CN105067889A - Method of measuring secondary cable transfer impedance caused by ground net impact current - Google Patents

Method of measuring secondary cable transfer impedance caused by ground net impact current Download PDF

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Publication number
CN105067889A
CN105067889A CN201510423841.8A CN201510423841A CN105067889A CN 105067889 A CN105067889 A CN 105067889A CN 201510423841 A CN201510423841 A CN 201510423841A CN 105067889 A CN105067889 A CN 105067889A
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current
secondary cable
heart yearn
grounded screen
voltage generator
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CN201510423841.8A
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CN105067889B (en
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肖磊石
李谦
张波
吴锦鹏
庄池杰
曾嵘
何金良
陈水明
胡军
余占清
张云
董玉玺
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Tsinghua University
Huizhou Power Supply Bureau of Guangdong Power Grid Co Ltd
Electric Power Research Institute of Guangdong Power Grid Co Ltd
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Tsinghua University
Huizhou Power Supply Bureau of Guangdong Power Grid Co Ltd
Electric Power Research Institute of Guangdong Power Grid Co Ltd
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Abstract

The invention discloses a method of measuring secondary cable transfer impedance caused by ground net impact current, comprising accessing an impulse t voltage generator in a transformer station ground net, laying a secondary cable, and using standard impact voltage and current waveforms to inject current into the current ground entry point of the ground net, and to extract current at a current discharge point; employing an oscilloscope to measure the output current waveform of the impulse voltage generator; employing the oscilloscope to measure the potential difference between core wires at any end of the laid secondary cable, and the potential difference between the core wires at the end and the ground net; respectively using 2 to divide the two measured potential differences; and respectively comparing the peak values of the two obtained potential differences with the output current peak values of the impulse voltage generator. The measurement method of the invention can obtain the transfer impedance between core wires of the secondary cable, and the transfer impedance between the core wires and the ground net to be used for assessing grounding system impact characteristics, and guiding grounding engineer construction.

