CN105740516A - Method for determining electric insulation reliability of power transmission line - Google Patents

Abstract

The invention discloses a method for determining the electric insulation reliability of a power transmission line. The method comprises the following steps: dividing pollution areas, counting salt density value data and insulator string configuration conditions of various pollution areas, building a pollution flashover evaluation probability analysis model to determine the pollution flashover reliability of an overall line; dividing ice areas, counting icing-thickness historical data, the salt density value data and the insulator string configuration conditions of various ice areas, and building an ice flashover evaluation probability analysis model to determine the ice flashover reliability of the overall line; and counting the species and number of towers adopted by the line, counting the topography distribution condition along the line, and building a lighting flashover evaluation probability analysis model to determine the lighting flashover reliability of the overall line. According to the method disclosed by the invention, the problems in configuration performance evaluation and risk and weak link prediction of transmission line insulation equipment are mainly solved; the line insulation level can be configured in a targeted manner; the operation and maintenance risk and key links of the power transmission line can be found out by 'suiting the remedy to the case'; the safety and the reliability of the power transmission line are improved; and the method has significant economic and social benefits.

Description

A kind of defining method of power transmission line electrical insulation reliability

Technical field

The invention belongs to work transmission line technical field, be specifically related to the defining method of a kind of power transmission line electrical insulation reliability.

Background technology

Along with Chinese national economy develops, power industry, also into UHV transmission technology such as high speed development stage, ± 800kV direct current, 1000V exchanges, has been widely used at state's net, south net, and extra-high voltage bulk transmission grid just gradually forms.UHV transmission line has that transmission capacity is big, fed distance remote, investment cost high, and extra high voltage line is once the stoppage in transit that has an accident, regional power failure will be caused, even jeopardize the stable operation of whole electrical network, cause more serious consequence, thereby ensure that the safe and reliable operation of extra high voltage line is extremely important.

In project engineering stage, accurate evaluation transmission line of electricity reliability, the operation safety after the reasonability of construction investment scale and transmission line of electricity are gone into operation is most important.

Both at home and abroad transmission line of electricity reliability is had carried out some research work, often stress the reliability of research tower structure, the reliability of electric insulation is also lacked system, comprehensively studies.Along with the erection of extra-high voltage bulk transmission grid develops, line insulation lost efficacy, and gently then caused line outage, weight then initiating system dead electricity risk.

Based on this, it is necessary to set about from circuit pollution flashover, icing flashover, lightning stroke flashover three aspect, the reliability of circuit electric insulation is carried out comprehensively, the analysis of system.

Summary of the invention

In order to overcome the disadvantages mentioned above of prior art, the invention provides the defining method of a kind of power transmission line electrical insulation reliability.

The technical solution adopted for the present invention to solve the technical problems is: the defining method of a kind of power transmission line electrical insulation reliability, including following content:

One, the pollution flashover reliability of whole piece circuit is determined:

(1) dirty district, statistics Ge Wu district salt density value data and insulator chain configuring condition are divided；

(2) pollution flashover assessment probability analysis model is set up, it is determined that the pollution flashover reliability of whole piece circuit；

Two, determine that the ice of whole piece circuit dodges reliability:

(1) divide ice formation, add up each ice formation ice covering thickness historical data, salt density value data and insulator chain configuring condition；

(2) set up ice and dodge assessment probability analysis model, it is determined that the ice of whole piece circuit dodges reliability；

Three, the lightning stroke flashover reliability of whole piece circuit is determined:

(1) shaft tower kind and the quantity that circuit adopts, the topography profile situation that statistics circuit is along the line are added up；

(2) the assessment probability analysis model of lightning stroke flashover is set up, it is determined that the lightning stroke flashover reliability of whole piece circuit.

