CN103901328A

CN103901328A - Method suitable for calculating transmission line pole tower grounding body lightning impulse characteristics

Info

Publication number: CN103901328A
Application number: CN201410117010.3A
Authority: CN
Inventors: 路永玲; 陶风波; 刘洋; 周志成
Original assignee: State Grid Corp of China SGCC; State Grid Jiangsu Electric Power Co Ltd; Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
Current assignee: State Grid Corp of China SGCC; State Grid Jiangsu Electric Power Co Ltd; Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
Priority date: 2014-03-26
Filing date: 2014-03-26
Publication date: 2014-07-02

Abstract

The invention discloses a calculation method suitable for the lightning impact characteristics of the grounding body of a transmission line pole tower. The method is based on circuit theory, and clarifies the calculation formulas of each basic parameter of the grounding body under the impact of lightning current, and uses the existing formula On the basis, combined with the theory of soil spark discharge, the nonlinear spark discharge adopts the calculation model of the dynamic change of circuit parameters, and the calculation idea and method are proposed in the present invention. The non-linear relationship between the current and the ground resistance (conductance) of this section, so as to realize the instantaneous change of the ground resistance with the branch current, taking into account the inductance effect, spark effect and time-varying characteristics of lightning current; at the same time, the calculation process It is simple and intuitive, with a small workload, and the parameters can be changed flexibly, which provides a shortcut for correctly studying the impact characteristics of the grounding body of the tower.

Description

A kind of computing method that are applicable to electric power line pole tower grounding body Lightning Characteristic

Technical field

The present invention relates to a kind of computing method that are applicable to electric power line pole tower grounding body Lightning Characteristic, belong to power technology field.

Background technology

Due to high-frequency and the high steepness of lightning current, make inductance important role in impact characteristics of grounding body, stop electric current to flow to a grounding body distant place, make impulse grounding coefficient be greater than 1, i.e. the inductive effect of lightning current; The amplitude of lightning current is very high, and then increase the electric field intensity in soil, in the time that being greater than the tolerance of soil, this electric field intensity just can there is non-linear puncturing, be equivalent to increase the effective dimensions of grounding body, now impulse earthed resistance is less than power frequency earthing resistance, and this feature is called the spark effect of lightning current; When lightning current injects when grounding body, just each branch's bamboo telegraph along grounding body with the form of ripple, in communication process the voltage and current ripple of each point can be with the difference in travel-time difference, i.e. the time-varying characteristics of lightning current.The calculating of grounding body Lightning Characteristic is not considered to inductive effect and spark effect both at home and abroad simultaneously, consider that inductive effect and spark effect can reflect the time-varying characteristics of grounding body impulse earthed resistance simultaneously.

At present mainly contain four about the theoretical system of Lightning Characteristic: Finite Element Method, transmission line theory, Theory of Electromagnetic Field and Circuit theory.Utilize finite element method matheematical equation, can solve engineering problem, but in impact characteristics numerical evaluation, finite element method thinks that the spark discharge of grounding body surrounding soil is uniformly approx, but in fact the power of spark effect is to change with the instantaneous size of dash current.The model of setting up according to transmission line theory and Theory of Electromagnetic Field can be considered the transient state process of impact characteristics, but two kinds of theories are not all considered the spark effect that grounding body presents under dash current; And Circuit theory can be calculated by setting up the model on road the transient characterisitics of grounding body, but need correct theoretical formula to derive, and non-linear spark discharge will be taken into account.

Summary of the invention

The deficiency existing for prior art, the object of the invention is to provide a kind of computing method that are applicable to electric power line pole tower grounding body Lightning Characteristic of simultaneously considering inductive effect and non-linear spark effect, computation process simple, intuitive, workload is little, parameter can change flexibly, for correct research tower grounding body impact characteristics provides quick means.

