CN105403797A - Ohm law-based evaluation method of soil ionization critical electric field intensity - Google Patents

Abstract

The invention discloses an ohm law-based evaluation method of soil ionization critical electric field intensity. The evaluation method comprises following steps of selecting a to-be-tested region and measuring resistivity, dielectric constant and magnetic permeability of soil in the region; establishing an to-the-ground discharging loop; arranging a test electrode; acquiring test voltage; converting the test voltage into electric field intensity; determining ionization time of the soil according to through of the function K; and obtaining the maximum changing curve of the electric filed intensity in the soil and determining the soil ionization critical electric field intensity by combining the precise ionization time of the soil. According to the invention, by directly testing the to-be-tested region of the soil, natural features of the soil will not be damaged; the obtained soil ionization critical electric field intensity is completely the same as the soil ionization critical electric field intensity in the natural environment; and high precision measurement can be realized.

Description

Based on the method for estimation of the soil ionization critical electric field strength of Ohm law

Technical field

The present invention relates to the method for estimation of a kind of soil ionization critical electric field strength, particularly relate to the method for estimation of a kind of soil based on Ohm law ionization critical electric field strength.

Background technology

The shock response of earthed system is different from the response in power current situation, when the electric field intensity in earthed system surrounding soil exceedes critical electric field strength E _c, soil will start ionization, and soil resistivity reduces simultaneously, and then causes impulse resistance to reduce.Therefore, soil ionization critical electric field strength E _cmost important for assessment earthed system performance.

The achievement in research of forefathers gives a lot about critical electric field strength E _creference value and scope.Such as: Oettle advises E _cvalue is taken as 1MV/m, is 600-800kV/m for the soil that water cut is higher; Mousa thinks and should be changed to 600-1850kV/m, considers the heterogeneity of field soil environment, and the soil that suggestion water cut is higher is 300-400kV/m; In addition, Mousa and Liew all thinks and can think 300kV/m for the critical electric field strength of typical soil.

But, obviously, soil critical electric field strength E _cshould change along with the change of soil types, even if same soil, along with the change of the factors such as water cut, temperature, season also can change to some extent, therefore, only have reference value and scope obviously inadequate.Therefore, scholars have carried out the research determining soil critical electric field strength method.Such as: Gonos and Stathopulos have studied E _cfor the change of soil resistivity; N.MohanmadNor etc. build pulse current test circuit, and the closed-loop formed by analyzing V-I curve judges and obtains E _c; T.K.Manna and P.Chouhuri tests for multiple soil, sums up the various soil critical electric field strength E of estimation _cformula; F.E.Asimakopoulou etc. analyze the uncertain factor of soil ionization, and under giving these uncertain factor situations of consideration, the voltage breakdown of critical electric field strength is estimated; The present inventor proposes tangential electric field method in recent years for estimating critical electric field strength.

Existing various technology is all build the critical electric field strength that experiment test circuit obtains soil ionization, therefore, when soil just ionizes in very little scope or region, then these class methods are difficult to find, that is, just must can obtain the change of electric signal when ionization largely occurs soil, but electric field intensity now in soil is large more than actual critical electric field strength, therefore can cause obvious error.

In addition, if build test circuit, test after soil collecting, the natural characteristic of soil such as water cut, temperature, caused by soil density etc. then must be caused to be seriously damaged, therefore, even if obtain measuring very accurately in test circuit, obtain data very accurately, now these data are also difficult to reflect the truth of soil critical electric field strength under physical environment.

Summary of the invention

Object of the present invention is just to provide a kind of soil based on Ohm law to ionize the method for estimation of critical electric field strength to solve the problem.

The present invention is achieved through the following technical solutions above-mentioned purpose:

Based on a method of estimation for the soil ionization critical electric field strength of Ohm law, comprise the following steps:

(1) selected test zone, and measure the resistivity of this regional soil, specific inductive capacity and magnetic permeability;

(2) discharge loop is over the ground built: be embedded in soil by a center-point earth pole and four the auxiliary earth poles be distributed in around center-point earth pole in this region, adopt pulse current source to central earthing pole direct feed, four auxiliary electrodes are used for setting up current return;

(3) test electrode is set: multiple electric field intensity sampled point is set straight down in the scope of distance center-point earth pole 0.03-0.08m, sampled point spacing is 0.183m, selects the tangential direction of any sampled point in multiple electric field intensity sampled point to arrange two test electrodes;

(4) collecting test voltage: pulse current source discharges over the ground, gathers the voltage between two test electrodes;

(5) test voltage is converted into electric field intensity;

(6) according to the time of the first wave trough position determination soil ionization as minor function K:

$K={(-\frac{d\left(\mathrm{\η}\right(t\left)\right)}{dt})}^{-1}$

In above formula, η represents soil ionization and the ratio of the tangential electric field intensity of this test point in unionized situation, is ratio η and differentiates to time t and get negative value again in function K bracket;

(7) according to the maximal value change curve of electric field intensity in each moment soil of theory calculate, then time corresponding to associative function K first trough value determine soil ionization critical electric field strength.