Further, described set up pollution flashover assessment probability analysis model method be:

1) calculate an insulator string and the probability P of pollution flashover occurs under the wet weather of mist₁:

$\begin{array}{c}{P}_1\left(\mathrm{\ρ}\right)=\frac{1}{\sqrt{2\mathrm{\π}}{\mathrm{\σ}}_j\left(\mathrm{\ρ}\right)}{\∫}_{-\mathrm{\∞}}^u{e}^{-\frac{{(U-U_j(\mathrm{\ρ}\left)\right)}^2}{2{\mathrm{\σ}}_j^2\left(\mathrm{\ρ}\right)}}du\\ =\frac{1}{\sqrt{2\mathrm{\π}}}{\∫}_{-\mathrm{\∞}}^{\frac{U-U_j\left(\mathrm{\ρ}\right)}{{\mathrm{\σ}}_j\left(\mathrm{\ρ}\right)}}{e}^{-\frac{t^2}{2}}dt\end{array}$

In formula: U is circuit working voltage, U_j(ρ) for 50% pollution flashover voltage of insulator chain, σ_j(ρ) for U_j(ρ) standard deviation；

2) probability of pollution severity of insulators salt density value is calculated:

$f\left(p\right)=\frac{1}{\sqrt{2\mathrm{\π}\mathrm{\σ}}\mathrm{\ρ}}\exp \[-\frac{(\ln p-\mathrm{\μ})}{2{\mathrm{\σ}}^2}\]$

In formula: ρ is salt density value, μ is the meansigma methods of the logarithm of ρ, and σ is the standard deviation of the logarithm of ρ；

3) probability of insulator pollution flashover under a wet fog weather is calculated:

$P^{\′}\left(\mathrm{\ρ}\right)={\∫}_0^{\mathrm{\∞}}f\left(\mathrm{\ρ}\right)P_1\left(\mathrm{\ρ}\right)d\mathrm{\ρ}$

4) the pollution flashover probability of circuit within the scope of wet fog weather under a wet fog weather is calculated:

P_I=1-(1-P'(ρ))^I

In formula: I is the insulator chain number in wet fog weather coverage；

5) flashover strike of annual per 100 km circuit is calculated:

$p=\frac{100M}{H}\·P_I$

In formula: H is the length of whole piece circuit, M is annual mist wet day natural law；

6) flashover strike of different part of paths be weighted obtain average flashover severity rate:

S in formula_KFor the length of k-th part of path, p_kFlashover strike for k-th part of path.

Further, described set up ice dodge assessment probability analysis model method be:

1) probability P that an insulator string occurs ice to dodge under the wet weather of mist is calculated₂:

$\begin{array}{c}{P}_2\left(\mathrm{\ω}\right)=\frac{1}{\sqrt{2\mathrm{\π}}{\mathrm{\σ}}_j(\mathrm{\ω},\mathrm{\ρ})}{\∫}_{-\mathrm{\∞}}^u{e}^{-\frac{{(U-U_j(\mathrm{\ω},\mathrm{\ρ}\left)\right)}^2}{2{\mathrm{\σ}}_j^2(\mathrm{\ω},\mathrm{\ρ})}}du\\ =\frac{1}{\sqrt{2\mathrm{\π}}}{\∫}_{-\mathrm{\∞}}^{\frac{U-U_j(\mathrm{\ω},\mathrm{\ρ})}{{\mathrm{\σ}}_j(\mathrm{\ω},\mathrm{\ρ})}}{e}^{-\frac{t^2}{2}}dt\end{array}$

In formula: U is circuit working voltage, U_j50% icing flashover voltage that (ω, ρ) is insulator chain, σ_j(ω, ρ) is U_jThe standard deviation of (ω, ρ)；

2) calculate icing in circuit Designed recurrence period and exceed the probability density function of design load:

G (ω)=aexp{-a (ω-u)-exp [-a (ω-u)] }

Wherein a is dimensional parameters, a=1.28255/ σ；U is location parameter,For the average of ice covering thickness, σ is standard deviation；

3) probability arbitrary year the icing of Xcm thickness occurring is calculated:

