CN116520030A - Cable insulation dielectric loss factor on-line monitoring method and system, electronic equipment and storage medium - Google Patents
Cable insulation dielectric loss factor on-line monitoring method and system, electronic equipment and storage medium Download PDFInfo
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Abstract
The invention discloses a cable insulation dielectric loss factor on-line monitoring method, a system, electronic equipment and a storage medium, which are used for acquiring the range of the dielectric loss factor of a cable with normal insulation performance; acquiring the range of dielectric loss factors of cables with different degradation degrees; and carrying out on-line monitoring on the dielectric loss factors of the cable according to the range of the dielectric loss factors of the cable with normal insulation performance and the range of the dielectric loss factors of the cable with different degradation degrees to obtain the insulation performance of the on-line cable. The cable insulation dielectric loss factor on-line monitoring method, system, electronic equipment and storage medium provided by the invention are used for on-line monitoring the cable insulation dielectric loss factor and provide necessary theoretical support for on-line monitoring of the cable insulation dielectric loss factor. The cable insulation dielectric loss factor on-line monitoring scheme is provided, and engineering application can be realized.
Description
Technical Field
The invention relates to a cable insulation dielectric loss factor on-line monitoring method, a system, electronic equipment and a storage medium, and belongs to the technical field of cable on-line detection.
Background
At present, as the process of urban treatment is continuously advanced, the overhead conductors are gradually replaced by cables, and the cable rate of part of cities is even 100%. The cable is one of the main transmission lines and plays a key role in the whole power grid. However, with the increase of the operation years, under the long-term action of electric and thermal fields, the cable insulation has the phenomena of high polymer cracking and defects, and starts to age, and some phenomena even have serious aging such as electric branches. In addition, part of the cable has no radial water blocking structure and is in a wet environment for a long time, and the insulation of the cable can form a water tree under an electric field. These conditions all cause deterioration of the cable insulation, i.e., an increase in dielectric loss tangent.
In China, the more mature method for online monitoring of the insulation performance of the cable mainly comprises the following steps: partial discharge, ground circulation, temperature testing, etc. While less practical research is being conducted on the dielectric loss tangent, a main performance index for cable insulation degradation, which is mainly represented by: firstly, domestic research on the online monitoring technology of the dielectric loss factor of the cable is carried out, but most of the research is limited to the feasibility of the method, and a specific theoretical expression is not provided; secondly, a specific and feasible online monitoring flow is not provided, and specific suggestions are not provided for the cable insulation degradation criteria.
Therefore, a set of specific and operable on-line monitoring flow is established by proposing corresponding expressions for the dielectric loss factors, summarizing specific degradation criteria and based on engineering field related parameters.
Disclosure of Invention
The purpose is as follows: in order to overcome the defects in the prior art, the invention provides an on-line monitoring method, an on-line monitoring system, electronic equipment and a storage medium for the loss factor of the cable insulation medium, and provides a theoretical expression for the loss factor of the cable insulation medium for on-line monitoring based on engineering parameters. And providing a cable insulation degradation criterion, and establishing an insulation dielectric loss factor on-line monitoring scheme.
The invention provides a cable insulation dielectric loss factor on-line monitoring method, a system, electronic equipment and a storage medium.
The technical scheme is as follows: in order to solve the technical problems, the invention adopts the following technical scheme:
in a first aspect, a method for on-line monitoring a loss factor of an insulating medium of a cable includes the steps of:
and step 1, acquiring the range of dielectric loss factors of the cable with normal insulation performance.
And 2, obtaining the range of dielectric loss factors of the cables with different degradation degrees.
And 3, carrying out on-line monitoring on the dielectric loss factors of the cable according to the range of the dielectric loss factors of the cable with normal insulation performance and the range of the dielectric loss factors of the cable with different degradation degrees to obtain the insulation performance of the on-line cable.
Further, the step 1 includes:
step 1.1, selecting a certain number of cables with normal insulating property.
