CN204462305U - A kind of distribution line disconnection monitor based on electric current and voltage vector - Google Patents

Abstract

A kind of distribution line disconnection monitor based on electric current and voltage vector, be applied to network system and be three-phase three-wire system and isolated neutral or not solidly grounded system, in the monitoring point of circuit, disconnection monitor is installed, disconnection monitor, by three-phase line voltage waveform, the three-phase current waveform of periodicity three-phase synchronous sampling distribution line, calculates the three-phase line voltage of synchronization, the effective value of three-phase current and phasing degree; By calculating, comparing in three-phase line voltage effective value maximum voltage respectively with the proportionate relationship of minimum, secondary small voltage sum, and the phase difference value relation of minimum, secondary small voltage, judge whether the upside circuit of monitoring point single-phase wire break fault occurs; By comparing the proportionate relationship of negative-sequence current and forward-order current, judge whether the upside of monitoring point or downside circuit single-phase wire break fault occurs; Calculate zero-sequence current numerical value, judge whether the downside circuit of monitoring point singlephase earth fault occurs.

Description

A kind of distribution line disconnection monitor based on electric current and voltage vector

Technical field

The utility model relates to a kind of distribution line disconnection monitor based on electric current and voltage vector.

Background technology

Existing distribution line disconnection monitoring technology is all under the precondition of the mains side voltage three-phase symmetrical of supposition power distribution network, supposition power distribution network threephase load symmetry, identified the single-phase wire break fault of distribution line as basis for estimation by the situation of change of voltage magnitude (or effective value), current amplitude (or effective value), but during power distribution network actual motion, always do not meet three-phase symmetrical running status.Therefore, high as the single-phase wire break Fault Identification decision method probability of miscarriage of justice of basis for estimation based on voltage magnitude (or effective value), current amplitude (or effective value), voltage magnitude method is only applicable to disconnection fault point situation on the upside of measurement mechanism, if disconnection fault point is on the downside of monitoring point, voltage method lost efficacy; Whether voltage method None-identified single-phase wire break has singlephase earth fault simultaneously; Current amplitude method had both been applicable to disconnection fault point on the upside of measurement mechanism, also the situation of disconnection fault point on the downside of monitoring point is applicable to, but current method signal is not necessarily obvious, in the asymmetric situation of distribution line load, probability of miscarriage of justice is high, easily to fail to judge in underloading situation erroneous judgement, circuit cannot judge time unloaded, and during circuit underloading, breakdown judge accuracy affects very large by single-phase-to-ground current.

Utility model content

The purpose of this utility model is for the deficiencies in the prior art, provides a kind of and adapts to various broken string situation and realize the distribution line disconnection monitor based on electric current and voltage vector that circuit breaking accurately judges.

The purpose of this utility model realizes by following technical solution:

A kind of distribution line disconnection monitor based on electric current and voltage vector, be arranged on the disconnection monitoring point of network system, it is characterized in that: comprise power module, processor, voltage collection circuit, current collection circuit, voltage transformer (VT) summation current transformer, voltage transformer (VT) comprises AB line voltage transformer (VT), BC line voltage transformer (VT) and the CA line voltage transformer (VT) that output terminal is connected with the input end of voltage collection circuit respectively; Current transformer comprises A phase current mutual inductor, B phase current mutual inductor and the C phase current mutual inductor that output terminal is connected with the input end of current collection circuit respectively; Voltage collection circuit and current collection circuit have included modulate circuit and A/D change-over circuit; Processor is connected with voltage collection circuit and current collection circuit respectively by data circuit; Processor is also connected with current collection circuit and voltage collection circuit respectively by synchronous signal line, regularly can send synchronous acquisition pulse signal starting voltage collection circuit, synchronous acquisition that current collection circuit carries out voltage, electric current.

Further, the utility model also comprises the remote communication module, data-carrier store and the display module that are connected with described processor respectively.

Further, described power module is rectification circuit, and the input end of described rectification circuit is connected with the output terminal of described AB line voltage transformer (VT), BC line voltage transformer (VT) and CA line voltage transformer (VT) respectively, and the output terminal of described rectification circuit is connected with described processor.

The utility model has following beneficial effect:

Cannot find and judge the orientation problem of single-phase wire break trouble spot on the downside of monitoring point for solving line voltage phase vector method, solve line current vector method and cannot judge single-phase wire break fault discovery in the unloaded or underloading situation of power distribution network and decision problem, solve and adopt electric current determining method because being subject to single-phase-to-ground current disturbing effect accuracy of judgement sex chromosome mosaicism under there is single-phase earthing disconnection fault situation, the utility model is for the single-phase wire break fault of isolated neutral or small current neutral grounding power distribution network, propose a kind of based on line voltage vector, current vector is as the monitoring decision method of the power distribution network single-phase disconnection fault of basis for estimation, by effective value between three-phase line voltage, phase relation compares the single-phase wire break Fault Identification that realization is criterion based on voltage vector, and by calculating the positive sequence of triple-phase line electric current, negative phase-sequence, zero-sequence current, on the downside of judgement monitoring point, the foundation of single-phase wire break fault or single-phase earthing disconnection fault whether is there is using negative phase-sequence-forward-order current proportionate relationship and zero-sequence current size, by comprehensive to above-mentioned two kinds of decision methods, realize judging whether power distribution network single-phase wire break fault occurs, the identification decision of singlephase earth fault, determine broken string phase sequence number, and the upper and lower sides relative position relation determining between break point and monitoring point.There is following beneficial effect:

1, have better versatility, the utility model is applicable to the isolated neutral of each electric pressure or not direct ground connection power distribution network, does not need to judge voltage criterion setting valve μ according to electric pressure adjustment single-phase wire break _dx, θ _dx.

2, have better adaptability, when between the portion actual measurement voltage effective value and rated voltage of power distribution network, the amount of deflection is larger, the monitoring method adopting the utility model to provide still can obtain result of determination accurately.

