CN105067889B - The measuring method of the secondary cable transfger impedance that grounded screen dash current causes - Google Patents

The measuring method of the secondary cable transfger impedance that grounded screen dash current causes Download PDF

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CN105067889B
CN105067889B CN201510423841.8A CN201510423841A CN105067889B CN 105067889 B CN105067889 B CN 105067889B CN 201510423841 A CN201510423841 A CN 201510423841A CN 105067889 B CN105067889 B CN 105067889B
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cable
heart yearn
grounded screen
current
voltage generator
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CN105067889A (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 the measuring method of the secondary cable transfger impedance that grounded screen dash current causes, impulse voltage generator, laying secondary cable, the surge voltage using standard and current waveform is accessed including at grounding net of transformer substation, enter place injection current to the electric current of grounded screen, and flow out some extraction electric current from electric current; Use the output current wave of oscilloscope measurement impulse voltage generator; Potential difference between the secondary cable that use oscilloscope measurement is laid potential difference and this end place heart yearn and grounded screen between the heart yearn and heart yearn of any end; Record two kinds of potential differences are respectively divided by 2; By the peak value of two potential differences of acquisition respectively compared with the output current peak measuring the impulse voltage generator obtained. The present invention is obtained in that the transfger impedance between the transfger impedance between secondary cable heart yearn and heart yearn and heart yearn and grounded screen by this measuring method, is used for assessing earthed system impact characteristics, instructs earth work construction.

