CN100335911C - Method for small current grounding selecting wire and fault positioning - Google Patents
Method for small current grounding selecting wire and fault positioning Download PDFInfo
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Abstract
The present invention relates to a method for small-current grounding line selection and fault positioning, which is a novel method and can accurately realize single phase grounding line selection and fault positioning. When a single-phase ground fault occurs, zero sequence voltage of the system and zero sequence current values of each branch line are detected in the first time; in the second time, ground capacitance values of a whole distribution network can be changed in an isolated neutral system, compensation degrees of arc suppression coils or the ground capacitance values of the whole distribution network are changed in an arc suppression coil grounding system, and the zero sequence voltage of the system and the zero sequence current values of each branch line in the second time are detected after the regulation. In the two times, the zero sequence current values of branch lines are respectively divided by the zero sequence voltage values of the system, and end values are obtained. The end values of branch lines which have the single-phase ground fault are changed twice, when the branch line with the single-phase ground fault is determined, the zero sequence current value detected on the branch line is uploaded, the detected zero sequence current value is divided by the zero sequence voltage value of the system, and then is discriminated, and thus, the position of the fault point can be determined.
Description
Affiliated technical field
The method of a kind of small current earthing wire-selecting of the present invention and localization of fault is a kind of new method that can accurately realize single-phase grounding selecting and fault status.
Background technology
At present, single-phase earth fault line selection relies on zero-sequence current relatively to carry out basically, when single-phase nonmetal ground connection is taken place on the circuit when, owing to be subjected to the influence of stake resistance, and the unbalanced influence of three-phase ground capacitance, it is very little to select the faulty line scope, and its theoretical derivation has many to the greatest extent falsities.For isolated neutral and small current neutral grounding system, the rules regulation, when singlephase earth fault takes place, allow to operate with failure two hours, because non-fault phase voltage is increased to line voltage, long-play might cause insulation breakdown, and therefore single-phase earth fault line selection and localization of fault are our problems for a long time always fast, are not well solved.Existing its principle of microcomputer ground fault line selection device is to utilize the first-harmonic of zero-sequence current and the size and Orientation of 5 subharmonic to differentiate, and is very ineffective in the practice, and its discrimination principles more complicated.Therefore, even to this day, the power supply department that has is still adopting " backguy method " to carry out failure line selection, and power distribution automation is being required perfect day by day today.This has a strong impact on power supply reliability.The method of developing a kind of new small current earthing wire-selecting and localization of fault at the existing in prior technology problem is very necessary.
Summary of the invention
Inventing in view of above-mentioned existing in prior technology problem is can accurately find the new single-phase grounding selecting of faulty line and position of failure point and the method for fault status in order to provide a kind of.
The method of a kind of small current earthing wire-selecting of the present invention and localization of fault,
It is divided into following steps:
(1) detects system zero sequence voltage and each branch line zero-sequence current value in the generation singlephase earth fault very first time;
(2) fault wire determines;
In second time, for isolated neutral system, only can change whole power distribution network ground capacitance value, detect the second time system residual voltage and each branch line zero-sequence current value after the adjustment; For arc suppression coil earthing system, can change the arc suppression coil compensation degree, perhaps change whole power distribution network ground capacitance value, detect the second time system residual voltage and each branch line zero-sequence current value after the adjustment.Twice time uses branch line zero-sequence current value divided by system zero sequence voltage value respectively, gets its end value.For the circuit that does not break down, twice time of this end value does not change, and for the circuit that breaks down, twice time of this end value, variation took place, when there is this changing value in definite certain branch line, just can determine that singlephase earth fault has taken place this branch line;
Through resistance eutral grounding, this method is suitable equally for neutral point, and method of adjustment can realize by changing the zero sequence system impedance;
(3) trouble spot determines;
After determining the singlephase earth fault branched line, by uploading the detected zero-sequence current value of each interval microcomputer-based intelligent distribution terminal of this branched line, after new small current earthing wire-selecting microcomputer device is accepted, with detected zero-sequence current value divided by residual voltage value in the system, and differentiated, just can localization of faults position.Trouble spot load side zero-sequence current value did not change in twice time of ratio of system zero sequence voltage value, and trouble spot mains side zero-sequence current value in twice time of ratio of system zero sequence voltage value variation has taken place.Just can determine position of failure point on the faulty line thus.
The method of a kind of small current earthing wire-selecting of the present invention and localization of fault,
(1) for isolated neutral system:
The current potential of neutral point n is made as Un, and when a through stake resistance R earth fault took place mutually, each electric current that flows out mutually was:
Ia＝Ua/R+jwCa·Ua＝(Ea+Un)/R+jwCa·(Ea+Un)
Ib＝jwCb·Ub＝jwCb·(Eb+Un)
Ic＝jwCc·Uc＝jwCc·(Ec+Un)
Because Ia+Ib+Ic=0
Set Ca=Cb=Cc=Cs
Ea+Un (1+j3wCsR)=0 so
Un＝-Ea/(1+j3wCsR) (1)
During distribution network system generation single-phase earthing, residual voltage will appear in full distribution system, adopt residual voltage to start, and differentiate faulty line with zero-sequence current division by 0 sequence voltage end value.On the non-fault branch line zero-sequence current is arranged after A mutually singlephase earth fault takes place on certain branch line, the actual direction of its capacitive character reactive power is a bus flow line trackside,
Zero-sequence current is on the non-fault branch line:
Icm＝jwCsm(Ua+Ub+Uc)＝j3wCsmUn (2)
Deduct the capacitive earth current of the branch line that breaks down own and its numerical value of the zero-sequence current on the branch line that breaks down equals whole distribution capacitive earth current sum, the actual direction of its capacitive character reactive power is that line flows is to bus bar side.Computing formula is as follows:
The capacitive earth current of the branch line that breaks down own:
Ic1＝jwCs1(Ua+Ub+Uc)＝j3wCs1Un
The branch line zero-sequence current breaks down:
Ic0＝∑Icm-Ic1＝j3w(∑Csm-Cs1)Un (3)
By formula (2), (3) as can be seen, in the system zero-sequence current be with system in the related amount of residual voltage, and by formula (1) as can be seen, in the system residual voltage be with trouble spot grounding resistance R, electrical network in all related variable quantity of capacitance Cs, especially trouble spot stake resistance R changes a very complicated amount in the system.When single-phase earthing in the system is not clearly the time, zero-sequence current can be very little in the system, and the way of each branch line zero-sequence current size or zero sequence reactive power direction can be difficult to determine to take place the branch line of singlephase earth fault in the therefore simple comparison system.If formula (2), (3) are changed into:
Icm/Un＝3wCsm (4)
Ic0/Un＝3w(∑Csm-Cs1) (5)
With zero-sequence current value on the branch line than residual voltage value in the last system, only relevant for non-its end value of branch line that breaks down with this branch line ground capacitance value Csm, relevant for its end value of branch line that breaks down with poor (the ∑ Csm-Cs1) of whole distribution and this branch line ground capacitance value, if drop in the system or excise a 10kV and allot circuit, change whole distribution ground capacitance value, so, the former is the value of a no change amount, and the latter is the value of an amount of changing, if checkout equipment detects this changing value in the system, just can determine to take place the branch line of singlephase earth fault.If can before measure the branch line ground capacitance value that breaks down, provide on this branch line the zero-sequence current value than the benchmark end value of residual voltage value in the last system, the zero-sequence current value has bigger variation than residual voltage value in the last system on detecting this branch line, can determine on this branch line singlephase earth fault to have taken place.