3, positive sequence, negative phase-sequence, zero-sequence current Symmetric Vector numerical value are calculated to row during three-phase current vector, by negative phase-sequence, forward-order current effective value scale-up factor ε are judged current vector criterion setting value ε with presetting single-phase wire break _dxcomparison, solve power distribution network load current and to fluctuate widely the reliable and stable sex chromosome mosaicism of judged result in situation.

4, under meeting distribution line asymmetric (comprise three-phase mains voltage is asymmetric, threephase load resistance value is asymmetric, threephase load angle of impedance asymmetric) running status within the specific limits, still single-phase disconnection fault can effectively be identified.

5, adopt voltage vector, current vector data as single-phase wire break fault verification foundation simultaneously, improve the confidence level of result of determination, and complement one another, realize the identification decision function to single-phase wire break fault in the distribution wire of measurement mechanism upper and lower side simultaneously.

6, by the zero-sequence current of computation and measurement device installation site, single-phase earthing type fault can be identified simultaneously, and prevent single-phase-to-ground current to based on the interference effect of current vector data as single-phase wire break fault verification foundation, improve and judge accuracy.

Accompanying drawing explanation

Below in conjunction with accompanying drawing, the utility model is described in further detail.

Fig. 1 is three-phase symmetrical circuit figure.

Fig. 2 is voltage, the current vector figure of three-phase symmetrical circuit.

Fig. 3 is that three-phase symmetrical circuit figure, B phase breaks.

Fig. 4 is that in Fig. 3, B phase breaks three-phase line voltage current vector figure, and angle of impedance balanced load, θ is 60 °.

Fig. 5 is that in Fig. 3, B phase breaks three-phase line voltage current vector figure, angle of impedance asymmetric load.

Fig. 6 is multiple three-phase load circuit, and the circuit diagram of earth-free single-phase wire break situation occurs in part threephase load.

Fig. 7 is that in Fig. 6, B phase breaks three-phase line voltage current vector figure.

Fig. 8 is that B phase breaks front and back three-phase line voltage situation of change, α≤60 °.

The circuit theory diagrams of the monitoring device that Fig. 9 provides for the utility model.

Embodiment

Circuit analysis and broken string resolution principle:

1, circuit analysis

Situation 1: three-phase three-wire system Y-Y symmetric circuit

If AB phases line voltage effective value is U _l, phasing degree is 0 degree, each phase of impedance is Z _a=Z _b=Z _c=Z, each phases line voltage vector can be expressed as follows:

Corresponding relation between each phases line voltage and phase voltage is

Then A phase line current is

B phase line current is

B phase line current is

In the case, the phase differential of electrical network three-phase line voltage, electric current is everywhere 120 °.Circuit diagram and voltage thereof, current vector are as shown in Figure 1, Figure 2.

Situation 2: three-phase three-wire system Y-Y symmetric circuit, B phase load breaks

On the upside of break point, (side near power supply) three-phase line voltage still remains unchanged.

Make Z _a=Z, then Z _a=Z _b=Z _c=Z, near on the upside of break point, (side near power supply) triple-phase line electric current is as follows:

${\stackrel{.}{I}}_b=0$

On the downside of break point, (side away from power supply) each line voltage is as follows:

Near on the downside of break point, each line current is as follows:

${\stackrel{.}{I}}_b=0$

In the case, on the upside of break point, three-phase line voltage still remains unchanged; On the downside of break point, AB, BC line voltage effective value is 1/2 times of line voltage, and phase place is identical, and CA line voltage still remains unchanged; Break point upper and lower sides A phase, C phase current equal and opposite in direction, phase differential is 180 °, and B phase current values is 0.Circuit diagram is as Fig. 3, and voltage, current vector are as Fig. 4.

Situation 3: three-phase three-wire system Y-Y power supply is symmetrical, load unsymmetric circuit, and B phase load breaks

If Z _a≠ Z _b≠ Z _c, then

On the upside of break point, (side near power supply) three-phase line voltage still remains unchanged.

(side near power supply) triple-phase line electric current near on the upside of break point

${\stackrel{.}{I}}_b=0$

On the downside of break point, (side away from power supply) each line voltage is as follows:

Near on the downside of break point, each line current is as follows:

${\stackrel{.}{I}}_b=0$

In the case, on the upside of break point, three-phase line voltage still remains unchanged; On the downside of break point, AB, BC line voltage effective value is respective series connection dividing potential drop impedance ratio, and its phase differential is the difference of A, C phase load angle of impedance, and CA line voltage still remains unchanged; Break point upper and lower sides A phase, C phase current equal and opposite in direction, phase differential is 180 °, and B phase current values is 0.Circuit diagram is as Fig. 3, and voltage, current vector are as Fig. 5.Situation 2 can be used as the special case into threephase load impedance full symmetric in situation 3, and situation 2 and situation 3 can merge into unified decision method.

Situation 4: multiple three-phase load circuit, there is the situation of earth-free single-phase wire break in part threephase load.When monitoring point is before B phase break point, and there is threephase load between monitoring point and break point, after break point.Circuit as shown in Figure 6.

Line voltage feature: on the upside of break point, (side near power supply) three-phase line voltage still remains unchanged.

Current characteristics: include symmetric three-phase load electric current or asymmetric threephase load electric current, and A, C two-phase series load electric current.No matter have how many three-phase loads in circuit, circuit can merger be all a symmetric three-phase load 1, two phase loads 2 in parallel.So the three-phase current vector of load 1 will meet the feature of situation 1, the three-phase current vector of load 2 will meet the feature of situation 2.

