CN102279349B - Low current grounding wire selection method based on residual current variable - Google Patents

Abstract

The invention discloses a low current grounding wire selection method based on residual current variable, and the method comprises the following steps of: (1) correctly identifying whether an electric distribution network has a single-phase ground fault by adopting the neutral point displacement voltage of the electric distribution network as characteristic quantity; (2) after the ground fault happens, compensating the grounding current of a fault point by virtue of an arc-suppression coil to achieve the effects of reducing the grounding current and extinguishing grounding arc light; (3) adjusting the tap position of a first tap arc-suppression coil on the premise of ensuring that the grounding residual current meets the standard request; (4) because the neutral point displacement voltagebefore and after the tap position adjustment of the arc-suppression coil changes, converting the zero-sequence current of each outgoing line subjected to the tap position adjustment to be below the voltage level before the top position adjustment by utilizing a voltage translation method so as to prevent the wire selection characteristic quantity from being influenced by the neutral point displacement voltage; and (5) selecting the line with the single-phase ground fault according to the change values of the zero-sequence current of each outgoing line after voltage translation before and after the tap position adjustment. The low current grounding wire selection method based on residual current variable can be used for improving the accuracy of wire selection.

Description

Small current earthing wire-selecting method based on the residual flow variable

Technical field

The invention belongs to power system automatic field, the present invention mainly is applicable to power network neutral point through arc suppression coil earthing system, more precisely a kind of method that the singlephase earth fault circuit takes place of selecting.

Background technology

Single phase grounding fault is multiple in China's power distribution network operational process, along with the urban power distribution network transformation, cable outlet day by day increases simultaneously, and system's capacitive earth current sharply increases, the ground connection arc light is difficult for extinguishing automatically, be easy to generate the gap arc overvoltage, if do not adopt an effective measure, very easily cause phase fault, accident is enlarged, influence power supply quality, therefore the earthing mode through arc suppression coil obtains approval gradually, progressively is widely adopted in low and medium voltage distribution network.

But, power distribution network has brought a difficult problem for the earthing wire-selecting technology after inserting arc suppression coil, because arc suppression coil compensates the fault current of earth point, make the zero-sequence current characteristic quantity of faulty line become very not obvious, thereby influenced the accuracy of single-phase earth fault line selection, reduce the automatization level of power distribution network operation control, increased the on-the-spot maintenance workload of operation.If on the basis of the system of realization arc suppression coil automatic tracking and compensating function, can provide significant route selection characteristic quantity for earthing wire-selecting, to solve the difficult problem that arc suppression coil impacts traditional single phase earthing wire-selecting technology, this all has very important meaning for the security, reliability, economy and the automatization level that improve the power distribution network operation.

Document one " a kind of novel fault selection method in the small current neutral grounding system " (Chinese patent application number 200910230433.5) has disclosed the method that a kind of quintuple harmonics that utilizes each bar circuit zero-sequence current in arc suppression coil earthing system carries out route selection, this method is selected the zero sequence quintuple harmonics electric current of three amplitude maximums earlier, then three zero sequence quintuple harmonics electric currents selecting are carried out the phase bit comparison, thereby determine faulty line or bus-bar fault.The described method of this patent is the route selection characteristic quantity with the quintuple harmonics, but because the compensation effect of arc suppression coil, the zero-sequence current value of each bar circuit is very little, its quintuple harmonics value is more faint, use on-the-spot electromagnetic interference (EMI) serious in addition, be difficult to accurately measure the quintuple harmonics value, make that the practical function of this method is undesirable, the route selection accuracy is not high.

Document two " fault line selection method for small electric current grounding system of distribution network " (Chinese patent application number 200910304934.3), disclosed a kind of method of utilizing parallel resistance to carry out route selection, this method is connected on parallel resistance between transformer neutral point and the ground, be connected in parallel with arc suppression coil, switching parallel resistance after distribution network system generation earth fault realizes failure line selection by the zero-sequence current of relatively parallel resistance switching each bar outlet of front and back.This method possesses certain practicality, but consider also to possess the space of lifting from the conspicuousness of route selection characteristic quantity, in addition, parallel resistance directly is connected between neutral point and the ground, requirement to resistance during actual motion is very high, so the accuracy of this method and reliability also need further raising.