In the above formula:
Ea-a responds to the phase electromotive force mutually; Eb-b responds to the phase electromotive force mutually; Ec-c responds to the phase electromotive force mutually;
The Ua-a phase-to-ground voltage; The Ub-b phase-to-ground voltage; The Uc-c phase-to-ground voltage;
Un-neutral point voltage-to-ground;
Ca-a is electric capacity relatively; Cb-b is electric capacity relatively; Cc-c is electric capacity relatively;
Ia-a is capacitance current relatively; Ib-b is capacitance current relatively; Ic-c is capacitance current relatively;
R-a phase stake resistance;
Each electric capacity (three-phase equilibrium) relatively of Cs1-branch line 1;
Each electric capacity (three-phase equilibrium) relatively of Cs2-branch line 2;
Each electric capacity (three-phase equilibrium) relatively of Csm-branch line m;
Ic1-branch line 1 capacitive earth current;
Ic2-branch line 2 capacitive earth currents;
Icm-branch line m capacitive earth current;
Ic0-branch line 1 zero-sequence current;
Each branch line capacitive earth current sum of ∑ Icm-;
(2) for the neutral by arc extinction coil grounding electrical network:
The current potential of neutral point n is made as Un ', and when a passed through stake resistance R ' generation earth fault mutually, each electric current that flows out mutually was:
Ia′＝Ua′/R′+jwCa′·Ua′＝(Ea+Un′)/R′+jwCa′·(Ea+Un′)
Ib′＝jwCb′·Ub′＝jwCb′·(Eb+Un′)
Ic′＝jwCc′·Uc′＝jwCc′·(Ec+Un′)
The arc suppression coil zero-sequence current of flowing through:
In′＝Un′/jwLn′＝-jUn′/wLn′
Because Ia '+Ib '+Ic '+In '=0
Set Ca '=Cb '=Cc '=Cs '
Ea+Un ' [1+j (3wCs ' R '-1/wLn ')]=0 so
Un′＝-Ea/[1+j(3wCs′R′-1/wLn′)] (6)
When distribution network system generation single-phase earthing, residual voltage will appear in full distribution system, adopt residual voltage to start, and differentiate with zero-sequence current division by 0 sequence voltage end value.On the non-fault branch line zero-sequence current is arranged after A mutually singlephase earth fault takes place on certain branch line, the actual direction of its capacitive character reactive power is a bus flow line trackside, and zero-sequence current is on the non-fault branch line:
Icm′＝jwCsm′(Ua′+Ub′+Uc′)＝j3wCsm′Un′ (7)
And its numerical value of the zero-sequence current on the branch line that breaks down equals the aftercurrent that the capacitive earth current of its branch line own deducts the trouble spot of flowing through, the aftercurrent of trouble spot is through the aftercurrent behind the arc suppression coil compensation because flow through, and adopt the over-compensation mode in system, under the little situation of over-compensation, the zero-sequence current value that breaks down on the branch line approaches the capacitive earth current of its branch line own, and the actual direction of capacitive character reactive power also is a bus flow line trackside.Computing formula is as follows:
The capacitive earth current of the branch line that breaks down own:
Ic1′＝jwCs1′(Ua′+Ub′+Uc′)＝j3wCs1′Un′
The arc suppression coil zero-sequence current of flowing through:
In′＝Un′/jwLn′＝-jUn′/wLn′
The aftercurrent of trouble spot after over-compensation:
In0′＝In′+∑Icm′＝-jUn′/wLn′+j3w∑Csm′
Un′＝j(3w∑Csm′-1/wLn′)Un′
The branch line zero-sequence current breaks down:
Ic0′＝Ic1′-In0′＝j[1/wLn′-3w(∑Csm′-Cs1′)]Un′ (8)
By formula (7), (8) as can be seen, in the system zero-sequence current be with system in the related amount of residual voltage, and by formula (2) as can be seen, in the system residual voltage be with trouble spot grounding resistance R ', electrical network in all related variable quantity of compensating arc-extinguishing coil inductance value Ln ' among the capacitance Cs ', system, especially trouble spot stake resistance R changes a very complicated amount in the system.The way of each branch line zero-sequence current size is difficult to determine to take place the branch line of singlephase earth fault in the therefore simple comparison system.If formula (7), (8) are changed into:
Icm′/Un′＝3wCsm′ (9)
Ic0′/Un′＝1/wLn′-3w(∑Csm′-Cs1′) (10)
With zero-sequence current value on the branch line than residual voltage value in the last system, only relevant for non-its end value of branch line that breaks down with this branch line ground capacitance value Csm ', relevant for its end value of branch line that breaks down with poor (the ∑ Csm '-Cs1 ') of arc suppression coil inductance value Ln ' and whole distribution and this branch line ground capacitance value, if change arc suppression coil inductance value Ln ', promptly suitably adjust the arc suppression coil compensation degree, perhaps, the same with previous way, drop in the system or excise a 10kV and allot circuit, change whole distribution ground capacitance value, so, the former is the value of a no change amount, and the latter is the value of an amount of changing, if checkout equipment detects this changing value in the system, just can determine to take place the branch line of singlephase earth fault.
In the above formula:
Ea-a responds to the phase electromotive force mutually; Eb-b responds to the phase electromotive force mutually; Ec-c responds to the phase electromotive force mutually;
Ua '-a phase-to-ground voltage; Ub '-b phase-to-ground voltage; Uc '-c phase-to-ground voltage;
Un '-neutral point voltage-to-ground;
Ca '-a is electric capacity relatively; Cb '-b is electric capacity relatively; Cc '-c is electric capacity relatively;
Ia '-a is capacitance current relatively; Ib '-b is capacitance current relatively; Ic '-c is capacitance current relatively;
R '-a phase stake resistance; Ln '-arc suppression coil inductance value;
Each electric capacity (three-phase equilibrium) relatively of Cs1 '-branch line 1;
Each electric capacity (three-phase equilibrium) relatively of Cs2 '-branch line 2;
Each electric capacity (three-phase equilibrium) relatively of Csm '-branch line m;
Ic1 '-branch line 1 capacitive earth current;
Ic2 '-branch line 2 capacitive earth currents;
Icm '-branch line m capacitive earth current;
Ic0 '-branch line 1 zero-sequence current;
∑ Icm '-each branch line capacitive earth current sum;
In '-arc suppression coil the zero-sequence current of flowing through;
In0 '-trouble spot aftercurrent after over-compensation
The method of a kind of small current earthing wire-selecting of the present invention and localization of fault is characterized in that the process of determining of trouble spot is as follows:
After determining the singlephase earth fault branched line, by uploading the detected zero-sequence current value of each interval microcomputer-based intelligent distribution terminal of this branched line, after new small current earthing wire-selecting microcomputer device is accepted, with detected zero-sequence current value divided by residual voltage value in the system, and differentiated, just can localization of faults position.
