RU2821018C1 - Grounding device of electrical equipment in soils of high specific resistance - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: grounding device of electrical equipment in soils of high specific resistance is intended for grounding of electrical equipment as protective measures of electrical safety and creation of necessary modes of operation of electrical networks. Physical essence of the coefficient of influence consists in the fact that the spreading current along one, for example, vertical electrode, leads to occurrence of the opposite induction EMF in the adjacent located vertical electrode, thus increasing resistance to spreading current.

EFFECT: reduction of resistance value of grounding device of electrical equipment from climatic effect, as well as reduction of electromagnetic effect from spreading currents in adjacent grounding metal conductors.

1 cl, 2 dwg

Description

The grounding device for electrical equipment in soils of high resistivity is intended for grounding electrical equipment as protective measures for electrical safety and creating the necessary operating modes of electrical networks.

A grounding device and electrical safety protective measures are known [1], consisting of a horizontal grounding conductor, made of a metal strip and laid in a trench, with parameters on average 1×0.5 meters and along the length of the switchgear, as well as vertical grounding conductors made of rolled metal (angle or round section), welded by welding to a horizontal grounding conductor, with a step determined by calculation.

The disadvantage of the grounding device [1] is that it cannot be optimally used in soils with high resistivity.

The depth of installation of the vertical grounding electrode in accordance with the calculation, the total resistance of current spreading through the grounding electrodes (vertical and horizontal) are standardized [1;3]. For example, at electrical substations 10/0.4 kV; 35/10 kV; 110/35/10 kV the resistance of the grounding device is strictly regulated in value based on the PUE [1]. So at substations PO kV and higher there should be no more than 0.5 Ohm. On complex soils with high ohmic resistance, such as rocks, sand, stone, gravel, etc., it is economically and technically difficult to achieve the standard.

A grounding device (GD) [2] on power lines is known. The disadvantage of [2] is that the influence coefficient of adjacent vertical grounding conductors increases the calculated resistance of the grounding device.

Grounding devices [1;2;3] are represented by series-connected resistances of the first and second, consisting of three connected in parallel to each other. The first is part of the total resistance of the desired charger, the resistance value of which reflects the function of the mutual influence of flowing pulse currents in adjacent ground electrodes. The second, consisting of three resistances connected in parallel. The first of the three resistances reflects the magnitude of the resistance as a function of the change in soil conductivity at the site of construction of the charger. The second, of the three resistances, reflects the magnitude of the resistance as a function of the change in the number of vertical grounding structures at the site of construction of the charger. The third, of the three resistances, reflects the magnitude of the resistance as a function of the change in the number of horizontal grounding structures at the site of construction of the charger [1;2;3]. If the values of the three parallel resistances are predictable from the actual amount of rolled metal and the physical and chemical properties of the soil, then the value of the first resistance is a function of the magnitudes and directions of currents in adjacent ground electrodes. The methodology provides for reducing the total value of the resistance of the charger by reducing the value of the first resistance, which depends on the current and its direction, by changing the directions of currents in adjacent ground electrodes.

In particular, costs can be up to a quarter of the cost of the entire facility with a large consumption of metal in the ground. To achieve the goal, one of the measures is to reduce the spacing between the vertical electrodes of the grounding device, which in turn leads to a decrease in the influence coefficient. The influence coefficient is determined according to standard tables [1;2;3], the value of which is in the range from 0.4-0.8. The decrease in the coefficient depends on the decrease in the spacing between the vertical electrodes.

The physical essence of the influence coefficient is that the spreading current along one, for example, a vertical electrode, leads to the appearance of an opposite induced emf in the adjacent vertical electrode, increasing the resistance to the spreading current.

The purpose of the proposed technical solution is to reduce the resistance value of the grounding device of electrical equipment from climatic influences, as well as to reduce the electromagnetic influence from spreading currents in adjacent grounding metal conductors.

The purpose of the technical solution is achieved by the fact that grounding devices for electrical equipment in soils of high resistivity, consisting of horizontal and vertical grounding metal conductors laid to the depth of a more active layer, taking into account climatic drying and freezing of the soil, while the horizontal grounding conductors are located in pairs at a distance from each other , whereby electrical equipment housings are connected to the first direct grounding conductor, and electrical equipment housings are not connected to the second reverse grounding conductor, while the vertical grounding conductors have V or U-shapes, laid with a calculated step along the horizontal grounding conductors, and the ends with the conductors directed downward, in depth, are connected by welding to the first direct horizontal grounding conductor, and the ends of the conductors, directed from bottom to top, are connected by welding to the second reverse grounding conductor.