$P_X=\frac{1}{T}a\exp \{-a(X-u)-\exp \[-a(X-u)\]\}\mathrm{\Δ}X$

In formula: T is the time limit of Designed recurrence period；Δ X is ice covering thickness increment；

4) probability of insulator arc-over in an icing weather is calculated:

$P^{\′}\left(\mathrm{\ω}\right)=\frac{1}{T}{\∫}_0^{\mathrm{\∞}}g\left(\mathrm{\ω}\right)P_2(\mathrm{\ω},\mathrm{\ρ})d\mathrm{\ω}$

5) ice calculating an icing weather line dodges probability:

P_N=1-(1-P'(ω))^N

In formula: N is the insulator chain number of Ice Area；

6) probability of flashover of annual per 100 km circuit is calculated:

$P=\frac{100M}{H}\·P_N$

In formula: H is the length of whole piece circuit, M is annual icing natural law.

Further, described set up lightning stroke flashover assessment probability analysis model method be:

1) average shielding or the counterattack flashover strike of circuit are calculated:

${\mathrm{\λ}}^{\′}=\underset{i}{\overset{N}{\Σ}}{\mathrm{\ω}}_i{\mathrm{\λ}}_i$

In formula: N is total tower number；ω_iIt is that i-th kind of tower is at percentage ratio shared completely, λ_iIt is shielding or the counterattack flashover strike of i-th kind of tower；

2) shielding or the counterattack flashover strike of circuit are calculated:

λ_Always=η_{Mountain region}λ'_{Mountain region}+η_Hillsλ'_Hills+η_{Level land}λ'_{Level land}

In formula: η_{Mountain region}For mountain region percentage；η_HillsFor hills percentage；η_{Level land}For level land percentage；

3) the unreliable degree of circuit is calculated:

P_f=λ_Always·H/M

In formula: H is the total length of circuit；M is annual thunderstorm natural law.

Compared with prior art, the method have the advantages that

The reliability of power transmission line electrical insulator arrangement, by transmission line of electricity is set up pollution flashover, ice sudden strain of a muscle, lightning stroke flashover probability analysis model, is carried out system, comprehensively analysis, quantification of targets by the present invention.The present invention is that first Application is in the probability analysis method of power transmission line electrical insulator arrangement reliability overall merit in the world, and emphasis solves the performance evaluation to the configuration of transmission line insulator equipment and risk, weak link are estimated.By to the probability assessment to power transmission line electrical insulator arrangement reliability, the configuration circuit dielectric level that can shoot the arrow at the target, suit the remedy to the case discovery transmission line of electricity O&M risk and key link, improve the security reliability of transmission line of electricity, there is significant economic and social benefit.

Accompanying drawing explanation

Examples of the present invention will be described by way of reference to the accompanying drawings, wherein:

Fig. 1 is ± 800kV waxy common wheat DC line wet fog natural law is to line flashover rate influence curve；

Fig. 2 is the ± 800kV waxy common wheat DC line wet fog weather coverage influence curve to circuit pollution flashover reliability；

Fig. 3 is ± 800kV waxy common wheat DC line icing natural law is to line flashover rate influence curve；

Fig. 4 is ± 800kV waxy common wheat DC line thunderstorm natural law is to circuit reliability influence curve.

Detailed description of the invention

Below in conjunction with accompanying drawing, for ± 800kV waxy common wheat DC line, the inventive method is described in detail as follows.

A kind of defining method of power transmission line electrical insulation reliability, including following content:

One, whole piece circuit pollution flashover reliability is determined:

(1) dirty district is divided, statistics Ge Wu district salt density value data, corresponding insulator chain configuring condition:

± 800kV waxy common wheat DC line is dirty Division such as Table A-1 completely:

Table A-1 is dirty district line length completely

Carry out filthy division and the design close combination of salt along the line such as shown in Table A-2:

Table A-2 dirty district close design value of salt

To " double; two V string " tower quantity statistics in shaft tower quantity, tangent tower quantity, angle tower quantity and tangent tower in each dirty district such as shown in Table A-3:

The shaft tower statistical result of Table A-3 Ge Wu district

In engineering, the dirty district difference according to shaft tower place have chosen dissimilar and different length or sheet number insulator.Insulator configuration is as follows:

Suspension insulator selects V-type synthesis rod type insulator, and strain insulator adopts disk insulator；

210kN, 300kN, 400kN insulator is the suspension insulator intensity pattern that circuit mainly uses；550kN insulator is the strain insulator intensity pattern that circuit mainly uses.

