CN102435908A - On-line ranging method for single-phase earth fault based on zero mode and phase mode current traveling waves - Google Patents
On-line ranging method for single-phase earth fault based on zero mode and phase mode current traveling waves Download PDFInfo
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Abstract
The invention provides an on-line ranging method for a single-phase earth fault based on zero mode and phase mode current traveling waves. The method comprises the following steps: adopting waveform comparison on specific frequency traveling wave current signals of a zero mode amperage and a phase mode amperage tested on a test point; and distinguishing waveforms of a fault initial traveling wave, a fault point reflected wave and a fault point transmission wave, wherein if current waveforms obtained after corresponding to t1, t2 and t3 moments are sequentially the initial traveling wave, a current reflected traveling wave and a current transmission traveling wave, the single-phase earth fault point happens on a front halfway of a tested circuit, so that a formula L is applied to calculate the distance from the fault point to the test point, and if current waveforms obtained after corresponding to t1, t2 and t3 are sequentially the initial traveling wave, the current transmission traveling wave and the current reflected traveling wave, the single-phase earth fault point happens on a rear halfway of the tested circuit, so that a formula is applied to calculate the distance from the fault point to the test point. The method provided by the invention has higher accuracy, is easy to realize, and can be applied to practical sites.
Description
Technical field
The present invention relates to the online distance-finding method of a kind of singlephase earth fault, relate in particular to a kind of based on zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually.
Background technology
Current, for ensureing the reliability of power supply, the distribution system of China adopts small current neutral grounding system usually, behind the small current neutral grounding system generation singlephase earth fault, as can not in time eliminating the electric arc possibility burning apparatus of trouble spot, and initiation phase-to phase fault, expansion accident.Along with expanding economy, power cable has obtained application more and more widely.In application, often be layed in undergroundly, in a single day cable breaks down, and difficulty is sought in the trouble spot, not only needs the labor intensive material resources, also will bring loss of outage difficult to the appraisal.
Mostly cable fault is singlephase earth fault, is line to line fault or three phase short circuit fault on a small quantity.China's Operation of Electric Systems regulation: small current neutral grounding system generation singlephase earth fault allows charging operation two hours; This means and in the extremely short time, to confirm abort situation; But little electric current single-phase earthing does not constitute tangible short-circuit loop; Steady-state signal is not obvious how accurately, rapidly, economically, find out the power cable Method of Cable Trouble Point in the current concern that receives domestic each power supply enterprise and technician day by day.
Further analysis obtains to power cable fault, and power cable fault mainly contains open circuit, low-impedance earthed system, high resistance ground, short circuit, three-phase shortcircuit or two-phase short-circuit fault, and wherein 70% is singlephase earth fault, therefore can be used as the emphasis direction of technical solution problem.The processing of power cable fault has fault type diagnosis, abort situation coarse localization (range finding) and accurate measurement location.What wherein have practical value mainly is the fault range finding.
The power cable fault distance-finding method can be divided into two big types on principle: traveling wave method and impedance method, be divided into the range finding of online range finding and off-line in the application, and wherein online range finding is divided into single-ended method and two kinds of distance-finding methods of both-end method again.
Impedance method is through the impedance of measurements and calculations trouble spot to measuring junction, and then according to line parameter circuit value, row are write and found the solution the trouble spot equation, try to achieve fault distance.This method is many sets up model with the lumped parameter of circuit, and principle is simple, be easy to realize, and be the focus that people pay close attention to for many years, major defect is that error is big.
The travelling wave ranging method: the research of traveling wave fault location can be traced back to the 1950's; People have these characteristics of fixing velocity of propagation (velocity of wave of power cable is 150～200m/ μ s) on the line according to the capable ripple of voltage and current, have proposed the traveling wave fault location method.Travelling wave ranging method utilization row ripple can obtain distance in the time of measurement point to round trip between the trouble spot through simple operation, and precision can reach more than 0.2 meter in theory.Chinese scholars has proposed many diverse ways on the obtaining and discern of travelling wave signal, and the first kind is to utilize the method for voltage traveling wave signal.But the voltage traveling wave signal is difficult for obtaining, and therefore, utilizes both-end voltage traveling wave signal that the method for cable fault localization is not applied.Second type is the distance-finding method that adopts the current traveling wave signal, when the bus outlet more for a long time, voltage signal is more weak, and current signal is very strong, current traveling wave signal ratio is easier to obtain.