To achieve these goals, the present invention realizes by the following technical solutions:

Method of the present invention specifically comprises following step:

(1) the spark discharge region under dash current effect by grounding body, is subdivided into the cylindrical of some sections of different sizes; According to the non-homogeneous transmission line theory that damages, set up grounding body basic circuit model, wherein, R _0i, L _i, C _iand G _ibe respectively every section of grounding body self-resistance, inductance, ground capacitance and over the ground electricity lead;

The calculating that electricity is led over the ground of unit length grounding body

G_{0} = \frac{2 π}{ρ (\ln \frac{l^{2}}{2 hr} - 0.61)}

Wherein, h is the buried degree of depth of grounding body; ρ is grounding body soil resistivity around; R is grounding body radius, can be by the equivalent radius r including bloom in the time that flashing discharges _ireplace; L is grounding body length;

(2) calculate each section of columniform grounding body soil be critical around the current density, J while puncturing _cfor:

J_{c} = \frac{E_{c}}{ρ} = \frac{i_{i}}{2 π {al}_{i}}

Wherein:

E _c=241r ⁰. ²¹⁵

J _ccurrent density while puncturing for soil is critical, E _cfor soil critical breakdown strength, i _ibe the diffusing size of i section, l _ibe i segment length, a is grounding body original radius;

(3) critical current of calculating i section grounding body generation spark discharge is:

i_{c} = \frac{482000 π {al}_{i}}{ρ^{0.785}}

Work as i _i<i _ctime, not flashing electric discharge; Otherwise, flashing electric discharge;

(4) in the time that flashing discharges, its region of discharge is equivalent to good conductor, the equivalent redius of i section spark discharge is:

r_{i} = \frac{{ρi}_{i}}{2 π l_{i} E_{c}}

In formula, i _ichange along with the variation of time, thus equivalent redius also change along with the variation of time, each section of impulse earthed resistance nature temporal evolution;

(5) while calculating spark discharge, the resistance to earth of each section of grounding body is:

\begin{matrix} R_{i} = \frac{1}{G_{i}} = \frac{1}{l_{i} G_{0}} \\ = \frac{ρ (In \frac{l^{2}}{2 {hr}_{i}}) - 0.61}{2 π l_{i}} \\ = \frac{ρ}{2 π l_{i}} [(In \frac{l^{2} π l_{i} E_{c}}{ρ {hi}_{i}}) - 0.61] \\ = \frac{ρ}{2 π l_{i}} [(In \frac{241 π l^{2} l_{i}}{ρ^{0.785} {hi}_{i}}) - 0.61] \\ = \frac{ρ}{2 π l_{i}} [In \frac{241 π l^{2} l_{i}}{ρ^{0.785} h} - {Ini}_{i} - 0.61] \end{matrix}

= \frac{ρ}{2 π l_{i}} (In \frac{241 π l^{2} l_{i}}{ρ^{0.785} h} - 0.61) - \frac{ρ}{2 π l_{i}} In i_{i}

If order

\frac{ρ}{2 π l_{i}} (In \frac{241 π l^{2} l_{i}}{ρ^{0.785} h} - 0.61), b = \frac{ρ}{2 π l_{i}},

:

R _i=1/G _i=a-bIn(i _i)

Electricity is led and is over the ground:

G_{i} = \frac{1}{a - bIn (i_{i})}

Wherein a, b is the undetermined coefficient that is greater than 0;

Thereby, determine that each section of grounding body is in spark discharge process, electric current and resistance to earth/nonlinear relationship between electric leading over the ground, utilizes this relation can realize the calculating of Lightning Characteristic.

In step (1), grounding body Parameter Calculation formula is as follows:

(1a) calculating of every section of grounding body self-resistance

R_{0} = \frac{1}{2 πr} \sqrt{\frac{ωμ}{2 σ}}

R _oi=R _o*l _i

In formula, R _ofor unit length grounding body self-resistance, σ is the conductivity of grounding body own, the magnetic permeability that μ is grounding body, and ω is dash current equivalence angular frequency;

(2a) calculating of every section of grounding body inductance

L_{0} = \frac{μ_{0}}{2 π} (\ln \frac{2 l}{r} - 1)

L _i=L _o*l _i

In formula, L _ofor unit length grounding body inductance, μ ₀for permeability of vacuum;

(3a) calculating of every section of grounding body ground capacitance

C ₀=e ₀e _rrG ₀

C _i=C _o*l _i

In formula, C _ofor unit length grounding body ground capacitance, ε ₀for permittivity of vacuum, ε _rfor soil relative dielectric constant, ε ₀ε _rbe the specific inductive capacity that is filled in grounding body surrounding soil.