In the classic design (installation) of vertical electrodes, the potential difference across them is determined [1;2;3]:

where L ₁ H is the inductance of the first vertical electrode;

derivative of the current in the first vertical electrode with respect to time.

component of mutual induction on an adjacent electrode from the current in the second electrode.

We conditionally neglect the active component and assume equality of currents in two adjacent vertical electrodes.

The proposed technical solution is the selection of the design configuration of the grounding device and the distribution of currents in it, which will lead to a decrease in the induced counter EMF.

In the classical sense (we conditionally neglect the active component), the voltage in the vertical electrode (first option):

Taking into account the proposed solution, the voltage will be (second option):

where U _I according to the second option is less than U _I according to the first option.

Sign (in the second version), reflects the direction of the current in one vertical electrode relative to the adjacent vertical electrode.

One vertical electrode (Fig. 1a; b) is connected to a horizontal ground electrode (direct) from electrical equipment, for example, from a power transformer, to the upper head. The other vertical electrode is connected to a horizontal ground electrode (reverse) from the same equipment, but to the lower head.

An innovative approach to the design of grounding devices, which consists in multidirectional distribution of currents in the elements of the charger (to increase the value of the influence coefficient in the calculated resistance), makes it possible to expand the creation of a design range of chargers.

To simplify the presentation of the essence, we consider a system of grounding devices and two vertical electrodes, distant from each other with a certain “step” [1;2;3]. In this case, the task is to create multidirectional spreading currents in the two mentioned electrodes, which reduces the influence of electromagnetic induction of two parallel vertical electrodes, that is, the influence coefficient in the example under consideration will be almost equal to 1.0.

The total resistance of vertical and horizontal electrodes, respectively [1;2;3]:

where R _B (Ohm);

R _g (Ohm);

n is the number of vertical electrodes;

η - influence coefficient.

Resulting resistance of the charger:

where ψ - coefficient takes into account seasonal changes in soil resistivity.

As you can see, with traditional installation component increases the potential, the closer to each other adjacent vertical electrodes are located, the less the influence (0.4 to 0.8), since they are in the denominator, a decrease in their value leads to an increase in the resulting resistance of the charger, which directly increases metal consumption and cost Memory With recommended installation a component with a minus sign means that the potential decreases, that is, at a constant current, the resistance of the charger decreases. The stated principle shows economic efficiency for use in power supply systems located in “bad” soils of the power supply system.

This technical solution is attached (Fig. 2) implementation, in Fig. 1 a; b.

In FIG. 2 given:

1 - horizontal grounding trench;

2 - horizontal grounding conductor (straight);

3 - horizontal grounding conductor (reverse);

4 - vertical grounding conductors;

5 - places of welding connections of vertical and horizontal grounding conductors;

6 - recess for vertical grounding conductors.

Used sources

1. Rules for electrical installations. Sixth and seventh edition. Siberian University Publishing House. 2011 - 484 p.

2. Akhmetshin R.S. Overhead power lines [Text]: textbook/R.S. Akhmetshin, L.M. Rybakov, N.L. Makarova. - Yoshkar-Ola: MarSU, 2014. - 152 p.

3. Akhmetshin R.S.[KiiaflzovA.A.NasibulUnR.T.]MethodIncreasingtheReliabiHtyofthe SoilMeasuredSpecificElectricalResistance in the Field//2019 International Multi-Conference on Industrial Engineering and Modern Technologies//October2019.DOI:10.1109/FarEastCon.2019.8934055 .Hay4Hafl SCOPUS article.

Claims (1)

A grounding device for electrical equipment in soils of high resistivity, consisting of horizontal and vertical grounding metal conductors laid to the depth of the active layer, taking into account climatic drying and freezing of the soil, characterized in that the horizontal grounding conductors are located in pairs at a distance from each other, and to the first direct grounding electrical equipment housings are connected to the conductor, and electrical equipment housings are not subject to connection to the second return grounding conductor, while the vertical grounding conductors have V or U-shapes, laid with a calculated step along the horizontal grounding conductors, and the ends with the conductors directed downward, in depth, are connected by welding to the first direct horizontal grounding electrode, and the ends of the conductors, directed from bottom to top, are connected by welding to the second reverse grounding electrode.

Images