Description

The measuring method of the secondary cable transfer impedance that grounded screen dash current causes
Technical field
The present invention relates to technical field of high voltage, specifically the measuring method of secondary cable transfer impedance that causes of finger earth mat dash current, for assessment of grounded screen impact on secondary cable when being subject to lightning impulse.
Background technology
In order to work and security needs in electric system, often some part of electric system and electrical equipment thereof need be connected with the earth, Here it is ground connection.Electric system ground connection can be divided into working earthing, lightning protection and protective ground three kinds with regard to its object.Wherein lightning protection is the harm in order to avoid thunder and lightning, and the thunder resisting equipments such as lightning rod, lightning conducter and lightning arrester all must be equipped with corresponding earthing device lightning current is imported the earth.Grounded screen guarantees the essential condition of substation safety stable operation, and its reliability and safety can be subject to the great attention of design and production run department always.
The index evaluating grounded screen has stake resistance, earth potential liter, contact potential difference, step potential difference etc., is all for situation during power frequency.In fact, problem with grounding during thunderbolt is more outstanding, especially to electrical secondary system.During thunderbolt, the earth potential of grounded screen is more uneven, also larger to the interference of electrical secondary system.During thunderbolt, undesired signal can pass to secondary device by electric current, voltage transformer (VT) by secondary cable, also can be coupled to secondary cable or secondary device by external electromagnetic field, can also be applied to electrical secondary system by transient state epd.In addition also there is perception and being coupled of capacitive between secondary cable and between secondary cable with grounded screen, these are coupled mainly between cable, the electric capacity between the core skin of cable and between cable and ground, inductance cause.
Wherein, by transient state epd be applied to electrical secondary system earth mat coupling secondary cable is had the greatest impact.Earth mat coupling mainly because transient state epd is applied to the screen layer of two sides earth cable, thus produces transient current at cable shield, causes at cable core induced voltage further; Or when secondary cable heart yearn also can act directly on secondary cable heart yearn by the potential difference (PD) between earth point during carrying ground.Therefore, in grounded screen assessment, be necessary that very much assessment grounded screen impact characteristics is on the impact of secondary cable, the potential difference (PD) of grounded screen between secondary cable heart yearn, the potential difference (PD) between heart yearn and ground under such as lightning impulse, and corresponding transfer impedance.But the parameter such as stake resistance, earth potential liter, contact potential difference, step potential difference evaluating grounded screen at present can not reflect this problem.
Analyze the harassing and wrecking more complicated that when being struck by lightning grounded screen, electrical secondary system is subject to, simple calculating simulation is difficult to actual consistent with engineering, and the most reliable method is experiment.Current test method uses impulse voltage generator (or impulse current generator) to inject lightning current in grounded screen, and this electric current turns back to impulse voltage generator (or impulse current generator) by the electric current pole outside grounded screen and lead-in wire.Because grounded screen is very large, the lead-in wire needed under this method is very long, simultaneously because the stake resistance of electric current pole is very large, seriously limit the key equipment in experiment---the fan-out capability of impulse voltage generator (or impulse current generator), its output waveform is caused to distort, output voltage reduces, and cannot meet actual measurement requirement.The method of this problem of solution normally developed more high-grade current feedback circuit in the past, and experimental cost is very high.
Summary of the invention
The object of this invention is to provide the measuring method of the secondary cable transfer impedance that grounded screen dash current causes, the transfer impedance between secondary cable heart yearn and heart yearn and the transfer impedance between heart yearn and grounded screen can be obtained by this measuring method, for assessment of earthed system impact characteristics, instruct earth work construction, this measuring method is not high to the parameter request of equipment simultaneously, greatly reduces experimental cost.
Above-mentioned purpose of the present invention realizes by following technical solution: the measuring method of the secondary cable transfer impedance that grounded screen dash current causes, it is characterized in that, the method comprises the steps:
(1) choose the earth point of two points in the middle part of grounding net of transformer substation opposite side as impulse voltage generator, one of them earth point is that electric current enters place, and another earth point is outflow of bus current point;
(2) impulse voltage generator is connected with the grounded screen of transformer station by two earth points chosen in step (1);
(3) mid point of impulse voltage generator two earth point lines is found out;
(4) on the line of impulse voltage generator two earth points, find out one using the mid point of this line as the line segment of symmetric points, the length of this line segment is 80% of impulse voltage generator two earth point wire lengths;
(5) establish secondary cable on line segment upper berth, the earthing mode of secondary cable is identical with actual motion cable;
(6) use the surge waveform of standard, the electric current to impulse voltage generator enters place Injection Current, and extracts electric current out from outflow of bus current point;
(7) output current wave of oscilloscope measurement impulse voltage generator is used;
(8) due to symmetry, the potential difference (PD) between the heart yearn at any one end of the secondary cable place using oscilloscope measurement to lay and heart yearn and the potential difference (PD) between this end place heart yearn and grounded screen;
(9) by two kinds of potential difference (PD) recording in step (8) respectively divided by 2, under namely obtaining grounded screen only having a dash current decanting point, the heart yearn on secondary cable and the potential difference (PD) between heart yearn and the potential difference (PD) between heart yearn and grounded screen;
(10), compared with the output current peak value peak value of two potential difference (PD) obtained in step (9) being measured with step (7) impulse voltage generator obtained respectively, the transfer impedance between secondary cable heart yearn that grounded screen dash current causes and heart yearn and the transfer impedance between heart yearn and grounded screen can be obtained.
In the present invention, the surge waveform of described step (6) Plays is the current wave of 2.6/50us or 8/20us.
In the present invention, the transfer impedance between secondary cable heart yearn and heart yearn refers to that secondary cable refers to the transfer impedance between any one end place's heart yearn and heart yearn, and the transfer impedance between heart yearn and grounded screen refers to the transfer impedance between any one end place's heart yearn and grounded screen.
Impulse voltage generator in the present invention also can substitute with impulse current generator.
