CN104992055A - Pollution-flashover-caused trip probability calculation method of overhead lines in sand and dust environment - Google Patents

Abstract

The invention provides a pollution-flashover-caused trip probability calculation method of overhead lines in a sand and dust environment. The method comprises: based on sandstorm weather information, building a deposit model of sand and dust particles on an overhead line insulator surface and calculates equivalent salt deposit density and equivalent dust deposit density on the insulator surface; by taking into account the feature that a dust-to-salt ratio in a sandstorm-prone area is high, building a transmission line pollution-flashover-caused trip probability model which comprehensively considers salt density and dust density on the insulator surface; combining relative studies on insulator probability statistics and line reliability theories, and assessing a overhead line pollution-flashover-caused trip risk in the sand and dust environment; and then, on the basis of relative humidity influence on insulator flashover leakage current, building a line pollution-flashover-caused trip model in wet weather after sandstorms, and assessing influence of relative humidity changes on the overhead line pollution-flashover-caused trip probability. According to the invention, possible overhead line trip faults are prevented, and a safe and stable operational level of a grid in sand and dust environment is improved.

Description

Contamination Flashover of Overhead Lines tripping operation method for calculating probability under Sand Dust Environment

Technical field

The present invention relates to Contamination Flashover of Overhead Lines tripping operation method for calculating probability under a kind of Sand Dust Environment.

Background technology

Electric transmission line isolator pollution flashover under sandstorm impact is determined by two factors, and one is the pollution severity of insulators deposition that in air, the sandy environment of dispersed causes; Two is to make to gather the meteorological condition that filthy material fully makes moist.There is following problem in prior art: under (1), existing extreme weather, overhead transmission line probability of malfunction computing method rely on electrical network historical failure statistics to predict failure rate, and electrical network relevant statistics sample size is little, impact prediction precision.(2), existing model fails to set up the concrete quantitative relation of Contamination Flashover of Overhead Lines tripping fault probability and dust and sand weather weather monitoring parameter, is unfavorable for effectively analyzing further.(3), existing model fail to set up dust and sand weather pass by after with the Contamination Flashover of Overhead Lines tripping operation probability model of wet weather, can not the change of accurate evaluation relative air humidity on the impact of circuit pollution flashover tripping operation probability.

Summary of the invention

Based on above weak point, the invention provides Contamination Flashover of Overhead Lines tripping operation method for calculating probability under a kind of Sand Dust Environment, for preventing the overhead transmission line tripping fault that may occur.

The technology used in the present invention is as follows: Contamination Flashover of Overhead Lines tripping operation method for calculating probability under a kind of Sand Dust Environment, comprise the calculation procedure of Contamination Flashover of Overhead Lines probability fault when dust and sand weather passes by and dust and sand weather pass by after with the calculation procedure of the Contamination Flashover of Overhead Lines tripping fault probability of wet weather, it is characterized in that, step is specific as follows:

(1) when, dust and sand weather passes by, the calculation procedure of Contamination Flashover of Overhead Lines probability fault is as follows:

(1.1) read the dust and sand weather weather data of each weather station, transmission line of electricity region record, weather station longitude and latitude, calculate overhead transmission line starting point longitude and latitude, electric pressure and span information;

(1.2) according to transmission line of electricity starting point latitude and longitude information and span, the longitude and latitude of overhead transmission line each span place insulator is calculated;

(1.3) based on the method for two-dimensional interpolation, the visibility at overhead transmission line each span insulator place is calculated;

(1.4) the insulator sandy environment maximum gauge meeting settling condition is calculated by formula (1)-Shi (4), according to the national Specification of dust and sand weather grade, utilize linear interpolation method to calculate sandy environment concentration that each span place meets settling condition;

The criterion that sandy environment adsorbs at insulating surface: as exit velocities V _y3during without real solution, sandy environment sedimentation, exit velocities is such as formula (1):

$V_{y3}=\sqrt{{\left(e{V}_{y0}\right)}^2-\frac{{2W}_a}{m}}---\left(1\right)$

In formula, e is coefficient of restitution; V _y0for the normal velocity of the incident insulator surface of filthy particle; W _afor filthy particle overcomes absorption affinity institute work; M is filthy granular mass;

Sandy environment is equivalent to spheroid, and calculating diameter is d _psandy environment quality such as formula (2):

$m=\frac{4}{3}\mathrm{\π}{\mathrm{\ρ}}_p{\left(\frac{d_p}{2}\right)}^3---\left(2\right)$

In formula, ρ _pfor sandy environment density, as exit velocities V _y3during without real solution, sandy environment is deposited in insulator surface, at this moment:

${\left({\mathrm{eV}}_{y0}\right)}^2-\frac{{2W}_a}{m}<0---\left(3\right)$

The sandy environment diameter that can be adsorbed onto insulator surface under sandstorm environment meets:

$d_{p\max }<\sqrt[3]{\frac{12W_a}{\mathrm{e\&pi;}{\mathrm{\&rho;}}_p{V}_{y0}}}---\left(4\right)$

Because sand and dust are insoluble filthy particles, it is close that sand and dust during sandstorm weather, insulator surface unit area deposited are ash, sandy environment diameter meets the sandy environment of formula above formula settling condition in the time t through electric transmission line isolator surface, and the equivalent grey Miru's following formula of insulator surface calculates:

${\mathrm{\&rho;}}_{\mathrm{NSDD}}={\&Integral;}_0^t{\&Integral;}_0^{d_{p\max }}{V}_{y0}\left(d_p\right)C(t,d_p)\mathrm{dtd}\left(d_p\right)---\left(5\right)$

In formula: V _y0(d _p) for sand and dust particle diameter be d _pthe sedimentation terminal velocity of particle on vertically insulated surface; C (t, d _p) particle diameter is less than d _pparticle in the filthy concentration of t, C (t, d _p) value under Sand Dust Environment, according to the meteorologic parameter of visibility, wind speed and relative air humidity, calculated by the method for linear interpolation;

The close ρ of insulator surface salt under sandstorm environment _eSDDby the close ρ of ash _nSDDconversion obtains as follows:

${\mathrm{\&rho;}}_{\mathrm{ESDD}}=\frac{{\mathrm{\&rho;}}_{\mathrm{NSDD}}}{K_e}---\left(6\right)$

In formula, K _efor the close ratio of ash/salt, close, the grey close computation model of above-mentioned insulator surface salt is used for the probability calculation of Section 3 insulator surface pollution flashover;