In the three-phase total current of monitoring point gained be

${\stackrel{\·}{I}}_a={\stackrel{\·}{I}}_{a1}+{\stackrel{\·}{I}}_{a2}$

${\stackrel{\·}{I}}_b={\stackrel{\·}{I}}_{b1}$

${\stackrel{\·}{I}}_c={\stackrel{\·}{I}}_{c1}+{\stackrel{\·}{I}}_{c2}$

Therefore, even if when multiple threephase load symmetry, if a phase circuit breaking of one of them balanced load, to the total current effective value size of each phase be caused to occur from waiting until not unequal change mutually, between the three-phase current of its total load, phase place also no longer meets difference 120 ° of symmetric relations.The change of its current vector as shown in Figure 7.

Power distribution network is in actual motion, no matter carry out actual current measurement at which position of electrical network, due to branch's in circuit load everywhere and not exclusively three-phase symmetrical, and load current is in fluctuation status all the time, therefore, unreliable using the size of each phase current, phase number as circuit breaking basis for estimation, easily occur failing to judge or judge by accident.Using the size of electric current, phase number as circuit breaking basis for estimation judgement confidence level by between load 1, load 2 separately institute to flow through current ratio relationship affect very large.Take break point as boundary, load 1 before break point can be considered as three-phase symmetrical or the load close to symmetry, load 2 after break point is considered as three-phase and does not claim load completely, the current data measured by monitoring point is the current vector generated data of load 1, load 2, is asymmetrical three-phase electric current.For this reason, current unbalance factor can be analyzed according to positive sequence, negative phase-sequence, zero sequence Symmetric Vector analytical approach, find the current signal Changing Pattern feature judging broken string.

For load 1, assuming that it is for asymmetric load current, if α=∠ 120 °, then according to positive sequence, negative phase-sequence, that zero-sequence current computing formula calculates its numerical value is as follows:

Forward-order current is ${\stackrel{\·}{I}}_{11}=\frac{1}{3}({\stackrel{\·}{I}}_{a1}+\mathrm{\α}{\stackrel{\·}{I}}_{b1}+{\mathrm{\α}}^2{\stackrel{\·}{I}}_{c1}),$ Substitution calculates ${\stackrel{\·}{I}}_{11}={\stackrel{\·}{I}}_{N1};$

Negative-sequence current is ${\stackrel{\·}{I}}_{12}=\frac{1}{3}({\stackrel{\·}{I}}_{a1}+{\mathrm{\α}}^2{\stackrel{\·}{I}}_{b1}+\mathrm{\α}{\stackrel{\·}{I}}_{c1}),$ Substitution calculates ${\stackrel{\·}{I}}_{12}=0;$

Zero-sequence current is ${\stackrel{\·}{I}}_{10}=\frac{1}{3}({\stackrel{\·}{I}}_{a1}+{\stackrel{\·}{I}}_{b1}+{\stackrel{\·}{I}}_{c1}),$ Substitution calculates ${\stackrel{\·}{I}}_{10}=0;$

So, the current unbalance factor ε of load 1 can be calculated ₁, its computing formula is

${\mathrm{\ϵ}}_1=\frac{\left|{\stackrel{\·}{I}}_{12}\right|}{\left|{\stackrel{\·}{I}}_{11}\right|}\×100\%$

Substitution calculates

ε ₁＝0

For load 2, size is identical, and direction is contrary, if then according to positive sequence, negative phase-sequence, that zero-sequence current computing formula calculates its numerical value is as follows:

Forward-order current is ${\stackrel{\·}{I}}_{21}=\frac{1}{3}({\stackrel{\·}{I}}_{a2}+\mathrm{\α}{\stackrel{\·}{I}}_{b2}+{\mathrm{\α}}^2{\stackrel{\·}{I}}_{c2}),$ Substitution calculates ${\stackrel{\·}{I}}_{21}=\frac{\sqrt{3}}{3}{e}^{j30}\·{\stackrel{\·}{I}}_{N2};$

Negative-sequence current is ${\stackrel{\·}{I}}_{22}=\frac{1}{3}({\stackrel{\·}{I}}_{a2}+{\mathrm{\α}}^2{\stackrel{\·}{I}}_{b2}+\mathrm{\α}{\stackrel{\·}{I}}_{c2}),$ Substitution calculates ${\stackrel{\·}{I}}_{22}=\frac{\sqrt{3}}{3}{e}^{-j30}\·{\stackrel{\·}{I}}_{N2};$

Zero-sequence current is ${\stackrel{\·}{I}}_{20}=\frac{1}{3}({\stackrel{\·}{I}}_{a2}+{\stackrel{\·}{I}}_{b2}+{\stackrel{\·}{I}}_{c2}),$ Substitution calculates ${\stackrel{\·}{I}}_{20}=0;$

So, the negative phase-sequence-forward-order current scale-up factor ε of load 2 can be calculated ₂, its computing formula is

${\mathrm{\ϵ}}_2=\frac{\left|{\stackrel{\·}{I}}_{22}\right|}{\left|{\stackrel{\·}{I}}_{21}\right|}\×100\%$

Substitution calculates

ε ₂＝100％

Change asymmetrical three-phase current vector into Symmetric Vector analysis, according to electric current superposition principle, the positive sequence of monitoring point, negative phase-sequence, zero-sequence current are listed formula respectively and are:

Forward-order current ${\stackrel{\·}{I}}_1={\stackrel{\·}{I}}_{11}+{\stackrel{\·}{I}}_{21},$ Substitute into after calculating ${\stackrel{\·}{I}}_1={\stackrel{\·}{I}}_{N1}+\frac{\sqrt{3}}{3}{e}^{j30}\·{\stackrel{\·}{I}}_{N2}$

Negative-sequence current ${\stackrel{\·}{I}}_2={\stackrel{\·}{I}}_{12}+{\stackrel{\·}{I}}_{22},$ Substitute into after calculating ${\stackrel{\·}{I}}_2=\frac{\sqrt{3}}{3}{e}^{-j30}\·{\stackrel{\·}{I}}_{N2}$