The present invention can truly reflect lightning current impact process on grounding body, comprises the time-varying characteristics of inductive effect, spark effect and impact characteristics; Meanwhile, this computation process simple, intuitive, workload is little, and parameter can change flexibly, for correct research tower grounding body impact characteristics provides quick means.

Brief description of the drawings

Fig. 1 is the spark discharge district schematic diagram of single horizontal grounding objects;

Fig. 2 is the isoboles in spark region;

Fig. 3 is the grounding body circuit model of considering transient process;

Fig. 4 is the circuit model of considering inductive effect and non-linear spark discharge.

Embodiment

For technological means, creation characteristic that the present invention is realized, reach object and effect is easy to understand, below in conjunction with embodiment, further set forth the present invention.

1, set up the equivalent-circuit model of non-linear spark discharge

Under lightning current impacts, the electric field intensity producing in soil can be calculated as follows:

E=ρJ （1）

Wherein ρ is the resistivity of soil of contacting with grounding body, and J is the diffusing density in soil.In the time that the field intensity of lightning current generation exceedes the withstand voltage of soil, grounding body soil around can puncture, and produces strong spark discharge, has been equivalent to increase the radius of grounding body, and diffusing effect is strengthened; The equivalent radius of transient state process of grounding body is taken as the equivalent radius at place place of spark discharge district.

The initial electric discharge field intensity of soil E _calong with the increase of soil resistivity increases, its data are well below the breakdown field strength of air.Adopt the initial breakdown field strength of soil of E.E.Oettle proposition and the relation of resistivity:

E _c=241r ⁰. ²¹⁵ （2）

In formula, the unit of Ec is kV/m, and the unit of ρ is Ω m.

The big or small time to time change of dash current causes the severe degree of spark discharge also to change along with the time, and the frequency of lightning current is very high in addition, and therefore conductor induction reactance is very large, hinders electric current wandering to other one end along grounding body.Earial drainage just because of each position along grounding body is inhomogeneous, and the equivalent radius of spark discharge in transient state process is just different, has maximum equivalent radius at grounding body electric current decanting point, along with larger from decanting point distance, equivalent radius is less, and whole breakdown area presents taper, as shown in Figure 1.In order to facilitate the calculating of circuit parameter, cremate district is subdivided into regular small cylindrical, as Fig. 2.In order to improve simulation nicety, segmentation hop count is abundant, and in figure, a is grounding body original radius, r _iit is the equivalent redius of i section.

Have for every a bit of cylindrical grounding body:

J_{c} = \frac{E_{c}}{ρ} = \frac{i_{i}}{2 π {al}_{i}} - - - (3)

Wherein J _ccurrent density while puncturing for soil is critical, E _cfor soil critical breakdown strength, i _ibe the diffusing size of i section, l _irefer to i segment length.Convolution (6) and (7) are tried to achieve i section grounding body and are produced the critical electric current value of spark discharge and be again:

i_{c} = \frac{482000 π {al}_{i}}{ρ^{0.785}}

（4）

Work as i _i<i _ctime, not flashing electric discharge; Otherwise, flashing electric discharge, and the equivalent redius of i section spark discharge is:

r_{i} = \frac{{ρi}_{i}}{2 π l_{i} E_{c}}

Because i _ichange along with the variation of time, thus equivalent redius also change along with the variation of time, impulse earthed resistance nature temporal evolution.