About problem online and the off-line range finding.Present most of cable fault localization method is mainly off-line to carry out; But online fault distance-finding method also occurs; Its starting point is with the loop line open circuit or at line end open circuit point to be set; Positive or negative total reflection takes place in open circuit point in surge voltage that produces when utilizing fault or electric current, obtains pulse signal through near the sensor of being located at the open circuit point, measures then and realizes range finding its interpulse period.Online range finding does not obtain promoting in practical application, and its reason is cable line in maintenance and the singularity aspect safeguarding, and does not have clear superiority at line method with respect to off-line method.On cable fault localization method, off-line and online distance-finding method will for a long time and be deposited, but in the long run, online range finding is only the development in future direction.
(1) the online cable fault localization of realization of application high speed optoelectronic sensing technology.
Document [1] N.inou.T.Tsunkage.S.Sakai.On-line fault location system for 66Kv underground cables with fast O/E and fast A/D technique [J] .IEEE Transactions on Power Delivery.1994; 9 (1): 579-584 has introduced a kind of cable fault localization system; And researched and developed realization equipment; Ultimate principle is following: when cable breaks down; The trouble spot produces surge current and propagates to the cable two ends, when surge current arrives test lead, and the corresponding t that constantly is respectively
1And t
2, then propagation time difference is Δ t=t just
1-t
2, the trouble spot can be expressed as to the distance of test lead:
Wherein L is a total cable length, and υ is the velocity of propagation of surge current in cable.
Visible by top formula, how to confirm mistiming Δ t exactly, be the key of dealing with problems.Because surge current is a very fast process; This system has adopted magneto-optical sensor, and in addition, this system adopts high-speed a/d converter; The surge waveform is sampled; Form data, so that confirm the mistiming that surge current arrives more accurately, this is just far better than traditional comparator sum counter.The A/D converter sampling rate is 16M/s.Surge current is in the cable communication process, because the frequency differential declines is different, dispersion phenomenon takes place, so the surge waveform distorts, and the rise time also produces delay.Surge current reaches the time delay before the fiducial value, concerning classic method, is a major reason that produces the fault localization error.Yet in this AD/ disposal route, the current waveform that does not reach fiducial value also is recorded in the preparatory flip-flop storage, so just can differentiate the rising point in the surge waveform, avoids taking place range error.Waveform can save as data file, so that later analysis and processing.In this system, magneto-optical sensor produces light signal, become electric signal to light signal through a high-speed light/electricity (O/E) converter.This electric signal becomes the discrete digital signal through high-speed a/d converter, gives CPU and handles.After calculating fault distance according to top formula, the result is presented on the LCDs.
This system makes substantial progress in the online fault localization of cable field, and precision can be found fault rapidly from actual require to hardly differ (in the 1000m experiment, being 1.99m than mistake), reduces loss of outage.But shortcoming still exists:
1. surge waveform rising point confirms; This system has adopted the method for calculating the discrete point number, and for the SF of 16M/s, the distance between two points is corresponding to the time of 62.5ns; Two waveforms all adopt identical point, should not have too big error in theory.But because dispersion phenomenon and the extraneous electromagnetic interference (EMI) of surge waveform in communication process, the method still has the possibility of makeing mistakes.
2. surge speed is got empirical value, and is also influential to distance accuracy.And, use this method, the trouble spot is near the cable mid point time, and distance accuracy is higher, and near the cable line two ends time, error is very big.This error root rises in the delay of fault waveform.
3. use fiber optic communications between magneto-optical sensor and the photoelectric commutator, for long transmission line, the investment of optical cable is too big.
Document [2] Cai Guirong. the method [J] of using optical fibre sensor location cable fault. electric wire .2000,2 (6): 31-37
[3] T.Wakai, N.Takinami, T.Chino; K.Amano, K.Watanabe, etc.A new approach to cable fault location using fiber optictechnology [J]; IEEE Transactions on Power Delivery.1995,10 (1): 85-91 utilizes optical fiber to carry out cable fault localization equally, but employing is the fiber optic temperature distribution sensor; Optical Fiber Composite in cable, is made the Optical Fiber Composite cable.The fiber optic temperature distribution sensor does not receive the influence of electromagnetic induction fully, behind the laser beam injection fibre, with spectroscope Raman (Rmana) back scattering light is separated, and the intensity of this light is with temperature variation.Through measuring light intensity,, whether normal through monitor temperature indirect monitoring cable line ruuning situation through reading temperature value after the formula conversion.And fault distance can calculate through the injection length of laser pulse and difference time of arrival of reflection ray, and the velocity of propagation of laser in this type optical fiber is 0.02m/ns.This method is accurate to failure location, and positioning time is few, and to the damage of cable less than other traveling wave method; But it is high to make composite fiber cable cost, and protection optical fiber is injury-free more difficult than cable itself.