For isolated neutral system:
The detected zero-sequence current of trouble spot load side (derivation of equation is seen before and stated):
I2＝j3wC2Un
I2/Un＝3wC2 (11)
The detected zero-sequence current of trouble spot mains side (derivation of equation is seen before and stated):
I1＝j3wC1Un
I1/Un＝3wC1 (12)
For the neutral by arc extinction coil grounding system:
The detected zero-sequence current of trouble spot load side FTU (derivation of equation is seen before and stated):
I2＝j3wC2Un′
I2/Un′＝3wC2 (13)
The detected zero-sequence current of trouble spot mains side (derivation of equation is seen before and stated):
I1＝j[1/wLn′-3wC1]Un′
I1/Un′＝1/wLn′-3wC1 (14)
In system, adjust the arc suppression coil compensation degree, change the arc suppression coil inductance value, perhaps, drop in the system or excise one time and allot circuit, when changing whole distribution ground capacitance value, by formula (11), (12), (13), (14) as can be seen, variation has taken place in the ratio of residual voltage value in the detected zero-sequence current value of trouble spot mains side and the system, and the ratio of residual voltage value is a fixed value in the detected zero-sequence current value of trouble spot load side and the system.Thereby determine the singlephase earth fault point.
In the above formula:
Each electric capacity (three-phase equilibrium) relatively of the whole power distribution network of C1-trouble spot mains side;
Each mutually remaining ground capacitance (three-phase equilibrium) of C2-branch line trouble spot load side.
The method of described a kind of small current earthing wire-selecting of the present invention and localization of fault is characterized in that trimming process is as follows:
Above-mentioned single-phase grounding selecting and localization of fault scheme are based on that a kind of idealized fully distribution network systems derives, and promptly whole distribution network systems and each branch line three-phase ground capacitance think in full accord.And actual distribution network systems situation is very complicated, and each branch line and whole distribution network systems three-phase ground capacitance might be different, brings variety of issue for failure line selection and location.When considering three-phase ground capacitance not simultaneously, actual zero-sequence current on the non-fault branch line:
Icm
Actual=jwCamUa+jwCbmUb+jwCcmUc
＝(jwCamEa+jwCbmEb+jwCcmEc)+j3wCsmUn
In the formula, Cam, Cbm, Ccm are respectively a phase, b phase, the c capacitances relatively of branch line m, and Csm is a branch line m three-phase ground capacitance mean value, and formula is changed into:
Icm
Actual=Icm
Uneven+ Icm
Desirable
In the formula, Icm
Uneven=jwCamEa+jwCbmEb+jwCcmEc is the uneven electric current that produces of branch line m three-phase ground capacitance value; Icm
DesirableBe branch line m perfect condition (three-phase equilibrium) zero-sequence current, its computing method are the same, Icm
Desirable=j3wCsmUn.
Work as Icm
UnevenValue is enough big, when can not ignore, will influence Icm
Actual/ Un ratio causes time non-fault branch line Icm twice
Actual/ Un ratio changes, and can not carry out accurate route selection.If with twice time detecting to the difference of the actual zero-sequence current vector of branch line and twice time detecting to the difference of system zero sequence voltage vector carry out ratio calculation, computing formula is as follows:
Δ Icm
Actual=Icm
Actual 2-Icm
Actual 1
=(Icm
Uneven+ Icm
Desirable 2)-(Icm
Uneven+ Icm
Desirable 1)
=Icm
Desirable 2-Icm
Desirable 1
=j3wCsm (Un
Actual 2-Un
Actual 1)
Δ Icm
Actual/ Δ Un
Actual=j3wCsm (Un
Actual 2-Un
Actual 1)/(Un
Actual 2-Un
Actual 1)
Δ Icm
Actual/ Δ Un
Actual=3wCsm
In the above formula:
Icm
Actual 1The zero-sequence current that non-fault branch line m actual detected arrives before-the adjustment;
Icm
Actual 2The zero-sequence current that the non-fault branch line m actual detected in-adjustment back arrives;
Icm
Desirable 1The zero-sequence current of-non-fault branch line m perfect condition (three-phase equilibrium) calculating before adjusting;
Icm
Desirable 2The zero-sequence current of-non-fault branch line m perfect condition (three-phase equilibrium) calculating after adjusting;
Icm
UnevenThe zero-sequence current that the forward and backward non-fault branch line m three-phase imbalance of-adjustment produces;
Un
Actual 1The residual voltage that system's actual detected arrives before-the adjustment;
Un
Actual 2The residual voltage that system actual detected in-adjustment back arrives;
Δ Icm
Actual-adjust the poor of zero-sequence current vector that forward and backward non-fault branch line m actual detected arrives;
Δ Un
Actual-adjust the poor of residual voltage vector that forward and backward system actual detected arrives.
By the top formula as seen, Δ Icm
Actual/ Δ Un
ActualRatio is only relevant with this branch line three-phase ground capacitance mean value Csm, is constant, when carrying out distribution network systems parameter adjustment second time (or wholely change distribution ground capacitance value, or change the arc suppression coil inductance value), twice adjustment time Δ Icm
Actual/ Δ Un
ActualRatio can not change.Above-mentioned viewpoint is at non-fault branch line.For the branch line that breaks down, Δ Icm
Actual/ Δ Un
ActualRatio is a very complicated amount of variation, when carrying out the distribution network systems parameter adjustment second time, twice adjustment time Δ Icm
Actual/ Δ Un
ActualRatio will change.Come therefrom, can find the branch line that breaks down very accurately.For localization of fault on the fault branch line, the way of employing is same.
Description of drawings
The present invention has two accompanying drawings, wherein:
Fig. 1 a: isolated neutral electric network composition synoptic diagram
Fig. 1 b: isolated neutral line voltage polar plot
Fig. 2 a: arc suppression coil earthing electric network structural representation
Fig. 2 b: arc suppression coil earthing electric network and voltage vector-diagram
Fig. 3: isolated neutral system single-phase earthing zero-sequence current distribution plan
Fig. 4: arc suppression coil earthing system single-phase earthing zero-sequence current distribution plan
Fig. 5 a: certain branch line structural representation
Fig. 5 b: electrical network parameter distribution plan before and after certain branch line singlephase earth fault point
Among the figure: Ea-a responds to the phase electromotive force mutually; Eb-b responds to the phase electromotive force mutually; Ec-c responds to the phase electromotive force mutually;
Ua (Ua ')-a phase-to-ground voltage; Ub (Ub ')-b phase-to-ground voltage;
Uc (Uc ')-c phase-to-ground voltage;
Un (Un ')-neutral point voltage-to-ground;
Ca (Ca ')-a is electric capacity relatively; Cb (Cb ')-b is electric capacity relatively;
Cc (Cc ')-c is electric capacity relatively;
Ia (Ia ')-a is capacitance current relatively; Ib (Ib ')-b is capacitance current relatively;
Ic (Ic ')-c is capacitance current relatively;
R (R ', RX)-a phase stake resistance;
Each electric capacity (three-phase equilibrium) relatively of Cs1 (Cs1 ')-branch line 1;
Each electric capacity (three-phase equilibrium) relatively of Cs2 (Cs2 ')-branch line 2;
Each electric capacity (three-phase equilibrium) relatively of Csm (Csm ')-branch line m;
Ic1 (Ic1 ')-branch line 1 capacitive earth current;
Ic2 (Ic2 ')-branch line 2 capacitive earth currents;
Icm (Icm ')-branch line m capacitive earth current;
Ic0 (Ic0 ')-branch line 1 zero-sequence current;
∑ Icm (∑ Icm ')-each branch line capacitive earth current sum;
Ln '-arc suppression coil inductance value;
In '-arc suppression coil the zero-sequence current of flowing through;
In0 '-trouble spot aftercurrent after over-compensation
Each electric capacity (three-phase equilibrium) relatively of the whole power distribution network of C1-trouble spot mains side;
Each mutually remaining ground capacitance (three-phase equilibrium) of C2-branch line trouble spot load side.