Insulator is lower than a certain voltage U ₀time discharge probability be zero, U ₀corresponding salt close being called, cuts off the close ρ of salt _e0, therefore, single insulator string pollution flashover probability P ₁(U) be corrected for and β, k, U ₀3 relevant parameter Weibull distributions:

$P_1\left(U\right)=1-e^{-{\left[\frac{1}{\mathrm{\&beta;}}(\frac{U}{U_0}-1)\right]}^k}---\left(7\right)$

In formula, β=nc/ (1-nc) (ln2) ^1/k; K=1.38/ln [n/ (n-1)]; N is disconnect parameter, and value is 2.5; C is the standard variance of insulator and the ratio of its withstand voltage of 50%, and when calculating β, c value is 0.2;

The close ρ of simple consideration insulator surface salt _eSDDto insulator contamination voltage U _fwhen affecting, single insulator string pollution flashover voltage U _fρ close with the salt of insulator surface _eSDDrelation is expressed as:

$U_f={\mathrm{NA\&rho;}}_{\mathrm{ESDD}}^{-\mathrm{\&alpha;}}---\left(8\right)$

In formula, N is the insulation sub-pieces number of single insulator string; A is the coefficient relevant with surface filth degree to insulator model; α characterizes the characteristic exponent on pollution flashover voltage impact;

Take into account that insulator surface salt is close, ash close on the affecting of pollution flashover voltage time, pollution flashover voltage is expressed as:

$U_f={\mathrm{NK\&rho;}}_{\mathrm{ESDD}}^{-i}{\mathrm{\&rho;}}_{\mathrm{NSDD}}^{-j}---\left(9\right)$

In formula, N is the insulation sub-pieces number of single insulator string; K is the coefficient relevant with surface filth degree to insulator model; I is for characterizing the close ρ of salt _eSDDon the characteristic exponent of pollution flashover voltage impact; J is for characterizing grey close ρ _nSDDon the characteristic exponent of pollution flashover voltage impact;

As the close ρ of insulator surface salt _eSDD, grey close ρ _nSDDand the relation between the pollution flashover probability of single insulator string, as shown in the formula:

$P_1({\mathrm{\&rho;}}_{\mathrm{ESDD}},{\mathrm{\&rho;}}_{\mathrm{NSDD}})=1-e^{-{\left\{\frac{1}{\mathrm{\&beta;}}\right[{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{ESDD}}}{{\mathrm{\&rho;}}_{e0}}\right)}^i{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{NSDD}}}{{\mathrm{\&rho;}}_{n0}}\right)}^j-1\left]\right\}}^k}---\left(10\right)$

Above formula, cuts off the close ρ of salt _e0=ρ _e50(1-nc) ^{1/ α}; N value is 2.5; ρ _e50insulator surface salt corresponding to 50% pollution flashover probability is close, ρ _e50=(NA/U) ^{1/ α}; Calculate ρ _e0during value, c value is 0.08, ρ _n0close for cutting off ash; ρ _n50ash corresponding to 50% pollution flashover probability is close, ρ _n0=ρ _n50(1-nc) ^1/j, ;

Under Sand Dust Environment during insulator contamination probability calculation, take into account the close ρ of insulator surface salt simultaneously _eSDD, grey close ρ _nSDDimpact;

In operation of power networks, insulator is paired running often, pollution flashover probability P during m insulator string paired running _m(ρ _eSDD, ρ _nSDD) be:

$P_m({\mathrm{\&rho;}}_{\mathrm{ESDD}},{\mathrm{\&rho;}}_{\mathrm{NSDD}})=1-e^{-m{\left\{\frac{1}{\mathrm{\&beta;}}\right[{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{ESDD}}}{{\mathrm{\&rho;}}_{e0}}\right)}^i{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{NSDD}}}{{\mathrm{\&rho;}}_{n0}}\right)}^j-1\left]\right\}}^k}---\left(11\right)$

Whole piece transmission line of electricity is considered as the series connection belief system be made up of some spans, has N number of span and whole piece transmission line of electricity pollution flashover probability P under sandstorm environment of m insulator string paired running in every span _las shown in the formula calculating:

$P_L=1-\underset{n=1}{\overset{N}{\mathrm{\&Pi;}}}(1-P_{m\left(n\right)})---\left(12\right)$

P in formula _mpollution flashover probability when () is transmission line of electricity No. n-th span place m insulator string paired running n;

(1.5) the soil deposition amount of sandy environment concentration by each span of formula (10) computing electric power line of settling condition is met according to insulator place;

(1.6) insulator surface salt is calculated according to the soil deposition amount at each span place by formula (5), formula (6) close, grey close;

(1.7) in conjunction with dust and sand weather feature, pollution severity of insulators parameter is brought into the pollution flashover probability that formula (10) calculates each insulator;

(1.8) by overhead transmission line cascade system characteristic, Contamination Flashover of Overhead Lines probability when passing by according to the dust and sand weather of formula (11), formula (12) calculating whole piece overhead transmission line;

(2), the calculation procedure of dust and sand weather Contamination Flashover of Overhead Lines tripping fault probability of adjoint wet weather after passing by is as follows:

(2.1) read the relative air humidity of each weather station, transmission line of electricity region record, weather station longitude and latitude, calculate the information such as overhead transmission line starting point longitude and latitude, electric pressure and span;

(2.2) according to transmission line of electricity starting point latitude and longitude information, transmission line of electricity each span place insulator latitude and longitude information;

(2.3) based on the method for two-dimensional interpolation, calculate the relative air humidity at overhead transmission line each span insulator place, and it is close with cut-out salt to insulator contamination voltage influence coefficient to calculate wet weather according to insulator model by formula (13)-Shi (17);

Leakage current and pollution flashover voltage are negative power function relation, meet following relation:

$U_f=K_{\mathrm{leak}}{I}_h^{-\mathrm{\&alpha;}}---\left(13\right)$

In formula, U _fit is pollution flashover voltage; K _leak, α is the coefficient relevant with insulator model; I _hit is leakage current;

When salt close identical, for different relative air humidities, leakage current formula (15) calculates:

$I_h=\left\{\begin{array}{cc}{\mathrm{Be}}^{\mathrm{aRH}}& 70\%\&le;\mathrm{RH}\&le;100\%\\ I_{h0}& 0\&le;\mathrm{RH}\&le;70\%\end{array}\right.---\left(14\right)$