(2) the online Two-terminal Fault Location of the cable of applying GPS
Document [4] Qin Jian; Chen Xiang standards etc. are utilized the both-end travelling wave ranging new method [J] of wavelet transformation, Proceedings of the CSEE; 2000.20 (8): 6-10. successfully is applied to cable fault localization with GPS (GPS), the cable fault localization technology is pushed away going a step further again.In this system, the mistiming of adopting the fault surge to arrive the cable two ends equally locatees.This just requires the time at cable two ends to want synchronously.This fault localization system that the rattan storehouse electric wire company of Japan produces utilizes the GPS technology, guarantees the precise synchronization at each terminal.The GPS synchronous satellite is equipped with the atomic clock of pin-point accuracy, has guaranteed the pin-point accuracy property of information such as time, position.The GPS synchronous satellite is to earth transmission high precision pulse signal (being called as the C/A sign indicating number), is installed in the timer at range finding terminal, utilize high-precision crystal oscillator and pulse signal synchronously, realize each terminal synchronous to the time.
The system works principle is summarized as follows: the trouble spot produces surge current, propagates to the cable two ends, when arriving two ends; The magneto-optical sensor that is installed in the cable two ends detects; Become electric signal through photoelectric commutator again, be sent to waveform processor, the count value that reaches certain amplitude is noted by waveform processor; Gps receiver is handled delivering CPU with data moment corresponding value, is sent to main website through Modem and telephone wire then.In main website, the computing formula cotype (1) of abort situation.Visible from its principle, the application of GPS makes that the acquisition of surge due in is more accurate, and the range error of system is also littler, and this system can reach the range error of 10m; Simultaneously since each terminal can be independently and synchronous satellite synchronous, just there is no need installation synchrodyne at the terminal, make system simpler, expense is also still less; Because the frequency response of cable resistance, the waveform of surge current can distort in the cable communication process, this system compensates this, further improves distance measuring precision.After the fault traveling wave crest generation chromatic dispersion, accurately confirming of rising point is relatively more difficult.Though this system has carried out correction-compensation to it, still can not get rid of above-mentioned difficulties fully, extraneous interference still can influence the range finding result.In addition, to the velocity of propagation of surge current, document is not discussed, and it also is one of key factor of influence range finding result.So, the propagation characteristic of row ripple in power cable also awaited further research.
Summary of the invention
The objective of the invention is in order to overcome the deficiency of above-mentioned technology, provide a kind of cable singlephase earth fault position is judged that precision is higher, realize easily based on zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually.
For realizing above-mentioned purpose, technical scheme of the present invention is:
In zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually, the step that it comprises is:
Phase mould electric current that step 3, real time record are sampled and zero mould electric current are judged to have or not the mutation current amount, have judged whether that promptly earth short circuit current takes place;
Described step 1 is included in the current sensor of mould mutually that is respectively equipped with on the every phase line with the current collecting device described in the step 2, with at three zero mould current sensors of suit on the circuit mutually.
Be specially in the described step 3; When earth fault not occurring with institute survey line road; Increase zero mould that synchronized sampling obtains in time and touch current value benchmark zero axle as a reference mutually, when earth fault took place, current collecting device collected the current signal of sudden change in real time; The current signal of said sudden change comprises the zero mould magnitude of current and the mould magnitude of current mutually; Extract each 1 second travelling wave current signal before and after the current signal of sudden change, when the current signal relative reference benchmark of measuring said sudden change zero axle up and down offset value set greater than institute's examining system scale the single-phase-to-ground current threshold value time, assert that singlephase earth fault takes place; Said ground current threshold setting interval is institute's examining system single-phase earth fault current peaked 50%～75%;
In the described step 4; The measured zero mould magnitude of current and mutually the aforesaid relatively reference data of the mould magnitude of current zero axle take place promutation the time; And the zero mould magnitude of current is right after appearance of negative to the mutation current trough with mould magnitude of current waveform mutually around zero mutation current crest that forward all occurs of reference data; When complete elder generation positive back negative current waveform promptly occurring, regard as the initial row ripple; Survey zero mould and be defined as t constantly with first mutation current ripple initial point position of initial row ripple of mould electric current mutually
1. constantly;
In conjunction with measured initial row ripple; Differentiate being right after initial row ripple current waveform afterwards; Be right after appearance of negative to the mutation current trough if the zero mould magnitude of current all occurs forward mutation assay electric current crest with mould magnitude of current waveform mutually around reference data zero axle, during the negative current waveform, regard as current reflection row ripple after promptly complete elder generation is positive; If the resulting zero mould magnitude of current and mould magnitude of current waveform mutually around reference data zero axle all occur complete elder generation negative after during the positive current waveform, regard as electric current transmission row ripple; The measured initial point position that is right after initial row ripple mutation current ripple afterwards is defined as t constantly
2Constantly;
In conjunction with measured initial row ripple, again to t