Summary of the invention

Goal of the invention of the present invention is: for power network neutral point provides a kind of accuracy high and reliable earthing wire-selecting method through arc suppression coil earthing system, this method can provide tangible route selection characteristic quantity, this method practicality is good simultaneously, the accuracy height, and can not reduce on-the-spot reliability of operation and security.

To achieve these goals, the present invention takes following technical scheme to realize:

Small current earthing wire-selecting method based on the residual flow variable comprises the following steps:

(1) adopts the power network neutral point displacement voltage as characteristic quantity, correctly identify power distribution network whether singlephase earth fault has taken place;

(2) after the generation earth fault, arc suppression coil compensates the ground current of trouble spot, to reach the effect that reduces ground current, extinguishes the ground connection arc light;

(3) when guaranteeing that the ground connection residual flow satisfies standard-required, make progress or the following gear of regulating one grade of arc suppression coil according to actual conditions;

(4) owing to neutral point displacement voltage before and after the adjusting of arc suppression coil gear can change, so adopt the voltage translation method, the zero-sequence current of each outlet after transferring the files is converted under the preceding electric pressure of transferring the files, to avoid neutral point displacement voltage to the influence of route selection characteristic quantity;

(5) according to the variable quantity of voltage conversion each outlet zero-sequence current of back before and after transferring the files, can select the circuit that singlephase earth fault takes place accurately, reliably.

Aforesaid small current earthing wire-selecting method is characterized in that: in described step (1), the method whether identification singlephase earth fault takes place is:

Neutral point displacement voltage U ₀Computing formula be:

${\stackrel{\·}{U}}_0={\stackrel{\·}{I}}_{\mathrm{\δ}}*\frac{1}{j(3\mathrm{\ωC}+\frac{1}{\mathrm{\ωL}})}=\frac{-{\stackrel{\·}{U}}_{\mathrm{\ψ}}}{(R_d+\frac{1}{j(3\mathrm{\ωC}+\frac{1}{\mathrm{\ωL}})})}*\frac{1}{j(3\mathrm{\ωC}+\frac{1}{\mathrm{\ωL}})}$

$=\frac{-{\stackrel{\·}{U}}_{\mathrm{\ψ}}}{1+j{R}_d(3\mathrm{\ωC}+\frac{1}{\mathrm{\ωL}})}---\left(1\right),$

U in the formula ₀Be neutral point displacement voltage; U _ψBe system's phase voltage; R _dBe stake resistance; L is the inductance of arc suppression coil; C is the single-phase ground capacitance of system; I _δBe the residual flow behind the arc suppression coil compensation,

As neutral point displacement voltage U ₀Value less than 15%U _ψThe time be normal operation, work as U ₀Greater than pre-set threshold U _0zd(common U _0zdDesirable 30%U _ψ), then be judged to be the generation singlephase earth fault.

Aforesaid small current earthing wire-selecting method is characterized in that: in described step (5), if the variable quantity of zero-sequence current is zero before and after transferring the files, then be non-fault line; If the zero-sequence current variable quantity of faulty line equals arc suppression coil output current variable quantity, it then is faulty line.

The beneficial effect that the present invention reaches: the small current earthing wire-selecting method based on the residual flow variable of the present invention behind power distribution network generation singlephase earth fault, makes the gear of turn-adjusting arc suppression coil regulate one grade, to improve the characteristic quantity of earthing wire-selecting.By the situation of change of each bar outlet zero-sequence current before and after relatively the turn-adjusting arc suppression coil is transferred the files, select the circuit that singlephase earth fault takes place.Characteristic quantity by each zero-sequence current before and after the turn-adjusting arc suppression coil is transferred the files carries out the voltage conversion, reduces the neutral point voltage variation to route selection result's influence, improves the accuracy of this selection method.The present invention realizes easy, and cost is controlled, and practicality is good, and does not influence on-the-spot reliability of operation and security, and is little to the compensation effect influence of arc suppression coil.