And step 1.2, respectively measuring the phase difference theta of the currents at the head and the tail of all the cables.
And 1.3, substituting the theta data corresponding to all the cables into a dielectric loss factor formula to obtain the range of the dielectric loss factor tan delta with normal cable insulation performance.
Further, the step 2 includes:
step 2.1, selecting cables with different insulation degradation degrees, and dividing the cables into a plurality of insulation degradation degrees
Grade. And 2.2, measuring the phase difference theta of the head-end currents of all the cables.
And 2.3, substituting the theta data corresponding to all the cables into a dielectric loss factor formula, and determining the range of dielectric loss factors tan delta corresponding to different insulation degradation degree grades.
Further, the step 3 includes:
step 3.1, measuring the phase difference theta between the head end and the tail end of the current of the running cable line to obtain the running voltage U of the running cable and the amplitude I of the head end current of the running cable 1 The length of the on-going cabling i, the insulation inner and outer radii r1 and r2 of the on-going cabling.
And 3.2, calculating the dielectric loss factor of the running cable according to a dielectric loss factor formula.
And 3.3, comparing the dielectric loss factor of the running cable with the range of the dielectric loss factor tan delta with normal cable insulation performance and the range of the dielectric loss factor tan delta corresponding to different insulation degradation degree grades, and determining that the running cable is normal in cable insulation performance or belongs to a certain insulation degradation degree grade.
Further, the dielectric loss factor formula is calculated as follows:
wherein delta is the effective value of the capacitive current of the cableAnd->Phase difference of->Effective value for capacitive current recovery of the cable +.>And resistive current complex effective value +.>And omega is the circular frequency, C is the capacitance per unit length of the cable, pi is the circumference rate, and epsilon is the insulating dielectric constant of the cable.
Further, the dielectric loss factor formula obtaining method includes:
obtaining the current complex effective value of the head end of the cable asThe terminal current complex effective value is +.>Capacitive current composite effective value of cable +.>And resistive current complex effective value +.>
Obtaining the effective value of the capacitive current of the cableAnd resistive current complex effective value +.>Sum to get->
Acquisition ofAnd->Phase difference θ, < ->And->Phase difference A, & lt & gt>And->Phase difference B, < >>And->Phase difference delta.
Respectively recovering the current to the effective valueAnd->The phase differences θ, A, B, δ are noted on a complex planar coordinate system with the x-axis as the real axis and the y-axis as the imaginary axis.
According to the sine theorem, equation (1) can be obtained, equation (1) as follows:
will beSubstituting formula (1) results in formula (2):
wherein I is C The calculation formula is as follows:
wherein, l, r 2 And r 1 The cable insulation dielectric constant is epsilon, U, omega, C, pi and U.S. rate, the cable length, the cable insulation outer radius and the cable insulation inner radius are respectively, the U is the cable voltage, the omega is the circular frequency, the C is the capacitance of the unit length of the cable, and the pi is the circumference rate.
Substituting formula (3) into formula (2) to obtain formula (4) as follows:
the expression for sin θ according to equation (4) is as follows:
as is known from common knowledge, the delta angle is the dielectric loss angle of the cable. Converting the formula (5) into a cable insulation dielectric loss tangent formula, wherein the calculation formula is as follows:
the formula (6) is simplified into a dielectric loss factor formula, and the calculation formula is as follows:
in a second aspect, an on-line monitoring system for loss factor of cable insulation medium includes the following modules:
normal range acquisition module: for determining the range of dielectric loss factors for normally insulated cables.
An abnormal range acquisition module: a range of dielectric loss factors for the cables of different degradation levels was analyzed.
And an online cable judging module: the method is used for on-line monitoring of the dielectric loss factor of the cable insulation, and the insulation performance of the on-line cable is obtained.
In a third aspect, a computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements a method for on-line monitoring of a loss tangent of a cable insulation medium according to any of the first aspects.
