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
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:
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:
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:
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:
If order
:
R
i=1/G
i=a-bIn(i
i)
Electricity is led and is over the ground:
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
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
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.
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:
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:
(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:
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:
(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:
If order
:
R
i=1/G
i=a-bIn(i
i) (7)
Electricity is led and is over the ground:
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:
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:
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:
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,
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.