Scientific Paper / Artículo Científico


pISSN: 1390-650X / eISSN: 1390-860X





Wilo Chiliquinga1 , Pablo Robles 2,*


Received: 23-05-2022, Received after review: 13-06-2022,  Accepted: 22-06-2022, Published: 01-07-2022




For designing and studying an electrical substation grounding system [GS], a simple remote substation is considered according to the safety procedures indicated in the IEEE 80 Standard. Buried metallic materials or nearby metallic structures permanently endanger human life when electrical faults occur. Scenarios related to the design of electrical substations that consider the transfer of electrical potentials that can occur between GS and buried metallic materials in their vicinity are presented, the behavior of potential transfer is evaluated, values of transferred voltages are calculated, and the main variables that influence the transferred voltage levels are identified. The simulations are performed with the CYMGRD program specific for GS calculations. Its analysis generates actual results in the potential transfer that must be considered by the GS design engineer, which leads to avoiding designing isolated substations without taking into account existing elements that may affect the substation contour.

Para el diseño y el estudio de un sistema de puesta a tierra de subestaciones eléctricas [GS], se considera una subestación remota simple según los procedimientos de seguridad indicados en la norma IEEE 80. Los materiales metálicos enterrados o las estructuras metálicas cercanas ponen en peligro permanente la vida humana cuando se producen fallos eléctricos. Se presentan escenarios relacionados con el diseño de subestaciones eléctricas que consideran la transferencia de potenciales eléctricos que puede producirse entre la GS y los materiales metálicos enterrados en sus proximidades, se evalúa el comportamiento de la transferencia de potencial, se calculan los valores de las tensiones transferidas y se identifican las principales variables que influyen en los niveles de tensión transferidos. Las simulaciones se realizan con el programa CYMGRD específico para el cálculo de GS. Su análisis genera resultados reales en la transferencia de potencial que deben ser considerados por el ingeniero de diseño de GS, lo que lleva a evitar el diseño de subestaciones aisladas sin tener en cuenta los elementos existentes que pueden afectar al contorno de la subestación.



Keywords: Electrical substation, grounding systems, ground grid, potential transfer, step and touch voltage, and buried metal structures.

Palabras clave: Subestación eléctrica, sistemas de puesta a tierra, red de tierra, transferencia de potencial, tensión de paso y de contacto, y estructuras metálicas enterradas.













1Master of Electricity Program, Universidad Politécnica Salesiana, Quito, Ecuador.

 2,*Research Group on Smart Grids GIREI, IUS-RECI Electricity Grids and Smart Cities, Universidad Politécnica Salesiana, Cuenca, Ecuador. Corresponding author :


Suggested citation: Chiliquinga, W. and Robles, P. “Considerations in the design of electrical substations, including the effect of potential gradient on surrounding metallic structures”. Ingenius, Revista de Ciencia y Tecnología. N.◦ 28, (julio-diciembre). pp. 9-24. 2022. doi: 


1. Introduction


The GS is an essential factor in human safety and maintenance of electrical inputs that make up a substation, considering its cost and durability [1]. In GS, ground fault currents must safely dissipate to return the ground to their sources; so that the protection devices can quickly disconnect the supply and eliminate the fault. However, fault currents flowing through the ground grid also flow through other buried metallic objects, including grounding systems connected to other facilities not affected by the faults [2], [3], [4], [5].

Although the GS may be physically isolated from each other, they are electrically linked through unwanted coupling, transferring dangerous electrical potentials from the meshes with fault currents to the non-energized passive meshes of other GS with a risk of electrocution for the personnel present. in those areas [6], [7], [8], [9]. Poor grounding in the oil and gas industry contributes to unnecessary downtime, but lack of good grounding is also dangerous and increases the risk of equipment failure leading to instrumentation errors, problems harmonic distortion, and power factor problems [10], [11, 12].

Oil and gas pipelines are large and sophisticated structures protecting against electrical discharge, especially corrosion. For the design of the GS, cathodic protection [CP] must be included, in addition to the electrical effects that can occur when these two systems are together GS, and CP [13], [14], [15], [16], [17].

This article aims to present case studies on the problems introduced by the presence of metallic structures and adjoining protection systems, among others, in the transfer of potential gradients [GPG] in passive GS.

The design procedures described in the standards related to GS of electrical substations in urban areas and oil stations allow the calculation of safe levels of step and touch voltages within the substation area, but adjacent GPG is not taken into account [18], [19], [20], [21], [22], [23], [24].