In a fourth aspect, a computer device comprises:
and the memory is used for storing the instructions.
A processor for executing the instructions to cause the computer device to perform the operations of a method for on-line monitoring of a loss tangent of a cable insulation medium as described in any of the first aspects.
The beneficial effects are that: the cable insulation dielectric loss factor on-line monitoring method, system, electronic equipment and storage medium provided by the invention are used for on-line monitoring the cable insulation dielectric loss factor and provide necessary theoretical support for on-line monitoring of the cable insulation dielectric loss factor. The cable insulation dielectric loss factor on-line monitoring scheme is provided, and engineering application can be realized.
Drawings
Fig. 1 is a schematic diagram of the cable start-end current, the resistance-capacitance current and the effective value.
FIG. 2 is a flow chart of the on-line monitoring method of the present invention.
Fig. 3 is a schematic structural diagram of the on-line monitoring system of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made more apparent and fully by reference to the accompanying drawings, in which embodiments of the invention are shown, and in which it is evident that the embodiments shown are only some, but not all embodiments of the invention. All other embodiments, which can be made by a person skilled in the art without any inventive effort, are intended to be within the scope of the present invention.
The invention will be further described with reference to specific examples.
As shown in fig. 1, the cable head-end current complex effective value isThe terminal current complex effective value is +.>Capacitive current composite effective value of cable +.>And resistive current complex effective value +.>The sum is-> And->The phase difference of (2) is θ, (+)>And->The phase difference is A and->Andphase difference of B, & lt & gt>And->The phase difference is delta. />And->The corresponding magnitudes are denoted as I respectively 1 、I 2 、I CR 、I C And I R 。
Due to the complex effective value of the line voltageAnd->The phases are the same; but->(j is imaginary unit, ω is circular frequency, C is cable unit length capacitance and l is cable length), so ∈ ->Phase ratio->The phase leads 90 DEG, also leads +.>Phase 90 °, i.e.)>And->Perpendicular. Likewise, resistive current +.>Also with->In phase, therefore->Phase lead->Phase 90 °,>also with->Perpendicular.
Respectively recovering the current to the effective valueAnd->The phase differences θ, A, B, δ are noted on a complex planar coordinate system with the x-axis as the real axis and the y-axis as the imaginary axis.
According to the sine-law of law,
wherein, will beSubstituting formula (1) results in formula (2):
wherein,,
wherein, l, r 2 And r 1 The cable insulation dielectric constant is epsilon, U, omega, C, pi and U.S. rate, the cable length, the cable insulation outer radius and the cable insulation inner radius are respectively, the U is the cable voltage, the omega is the circular frequency, the C is the capacitance of the unit length of the cable, and the pi is the circumference rate. Will be maleSubstituting formula (3) into formula (2) to obtain formula (4) as follows:
the expression for sin θ is derived according to equation (4) as follows:
as can be seen from the formula (5), the angle θ has a proportional relationship with the angle δ, the voltage U, the cable length l, and the head-end current I 1 Cable insulation outer and inner radius ratio r 2 \r 1 There is an inverse relationship.
As is known from common knowledge, the delta angle is the dielectric loss angle of the cable. Converting equation (5) into a cable insulation dielectric loss tangent equation, i.e., a dielectric loss tangent equation, as follows:
for cable insulation, tan delta is typically 10 -3 And below, i.e. δ tends to be 0, giving b≡90°. In addition, a+b+θ=180°, θ also tends to be 0, so a≡90 °, sinA taste 1. Thus, formula (6) can be simplified as:
this means that the angle θ can reflect the cable insulation dielectric loss (tan δ) condition with other parameters fixed.
As shown in fig. 2, the method for on-line monitoring of dielectric loss factor of cable insulation according to the first embodiment of the present invention mainly obtains a dielectric loss factor criterion for evaluating insulation state of the cable by analyzing dielectric loss factors of existing cables with normal and abnormal insulation properties, and is applied to on-line monitoring of cable lines, and includes the following steps:
and 1, determining the range of dielectric loss factors of the cable with normal insulation performance.