Unit length over the ground electricity is led formula and is:

G_{0} = \frac{2 π}{ρ (\ln \frac{l^{2}}{2 hr} - 0.61)}

（6）

The resistance to earth that simultaneous formula (2), (3), (5) and (6) can obtain i article of branch road with the variation pass of branch current is:

\begin{matrix} R_{i} = \frac{1}{G_{i}} = \frac{1}{l_{i} G_{0}} \\ = \frac{ρ (In \frac{l^{2}}{2 {hr}_{i}}) - 0.61}{2 π l_{i}} \\ = \frac{ρ}{2 π l_{i}} [(In \frac{l^{2} π l_{i} E_{c}}{ρ {hi}_{i}}) - 0.61] \\ = \frac{ρ}{2 π l_{i}} [(In \frac{241 π l^{2} l_{i}}{ρ^{0.785} {hi}_{i}}) - 0.61] \\ = \frac{ρ}{2 π l_{i}} [In \frac{241 π l^{2} l_{i}}{ρ^{0.785} h} - {Ini}_{i} - 0.61] \\ = \frac{ρ}{2 π l_{i}} (In \frac{241 π l^{2} l_{i}}{ρ^{0.785} h} - 0.61) - \frac{ρ}{2 π l_{i}} I {ni}_{i} \end{matrix}

If order

\frac{ρ}{2 π l_{i}} (In \frac{241 π l^{2} l_{i}}{ρ^{0.785} h} - 0.61), b = \frac{ρ}{2 π l_{i}},

:

R _i=1/G _i=a-bIn(i _i) （7）

Electricity is led and is over the ground:

G_{i} = \frac{1}{a - bIn (i_{i})}

Wherein a, b is the undetermined coefficient that is greater than 0; Determine that thus every a bit of earth conductor is in spark discharge process, the nonlinear relationship between this section of electric current and this section of resistance to earth (electricity is led).

In order to realize above nonlinear relationship, just need to calculate in each moment the new equivalent radius of each section of grounding body according to the current value of tried to achieve each node, can make the resistance to earth of this section by program means was a fixed value for this reason before critical current; And reaching critical current back-pushed-type (7) variation, thus be grounded the transient change of electrical resistance branch current, by inductive effect, the time varying characteristic of spark effect and lightning current is taken into account simultaneously.

For example in ATPDraw, introduce MODELS module, as Fig. 4.G in figure _iwith i _ivariation and the moment change, as long as collect i _isize, just can change the size of every section of grounding body resistance to earth, wherein MODELS embeds following program:

MODEL ModelDef

INPUT i1

OUTPUT o1

VAR o1

INIT

o1:=0

ENDINIT

EXEC

if i1>ic then

o1:=a-b*ln(i1)

else o1:=R(0)

endif

ENDEXEC

ENDMODEL

2, set up complete impact characteristics circuit model

As shown in Figure 3, under the effect of dash current, grounding body can be regarded the non-homogeneous transmission line that damages as, and grounding body is divided into a lot of segments, and each section of grounding body can be regarded as by R _0i, L _i, C _iand G _ithe equivalent circuit of composition; If spark effect is taken into account, obtain complete impact characteristics computation model, see Fig. 4.The Parameter Calculation formula of constituent parts length is as follows:

1) calculating of unit length grounding body self-resistance

The size of unit length grounding body resistance depends primarily on size and the conductor resistance rate of itself, with whether have spark effect irrelevant, but because lightning current equivalent frequency is very high, in the time flowing through grounding body, there is obvious skin effect on its surface, now the resistance of grounding body can become greatly, considers that the unit conductor resistance computing formula of lightning current high frequency characteristics has:

R_{0} = \frac{1}{2 πr} \sqrt{\frac{ωμρ}{2}}

In formula, r is grounding body radius; R is the resistivity of metallic conductor own; M is the magnetic permeability of conductor; W is dash current equivalence angular frequency.To general iron and steel grounding body, test real side result between 0.04-0.05 Ω/m.