The type of material used can be a decisive factor in human electrocution. Inside the substations, the touch voltage [MTV] and step voltage [MSV] are less dangerous due to the high resistivity surface layer [25]. However, this layer does not extend outside the substations, where the transferred touch and step voltages can be harmful and much more if there are adjoining buried metallic structures not connected to the GS [26], [27], [28]; [29].


1.1.  Related Works


The potential gradient generated [30], [31]in oil refining complexes in the event of a failure in an electrical substation causes its transfer to the process areas, causing damage to the instrumentation system, [32, 33].

Metallic parts such as water and gas pipes, rails, and building foundations can modify the distribution of electrical potential in the area, depending on the structural topology, which triggers the effect of the GPG, [8].

The GS must consider the conductors directly involved in the protected installation, and any other, connected or not, can interact with the whole GS (Figure 1).


Figure 1. Equi- potential contour of a mesh of one GS


The pipelines carrying harmful products are protected against corrosion, usually by layers of coating materials integrated with active cathodic protection systems [34, 35]. The current flow, typically adopted for large or long structures, force the pipe to behave as a cathode, thus providing corrosion protection of its exposed parts when the coating fails. However, buried lines with cathodic protection, close to the grounding networks of electrical substations, allow the possibility of bonding and reduce the risk of metal-to-metal contact voltages. This bonding connection, necessary for the safety of operating personnel, can compromise the CP’s effectiveness. To avoid corrosion of the CP and bonding with the mesh, mineral salts, which ionize, forming a solid electrolyte with a pH varying from 8 to 10, must be considered.

In electrical substations in urban areas, metal parts that can modify potential electrical distribution are



contemplated [36], [37], [38]. If they are attached to the main ground connection terminal of buildings, as recommended by the standards, it allows it to function as a connection between the GS, this type of grounding is known in the literature as Ufer grounding, which considers that the metal encapsulated with concrete acts as an effective grounding electrode. However, they are not part of the GS and are buried in their environment, maintaining direct contact with the soil; they modify the potential profile on their surface [39].

The GS is solid to limit ground potential gradients to levels that avoid endangering human safety and proper equipment operation under normal and fault conditions. [40], [16]. What will allow us to comply with the normal conditions and the fault conditions of a substation?

Additionally, provide the means to dissipate electrical ground fault currents. [41], or prevent human beings inside the substation and in its adjoining areas from being exposed to electrification or electrocution. Failure to pay attention to safety in the design will cause potential gradients along the analyzed surface to endanger humans [42]. Events caused by atmospheric discharges: High ground-fault current circulation concerning the grounding system area nad is remote resistance [43]. Soil resistivity and its distribution of ground currents can produce high GPG at points on the substation surface under design [44].

Presence of the human being so that his body forms part of a circuit between two points with different potentials.


The absence of sufficient contact resistance or other resistance in series limits current flow through the body. The duration of the failure is a function of the impact on the human being. Due to these conditions, the low accident rate is due to a low probability of coincidence of the favorable conditions mentioned above. Table 1 shows the nomenclature of the variables used to analyze the exposed case studies present in the electrical substations versus surrounding metallic structures. Table 2 summarizes related works of the recommendations proposed by several authors concerning the design of grounding systems and the behavior of the potential gradient that occurs in surrounding metallic structures.


Table 1. Nomeclature & Description



Table 2. Summary of articles related to grounding systems  



2. Materials and methods


2.1. Problem Formulation


Figure 2 presents a flow chart of the electrical substation design methodology, including the effect of the potential gradient on the surrounding metallic structures, where the designer’s expertise allows obtaining results according to the threshold contact voltages and the threshold step voltage.

Figure 2. Methodology used for the design


Case studies are presented, which will allow analyzing the transfer of potential. The simulation of the scenarios is carried out with specialized CYMGRD software using the finite element method (FEM) developed by EATON; it allows the interpretation of soil resistivity measurements, elevation of earth potential, and evaluation of dangerous points in any area of additional interest, generates a visual representation of the results of the analysis on the potential of the mesh. The proposed scenarios are according to the type of surface layer used and the potential transfer analysis; the input data presented correspond to the following:


Table 3. General Notation & Descriptions


The present study focuses on the variation of the surface layer, the physical location of the mesh, and the different locations of the surrounding metallic structures.


Figure 3. Top view of GS case study 1


In the case of asymmetric grids, the analysis study is similar; taking the stratigraphy of the terrain, the exposed potential gradients transfer study metric is applied for any grid configuration.