2The elder generation that constantly the judges negative current reflection row wave-wave shape in positive back; Or the positive electric current transmission row wave-wave shape current waveform following closely in negative earlier back is differentiated; If the zero mould magnitude of current and mould magnitude of current waveform mutually around reference data zero axle all occur with the described complete elder generation of initial row ripple positive after during the negative current waveform; Regard as current reflection row ripple, if the zero mould magnitude of current of gained is right after forward mutation assay electric current crest around the equal appearance of negative of reference data zero axle to the mutation current trough with mould magnitude of current waveform mutually, when promptly complete elder generation bears the after-current waveform; Regard as electric current transmission row ripple, the measured t that follows closely
2The initial point position of the mutation current ripple after the initial full current waveform is defined as t constantly constantly
3Constantly;
In the said step 5, if respectively with t
1, t
2, t
3The corresponding current waveform that obtains is followed successively by initial row ripple, current reflection row ripple, electric current transmission row ripple and explains that then the singlephase earth fault point occurs in the first half term on institute survey line road constantly; Using formula
Calculate the distance of trouble spot to test point; If the current waveform that institute correspondence obtains is followed successively by initial row ripple, electric current transmission row ripple, current reflection row ripple and explains that then the singlephase earth fault point occurs in the second half on institute survey line road; Using formula
Calculate the distance of trouble spot to test point;
Described first half term and the second half are for being the boundary with cable line total length mid point, and test point place cut cable is defined as the first half term cable section, the cable section after the phase alignment be the second half cable section;
X is the distance of trouble spot distance test point in the formula; L is the power cable line total length;
t
1It is zero mould and first mutation current ripple initial point position moment of initial row ripple of mould electric current mutually; Be the trouble spot when breaking down current traveling wave reach moment of test point for the first time from the trouble spot;
t
2Be that the measured initial point position that is right after initial row ripple mutation current ripple afterwards defines constantly; Promptly zero mould current traveling wave is t with reference data zero axle of crossing first after mould current traveling wave mutually is right after the initial row ripple constantly
2Constantly;
t
3Be the measured t of following closely
2The initial point position of the mutation current ripple after the initial full current waveform constantly constantly; Promptly zero mould current traveling wave follows t closely with mould current traveling wave mutually
2Constantly the current traveling wave after the current traveling wave to cross reference data zero axle first be t constantly
3Constantly.
Described sampling rate is set at 10MHz.
Extract the sudden change current signal in 10KHz～100KHz frequency band.
When earth fault took place, phase mould electric current was similar with zero mould current waveform shape, and zero mould current amplitude is big, judged that easily catastrophe point takes place constantly, and the phase mould current amplitude of fault phase is little, and earth fault takes place mutually for which to be used for confirming three-phase line.When earth fault takes place, mainly catch first three travelling wave current (first three catastrophe point on zero mould electric current, the phase mould electric current), theory is verified, and when fault occurred in first half term, three travelling wave currents were respectively initial row ripple, reflected traveling wave, transmission row ripple.When fault occurred in the second half, three travelling wave currents were respectively initial row ripple, transmission row ripple, reflected traveling wave.Judge that the purpose that three capable ripples are initial row ripple, transmission row ripple, reflected traveling wave mainly is to confirm that fault occurs in first half term or the second half.
Three initial tangible crests of zero crossing of sudden change fluctuation first are defined as initial row ripple and the two or three capable ripple respectively; Find out that first and second crest is similar; Judging for the second time through polarity, the row ripple is a reflection wave; The ripple of going for the third time is a transmitted wave, and later waveform is the repeatedly reflection wave of fault traveling wave in electrical network, the waveform sum of transmitted wave, and the crest that is not easy to the row ripple is distinguished.
In relating to the real system course of work, when not having the cable grounding fault just often " current signal harvester " gather current signal always with the SF of 10MHz; Preserve signal storage in preceding 1 second in storer, in the time of next one second, data are covered previous one second ground data; " current signal harvester " preserved preceding 1 second current signal when fault took place; Continue to gather next second vagabond current signal then, " the localization of fault ranging procedure " after 1 second in " intelligent computer " is to the data analysis in 2 seconds, at first according to the current signal mutability; Judge preceding 3 jump signals; Analyze the change in polarity of jump signal then: first jump signal is the initial row ripple, and second jump signal is similar with first waveform shape to be reflection wave then, and waveform similarity then is a transmitted wave after the pole reversal.Second jump signal is that reflection wave is judged earth fault in view of the above and occurred in first half term, and second jump signal is that transmitted wave is judged earth fault in view of the above and occurred in the second half.The 3rd jump signal mainly is the moment of judging that catastrophe point takes place.Waveform extracting according to storage goes out first jump signal generation t constantly
1, t constantly takes place in second jump signal
2, t constantly takes place in the 3rd jump signal
3
Computing machine occurs in first half term using formula
according to fault
Fault occurs in the second half using formula
Calculate the position of the distance test point of earth fault generation, which is determined according to phase mould electric current ground connection is taken place mutually.