In formula, RH is relative air humidity; B is the coefficient relevant with insulator structure, material; α is the characteristic exponent that relative air humidity RH affects leakage current amplitude; I _h0the leakage current of air humidity when being less than 70%;

To same insulator chain, pollution flashover voltage when above formula both members is simultaneously less than 70% divided by relative air humidity, is normalized:

$K_U=\frac{U_f}{U_{f0}}={\left(\frac{I_h}{I_{h0}}\right)}^{-\mathrm{\&alpha;}}---\left(15\right)$

In formula, U _f0for insulator contamination voltage when relative air humidity is less than 70%; K _ufor the ratio of pollution flashover voltage when pollution flashover voltage when relative air humidity is greater than 70% and relative air humidity are less than 70%, show to be greater than the relative air humidity of 70% to the influence coefficient of pollution flashover voltage, K _ufor being less than the value of 1, calculated according to the impact of relative air humidity on Leakage Current, pollution flashover voltage, on the computing formula of the impact of insulator contamination voltage, is corrected for by the change obtaining relative air humidity:

$U_f=\left\{\begin{array}{cc}{\mathrm{NA\&rho;}}_{\mathrm{ESDD}}^{-\mathrm{\&alpha;}}& 0\&le;\mathrm{RH}\&le;70\%\\ K_U{\mathrm{NA\&rho;}}_{\mathrm{ESDD}}^{-\mathrm{\&alpha;}}& 70\%\&le;\mathrm{RH}\&le;100\%\end{array}\right.---\left(16\right)$

When relative air humidity is less than 70%, the impact of change on insulator contamination voltage of air humidity is ignored, and when being greater than 70%, then will take into account the influence coefficient K of air humidity to pollution flashover voltage _u;

When to calculate relative air humidity be 70%-100%, consider that relative air humidity is to pollution flashover voltage influence coefficient K _uafter cut-out salt close:

${\mathrm{\&rho;}}_{e0}=\sqrt[\mathrm{\&alpha;}]{\frac{K_U\mathrm{NA}}{U}}{(1-\mathrm{nc})}^{\frac{1}{\mathrm{\&alpha;}}}---\left(17\right)$

(2.4) read overhead transmission line each span place pollution severity of insulators degree information, comprise that insulator surface ash is close, salt is close;

(2.5) insulator surface salt is calculated according to the soil deposition amount at each span place by formula (5), formula (6) close, grey close;

(2.6) in conjunction with dust and sand weather feature, pollution severity of insulators parameter is brought into formula (11), pollution flashover probability that formula (12) calculates each insulator.

Contamination Flashover of Overhead Lines tripping operation method for calculating probability under Sand Dust Environment proposed by the invention, early warning can be carried out to the excessive risk tripping fault overhead transmission line in electrical network under Sand Dust Environment, reduce early warning range, the overhead transmission line tripping fault that prevention may occur, improve the reliability level of each overhead transmission line under Sand Dust Environment in electrical network, based on the result of computing method that this patent proposes, can clean in time the insulator of high-risk circuit, improve the safe and stable operation level of electrical network under Sand Dust Environment.

Accompanying drawing explanation

Fig. 1 is the series connection belief system schematic diagram of unit span railway superstructures;

Fig. 2 is transmission line of electricity pollution flashover tripping operation probability calculation process flow diagram;

Fig. 3 is Contamination Flashover of Overhead Lines tripping operation probability calculation process flow diagram under wet weather;

Salt is close, ash is close and only consider the close single insulator string pollution flashover probability comparison diagram of salt in order to consider for Fig. 4;

Air humidity variation diagram when Fig. 5 is foggy weather;

Fig. 6 is insulator chain pollution flashover probability graph under different humidity.

Embodiment

According to Figure of description, the present invention will be further described below:

Embodiment 1

The criterion that sandy environment adsorbs at insulating surface: as exit velocities V _y3during without real solution, sandy environment sedimentation, exit velocities is such as formula (1):

$V_{y3}=\sqrt{{\left(e{V}_{y0}\right)}^2-\frac{{2W}_a}{m}}---\left(18\right)$

In formula, e is coefficient of restitution; V _y0for the normal velocity of the incident insulator surface of filthy particle; W _afor filthy particle overcomes absorption affinity institute work; M is filthy granular mass.

Sandy environment is equivalent to spheroid, and can calculate diameter is d _psandy environment quality such as formula (2):

$m=\frac{4}{3}\mathrm{\&pi;}{\mathrm{\&rho;}}_p{\left(\frac{d_p}{2}\right)}^3---\left(19\right)$

In formula, ρ _pfor sandy environment density.As exit velocities V _y3during without real solution, sandy environment is deposited in insulator surface, at this moment:

${\left({\mathrm{eV}}_{y0}\right)}^2-\frac{{2W}_a}{m}<0---\left(20\right)$

The sandy environment diameter that can be adsorbed onto insulator surface under sandstorm environment meets:

$d_{p\max }<\sqrt[3]{\frac{12W_a}{\mathrm{e\&pi;}{\mathrm{\&rho;}}_p{V}_{y0}}}---\left(21\right)$

Because sand and dust are insoluble filthy particles, it is close that sand and dust during sandstorm weather, insulator surface unit area deposited are ash, sandy environment diameter meets the sandy environment of formula above formula settling condition in the time t through electric transmission line isolator surface, and the equivalent grey Miru's following formula of insulator surface calculates:

${\mathrm{\&rho;}}_{\mathrm{NSDD}}={\&Integral;}_0^t{\&Integral;}_0^{d_{p\max }}{V}_{y0}\left(d_p\right)C(t,d_p)\mathrm{dtd}\left(d_p\right)---\left(22\right)$

In formula: V _y0(d _p) for sand and dust particle diameter be d _pthe sedimentation terminal velocity of particle on vertically insulated surface; C (t, d _p) particle diameter is less than d _pparticle in the filthy concentration of t.C (t, d _p) value under Sand Dust Environment, according to the meteorologic parameter of visibility, wind speed and relative air humidity, can be calculated by the method for linear interpolation.

The close ρ of insulator surface salt under sandstorm environment _eSDDby the close ρ of ash _nSDDconversion obtains as follows:

${\mathrm{\&rho;}}_{\mathrm{ESDD}}=\frac{{\mathrm{\&rho;}}_{\mathrm{NSDD}}}{K_e}---\left(23\right)$

In formula, K _efor the close ratio of ash/salt, close, the grey close computation model of above-mentioned insulator surface salt is used for the probability calculation of Section 3 insulator surface pollution flashover.