Zero-sequence current ${\stackrel{\·}{I}}_0={\stackrel{\·}{I}}_{10}+{\stackrel{\·}{I}}_{20},$ Substitute into after calculating ${\stackrel{\·}{I}}_0=0$

So can calculate the negative phase-sequence-positive sequence total current scale-up factor ε comprising load 1,2 in monitoring point, its computing formula is

$\mathrm{\ϵ}=\frac{\left|{\stackrel{\·}{I}}_2\right|}{\left|{\stackrel{\·}{I}}_1\right|}\×100\%=\frac{{|\stackrel{\·}{I}}_{22}|}{|{\stackrel{\·}{I}}_{11}+{\stackrel{\·}{I}}_{21}|}\×100\%$

Substitution calculates

$\mathrm{\ϵ}=\frac{\frac{\sqrt{3}}{3}\left|{\stackrel{\·}{I}}_{N2}\right|}{|{\stackrel{\·}{I}}_{N1}+\frac{\sqrt{3}}{3}{e}^{j30}{\stackrel{\·}{I}}_{N2}|}\×100\%$

In the case, the three-phase line voltage Changing Pattern of break point upper and lower sides still meets situation 2 or the rule described in situation 3.

In electric current, can draw following rule by above formula: when monitoring point is before B phase break point, and when having threephase load between monitoring point and break point, after break point, measured by monitoring point, three-phase current vector is asymmetric vector; Three phase symmetry load electric current I before break point _n1trend towards being far longer than load current I on the downside of break point _n2time, negative phase-sequence-forward-order current scale-up factor ε tends to close to 0; Three phase symmetry load electric current I before break point _n1trend towards being far smaller than load current I on the downside of break point _n2time, negative phase-sequence-forward-order current scale-up factor ε trends towards 100%.The size reflection of coefficient ε numerical value be the numerical value of the possibility of the single-phase disconnected phase of distribution line, indirect judgement can may there is single-phase wire break probability of malfunction size on the downside of this moment monitoring point.Following criterion can be drawn: for an isolated neutral system power distribution network by above-mentioned rule, have under certain normally loaded ruuning situation, when measured negative phase-sequence-forward-order current scale-up factor ε is 0, then can determine, on the downside of its circuit, a phase line disconnection failure does not occur; When measured negative phase-sequence-forward-order current scale-up factor ε is 100%, then can determine that on the downside of its circuit, one phase line disconnection failure necessarily occurs in somewhere; When negative phase-sequence-forward-order current scale-up factor ε is between 0-100%, then can according to ε numerical values recited and then the probability size inferring disconnection fault, ε is larger, then the probability of circuit one phase broken string possibility is higher, can setup parameter ε _dxsingle-phase wire break fault whether is there is, parameter ε as side line under comparing to determine monitoring point _dxsize setting can normal operation according to power distribution network time three-phase imbalance situation set.

Situation 5: multiple three-phase load circuit, there is the situation of ground connection single-phase wire break in part threephase load.When monitoring point is before B phase break point, and there is threephase load between monitoring point and break point, after break point, and at least one end ground connection of break point.

Line voltage feature: on the upside of break point, (side near power supply) three-phase line voltage still remains unchanged.

Current characteristics: on the downside of monitoring point, because B phase break point has one end ground connection at least, affect (i.e. zero-sequence current) by power distribution network ground current, even if do not have other load between monitoring point and break point, the electric current measured by non-broken string phase A, C phase no longer meets size close to relation that is equal, phase place angle 180 °.For broken string phase B phase, if earth point is on the downside of break point, then B phase current is 0, if earth point is on the upside of break point, then B phase current is electrical network ground current (i.e. 3I ₀electric current, namely 3 times of zero-sequence currents), if break point upper and lower sides is ground connection all simultaneously, then be equivalent to B phase circuit to connect at break point place a resistance and break point two ends ground connection simultaneously, most ground current flows through wire on the upside of break point, and still can be similar to and make B phase current is power distribution network ground current.

Calculate the symmetrical components of three-phase current, comprise forward-order current negative-sequence current zero-sequence current and analyze.

Forward-order current is ${\stackrel{\·}{I}}_1=\frac{1}{3}({\stackrel{\·}{I}}_a+\mathrm{\α}{\stackrel{\·}{I}}_b+{\mathrm{\α}}^2{\stackrel{\·}{I}}_c)$

Negative-sequence current is ${\stackrel{\·}{I}}_2=\frac{1}{3}({\stackrel{\·}{I}}_a+{\mathrm{\α}}^2{\stackrel{\·}{I}}_b+\mathrm{\α}{\stackrel{\·}{I}}_c)$

Zero-sequence current is ${\stackrel{\·}{I}}_0=\frac{1}{3}({\stackrel{\·}{I}}_a+{\stackrel{\·}{I}}_b+{\stackrel{\·}{I}}_c)$

For isolated neutral distribution network systems, power distribution network has comparatively heavy load and in threephase load almost symmetry situation, when there is not broken string but B phase singlephase earth fault occur in circuit, due to the capacitive earth current that the electric current of the earth point of power distribution network is all three-phase distribution circuits under whole section of bus, its effective value is generally much smaller than phase current, size is the zero-sequence current of 3 times, i.e. 3I ₀, then between each symmetrical components, the pass of size is

$\left\{\begin{array}{c}\left|{\stackrel{\·}{I}}_1\right|>>\left|{\stackrel{\·}{I}}_2\right|\\ \left|{\stackrel{\·}{I}}_1\right|>>\left|{\stackrel{\·}{I}}_0\right|\\ \left|{\stackrel{\·}{I}}_0\right|\≠0\end{array}\right.$

Therefore, negative phase-sequence in the case-forward-order current scale-up factor ε is general very little, and its size is the numerical value close to 0.