I1-trouble spot mains side zero-sequence current
I2-trouble spot load side zero-sequence current
S1 (S2, S3, S4, S5, S6, S7)-branch line interconnection switch
G (g ')-the earth
The F-trouble spot
Embodiment
The embodiment of the method for a kind of small current earthing wire-selecting of the present invention and localization of fault as shown in drawings, the present invention is an example with the 10kV power distribution network, set forth under neutral by arc extinction coil grounding and the earth-free mode method of small current earthing wire-selecting and localization of fault.The method of a kind of small current earthing wire-selecting of the present invention and localization of fault, it is divided into following steps:
(1) detects system zero sequence voltage and each branch line zero-sequence current value in the generation singlephase earth fault very first time;
(2) fault wire determines;
In second time, for isolated neutral system, only can change whole power distribution network ground capacitance value, detect the second time system residual voltage and each branch line zero-sequence current value after the adjustment; For arc suppression coil earthing system, can change the arc suppression coil compensation degree, perhaps change whole power distribution network ground capacitance value, detect the second time system residual voltage and each branch line zero-sequence current value after the adjustment.Twice time uses branch line zero-sequence current value divided by system zero sequence voltage value respectively, gets its end value.For the circuit that does not break down, twice time of this end value does not change, and for the circuit that breaks down, twice time of this end value, variation took place, when there is this changing value in definite certain branch line, just can determine that singlephase earth fault has taken place this branch line;
Through resistance eutral grounding, this method is suitable equally for neutral point, and method of adjustment can realize by changing the zero sequence system impedance;
(3) trouble spot determines;
After determining the singlephase earth fault branched line, by uploading the detected zero-sequence current value of each interval microcomputer-based intelligent distribution terminal of this branched line, after new small current earthing wire-selecting microcomputer device is accepted, with detected zero-sequence current value divided by residual voltage value in the system, and differentiated, just can localization of faults position.Twice time of ratio of trouble spot load side zero-sequence current value and system zero sequence voltage value does not change, and twice time of ratio of trouble spot mains side zero-sequence current value and system zero sequence voltage value, variation took place.Just can determine position of failure point on the faulty line thus.
(1) for isolated neutral system: Fig. 1 a is an isolated neutral electric network composition synoptic diagram, and Fig. 1 b is an isolated neutral line voltage polar plot,
Among the figure, the current potential of neutral point n is made as Un, and the earth is made as g.When a through stake resistance R earth fault took place mutually, each electric current that flows out mutually was:
Ia＝Ua/R+jwCa·Ua＝(Ea+Un)/R+jwCa·(Ea+Un)
Ib＝jwCb·Ub＝jwCb·(Eb+Un)
Ic＝jwCc·Uc＝jwCc·(Ec+Un)
Because Ia+Ib+Ic=0
Set Ca=Cb=Cc=Cs
Ea+Un (1+j3wCsR)=0 so
Un＝-Ea/(1+j3wCsR) (1)
Shown in Fig. 1 b, (1) formula represents that neutral point voltage-to-ground Un moves on circular arc a-g-n, and the diameter of circular arc is Ea.
When R=0 (metal ground connection), → g point overlaps with a point, neutral point voltage-to-ground Un=-Ea, non-fault phase voltage Ub=Uc=_Ea, fault phase voltage Ua=0.
When R=∞ (unfaulty conditions), → g point overlaps with the n point, neutral point voltage-to-ground Un=0.
According to the variation of R value size, might produce non-fault phase voltage Uc＞_ Ea.
When 10kV distribution system generation single-phase earthing, residual voltage will appear in full 10kV distribution system, adopt residual voltage to start, and differentiate with zero-sequence current division by 0 sequence voltage end value.Singlephase earth fault zero-sequence current distribution plan takes place for A on certain 10kV of transformer station distribution system branch line in Fig. 3 mutually, the 10kV power network neutral point adopts earth-free mode among the figure, as shown in Figure 3, after A mutually singlephase earth fault takes place on certain branch line, on the non-fault branch line zero-sequence current is arranged, the actual direction of its capacitive character reactive power is a bus flow line trackside
Zero-sequence current is on the non-fault branch line:
Icm＝jwCsm(Ua+Ub+Uc)＝j3wCsmUn (2)
Deduct the capacitive earth current of the branch line that breaks down own and its numerical value of the zero-sequence current on the branch line that breaks down equals whole distribution capacitive earth current sum, the actual direction of its capacitive character reactive power is that line flows is to bus bar side.Computing formula is as follows:
The capacitive earth current of the branch line that breaks down own:
Ic1＝jwCs1(Ua+Ub+Uc)＝j3wCs1Un
The branch line zero-sequence current breaks down:
Ic0＝∑Icm-Ic1＝j3w(∑Csm-Cs1)Un (3)
By formula (2), (3) as can be seen, in the system zero-sequence current be with system in the related amount of residual voltage, and by formula (1) as can be seen, in the system residual voltage be with trouble spot grounding resistance R, electrical network in all related variable quantity of capacitance Cs, especially trouble spot stake resistance R changes a very complicated amount in the system.When single-phase earthing in the system is not clearly the time, zero-sequence current can be very little in the system, and the way of each branch line zero-sequence current size or zero sequence reactive power direction can be difficult to determine to take place the branch line of singlephase earth fault in the therefore simple comparison system.If formula (2), (3) are changed into:
Icm/Un＝3wCsm (4)
Ic0/Un＝3w(∑Csm-Cs1) (5)
With zero-sequence current value on the branch line than residual voltage value in the last system, only relevant for non-its end value of branch line that breaks down with this branch line ground capacitance value Csm, relevant for its end value of branch line that breaks down with poor (the ∑ Csm-Cs1) of whole distribution and this branch line ground capacitance value, if drop in the system or excise a 10kV and allot circuit, perhaps, on bus, adjust capacitor for one group in parallel, it is dropped into and excises operation, change whole distribution ground capacitance value, so, the former is the value of a no change amount, and the latter is the value of an amount of changing, if checkout equipment detects this changing value in the system, just can determine to take place the branch line of singlephase earth fault.If can before measure the branch line ground capacitance value that breaks down, provide on this branch line the zero-sequence current value than the benchmark end value of residual voltage value in the last system, the zero-sequence current value has bigger variation than residual voltage value in the last system on detecting this branch line, can determine on this branch line singlephase earth fault to have taken place.