The disk insulator insulation configuration sheet number of strain insulator-string is such as shown in Table A-4:

The basic configuration of Table A-4 strain insulator-string

Suspension string composite insulator insulation configuration length is such as shown in Table A-5:

This engineering recommendation of Table A-5 different altitude height ± 800kV DC composite insulator insulation configuration

(2) obtain the probability density function of salt density value according to statistical data, calculate and obtain pollution flashover probability, according to train principle, obtain whole piece circuit pollution flashover reliability.Concrete grammar is as follows:

1) calculate an insulator string and the probability P of pollution flashover occurs under the wet weather of mist₁:

$\begin{array}{c}{P}_2\left(\mathrm{\ω}\right)=\frac{1}{\sqrt{2\mathrm{\π}}{\mathrm{\σ}}_j(\mathrm{\ω},\mathrm{\ρ})}{\∫}_{-\mathrm{\∞}}^u{e}^{-\frac{{(U-U_j(\mathrm{\ω},\mathrm{\ρ}\left)\right)}^2}{2{\mathrm{\σ}}_j^2(\mathrm{\ω},\mathrm{\ρ})}}du\\ =\frac{1}{\sqrt{2\mathrm{\π}}}{\∫}_{-\mathrm{\∞}}^{\frac{U-U_j(\mathrm{\ω},\mathrm{\ρ})}{{\mathrm{\σ}}_j(\mathrm{\ω},\mathrm{\ρ})}}{e}^{-\frac{t^2}{2}}dt\end{array}$

In formula: U circuit working voltage (kv)；U_j(ρ) 50% pollution flashover voltage of insulator chain；σ_j(ρ)—U_j(ρ) standard deviation.

2) probability of pollution severity of insulators salt density value is calculated:

$f\left(p\right)=\frac{1}{\sqrt{2\mathrm{\π}\mathrm{\σ}}\mathrm{\ρ}}\exp \[-\frac{(\ln p-\mathrm{\μ})}{2{\mathrm{\σ}}^2}\]$

In formula: ρ is salt density value；μ is the meansigma methods of the logarithm of ρ；σ is the standard deviation of the logarithm of ρ.

3) according to train reliability model, the probability of insulator pollution flashover under a wet fog weather is calculated:

$P^{\′}\left(\mathrm{\ρ}\right)={\∫}_0^{\mathrm{\∞}}f\left(\mathrm{\ρ}\right)P_1\left(\mathrm{\ρ}\right)d\mathrm{\ρ}$

4) the pollution flashover probability of circuit within the scope of wet fog weather under a wet fog weather is calculated:

P_I=1-(1-P'(ρ))^I

In formula: I is the insulator chain number in wet fog weather coverage.

5) flashover strike of annual per 100 km circuit is calculated:

$p=\frac{100M}{H}\·P_I$

In formula: H is the length (km) of whole piece circuit；M is annual mist wet day natural law.

6) flashover strike of different part of paths be weighted obtain average flashover severity rate:

S in formula_KLength for k-th part of path；p_kFlashover strike for k-th part of path.

± 800kV waxy common wheat DC line in 1 year wet fog natural law be respectively grouped the probability such as Table A-6 of the flashover of insulator chain when being 40 days:

Table A-6 pollution flashover probability tables

Consider that wet fog weather coverage is 100km, ruling span 500m, therefore in coverage, tower number is:

N=100/0.5=200

Waxy common wheat is Dan Huita, therefore has 2 groups of insulator chains on every Ji Ta, and total insulator chain number is 400,

The reliability of circuit: 99.98%

The unreliable degree of circuit: 0.02%

The pollution flashover fault rate of circuit: 0.008 time/hundred kilometers years.