Description

The measuring method of the secondary cable transfger impedance that grounded screen dash current causes
Technical field
The present invention relates to technical field of high voltage, specifically refer to the measuring method of the secondary cable transfger impedance that grounded screen dash current causes, for assessing grounded screen impact on secondary cable when being subject to lightning impulse.
Background technology
In order to work and security needs in power system, often some part of power system and electrical equipment thereof need to be connected with the earth, here it is ground connection. Power system ground connection can be divided into working earthing, lightning protection and protective grounding three kinds with regard to its purpose. Wherein lightning protection is the harm in order to avoid thunder and lightning, and the thunder resisting equipment such as discharging rod, lightning conducter and spark gap all must be equipped with corresponding grounding device lightning current is imported the earth. Grounded screen is to ensure that the essential condition of substation safety stable operation, and its reliability and safety can be constantly subjected to the great attention of design and production run department.
The index evaluating grounded screen has earth resistance, earth potential liter, contact electromotive force, step potential difference etc., is all situation during for power frequency. It practice, problem with grounding during thunderbolt is more prominent, especially to electrical secondary system. During thunderbolt, the earth potential of grounded screen is more uneven, and the interference of electrical secondary system is also bigger. Disturb signal can be passed to secondary device by electric current, voltage transformer by secondary cable during thunderbolt, it is also possible to be coupled to secondary cable or secondary device by external electromagnetic field, it is also possible to be applied to electrical secondary system by transient state epd. In addition there is also perception and the coupling of capacitive between secondary cable and between secondary cable with grounded screen, these couplings are mainly between cable, the electric capacity between the core skin of cable and 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 is applied to the screen layer of two sides earth cable mainly due to transient state epd, thus produce transient current at cable shield, cause at cable core induced voltage further; Or the potential difference between earth point also can act directly on secondary cable heart yearn when secondary cable heart yearn is by carrying ground. Therefore, in grounded screen is assessed, it is highly desirable to the assessment grounded screen impact characteristics impact on secondary cable, grounded screen potential difference between secondary cable heart yearn, the potential difference between heart yearn and ground under such as lightning impulse, and corresponding transfger impedance. But evaluate the parameters such as the earth resistance of grounded screen, earth potential liter, contact electromotive force, step potential difference at present and can not reflect this problem.
The harassing and wrecking that when analyzing thunderbolt grounded screen, electrical secondary system is subject to are more complicated, and simple calculating simulation is difficult to actual consistent with engineering, and the most reliable method is experiment. Current test method be use impulse voltage generator (or impulse current generator) in grounded screen, inject lightning current, this electric current by grounded screen outside electric current pole and lead-in wire return to impulse voltage generator (or impulse current generator). Owing to grounded screen is very big, the lead-in wire needed under this method is very long, simultaneously because the earth resistance of electric current pole is very big, seriously limit the fan-out capability of key equipment impulse voltage generator (or impulse current generator) in experiment, cause that its output waveform distorts, output voltage reduces, it is impossible to meet actual measurement requirement. The method solving this problem in the past usually develops the current feedback circuit of greater degree, and experimental cost is significantly high.
Summary of the invention
It is an object of the invention to provide the measuring method of the secondary cable transfger impedance that grounded screen dash current causes, it is obtained in that the transfger impedance between the transfger impedance between secondary cable heart yearn and heart yearn and heart yearn and grounded screen by this measuring method, for assessing 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.
The above-mentioned purpose of the present invention realizes by following technical solution: the measuring method of the secondary cable transfger impedance that grounded screen dash current causes, it is characterised in that the method comprises the steps:
(1) choosing the earth point as impulse voltage generator of two points in the middle part of grounding net of transformer substation opposite side, one of them earth point is that electric current enters place, and another earth point is that electric current flows out point;
(2) impulse voltage generator is connected with the grounded screen of transformer station by two earth points chosen in step (1);
(3) midpoint of two earth point lines of impulse voltage generator is found out;
(4) on the line of two earth points of impulse voltage generator, find out one using the midpoint of this line the line segment as point of symmetry, the length of this line segment is the 80% of two earth point wire lengths of impulse voltage generator;
(5) setting 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, enter place injection current to the electric current of impulse voltage generator, and flow out some extraction electric current from electric current;
(7) output current wave of oscilloscope measurement impulse voltage generator is used;
(8) potential difference between potential difference and this end place heart yearn and grounded screen due to symmetry, between heart yearn and the heart yearn of any end of secondary cable that use oscilloscope measurement is laid;
(9) the two kinds of potential differences recorded in step (8) are respectively divided by 2, namely obtain in grounded screen under only one of which dash current decanting point, the potential difference between potential difference and heart yearn and grounded screen between heart yearn and heart yearn on secondary cable;
(10) by the peak value of two potential differences obtained in step (9) respectively compared with the output current peak of the impulse voltage generator that step (7) measurement obtains, the transfger impedance between transfger impedance and heart yearn and the grounded screen between secondary cable heart yearn and the heart yearn that grounded screen dash current causes can be obtained.
In the present invention, the current wave that surge waveform is 2.6/50us or 8/20us of described step (6) Plays.
In the present invention, the transfger impedance between secondary cable heart yearn and heart yearn refers to that secondary cable refers to the transfger impedance between any end heart yearn and heart yearn, and the transfger impedance between heart yearn and grounded screen refers to the transfger impedance between any end heart yearn and grounded screen.
Impulse voltage generator in the present invention can also substitute with impulse current generator.
Owing to grounding net of transformer substation is laid closeer, also seldom having electric discharge phenomena under heavy impulse current in soil, therefore whole test system still may be considered linear system. Thus, can by experiment being arranged symmetrically with of system, impulse voltage generator (or impulse current generator) two ends are all connected in grounded screen, realizing 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, owing to 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 only small, easily produce big electric current, therefore that the parameter request of impulse voltage generator (or impulse current generator) is not high, greatly reduce experimental cost.
2, the present invention can flow through relatively larger dash current easily in grounded screen, produces relatively larger transient state epd in grounded screen, therefore the ground connection of secondary cable is coupled and inductively all relatively larger, it is simple to measures.
3, due to the fact that experiment only carries out in transformer station, it is not necessary to external earth polar of standing, therefore eliminate the outer safety measure taked at station, and current feedback circuit parameter is not high, tests safer.
4, due to the fact that and employ symmetry principle, measurement result can equivalence single-point electric current result when entering ground. Simultaneously as symmetry, it is only necessary to measure secondary cable and refer to the transfger impedance of any end, it is not necessary to all 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 attachment structure 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 between secondary cable heart yearn and the grounded screen that the present invention measures;
Fig. 4 is that in prior art, single-point injects the potential difference impacted between lower secondary cable heart yearn and the grounded screen measured.
Description of reference numerals
1, impulse voltage generator; 2, oscillograph; 3, secondary cable
Detailed description of the invention
The measuring method of the secondary cable transfger 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, choose in the grounded screen that certain transformer station's length of side is 100m the earth point as impulse voltage generator 1 of two points in the middle part of opposite side, one of them earth point is that electric current enters place, another earth point is that electric current flows out 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) midpoint of 1 two earth point lines of impulse voltage generator is found out;
(4) on the line of 1 two earth points of impulse voltage generator, find out one using the midpoint of this line the line segment as the 80m length of point of symmetry, the length of this line segment is the 80% of 1 two earth point wire lengths of impulse voltage generator;
(5) set the coaxial secondary cable 3 of 80m length 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, enter place injection current to the electric current of grounded screen, and flow out some extraction electric current from electric current;
(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, oscillograph 2 is used to measure the potential difference between heart yearn and the heart yearn of secondary cable 3 end wherein laid and secondary cable 3 with the potential difference between end heart yearn and grounded screen;
(9) the two kinds of potential differences recorded in step (8) are respectively divided by 2, namely obtain under only one of which dash current decanting point, the potential difference between potential difference and heart yearn and grounded screen between heart yearn and heart yearn on secondary cable 3, measurement result is as shown in Figure 3;
(10) by the peak value of two potential differences obtained in step (9) respectively compared with the output current peak of the impulse voltage generator 1 that step (7) measurement obtains, can obtaining the transfger impedance between transfger impedance and heart yearn and the grounded screen between secondary cable 3 heart yearn and the heart yearn that grounded screen dash current causes, concrete result of calculation is as shown in table 1.
Table 1: the transfger impedance between transfger impedance and end heart yearn and grounded screen between heart yearn and the heart yearn at secondary cable two ends
Between heart yearn and heart yearn Between heart yearn and grounded screen
Transfger impedance (Europe) 0.03 0.11
Fig. 4 is that in prior art, single-point injects the potential difference impacted between lower secondary cable heart yearn and the grounded screen measured, and its experimental condition is identical with the experimental 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 the method for the present invention is obtained is consistent with traditional test result. But compared with injecting impact with single-point of the prior art, the present invention adopts the two point of symmetry to inject impact, for impulse current generator, its load is only small, easily produce big electric current, the parameter request of impulse current generator is not high, greatly reduce experimental cost.
As the conversion of the present embodiment, the impulse current waveform in step (6) can also use the standard impulse current waveform of 2.6/50us.
As the conversion of the present embodiment, step (8) can also adopt following steps to step (10), it may be assumed that
(8) due to symmetry, oscillograph 2 is used to measure the potential difference between the secondary cable 3 laid potential difference and this end place heart yearn and grounded screen between other end place heart yearn and heart yearn;
(9) the two kinds of potential differences recorded in step (8) are respectively divided by 2, namely obtain under only one of which dash current decanting point, the potential difference between potential difference and heart yearn and grounded screen between heart yearn and heart yearn on secondary cable 3;
(10) by the peak value of two potential differences obtained in step (9) respectively compared with the output current peak of the impulse voltage generator 1 that step (7) measurement obtains, the transfger impedance between transfger impedance and heart yearn and the grounded screen between secondary cable 3 heart yearn and the heart yearn that grounded screen dash current causes can be obtained.
So can obtain the transfger impedance between the transfger impedance between secondary cable heart yearn and the heart yearn that grounded screen dash current causes and 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 to this; foregoing according to the present invention; ordinary technical knowledge and customary means according to this area; without departing under the above-mentioned basic fundamental thought premise of the present invention; to the amendment of other various ways that said structure of the present invention is made, replacement or change, all fall within protection scope of the present invention.