Because grounding net of transformer substation is laid closeer, also seldom have electric discharge phenomena in soil under heavy impulse current, therefore whole test macro still can think linear system.Thus, can all be connected in grounded screen in being arranged symmetrically with of system, impulse voltage generator (or impulse current generator) two ends by experiment, realize convenient, the security measurement under little impulse voltage generator (or impulse current generator) device, concrete methods of realizing is as follows:
Compared with prior art, the present invention has following remarkable result:
1, click and enter with traditional dash current one compared with, because the dash current of the inventive method a bit injects grounded screen, flow out from another point, therefore for impulse voltage generator (or impulse current generator), its load is very little, easy generation big current, therefore not high to the parameter request of impulse voltage generator (or impulse current generator), greatly reduce experimental cost.
2, the present invention can flow through larger dash current easily in grounded screen, and grounded screen produces larger transient state epd, is therefore coupled with inductively all larger to the ground connection of secondary cable, is convenient to measure.
3, the present invention only carries out due to experiment in transformer station, does not need external earth polar of standing, and therefore eliminate the outer safety practice taked at station, and current feedback circuit parameter is not high, tests safer.
4, the present invention is owing to employing symmetry principle, measurement result can equivalent single-point electric current enter ground time result.Meanwhile, due to symmetry, only need measurement secondary cable to refer to the transfer impedance at any one end place, do not need all to survey at secondary cable two ends.
Accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the present invention is described in further details.
Fig. 1 is the syndeton schematic diagram of measuring method of the present invention;
Fig. 2 is the current waveform of input grounding net of the present invention;
Fig. 3 is the potential difference (PD) between the secondary cable heart yearn measured of the present invention and grounded screen;
Fig. 4 is that in prior art, single-point injects the potential difference (PD) between secondary cable heart yearn and grounded screen of impacting lower measurement.
Description of reference numerals
1, impulse voltage generator; 2, oscillograph; 3, secondary cable
Embodiment
The measuring method of the secondary cable transfer impedance that grounded screen dash current of the present invention causes, the method comprises the steps:
(1) survey for certain transformer station, as shown in Figure 1, choosing certain transformer station's length of side is the earth points of two points in the grounded screen of 100m in the middle part of opposite side as impulse voltage generator 1, one of them earth point is that electric current enters place, another earth point is outflow of bus current point, the concrete impulse voltage generator 1 adopting EMCpro;
(2) impulse voltage generator 1 is connected with the grounded screen of transformer station by two earth points chosen in step (1);
(3) mid point of impulse voltage generator 1 two earth point lines is found out;
(4) on the line of impulse voltage generator 1 two earth points, find out one using the mid point of this line as the line segment that the 80m of symmetric points is long, the length of this line segment is 80% of impulse voltage generator 1 two earth point wire lengths;
(5) establish the coaxial secondary cable 3 that 80m is long on line segment upper berth, the earthing mode of secondary cable 3 is identical with actual motion cable;
(6) use the impulse current waveform of the standard of 8/20us, the electric current to grounded screen enters place Injection Current, and extracts electric current out from outflow of bus current point;
(7) oscillograph 2 is used to measure the output current wave of impulse voltage generator 1, as shown in Figure 2;
(8) due to symmetry, the potential difference (PD) of the secondary cable 3 using oscillograph 2 to measure to lay wherein between the heart yearn at one end place and heart yearn and secondary cable 3 are with the potential difference (PD) between one end place heart yearn and grounded screen;
(9) by two kinds of potential difference (PD) recording in step (8) respectively divided by 2, namely under obtaining only having a dash current decanting point, heart yearn on secondary cable 3 and the potential difference (PD) between heart yearn and the potential difference (PD) between heart yearn and grounded screen, measurement result is as shown in Figure 3;
(10) compared with the output current peak value peak value of two potential difference (PD) obtained in step (9) being measured with step (7) impulse voltage generator 1 obtained respectively, can obtain the transfer impedance between secondary cable 3 heart yearn that grounded screen dash current causes and heart yearn and the transfer impedance between heart yearn and grounded screen, concrete result of calculation is as shown in table 1.
Table 1: the transfer impedance between the heart yearn at secondary cable two ends and heart yearn and the transfer impedance between end heart yearn and grounded screen
Between heart yearn and heart yearn Between heart yearn and grounded screen
Transfer impedance (Europe) 0.03 0.11
Fig. 4 is that in prior art, single-point injects the potential difference (PD) between secondary cable heart yearn and grounded screen of impacting lower measurement, and its test condition is identical with the test condition in the present embodiment, also uses the impulse current waveform of the standard of 8/20us.From Fig. 3 and Fig. 4, the test result that method of the present invention obtains is consistent with traditional test result.But compared with injecting impact with single-point of the prior art, the present invention adopts symmetrical two point to inject impact, for impulse current generator, its load is very little, easy generation big current, not high to the parameter request of impulse current generator, greatly reduce experimental cost.
As the conversion of the present embodiment, the impulse current waveform in step (6) also can use the standard impulse current waveform of 2.6/50us.
As the conversion of the present embodiment, step (8) also can adopt following steps to step (10), that is:
(8) due to symmetry, oscillograph 2 is used to measure the potential difference (PD) of secondary cable 3 between other end place heart yearn and heart yearn and the potential difference (PD) between this end place heart yearn and grounded screen of laying;
(9) by two kinds of potential difference (PD) recording in step (8) respectively divided by 2, under namely obtaining only having a dash current decanting point, the heart yearn on secondary cable 3 and the potential difference (PD) between heart yearn and the potential difference (PD) between heart yearn and grounded screen;
(10), compared with the output current peak value peak value of two potential difference (PD) obtained in step (9) being measured with step (7) impulse voltage generator 1 obtained respectively, the transfer impedance between secondary cable 3 heart yearn that grounded screen dash current causes and heart yearn and the transfer impedance between heart yearn and grounded screen can be obtained.
So can obtain the transfer impedance between secondary cable heart yearn that grounded screen dash current causes and heart yearn and the transfer impedance between secondary cable heart yearn and grounded screen.
The above embodiment of the present invention is not limiting the scope of the present invention; embodiments of the present invention are not limited thereto; according to foregoing of the present invention; according to ordinary technical knowledge and the customary means of this area; do not departing under the present invention's above-mentioned basic fundamental thought prerequisite; to the amendment of other various ways that said structure of the present invention is made, replacement or change, all drop within protection scope of the present invention.