In said method, (3) step and (6) step are innovation emphasis of the present invention, and other step independent solution is all conventional method, are also one of innovations by combining in steps.

As preferably, in described step (3), 5 electric field intensity sampled points are set straight down in the position of distance center-point earth pole 0.061m, wherein the sampled point distance ground 0.915m of bottom.

Beneficial effect of the present invention is:

The present invention adopts the mode of directly testing in soil testing region, can not spoiled soil natural characteristic, so the truth of soil critical electric field strength is completely the same under the soil critical electric field strength measured and physical environment, can realize high-acruracy survey.

Accompanying drawing explanation

Fig. 1 is the structural representation of discharge loop over the ground of the present invention;

Fig. 2 is the installation site schematic diagram of test electrode of the present invention;

Fig. 3 is the tangential electric field strength profile schematic diagram in embodiment in sampled point P3 unionized situation;

Fig. 4 is the tangential electric field strength profile schematic diagram in embodiment in sampled point P3 ionization situation;

Fig. 5 is the oscillogram of P3 point function K of the present invention.

Embodiment

Below in conjunction with drawings and Examples, the invention will be further described:

As shown in Figure 1, the method for estimation of the ionization of the soil based on Ohm law critical electric field strength of the present invention comprises the following steps:

(1) selected test zone, and measure the resistivity of this regional soil, specific inductive capacity and magnetic permeability;

(2) discharge loop is over the ground built: as shown in Figure 1, in this region a center-point earth pole 2 and four the auxiliary earth poles 1 be distributed in around center-point earth pole 2 are embedded in soil, adopt pulse current source to the direct feed of central earthing pole 2, four auxiliary electrodes 1 are for setting up current return, and the distance between the auxiliary earth pole 1 of this example and center-point earth pole 2 is 2.12m; Also show soil horizon 4 and air layer 3 in Fig. 1, be convenient to understand vividerly;

(3) test electrode is set: as shown in Figure 2, in the position of distance center-point earth pole 0.061m (also can be other distance in 0.03-0.08m), 5 electric field intensity sampled points are set straight down, i.e. P0, P1, P2, P3, P4, each sampled point spacing is 0.183m, wherein the sampled point P4 distance ground 0.915m of bottom, selects the tangential direction of any sampled point in 5 electric field intensity sampled points P0, P1, P2, P3, P4 to arrange two test electrodes; Here 5 electric field intensity sampled points are preferably, also can select the electric field intensity sampled point of other quantity as required;

(4) collecting test voltage: pulse current source discharges over the ground, gathers the voltage between two test electrodes;

(5) test voltage is converted into electric field intensity;

(6) according to the time of the first wave trough position determination soil ionization as minor function K:

$K={(-\frac{d\left(\mathrm{\η}\right(t\left)\right)}{dt})}^{-1}$

In above formula, η represents soil ionization and the ratio of the tangential electric field intensity of this test point in unionized situation, is ratio η and differentiates to time t and get negative value again in function K bracket;

(7) according to the maximal value change curve of electric field intensity in each moment soil of theory calculate, then time corresponding to associative function K first trough value determine soil ionization critical electric field strength.

In said method, the acquisition process of the function K of (6) step is as follows:

If pulse current source waveform is double-exponential function waveform, function expression is as follows:

I＝(I ₀×(e ^-At-e ^-Bt)

Wherein, I ₀=8000, A=7.714 × 10 ⁴μ s, B=2.489 × 10 ⁵μ s;

So, according to electromagnetic theory, electric field intensity in isotropy, linear conducting medium and current density between there is the Ohm law relation of following differential form:

In formula, σ is the conductivity of soil, represent electric field intensity.When soil electric field intensity meets or exceeds critical electric field strength, resistivity diminishes, and namely in formula, conductivityσ increases, and soil conductivity characteristic strengthens.Suppose that certain soil conductivity is σ ₀no matter electric field intensity is much in soil, soil does not ionize all the time, then, in this situation, in soil, earthing pole near zone current density and this region electric field intensity should meet following formula:

In formula (1), σ ₀for the conductivity in the unionized situation of soil, represent the electric field intensity in the unionized situation of soil.

When ionization occurs soil, following relational expression is had to set up:

In formula (2), σ _ifor the conductivity in soil ionization situation, represent the electric field intensity in soil ionization situation.