Description of drawings

Fig. 1 adopts power network neutral point of the present invention through the structural drawing of arc suppression coil earthing system;

Fig. 2 is that power distribution network is through the equivalent circuit diagram of neutral point arc suppression coil earthing system;

Fig. 3 is the equivalent circuit diagram after the power network neutral point arc suppression coil earthing system is transferred the files;

Fig. 4 is the system construction drawing of embodiment;

Fig. 5 is the simulation waveform figure of embodiment.

Embodiment

In the present invention, disclosed the method for carrying out earthing wire-selecting by the running status that changes arc suppression coil.Fig. 1 is that power network neutral point is through the system model of grounding through arc, when power distribution network generation singlephase earth fault, after the malfunction to be confirmed, arc suppression coil is regulated one grade, can produce tangible zero-sequence current characteristic quantity like this, be conducive to accurately select faulty line.

Fig. 2 is when singlephase earth fault takes place, and inserts the power distribution network equivalent electrical circuit of arc suppression coil.U among the figure ₀Be neutral point displacement voltage; U _ψBe system's phase voltage; R _dBe stake resistance; L is the inductance of arc suppression coil; C is the single-phase ground capacitance of system; I _δBe the residual flow behind the arc suppression coil compensation.

Neutral point displacement voltage U ₀Computing formula be:

${\stackrel{\·}{U}}_0={\stackrel{\·}{I}}_{\mathrm{\δ}}*\frac{1}{j(3\mathrm{\ωC}-\frac{1}{\mathrm{\ωL}})}=\frac{-{\stackrel{\·}{U}}_{\mathrm{\ψ}}}{(R_d+\frac{1}{j(3\mathrm{\ωC}-\frac{1}{\mathrm{\ωL}})})}*\frac{1}{j(3\mathrm{\ωC}-\frac{1}{\mathrm{\ωL}})}$

$=\frac{-{\stackrel{\·}{U}}_{\mathrm{\ψ}}}{1+j{R}_d(3\mathrm{\ωC}-\frac{1}{\mathrm{\ωL}})}---\left(1\right)$

In the formula, ω is the system angle frequency, and j is imaginary unit

Circuit i (i ≠ n) is non-fault line, and its zero-sequence current is:

${\stackrel{\·}{I}}_{0i}={\stackrel{\·}{I}}_{\mathrm{Ai}}+{\stackrel{\·}{I}}_{\mathrm{Bi}}+{\stackrel{\·}{I}}_{\mathrm{Ci}}$

$=\mathrm{j\ω}{C}_{0i}{{\stackrel{\·}{U}}_A}^{,}+\mathrm{j\ω}{C}_{0i}{{\stackrel{\·}{U}}_B}^{,}+\mathrm{j\ω}{C}_{0i}{{\stackrel{\·}{U}}_C}^{,}$

$=\mathrm{j\ω}{C}_{0i}({\stackrel{\·}{U}}_0+{\stackrel{\·}{U}}_A)+\mathrm{j\ω}{C}_{0i}({\stackrel{\·}{U}}_0+{\stackrel{\·}{U}}_B)+\mathrm{j\ω}{C}_{0i}({\stackrel{\·}{U}}_0+{\stackrel{\·}{U}}_C)$

$=j3{\stackrel{\·}{U}}_0\mathrm{\ω}{C}_{0i}---\left(2\right)$

Wherein, C _0iBe the single-phase ground capacitance of circuit i, I _Ai, I _Bi, I _CiBe circuit i three-phase ground capacitance electric current, U _A, U _B, U _CBe system's phase voltage.

If circuit n is for the circuit of singlephase earth fault takes place, the electric current of its fault phase C phase is:

${\stackrel{\·}{I}}_{\mathrm{Cn}}=-(\underset{i=1}{\overset{n-1}{\mathrm{\Σ}}}{\stackrel{\·}{I}}_{0i}+{\stackrel{\·}{I}}_{\mathrm{An}}+{\stackrel{\·}{I}}_{\mathrm{Bn}})+{\stackrel{\·}{I}}_L---\left(3\right)$

In the formula, I _An, I _Bn, I _CnBe faulty line n three-phase ground capacitance electric current, I _LBe arc suppression coil outputting inductance electric current.