As seen from Figure 1, along with wet fog natural law increases, when wet fog natural law changed from 10 70 days, line flashover rate is risen to 0.014 time/hundred kilometers years year by 0.002 time/hundred kilometers, illustrate that the flashover strike of circuit is had a certain impact by year wet fog natural law, but impact is little, and circuit reliability remains at a higher level.

As seen from Figure 2 along with the increase of wet fog weather coverage, circuit reliability is gradually lowered, and when wet fog weather coverage increases to 400km, circuit reliability is reduced to 99.92%.Circuit reliability remains at a higher level, and fault rate is relatively low.

Two, whole piece the ice flash-over in transmission lines reliability is determined:

(1) divide ice formation, add up each ice formation ice covering thickness historical data, salt density value data, corresponding insulator chain configuring condition.

± 800kV waxy common wheat DC line icing zone plotting is shown in following table A-7:

Table A-7 is icing zone plotting situation completely

" double; two V string " tower quantity statistics such as shown in Table A-8 in shaft tower quantity, tangent tower quantity, angle tower quantity and tangent tower in each dirty district:

Table A-8 each ice formation shaft tower statistical result

By corresponding ice formation and dirty district, shaft tower being divided into 12 groups, each group shaft tower is added up as shown in Table A-9:

Table A-9 shaft tower number statistical result

Insulator configuring condition is shown in Table A-4, A-5.

(2) obtain ice covering thickness probability density function according to statistical data, calculate and obtain ice sudden strain of a muscle probability, according to train principle, obtain whole piece the ice flash-over in transmission lines reliability.Concrete grammar is as follows:

1) probability P that an insulator string occurs ice to dodge under the wet weather of mist is calculated₂:

$\begin{array}{c}{P}_2\left(\mathrm{\ω}\right)=\frac{1}{\sqrt{2\mathrm{\π}}{\mathrm{\σ}}_j(\mathrm{\ω},\mathrm{\ρ})}{\∫}_{-\mathrm{\∞}}^u{e}^{-\frac{{(U-U_j(\mathrm{\ω},\mathrm{\ρ}\left)\right)}^2}{2{\mathrm{\σ}}_j^2(\mathrm{\ω},\mathrm{\ρ})}}du\\ =\frac{1}{\sqrt{2\mathrm{\π}}}{\∫}_{-\mathrm{\∞}}^{\frac{U-U_j(\mathrm{\ω},\mathrm{\ρ})}{{\mathrm{\σ}}_j(\mathrm{\ω},\mathrm{\ρ})}}{e}^{-\frac{t^2}{2}}dt\end{array}$

In formula: U circuit working voltage (kv)；U_j50% icing flashover voltage of (ω, ρ) insulator chain；σ_j(ω, ρ) U_jThe standard deviation of (ω, ρ).

2) calculate icing in circuit Designed recurrence period to exceed the probability density function of design load and be:

G (ω)=aexp{-a (ω-u)-exp [-a (ω-u)] }

Wherein a is dimensional parameters, a=1.28255/ σ；U is location parameter,For the average of ice covering thickness, σ is standard deviation.

3) probability calculating the icing occurring Xcm thickness arbitrary year is:

$P_X=\frac{1}{T}a\exp \{-a(X-u)-\exp \[-a(X-u)\]\}\mathrm{\Δ}X$

In formula: T is Designed recurrence period (year)；Δ X is ice covering thickness increment (mm).

4) probability of insulator arc-over in an icing weather is calculated:

$P^{\′}\left(\mathrm{\ω}\right)=\frac{1}{T}{\∫}_0^{\mathrm{\∞}}g\left(\mathrm{\ω}\right)P_2(\mathrm{\ω},\mathrm{\ρ})d\mathrm{\ω}$

5) according to train reliability model, the ice calculating an icing weather line dodges probability:

P_N=1-(1-P'(ω))^N

In formula: N is the insulator chain number of Ice Area.