(2) for the neutral by arc extinction coil grounding electrical network:
Fig. 2 a is the arc suppression coil earthing electric network structural representation, and Fig. 2 b is arc suppression coil earthing electric network and voltage vector-diagram, and among the figure, the current potential of neutral point n is made as Un ', and the earth is made as g '.When a passed through stake resistance R ' generation earth fault mutually, each electric current that flows out mutually was:
Ia′＝Ua′/R′+jwCa′·Ua′＝(Ea+Un′)/R′+jwCa′·(Ea+Un′)
Ib′＝jwCb′·Ub′＝jwCb′·(Eb+Un′)
Ic′＝jwCc′·Uc′＝jwCc′·(Ec+Un′)
The arc suppression coil zero-sequence current of flowing through:
In′＝Un′/jwLn′＝-jUn′/wLn′
Because Ia '+Ib '+Ic '+In '=0
Set Ca '=Cb '=Cc '=Cs '
Ea+Un ' [1+j (3wCs ' R '-1/wLn ')]=0 so
Un′＝-Ea/[1+j(3wCs′R′-1/wLn′)] (6)
As among Fig. 2 shown in the voltage vector-diagram, (6) formula represents that neutral point voltage-to-ground Un ' moves on whole round a-g-n, and diameter of a circle is Ea.
When R=0 (metal ground connection), → g point overlaps with a point.(6) in the formula, the neutral point voltage-to-ground
Un '=-Ea/ (1-j/wLn), in fact the g point does not overlap with a point among Fig. 2, this is because A phase electromotive force changes in the system, change the new A phase electromotive force Ea ' in back=Ea/ (1-j/wLn), non-fault phase voltage Ub '=Uc '=_ Ea no longer sets up, and this is inconsistent with traditionally view.And fault phase voltage Ua=0.
When R '=∞ (unfaulty conditions), → g point overlaps with the n point, neutral point voltage-to-ground Un '=0.
According to the variation of R ' value and Ln ' value size, might produce non-fault phase voltage Uc '＞_ Ea, perhaps, Ub '＞_ Ea.
During formula (6) calculates, do not consider the zero sequence series loop generation condition of resonance of 3Cs ' (Ca ' ∥ Cb ' ∥ Cc ') and Ln ' composition, when this series loop during near condition of resonance, neutral point voltage-to-ground Un ' can become very big.Since regulation neutral point voltage-to-ground Un ' in service be not more than 15% phase voltage (Un '＜0.15Ea), the common practice is that serial or parallel connection resistance increases damping in the arc suppression coil loop in the system, perhaps adjust the arc suppression coil inductance, the incomplete resonance of LC is realized.
When 10kV distribution system generation single-phase earthing, residual voltage will appear in full 10kV distribution system, and new solution is to adopt residual voltage to start, and differentiate with zero-sequence current division by 0 sequence voltage end value.Single-phase earthing zero-sequence current distribution plan takes place for A on certain 10kV of transformer station distribution system branch line in Fig. 4 mutually, the 10kV power network neutral point adopts the grounding through arc mode among the figure, as shown in Figure 4, after A mutually singlephase earth fault takes place on certain branch line, on the non-fault branch line zero-sequence current is arranged, the actual direction of its capacitive character reactive power is a bus flow line trackside, and zero-sequence current is on the non-fault branch line:
Icm′＝jwCsm′(Ua′+Ub′+Uc′)＝j3wCsm′Un′ (7)
And its numerical value of the zero-sequence current on the branch line that breaks down equals the aftercurrent that the capacitive earth current of its branch line own deducts the trouble spot of flowing through, the aftercurrent of trouble spot is through the aftercurrent behind the arc suppression coil compensation because flow through, and adopt the over-compensation mode in system, under the little situation of over-compensation, the zero-sequence current value that breaks down on the branch line approaches the capacitive earth current of its branch line own, and the actual direction of capacitive character reactive power also is a bus flow line trackside.Computing formula is as follows:
The capacitive earth current of the branch line that breaks down own:
Ic1′＝jwCs1′(Ua′+Ub′+Uc′)＝j3wCs1′Un′
The arc suppression coil zero-sequence current of flowing through:
In′＝Un′/jwLn′＝-jUn′/wLn′
The aftercurrent of trouble spot after over-compensation:
In0′＝In′+∑Icm′＝-jUn′/wLn′+j3w∑Csm′
Un′＝j(3w∑Csm′-1/wLn′)Un′
The branch line zero-sequence current breaks down:
Ic0′＝Ic1′-In0′＝j[1/wLn′-3w(∑Csm′-Cs1′)]Un′ (8)
By formula (7), (8) as can be seen, in the system zero-sequence current be with system in the related amount of residual voltage, and by formula (6) as can be seen, in the system residual voltage be with trouble spot grounding resistance R ', electrical network in all related variable quantity of compensating arc-extinguishing coil inductance value Ln ' among the capacitance Cs ', system, especially trouble spot stake resistance R changes a very complicated amount in the system.The way of each branch line zero-sequence current size is difficult to determine to take place the branch line of singlephase earth fault in the therefore simple comparison system.If formula (7), (8) are changed into:
Icm′/Un′＝3wCsm′ (9)
Ic0′/Un′＝1/wLn′-3w(∑Csm′-Cs1′) (10)
With zero-sequence current value on the branch line than residual voltage value in the last system, only relevant for non-its end value of branch line that breaks down with this branch line ground capacitance value Csm ', relevant for its end value of branch line that breaks down with poor (the ∑ Csm '-Cs1 ') of arc suppression coil inductance value Ln ' and whole distribution and this branch line ground capacitance value, if change arc suppression coil inductance value Ln ', promptly suitably adjust the arc suppression coil compensation degree, perhaps, the same with previous way, drop in the system or excise a 10kV and allot circuit, perhaps, on bus, adjust capacitor for one group in parallel, it is dropped into and excises operation, adjust whole distribution ground capacitance value, so, the former is the value of a no change amount, and the latter is the value of an amount of changing, if checkout equipment detects this changing value in the system, just can determine to take place the branch line of singlephase earth fault.
The method of a kind of small current earthing wire-selecting of the present invention and localization of fault is characterized in that the process of determining of trouble spot is as follows:
After determining the singlephase earth fault branched line, by uploading the detected zero-sequence current value of each interval microcomputer-based intelligent distribution terminal of this branched line, after new small current earthing wire-selecting microcomputer device is accepted, with detected zero-sequence current value divided by residual voltage value in the system, and differentiated, just can localization of faults position.