Then the zero-sequence current of circuit n is:

${\stackrel{\·}{I}}_{0n}={\stackrel{\·}{I}}_{\mathrm{An}}+{\stackrel{\·}{I}}_{\mathrm{Bn}}+{\stackrel{\·}{I}}_{\mathrm{Cn}}=-\underset{i=1}{\overset{n-1}{\mathrm{\Σ}}}{\stackrel{\·}{I}}_{0i}+{\stackrel{\·}{I}}_L---\left(4\right)$

Be that faulty line zero-sequence current size is non-fault line zero sequence capacitance current and arc suppression coil zero sequence inductive current sum, direction is relevant with the compensativity of arc suppression coil.

Fig. 3 is when singlephase earth fault takes place, the power distribution network equivalent electrical circuit behind the change arc suppression coil gear, wherein U ₀' being the back neutral point displacement voltage of transferring the files, L ' is the back arc suppression coil inductance value of transferring the files.At this moment, the variable quantity of neutral point displacement voltage is:

$\mathrm{\Δ}{\stackrel{\·}{U}}_0={\stackrel{\·}{U}}_{0^{\′}}-{\stackrel{\·}{U}}_0=\frac{{\stackrel{\·}{U}}_{\mathrm{\Ψ}}}{1+j{R}_d(3\mathrm{\ωC}-\frac{1}{\mathrm{\ωL}})}-\frac{{\stackrel{\·}{U}}_{\mathrm{\ψ}}}{1+j{R}_d(3\mathrm{\ωC}-\frac{1}{{\mathrm{\ωL}}^{\′}})}---\left(5\right)$

The zero-sequence current variable quantity of voltage conversion back non-fault line i is:

${\mathrm{\&Delta;I}}_{0i}=\frac{U_0}{{{\mathrm{<figure-callout\; id="0"\; label="U"\; filenames="HDA0000075414380000031.png"\; state="\{\{state\}\}">U</figure-callout>}}_0}^{\&prime;}}{I_{0i}}^{\&prime;}-I_{0i}=\frac{U_0}{{{\mathrm{<figure-callout\; id="0"\; label="U"\; filenames="HDA0000075414380000031.png"\; state="\{\{state\}\}">U</figure-callout>}}_0}^{\&prime;}}\left(\frac{{U_0}^{\&prime;}}{U_0}{I}_{0i}\right)-I_{0i}=I_{0i}-I_{0i}=0---\left(6\right)$

The zero-sequence current variable quantity of voltage conversion back faulty line is:

${\mathrm{\&Delta;I}}_{0n}=\frac{U_0}{{\mathrm{<figure-callout\; id="0"\; label="U"\; filenames="HDA0000075414380000031.png"\; state="\{\{state\}\}">U</figure-callout>}}_0^{\&prime;}}\mathrm{\&Delta;}{I}_L-\mathrm{\&Sigma;}{\mathrm{\&Delta;I}}_{0i}=\frac{U_0}{{\mathrm{<figure-callout\; id="0"\; label="U"\; filenames="HDA0000075414380000031.png"\; state="\{\{state\}\}">U</figure-callout>}}_0^{\&prime;}}{\mathrm{\&Delta;I}}_L---\left(7\right)$

Δ I _LBe arc suppression coil output current variable quantity before and after transferring the files.

According to above analysis as can be known, for non-fault line, adopt voltage conversion principle, the variable quantity of zero-sequence current is zero before and after transferring the files; For faulty line, the variable quantity of zero-sequence current is the poor of the variable quantity of arc suppression coil output inductance current and non-fault line zero-sequence current variable quantity, and the latter is zero, so the zero-sequence current variable quantity of faulty line equals arc suppression coil output current variable quantity.