2) calculating of unit length grounding body inductance

Under lightning current percussive action, the inductance of magnetic linkage and current ratio is no longer a constant, but an amount with wave process dynamic change.In the process of propagating before wave direction, when the initial time that shock wave injects from conductor head end, conductor head end unit length dynamic inductance value is about stablizes 58% of inductance, and in the time that wave head arrives conductor ends, this value is close to 90%, and now dynamic inductance levels off to corresponding stable state inductance.The stable state inductance of unit length grounding body is calculated as follows:

L_{0} = \frac{μ_{0}}{2 π} (\ln \frac{2 l}{r} - 1)

3) the unit length grounding body calculating that electricity is led over the ground

Unit length over the ground electricity is led formula and is:

G_{0} = \frac{2 π}{ρ (\ln \frac{l^{2}}{2 hr} - 0.61)}

Wherein h is the buried degree of depth of grounding body, and ρ is grounding body soil resistivity around; R is grounding body radius, under large electric current, in soil, non-linear puncturing occurs, and considers that the pressure drop in arc discharge area and spark region is very little, and the radius r in this formula must replace with the equivalent radius including bloom.The lightning current instantaneous value that is strongly subject to of spark discharge must affect, so equivalent radius temporal evolution, to lead be also time dependent nonlinear parameter to electricity over the ground.

4) calculating of unit length grounding body ground capacitance

Under power frequency steady-state current, the calculating formula of unit length grounding body ground capacitance is as follows:

C ₀=e ₀e _rrG ₀

In formula, ε ₀for permittivity of vacuum; ε _rfor soil relative dielectric constant; ε ₀ε _rbe and be filled in grounding body

The specific inductive capacity of surrounding soil, general value is 9 × 8.86 × 10 ^-12.

In general soil (m), grounding body size is limited for ρ=10～1000 Ω,

\frac{ω C_{0}}{G_{0}} = 2 πfϵρ = \frac{2 π}{4 \times 2.6 \times 10^{- 6}} \times 9 \times 8.86 \times 10^{- 12} \times (10 ~ 1000) \approx 4.8 \times 10^{- 4} ~ 4.8 \times 10^{- 2}

Can be found out G completely by result of calculation ₀effect than C ₀effect much bigger, now can be by C ₀ignore over time.

More than show and described ultimate principle of the present invention and principal character and advantage of the present invention.The technician of the industry should understand; the present invention is not restricted to the described embodiments; that in above-described embodiment and instructions, describes just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and these changes and improvements all fall in the claimed scope of the invention.The claimed scope of the present invention is defined by appending claims and equivalent thereof.

Claims

1. A calculation method applicable to the lightning impulse characteristics of the transmission line pole tower grounding body is characterized in that it specifically comprises the following steps:

(1) Subdivide the spark discharge area of the grounding body under the action of the impact current into several cylindrical sections of different sizes; according to the theory of non-uniform lossy transmission lines, establish the basic circuit model of the grounding body, where R _0i , L _i , C _i and G _i are the resistance, inductance, capacitance to ground and conductance to ground of each grounding body, respectively;

Calculation of unit length grounding body to ground conductance

{G G}_{00} = = \frac{22 π π}{ρ ρ ((ln ln \frac{{l l}^{22}}{22 hr hr} - - 0.61 0.61))}

Among them, h is the buried depth of the grounding body; ρ is the resistivity of the soil around the grounding body; r is the radius of the grounding body, which can be replaced by the equivalent radius r _i including the spark area when spark discharge occurs; l is the length of the grounding body ;

(2) Calculate the current density J _c of each section of cylindrical grounding body when critical breakdown occurs in the surrounding soil as:

{J J}_{c c} = = \frac{{E E.}_{c c}}{ρ ρ} = = \frac{{i i}_{i i}}{22 π π {al al}_{i i}}

in:

E _c =241r ⁰ . ²¹⁵

J _c is the current density at the critical breakdown of the soil, E _c is the critical breakdown field strength of the soil, i _i is the size of the scattered flow of the i-th section, l _i is the length of the i-th section, and a is the original radius of the grounding body;

(3) Calculate the critical current of the spark discharge generated by the i-th section grounding body as:

{i i}_{c c} = = \frac{482000482000 π π {al al}_{i i}}{{ρ ρ}^{0.785 0.785}}

That is, when i _i < _ic , spark discharge does not occur; otherwise, spark discharge occurs;

