CN112505411A - Method for identifying cable transfer function on line - Google Patents

Method for identifying cable transfer function on line Download PDF

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Publication number
CN112505411A
CN112505411A CN202011184587.8A CN202011184587A CN112505411A CN 112505411 A CN112505411 A CN 112505411A CN 202011184587 A CN202011184587 A CN 202011184587A CN 112505411 A CN112505411 A CN 112505411A
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China
Prior art keywords
cable
identified
transfer function
frequency current
current sensor
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CN202011184587.8A
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Chinese (zh)
Inventor
卫永琴
李金穗
高建峰
吴杰
王学智
李震
唐巧巧
岳玉丹
岳召
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Shandong University of Science and Technology
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Shandong University of Science and Technology
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Priority to CN202011184587.8A priority Critical patent/CN112505411A/en
Publication of CN112505411A publication Critical patent/CN112505411A/en
Pending legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
    • G01R23/16—Spectrum analysis; Fourier analysis
    • 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
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G06F17/15—Correlation function computation including computation of convolution operations

Abstract

The invention discloses a method for identifying a cable transfer function on line, which belongs to the field of cable partial discharge detection and positioning research. When the cable works, three high-frequency current sensors are arranged around the cable shielding layer and used for signal injection and detection; firstly, injecting signals generated by a partial discharge calibrator into a cable shielding layer through a high-frequency current sensor, then detecting the signals at two ends of a cable to be identified by the high-frequency current sensors arranged at the two ends of the cable to be identified, and finally calculating a transfer function of the cable to be identified through a formula. The method of the invention does not need to know the geometric structure and material specification of the cable, does not need to stop the operation of the cable system, and has simple and reliable operation.