By comparing (6) formula and (7) formula as can be seen, adopt method of the present invention, the zero-sequence current characteristic quantity of faulty line and non-fault line has difference clearly, utilizes these characteristics can select faulty line accurately and reliably.

Be a preferred embodiment of the present invention below, this embodiment adopts method of the present invention to realize the single-phase earth fault line selection function at a certain concrete power distribution network.Other feature, purpose and advantage of the present invention also can be found out from the explanation of embodiment and accompanying drawing.

10kV power distribution network among Fig. 4 has 5 circuits, wherein in circuit 5 head ends simulation Single Phase Metal earth fault.Regulate gear of arc suppression coil after the fault, analyze the zero-sequence current situation of change of each bar circuit, select faulty line.

Can get by data analysis, the zero-sequence current variable quantity of faulty line is 2A, and the zero-sequence current variable quantity of non-fault line is 0.001A to the maximum, and the variation waveform of each characteristic quantity as shown in Figure 5.Situation of change by characteristic quantity can be selected faulty line exactly, instructs the field operator accurately to excise the barrier circuit, reaches the purpose that ensures the power distribution network safe and stable operation.

The present invention is illustrated according to the preferred embodiment, should be appreciated that but above-described embodiment does not limit the present invention in any form, and all employings are equal to replaces or technical scheme that the form of equivalent transformation obtains, all drops within protection scope of the present invention.

Claims (2)

1. the small current earthing wire-selecting method based on the residual flow variable is characterized in that, comprises the following steps:

(1) adopts the power network neutral point displacement voltage as characteristic quantity, correctly identify power distribution network whether singlephase earth fault takes place;

(2) after the generation earth fault, arc suppression coil compensates the ground current of trouble spot, to reach the effect that reduces ground current, extinguishes the ground connection arc light;

(3) when guaranteeing that the ground connection residual flow satisfies standard-required, regulate the gear of one grade of arc suppression coil up or down;

(4) owing to neutral point displacement voltage before and after the adjusting of arc suppression coil gear can change, so adopt the voltage translation method, the zero-sequence current of each outlet after transferring the files is converted under the preceding electric pressure of transferring the files, to avoid neutral point displacement voltage to the influence of route selection characteristic quantity;

(5) select the circuit that singlephase earth fault takes place according to each outlet zero-sequence current of voltage conversion back at the variable quantity before and after transferring the files,

In described step (5), if the variable quantity of zero-sequence current is zero before and after transferring the files, then be non-fault line; If the zero-sequence current variable quantity of faulty line equals arc suppression coil output current variable quantity, it then is faulty line.

2. small current earthing wire-selecting method according to claim 1 is characterized in that: in described step (1), the method whether identification singlephase earth fault takes place is:

Neutral point displacement voltage U ₀Computing formula be:

${\stackrel{\&CenterDot;}{U}}_0={\stackrel{\&CenterDot;}{I}}_{\mathrm{\&delta;}}*\frac{1}{(3\mathrm{\&omega;C}+\frac{1}{\mathrm{\&omega;L}})}=\frac{-{\stackrel{\&CenterDot;}{U}}_{\mathrm{\&psi;}}}{(R_d+\frac{1}{j(3\mathrm{\&omega;C}+\frac{1}{\mathrm{\&omega;L}})})}*\frac{1}{j(3\mathrm{\&omega;C}+\frac{1}{\mathrm{\&omega;L}})}$

$=\frac{-{\stackrel{\&CenterDot;}{U}}_{\mathrm{\&psi;}}}{1+j{R}_d(3\mathrm{\&omega;C}+\frac{1}{\mathrm{\&omega;L}})}---\left(1\right),$

U in the formula ₀Be neutral point displacement voltage; U _ψBe system's phase voltage; R _dBe stake resistance; L is the inductance of arc suppression coil; C is the single-phase ground capacitance of system; I _δBe the residual flow behind the arc suppression coil compensation, ω is the system angle frequency,

As neutral point displacement voltage U ₀Value less than 15%U _ψThe time be normal operation, work as U ₀More than or equal to pre-set threshold, then be judged to be the generation singlephase earth fault.

Images