The pollution source of overhead transmission line are different because location is different, and different types of pollution source can cause different insulator surface ashes/salt ratio.China's Coastal Areas economy is relatively flourishing, and pollution source mostly are industrial enterprise, chemical plant etc., and many places, China's sandstorm prone areas are in inland, and grey salt compares K _ehigher.

Experiment shows, insulator is lower than a certain voltage U ₀time discharge probability be zero, U ₀corresponding salt close being called, cuts off the close ρ of salt _e0.Therefore, single insulator string pollution flashover probability P ₁(U) can be corrected for and β, k, U ₀3 relevant parameter Weibull distributions:

$P_1\left(U\right)=1-e^{-{\left[\frac{1}{\mathrm{\&beta;}}(\frac{U}{U_0}-1)\right]}^k}---\left(24\right)$

In formula, β=nc/ (1-nc) (ln2) ^1/k; K=1.38/ln [n/ (n-1)]; N is disconnect parameter, and value is 2.5; C is the standard variance of insulator and the ratio of its withstand voltage of 50%, and when calculating β, c value is 0.2.

The close ρ of simple consideration insulator surface salt _eSDDto insulator contamination voltage U _fwhen affecting, single insulator string pollution flashover voltage U _fρ close with the salt of insulator surface _eSDDrelation can be expressed as:

$U_f={\mathrm{NA\&rho;}}_{\mathrm{ESDD}}^{-\mathrm{\&alpha;}}---\left(25\right)$

In formula, N is the insulation sub-pieces number of single insulator string; A is the coefficient relevant with surface filth degree to insulator model; α characterizes the characteristic exponent on pollution flashover voltage impact.

Take into account that insulator surface salt is close, ash close on the affecting of pollution flashover voltage time, pollution flashover voltage can be expressed as:

$U_f={\mathrm{NK\&rho;}}_{\mathrm{ESDD}}^{-i}{\mathrm{\&rho;}}_{\mathrm{NSDD}}^{-j}---\left(26\right)$

In formula, N is the insulation sub-pieces number of single insulator string; K is the coefficient relevant with surface filth degree to insulator model; I is for characterizing the close ρ of salt _eSDDon the characteristic exponent of pollution flashover voltage impact; J is for characterizing grey close ρ _nSDDon the characteristic exponent of pollution flashover voltage impact.

As the close ρ of insulator surface salt _eSDD, grey close ρ _nSDDand the relation between the pollution flashover probability of single insulator string, as shown in the formula:

$P_1({\mathrm{\&rho;}}_{\mathrm{ESDD}},{\mathrm{\&rho;}}_{\mathrm{NSDD}})=1-e^{-{\left\{\frac{1}{\mathrm{\&beta;}}\right[{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{ESDD}}}{{\mathrm{\&rho;}}_{e0}}\right)}^i{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{NSDD}}}{{\mathrm{\&rho;}}_{n0}}\right)}^j-1\left]\right\}}^k}---\left(27\right)$

Above formula, cuts off the close ρ of salt _e0=ρ _e50(1-nc) ^{1/ α}; N value is 2.5; ρ _e50insulator surface salt corresponding to 50% pollution flashover probability is close, ρ _e50=(NA/U) ^{1/ α}; Calculate ρ _e0during value, c value is 0.08.ρ _n0close for cutting off ash; ρ _n50ash corresponding to 50% pollution flashover probability is close, ρ _n0=ρ _n50(1-nc) ^1/j, .

When sandstorm weather occurs, overhead transmission line insulator surface sand and dust particulate deposits at short notice in a large number, the primary pollution source of circuit, and sand and dust particulate is a kind of insoluble filthy particle, therefore the sand and dust short time a large amount of depositions can the ash of direct raising insulator surface close, in addition China's sandstorm prone areas is in inland, and grey salt compares K _ehigher, therefore dust and sand weather can increase insulator surface ash/salt ratio further, reduces the flashover voltage of the insulator, thus increases insulator contamination probability.

Consider These characteristics, under Sand Dust Environment during insulator contamination probability calculation, take into account the close ρ of insulator surface salt simultaneously _eSDD, grey close ρ _nSDDimpact, assess overhead transmission line reliability under sandstorm environment more accurately.

In actual electric network is run, insulator is paired running often, pollution flashover probability P during m insulator string paired running _m(ρ _eSDD, ρ _nSDD) be:

$P_m({\mathrm{\&rho;}}_{\mathrm{ESDD}},{\mathrm{\&rho;}}_{\mathrm{NSDD}})=1-e^{-m{\left\{\frac{1}{\mathrm{\&beta;}}\right[{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{ESDD}}}{{\mathrm{\&rho;}}_{e0}}\right)}^i{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{NSDD}}}{{\mathrm{\&rho;}}_{n0}}\right)}^j-1\left]\right\}}^k}---\left(28\right)$

Whole piece transmission line of electricity is considered as the series connection belief system be made up of some spans, as shown in Figure 1.Therefore, there is N number of span and whole piece transmission line of electricity pollution flashover probability P under sandstorm environment of m insulator string paired running in every span _las shown in the formula calculating:

$P_L=1-\underset{n=1}{\overset{N}{\mathrm{\&Pi;}}}(1-P_{m\left(n\right)})---\left(29\right)$

P in formula _mpollution flashover probability when () is transmission line of electricity No. n-th span place m insulator string paired running n.

To sum up, as shown in Figure 2, when dust and sand weather passes by, the calculation procedure of Contamination Flashover of Overhead Lines probability fault is as follows:

(1) read the dust and sand weather weather data of each weather station, transmission line of electricity region record, weather station longitude and latitude, calculate overhead transmission line starting point longitude and latitude, electric pressure and span information;

(2) according to transmission line of electricity starting point latitude and longitude information and span, the longitude and latitude of overhead transmission line each span place insulator is calculated;

(3) based on the method for two-dimensional interpolation, the visibility at overhead transmission line each span insulator place is calculated;

(4) the insulator sandy environment maximum gauge meeting settling condition is calculated by formula (1)-Shi (4), according to the national Specification of dust and sand weather grade, utilize linear interpolation method to calculate sandy environment concentration that each span place meets settling condition;

(5) the soil deposition amount of sandy environment concentration by each span of formula (10) computing electric power line of settling condition is met according to insulator place;

(6) insulator surface salt is calculated according to the soil deposition amount at each span place by formula (5), formula (6) close, grey close;

(7) in conjunction with dust and sand weather feature, pollution severity of insulators parameter is brought into the pollution flashover probability that formula (10) calculates each insulator;

(8) by overhead transmission line cascade system characteristic, according to the pollution flashover tripping operation probability of formula (11), formula (12) calculating whole piece overhead transmission line.