During according to power requirement medium voltage network generation singlephase earth fault, the operation charging operation.The electric leakage custodial care facility is reported to the police when therefore breaking down, and fault locator is quoted the position that fault takes place.
At this to the explanation that makes an explanation of several notions:
The phase mould magnitude of current: adopt three phase supply in the Alternating Current Power Supply electrical network; It is respectively A phase line, B phase line, C phase line that balanced load is down adopted three-way; It is respectively A phase line, B phase line, C phase line and zero line (not being ground wire) that four lines are adopted in the lack of balance load, and on every phase line, recording the magnitude of current is the phase mould magnitude of current.
The topotype magnitude of current: refer to that each forms electric current mutually and between the earth in the Alternating Current Power Supply electrical network; During normal power supply; Each does not have electric current mutually and between the earth, in case a certain position ground connection of breaking down on the phase circuit, other two phases circuits form the loop through ground capacitance, the earth, earth point, the cable of cable; The magnitude of current that produces is in the topotype electric current, the topotype electric current be three-phase current vector and.
The line mould magnitude of current: adopt three phase supply in the Alternating Current Power Supply electrical network, the mathematical description of each phase is according to the definition of three phase coordinate systems in space, each alternate 120 degree angle that differ.In Power System Analysis,, be transformed to i through Parker (Park) conversion in order to analyze the convenience of synchronous motor characteristic
dComponent, i
qComponent and i
0Zero mold component, i
dComponent, i
qComponent is the line mold component,
From formula, can find out zero mold component i
0Be exactly mold component, claim zero-sequence current component again.
For the three-phase imbalance circuit, the wave impedance under each modulus is different with the travel-time.A way that addresses this problem is to utilize the uncoupling of modulus analytic approach; Be decomposed into a plurality of single mode amounts loop of removing coupling to the multi-phase circuit model that has coupling, thereby reach the purpose of finding the solution the multiphase coupled equations of line with frequency dependence distributed constant circuit principle.Modulus mainly is divided into two types: zero mould and line mould.Zero mould electric current is a zero sequence mould electric current, as long as ground current is arranged, zero mould electric current is just non-vanishing.
The electric power system alternating current electric line all is made up of three-phase line mostly, and electromagnetic connection (i.e. coupling mutually) is arranged between each phase circuit.When carrying out the electro-magnetic transient analysis, need use the distributed constant circuit model of frequency dependence, the realization of this model can only be based on single-phase (or single mode amount) loop.Capable wave property when therefore analyzing singlephase earth fault with the phase modulus earlier.
For the not direct earthing electric network system of neutral point,, shown in Figure 2 if having only one tunnel outlet.Singlephase earth fault phase mould current diagram in the power cable, the phase mould current i that A phase line current transformer is surveyed among the figure
A, the phase mould current i surveyed of B phase line current transformer
B, the phase mould current i surveyed of C phase line current transformer
C, zero sequence current mutual inductor records zero mould magnitude of current i
0, the fault traveling wave electric current when arrow is represented earth fault.
Under normal condition, the threephase load balance records each phase mould current i in test point
A, i
B, i
C, be line modulus i according to the Park shift conversion with the three-phase vector current
d, i
qWith zero mould magnitude of current i
0, wherein the zero modulus vector that is equivalent to the three-phase vector current with:
Under normal condition, the threephase load balance is if actual field adopts a zero sequence current mutual inductor to measure zero sequence current signal i on triple-phase line
0, recording zero modulus electric current the same with zero-sequence current is zero.
If as shown in Figure 2ly apart from position, current transformer x place earth fault is taking place in the C phase line, singlephase earth fault (having only single conductor and the earth formation loop) promptly takes place.C phase road ground connection moment need discharge the electric charge of circuit capacitive accumulation, be equivalent to insert an anti-power supply at earth point, through C phase circuit, A and B mutually anti-, the earth point of circuit, A and the B phase line appearance of a street constitute the loop, produce ground current i
g, the phase mould current i that promptly when ground connection is taken place, on C phase circuit, records '
C=i
C+ i
gInstantaneous travelling wave current i when power frequency load current and single-phase earthing are arranged
gSignal.