If B phase single-phase wire break earth fault, then zero-sequence current, negative-sequence current are all non-vanishing, namely then when ground connection one-sided on the upside of break point or break point upper and lower sides ground connection and when not having other load between monitoring point and break point simultaneously, and because most of zero-sequence current flows through broken string end upside electric wire earth point, its effective value magnitude relationship is

$\left|{\stackrel{\·}{I}}_b\right|=\left|3{\stackrel{\·}{I}}_0\right|$

When unsettled on the upside of break point, the one-sided ground connection in downside and when there is no other load between monitoring point and break point, and because the electric current on the downside of break point is ground current, therefore, its effective value magnitude relationship is

$\left|{\stackrel{\&CenterDot;}{I}}_b\right|<\left|3{\stackrel{\&CenterDot;}{I}}_0\right|$

Therefore, above-mentioned two kinds of single-phase wire breaks and a relational expression of merging into of the fault of ground connection judge, namely when B phase single-phase wire break and earth fault time, no matter earth point is on the upside of break point or downside, broken string phase line current effective value measured near on the upside of break point is less than or equal to zero-sequence current effective value, namely

$\left|{\stackrel{\&CenterDot;}{I}}_b\right|\&le;\left|3{\stackrel{\&CenterDot;}{I}}_0\right|$

Identical with situation 4, when having threephase load before and after break point, by monitoring the size of negative phase-sequence-forward-order current scale-up factor ε, the size of power distribution network single-phase disconnection probability can be inferred, when occur single-phase wire break and the fault of ground connection time, the factor of zero-sequence current can cause negative-sequence current to increase, thus superpose and increase the numerical value of negative phase-sequence-forward-order current scale-up factor ε, even may occur that negative-sequence current size exceedes the situation of forward-order current size, i.e. negative phase-sequence-forward-order current scale-up factor ε is greater than 100%.

In actual motion, although the end loads equipment that medium voltage distribution network accesses carries out mounting arrangements according to the mode of threephase load balance as far as possible, under its normal operation, the degree of unbalancedness of three-phase current is very little, but in medium-voltage distribution circuit actual motion, still three-phase current complete equipilibrium cannot be realized, its influence factor has: the threephase load of (1) substation transformer low-pressure side is uneven, and on high-tension side three-phase current will be caused to there are differences; (2) power distribution network may be provided with a small amount of single phase distribution transformer, causes three-phase line electric current there are differences; (3) there is a large amount of two element measurements, measuring apparatus in power distribution network, voltage two element measurement mechanism is as AB, BC phase PT (voltage transformer (VT)), electric current two element measurement mechanism is as A, C phase CT (current transformer), although itself micro power consumption, this also will cause electrical network to there is a small amount of three phase unbalance current all the time; (4) arrangement mode of distribution network line three-phase conducting wire, each phase conductor over the ground the factor such as heartless condition also will circuit three-phase current size be made to there is small differentia influence.

In these cases, the three-phase line voltage Changing Pattern of break point upper and lower sides still meets situation 2 or the rule described in situation 3; Three-phase current Changing Pattern then meets following rule.

In conjunction with related law and the conclusion of situation 4, and consider the factor of the single-phase-to-ground current of situation 5, then three-phase current unbalance situation when overall power distribution net itself normally runs, can with negative phase-sequence-forward-order current scale-up factor ε for judgment basis, setup parameter ε _dxwhether there is single-phase wire break fault as side line under comparing to determine monitoring point, whether be greater than 0 as the foundation judging whether to occur on the downside of monitoring point singlephase earth fault using zero-sequence current effective value.Therefore, situation 4 and situation 5 can merge into unified decision method.

2. break resolution principle and method

By the circuit analysis of above-mentioned situation 1-5, carry out judgement principle and the computing formula of distribution line single-phase wire break fault with three-phase line voltage, line current vector for data source by discussing below.

(1) based on single-phase wire break breakdown judge principle and the computing formula of three-phase line voltage vector

Known conditions:

By measuring, three-phase line voltage vector can be obtained the effective value of each vector all should much larger than 0, and no matter whether single-phase wire break fault occurs on the upside of monitoring point, meets all the time

According to power distribution network operating standard and electrical network actual conditions, resistance value, the angle of impedance difference in size of the loaded impedance of any two-phase of power distribution network are also little, therefore, angle of impedance phase differential α≤60 ° of impedance magnitude variance rate Δ R≤25%, each phase of impedance between threephase load can be established.

Fig. 8 is three-phase line voltage vector and loaded impedance relation schematic diagram, can find out following rule by schematic diagram, and when single-phase wire break fault does not occur circuit, the effective value size of three-phase line voltage is close, and phase angle difference is about 120 °.If when B phase disconnection fault occurs circuit, by the analysis result of situation 3, can learn, size and phasing degree remain unchanged, size and phasing degree all there is larger change, the size of the two depends on that it is in the proportionate relationship of corresponding phase of impedance value Z, two all phase place angle depend on the difference at corresponding phase of impedance angle.Can intuitively be found out and proof of deriving by Fig. 4, the angle of impedance difference accessed when AB, BC phase is 60 °, and during AB, BC phase of impedance value equal and opposite in direction, effective value sum maximum; When the angle of impedance difference that AB, BC phase accesses is 0 °, no matter AB, BC phase of impedance value equal and opposite in direction or unequal, its effective value sum all with constant; When the angle of impedance difference that AB, BC phase accesses be greater than 0 ° and be less than 60 ° interval time, if during AB, BC phase of impedance value equal and opposite in direction, effective value sum maximum.

When carrying out AB, BC phase of impedance value equal and opposite in direction below B phase break after the analysis of size and phase angle relationship situation of change between three-phase line voltage.

Relatively line voltage effective value size, distinguishes voltage effective value data maximums, sub-minimum and minimum value and distinguishes assignment to variable U _max, U _mid, U _min, by its corresponding phase angle assignment to variable φ _max, φ _mid, φ _min.