6) probability of flashover of annual per 100 km circuit is:

$P=\frac{100M}{H}\·P_N$

In formula: H is the length (km) of whole piece circuit, and M is annual icing natural law.

± 800kV waxy common wheat DC line in 1 year icing natural law be respectively grouped when being taken as 15 days insulator chain ice dodge probability such as Table A-10:

Table A-10 ice dodges probability tables

Dodge probability from the ice of each group insulator chain it can be seen that 2 groups, namely the suspension insulator in Zhong Wu district, middle ice formation is the principal element affecting circuit reliability.

Calculating the reliability of circuit and unreliable degree, result of calculation is:

The reliability of circuit: 99.92%

The unreliable degree of circuit: 0.08%

The ice arcing fault rate of circuit: 0.000834 time/hundred kilometers years.

As seen from Figure 3, when icing natural law changed from 0 30 days, the flashover strike of circuit has been increased to 0.0016 time/hundred kilometers years year by 0 time/hundred kilometers, illustrates that the flashover strike of circuit is had a certain impact by the natural law of year icing, but circuit reliability level is significantly high, impact is little.

Three, whole piece circuit lightning stroke flashover reliability is determined:

(1) shaft tower kind and the quantity that circuit adopts, the topography profile situation that statistics circuit is along the line are added up；

Shaft tower model that ± 800kV waxy common wheat DC line utilization rate along the line is higher and account for the percentage of total shaft tower quantity such as shown in Table A-11:

Table A-11 shaft tower model and utilization rate

Circuit landform statistical conditions such as Table A-12 along the line:

Table A-12 DC line is through regional ground inclination angle and earth resistance

(2) base area graphic data, shielding data and counterattack data obtain being subject to thunderbolt to affect the line flashover rate caused, and according to train principle, obtain whole piece circuit lightning stroke flashover reliability.

1) employing is hit from the various shaft tower shielding flashover strike of method calculating ± 800kV waxy common wheat DC line, the various shaft tower of EMTP program computation is adopted to strike back resistance to thunder level and counterattack flashover strike, Z2711 tower head shielding flashover strike is such as shown in Table A-13, and all the other towers in like manner can obtain result.

Table A-13Z2711 tower head shielding flashover strike

Z2711 strikes back resistance to thunder level and counterattack flashover strike such as shown in Table A-14, and all the other towers in like manner can obtain result.

Table A-14Z2711 strikes back Lightning performance result of calculation

2) according to the various shaft tower shielding data obtained, counterattack data, by train reliability model, average shielding (counterattack) flashover strike of circuit is calculated:

${\mathrm{\λ}}^{\′}=\underset{i}{\overset{N}{\Σ}}{\mathrm{\ω}}_i{\mathrm{\λ}}_i$

In formula: N is total tower number；ω_iIt is that i-th kind of tower is at percentage ratio shared completely, λⁱShielding (counterattack) flashover strike of i-th kind of tower.

3) shielding (counterattack) flashover strike of circuit is calculated:

λ_Always=η_{Mountain region}λ'_{Mountain region}+η_Hillsλ'_Hills+η_{Level land}λ'_{Level land}

In formula: η_{Mountain region}For mountain region percentage；η_HillsFor hills percentage；η_{Level land}For level land percentage.

4) the unreliable degree of circuit is calculated:

P_f=λ_Always·H/M

In formula: H is the total length of circuit；M is annual thunderstorm natural law.

± 800kV waxy common wheat the DC line average shielding flashover strike under different terrain, on average strike back flashover strike (by calculating average 80 days thunderstorm days completely) as shown in Table A-15:

Average shielding/counterattack the flashover strike (secondary/100km.a) of Table A-15

As seen from Figure 4, when thunderstorm natural law changed from 0-80 days, the reliability of circuit has been reduced to 0.9862 by 1, and the unreliable degree of circuit has then been increased to 0.0138 by 0, illustrates that the reliability of circuit is had a certain impact by the natural law of year thunderstorm.