For isolated neutral system:
The detected zero-sequence current of trouble spot load side (derivation of equation is seen before and stated):
I2＝j3wC2Un
I2/Un＝3wC2 (11)
The detected zero-sequence current of trouble spot mains side (derivation of equation is seen before and stated):
I1＝j3wC1Un (12)
I1/Un＝3wC1
For the neutral by arc extinction coil grounding system:
The detected zero-sequence current of trouble spot load side FTU (derivation of equation is seen before and stated):
I2＝j3wC2Un′
I2/Un′＝3wC2 (13)
The detected zero-sequence current of trouble spot mains side (derivation of equation is seen before and stated):
I1＝j[1/wLn′-3wC1]Un′
I1/Un′＝1/wLn′-3wC1 (14)
Shown in Fig. 5 a, intelligent power distribution terminal (FTU) can be installed by branch line interconnection switch place, setting the trouble spot occurs between the branch line interconnection switch S4-S5, in system, adjust the arc suppression coil compensation degree, change the arc suppression coil inductance value, perhaps, drop in the system or excise a 10kV and allot circuit, perhaps, on bus, adjust capacitor for one group in parallel, it is dropped into and excises operation, when changing whole distribution ground capacitance value, by formula (11), (12), (13), (14) as can be seen, change before and after the ratio adjustment of residual voltage value in detected zero-sequence current value of intelligent power distribution terminal (FTU) before branch line interconnection switch S4 place and the S4 place and the system, and the ratio of residual voltage value is a fixed value in detected zero-sequence current value of intelligent power distribution terminal (FTU) behind branch line interconnection switch S5 place and the S5 place and the system.Therefore, when system detects the fixed value that branch line interconnection switch S5 is a residual voltage value ratio in first zero-sequence current value and the system, just can determine that the singlephase earth fault point occurs between the branch line interconnection switch S4-S5.
The trimming process of failure line selection and location is as follows:
Above-mentioned single-phase grounding selecting and localization of fault scheme are based on that a kind of idealized fully distribution network systems derives, and promptly whole distribution network systems and each branch line three-phase ground capacitance think in full accord.And actual distribution network systems situation is very complicated, and each branch line and whole distribution network systems three-phase ground capacitance might be different, brings variety of issue for failure line selection and location.When considering three-phase ground capacitance not simultaneously, actual zero-sequence current on the non-fault branch line:
Icm
Actual=jwCamUa+jwCbmUb+jwCcmUc
＝(jwCamEa+jwCbmEb+jwCcmEc)+j3wCsmUn
In the formula, Cam, Cbm, Ccm are respectively a phase, b phase, the c capacitances relatively of branch line m, and Csm is a branch line m three-phase ground capacitance mean value, and formula is changed into:
Icm
Actual=Icm
Uneven+ Icm
Desirable
In the formula, Icm
Uneven=jwCamEa+jwCbmEb+jwCcmEc is the uneven electric current that produces of branch line m three-phase ground capacitance value; Icm
DesirableBe branch line m perfect condition (three-phase equilibrium) zero-sequence current, its computing method are the same, Icm
Desirable=j3wCsmUn.
Work as Icm
UnevenValue is enough big, when can not ignore, will influence Icm
Actual/ Un ratio causes time non-fault branch line Icm twice
Actual/ Un ratio changes, and can not carry out accurate route selection.If with twice time detecting to the difference of the actual zero-sequence current vector of branch line and twice time detecting to the difference of system zero sequence voltage vector carry out ratio calculation, computing formula is as follows:
Δ Icm
Actual=Icm
Actual 2-Icm
Actual 1
=(Icm
Uneven+ Icm
Desirable 2)-(Icm
Uneven+ Icm
Desirable 1)
=Icm
Desirable 2-Icm
Desirable 1
=j3wCsm (Un
Actual 2-Un
Actual 1)
Δ Icm
Actual/ Δ Un
Actual=j3wCsm (Un
Actual 2-Un
Actual 1)/(Un
Actual 2-Un
Actual 1)
Δ Icm
Actual/ Δ Un
Actual=3wCsm
In the above formula:
Icm
Actual 1The zero-sequence current that non-fault branch line m actual detected arrives before-the adjustment;
Icm
Actual 2The zero-sequence current that the non-fault branch line m actual detected in-adjustment back arrives;
Icm
Desirable 1The zero-sequence current of-non-fault branch line m perfect condition (three-phase equilibrium) calculating before adjusting;
Icm
Desirable 2The zero-sequence current of-non-fault branch line m perfect condition (three-phase equilibrium) calculating after adjusting;
Icm
UnevenThe zero-sequence current that the forward and backward non-fault branch line m three-phase imbalance of-adjustment produces;
Un
Actual 1The residual voltage that system's actual detected arrives before-the adjustment;
Un
Actual 2The residual voltage that system actual detected in-adjustment back arrives;
Δ Icm
Actual-adjust the poor of zero-sequence current vector that forward and backward non-fault branch line m actual detected arrives;
Δ Un
Actual-adjust the poor of residual voltage vector that forward and backward system actual detected arrives.
By the top formula as seen, Δ Icm
Actual/ Δ Un
ActualRatio is only relevant with this branch line three-phase ground capacitance mean value Csm, is constant, when carrying out distribution network systems parameter adjustment second time (or wholely change distribution ground capacitance value, or change the arc suppression coil inductance value), twice adjustment time Δ Icm
Actual/ Δ Un
ActualRatio can not change.Above-mentioned viewpoint is at non-fault branch line.For the branch line that breaks down, Δ Icm
Actual/ Δ Un
ActualRatio is a very complicated amount of variation, when carrying out the distribution network systems parameter adjustment second time, twice adjustment time Δ Icm
Actual/ Δ Un
ActualRatio will change.Come therefrom, can find the branch line that breaks down very accurately.For localization of fault on the fault branch line, the way of employing is same.
Claims (4)
1, the method for a kind of small current earthing wire-selecting and localization of fault is characterized in that it is divided into following steps:
(1) detects system zero sequence voltage and each branch line zero-sequence current value in the generation singlephase earth fault very first time;
(2) determining of fault wire:
In second time, for isolated neutral system, only can change whole power distribution network ground capacitance value, detect the second time system residual voltage and each branch line zero-sequence current value after the adjustment; For arc suppression coil earthing system, can change the arc suppression coil compensation degree, perhaps change whole power distribution network ground capacitance value, detect the second time system residual voltage and each branch line zero-sequence current value after the adjustment; Twice time uses branch line zero-sequence current value divided by system zero sequence voltage value respectively, gets its end value; For the circuit that does not break down, twice time of this end value does not change, and for the circuit that breaks down, twice time of this end value, variation took place, when there is this changing value in definite certain branch line, just can determine that singlephase earth fault has taken place this branch line;
Through resistance eutral grounding, this method is suitable equally for neutral point, and method of adjustment can realize by changing the zero sequence system impedance;
(3) determining of trouble spot:
After determining the singlephase earth fault branched line, by uploading the detected zero-sequence current value of each interval microcomputer-based intelligent distribution terminal of this branched line, after new small current earthing wire-selecting microcomputer device is accepted, with detected zero-sequence current value divided by residual voltage value in the system, and differentiated, just can localization of faults position; Twice time of ratio of trouble spot load side zero-sequence current value and system zero sequence voltage value does not change, and twice time of ratio of trouble spot mains side zero-sequence current value and system zero sequence voltage value, variation took place; Just can determine position of failure point on the faulty line thus.