Electric transmission line isolator pollution flashover under sandstorm impact is determined by two factors, and one is the pollution severity of insulators deposition that in air, the sandy environment of dispersed causes; Two is to make to gather the meteorological condition that filthy material fully makes moist.Consider transmission line of electricity pollution flashover probability with wet weather after sandstorm is passed by below.

The wet weather such as mist, drizzle Water Vapor Distribution is wide and the duration is long, moistening mode the most dangerous when being Operation of Electric Systems.Along with the increase of humidity, the close increase degree of ionization along with humidity of filthy material salt improves, and leakage current becomes large thereupon, and the flashover voltage of the insulator reduces, and probability of flashover increases.

Leakage current and pollution flashover voltage are negative power function relation, meet following relation:

$U_f=K_{\mathrm{leak}}{I}_h^{-\mathrm{\&alpha;}}---\left(30\right)$

In formula, U _fit is pollution flashover voltage; K _leak, α is the coefficient relevant with insulator model; I _hit is leakage current.

When salt close identical, for different relative air humidities, leakage current can use formula (15) to calculate:

$I_h=\left\{\begin{array}{cc}{\mathrm{Be}}^{\mathrm{aRH}}& 70\%\&le;\mathrm{RH}\&le;100\%\\ I_{h0}& 0\&le;\mathrm{RH}\&le;70\%\end{array}\right.---\left(31\right)$

In formula, RH is relative air humidity; B is the coefficient relevant with insulator structure, material; α is the characteristic exponent that relative air humidity RH affects leakage current amplitude; I _h0the leakage current of air humidity when being less than 70%.

To same insulator chain, pollution flashover voltage when above formula both members is simultaneously less than 70% divided by relative air humidity, is normalized:

$K_U=\frac{U_f}{U_{f0}}={\left(\frac{I_h}{I_{h0}}\right)}^{-\mathrm{\&alpha;}}---\left(32\right)$

In formula, U _f0for insulator contamination voltage when relative air humidity is less than 70%; K _ufor the ratio of pollution flashover voltage when pollution flashover voltage when relative air humidity is greater than 70% and relative air humidity are less than 70%, show to be greater than the relative air humidity of 70% to the influence coefficient of pollution flashover voltage, K _ufor being less than the value of 1, can be calculated according to the impact of relative air humidity on Leakage Current, the change of relative air humidity can be obtained like this on the computing formula of the impact of insulator contamination voltage.Pollution flashover voltage can be corrected for:

$U_f=\left\{\begin{array}{cc}{\mathrm{NA\&rho;}}_{\mathrm{ESDD}}^{-\mathrm{\&alpha;}}& 0\&le;\mathrm{RH}\&le;70\%\\ K_U{\mathrm{NA\&rho;}}_{\mathrm{ESDD}}^{-\mathrm{\&alpha;}}& 70\%\&le;\mathrm{RH}\&le;100\%\end{array}\right.---\left(33\right)$

This shows, when relative air humidity is less than 70%, the change of air humidity can be ignored on the impact of insulator contamination voltage, when being greater than 70%, then will take into account the influence coefficient K of air humidity to pollution flashover voltage _u.

When to calculate relative air humidity be 70%-100%, consider that relative air humidity is to pollution flashover voltage influence coefficient K _uafter cut-out salt close:

${\mathrm{\&rho;}}_{e0}=\sqrt[\mathrm{\&alpha;}]{\frac{K_U\mathrm{NA}}{U}}{(1-\mathrm{nc})}^{\frac{1}{\mathrm{\&alpha;}}}---\left(34\right)$

Due to K _ufor being less than the value of 1, thus to reduce the cut-out salt of insulator contamination close for relative air humidity, adds the probability of insulator contamination.After determining that the cut-out salt of insulator under different humidity is close, can the pollution flashover tripping operation probability of computing electric power line under different relative air humidity.

As shown in Figure 3, the calculation procedure of dust and sand weather Contamination Flashover of Overhead Lines tripping fault probability of adjoint wet weather after passing by is as follows:

(1) read the relative air humidity of each weather station, transmission line of electricity region record, weather station longitude and latitude, calculate the information such as overhead transmission line starting point longitude and latitude, electric pressure and span;

(2) according to transmission line of electricity starting point latitude and longitude information, transmission line of electricity each span place insulator latitude and longitude information;

(3) based on the method for two-dimensional interpolation, calculate the relative air humidity at overhead transmission line each span insulator place, and it is close with cut-out salt to insulator contamination voltage influence coefficient to calculate wet weather according to insulator model by formula (13)-Shi (17);

(4) read overhead transmission line each span place pollution severity of insulators degree information, comprise that insulator surface ash is close, salt is close;

(5) insulator surface salt is calculated according to the soil deposition amount at each span place by formula (5), formula (6) close, grey close;

(6) in conjunction with dust and sand weather feature, pollution severity of insulators parameter is brought into formula (11), pollution flashover probability that formula (12) calculates each insulator.

Embodiment 2

For north, Middle-west Inner Mongolia packet header under on March 19th, 2010 8:00-14:00 strong chromatic number environment to the transmission line of electricity of Huhehaote Ed_1 member 500kV, analyze the pollution flashover tripping operation probability of transmission line of electricity.This circuit list returns erection, and length is 155.35km.According to " 110kV-500kV aerial power transmission line designing technique code ", insulator model selects XWP2-160, pendency duplex is run, insulator chain sheet number 32, span 650 meters, design wind speed 28m/s, only considers the mechanics influence that sandstorm is disregarded the impact of circuit pollution flashover probability of malfunction and caused transmission line of electricity when sandstorm wind speed is less than this value.The parameter of monolithic XWP2-160 type insulator is A=7.255, α=0.219, K=4.79, i=0.34, j=0.13.

Weather data is from the sandstorm weather data of Middle-west Inner Mongolia 26 weather stations of U.S.National Oceanic and air management office weather data central store.Two-dimensional interpolation is carried out to these data and calculates the horizontal visibility obtaining transmission line of electricity each span insulator place.According to the national sandstorm weather classification standard shown in table 1, determine that each moment meets the sandy environment concentration value of settling condition by the horizontal visibility of sandstorm weather grade and each span based on the method for linear interpolation.