Claims (6)

1. the defining method of a power transmission line electrical insulation reliability, it is characterised in that: include following content:

One, the pollution flashover reliability of whole piece circuit is determined:

(1) dirty district, statistics Ge Wu district salt density value data and insulator chain configuring condition are divided；

(2) pollution flashover assessment probability analysis model is set up, it is determined that the pollution flashover reliability of whole piece circuit；

Two, determine that the ice of whole piece circuit dodges reliability:

(1) divide ice formation, add up each ice formation ice covering thickness historical data, salt density value data and insulator chain configuring condition；

(2) set up ice and dodge assessment probability analysis model, it is determined that the ice of whole piece circuit dodges reliability；

Three, the lightning stroke flashover reliability of whole piece circuit is determined:

(1) shaft tower kind and the quantity that circuit adopts, the topography profile situation that statistics circuit is along the line are added up；

(2) the assessment probability analysis model of lightning stroke flashover is set up, it is determined that the lightning stroke flashover reliability of whole piece circuit.

2. a kind of power transmission line electrical according to claim 1 insulation reliability defining method, it is characterised in that: described set up pollution flashover assessment probability analysis model method be:

1) calculate an insulator string and the probability P of pollution flashover occurs under the wet weather of mist₁:

$\begin{array}{c}{P}_1\left(\mathrm{\ρ}\right)=\frac{1}{\sqrt{2\mathrm{\π}}{\mathrm{\σ}}_j\left(\mathrm{\ρ}\right)}{\∫}_{-\mathrm{\∞}}^u{e}^{-\frac{{(U-U_j(\mathrm{\ρ}\left)\right)}^2}{2{{\mathrm{\σ}}_j}^2\left(\mathrm{\ρ}\right)}}du\\ =\frac{1}{\sqrt{2\mathrm{\π}}}{\∫}_{-\mathrm{\∞}}^{\frac{U-U_j\left(\mathrm{\ρ}\right)}{{\mathrm{\σ}}_j\left(\mathrm{\ρ}\right)}}{e}^{-\frac{t^2}{2}}du\end{array}$

In formula: U is circuit working voltage, U_j(ρ) for 50% pollution flashover voltage of insulator chain, σ_j(ρ) for U_j(ρ) standard deviation；

2) probability of pollution severity of insulators salt density value is calculated:

$f\left(p\right)=\frac{1}{\sqrt{2\mathrm{\π}\mathrm{\σ}}\mathrm{\ρ}}\exp \[-\frac{(lnp-\mathrm{\μ})}{2{\mathrm{\σ}}^2}\]$

In formula: ρ is salt density value, μ is the meansigma methods of the logarithm of ρ, and σ is the standard deviation of the logarithm of ρ；

3) probability of insulator pollution flashover under a wet fog weather is calculated:

$P^{\′}\left(\mathrm{\ρ}\right)={\∫}_0^{\mathrm{\∞}}f\left(\mathrm{\ρ}\right)P_1\left(\mathrm{\ρ}\right)d\mathrm{\ρ}$

4) the pollution flashover probability of circuit within the scope of wet fog weather under a wet fog weather is calculated:

P_I=1-(1-P'(ρ))^I

In formula: I is the insulator chain number in wet fog weather coverage；

5) flashover strike of annual per 100 km circuit is calculated:

$p=\frac{100M}{H}\·P_I$

In formula: H is the length of whole piece circuit, M is annual mist wet day natural law；

6) flashover strike of different part of paths be weighted obtain average flashover severity rate:

S in formula_KFor the length of k-th part of path, p_kFlashover strike for k-th part of path.