Parameter values of the GS are taken based on the mesh indicated in figure 3 so that the importance of step and touch voltage does not exceed the maximum allowed values; the use of copper rods or electrodes is not considered for these simulations.

For the design and simulation of the scenarios, the bodyweight of a 50kg person is taken.

Assuming the most sensitive case that can occur, the optimal mesh conductor for this configuration is a copper conductor of 20.3776 mm2, equivalent to 2/0 AWG for the simulations of the scenarios, a 4/0 AWG copper conductor is taken up, where the IEEE 80 standard suggests considering the effects of corrosion present by the PH of the soil stratigraphy, [22].


2.1.1.      Case Study 1


Figure 3 shows a substation grounding mesh; its dimensions correspond to 50×50 meters with 10-meter grids; the perimeter conductor GS at 1 m depth in uniform soil with a straight metallic cylindrical tube at 2 m depth.



It is analyzed such as a) effects are produced by the transfer of potentials in the mesh when having the presence of an underground metal perimeter fence, and b) the effects are due to potential transfers caused by the presence of a metallic pipe buried under the GS.



For the analysis, different configurations of the GS and the underground pipeline.

Potentials are analyzed in an asymmetric mesh; a case presented depending on the topology and the facilities offered by its on-site construction.

Figure 4. Top view of asymmetrical L-type mesh


2.1.2.      Case Study 2


In Figure 5, rails located at a distance "d" from the mesh are added; for study case 2, the transfer of potential is reflected in changes of touch, step, GPG, and Rg voltages that occur in the directions will be analyzed indicated.

Figure 5. Top view Mesh- Rails

2.1.3.      Case Study 3


The mutual interference of nearby ground grids is analyzed to assess the potentially dangerous circumstances in sites protected by the primary grid, including proximity to an adjoining one that dissipates the ground fault current in the surrounding ground, mainly in urban areas, a) mesh 1 Main and Mesh 2 Offline, b) mesh one primary and mesh two connected, c) mesh one primary and Mesh 2 are connected to other GS.

Two meshes of the grounding system are considered, with similar topology and technical parameters. Adjacent edges of the meshes are spaced a distance d meters apart.

Figure 6. Nearby grounding grids


2.2.      Interferences between GS and cathodic protection


The standards and recommended practices for the design of cathodic protection systems establish the need to interconnect metallic structures with each other. However, this equipotential bonding can compromise cathodic protection and safety effectiveness. GS traditionally built with copper electrodes, due to their stability characteristics over time, present problems concerning cathodic protection: a copper ground mesh connected to the structure under cathodic protection can drain a considerable amount of the protection current. It may be impossible to polarize the steel structure correctly in specific scenarios. If the cathodic protection is no longer adequate, corrosion is at risk due to a galvanic coupling between copper and steel.


2.3.      Impact of groud faults on pipelines and possible solutions.

Destructive electrical arcs can be prevented by bonding the GS to the pipe. However, such a connection would cause the cathodic protection system to drain; this is solved by inserting an ISP or a polarization cell in said connection. The fault current impressed on the pipe must be safely dissipated to earth employing uncoupled intentional sacrificial anodes, e.g., magnesium or zinc materials, connected and installed along the pipe with a low resistivity. These sacrificial anodes would also facilitate the dissipation to the ground of currents 


conducted to the pipeline from locations remote from the substation area.

Instead of bonding conductors, installing decoupling devices, such as insulator surge protectors between grounding electrodes and pipelines, is the best compromise to safeguard safety and functionality during ground faults. Decouplers minimize the impact of ground faults on channels while preserving the effectiveness of the cathodic protection.

Human safety depends on the energy absorbed before the fault is cleared and the system is deactivated; it is suggested to establish step voltage and touch voltage limits which are called thresholds, depending on the material used as the surface layer and its reduction factor, Dalziel and Lee set constants related to the electrical discharge energy tolerated.


3.           Results and discussion


3.1.      Analysis of Results


3.1.1.      Effects of perimeter mesh earth conductor


The underground metallic pipe is not considered; the contour and profile graphs of the potential gradient of the cases are made, considering the finished floor as the asphalt ρs = 10000Ω − m.

Figure 7.  Touch voltage, insulated mesh- -ρs asphalt


The underground metallic pipe is not considered; the contour and profile graphs of the potential gradient of the cases are made, considering the finished floor as the asphalt (Figure 7 and 8). Ground mesh and perimeter fence without connection see (Figure 9 and 10).