Table 1 dust and sand weather grade

According to weather station sandstorm information, two-dimensional interpolation obtains the weather information of each span of transmission line of electricity, calculates transmission line of electricity part typical case span visibility when sandstorm is passed by as shown in table 2.

The visibility at the transmission line of electricity part typical case span place that table 2 calculates through weather station data two-dimensional interpolation

Transmission line of electricity each span visibility when passing by according to the sandstorm calculated during two-dimensional interpolation, calculate by sandstorm weather grade classification linear interpolation the sandy environment concentration that each span of transmission line of electricity meets settling condition, part typical span place sandy environment concentration is as shown in table 3.

Table 3 obtains according to the linear interpolation of sandstorm weather grade the sandy environment concentration that part span place meets settling condition

K is compared at the insulator ash salt of formula (6) _ewhen=4.5, consider close, the close impact on insulator contamination probability of salt of ash simultaneously and only take into account surface salt deposit density to the contrast of insulator contamination impact probability as shown in Figure 4, under the prerequisite of identical ash/salt ratio, take into account insulator surface ash close to insulator contamination impact probability time, insulator contamination probability significantly increases, thus, when calculating sandstorm environment line pollution flashover tripping operation probability, the close impact on pollution flashover probability of insulator ash should be taken into account.

According to weather station sandstorm information, interpolation obtains the weather information of each span of transmission line of electricity, calculates transmission line of electricity part typical case span insulator surface soil deposition amount when sandstorm is passed by as shown in table 4.From table 4, at the initial stage in transmission line of electricity region of passing by sandstorm, insulator surface soil deposition amount gathers way comparatively fast.Then the soil deposition amount of insulator surface constantly increases along with passage of time, gathers way and slows down, and insulator surface soil deposition amount is tending towards saturated.

Typical span insulator chain surface soil deposition amount (NSDD) of table 4 500KV transmission line of electricity 8:00-14:00 part

When sandstorm is passed by, 500KV transmission line of electricity part typical case span insulator chain pollution flashover probability is as shown in table 5.

Table 5 500KV transmission line of electricity 8:00-14:00 part typical span insulator chain pollution flashover probability

As shown in Table 5, sandstorm initial stage 8:00-10:00, because insulator surface soil deposition amount is less, the dielectric level of insulator is substantially unaffected, and insulator chain pollution flashover probability is zero.Voltage levels transmission line of electricity span is comparatively large, and the sandstorm weather grade in region residing for each span insulator of overhead transmission line is different, and sandstorm is passed by and is different from other extreme weathers such as wind lotus to the impact of electrical network, and it has cumulative effect in time.Along with the continuous passing of duration, the sand and dust of insulator surface constantly deposit, and cause insulator contamination voltage to reduce, and the insulator chain pollution flashover probability that part meets with strong chromatic number or Severe Sand-Dust Storms constantly rises, and circuit pollution flashover probability synchronously increases.

According to transmission line of electricity each span place insulator contamination probability, whole piece 500KV transmission line of electricity pollution flashover tripping operation probability can be obtained, as shown in table 6.The impact of sandstorm weather on transmission line of electricity has accumulative effect, and the duration is longer, and the pollution flashover tripping operation probability of transmission line of electricity is higher.Therefore, after continuation sandstorm appears in electrical network region, as without Rainfall simulator erosion or manual cleaning, the probability of circuit generation arcing fault will increase greatly.Therefore, after sandstorm is passed by, the dust-proof abatement processes on electric transmission line isolator surface should be carried out in time, avoid the increase of circuit pollution flashover probability of malfunction.

Table 6 500KV transmission line of electricity 8:00-14:00 pollution flashover tripping operation probability

Based on above example, after considering that sandstorm is passed by, the wet weather that electrical network region occurs is on the impact of transmission line of electricity pollution flashover probability.Assuming that there is foggy weather in north, packet header to east, the Huhehaote 14:00-15:30 of 500kV transmission line of electricity region after sandstorm is passed by, if from 14:00, relative air humidity rises from 30%, during 14:40, relative air humidity reaches 70%, 80% is reached to 14:50,15:30 is continued to, as shown in Figure 5 after 15:00 reaches 90%.Insulator surface sand and dust contamination level remains unchanged, and compares K at the insulator ash salt of formula (6) _ewhen=4.5, under different humidity environment, insulator chain pollution flashover probability as shown in Figure 6, and when relative air humidity rises, single insulator string pollution flashover probability increases, this is because the increase of air humidity makes pollution severity of insulators material dissolve further, causes cutting off the close ρ of salt _e0reduce, from formula (10), the rising of relative air humidity can make insulator contamination probability increase, and then causes the pollution flashover tripping operation probability of whole piece transmission line of electricity to increase.

If the not cleaning after sandstorm is passed by of each span insulator of transmission line of electricity, then transmission line of electricity typical case span insulator chain on March 19th, 2010 14:00-15:30 pollution flashover probability and transmission line of electricity pollution flashover tripping operation probability in table 7, table 8.

Table 7 500KV transmission line of electricity 14:00-15:30 part typical span insulator chain pollution flashover probability

Table 8 500KV transmission line of electricity 14:00-15:30 pollution flashover tripping operation probability

By table 7, table 8 is visible, if there is the wet weather that relative air humidity increases in transmission line of electricity region after sandstorm is passed by, under the poor prerequisite of insulator surface contamination (identical with insulator surface contamination level during 14:00), each insulator chain pollution flashover probability significantly increases, and then cause whole piece 500kV transmission line of electricity pollution flashover tripping operation probability to increase, rise to 0.3162 of 16:00 by sandstorm 0.0639 behind border during 14:00.The main cause of transmission line of electricity pollution flashover tripping operation is due to after air humidity increase, conductive materials in the sandy environment that hydrone in air makes insulator surface deposit dissolves, the close reduction of cut-out salt of insulator surface, therefore from formula (10), insulator contamination probability increases, and then causes the synchronous rising of 500kV transmission line of electricity pollution flashover probability.Therefore, the wet weather after sandstorm is passed by is necessary the artificial dedusting scale removal carrying out electric transmission line isolator, the high probability line tripping accident caused to avoid wet weather before occurring.