2, the method for a kind of small current earthing wire-selecting according to claim 1 and localization of fault is characterized in that
(1) for isolated neutral system:
The current potential of neutral point n is made as Un, and when a through stake resistance R earth fault took place mutually, each electric current that flows out mutually was:
Ia＝Ua/R+jwCa·Ua＝(Ea+Un)/R+jwCa·(Ea+Un)
Ib＝jwCb·Ub＝jwCb·(Eb+Un)
Ic＝jwCc·Uc＝jwCc·(Ec+Un)
Because Ia+Ib+Ic=0
Set Ca=Cb=Cc=Cs
Ea+Un (1+j3wCsR)=0 so
Un＝-Ea/(1+j3wCsR) (1)
During distribution network system generation single-phase earthing, residual voltage will appear in full distribution system, adopt residual voltage to start, and differentiate faulty line with zero-sequence current division by 0 sequence voltage end value; On the non-fault branch line zero-sequence current is arranged after A mutually singlephase earth fault takes place on certain branch line, the actual direction of its capacitive character reactive power is a bus flow line trackside,
Zero-sequence current is on the non-fault branch line:
Icm＝jwCsm(Ua+Ub+Uc)＝j3wCsmUn (2)
Deduct the capacitive earth current of the branch line that breaks down own and its numerical value of the zero-sequence current on the branch line that breaks down equals whole distribution capacitive earth current sum, the actual direction of its capacitive character reactive power is that line flows is to bus bar side; Computing formula is as follows:
The capacitive earth current of the branch line that breaks down own:
Ic1＝jwCs1(Ua+Ub+Uc)＝j3wCs1Un
The branch line zero-sequence current breaks down:
Ic0＝∑Icm-Ic1＝j3w(∑Csm-Cs1)Un (3)
By formula (2), (3) as can be seen, in the system zero-sequence current be with system in the related amount of residual voltage, and by formula (1) as can be seen, in the system residual voltage be with trouble spot grounding resistance R, electrical network in all related variable quantity of capacitance Cs, especially trouble spot stake resistance R changes a very complicated amount in the system; If formula (2), (3) are changed into:
Icm/Un＝3wCsm (4)
Ic0/Un＝3w(∑Csm-Cs1) (5)
With zero-sequence current value on the branch line than residual voltage value in the last system, only relevant for non-its end value of branch line that breaks down with this branch line ground capacitance value Csm, relevant for its end value of branch line that breaks down with poor (the ∑ Csm-Cs1) of whole distribution and this branch line ground capacitance value, if change whole distribution ground capacitance value, so, the former is the value of a no change amount, and the latter is the value of an amount of changing, if checkout equipment detects this changing value in the system, just can determine to take place the branch line of singlephase earth fault; If can before measure the branch line ground capacitance value that breaks down, provide on this branch line the zero-sequence current value than the benchmark end value of residual voltage value in the last system, the zero-sequence current value has bigger variation than residual voltage value in the last system on detecting this branch line, can determine on this branch line singlephase earth fault to have taken place;
In the above formula:
Ea-a responds to the phase electromotive force mutually; Eb-b responds to the phase electromotive force mutually; Ec-c responds to the phase electromotive force mutually;
The Ua-a phase-to-ground voltage; The Ub-b phase-to-ground voltage; The Uc-c phase-to-ground voltage;
Un-neutral point voltage-to-ground;
Ca-a is electric capacity relatively; Cb-b is electric capacity relatively; Cc-c is electric capacity relatively;
Ia-a is capacitance current relatively; Ib-b is capacitance current relatively; Ic-c is capacitance current relatively;
R-a phase stake resistance;
Each electric capacity (three-phase equilibrium) relatively of Cs1-branch line 1;
Each electric capacity (three-phase equilibrium) relatively of Cs2-branch line 2;
Each electric capacity (three-phase equilibrium) relatively of Csm-branch line m;
Ic1-branch line 1 capacitive earth current;
Ic2-branch line 2 capacitive earth currents;
Icm-branch line m capacitive earth current;
Ic0-branch line 1 zero-sequence current;
Each branch line capacitive earth current sum of ∑ Icm-;
(2) for the neutral by arc extinction coil grounding electrical network:
The current potential of neutral point n is made as Un ', and when a passed through stake resistance R ' generation earth fault mutually, each electric current that flows out mutually was:
Ia′＝Ua′/R′+jwCa′·Ua′＝(Ea+Un′)/R′+jwCa′·(Ea+Un′)
Ib′＝jwCb′·Ub′＝jwCb′·(Eb+Un′)
Ic′＝jwCc′·Uc′＝jwCc′·(Ec+Un′)
The arc suppression coil zero-sequence current of flowing through:
In′＝Un′/jwLn′＝-jUn′/wLn′
Because Ia '+Ib '+Ic '+In '=0
Set Ca '=Cb '=Cc '=Cs '
Ea+Un ' [1+j (3wCs ' R '-1/wLn ')]=0 so
Un′＝-Ea/[1+j(3wCs′R′-1/wLn′)] (6)
When distribution network system generation single-phase earthing, residual voltage will appear in full distribution system, adopt residual voltage to start, and differentiate with zero-sequence current division by 0 sequence voltage end value; On the non-fault branch line zero-sequence current is arranged after A mutually singlephase earth fault takes place on certain branch line, the actual direction of its capacitive character reactive power is a bus flow line trackside, and zero-sequence current is on the non-fault branch line:
Icm′＝jwCsm′(Ua′+Ub′+Uc′)＝j3wCsm′Un′ (7)
And its numerical value of the zero-sequence current on the branch line that breaks down equals the aftercurrent that the capacitive earth current of its branch line own deducts the trouble spot of flowing through, the aftercurrent of trouble spot is through the aftercurrent behind the arc suppression coil compensation because flow through, and adopt the over-compensation mode in system, under the little situation of over-compensation, the zero-sequence current value that breaks down on the branch line approaches the capacitive earth current of its branch line own, and the actual direction of capacitive character reactive power also is a bus flow line trackside; Computing formula is as follows:
The capacitive earth current of the branch line that breaks down own:
Ic1′＝jwCs1′(Ua′+Ub′+Uc′)＝j3wCs1′Un′
The arc suppression coil zero-sequence current of flowing through:
In′＝Un′/jwLn′＝-jUn′/wLn′
The aftercurrent of trouble spot after over-compensation:
In0′＝In′+∑Icm′＝-jUn′/wLn′+j3w∑Csm′
Un′＝j(3w∑Csm′-1/wLn′)Un′
The branch line zero-sequence current breaks down:
Ic0′＝Ic1′-In0′＝j[1/wLn′-3w(∑Csm′-Cs1′)]Un′(8)
By formula (7), (8) as can be seen, in the system zero-sequence current be with system in the related amount of residual voltage, and by formula (6) as can be seen, in the system residual voltage be with trouble spot grounding resistance R ', electrical network in all related variable quantity of compensating arc-extinguishing coil inductance value Ln ' among the capacitance Cs ', system, especially trouble spot stake resistance R ' changes a very complicated amount in the system; Formula (7), (8) are changed into:
Icm′/Un′＝3wCsm′ (9)
Ic0′/Un′＝1/wLn′-3w(∑Csm′-Cs1′) (10)
With zero-sequence current value on the branch line than residual voltage value in the last system, only relevant for non-its end value of branch line that breaks down with this branch line ground capacitance value Csm ', relevant for its end value of branch line that breaks down with poor (the ∑ Csm '-Cs1 ') of arc suppression coil inductance value Ln ' and whole distribution and this branch line ground capacitance value, if change arc suppression coil inductance value Ln ', promptly adjust the arc suppression coil compensation degree, perhaps, the same with previous way, change whole distribution ground capacitance value, so, the former is the value of a no change amount, and the latter is the value of an amount of changing, if checkout equipment detects this changing value in the system, just can determine to take place the branch line of singlephase earth fault;
In the above formula:
Ea-a responds to the phase electromotive force mutually; Eb-b responds to the phase electromotive force mutually; Ec-c responds to the phase electromotive force mutually;
Ua '-a phase-to-ground voltage; Ub '-b phase-to-ground voltage; Uc '-c phase-to-ground voltage;
Un '-neutral point voltage-to-ground;
Ca '-a is electric capacity relatively; Cb '-b is electric capacity relatively; Cc '-c is electric capacity relatively;
Ia '-a is capacitance current relatively; Ib '-b is capacitance current relatively; Ic '-c is capacitance current relatively;
R '-a phase stake resistance; Ln '-arc suppression coil inductance value;
Each electric capacity (three-phase equilibrium) relatively of Cs1 '-branch line 1;
Each electric capacity (three-phase equilibrium) relatively of Cs2 '-branch line 2;
Each electric capacity (three-phase equilibrium) relatively of Csm '-branch line m;
Ic1 '-branch line 1 capacitive earth current;
Ic2 '-branch line 2 capacitive earth currents;
Icm '-branch line m capacitive earth current;
Ic0 '-branch line 1 zero-sequence current;
∑ Icm '-each branch line capacitive earth current sum;
In '-arc suppression coil the zero-sequence current of flowing through;
In0 '-trouble spot aftercurrent after over-compensation.