Description

Method for identifying cable transfer function on line
Technical Field
The invention belongs to the technical field of cable partial discharge detection and positioning research, and particularly relates to a method for identifying a cable transfer function on line.
Background
There is a lot of literature on the transfer function identification and high frequency modeling of power cables investigating this problem. At present, a transfer function identification method of a power cable is divided into an experimental modeling method and a mathematical method. In experimental modelling, there are methods based on signal injection between the cable core and the shield layer and methods calculated by applying an identification pulse directly between the cable core and the shield layer, but this method requires the cable to be taken out of service in order to inject the identification signal directly into the cable core. The mathematical method is to fit the propagation parameters to the delay model of the cable transfer function, and to take the transfer function and the signal propagation parameters obtained from the measurement as references, and verify the obtained results through mathematical modeling, which requires knowing the geometric and physical parameters of the cable and using more mathematical formulas.
Mathematical methods require a thorough understanding of the physical and geometrical properties of the cable, and are less accurate than experimental modeling. However, when transient signals cannot be injected directly between the cable core and the shielding, mathematical methods have a higher priority than experimental identification methods, especially in a line work cable system.
Disclosure of Invention
In order to solve the above problems, the invention provides a method for identifying a cable transfer function on line, which is reasonable in design, overcomes the defects of the prior art, and has a good effect.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for identifying a cable transfer function on line selects a partial discharge calibrator, a first high-frequency current sensor, a second high-frequency current sensor, a third high-frequency current sensor, a PD calibrator, a first oscilloscope and a second oscilloscope to form an experimental system, and identifies the transfer function of a cable with the length of L;
preferably, a method for identifying a cable transfer function online includes the following steps:
step 1: the first high-frequency current sensor injects a signal into a shielding layer of the cable;
step 2: selecting a section of cable to be identified with the length of L, wherein the first end of the cable to be identified is a signal injection point and is connected with a second high-frequency current sensor, the second end of the cable to be identified is connected with a third high-frequency current sensor, and the second high-frequency current sensor and the third high-frequency current sensor respectively detect signals of the first end and the second end of the cable to be identified;
and step 3: the transfer function of the cable to be identified of length L is calculated.
Preferably, a partial discharge calibrator is employed as the injection signal source.
Preferably, the second high frequency current sensor and the third high frequency current sensor are of the same type.
Preferably, the experimental system is assumed to be linear time invariant.
Preferably, at the first end of the cable to be identified, the frequency spectrum of the signal detected by the first oscilloscope is:
S1(jω)＝HI(jω)×HD(jω)×I(jω) (1)
at the second end of the cable to be identified, the frequency spectrum of the signal detected by the second oscilloscope is as follows:
S2(jω)＝HI(jω)×HD(jω)×HL(jω)I(jω) (2)
where I (j ω) is the frequency spectrum of the signal generated by the PD calibrator at the first end of the cable to be identified, HI(j ω) and HD(j ω) is the total transfer function, H, at the first and second ends, respectively, of the cable to be identifiedL(j ω) is the transfer function of the cable to be identified of length L, ω being the angular frequency;
transfer function H of cable to be identified with length LL(j ω) is:
HL(jω)＝S2(jω)/S1(jω) (3)
where equation (3) gives the transfer function for the cable length L, it can also be used to find the transfer function for any other part of the same cable.
The beneficial and technical effects brought by the invention are as follows:
the method of the present invention identifies the transfer function of the cable without knowing the geometry and material specifications of the cable and without requiring the cable system to be shut down. In the case where the propagation and attenuation characteristics of a given length of cable are known, a high frequency current sensor (HFCT) injects a current through the cable shield and the transfer function of the cable can be identified by measuring the injected signal at two different locations of the cable through the high frequency current sensor clamped to the shield.
Drawings
FIG. 1 is a schematic diagram of a cable transfer function identification experiment according to the present invention;
FIG. 2 is a block diagram of a cable transfer function identification experiment in accordance with the present invention;
Detailed Description
To facilitate understanding and practice of the invention by those of ordinary skill in the art, embodiments of the invention are further described below with reference to the accompanying drawings and specific examples:
fig. 1 is a schematic diagram of a cable transfer function identification experiment, which is composed of a partial discharge calibrator, a high-frequency current sensor 1, a high-frequency current sensor 2, a high-frequency current sensor 3, a PD calibrator, an oscilloscope 1, and an oscilloscope 2, and identifies a transfer function of a cable with a length L;
further, as shown in fig. 2, the method for identifying the cable transfer function of the present invention includes the following steps:
step 1: the high-frequency current sensor 1 injects a signal into a shielding layer of the cable;
step 2: selecting a section of cable to be identified with the length of L, wherein the first end of the cable to be identified is a signal injection point and is connected with a high-frequency current sensor 2, the second end of the cable to be identified is connected with a high-frequency current sensor 3, and the high-frequency current sensor 2 and the high-frequency current sensor 3 respectively detect signals of the first end and the second end of the cable to be identified;
and step 3: the transfer function of the cable to be identified of length L is calculated.
Specifically, a partial discharge calibrator is employed as the injection signal source.
Specifically, the high-frequency current sensor 2 and the high-frequency current sensor 3 are of the same type.
In particular, the experimental system is assumed to be linear time invariant.
Specifically, at the first end of the cable to be identified, the frequency spectrum of the signal detected by the oscilloscope 1 is:
S1(jω)＝HI(jω)×HD(jω)×I(jω) (1)
at the second end of the cable to be identified, the signal spectrum detected by the oscilloscope 2 is:
S2(jω)＝HI(jω)×HD(jω)×HL(jω)I(jω) (2)
where I (j ω) is the frequency spectrum of the signal generated by the PD calibrator at the first end of the cable to be identified, HI(j ω) and HD(j ω) is the total transfer function, H, of the first and second ends, respectively, of the cable to be identifiedL(j ω) is the transfer function of the cable to be identified of length L, ω being the angular frequency;
therefore, the transfer function H of the cable to be identified with a length LL(j ω) is:
HL(jω)＝S2(jω)/S1(jω) (3)
where equation (3) gives the transfer function for the cable length L, it can also be used to find the transfer function for any other part of the same cable.
It is to be understood that the above description is not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art may make modifications, alterations, additions or substitutions within the spirit and scope of the present invention.

