CN101860000B - Quick identification method for permanent fault before single-phase reclosing of power transmission line - Google Patents

Abstract

The invention relates to the field of power transmission line relay protection of a power system, and discloses a quick identification method for a permanent fault before single-phase reclosing of a power transmission line. At least one end of the power transmission line is provided with a three-phase parallel reactor and a neutral-point small reactor. The method comprises the following steps of: firstly, acquiring real-time current iLphi(t) of the three-phase parallel reactor, and performing single-phase fault identification and tripping state determination; secondly, disconnecting a least square fitting model of the current iLphi(t) of the parallel reactor after temporary fault arc blowout of a preset line, and solving a low-frequency free oscillating component initial amplitude IL and a power frequency component amplitude I1 of the current of the disconnected parallel reactor; and finally, performing single-phase fault property judgment according to the permanent fault criteria that IL is less than KkI1 and Kk is equal to 0.1 to 0.3.

Description

Quick identification method for permanent fault before a kind of single-phase reclosing of power transmission line

Technical field

The present invention relates to power system transmission line relaying protection field, be specifically related to the preceding quick identification method for permanent fault of a kind of single-phase reclosing of power transmission line.

Background technology

The single-pole reclosing technology is the effective measures that modern ultra-high/extra-high voltage electrical network restored electricity and kept system stability fast.But there is blindness in the action of existing single-pole reclosing, and single-phase fault trips after coincidence automatically behind definite-time 0.5s～1.5s exists to coincide with the second short circuit danger of burst that permanent fault is brought; Simultaneously, under the situation of the unsuccessful coincidence of ultra-high/extra-high voltage circuit, the asynchronous of secondary trip will produce dangerous overvoltage in the short time, the stability that the safety of the electric main equipment of serious threat and system move.For fear of blindly overlapping the potential hazard of bringing, confirm that circuit is transient fault or permanent fault before just must accomplishing to overlap, realize the transient fault coincidence and permanent fault does not overlap, i.e. adaptive reclose.

Its core of adaptive reclose is distinguished transient fault and permanent fault exactly, and existing method of discrimination mainly comprises based on the recovery voltage characteristic with based on two types of transient fault arc characteristics.The former has utilized the capacitor coupling voltage characteristic to distinguish transient fault and permanent fault, and its sensitivity and anti-transition resistance ability are influenced by line length; The latter mainly utilize fault once, the harmonic characteristic of secondary arc stage transient signal distinguishes transient fault and permanent fault, its discrimination precision and electric arc blow-out process, high-frequency signal obtains precision and malfunction is closely related, is difficult to practicability.In addition; Be accompanied by the application in the ultra-high/extra-high voltage transmission system of rapid protecting device and high-speed circuit breaker, fault once, secondary arc stage life period shortens greatly, and the input of high compensativity shunt reactor; No matter be that electric arc stage or recovery voltage stage corresponding fault phase terminal voltage amplitude is low; Even less than 5% of circuit rated voltage, the line voltage distribution instrument transformer is measured the confidence level of breaking off phase terminal voltage and is reduced, and differentiates result reliability simultaneously and reduces.

Summary of the invention

The object of the present invention is to provide the preceding quick identification method for permanent fault of a kind of single-phase reclosing of power transmission line; Can be based on the reliable and stable electric parameters in recovery voltage stage; Utilize the low frequency free component amplitude characteristic that breaks off the reactor current that is in parallel; Discern the single-phase permanent fault of transmission line more reliably, the reliability that solves existing method is low, the differentiation time long, the problem of poor practicability.

In order to achieve the above object, the present invention adopts following technical scheme to be achieved.