Step 1.1, selecting a certain number of cables with normal insulating performance, including new cables which are not put into operation or cables which are normal in operation, wherein the insulating performance at least does not contain the defects of water tree, electric tree and the like.
Step 1.2, measuring the phase difference theta of the head and tail currents of the cable by using double CT in a laboratory. The phase difference theta of the operation cable can also be measured by using double CT in engineering sites.
And 1.3, substituting the theta data corresponding to all the cables into the formula (7) to obtain the range of the dielectric loss factor tan delta with normal cable insulation performance.
And 2, analyzing the range of dielectric loss factors of the cables with different degradation degrees.
And 2.1, selecting cables with different insulation degradation degrees according to the on-line monitoring research requirement, and classifying the cables into a plurality of insulation degradation degree grades. The cable can be derived from engineering field fault cables or from cables subjected to degradation treatment in laboratories.
Step 2.2, measuring the phase difference theta of the head and tail currents of the cable by using double CT in a laboratory.
And 2.3, substituting the theta data corresponding to all the cables into the formula (7) to determine the range of the dielectric loss factor tan delta corresponding to different insulation degradation degree grades.
And step 3, monitoring the dielectric loss factor of the cable insulation on line to obtain the insulation performance of the cable on line.
Step 3.1, for on-line monitoring of the dielectric loss factor of the running cable, the phase difference theta of the head end and the tail end currents of the running cable line is measured on line by using double CT to obtain the running voltage U of the running cable and the amplitude I of the head end currents of the running cable 1 The length of the on-going cabling i, the insulation inner and outer radii r1 and r2 of the on-going cabling.
And 3.2, calculating the dielectric loss factor of the running cable according to the formula (7).
And 3.3, comparing the dielectric loss factor of the running cable with the range of the dielectric loss factor tan delta with normal cable insulation performance and the range of the dielectric loss factor tan delta corresponding to different insulation degradation degree grades, and determining that the running cable is normal in cable insulation performance or belongs to a certain insulation degradation degree grade.
According to the degradation degree criterion obtained in the two steps, the cable insulation performance can be monitored on line.
As shown in fig. 3, a second embodiment of the present invention is a cable insulation dielectric loss factor on-line monitoring system, which includes the following modules:
normal range acquisition module: for determining the range of dielectric loss factors for normally insulated cables.
An abnormal range acquisition module: a range of dielectric loss factors for the cables of different degradation levels was analyzed.
And an online cable judging module: the method is used for on-line monitoring of the dielectric loss factor of the cable insulation, and the insulation performance of the on-line cable is obtained.
The normal range acquisition module specifically includes:
and selecting a certain number of cables with normal insulating performance, including new cables which are not put into operation or cables which are normal in operation, wherein the insulating performance at least does not contain the defects of water tree, electric tree and the like.
The phase difference θ of the cable head-end currents was measured in the laboratory using dual CT. The phase difference theta of the operation cable can also be measured by using double CT in engineering sites.
And substituting the theta data corresponding to all the cables into the formula (7) to obtain the range of the dielectric loss factor tan delta with normal cable insulation performance.
The abnormal range obtaining module specifically comprises:
according to the on-line monitoring research requirement, cables with different insulation degradation degrees are selected, and the cables are classified into several insulation degradation degree grades. The cable can be derived from engineering field fault cables or from cables subjected to degradation treatment in laboratories.
The phase difference θ of the cable head-end currents was measured in the laboratory using dual CT.
And substituting the theta data corresponding to all the cables into the formula (7) to determine the range of the dielectric loss factors tan delta corresponding to different insulation degradation degree grades.
The online cable judging module specifically comprises:
for on-line monitoring of dielectric loss factors of running cables, the phase difference theta of the currents at the head end and the tail end of the running cable line is measured on line by double CT to obtain the running voltage U of the running cable and the amplitude I of the current at the head end of the running cable 1 The length of the on-going cabling i, the insulation inner and outer radii r1 and r2 of the on-going cabling.