A summary of the simulations with the conditions set out for study case 1, with surface layers of concrete, gravel, and asphalt is presented.

At ρs = 200Ω − m concrete, the touch and step threshold voltages correspond to 457.82 V and 730.83 V.


Figure 8.  Insulated mesh potential profile -ρs asphalt


Table 4.  Mesh and perimeter fence without connection


Figure 9. Touch voltage, mesh and fence without asphalt -ρs connection


Changing for a finished gravel floor, ρs = 5000Ω − m, the threshold voltages of touch and step vary to 2489.47 V



and 8857.39 V, with the change to asphalt
ρs = 10000Ω − m, touch and step voltages thresholds are 4605.76 V and 17322.6 V. The material used as surface layer allows to have a mesh resistance Rg at 0.476 Ω and for an isolated mesh with near no connection at a value of 0.35 Ω. The maximum touch voltages [MTV], maximum step voltage [MSV], and GPG see the Table 4.


Figure 10. Potential mesh and fence profile without asphalt-ρs connection


Figure 11. Modified mesh and mesh connected to fence


According to the simulations carried out with different values of the surface layer, the threshold touch voltages [TTV] and threshold step voltage [TSV] are directly related to the surface layer’s resistivity. The change of material in the surface layer to gravel or asphalt allows the touch voltages, step voltage, GS, and Rg to vary in favor of the safety of the human being when the perimeter fence is implanted. The surface layer of concrete allows the MTV to exceed the values of TTV and TSV, which suggests improving the architecture of the mesh. Based on the mesh and perimeter fence indicated in figure 3, the modifications

made to the architecture of the mesh to reduce the MTV and MSV when there is a surface ρs =200 Ω-m, suggest a) attach the mesh to the perimeter fence, b) modify the mesh, increasing more loops on the outer parts. See figure 11. In case 1, with the architecture change, the TTV and TSV correspond to 457.82V and 730.83V, the Rg = 0.34Ω does not vary, and the MTV and MSV, as well as the GS, are shown in Table 5.


Table 5. Mesh and Perimeter Mint


Figure 12. Metric with mesh architecture change


3.1.2.      Influence of the perimeter mesh


The results allow us to observe the effects of the perimeter fence on the MTV, MSV, GPG, and Rg: If the earth conductor of the perimeter fence encloses the substation mesh, its effects on the MTV of the mesh decrease up to 48%, and the GS and Rg decrease by 27%. The most typical configurations used to decrease the touch voltage are observed in figure 11; in table 5, the MTV and MSV decrease in case 1. In case 2, with the modified mesh, the MTV decreases, and MSV increases concerning the values indicated in table 3 when there is a mesh and fence without a connection. If the GS increases, the Rg increases; this is logical since the GS is proportional to Rg, according to its formula, GP G = Ig.Rg. When the GS increases, the peak touch voltage decreases. In case 1, mesh and fence connected, the maximum voltage value decreases by 8%, especially where the mesh and rail are not connected. In case 2, modified mesh, the maximum touch voltage decreases by 16% for the case in which the mesh is present and the fence is offline.


3.1.3.      The buried metal pipe effects


For the analysis of the effects of the pipe on the ground grid, the fence indicated in figure 2 is not taken into account; the touch, step, and GS voltage simulations are carried out on the grid and direction 1. Metal pipe of a fixed diameter, buried at different depths. See Table 5. A metal pipe is buried at a fixed depth and variable diameters. See Table 6. An example of item a is simulated, with a surface layer of asphalt for the case of a 400 mm diameter pipe case and a depth of 2m, Table 6.


Figure 13. Touch voltage, mesh and asphalt-ρs pipe


Figure 14. Potential direction profile 1 - mesh and pipe - ρs asphalt


A summary of the simulations carried out with pipes of different diameters, depths, and surface layers of concrete,

gravel, and asphalt are present. ρs = 200Ω − m [concrete], constant diameter pipe, and underground metallic line at depths of 2, 3, 4, and 5 m, TTV, and TSV correspond to 457.82 V and 730.83 V when changing the scenario For the surface layer of gravel [ρs = 5000Ω − m], the TTV and TSV vary between 2489.47 V and 8857.39 V, for the case of asphalt as a surface layer being its ρs = 10000Ω − m, the TTV. TSV equal 4605.76 V and 17322.6 V, Rg is set to 0.47 Ω. The maximum touch, step, and PG voltages present a variation presented in Table.