3, the method for a kind of small current earthing wire-selecting according to claim 1 and 2 and localization of fault is characterized in that the process of determining of trouble spot is as follows:
After determining the singlephase earth fault branched line, by uploading the detected zero-sequence current value of each interval microcomputer-based intelligent distribution terminal of this branched line, after new small current earthing wire-selecting microcomputer device is accepted, with detected zero-sequence current value divided by residual voltage value in the system, and differentiated, just can localization of faults position;
For isolated neutral system:
The detected zero-sequence current of trouble spot load side (derivation of equation is seen before and stated):
I2＝j3wC2Un
I2/Un＝3wC2 (11)
The detected zero-sequence current of trouble spot mains side (derivation of equation is seen before and stated):
I1＝j3wC1Un
I1/Un＝3wC1 (12)
For the neutral by arc extinction coil grounding system:
The detected zero-sequence current of trouble spot load side (derivation of equation is seen before and stated):
I2＝j3wC2Un′
I2/Un′＝3wC2 (13)
The detected zero-sequence current of trouble spot mains side (derivation of equation is seen before and stated):
I1＝j[1/wLn′-3wC1]Un′
I1/Un′＝1/wLn′-3wC1 (14)
In system, adjust the arc suppression coil compensation degree, change the arc suppression coil inductance value, perhaps, drop in the system or excise one time and allot circuit, when changing whole distribution ground capacitance value, by formula (11), (12), (13), (14) as can be seen, variation has taken place in the ratio of residual voltage value in detected zero-sequence current value of trouble spot mains side and the system, and the ratio of residual voltage value is a fixed value in detected zero-sequence current value of trouble spot load side and the system; Can determine the singlephase earth fault point thus;
In the above formula:
Each electric capacity (three-phase equilibrium) relatively of the whole power distribution network of C1-trouble spot mains side;
Each mutually remaining ground capacitance (three-phase equilibrium) of C2-branch line trouble spot load side.
4, according to the method for claim 1 or 2 or 3 described a kind of small current earthing wire-selectings and localization of fault, it is characterized in that trimming process is as follows:
Above-mentioned single-phase grounding selecting and localization of fault scheme are based on that a kind of idealized fully distribution network systems derives, and promptly whole distribution network systems and each branch line three-phase ground capacitance think in full accord; When considering three-phase ground capacitance not simultaneously, the actual zero-sequence current of non-fault branch line m:
Icm
Actual=jwCamUa+jwCbmUb+jwCcmUc
＝(jwCamEa+jwCbmEb+jwCcmEc)+j3wCsmUn
In the formula, Cam, Cbm, Ccm are respectively a phase, b phase, the c capacitances relatively of branch line m, and Csm is a branch line m three-phase ground capacitance mean value, and formula is changed into:
Icm
Actual=Icm
Uneven+ Icm
Desirable
In the formula, Icm
Uneven=jwCamEa+jwCbmEb+jwCcmEc is the uneven electric current that produces of branch line m three-phase ground capacitance value; Icm
DesirableBe branch line m perfect condition (three-phase equilibrium) zero-sequence current, its computing method are the same, Icm
Desirable=j3wCsmUn;
Work as Icm
UnevenValue is enough big, when can not ignore, will influence Icm
Actual/ Un ratio causes time non-fault branch line Icm twice
Actual/ Un ratio changes, and can not carry out accurate route selection; If with twice time detecting to the difference of the actual zero-sequence current vector of branch line and twice time detecting to the difference of system zero sequence voltage vector carry out ratio calculation, computing formula is as follows:
Δ Icm
Actual=Icm
Actual 2-Icm
Actual 1
=(Icm
Uneven+ Icm
Desirable 2)-(Icm
Uneven+ Icm
Desirable 1)
=Icm
Desirable 2-Icm
Desirable 1
=j3wCsm (Un
Actual 2-Un
Actual 1)
Δ Icm
Actual/ Δ Un
Actual=j3wCsm (Un
Actual 2-Un
Actual 1)/(Un
Actual 2-Un
Actual 1)
Δ Icm
Actual/ Δ Un
Actual=3wCsm
In the above formula:
Icm
Actual 1The zero-sequence current that non-fault branch line m actual detected arrives before-the adjustment;
Icm
Actual 2The zero-sequence current that the non-fault branch line m actual detected in-adjustment back arrives;
Icm
Desirable 1The zero-sequence current of-non-fault branch line m perfect condition (three-phase equilibrium) calculating before adjusting;
Icm
Desirable 2The zero-sequence current of-non-fault branch line m perfect condition (three-phase equilibrium) calculating after adjusting;
Icm
UnevenThe zero-sequence current that the forward and backward non-fault branch line m three-phase imbalance of-adjustment produces;
Un
Actual 1The residual voltage that system's actual detected arrives before-the adjustment;
Un
Actual 2The residual voltage that system actual detected in-adjustment back arrives;
Δ Icm
Actual-adjust the poor of zero-sequence current vector that forward and backward non-fault branch line m actual detected arrives;
Δ Un
Actual-adjust the poor of residual voltage vector that forward and backward system actual detected arrives;
By the top formula as seen, Δ Icm
Actual/ Δ Un
ActualRatio is only relevant with this branch line three-phase ground capacitance mean value Csm, is constant, when carrying out distribution network systems parameter adjustment second time (or wholely change distribution ground capacitance value, or change the arc suppression coil inductance value), twice adjustment time Δ Icm
Actual/ Δ Un
ActualRatio can not change; Above-mentioned viewpoint is at non-fault branch line; For the branch line that breaks down, Δ Icm
Actual/ Δ Un
ActualRatio is a very complicated amount of variation, when carrying out the distribution network systems parameter adjustment second time, twice adjustment time Δ Icm
Actual/ Δ Un
ActualRatio will change; Come therefrom, can find the branch line that breaks down very accurately; For localization of fault on the fault branch line, the way of employing is same.
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