(4) When a spark discharge occurs, the discharge area is equivalent to a good conductor, then the equivalent radius of the i-th spark discharge is:

{r r}_{i i} = = \frac{{ρi ρi}_{i i}}{22 π π {l l}_{i i} {E E.}_{c c}}

In the formula, i _i changes with time, so the equivalent radius also changes with time, and the impact grounding resistance of each segment naturally changes with time;

(5) When calculating the spark discharge, the resistance to ground of each grounding body is:

\begin{matrix} {R R}_{i i} = = \frac{11}{{G G}_{i i}} = = \frac{11}{{l l}_{i i} {G G}_{00}} \\ = = \frac{ρ ρ ((In In \frac{{l l}^{22}}{22 {hr hr}_{i i}})) - - 0.61 0.61}{22 π π {l l}_{i i}} \\ = = \frac{ρ ρ}{22 π π {l l}_{i i}} [[((In In \frac{{l l}^{22} π π {l l}_{i i} {E E.}_{c c}}{ρ ρ {hi hi}_{i i}})) - - 0.61 0.61]] \\ = = \frac{ρ ρ}{22 π π {l l}_{i i}} [[((In In \frac{241241 π π {l l}^{22} {l l}_{i i}}{{ρ ρ}^{0.785 0.785} {hi hi}_{i i}})) - - 0.61 0.61]] \\ = = \frac{ρ ρ}{22 π π {l l}_{i i}} [[In In \frac{241241 π π {l l}^{22} {l l}_{i i}}{{ρ ρ}^{0.785 0.785} h h} - - {Ini ini}_{i i} - - 0.61 0.61]] \\ = = \frac{ρ ρ}{22 π π {l l}_{i i}} ((In In \frac{241241 π π {l l}^{22} {l l}_{i i}}{{ρ ρ}^{0.785 0.785} h h} - - 0.61 0.61)) - - \frac{ρ ρ}{22 π π {l l}_{i i}} I I {ni ni}_{i i} \end{matrix}

Ruoling

\frac{ρ}{2 π l_{i}} (In \frac{241 π l^{2} l_{i}}{ρ^{0.785} h} - 0.61), b = \frac{ρ}{2 π l_{i}},

but:

R _i =1/G _i =a-bIn(i _i )

Conductance to ground is:

{G G}_{i i} = = \frac{11}{a a - - bIn bIn (({i i}_{i i}))}

Where a and b are undetermined coefficients greater than 0;

Therefore, the nonlinear relationship between the current and the ground resistance/conductance of each grounding body during the spark discharge process is determined, and the calculation of the lightning impulse characteristics can be realized by using this relationship.

2. according to claim 1, be applicable to the calculation method of the lightning impulse characteristic of transmission line tower grounding body, it is characterized in that,

In step (1), the calculation formula of the basic parameters of the grounding body is as follows:

(1a) Calculation of the resistance of each grounding body

{R R}_{00} = = \frac{11}{22 πr πr} \sqrt{\frac{ωμ ωμ}{22 σ σ}}

R _oi =R _o *l _i

In the formula, R _o is the resistance of the grounding body itself per unit length, σ is the electrical conductivity of the grounding body itself, μ is the magnetic permeability of the grounding body, and ω is the equivalent angular frequency of the impulse current;

(2a) Calculation of the inductance of each grounding body

{L L}_{00} = = \frac{{μ μ}_{00}}{22 π π} ((ln ln \frac{22 l l}{r r} - - 11))

L _i =L _o *l _i

In the formula, L _o is the grounding body inductance per unit length, μ ₀ is the vacuum permeability;

(3a) Calculation of the ground capacitance of each ground body

C ₀ =e ₀ e _r rG ₀

C _i =C _o *l _i

In the formula, C _o is the capacitance of the grounding body to the ground per unit length, ε ₀ is the vacuum dielectric constant, ε _r is the relative dielectric constant of the soil, and ε ₀ ε _r is the dielectric constant of the soil filled around the grounding body.