Quick identification method for permanent fault before a kind of single-phase reclosing of power transmission line, at least one end of its transmission line is provided with parallel three phase reactor and the little reactor of neutral point, it is characterized in that, may further comprise the steps:

(1) the real-time current i of collection parallel three phase reactor _{L φ}(t), its amplitude is I _{FL φ}, wherein φ=A, B, C have and only have one to satisfy formula I mutually _{FL φ}≤(0.70～0.80) I _LeThe time confirm as single-phase fault and corresponding fault is separate, I wherein _LeRunning current amplitude for the parallel three phase reactor; And real-time current amplitude I when the single-phase fault phase _{TL φ}Satisfy formula I _{TL φ}≤(0.40～0.50) I _LeWhen φ=A, B, C, judge that this fault is in the tripping operation off-state mutually, for breaking off phase;

Break off the low frequency free oscillation component frequencies omega of the reactor current that is in parallel when (2) calculating transient fault _L,

${\mathrm{\ω}}_L=\sqrt{\frac{L_P+2L_n}{L_P(L_P+3L_n)(2C_m+C_0)}}$

Wherein:

L _P, L _nBe respectively the equivalent inductance of shunt reactor and the little reactor of neutral point,

C _m, C ₀Be respectively alternate electric capacity of transmission line total length and direct-to-ground capacitance;

(3) break off the reactor current i that is in parallel after the preset circuit transient fault blow-out _{L φ}(t) least square fitting model does $i_{\mathrm{L\&phi;}}\left(t\right)=I_L{e}^{-{\mathrm{\&lambda;}}_{L}t}\mathrm{Sin}({\mathrm{\&omega;}}_{L}t+{\mathrm{\&theta;}}_L)+{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">I</figure-callout>}}_1\mathrm{Sin}({\mathrm{\&omega;}}_{1}t+{\mathrm{\&theta;}}_1),$

Wherein, I _LBe the be in parallel low frequency free oscillation component initial magnitude of reactor current of disconnection, I ₁Be power frequency component amplitude, λ _LBe the inverse of low frequency free oscillation component damping time constant, θ _LBe low frequency free oscillation component initial phase, θ ₁Be power frequency component initial phase, ω _LBe low frequency free oscillation component frequency, ω ₁Be power frequency;

Making

is 1, simplifies the least square fitting model to do

i _Lφ(t)＝[I _L?cosθ _L?sin(ω _Lt)+I _L?sinθ _L?cos(ω _Lt)]+[I ₁?cosθ ₁sin(ω ₁t)+I ₁?sinθ ₁?cos(ω ₁t)]

For sampled value i _{L φ}(t ₁), i _{L φ}(t ₂) ..., i _{L φ}(t _N) constitute N equation, can be expressed as following matrix form equation

$\underset{N\&times;4}{\left[A\right]}\underset{4\&times;1}{\left[X\right]}=\underset{N\&times;1}{\left[B\right]}$

Wherein:

$A=\left[\begin{array}{cccc}\sin {\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="1"\; label="L\; t"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">L</figure-callout>}}{t}_{}{}_1& \cos {\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="1"\; label="L\; t"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">L</figure-callout>}}{t}_{}{}_1& \sin {\mathrm{\&omega;}}_1{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">t</figure-callout>}}_1& \cos {\mathrm{\&omega;}}_1{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">t</figure-callout>}}_1\\ \sin {\mathrm{\&omega;}}_L{t}_2& \cos {\mathrm{\&omega;}}_L{t}_2& \sin {\mathrm{\&omega;}}_1{t}_2& \cos {\mathrm{\&omega;}}_1{t}_2\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \sin {\mathrm{\&omega;}}_L{t}_N& \cos {\mathrm{\&omega;}}_L{t}_N& \sin {\mathrm{\&omega;}}_1{t}_N& \cos {\mathrm{\&omega;}}_1{t}_N\end{array}\right],$

X＝[I _L?cosθ _L，I _L?sinθ _L，I ₁?cosθ ₁，I ₁?sinθ ₁] ^T，

B＝[i _Lφ(t ₁)，i _Lφ(t ₂)，…，i _Lφ(t _N)] ^T，

A is a coefficient matrix, and X is parameter matrix to be asked, and comprises 4 parameters to be asked; B serves as reasons and breaks off the real-time current i of the reactor that is in parallel _{L φ}(t) constant matrices that sampled value constitutes; N>=4;