Claims (1)

1. Contamination Flashover of Overhead Lines tripping operation method for calculating probability under Sand Dust Environment, comprise the calculation procedure of Contamination Flashover of Overhead Lines probability fault when dust and sand weather passes by and dust and sand weather pass by after with the calculation procedure of the Contamination Flashover of Overhead Lines tripping fault probability of wet weather, it is characterized in that, step is specific as follows:

(1) when, dust and sand weather passes by, the calculation procedure of Contamination Flashover of Overhead Lines probability fault is as follows:

(1.1) read the dust and sand weather weather data of each weather station, transmission line of electricity region record, weather station longitude and latitude, calculate overhead transmission line starting point longitude and latitude, electric pressure and span information;

(1.2) according to transmission line of electricity starting point latitude and longitude information and span, the longitude and latitude of overhead transmission line each span place insulator is calculated;

(1.3) based on the method for two-dimensional interpolation, the visibility at overhead transmission line each span insulator place is calculated;

(1.4) the insulator sandy environment maximum gauge meeting settling condition is calculated by formula (1)-Shi (4), according to the national Specification of dust and sand weather grade, utilize linear interpolation method to calculate sandy environment concentration that each span place meets settling condition;

The criterion that sandy environment adsorbs at insulating surface: as exit velocities V _y3during without real solution, sandy environment sedimentation, exit velocities is such as formula (1):

$V_{y3}=\sqrt{{\left(e{V}_{y0}\right)}^2-\frac{2W_a}{m}}---\left(1\right)$

In formula, e is coefficient of restitution; V _y0for the normal velocity of the incident insulator surface of filthy particle; W _afor filthy particle overcomes absorption affinity institute work; M is filthy granular mass;

Sandy environment is equivalent to spheroid, and calculating diameter is d _psandy environment quality such as formula (2):

$m=\frac{4}{3}{\mathrm{\&pi;\&rho;}}_p{\left(\frac{d_p}{2}\right)}^3---\left(2\right)$

In formula, ρ _pfor sandy environment density, as exit velocities V _y3during without real solution, sandy environment is deposited in insulator surface, at this moment:

${\left(e{V}_{y0}\right)}^2-\frac{2W_a}{m}<0---\left(3\right)$

The sandy environment diameter that can be adsorbed onto insulator surface under sandstorm environment meets:

$d_{p\max }<\sqrt[3]{\frac{12W_a}{e{\mathrm{\&pi;\&rho;}}_p{V}_{y0}}}---\left(4\right)$

Because sand and dust are insoluble filthy particles, it is close that sand and dust during sandstorm weather, insulator surface unit area deposited are ash, sandy environment diameter meets the sandy environment of formula above formula settling condition in the time t through electric transmission line isolator surface, and the equivalent grey Miru's following formula of insulator surface calculates:

${\mathrm{\&rho;}}_{\mathrm{NSDD}}={\&Integral;}_0^t{\&Integral;}_0^{d_{p\max }}{V}_{y0}\left(d_p\right)C(t,d_p)\mathrm{dtd}\left(d_p\right)---\left(5\right)$

In formula: V _y0(d _p) for sand and dust particle diameter be d _pthe sedimentation terminal velocity of particle on vertically insulated surface; C (t, d _p) particle diameter is less than d _pparticle in the filthy concentration of t, C (t, d _p) value under Sand Dust Environment, according to the meteorologic parameter of visibility, wind speed and relative air humidity, calculated by the method for linear interpolation;

The close ρ of insulator surface salt under sandstorm environment _eSDDby the close ρ of ash _nSDDconversion obtains as follows:

${\mathrm{\&rho;}}_{\mathrm{ESDD}}=\frac{{\mathrm{\&rho;}}_{\mathrm{NSDD}}}{K_e}---\left(6\right)$

In formula, K _efor the close ratio of ash/salt, close, the grey close computation model of above-mentioned insulator surface salt is used for the probability calculation of Section 3 insulator surface pollution flashover;

Insulator is lower than a certain voltage U ₀time discharge probability be zero, U ₀corresponding salt close being called, cuts off the close ρ of salt _e0, therefore, single insulator string pollution flashover probability P ₁(U) be corrected for and β, k, U ₀3 relevant parameter Weibull distributions:

$P_1\left(U\right)=1-e^{-{\left[\frac{1}{\mathrm{\&beta;}}(\frac{U}{U_0}-1)\right]}^k}---\left(7\right)$

In formula, β=nc/ (1-nc) (ln2) ^1/k; K=1.38/ln [n/ (n-1)]; N is disconnect parameter, and value is 2.5; C is the standard variance of insulator and the ratio of its withstand voltage of 50%, and when calculating β, c value is 0.2;

The close ρ of simple consideration insulator surface salt _eSDDto insulator contamination voltage U _fwhen affecting, single insulator string pollution flashover voltage U _fρ close with the salt of insulator surface _eSDDrelation is expressed as:

$U_f=\mathrm{NA}{\mathrm{\&rho;}}_{\mathrm{ESDD}}^{-\mathrm{\&alpha;}}---\left(8\right)$

In formula, N is the insulation sub-pieces number of single insulator string; A is the coefficient relevant with surface filth degree to insulator model; α characterizes the characteristic exponent on pollution flashover voltage impact;

Take into account that insulator surface salt is close, ash close on the affecting of pollution flashover voltage time, pollution flashover voltage is expressed as:

$U_f=\mathrm{NK}{\mathrm{\&rho;}}_{\mathrm{ESDD}}^{-i}{\mathrm{\&rho;}}_{\mathrm{NSDD}}^{-j}---\left(9\right)$

In formula, N is the insulation sub-pieces number of single insulator string; K is the coefficient relevant with surface filth degree to insulator model; I is for characterizing the close ρ of salt _eSDDon the characteristic exponent of pollution flashover voltage impact; J is for characterizing grey close ρ _nSDDon the characteristic exponent of pollution flashover voltage impact;

As the close ρ of insulator surface salt _eSDD, grey close ρ _nSDDand the relation between the pollution flashover probability of single insulator string, as shown in the formula:

$P_1({\mathrm{\&rho;}}_{\mathrm{ESDD}},{\mathrm{\&rho;}}_{\mathrm{NSDD}})=1-e^{-{\left\{\frac{1}{\mathrm{\&beta;}}\right[{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{ESDD}}}{{\mathrm{\&rho;}}_{e0}}\right)}^i{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{NSDD}}}{{\mathrm{\&rho;}}_{n0}}\right)}^j-1\left]\right\}}^k}---\left(10\right)$