Claims (2)

1. the measuring method of the secondary cable transfger impedance that grounded screen dash current causes, it is characterised in that the method comprises the steps:
(1) choosing the earth point as impulse voltage generator of two points in the middle part of grounding net of transformer substation opposite side, one of them earth point is that electric current enters place, and another earth point is that electric current flows out point;
(2) impulse voltage generator is connected with the grounded screen of transformer station by two earth points chosen in step (1);
(3) midpoint of two earth point lines of impulse voltage generator is found out;
(4) on the line of two earth points of impulse voltage generator, find out one using the midpoint of this line the line segment as point of symmetry, the length of this line segment is the 80% of two earth point wire lengths of impulse voltage generator;
(5) setting 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, enter place injection current to the electric current of grounded screen, and flow out some extraction electric current from electric current;
(7) output current wave of oscilloscope measurement impulse voltage generator is used;
(8) potential difference between potential difference and this end place heart yearn and grounded screen due to symmetry, between heart yearn and the heart yearn of the secondary cable end wherein that use oscilloscope measurement is laid;
(9) the two kinds of potential differences recorded in step (8) are respectively divided by 2, namely obtain under grounded screen only one of which dash current decanting point, the potential difference between potential difference and heart yearn and grounded screen between heart yearn and heart yearn on secondary cable;
(10) by the peak value of two potential differences obtained in step (9) respectively compared with the output current peak of the impulse voltage generator that step (7) measurement obtains, the transfger impedance between transfger impedance and heart yearn and the grounded screen between secondary cable heart yearn and the heart yearn that grounded screen dash current causes can be obtained.
2. the measuring method of the secondary cable transfger impedance that grounded screen dash current according to claim 1 causes, it is characterised in that: the impulse current waveform of described step (6) Plays is 2.6/50 �� s or 8/20 �� s.
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