If coefficient μ is the scale-up factor of voltage maximal phase effective value and time little, minimum two-phase voltage effective value sum, coefficient θ is the phase difference value between voltage time little, minimum phase, and its computing formula is expressed as follows:

$\mathrm{\&mu;}=\frac{U_{\max }}{U_{\min }+U_{\mathrm{mid}}}---\left(1\right)$

θ＝|φ _mid-φ _min| (2)

When there is not single-phase wire break fault, three-phase line voltage size is close to equal, and phase differential all differs about 120 °, i.e. U _max≈ U _mid≈ U _min, | φ _mid-φ _min| ≈ 120 °, therefore, can calculate

μ≈0.5

θ≈120°

After B phase disconnection fault occurs, if the angle of impedance of load that AB, BC phase accesses is equal, then meet the discussion conclusion of situation 2, i.e. U _max=U _min+ U _mid, | φ _mid-φ _min| ≈ 0 °, therefore, can calculate

μ＝1

θ＝0°

After B phase disconnection fault occurs, if the angle of impedance of load that AB, BC phase accesses is unequal, the according to circumstances discussion of 3, and limit that the impedance magnitude that AB, BC phase accesses is equal, angle of impedance differs 60 °, i.e. U _min=U _mid, | φ _mid-φ _min|=60 °, therefore, can calculate

$\mathrm{\&mu;}=\frac{U_{\max }}{U_{\min }+U_{\mathrm{mid}}}=\frac{\sqrt{3}}{2}=0.866$

θ＝60°

Whether coefficient μ, θ be there is the judgment basis of single-phase wire break as circuit, can draw the following conclusions:

As μ ≈ 0.5 and θ ≈ 120 ° time, on the upside of monitoring point there is not single-phase wire break fault in circuit;

When 1 >=μ >=0.866 and 0 °≤θ≤60 ° time, (namely by mains side) circuit generation single-phase wire break fault on the upside of monitoring point, single-phase fault is the leading phase of the maximum corresponding phase of line voltage mutually.

(2) based on single-phase wire break breakdown judge principle and the computing formula of three-phase current vector

Known conditions:

By measuring, triple-phase line current vector can be obtained positive sequence, negative phase-sequence, zero-sequence current can be calculated by triple-phase line current vector

Due in power distribution network actual motion, load is in random fluctuation state all the time, the fluctuating range of electric current, frequency are much larger than voltage, the direct effective value according to triple-phase line electric current, relative phase angle judge whether circuit breaks, the probability of then judging by accident is very high, can cannot judge whether circuit single-phase wire break fault occurs when circuit zero load or pole underloading.Therefore, the single-phase wire break breakdown judge applied based on triple-phase line current vector must have a precondition, namely the effective value of three-phase current must have at least biphase current to be greater than the minimum setting valve parameter I of electric current _ini, namely meet relation formula

If three-phase current effective value does not meet above-mentioned relation formula, then show circuit unloaded or gather current data and cannot meet the demands, do not carry out the single-phase wire break breakdown judge based on three-phase current vector.

Carry out the analysis of single-phase wire break fault judgment method below.

If coefficient ε is negative phase-sequence-forward-order current scale-up factor, its computing formula is expressed as follows:

$\mathrm{\&epsiv;}=\frac{\left|{\stackrel{\&CenterDot;}{I}}_2\right|}{\left|{\stackrel{\&CenterDot;}{I}}_1\right|}---\left(4\right)$

Because negative phase-sequence-forward-order current scale-up factor ε is used to the coefficient reflecting distribution line single-phase wire break probability height, judging precision for improving, according to the characteristic of power distribution network, one can be set and suitably compare with reference to parameter ε _dxjudge whether circuit single-phase wire break fault occurs.According to relevant code, under electrical network normal operation, the degree of unbalancedness of three-phase current is generally not more than 25%, if the impedance of threephase load is unequal but angle of impedance is equal, in this condition, simulation calculation can go out negative phase-sequence-forward-order current scale-up factor ε=0.1644; If the impedance of threephase load is equal but angle of impedance is unequal, if in threephase load impedance, two-phase is equal, wherein have the angle of impedance difference of a phase of impedance and other two-phase to be 60 °, then simulation calculation can go out its tri-phase unbalance factor and be greater than 25%, negative phase-sequence-forward-order current scale-up factor ε=0.3725.Therefore, the constraint condition normally run at power distribution network is: coefficient ε is less than 0.3725.Consider the unsymmetrical factors such as maximum asymmetric load possible in electrical network, threephase load variation, the broken string of coefficient ε judges increase with reference to setting valve and be set to ε by the utility model _dx=0.5, setting valve ε _dxlarge I adjusts according to the practical operation situation of power distribution network.

Coefficient in be zero-sequence current effective value, its numerical values recited reflects power distribution network and whether there is single-phase earthing, when time, there is not singlephase earth fault in distribution network line; When distribution network line generation singlephase earth fault.

Whether coefficient ε be there is the judgment basis of single-phase wire break as circuit, can draw the following conclusions:

As ε < ε _dxtime, on the downside of monitoring point, circuit generation single-phase wire break probability of malfunction is less;

As ε>=ε _dxand time, on the downside of monitoring point there is single-phase earth-free disconnection fault probability comparatively greatly in circuit, its probability size and being proportionate property of coefficient ε, and broken string is the minimum phase of three-phase current effective value mutually;

As ε>=ε _dxand time, on the downside of monitoring point, circuit generation single-phase earthing disconnection fault probability is comparatively large, its probability size and being proportionate property of coefficient ε, and broken string is the minimum phase of three-phase current effective value mutually.

