CN108020739A - A kind of method for reducing deep well grounding electrode maximum current density - Google Patents

Abstract

The invention discloses a method for reducing the maximum current density of a deep well ground electrode, which comprises the following steps: S1 determines the parameters of the deep well ground electrode according to the actual situation; S2 performs modeling according to the parameters in S1, and calculates the distribution of the current density of the ground electrode and the distribution of the surface potential ; S3 determines the specification parameters of the auxiliary overflow pole ring according to the actual situation in S1; S4 checks and calculates the deep well ground electrode added to the auxiliary overflow pole ring; S5 calculates whether the step voltage meets the requirements of the regulations, and adjusts the auxiliary pole accordingly ring parameters; S6 determines the scope of influence of the auxiliary polar ring on the environment by comparing the surface potential distribution. This method has the advantages of being simple to implement and having a good inhibitory effect on the deep well grounding electrode with the maximum current density at the top.

Description

A Method of Reducing the Maximum Current Density of Grounding Electrodes in Deep Wells

technical field

The invention relates to the field of high-voltage direct current transmission, in particular to a method for reducing the maximum current density of a deep well ground electrode.

Background technique

Most of the DC transmission projects that have been built today are grounded at the neutral point at both ends of the bipolar. This type of DC transmission system needs to use the grounding electrode to overflow the unbalanced current in the system during normal operation. The rated current or fault current in the system needs to be overflowed through the grounding electrode in the case of a large return line or in the event of a fault. Therefore, in the DC transmission system, the grounding characteristics of the grounding electrode are very important.

The grounding poles in the current HVDC transmission projects that have been built are mainly horizontal shallow buried grounding poles. Only the Pu’er converter station at the sending end of the ±800kV DC transmission project in Nuozhadu power transmission in Guangdong has adopted vertical grounding poles. So far , there is no deep well grounding electrode that has been used in actual engineering. The main advantages of the horizontal shallow-buried grounding electrode are simple construction and good effect on current spillage. The commonly used ring-shaped grounding electrode has even current spillover and no end effect; the disadvantage is that it occupies a large area and requires high pole location. , Usually built in the plains and open areas with few people. In order to solve the problem of site selection for ground electrodes, consider using vertical ground electrodes. The vertical ground electrode occupies less land and does not require a flat topography, so it can greatly reduce the difficulty of site selection for the ground electrode. However, the vertical ground electrode conductor is a linear conductor, with high overflow density at the end, serious heat generation, and difficulty in heat dissipation due to large buried depth. Compared with conventional vertical grounding electrodes, deep wells have fewer conductors, larger embedding depths, and more difficult heat dissipation. It is more important to control the current density at the end. A method for limiting the current density at the end of deep well grounding electrode conductors is proposed.

Contents of the invention

In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides a method for reducing the maximum current density of the deep well ground electrode.

In the present invention, a circular auxiliary overflow pole ring is added above the deep well ground electrode, and part of the current is overflowed through the auxiliary overflow pole ring, thereby reducing the maximum overflow density on the electrode.

The present invention adopts following technical scheme:

A method for reducing the maximum current density of a deep well grounding electrode, comprising the steps of:

S1 determines the parameters of the deep well ground electrode in the actual project. In the prior art, the deep well ground electrode is buried in the deep well, and the deep well is generally filled with coke, and the ground conductor of the deep well ground electrode is inserted in the coke layer. The parameters include the deep well ground electrode. The number, the depth of each deep well, the layout of the deep well, the buried depth and the soil type of the corresponding buried site and the size of the ground electrode overflow flow.

S2 establishes the deep well grounding electrode model in CDEGS according to the parameters determined in S1, and performs simulation calculations on it to obtain the preliminary current distribution and surface potential distribution on the grounding electrode;

S3 determines the parameters for adding the auxiliary overflow electrode ring according to the parameters of the deep well ground electrode in S1, including the size of the auxiliary overflow electrode ring, the embedding depth of the auxiliary overflow electrode ring, and the thickness of the coke layer laid by the auxiliary overflow electrode ring. The flow electrode ring is arranged horizontally, generally located above the deep well ground electrode, or arranged in parallel with the upper end of the deep well ground electrode, and connected with the deep well ground electrode through cables, generally buried at a depth of 3-5 meters.