Find the solution and wait to ask parameter matrix X=[I _LCos θ _L, I _LSin θ _L, I ₁Cos θ ₁, I ₁Sin θ ₁] ^T

By following formula

$\left\{\begin{array}{c}{I}_L=\sqrt{{\left(I_L\cos {\mathrm{\&theta;}}_L\right)}^2+{\left(I_L\sin {\mathrm{\&theta;}}_L\right)}^2}\\ {\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">I</figure-callout>}}_1=\sqrt{{\left(I_1\cos {\mathrm{\&theta;}}_1\right)}^2+{\left(I_1\sin {\mathrm{\&theta;}}_1\right)}^2}\end{array}\right.$

The low frequency free oscillation component initial magnitude I that breaks off the reactor current that is in parallel is obtained in calculating _LWith power frequency component amplitude I ₁

(4) if I _L＜K _kI ₁, safety factor K wherein _k=0.1～0.3, will break off and be judged to permanent fault mutually, send the reclosing block order; Otherwise, be judged to transient fault, send the reclosing order.

Further improvement of the present invention is, in the step (4), if I _L＜K _kI ₁Continue to set up 100～200ms, will break off and be judged to permanent fault mutually, send reclosing block order; Otherwise, be judged to transient fault, send the reclosing order.

Quick identification method for permanent fault before the single-phase reclosing of power transmission line that the present invention proposes; Based on the be in parallel low frequency free component amplitude characteristic of reactor current of disconnection; Utilize the least-squares calculation result of the low frequency free component amplitude of breaking off the reactor current that is in parallel, realize the differentiation of transient fault and permanent fault.The transmission line that this method can be used for one end/two ends band shunt reactor carries out the single-phase fault property identification, does not receive the influence of position of failure point, transition resistance, load current on the principle, continues to judge in the long period before can behind fault phase trip, extremely overlapping.Compared with prior art, the present invention has following remarkable advantage:

(1) only the reactor current amount that is in parallel is broken off in utilization, has guaranteed to utilize the high reliability of electric signal, and not influenced by passage, all can independently realize the differentiation of single-phase fault character for both-end band shunt reactor circuit both sides.Transmission line for the band shunt reactor; The shunt reactor side is equipped with the high current transformer of the little certainty of measurement of no-load voltage ratio usually; Measurement is broken off the little magnitude of current of reactor amplitude that is in parallel and is had higher precision, and relative voltage amount method of discrimination has more the engineering Practical significance.

(2) the least square fitting model of preset shunt reactor electric current utilizes short data window can calculate the low frequency free component initial magnitude and the power frequency component amplitude of breaking off the reactor current that is in parallel fast; The influence of beat frequency characteristic when not receiving transient fault, having solved existing differentiation algorithm extraction power frequency component preferably need be than the deficiency of long data window.

(3) this method has favorable applicability, is applicable to the permanent failure judgement of an end, the single-phase fault of two ends band shunt reactor circuit under diverse location, different transition resistance, different compensativity.

Description of drawings

Below in conjunction with accompanying drawing and embodiment the present invention is explained further details

Fig. 1 has the hardware block diagram of reactor protection for transmission line.

Embodiment

With reference to Fig. 1, the reactor at transmission line MN two ends has been installed reactor protection respectively respectively, and current transformer TA1, TA2 detect the real-time current of M end, N end parallel three phase reactor respectively.In the frame of broken lines is hardware configuration, is made up of data acquisition system, microcomputer main system, input-output system three parts, and method of the present invention is realized by microcomputer DSP main system through programming.With the N side is example; Input variable is a parallel three phase reactor current amount, and TA2 obtains by shunt reactor side current transformer, and the analog quantity of the parallel three phase reactor current that obtains is after preposition LPF, sampling maintenance and A/D conversion; Deliver to microcomputer DSP main system; At first carry out fault through this method and select phase, confirmation form phase fault and tripping operation calculate the low frequency self-vibration component initial magnitude of breaking off the reactor current that is in parallel afterwards; According to low frequency self-vibration component initial magnitude result of calculation, judge that the single-phase fault that circuit takes place is transient fault or permanent fault then.