Adopt three phase supply in the Alternating Current Power Supply electrical network, the mathematical description of each phase is according to the definition of three phase coordinate systems in space, each alternate 120 degree angle that differ.In Power System Analysis,, be transformed to i through Parker (Park) conversion in order to analyze the convenience of synchronous motor characteristic
dComponent, i
qComponent and i
0Zero mold component, i
dComponent, i
qComponent is the line mold component,
From formula, can find out zero mold component i
0Be exactly zero mold component, claim zero-sequence current component again
Derivation of equation explanation of the present invention, the general non-direct ground system that adopts through reactor, high resistant etc. of the mesolow AC network of current our country, the electric network protection when being convenient to ground connection.High-voltage fence adopts isolated neutral system.The power cable line total length is L, and singlephase earth fault takes place in the trouble spot that is located in the circuit first half term, and the trouble spot is x apart from the distance of M end test point, and the velocity of propagation of capable ripple in cable of CF ω is υ, holds test point successively at t at M
1, t
2And t
3First three the row wave-wave peak that constantly records, the time sequencing of generation is shown in figure four.t
1Capable ripple constantly be the trouble spot when breaking down current traveling wave reach the waveform of test point for the first time from the trouble spot; The capable ripple of ground current at first is transferred to bus and produces reflection wave (polarity of traveling wave is for negative) through the bus emission then in that touchdown time takes place from the trouble spot; Crest polarity is that positive earlier back is negative; Reflection wave produces reflection (polarity of traveling wave for just) behind the trouble spot once more, at t
2Row ripple road along the line transmission constantly reflects back to bus from the trouble spot through test point then.The capable ripple of in like manner analyzing when breaking down in the trouble spot is transferred to opposite end bus N in opposite direction, reflexes to the trouble spot through N end bus, then through the transmission (polarity of traveling wave is constant) of trouble spot at t
3Constantly be transferred to test point.
Foundation obtains relational expression:
Remove the influence of capable ripple transmission speed, obtain trouble spot distance test point distance:
In like manner analyze when circuit the second half breaks down, then t
1, t
2And t
3Be respectively fault initial row ripple, trouble spot transmitted wave and trouble spot reflection wave and arrive measuring junction constantly.Obtain trouble spot distance test point distance:
Can find out from formula
and formula
formula; The fault localization formula that is drawn through deriving does not contain capable this variable of wave-wave speed; Therefore eliminated the influence of velocity of wave in theory, formed the irrelevant traveling wave fault location method of velocity of wave distance accuracy.It is fault point reflection ripple or circuit opposite end reflection wave that the key of this method is accurately to discern second capable ripple that measuring junction M obtained.And the zero mould that adopts obtains two groups of identical travelling wave current signals with phase mould current filtering, and the waveform starting point is apparent in view, for identifying transmitted wave and reflection wave has great importance.
Description of drawings
Fig. 1 is based on zero mould and the online distance-finding method process flow diagram of mould current traveling wave singlephase earth fault mutually.
Singlephase earth fault phase mould current diagram in Fig. 2 power cable.
The capable ripple of ground current communication process in the line during Fig. 3 generation earth fault.
The zero mould magnitude of current that Fig. 4 test point is tested or the filtered waveform of the phase mould magnitude of current.
Fig. 5 singlephase earth fault test circuit.
Phase mould current traveling wave during Fig. 6 generation earth fault (on) and 10 milliseconds of zero mould current traveling waves (descending) in waveform.
Phase mould current traveling wave during Fig. 7 generation earth fault (on) and the capable ripple of zero mould current traveling wave (descending) ground connection moment.
Phase mould current traveling wave during Fig. 8 generation earth fault (on) and zero mould current traveling wave (descending) ground connection three crests moment of moment synoptic diagram.
Phase mould current traveling wave during Fig. 9 the second half generation earth fault (on) and the capable ripple of zero mould current traveling wave (descending) ground connection moment.
Phase mould current traveling wave during Figure 10 the second half generation earth fault (on) and zero mould current traveling wave (descending) ground connection three crests moment of moment synoptic diagram.
Embodiment
Further specify below in conjunction with accompanying drawing and specific embodiment:
Carry out the fault localization test in conjunction with Fig. 1 and Fig. 3 and Fig. 4 central substation 10kV power cable line under the coal mine of eastern beach, as shown in Figure 5, wherein, total track length is L=2.25km, and cable line adopts crosslinked polyetylene insulated PVC three core power cables.