Formula (1) and formula (2) are divided by, have following relation to set up:

From above formula, the molecule of both members all can be used as known quantity, obtain, therefore, as long as can determine by actual measurement σ can be obtained _ichange curve, simultaneously can obtain σ _iin the moment changed, namely there is the moment of ionization in soil.

Meanwhile, if processing procedure adopts current source, regardless of external circuits, its output current intensity is similar to constant, therefore just presses close to regard to earthing pole region, following relation should be had to set up in the moment that soil has just occurred to ionize:

So by (4) formula, can be by (3) formula abbreviation:

σ is obtained by formula (5) _iabout the electric field intensity in soil ionization situation with the electric field intensity in unionized situation relation:

According to the Research Literature of LIEW, in ionization situation, following nonlinear function is obeyed in soil resistivity change:

${\mathrm{\ρ}}_i={\mathrm{\ρ}}_0{e}^{(-t/{\mathrm{\τ}}_1)}---\left(7\right)$

In formula, ρ ₀for soil unionized time initial electrical resistivity, τ ₁for ionization time constant, there is the moment of ionization in t=0 and corresponding soil.Associating (6) and (7), can obtain about timeconstantτ ₁nonlinear function:

Order then (8) formula both sides are obtained time t differentiate:

$-\frac{1}{{\mathrm{\τ}}_1}{e}^{(-\frac{t}{{\mathrm{\τ}}_1})}=\frac{d\left(\mathrm{\η}\right(t\left)\right)}{dt}$

As t=0, namely when ionization occurs soil, have

${\mathrm{\τ}}_1={(-\frac{d\left(\mathrm{\η}\right(t\left)\right)}{dt}{|}_{t=0})}^{-1}---\left(9\right)$

The moment that can be ionized soil by (9) and t=0, determine τ ₁.Data analysis is from behind visible, is positioned at curve in fact in the t=0 moment first trough point, the position of this trough both can help us to determine τ ₁, also can help to determine critical electric field strength E _c.

Because the location comparison of sampled point is close, the electric field intensity information therefore gathered on these aspects is all quite similar, therefore uses the electric field intensity map of wherein sampled point P3 to describe the change of electric field intensity in ionization and unionized situation.

Embodiment:

With soil A (σ=0.02S/m, E in LIEW document _c=110kV/m, τ ₁=2.0 μ s) be example, soil A ionization and unionized situation under electric field intensity as shown in Figure 3 and Figure 4.

Obtain function thus curve map is (order as shown in Figure 5 ).

For unionized uniform soil, the electric field intensity of sampled point P3 can be obtained by theory calculate.The critical electric field strength of maximum field intensity and the ionization of corresponding soil in the soil that the P3 point K function first valley point moment is corresponding, for the critical electric field strength estimated value of all sampled points of P0-P4 and error log in following table 1.

Table 15 sampled point estimated value and error thereof

Above-described embodiment is preferred embodiment of the present invention; it is not the restriction to technical solution of the present invention; as long as without the technical scheme that creative work can realize on the basis of above-described embodiment, all should be considered as falling within the scope of the rights protection of patent of the present invention.

Claims (2)

1., based on a method of estimation for the soil ionization critical electric field strength of Ohm law, it is characterized in that: comprise the following steps:

(1) selected test zone, and measure the resistivity of this regional soil, specific inductive capacity and magnetic permeability;

(2) discharge loop is over the ground built: be embedded in soil by a center-point earth pole and four the auxiliary earth poles be distributed in around center-point earth pole in this region, adopt pulse current source to central earthing pole direct feed, four auxiliary electrodes are used for setting up current return;

(3) test electrode is set: multiple electric field intensity sampled point is set straight down in the scope of distance center-point earth pole 0.03-0.08m, sampled point spacing is 0.183m, selects the tangential direction of any sampled point in multiple electric field intensity sampled point to arrange two test electrodes;

(4) collecting test voltage: pulse current source discharges over the ground, gathers the voltage between two test electrodes;

(5) test voltage is converted into electric field intensity;

(6) according to the time of the first wave trough position determination soil ionization as minor function K:

$K={(-\frac{d\left(\mathrm{\η}\right(t\left)\right)}{dt})}^{-1}$

In above formula, η represents soil ionization and the ratio of the tangential electric field intensity of this test point in unionized situation, is ratio η and differentiates to time t and get negative value again in function K bracket;

(7) according to the maximal value change curve of electric field intensity in each moment soil of theory calculate, then time corresponding to associative function K first trough value determine soil ionization critical electric field strength.

2. the method for estimation of the ionization of the soil based on Ohm law critical electric field strength according to claim 1, it is characterized in that: in described step (3), 5 electric field intensity sampled points are set straight down in the position of distance center-point earth pole 0.061m, wherein the sampled point distance ground 0.915m of bottom.