3. a kind of power transmission line electrical according to claim 1 insulation reliability defining method, it is characterised in that: described set up ice dodge assessment probability analysis model method be:

1) probability P that an insulator string occurs ice to dodge under the wet weather of mist is calculated₂:

$\begin{array}{c}{P}_2\left(\mathrm{\ω}\right)=\frac{1}{\sqrt{2\mathrm{\π}}{\mathrm{\σ}}_j(\mathrm{\ω},\mathrm{\ρ})}{\∫}_{-\mathrm{\∞}}^u{e}^{-\frac{{(U-U_j(\mathrm{\ω},\mathrm{\ρ}\left)\right)}^2}{2{\mathrm{\σ}}_j^2(\mathrm{\ω},\mathrm{\ρ})}}du\\ =\frac{1}{\sqrt{2\mathrm{\π}}}{\∫}_{-\mathrm{\∞}}^{\frac{U-U_j(\mathrm{\ω},\mathrm{\ρ})}{{\mathrm{\σ}}_j(\mathrm{\ω},\mathrm{\ρ})}}{e}^{-\frac{t^2}{2}}dt\end{array}$

In formula: U is circuit working voltage, U_j50% icing flashover voltage that (ω, ρ) is insulator chain, σ_j(ω, ρ) is U_jThe standard deviation of (ω, ρ)；

2) calculate icing in circuit Designed recurrence period and exceed the probability density function of design load:

G (ω)=aexp{-a (ω-u)-exp [-a (ω-u)] }

Wherein a is dimensional parameters, a=1.28255/ σ；U is location parameter, For the average of ice covering thickness, σ is standard deviation；

3) probability arbitrary year the icing of Xcm thickness occurring is calculated:

$P_X=\frac{1}{T}a\exp \{-a(X-u)-\exp \[-a(X-u)\]\}\mathrm{\Δ}X$

In formula: T is the time limit of Designed recurrence period；Δ X is ice covering thickness increment；

4) probability of insulator arc-over in an icing weather is calculated:

$P^{\′}\left(\mathrm{\ω}\right)=\frac{1}{T}{\∫}_0^{\mathrm{\∞}}g\left(\mathrm{\ω}\right)P_2(\mathrm{\ω},\mathrm{\ρ})d\mathrm{\ω}$

5) ice calculating an icing weather line dodges probability:

P_N=1-(1-P'(ω))^N

In formula: N is the insulator chain number of Ice Area；

6) probability of flashover of annual per 100 km circuit is calculated:

$P=\frac{100M}{H}\·P_N$

In formula: H is the length of whole piece circuit, M is annual icing natural law.

4. a kind of power transmission line electrical according to claim 1 insulation reliability defining method, it is characterised in that: described set up lightning stroke flashover assessment probability analysis model method be:

1) average shielding or the counterattack flashover strike of circuit are calculated:

${\mathrm{\λ}}^{\′}=\underset{i}{\overset{N}{\Σ}}{\mathrm{\ω}}_i{\mathrm{\λ}}_i$

In formula: N is total tower number；ω_iIt is that i-th kind of tower is at percentage ratio shared completely, λ_iIt is shielding or the counterattack flashover strike of i-th kind of tower；

2) shielding or the counterattack flashover strike of circuit are calculated:

λ_Always=η_{Mountain region}λ'_{Mountain region}+η_Hillsλ'_Hills+η_{Level land}λ'_{Level land}

In formula: η_{Mountain region}For mountain region percentage；η_HillsFor hills percentage；η_{Level land}For level land percentage；

3) the unreliable degree of circuit is calculated:

P_f=λ_Always·H/M

In formula: H is the total length of circuit；M is annual thunderstorm natural law.

5. the defining method of a kind of power transmission line electrical according to claim 4 insulation reliability, it is characterised in that: the shielding flashover strike of described various towers adopts to hit to calculate from method and obtains.

6. the defining method of a kind of power transmission line electrical according to claim 4 insulation reliability, it is characterised in that: the counterattack flashover strike of described various towers adopts EMTP program computation to obtain.