In S4, an auxiliary overflow pole ring is added to the deep well ground electrode model of CDEGS, and the simulation calculation of the deep well ground electrode is re-calculated to calculate the current distribution on the ground electrode and the distribution of the surface potential, and at the same time calculate the step voltage on the ground surface.

The auxiliary overflow pole ring is arranged above the deep well ground pole conductor.

S5 compares the calculated step voltage with the actual engineering step voltage limit, if the calculated step voltage is greater than the engineering step voltage limit, then repeat S3 to adjust the parameters of the auxiliary overflow pole ring, such as increasing Increase the radius of the pole ring and increase the buried depth, etc.; if the calculated step voltage meets the engineering step voltage limit, proceed to S6.

S6 compares the electric meter potential calculated in S4 with the surface potential without adding the auxiliary overflow pole ring, and determines the range of influence of the addition of the auxiliary overflow pole ring on the surface. Before the auxiliary overflow pole ring is added, the current passes through the deep well ground electrode The spillage is carried out at a place far from the surface, and the impact on the surface is small. After adding the auxiliary overflow pole ring, part of the current overflows from the auxiliary overflow pole ring close to the ground surface, which may increase the impact on the ground surface, so it needs to be evaluated.

The step voltage limit is calculated according to the following formula:

U _max ＝5+0.03ρ _s

Where U _max is the step voltage limit, ρ _s is the resistivity of the soil surface.

Beneficial effects of the present invention:

This method can reduce the maximum current density of the deep well ground electrode, leaving a greater margin for the operation mode of the single pole ground return line of the DC transmission system, and at the same time, the implementation is relatively simple and easy to realize.

Description of drawings

Fig. 1 is a deep well ground electrode model without auxiliary overflow ring;

Figure 2 shows the distribution of overflow density along the grounding electrode conductor when no auxiliary overflow pole ring is added;

Fig. 3 is the grounding electrode model of the deep well after adding the auxiliary overflow electrode ring;

Figure 4 shows the distribution of the overflow density along the grounding electrode conductor after adding the auxiliary overflow pole ring

Fig. 5 is a comparison diagram of the surface potential distribution after adding the auxiliary overflow pole ring and without adding the auxiliary overflow pole ring.

Detailed ways

The present invention will be described in further detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example

A method for reducing the maximum current density of a deep well grounding electrode, comprising the steps of:

S1 Assume that a deep well grounding electrode consists of three deep wells, each deep well is 1000m deep, arranged in an equilateral triangle with a side length of 100m, the buried depth is 4m, and the diameter of the coke layer around the grounding electrode conductor is Φ70 round steel conductor is 550mm. According to the rated current value of the 500MW ±800kV UHV DC transmission system, the ground-to-ground current flowing through the ground electrode is taken as 3125A. Considering that the soil model with low soil resistivity in the lower layer is preferred for site selection of deep well ground electrodes, the typical layered soil model is shown in Table 1:

Table 1 Layered soil resistivity

S2 establishes a deep well grounding electrode model in CDEGS according to the parameters in S1, as shown in Figure 1, and calculates the distribution of overflow current density with the surface of the grounding electrode conductor as shown in Figure 2, and calculates the distribution of surface potential at this time, Figure 5.

In S3, according to the layout of the deep well ground electrode in S1, the radius of the auxiliary overflow pole ring is 57.735m, and the buried depth is 4m. At this time, the auxiliary pole ring is just in contact with the upper end of the deep well ground electrode conductor.