Above formula, cuts off the close ρ of salt _e0=ρ _e50(1-nc) ^{1/ α}; N value is 2.5; ρ _e50insulator surface salt corresponding to 50% pollution flashover probability is close, ρ _e50=(NA/U) ^{1/ α}; Calculate ρ _e0during value, c value is 0.08, ρ _n0close for cutting off ash; ρ _n50ash corresponding to 50% pollution flashover probability is close, ρ _n0=ρ _n50(1-nc) ^1/j,

Under Sand Dust Environment during insulator contamination probability calculation, take into account the close ρ of insulator surface salt simultaneously _eSDD, grey close ρ _nSDDimpact;

In operation of power networks, insulator is paired running often, pollution flashover probability P during m insulator string paired running _m(ρ _eSDD, ρ _nSDD) be:

$P_m({\mathrm{\&rho;}}_{\mathrm{ESDD}},{\mathrm{\&rho;}}_{\mathrm{NSDD}})=1-e^{-{m\left\{\frac{1}{\mathrm{\&beta;}}\right[{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{ESDD}}}{{\mathrm{\&rho;}}_{e0}}\right)}^i{\left(\frac{{\mathrm{\&rho;}}_{\mathrm{NSDD}}}{{\mathrm{\&rho;}}_{n0}}\right)}^j-1\left]\right\}}^k}---\left(11\right)$

Whole piece transmission line of electricity is considered as the series connection belief system be made up of some spans, has N number of span and whole piece transmission line of electricity pollution flashover probability P under sandstorm environment of m insulator string paired running in every span _las shown in the formula calculating:

$P_L=1-\underset{n=1}{\overset{N}{\mathrm{\&Pi;}}}(1-P_{m\left(n\right)})---\left(12\right)$

P in formula _mpollution flashover probability when () is transmission line of electricity No. n-th span place m insulator string paired running n;

(1.5) the soil deposition amount of sandy environment concentration by each span of formula (10) computing electric power line of settling condition is met according to insulator place;

(1.6) insulator surface salt is calculated according to the soil deposition amount at each span place by formula (5), formula (6) close, grey close;

(1.7) in conjunction with dust and sand weather feature, pollution severity of insulators parameter is brought into the pollution flashover probability that formula (10) calculates each insulator;

(1.8) by overhead transmission line cascade system characteristic, Contamination Flashover of Overhead Lines probability when passing by according to the dust and sand weather of formula (11), formula (12) calculating whole piece overhead transmission line;

(2), the calculation procedure of dust and sand weather Contamination Flashover of Overhead Lines tripping fault probability of adjoint wet weather after passing by is as follows:

(2.1) read the relative air humidity of each weather station, transmission line of electricity region record, weather station longitude and latitude, calculate the information such as overhead transmission line starting point longitude and latitude, electric pressure and span;

(2.2) according to transmission line of electricity starting point latitude and longitude information, transmission line of electricity each span place insulator latitude and longitude information;

(2.3) based on the method for two-dimensional interpolation, calculate the relative air humidity at overhead transmission line each span insulator place, and it is close with cut-out salt to insulator contamination voltage influence coefficient to calculate wet weather according to insulator model by formula (13)-Shi (17);

Leakage current and pollution flashover voltage are negative power function relation, meet following relation:

$U_f=K_{\mathrm{leak}}{I}_h^{-\mathrm{\&alpha;}}---\left(13\right)$

In formula, U _fit is pollution flashover voltage; K _leak, α is the coefficient relevant with insulator model; I _hit is leakage current;

When salt close identical, for different relative air humidities, leakage current formula (15) calculates:

$I_h=\left\{\begin{array}{cc}{\mathrm{Be}}^{\mathrm{aRH}}& 70\%\&le;\mathrm{RH}\&le;100\%\\ I_{h0}& 0\&le;\mathrm{RH}\&le;70\%\end{array}\right.---\left(14\right)$

In formula, RH is relative air humidity; B is the coefficient relevant with insulator structure, material; α is the characteristic exponent that relative air humidity RH affects leakage current amplitude; I _h0the leakage current of air humidity when being less than 70%;

To same insulator chain, pollution flashover voltage when above formula both members is simultaneously less than 70% divided by relative air humidity, is normalized:

$K_U=\frac{U_f}{U_{f0}}={\left(\frac{I_h}{I_{h0}}\right)}^{-\mathrm{\&alpha;}}---\left(15\right)$

In formula, U _f0for insulator contamination voltage when relative air humidity is less than 70%; K _ufor the ratio of pollution flashover voltage when pollution flashover voltage when relative air humidity is greater than 70% and relative air humidity are less than 70%, show to be greater than the relative air humidity of 70% to the influence coefficient of pollution flashover voltage, K _ufor being less than the value of 1, calculated according to the impact of relative air humidity on Leakage Current, pollution flashover voltage, on the computing formula of the impact of insulator contamination voltage, is corrected for by the change obtaining relative air humidity:

$U_f=\left\{\begin{array}{cc}\mathrm{NA}{\mathrm{\&rho;}}_{\mathrm{ESDD}}^{-\mathrm{\&alpha;}}& 0\&le;\mathrm{RH}\&le;70\%\\ K_U\mathrm{NA}{\mathrm{\&rho;}}_{\mathrm{ESDD}}^{-\mathrm{\&alpha;}}& 70\%\&le;\mathrm{RH}\&le;100\%\end{array}\right.---\left(16\right)$

When relative air humidity is less than 70%, the impact of change on insulator contamination voltage of air humidity is ignored, and when being greater than 70%, then will take into account the influence coefficient K of air humidity to pollution flashover voltage _u;

When to calculate relative air humidity be 70%-100%, consider that relative air humidity is to pollution flashover voltage influence coefficient K _uafter cut-out salt close:

${\mathrm{\&rho;}}_{e0}=\sqrt[\mathrm{\&alpha;}]{\frac{K_U\mathrm{NA}}{U}}{(1-\mathrm{nc})}^{\frac{1}{\mathrm{\&alpha;}}}---\left(17\right)$

(2.4) read overhead transmission line each span place pollution severity of insulators degree information, comprise that insulator surface ash is close, salt is close;

(2.5) insulator surface salt is calculated according to the soil deposition amount at each span place by formula (5), formula (6) close, grey close;

(2.6) in conjunction with dust and sand weather feature, pollution severity of insulators parameter is brought into formula (11), pollution flashover probability that formula (12) calculates each insulator.