Disconnection monitor

In distribution line, install one or more disconnection monitor, three-phase line voltage waveform, the three-phase current waveform of this device periodicity three-phase synchronous sampling distribution line, calculate the three-phase line voltage of synchronization, the effective value of three-phase current and phasing degree; By calculating, comparing in three-phase line voltage effective value maximum voltage respectively with the proportionate relationship of minimum, secondary small voltage sum, and the phase difference value relation of minimum, secondary small voltage, judge whether the upside circuit (namely near mains side) of monitoring place single-phase wire break fault occurs; By comparing the proportionate relationship of negative-sequence current and forward-order current, whether the upside (namely near mains side) of judgment means infield or downside circuit (namely away from mains side) there is single-phase wire break fault; Calculate zero-sequence current numerical value, whether the downside circuit of judgment means infield there is singlephase earth fault.

Concrete, multiple monitoring point is set on the line, each monitoring point arranges at least one disconnection monitor, and this disconnection monitor can be used as what's new and is integrated in the intelligent controller of substation feeder wire-outgoing breaker, section switch, segmentation on-load switch, demarcation circuit breaker or the demarcation load switch including the peripheral measuring sensor of voltage transformer (VT) summation current transformer.

With reference to shown in Fig. 9, a kind of distribution line disconnection monitor based on electric current and voltage vector, comprise power module 6, microprocessor 1, voltage collection circuit 2, current collection circuit 3, voltage transformer (VT) summation current transformer, voltage transformer (VT) comprises AB line voltage transformer (VT) 41, BC line voltage transformer (VT) 42 and CA line voltage transformer (VT) 43, and its output terminal is connected with the input end of voltage collection circuit 2 respectively; Current transformer comprises A phase current mutual inductor 51, B phase current mutual inductor 52 and C phase current mutual inductor 53, and its output terminal is connected with the input end of current collection circuit 3 respectively; Voltage collection circuit 2 and current collection circuit 3 have included modulate circuit and A/D change-over circuit; Microprocessor 1 is connected with voltage collection circuit 2, current collection circuit 3, remote communication module 12, clock module 11, data-carrier store 13, local I/O equipment 15 and display module 14 respectively by data circuit; Microprocessor 1 is also connected with current collection circuit 2 and voltage collection circuit 3 respectively by synchronous signal line, regularly can send synchronous acquisition pulse signal starting voltage collection circuit 2, synchronous acquisition that current collection circuit 3 carries out voltage, electric current.Power module 6 is rectification circuit, the input end of rectification circuit is connected with the output terminal of AB line voltage transformer (VT) 41, BC line voltage transformer (VT) 42 and CA line voltage transformer (VT) 43 respectively, the output terminal of rectification circuit is connected with microprocessor 1, can send monitoring information for background monitoring by remote communication module 12 to backstage watch-dog 16.

Specific works principle is: microprocessor 1 timing sends synchronous acquisition pulse signal to the A/D change-over circuit of the A/D change-over circuit of voltage collection circuit 2 and current collection circuit 3, make A/D change-over circuit that six tunnel simulating signals (three road voltages, three road electric currents) are synchronously converted to digital signal and feed back to microprocessor 1, carry out broken string by microprocessor 1 according to voltage and current data to judge, and by judgment result displays in display screen 14, and flow to background monitoring equipment 16 by remote communication module 12.

Concrete grammar is as follows:

1, synchronous acquisition three-phase line voltage, line current vector data.

Feature: periodic synchronous sampling three-phase line voltage waveform, three-phase current waveform, calculates, adds up effective value, the phasing degree of phase each line voltage vector in the same time, be denoted as

${\stackrel{\&CenterDot;}{U}}_{\mathrm{bc}}=U_{\mathrm{bc}}\&angle;{\mathrm{\&phi;}}_{\mathrm{bc}}$

${\stackrel{\&CenterDot;}{U}}_{\mathrm{ca}}=U_{\mathrm{ca}}\&angle;{\mathrm{\&phi;}}_{\mathrm{ca}}$

Calculate, add up effective value, the phasing degree of phase each line current vector in the same time, be denoted as

${\stackrel{\&CenterDot;}{I}}_a=I_a\&angle;{\mathrm{\&phi;}}_a$

${\stackrel{\&CenterDot;}{I}}_b=I_b\&angle;{\mathrm{\&phi;}}_b$

${\stackrel{\&CenterDot;}{I}}_c=I_c\&angle;{\mathrm{\&phi;}}_c$

If gather the line voltage that calculates or current effective value data minimum, its accuracy of data acquisition and discrimination are difficult to meet and judge requirement, then this line voltage or current vector numerical value are denoted as 0, i.e. line voltage or or line (phase) electric current or or if the effective value numerical value of three-phase line voltage or triple-phase line electric current is all 0, then show that distribution line has a power failure or all measurement mechanism itself breaks down, do not perform follow-up voltage, electric current checking procedure, do not perform follow-up accordingly according to voltage vector or the current vector single line disconnection fault determining step as criterion yet, if line voltage is not all 0, but triple-phase line current effective value is all less than or equal to the minimum value I that can ensure broken string judging nicety rate _ini, then circuit is light condition or close to light condition, adopts current effective value/current phase method to lose efficacy, and the electric current therefore do not performed below veritifies step, according to the single line disconnection fault determining step of current vector as criterion after also not performing.

2, line voltage check, line current verification, calculating negative phase-sequence-forward-order current scale-up factor.

Calibration voltage, current data: due to measure to as if operating power distribution network, network system is three-phase three-wire system and isolated neutral or not solidly grounded system, correct and precision meets the demands under prerequisite in the data gathered, then gathered three-phase line voltage vector sum should be zero or close to zero numerical value, if this setting valve is U _jy, then

If relational expression then voltage measurement circuit and measurement mechanism gather voltage vector data normally, and the verification of line voltage data is passed through.

If relational expression then show that gathered current vector data fit is as the pacing items of carrying out single-phase wire break judgement, current data verification is passed through.Then carry out positive sequence, negative phase-sequence, zero-sequence current calculates and whether electrical network exists singlephase earth fault judgement.