The dielectric loss tangent of the running cable is calculated according to equation (7).
The dielectric loss tangent of the running cable is compared with the range of the dielectric loss tangent tan delta of the cable with normal insulation performance and the range of the dielectric loss tangent tan delta corresponding to different insulation degradation degree grades, and the running cable is determined to be normal in cable insulation performance or belong to a certain insulation degradation degree grade.
A third embodiment is a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements a method for on-line monitoring of a loss tangent of a cable insulation medium as described in any of the first embodiments.
A fourth embodiment is a computer device comprising:
and the memory is used for storing the instructions.
A processor for executing the instructions to cause the computer device to perform the operations of a method for on-line monitoring of a loss tangent of a cable insulation medium as described in any of the first embodiments.
Example 1:
on-line monitoring is carried out on the 10kV cable, and the method specifically comprises the following steps:
for a crosslinked polyethylene (XLPE) insulated cable with a voltage of 10kV, the phase voltage u=6 kV and the length l=550 m. Inner radius r of cable insulation 1 External radius r =10mm 2 =14.5 mm. Considering XLPE relative permittivity epsilon r =2.3, then dielectric constant ε=ε r ε 0 ＝2×10 -11 F/m。
(1) And obtaining the dielectric loss factor range of the cable with normal insulation performance.
Firstly, 10 cables with normal insulation performance are selected, wherein the cables comprise new cables and cables with normal operation, and the insulation of the cables does not contain water tree, electric tree, defect and the like.
Then, the phase difference θ=0.10 °, 0.10 °, 0.11 °, 0.10 °, 0.11 ° of the cable head-end current was measured in the laboratory using dual CT.
Finally, substituting the theta data into the formula (7) to obtain the dielectric loss factor range tan delta of the cable with normal insulation performance which is less than or equal to 5 multiplied by 10 -3 。
(2) And acquiring a dielectric loss factor range of the insulated and degraded cable.
First, 10 cables with insulation degradation are selected, and water tree, electric tree, defect and the like exist in the insulation, so that the insulation resistance is smaller than that of a normal cable.
Then, the phase difference θ=0.14 °, 0.15 °, 0.14 °, 0.15 °, 0.14 °, 0.15 ° of the cable head-end current was measured in the laboratory using dual CT.
Finally, substituting the θ data into the formula (7) to obtain a dielectric loss tangent range of 8.0X10 for the insulation-degraded cable -2 ≤tanδ。
(3) On-line monitoring application of dielectric loss factor of cable insulation
As can be seen from the section (1), the insulation dielectric loss factor range of the cable with normal performance is tan delta less than or equal to 5 multiplied by 10 after the test of a plurality of cables -3 And the national standard prescribes that tan delta is less than or equal to 8 multiplied by 10 -3 . Considering that certain errors exist in the measurement process, the range of dielectric loss factors of the cable insulation with normal performance can be properly enlarged, and the method is suggested as follows:
tanδ≤8×10 -3 (8)
similarly, the dielectric loss factor of the insulation degradation cable is limited to 8.0 multiplied by 10 according to the related measurement data of the section (2) and taking the error into consideration -2 Suitably up to 1.0X10 -1 Suggested as：
1.0×10 -1 ≤tanδ (9)
In this way, in the cable on-line monitoring process, the cable head-end current phase difference theta, the operation voltage U and the current I 1 Line length l, cable structural dimension parameter r 1 And r 2 Substituting the same relevant parameters into the formula (7) to obtain tan delta. And (3) comparing the tan delta value with criteria (formulas (8) and (9)), and thus completing the on-line monitoring of the insulation state of the cable.