Concrete steps of the present invention are following:

(1) fault reaches the tripped condition affirmation mutually

Gather the real-time current i of parallel three phase reactor _{L φ}(t), its amplitude is I _{FL φ}, wherein φ=A, B, C have and only have one to satisfy formula I mutually _{FL φ}≤(0.70～0.80) I _LeConfirmation form phase fault and fault are separate, wherein I _LeRunning current amplitude for the parallel three phase reactor; And real-time current amplitude I when the single-phase fault phase _{TL φ}Satisfy formula I _{TL φ}≤(0.40～0.50) I _LeWhen φ=A, B, C, judge that this fault is in the tripping operation off-state mutually, for breaking off phase.

Because the present invention is the permanent failure judgement of single-phase reclosing of power transmission line, can not be suitable for for phase-to phase fault.Therefore, after line fault, rapid and reliable confirmation form phase fault and tripped condition are particularly important, then do not carry out single-phase fault character for phase-to phase fault and differentiate by the existing policy action that overlaps.

A) the separate affirmation of single-phase fault

Behind the line failure, the normal operating voltage of fault phase voltage reduces to some extent, and the corresponding fault normal operating current of reactor current that is in parallel also reduces to some extent; Then approaching for the non-fault reactor current that is in parallel with running current.

Characteristics provide formula (1) and carry out the separate differentiation of single-phase fault in view of the above.Promptly

I _FLφ≤(0.70～0.80)I _Le (φ＝A、B、C、) (1)

Wherein: I _{FL φ}Be parallel three phase reactor current initial magnitude; I _LeBe parallel three phase reactor running current amplitude.Has only parallel three phase reactor current I _{FL φ}Have and only have one to satisfy formula (1) mutually, then be judged to single-phase fault and confirm that fault is separate; Otherwise, be judged to non-single-phase fault and do not carry out single-phase permanent failure judgement.

B) the single-phase fault tripped condition is confirmed

After treating that single-phase fault trips mutually, fault is in parallel, and normally operating voltage is little for the reactor terminal voltage, and reactor current amplitude and running current are approaching but not fault is in parallel.Provide formula (2) and carry out the fault phase trip state confirmation:

I _TLφ≤(0.40～0.50)I _Le (φ＝A、B、C) ?(2)

Wherein: I _{TL φ}Be parallel three phase reactor current amplitude; I _LeBe parallel three phase reactor running current amplitude.Have only the parallel three phase reactor current to have and only have fault to satisfy formula (2) mutually, then be judged to fault and trip mutually; Otherwise single-phase fault does not trip or is external area error, does not then carry out single-phase permanent failure judgement.

(2) nature of trouble is differentiated

During ultra-high/extra-high voltage transmission line generation permanent fault, because the fault point exists always, line mutual-ground capacitor reliably discharges, and breaking off the reactor current that is in parallel is main with power frequency component mainly, does not contain the low frequency free component.And when transient fault; Break off the LC oscillation circuit that the phase loop is made up of shunt reactor and line capacitance behind the pending fault point arc extinction and produced the low frequency free component of frequency near power frequency, the disconnection of the correspondence reactor current that is in parallel has comprised low frequency free component and two kinds of periodic components of power frequency component.Analysis by the front can know, the existence of low frequency free component is to cause the transient fault electric current to have the immediate cause of beat frequency phenomenon, and only comprises the power frequency period component during permanent fault.Therefore, can realize the differentiation of single-phase fault instantaneity and permanent fault according to these characteristics of low frequency free component.

A) calculate low frequency self-vibration component frequencies omega _L

Circuit for most shunt reactors; Because the reactor parameter is the fixed constant parameter; The free component frequency is only determined by the intrinsic physical parameter in the equivalent loop of transient fault blow-out; Basically do not receive system impedance and position of failure point variable effect, but this free oscillation frequency off-line calculates accurately.Can calculate by formula (3):

${\mathrm{\&omega;}}_L=\sqrt{\frac{L_P+2L_n}{L_P(L_P+3L_n)(2C_m+C_0)}}---\left(3\right)$

Wherein:

L _P, L _nEquivalent inductance for shunt reactor and the little reactor of neutral point;

C _m, C ₀Be alternate electric capacity of total track length and direct-to-ground capacitance.