Table 6. Constant pipe diameter and variable depth


ρs = 200Ω − m [concrete], pipe diameter variation at 0.8, 0.6, 0.4, 0.2m at constant depth, TTV and TSV at 457.82V and 730.83V, yes gravel with ρs = 5000Ω − m is used as a surface layer, TTV and TSV indicate values in 2489.47 V and 8857.39V. For the scenario of using asphalt as the surface layer, knowing that its ρs = 10000Ω − m, the result corresponds to 4505.76 V and 17322.6 V, indicating that Rg = 0.47Ω. The MTV, MSV, and PG present a variation presented in Table 7.


Figure 15. Metric mesh and underground metallic pipe



 Tabla 7. Variable diameter and constant depth pipe - ρ concrete


Figure 16. Display of values Table 8


In the presence of an underground metal pipe that crosses under the mesh, with a constant diameter and variable depth, the MTV and MSV decrease the deeper it is, while the Rg and GS do so on a smaller scale. If its diameter is variable and its depth constant, the MTV and MSV increase when the pipe diameter decreases, and the Rg and GS increase to a lesser extent. In figure 3, different scenarios are proposed, keeping constant the parameters of the mesh, diameter, and variable depth, the objective of these configurations allows to determine which strategy is more favorable for the decrease of TTV and TSV that can be generated on the surface area of the pipeline when a fault occurs in the electrical system.


3.1.4.      Analysis of results of underground metallic pipelines


The voltages MTV [457.82 V] and MSV [730.83 V] of case 1 indicated in table 1 are taken as reference, where it is recommended to install more ground mesh conductors parallel to the underground pipe that passes below; this helps to decrease the TTV and TSV in the mesh, due to the

 increase in electromagnetic fields. Another way to reduce TTV and TSV is to make the pipe cross diagonally as much as possible. An exhaustive analysis suggests underground pipes leave an electrical substation area because voltage-transfer generates GPG and TTV values higher than those admissible for its configuration. In these cases, installing copper weld rods attached to the beginning and end of the pipe is recommended. According to the studies carried out on the metallic pipe, it is possible to observe that this affects the potential of the mesh.

Figure 17. Asymmetrical mesh touch voltage - ρs concrete


When inside the grid area, the buried metal pipe decreases the TTV and TSV; in real situations, this does not happen because the pipes always enter and leave the ground grid area. When a metal pipe leaves or is outside the mesh area, it causes elevation of TTV and GPG in regions outside the mesh; this is logical since by increasing the length of the pipe, the increase in potential will approach the rise in network potential. When a fault occurs in the electrical system, a current is generated in the pipe; this increases when the pipe is further away. The scenarios presented with underground metallic pipes clearly show the danger of transferred potentials. For GS designs in electrical substations, corrective measures must be taken when metallic structures are nearby; the designer must know their influence with acceptable precision; otherwise, they may apply erroneous or unjustified measures.



According to sound engineering practices, corrective procedures are in place to minimize the transfer of potential when metallic structures are buried. Joining the metallic structure to the main mesh, however, the consequences of the said procedure is carefully verified due to the possible transfer of the increase in the potential of the networks [reverse situation]. Provide denser meshes for the grid over the buried pipe. These



meshes can, in some cases, act as a protective mesh by reducing the magnitude of the touch voltage. Install insulating flanges on underground metal piping at suitable locations. The optimal solution in the corrective methods to be used will depend on several factors, such as the properties of the soil, the location of the metallic structure, and the fault current, among others.


3.1.5.      Mesh Type L


An GS study of an asymmetric mesh is presented, see figure 4, for this case, a surface layer of resistivity ρs = 200Ω − m [concrete] is considered, obtaining the values shown in Table 8. 

Table 8. Asymmetric mesh type L


Figure 18. Mesh potential contour - without rails


In the exposed case, it is observed that with the surface layer of concrete, the MTV exceeds the MSV; in figure 16, the procedures to improve the TTV are the same as those exposed in symmetric or asymmetric meshes. 


3.1.6.      Analysis of results Scenario 2


A mesh and nearby rails are considered, the configuration of the mesh indicated in figure 3 is used, the study is made based on what is shown in figure 5, and a surface layer of asphalt is considered. 


3.1.7.      Case 2.1 Ground grid without considering nearby rails


An analysis of the potential contour of the ground grid is made without considering the rails; figure 18 shows the potential distribution on the ground surface when a fault condition occurs.