Claims (2)

1. the measuring method of secondary cable transfer impedance that causes of grounded screen dash current, it is characterized in that, the method comprises the steps:
(1) choose the earth point of two points in the middle part of grounding net of transformer substation opposite side as impulse voltage generator, one of them earth point is that electric current enters place, and another earth point is outflow of bus current point;
(2) impulse voltage generator is connected with the grounded screen of transformer station by two earth points chosen in step (1);
(3) mid point of impulse voltage generator two earth point lines is found out;
(4) on the line of impulse voltage generator two earth points, find out one using the mid point of this line as the line segment of symmetric points, the length of this line segment is 80% of impulse voltage generator two earth point wire lengths;
(5) establish secondary cable on line segment upper berth, the earthing mode of secondary cable is identical with actual motion cable;
(6) use the impulse current waveform of standard, the electric current to grounded screen enters place Injection Current, and extracts electric current out from outflow of bus current point;
(7) output current wave of oscilloscope measurement impulse voltage generator is used;
(8) due to symmetry, the potential difference (PD) of secondary cable wherein between the heart yearn at one end place and heart yearn using oscilloscope measurement to lay and the potential difference (PD) between this end place heart yearn and grounded screen;
(9) by two kinds of potential difference (PD) recording in step (8) respectively divided by 2, namely obtain under grounded screen only has a dash current decanting point, the heart yearn on secondary cable and the potential difference (PD) between heart yearn and the potential difference (PD) between heart yearn and grounded screen;
(10), compared with the output current peak value peak value of two potential difference (PD) obtained in step (9) being measured with step (7) impulse voltage generator obtained respectively, the transfer impedance between secondary cable heart yearn that grounded screen dash current causes and heart yearn and the transfer impedance between heart yearn and grounded screen can be obtained.
2. the measuring method of secondary cable transfer impedance that causes of grounded screen dash current according to claim 1, is characterized in that: the impulse current waveform of described step (6) Plays is 2.6/50us or 8/20us.
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107271758A (en) * 2017-05-28 2017-10-20 西南交通大学 Thunderbolt shaft tower earth current evaluation system and method based on bipolar plate structure
CN107728024A (en) * 2017-10-27 2018-02-23 清华大学 A kind of large-scale grounding network impact characteristics method of testing to be flowed back using earth mat
CN111624405A (en) * 2020-04-08 2020-09-04 南京航空航天大学 Long-wire shielded cable transfer impedance measurement system and method based on wavelet denoising
CN113419142A (en) * 2021-05-18 2021-09-21 国家电网有限公司 Method for analyzing safety performance of secondary cable when lightning flows into ground

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107271758A (en) * 2017-05-28 2017-10-20 西南交通大学 Thunderbolt shaft tower earth current evaluation system and method based on bipolar plate structure
CN107728024A (en) * 2017-10-27 2018-02-23 清华大学 A kind of large-scale grounding network impact characteristics method of testing to be flowed back using earth mat
CN111624405A (en) * 2020-04-08 2020-09-04 南京航空航天大学 Long-wire shielded cable transfer impedance measurement system and method based on wavelet denoising
CN113419142A (en) * 2021-05-18 2021-09-21 国家电网有限公司 Method for analyzing safety performance of secondary cable when lightning flows into ground

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