B) each the component amplitude I of reactor current that is in parallel is broken off in calculating _L, I ₁

In theory, break off the amplitude I of the low frequency free oscillation component of the reactor current amount that is in parallel during transient fault _LNear or greater than the amplitude I of power frequency component ₁And during permanent fault, breaking off the reactor current amount that is in parallel is principal mode with the power frequency period component, does not have low frequency free oscillation component, the low frequency free oscillation component amplitude I that this moment is corresponding _LShould be near 0.In fact; The error of calculation of free oscillation component frequency can influence power frequency, free oscillation component amplitude computational accuracy; Therefore adopted least-square fitting approach, can reduce the influence that free oscillation component frequency error brings to a certain extent with good stability.

Shunt reactor electric current I after the preset circuit transient fault blow-out _{L φ}(t) least square fitting model, promptly

$i_{\mathrm{L\&phi;}}\left(t\right)=I_L{e}^{-{\mathrm{\&lambda;}}_{L}t}\sin ({\mathrm{\&omega;}}_{L}t+{\mathrm{\&theta;}}_L)+I_1\sin ({\mathrm{\&omega;}}_{1}t+{\mathrm{\&theta;}}_1)---\left(4\right)$

In the formula (4), I _LBe low frequency free oscillation component initial magnitude, I ₁Be power frequency component amplitude, λ _LBe low frequency free oscillation component damping time constant T _sInverse, θ _LBe low frequency free oscillation component initial phase, θ ₁Be power frequency component initial phase, ω _LBe low frequency free oscillation component angular frequency, ω ₁Be power frequency.

Low frequency free oscillation component during ultra-high/extra-high voltage transmission system transient fault is longer die-away time; Then can ignore the influence of amplitude attenuation for the short data window algorithm,

can be similar to and get 1.Thus; Making

is 1, simplifies least square fitting modular form (4) for being following form

i _Lφ(t)＝[I _L?cosθ _L?sin(ω _Lt)+I _L?sinθ _L?cos(ω _Lt)]+[I ₁?cosθ ₁?sin(ω ₁t)+I ₁?sinθ ₁?cos(ω ₁t)](5)

Obviously, break off the reactor current i that is in parallel during transient fault _{L φ}(t) each sampled value constantly all satisfies formula (5).For sampled value i _{L φ}(t ₁), i _{L φ}(t ₂) ..., i _{L φ}(t _N) constitute N equation, can be expressed as following matrix form equation

$\underset{N\&times;4}{\left[A\right]}\underset{4\&times;1}{\left[X\right]}=\underset{N\&times;1}{\left[B\right]}---\left(6\right)$

Wherein:

$A=\left[\begin{array}{cccc}\sin {\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="1"\; label="L\; t"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">L</figure-callout>}}{t}_{}{}_1& \cos {\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="1"\; label="L\; t"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">L</figure-callout>}}{t}_{}{}_1& \sin {\mathrm{\&omega;}}_1{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">t</figure-callout>}}_1& \cos {\mathrm{\&omega;}}_1{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000021381090000011.png"\; state="\{\{state\}\}">t</figure-callout>}}_1\\ \sin {\mathrm{\&omega;}}_L{t}_2& \cos {\mathrm{\&omega;}}_L{t}_2& \sin {\mathrm{\&omega;}}_1{t}_2& \cos {\mathrm{\&omega;}}_1{t}_2\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \sin {\mathrm{\&omega;}}_L{t}_N& \cos {\mathrm{\&omega;}}_L{t}_N& \sin {\mathrm{\&omega;}}_1{t}_N& \cos {\mathrm{\&omega;}}_1{t}_N\end{array}\right]$

X＝[I _L?cosθ _L，I _L?sinθ _L，I ₁?cosθ ₁，I ₁?sinθ ₁] ^T

B＝[i _Lφ(t ₁)，i _Lφ(t ₂)，…，i _Lφ(t _N)] ^T

A is a coefficient matrix, but calculated off-line is accomplished; X is parameter matrix to be asked, and comprises 4 parameters to be asked; B serves as reasons and breaks off the real-time current i of the reactor that is in parallel _{L φ}(t) constant matrices that sampled value constitutes; N>=4.