Claims (5)

1. A method for identifying a cable transfer function on line selects a partial discharge calibrator, a first high-frequency current sensor, a second high-frequency current sensor, a third high-frequency current sensor, a PD calibrator, a first oscilloscope and a second oscilloscope to form an experimental system, and identifies the cable transfer function;
the method is characterized by comprising the following steps:
step 1: the first high-frequency current sensor injects a signal into a shielding layer of the cable;
step 2: selecting a section of cable to be identified with the length of L, wherein the first end of the cable to be identified is a signal injection point and is connected with a second high-frequency current sensor, the second end of the cable to be identified is connected with a third high-frequency current sensor, and the second high-frequency current sensor and the third high-frequency current sensor respectively detect signals of the first end and the second end of the cable to be identified;
and step 3: the transfer function of the cable to be identified of length L is calculated.
2. A method for on-line identification of cable transfer function as claimed in claim 1 wherein a partial discharge calibrator is used as the injection signal source.
3. The method for on-line identification of cable transfer function as claimed in claim 1, wherein the second high frequency current sensor and the third high frequency current sensor are of the same type.
4. The method of claim 1, wherein the experimental system is assumed to be linear and time-invariant.
5. The method for on-line identification of cable transfer function as claimed in claim 1, wherein at the first end of the cable to be identified, the frequency spectrum of the signal detected by the first oscilloscope is:
S1(jω)＝HI(jω)×HD(jω)×I(jω) (1)
at the second end of the cable to be identified, the signal spectrum detected by the second oscilloscope is as follows:
S2(jω)＝HI(jω)×HD(jω)×HL(jω)I(jω) (2)
where I (j ω) is the frequency spectrum of the signal generated by the PD calibrator at the first end of the cable to be identified, HI(j ω) and HD(j ω) is the total transfer function, H, of the first and second ends, respectively, of the cable to be identifiedL(j ω) is the transfer function of the cable to be identified of length L, ω being the angular frequency;
HL(jω)＝S2(jω)/S1(jω) (3)
the transfer function H of the cable to be identified with the length L can be obtained by the formula (3)L(jω)。
CN202011184587.8A 2020-10-30 2020-10-30 Method for identifying cable transfer function on line Pending CN112505411A (en)

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Application Number Priority Date Filing Date Title
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Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102565634A (en) * 2012-01-10 2012-07-11 广东电网公司电力科学研究院 Power cable fault location method based on transfer function method
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CN107656226A (en) * 2017-09-05 2018-02-02 四川大学 HFCT electrical parameter test devices and method of testing based on transmission coefficient
CN108226842A (en) * 2017-12-29 2018-06-29 诺仪器（中国）有限公司 The amplitude-frequency calibration system and method for current sensor
CN108562834A (en) * 2018-02-06 2018-09-21 武汉康电电气有限公司 A kind of high-tension cable partial discharge monitoring system and the method for correcting amplitude
CN108710774A (en) * 2018-06-20 2018-10-26 华中科技大学 A kind of current sensor frequency characteristic modeling method
CN109541509A (en) * 2017-09-21 2019-03-29 诺仪器（中国）有限公司 The phase frequency calibration system and method for current sensor
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Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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CN104267241A (en) * 2014-10-20 2015-01-07 国网吉林省电力有限公司长春供电公司 High-frequency current partial discharge signal acquisition sensor
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CN107390100A (en) * 2017-08-03 2017-11-24 四川大学 A kind of power cable partial discharge positioning method based on time reversal
CN107656226A (en) * 2017-09-05 2018-02-02 四川大学 HFCT electrical parameter test devices and method of testing based on transmission coefficient
CN109541509A (en) * 2017-09-21 2019-03-29 诺仪器（中国）有限公司 The phase frequency calibration system and method for current sensor
CN108226842A (en) * 2017-12-29 2018-06-29 诺仪器（中国）有限公司 The amplitude-frequency calibration system and method for current sensor
CN108562834A (en) * 2018-02-06 2018-09-21 武汉康电电气有限公司 A kind of high-tension cable partial discharge monitoring system and the method for correcting amplitude
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Application publication date: 20210316