The resistance per unit length of cable line, inductance and capacitance parameter are R
1=0.193ohm/km, L
1=0.2573 * 10
-3H/km,, L
2=6.6904 * 10
-3H/km, c
1=c
2=0.2390 * 10
-6F/km.Apart from route survey end (zero sequence current mutual inductor and phase current mutual inductor) 0.5km place A singlephase earth fault mutually takes place, SF is 10MHz;
Described step 4 does, in the ground connection row ripple; Because it is identical to obtain two groups of row wave-wave shape phase places after zero mould electric current and the filtering of the phase mould magnitude of current, but amplitude current signal is bigger than phase mould electric current, differentiates more easily and go the wave-wave peak.Therefore can use for reference for being equal to measuring amount, through extracting t
1, t
2And t
3Constantly:
t
1Be the trouble spot when breaking down current traveling wave reach moment of test point for the first time from the trouble spot;
t
2Be that row ripple road along the line is transferred to test point from the trouble spot and reflects back then through bus, arrive the trouble spot after, this reflexes to the moment of test point again through the trouble spot;
t
3Be that trouble spot row ripple is transferred to the opposite end bus in opposite direction, reflex to the trouble spot, be transmitted to the moment of test point then through the trouble spot through the opposite end bus;
Obtain two groups of identical travelling wave current signals and comprise fault initial row ripple, trouble spot reflection wave and opposite end, trouble spot transmitted wave; The crest of reflection wave is similar with initial row wave-wave peak, and the crest of transmitted wave is opposite with reflection wave crest polarity, can judge that like this secondary peak is reflection wave or transmitted wave; From one to the other the 3rd capable wave-wave peak transmitted wave of nature obtains simultaneously; Among Fig. 3, d representes that the crest of reflection wave is similar with initial row wave-wave peak, and e representes that the crest of transmitted wave is opposite with reflection wave crest polarity.
Actual samples signal such as Fig. 5, shown in Fig. 6, Fig. 7, Fig. 8,
1) phase mould electric current of testing during fault and zero mould electric current, visible zero mould current ratio phase mould electric current is big, differentiates row wave-wave peak more easily.
2) phase mould current waveform is similar at higher frequency band (10KHz--100KHz) with zero mould current waveform shape, for the reliability of judging that row wave-wave peak doubles.
At test lead first three crest relatively, though crest is lossy in transmission, dispersion phenomenon takes place, contrast zero mould and mold component mutually, can find out that first and second crest is similar, the 3rd the crest pole reversal is transmitted wave.A, b, the corresponding t of c difference among Fig. 3
1, t
2And t
3Constantly:
calculates the distance of trouble spot to test point;
Adopt that similitude records t as comparison point in three crests
2-t
1=4500ns, t
3-t
2=11300ns, the 3rd crest is transmitted wave, so the distance of trouble spot is 498 meters: error is 2 meters.
Among Fig. 9, Figure 10, can decision line wave-wave shape be followed successively by initial row ripple, transmission row ripple, reflected traveling wave according to waveform shape, earth fault occurs in the second half, using formula:
Pattern analysis can find out that cable distance is nearer, and initial row wave-wave shape is obvious, and t constantly takes place
1, be transmitted wave after following closely, t constantly takes place in transmitted wave
2, transmitted wave is long perdurability, and the head of the latter half of and reflection wave of transmitted wave produces folding, causes tangible peak value behind the transmitted wave, and the generation of reflection wave is constantly not obvious.Adopt initial waveform, transmission waveform near the 3rd moment, to move relatively, judge the generation moment t of reflection wave
3, actual measuring:
t
2-t
1＝6250ns；
t
3-t
2＝8000ns
With measured value substitution formula:
Through metal wire ground connection, junction box is 1565 meters apart from the cable initial end in the junction box of actual earth test point employing cable latter half, and apart from 685 meters of cable end pieces, bending is not considered in the centre, and measuring error is less than 2 meters.
Though the above-mentioned accompanying drawing specific embodiments of the invention that combines is described; But be not restriction to protection domain of the present invention; One of ordinary skill in the art should be understood that; On the basis of technical scheme of the present invention, those skilled in the art need not pay various modifications that creative work can make or distortion still in protection scope of the present invention.
Claims (7)
1. one kind based on zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually, it is characterized in that,
The step that it comprises is:
Step 1 is provided with a test point on bus, the place is provided with current collecting device in test point;
Step 2 is carried out synchronized sampling to zero mould with mould current value setting sampling rate mutually; Gather the respective electrical flow data and be transferred to computer data acquisition system through current collecting device;
Phase mould electric current that step 3, real time record are sampled and zero mould electric current are judged to have or not the mutation current amount, have judged whether that promptly earth short circuit current takes place;
Step 4 is analyzed current waveform, confirms that initial row ripple, current reflection row ripple, electric current transmission row ripple take place constantly and the order that arrives test point first, thereby infers that the singlephase earth fault point occurs in the first half term or the second half on institute survey line road;
Step 5 uses corresponding formula to calculate grounding fault point position respectively to the first half term or the second half on institute survey line road.
2. as claimed in claim 1 based on zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually; It is characterized in that; Described step 1 is included in the current sensor of mould mutually that is respectively equipped with on the every phase line with the current collecting device described in the step 2, with at three zero mould current sensors of suit on the circuit mutually.