In theory, for the parameter in the formula (6) can by 4 independently linear equation accomplish, but take to enlarge the redundancy approach of matrix A scale in order to improve computational accuracy usually.Corresponding asking for of matrix X can be accomplished by formula (7)

$\underset{4\&times;1}{\left[X\right]}={\underset{N\&times;4}{\left[A\right]}}^{+}\underset{N\&times;1}{\left[B\right]}---\left(7\right)$

In the formula (7);

is generalized inverse matrix; Its concrete computational methods can be accomplished with reference to relevant mathematical method, repeat no more.

Can try to achieve the I among the matrix X by formula (7) _LCos θ _L, I _LSin θ _L, I ₁Cos θ ₁, I ₁Sin θ ₁, can obtain the low frequency free oscillation component initial magnitude I that breaks off the reactor current that is in parallel by formula (8) _L, and power frequency component amplitude I ₁:

$\left\{\begin{array}{c}{I}_L=\sqrt{{\left(I_L\cos {\mathrm{\&theta;}}_L\right)}^2+{\left(I_L\sin {\mathrm{\&theta;}}_L\right)}^2}\\ I_1=\sqrt{{\left(I_1\cos {\mathrm{\&theta;}}_1\right)}^2+{\left(I_1\sin {\mathrm{\&theta;}}_1\right)}^2}\end{array}\right.---\left(8\right)$

C) permanent failure judgement

The permanent fault criterion:

I _L＜K _kI ₁ (9)

Consider various errors and nargin, wherein safety factor K _k=0.1～0.3.

With the disconnection reactor current low frequency self-vibration component initial magnitude I that is in parallel _LWith power frequency component amplitude I ₁Result of calculation substitution formula (9) judge.When formula (9) is set up, send the reclosing block order; Otherwise, be judged to transient fault, send the reclosing order.In order to improve the reliability of above-mentioned criterion, if I _L＜K _kI ₁Continue to set up 100ms～200ms, be judged to permanent fault, send the reclosing block order; Otherwise, be judged to transient fault, send the reclosing order.

Claims (2)

1. the quick identification method for permanent fault before the single-phase reclosing of power transmission line, at least one end of its transmission line is provided with parallel three phase reactor and the little reactor of neutral point, it is characterized in that, may further comprise the steps:

(1) the real-time current i of collection parallel three phase reactor _{L φ}(t), its amplitude is I _{FL φ}, wherein φ=A, B, C have and only have one to satisfy formula I mutually _{FL φ}≤(0.70～0.80) I _LeThe time confirm as single-phase fault and corresponding fault is separate, I wherein _LeRunning current amplitude for the parallel three phase reactor; And real-time current amplitude I when the single-phase fault phase _{TL φ}Satisfy formula I _{TL φ}≤(0.40～0.50) I _LeWhen φ=A, B, C, judge that this fault is in the tripping operation off-state mutually, for breaking off phase;

Break off the low frequency free oscillation component frequencies omega of the reactor current that is in parallel when (2) calculating transient fault _L,

${\mathrm{\&omega;}}_L=\sqrt{\frac{L_P+2L_n}{L_P(L_P+3L_n)(2C_m+C_0)}}$

Wherein:

L _P, L _nBe respectively the equivalent inductance of shunt reactor and the little reactor of neutral point,

C _m, C ₀Be respectively alternate electric capacity of transmission line total length and direct-to-ground capacitance;

