end of the first electrode lead is connected to a high-voltage electrode of the megohmmeter, and the other end of the first electrode lead is connected to a copper conductor at the end part of the cable to be tested; one end of the second electrode lead is connected to a measuring electrode of the megohmmeter, and the other end of the second electrode lead is connected to a copper strip wound on an outer shielding layer at the end part of the cable to be measured; one end of the third electrode lead is connected to a shielding pole of the megohmmeter, and the other end of the third electrode lead is connected to an outer shielding layer at the end part of the cable to be tested; the outer shielding layers connected with the second electrode and the third electrode are separated by a certain distance.
CN202010570412.4A 2020-06-19 2020-06-19 XLPE cable degassing state evaluation method based on insulation resistance Pending CN111736042A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113092204A (en) * 2021-03-30 2021-07-09 重庆泰山电缆有限公司 Method for making insulation degassing process of high-voltage cross-linked polyethylene insulated power cable

Citations (1)

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Publication number Priority date Publication date Assignee Title
CN102426885A (en) * 2011-04-26 2012-04-25 上海市电力公司 Method for degassing flexible direct current transmission cable

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Publication number Priority date Publication date Assignee Title
CN102426885A (en) * 2011-04-26 2012-04-25 上海市电力公司 Method for degassing flexible direct current transmission cable

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Application publication date: 20201002