Calculate the symmetrical components of three-phase current, comprise forward-order current negative-sequence current zero-sequence current and analyze.

Forward-order current is ${\stackrel{\&CenterDot;}{I}}_1=\frac{1}{3}({\stackrel{\&CenterDot;}{I}}_a+\mathrm{\&alpha;}{\stackrel{\&CenterDot;}{I}}_b+{\mathrm{\&alpha;}}^2{\stackrel{\&CenterDot;}{I}}_c)$

Negative-sequence current is ${\stackrel{\&CenterDot;}{I}}_2=\frac{1}{3}({\stackrel{\&CenterDot;}{I}}_a+{\mathrm{\&alpha;}}^2{\stackrel{\&CenterDot;}{I}}_b+\mathrm{\&alpha;}{\stackrel{\&CenterDot;}{I}}_c)$

Zero-sequence current is ${\stackrel{\&CenterDot;}{I}}_0=\frac{1}{3}({\stackrel{\&CenterDot;}{I}}_a+{\stackrel{\&CenterDot;}{I}}_b+{\stackrel{\&CenterDot;}{I}}_c)$

Wherein, when namely the triple-phase line current vector gathered and should be close to remainder value, if this setting valve is I _jd, then

If then on the downside of monitoring point there is not singlephase earth fault in circuit.

If then on the downside of monitoring point there is singlephase earth fault in circuit.

3, effective value, phase compare (determine whether a phase broken string, which breaks mutually) between three-phase line voltage

Relatively line voltage effective value size, distinguishes voltage effective value data maximums, minimum value and intermediate value and distinguishes assignment to variable U _max, U _min, U _mid, correspondence represents maximal phase, minimum phase and secondary little phase voltage respectively; Relatively φ _ab, φ _bc, φ _carelation between phasing degree, calculates the phase angle difference φ between its adjacent two-phase ₁=φ _bc-φ _ab, φ ₂=φ _ca-φ _bc, φ ₃=φ _ab-φ _ca, according to the result of voltage compare, the phase differential absolute value assignment of voltage is time little and minimum phase is to coefficient θ.

If single-phase wire break judges that voltage criterion setting valve is μ _dx=0.866, θ _dx=60 °.

If the relation between maximum, minimum, the secondary little phase voltage effective value of three-phase line voltage meets

$\mathrm{\&mu;}=\frac{U_{\max }}{U_{\min }+U_{\mathrm{mid}}}\&GreaterEqual;{\mathrm{\&mu;}}_{\mathrm{dx}}$

Further, line voltage time between little phase with minimum phase phase difference value meet

θ≤θ _dx

Then circuit generation single-phase wire break fault on the upside of monitoring point, broken string is the leading phase of voltage maximal phase mutually.

4, effective value, phase compare (determine whether a phase broken string, which breaks mutually) between triple-phase line electric current

If single-phase wire break judges that current vector criterion setting value is ε _dx=0.5.

Utilize step 2 to calculate the symmetrical components of three-phase current, comprise forward-order current negative-sequence current zero-sequence current again according to the size of zero-sequence current effective value, judge in two kinds of situation:

(1) calculate numerical value.When time, if during ε ≈ 1, then near judging monitoring point must there is single-phase wire break fault in circuit; If ε _dxduring≤ε < 1, then near judging monitoring point may there is single-phase earth-free disconnection fault in circuit; If ε < is ε _dxtime, then judge that single-phase earth-free disconnection fault possibility occurs near monitoring point lower.

(2) calculate numerical value.When time, if during ε>=1, then near judging monitoring point must there is single-phase earthing disconnection fault in circuit; If ε _dxduring≤ε, then near judging monitoring point may there is single-phase earthing disconnection fault in circuit; If ε < is ε _dxtime, then judge that single-phase wire break possibility occurs near monitoring point lower, but there is singlephase earth fault in circuit.

5, (upside, downside) and basis for estimation type (according to voltage or electric current) is judged by 3,4 result combination break points.

6, result of determination data are exported.

The above, be only preferred embodiment of the present utility model, therefore can not limit with this scope that the utility model implements, the equivalence namely done according to the utility model claim and description change with modify, all should still belong in scope that the utility model patent contains.

Claims (3)

1. the distribution line disconnection monitor based on electric current and voltage vector, be arranged on the disconnection monitoring point of network system, it is characterized in that: comprise power module, processor, voltage collection circuit, current collection circuit, voltage transformer (VT) summation current transformer, voltage transformer (VT) comprises AB line voltage transformer (VT), BC line voltage transformer (VT) and the CA line voltage transformer (VT) that output terminal is connected with the input end of voltage collection circuit respectively; Current transformer comprises A phase current mutual inductor, B phase current mutual inductor and the C phase current mutual inductor that output terminal is connected with the input end of current collection circuit respectively; Voltage collection circuit and current collection circuit have included modulate circuit and A/D change-over circuit; Processor is connected with voltage collection circuit and current collection circuit respectively by data circuit; Processor is also connected with current collection circuit and voltage collection circuit respectively by synchronous signal line, regularly can send synchronous acquisition pulse signal starting voltage collection circuit, synchronous acquisition that current collection circuit carries out voltage, electric current.

2. a kind of distribution line disconnection monitor based on electric current and voltage vector according to claim 1, is characterized in that: also comprise the remote communication module, data-carrier store and the display module that are connected with described processor respectively.

3. a kind of distribution line disconnection monitor based on electric current and voltage vector according to claim 1 and 2, it is characterized in that: described power module is rectification circuit, the input end of described rectification circuit is connected with the output terminal of described AB line voltage transformer (VT), BC line voltage transformer (VT) and CA line voltage transformer (VT) respectively, and the output terminal of described rectification circuit is connected with described processor.