Example 2:
the 220kV cable is monitored on line, and the method specifically comprises the following steps:
for a crosslinked polyethylene (XLPE) insulated cable with a voltage of 220kV, its phase voltage u=127 kV, head-end current I 1 =1000a, length l=5 km. Inner radius r of cable insulation 1 External radius r =20mm 2 =44 mm. Considering XLPE relative permittivity epsilon r =2.3, then dielectric constant ε=ε r ε 0 ＝2×10 -11 F/m。
(1) And obtaining the dielectric loss factor range of the cable with normal insulation performance.
Firstly, 10 cables with normal insulation performance are selected, wherein the cables comprise new cables and cables with normal operation, and the insulation of the cables does not contain water tree, electric tree, defect and the like.
Then, the phase difference θ=1.82 °, 1.83 °, 1.82 ° of the cable head-end current was measured in the laboratory using dual CT.
Finally, substituting the theta data into the formula (7) to obtain the dielectric loss factor range tan delta which is less than or equal to 8 multiplied by 10 and has normal cable insulation performance -4 。
(2) And acquiring a dielectric loss factor range of the insulated and degraded cable.
Firstly, 10 cables with insulation degradation are selected, wherein electrical trees, micropores, defects and the like exist in the insulation, and the insulation resistance is smaller than that of a normal cable;
then, the phase difference θ=1.86 °, 1.86 °, 1.87 °, 1.86 °, 1.87 °, 1.86 °;
finally, substituting the θ data into the formula (7) to obtain the dielectric loss tangent range 1.0X10 of the insulation-deteriorated cable -2 ≤tanδ。
(3). Cable insulation dielectric loss factor on-line monitoring application
As can be seen from the section (1), the insulation dielectric loss factor range of the cable with normal performance is tan delta less than or equal to 8 multiplied by 10 after the test of a plurality of cables -4 Compared with the national standard, the tan delta is less than or equal to 8 multiplied by 10 -4 And consistent. Considering that certain errors exist in the measurement process, the range of dielectric loss factors of the cable insulation with normal performance can be properly enlarged, and the method is suggested as follows:
tanδ≤1×10 -3 (10)
similarly, the dielectric loss factor of the insulation degradation cable is limited to be 1.0 multiplied by 10 according to the related measurement data of the section (2) and taking the error into consideration -2 Suitably up to 2.0X10 -2 The proposal is as follows:
tanδ≥2.0×10 -2 (11)
in this way, in the cable on-line monitoring process, the cable head-end current phase difference theta, the operation voltage U and the current I 1 Line length l, cable structural dimension parameter r 1 And r 2 Substituting the same relevant parameters into the formula (7) to obtain tan delta. And (3) comparing the tan delta value with criteria (formulas (10) and (11)), and thus completing the on-line monitoring of the insulation state of the cable.
It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The foregoing is only a preferred embodiment of the invention, it being noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the invention.
Claims (9)
1. An on-line monitoring method for the loss factor of cable insulation medium is characterized in that: the method comprises the following steps:
step 1, obtaining a range of dielectric loss factors of a cable with normal insulation performance;
step 2, obtaining the range of dielectric loss factors of cables with different degradation degrees;
and 3, carrying out on-line monitoring on the dielectric loss factors of the cable according to the range of the dielectric loss factors of the cable with normal insulation performance and the range of the dielectric loss factors of the cable with different degradation degrees to obtain the insulation performance of the on-line cable.
2. The on-line monitoring method for dielectric loss tangent of cable according to claim 1, wherein: the step 1 comprises the following steps:
step 1.1, selecting a certain number of cables with normal insulating properties;
step 1.2, respectively measuring phase differences theta of the currents at the head and the tail of all the cables;
and 1.3, substituting the theta data corresponding to all the cables into a dielectric loss factor formula to obtain the range of the dielectric loss factor tan delta with normal cable insulation performance.