3. as claimed in claim 1 based on zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually; It is characterized in that; Be specially in the described step 3, when earth fault not occurring, increase zero mould that synchronized sampling obtains in time and touch current value benchmark zero axle as a reference mutually with institute survey line road; When earth fault takes place when; Current collecting device collects the current signal of sudden change in real time, and the current signal of said sudden change comprises the zero mould magnitude of current and the mould magnitude of current mutually, extracts before and after the current signal of sudden change respectively 1 second travelling wave current signal; When the current signal relative reference benchmark of measuring said sudden change zero axle up and down offset value set greater than institute's examining system scale the single-phase-to-ground current threshold value time, assert that singlephase earth fault takes place; Said ground current threshold setting interval is institute's examining system single-phase earth fault current peaked 50%～75%.
4. as claimed in claim 1 based on zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually; It is characterized in that; In the described step 4; The measured zero mould magnitude of current and mutually the aforesaid relatively reference data of the mould magnitude of current zero axle take place promutation the time; And the zero mould magnitude of current is right after appearance of negative to the mutation current trough with mould magnitude of current waveform mutually around the mutation current crest that forward all appears in reference data zero axle, promptly occur complete elder generation positive after during the negative current waveform, regard as the initial row ripple; Survey zero mould and be defined as t constantly with first mutation current ripple initial point position of initial row ripple of mould electric current mutually
1. constantly;
In conjunction with measured initial row ripple; Differentiate being right after initial row ripple current waveform afterwards; Be right after appearance of negative to the mutation current trough if the zero mould magnitude of current all occurs forward mutation assay electric current crest with mould magnitude of current waveform mutually around reference data zero axle, during the negative current waveform, regard as current reflection row ripple after promptly complete elder generation is positive; If the resulting zero mould magnitude of current and mould magnitude of current waveform mutually around reference data zero axle all occur complete elder generation negative after during the positive current waveform, regard as electric current transmission row ripple; The measured initial point position that is right after initial row ripple mutation current ripple afterwards is defined as t constantly
2Constantly;
In conjunction with measured initial row ripple, again to t
2The elder generation that constantly the judges negative current reflection row wave-wave shape in positive back; Or the positive electric current transmission row wave-wave shape current waveform following closely in negative earlier back is differentiated; If the zero mould magnitude of current and mould magnitude of current waveform mutually around reference data zero axle all occur with the described complete elder generation of initial row ripple positive after during the negative current waveform; Regard as current reflection row ripple, if the zero mould magnitude of current of gained is right after forward mutation assay electric current crest around the equal appearance of negative of reference data zero axle to the mutation current trough with mould magnitude of current waveform mutually, when promptly complete elder generation bears the after-current waveform; Regard as electric current transmission row ripple, the measured t that follows closely
2The initial point position of the mutation current ripple after the initial full current waveform is defined as t constantly constantly
3Constantly.
5. as claimed in claim 1ly it is characterized in that based on zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually, in the said step 5, as if respectively with t
1, t
2, t
3The corresponding current waveform that obtains is followed successively by initial row ripple, current reflection row ripple, electric current transmission row ripple and explains that then the singlephase earth fault point occurs in the first half term on institute survey line road constantly; Using formula
Calculate the distance of trouble spot to test point; If the current waveform that institute correspondence obtains is followed successively by initial row ripple, electric current transmission row ripple, current reflection row ripple and explains that then the singlephase earth fault point occurs in the second half on institute survey line road; Using formula
Calculate the distance of trouble spot to test point;
Described first half term and the second half are for being the boundary with cable line total length mid point, and test point place cut cable is defined as the first half term cable section, the cable section after the phase alignment be the second half cable section;
X is the distance of trouble spot distance test point in the formula; L is the power cable line total length;
t
1It is zero mould and first mutation current ripple initial point position moment of initial row ripple of mould electric current mutually; Be the trouble spot when breaking down current traveling wave reach moment of test point for the first time from the trouble spot;
t
2Be that the measured initial point position that is right after initial row ripple mutation current ripple afterwards defines constantly; Promptly zero mould current traveling wave is t with reference data zero axle of crossing first after mould current traveling wave mutually is right after the initial row ripple constantly
2Constantly;
t
3Be the measured t of following closely
2The initial point position of the mutation current ripple after the initial full current waveform constantly constantly; Promptly zero mould current traveling wave follows t closely with mould current traveling wave mutually
2Constantly the current traveling wave after the current traveling wave to cross reference data zero axle first be t constantly
3Constantly.
6. as claimed in claim 1 a kind of based on zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually, it is characterized in that described sampling rate is set at 10MHz.
7. as claimed in claim 1 a kind ofly it is characterized in that based on zero mould and the online distance-finding method of mould current traveling wave singlephase earth fault mutually, extract the current signal that suddenlys change in 10KHz～100KHz frequency band.
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