S4 According to the parameters in S3, an auxiliary overflow electrode ring is added to the deep well ground electrode model established in S2. As shown in Figure 3, the radius and buried depth of the auxiliary overflow electrode ring 2 are equal to the radius and buried depth of the deep well ground electrode 1 In this situation, the simulation calculation of the deep well grounding electrode model was carried out again, and the maximum step voltage at this time was calculated to be 2.913V. The calculated overflow current density distribution along the grounding electrode conductor is shown in Figure 4. It can be seen that after adding the auxiliary overflow electrode ring, the maximum current density on the deep well ground electrode conductor is reduced from 8.1A/m ^-2 to 6.9A/m ^-2 , which is about 15% lower.

The S5 step voltage limit is calculated according to the following formula:

U _max ＝5+0.03ρ _s

Among them, U _max is the limit value of step voltage, and ρ _s is the resistivity of the soil surface layer. It is calculated (under) the soil model that the limit value of step voltage is 9.5V, and the step voltage meets the requirements.

Calculate the surface potential distribution after adding the auxiliary overflow pole ring, and the results are shown in Figure 5.

S6 compares the distribution of surface potential with and without auxiliary overflow pole ring, and the results are shown in Figure 5. It can be seen that the impact of adding the auxiliary overflow pole ring on the surrounding environment has no obvious change, and it is almost the same after the distance exceeds 300m.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the embodiment, and any other changes, modifications, substitutions and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (6)

1. A kind of 1. method for reducing deep well grounding electrode maximum current density, it is characterised in that include the following steps：

   S1 determines the parameter of Practical Project middle-deep well earthing pole, and the parameter includes earthing pole conductor parameter, earthing pole buries ginseng Number, soil model and DC transmission system are overflow scattered size of current by earthing pole；

   S2 establishes deep well grounding electrode model according to the parameter determined in S1 in CDEGS, and carries out simulation calculation to it, is connect Preliminary current distributions and surface potential distribution situation on earth polar；

   S3 determines the parameter of addition auxiliary overflow polar ring, including aid in overflow polar ring big according to the parameter of S1 middle-deep well earthing poles Small, the auxiliary overflow polar ring depth of burying and auxiliary overflow polar ring laying coke layer thickness；

   S4, which is established in S2 in deep well grounding electrode model, adds auxiliary overflow polar ring, carries out emulation meter to deep well grounding electrode again Calculate, recalculate current distributions and ammeter Potential distribution situation on earthing pole, while the step voltage for calculating earth's surface is big It is small；

   S5 is calculated step voltage and is compared with the step voltage limit value set in Practical Project, if the electricity that strides being calculated Pressure is more than the step voltage limit value that sets in Practical Project, then the repeatedly parameter of S3, then adjustment auxiliary overflow polar ring, after making calculating Step voltage be less than or equal to step voltage limit value, then carry out S6；

   S6 is contrasted the ammeter current potential that S4 is calculated with not increasing the surface potential of auxiliary overflow polar ring, determines that increase is auxiliary Help scope of the overflow polar ring to earth surface effects.
2. 2. according to the method described in claim 1, it is characterized in that, in the S5, adjustment aids in the parameter of overflow polar ring, specifically For：Increase polar ring radius and the increase depth of burying.
3. 3. according to the method described in claim 1, it is characterized in that, the auxiliary overflow polar ring is arranged on the upper of deep well grounding electrode Side is parallel with the upper end of deep well grounding electrode, and is electrically connected with deep well grounding electrode.
4. 4. according to the method described in claim 1, it is characterized in that, the Practical Project middle-deep well earthing pole conductor parameter is also wrapped Include number, the depth and arrangement form of every mouthful of deep-well of deep well grounding electrode.
5. 5. according to the method described in claim 1, it is characterized in that, the step voltage limit value is calculated according to the following formula：

   U_max=5+0.03 ρ_s

   Wherein U_maxFor step voltage limit value, ρ_sFor upper soll layer resistivity.
6. 6. according to the method described in claim 3, it is characterized in that, 3 meters -5 meters of the auxiliary overflow polar ring depth of burying, horizontal Set.