(3) break off the reactor current i that is in parallel after the preset circuit transient fault blow-out _{L φ}(t) least square fitting model does $i_{\mathrm{L\&phi;}}\left(t\right)=I_L{e}^{-{\mathrm{\&lambda;}}_{L}t}\mathrm{Sin}({\mathrm{\&omega;}}_{L}t+{\mathrm{\&theta;}}_L)+I_1\mathrm{Sin}({\mathrm{\&omega;}}_{1}t+{\mathrm{\&theta;}}_1),$

Wherein, I _LBe the be in parallel low frequency free oscillation component initial magnitude of reactor current of disconnection, I ₁Be power frequency component amplitude, λ _LBe the inverse of low frequency free oscillation component damping time constant, θ _LBe low frequency free oscillation component initial phase, θ ₁Be power frequency component initial phase, ω _LBe low frequency free oscillation component frequency, ω ₁Be power frequency;

Making

is 1, simplifies the least square fitting model to do

i _Lφ(t)＝[I _L?cosθ _L?sin(ω _Lt)+I _L?sinθ _L?cos(ω _Lt)]+[I ₁?cosθ ₁?sin(ω ₁t)+I ₁?sin?θ ₁?cos(ω ₁t)]

For sampled value i _{L φ}(t ₁), i _{L φ}(t ₂) ..., i _{L φ}(t _N) constitute N equation, can be expressed as following matrix form equation

$\underset{N\&times;4}{\left[A\right]}\underset{4\&times;1}{\left[X\right]}=\underset{N\&times;1}{\left[B\right]}$

Wherein:

$A=\left[\begin{array}{cccc}\sin {\mathrm{\&omega;}}_L{t}_1& \cos {\mathrm{\&omega;}}_L{t}_1& \sin {\mathrm{\&omega;}}_1{t}_1& \cos {\mathrm{\&omega;}}_1{t}_1\\ \sin {\mathrm{\&omega;}}_L{t}_2& \cos {\mathrm{\&omega;}}_L{t}_2& \sin {\mathrm{\&omega;}}_1{t}_2& \cos {\mathrm{\&omega;}}_1{t}_2\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \sin {\mathrm{\&omega;}}_L{t}_N& \cos {\mathrm{\&omega;}}_L{t}_N& \sin {\mathrm{\&omega;}}_1{t}_N& \cos {\mathrm{\&omega;}}_1{t}_N\end{array}\right],$

X＝[I _L?cosθ _L，I _L?sinθ _L，I ₁?cosθ ₁，I ₁?sinθ ₁] ^T，

B＝[i _Lφ(t ₁)，i _Lφ(t ₂)，…，i _Lφ(t _N)] ^T，

A is a coefficient matrix, and X is parameter matrix to be asked, and comprises 4 parameters to be asked; B serves as reasons and breaks off the real-time current i of the reactor that is in parallel _{L φ}(t) constant matrices that sampled value constitutes; N>=4;

Find the solution and wait to ask parameter matrix X=[I _LCos θ _L, I _LSin θ _L, I ₁Cos θ ₁, I ₁Sin θ ₁] ^T

By following formula

$\left\{\begin{array}{c}{I}_L=\sqrt{{\left(I_L\cos {\mathrm{\&theta;}}_L\right)}^2+{\left(I_L\sin {\mathrm{\&theta;}}_L\right)}^2}\\ I_1=\sqrt{{\left(I_1\cos {\mathrm{\&theta;}}_1\right)}^2+{\left(I_1\sin {\mathrm{\&theta;}}_1\right)}^2}\end{array}\right.$

The low frequency free oscillation component initial magnitude I that breaks off the reactor current that is in parallel is obtained in calculating _LWith power frequency component amplitude I ₁

(4) if I _L＜K _kI ₁, safety factor K wherein _k=0.1～0.3, will break off and be judged to permanent fault mutually, send the reclosing block order; Otherwise, be judged to transient fault, send the reclosing order.

2. the quick identification method for permanent fault before the single-phase reclosing of power transmission line according to claim 1 is characterized in that, in the step (4), if I _L＜K _kI ₁Continue to set up 100～200ms, will break off and be judged to permanent fault mutually, send reclosing block order; Otherwise, be judged to transient fault, send the reclosing order.

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