3. The on-line monitoring method for dielectric loss tangent of cable according to claim 1, wherein: the step 2 includes:
step 2.1, selecting cables with different insulation degradation degrees, and dividing the cables into several insulation degradation degree grades;
step 2.2, measuring the phase difference theta of the currents at the head and the tail of all the cables;
and 2.3, substituting the theta data corresponding to all the cables into a dielectric loss factor formula, and determining the range of dielectric loss factors tan delta corresponding to different insulation degradation degree grades.
4. The on-line monitoring method for dielectric loss tangent of cable according to claim 1, wherein: the step 3 includes:
step 3.1, measuring the phase difference theta between the head end and the tail end of the current of the running cable line to obtain the running voltage U of the running cable and the amplitude I of the head end current of the running cable 1 The length l of the on-going cable, the insulation inner and outer radii r1 and r2 of the on-going cable;
step 3.2, calculating the dielectric loss factor of the running cable according to a dielectric loss factor formula;
and 3.3, comparing the dielectric loss factor of the running cable with the range of the dielectric loss factor tan delta with normal cable insulation performance and the range of the dielectric loss factor tan delta corresponding to different insulation degradation degree grades, and determining that the running cable is normal in cable insulation performance or belongs to a certain insulation degradation degree grade.
5. An on-line monitoring method for dielectric loss tangent of cable according to any one of claims 2 to 4, wherein: the dielectric loss factor formula is calculated as follows:
wherein delta is the effective value of the capacitive current of the cableAnd->Phase difference of->Effective value for capacitive current recovery of the cable +.>And resistive current complex effective value +.>And omega is the circular frequency, C is the capacitance per unit length of the cable, pi is the circumference rate, and epsilon is the insulating dielectric constant of the cable.
6. The on-line monitoring method for dielectric loss tangent of cable according to claim 5, wherein: the dielectric loss factor formula acquisition method comprises the following steps:
obtaining the current complex effective value of the head end of the cable asThe terminal current complex effective value is +.>Capacitive current composite effective value of cable +.>And resistive current complex effective value +.>
Obtaining the effective value of the capacitive current of the cableAnd resistive current complex effective value +.>Sum to get->
Acquisition ofAnd->Phase difference θ, < ->And->Phase difference A, & lt & gt>And->Phase difference B, < >>And->A phase difference delta;
respectively recovering the current to the effective valueAnd->The phase differences theta, A, B and delta are marked on a complex plane coordinate system which takes the x axis as the real axis and takes the y axis as the imaginary axis;
according to the sine theorem, equation (1) can be obtained, equation (1) as follows:
will beSubstituting formula (1) results in formula (2):
wherein I is C The calculation formula is as follows:
wherein, l, r 2 And r 1 The cable insulation dielectric constant is epsilon, the cable voltage is U, omega is the circular frequency, C is the capacitance of the unit length of the cable, and pi is the circumference ratio;
substituting formula (3) into formula (2) to obtain formula (4) as follows:
the expression for sin θ according to equation (4) is as follows:
as known from common knowledge, the delta angle is the insulation dielectric loss angle of the cable; converting the formula (5) into a cable insulation dielectric loss tangent formula, wherein the calculation formula is as follows:
the formula (6) is simplified into a dielectric loss factor formula, and the calculation formula is as follows:
7. an on-line monitoring system for the loss factor of cable insulation medium is characterized in that: the device comprises the following modules:
normal range acquisition module: a range of dielectric loss factors for determining a normally insulated cable;
an abnormal range acquisition module: a range of dielectric loss factors for analyzing cables of different degradation levels;
and an online cable judging module: the method is used for on-line monitoring of the dielectric loss factor of the cable insulation, and the insulation performance of the on-line cable is obtained.
8. A computer-readable storage medium, characterized by: a computer program stored thereon, which, when executed by a processor, implements a method for on-line monitoring of the loss tangent of a cable insulation medium as claimed in any of claims 1-6.
9. A computer device, characterized by: comprising the following steps:
a memory for storing instructions;
a processor for executing the instructions to cause the computer device to perform the operations of a cable insulation loss factor on-line monitoring method according to any one of claims 1-6.
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