3.1.8.      Case 2.2 Ground Grid considers rails without connection to the grid


It is proposed to analyze the potential contour of the ground grid considering the rails at a distance [d=30m] without connection; this is a common situation in electrical substations and power plants, the simulation of the rails is done through steel conductors 90 mm diameter aluminum-clad separated at a distance of 1.5 m and a length of 50 m. Figure 19.


3.1.9.      Case 2.3 Earth grid considering the rails connected to the grid


Figure 19. Mesh potential contour - with rails



Figure 20. Touch voltage mesh and rails without connection



The potential contour of the ground grid, considering the rails connected to the ground grid employing 4/0 AWG copper cables at 5 points uniformly distributed on the rails, is presented as a case study. See figure 20. Figures 17, 18, and 19 show the change in potential curves when the rails are installed; the most



important differences can be seen in the distribution of potentials in the surroundings since high GS are generated to be considered. Figures 19 and 20 show that the TTV values increase in the area between the rails and the mesh when they are not connected; they are joined with the mesh to reduce these potentials. Figures 21 and 22.

Figure 21. Mesh potential contour with rail connection


Table 9. Variable diameter and constant depth pipe - ρ concrete


Figure 22. Voltage of touch screen and connected rails


If the rails are not connected to the mesh, the TTV and TSV values are high, see Table 9, item 2, if they are connected to the mesh, they decrease, and the GP and

Rg values. Another way to reduce the potentials in the rails when they are not connected to the mesh is to insulate the union joints, see Table 9, item 8; in the same way, the rails can be grounded using metal rods or copper-weld.


Figure 23. Display of values table 6


3.1.10.  Analysis of Results Scenario 3


Mesh 1 and mesh two are considered; Figure 6, the mesh configuration indicated in figure 3 is used with a surface layer of gravel and a short-circuit current of 10 kA.



3.1.11.  Mesh 1 and Mesh 2 No Connection


When an electrical fault occurs in mesh 1, it affects mesh two due to the difference between the potentials of the ground surface and the potential in mesh 2; the simulation for the two meshes is done by varying their distance, starting from 10 up to 120 meters; obtaining TTV= 2489.47 V and TSV=8857.39 V.

Figure 24. Touch and step voltage on the measuring axis of the meshes. Mesh 1 and Mesh 2 without connection



Table 10.  Voltages touch step Rg GPG − Insulated mesh


The MTV generated by mesh 1 in mesh 2 grow as they move away, reaching their maximum value of 2464.27 V at a distance of 120m; otherwise, the MSV decreases as they move away. In meshes 1 and 2, the Rg values are maintained at all separation distances, while in Mesh 2, the GPG decreases as they move away. On the line of the measurement axis, a graph of the touch and step voltage is plotted for insulated grids 1 and 2, for a distance d=30m, Figure 24.


3.1.12.  Mesh 1 and Mesh 2 are Connected


If meshes 1 and 2 are connected, the leak fault currents are the same, and the potentially dangerous voltages are generated due to their geometric symmetry. The meshes may be intentionally or unintentionally attached through various metal installations such as cables, pipes, or metal rails.


Table 11. Voltages touch, step, Rg, GPG.Mesh 1 and 2 joined


The union of the two meshes is considered using an isolated cable with the same characteristics as those that make up the respective meshes, obtaining similarity between MTV and MSV in both meshes, see table 10. In an electrical failure, the voltage values are reflected in mesh 2. It indicates the need for an exhaustive analysis; before intentionally connecting mesh 1 with mesh 2, it is necessary to check if the security measures applied in the Mesh 2 installations can build up to dangerous voltages and ground currents. On the other hand, the parallel connection of the grounding system meshes decreases the ground currents and the TTV associated with mesh 1. The

TTV and TSV metrics at a distance d=30m are shown in Figure 25.



Figure 25. Voltages touch and step - on the measuring axis of mesh 1 and mesh 2 connected


3.1.13.  Mesh 1 and Mesh 2 without Connection- Mesh 2 Underground.


Distribution source transformer stations are often located close to surrounding buildings in urban areas. On the other hand, GS’s are often intentionally or unintentionally interconnected; therefore, they tend to have a very low Rg. It is essential to assess potentially dangerous voltages that may appear on the ground grid of an adjacent building closest to the substation.


Figure 26. Touch and step voltages on the measuring axis - Mesh 1 and Mesh 2 isolated - Mesh 2 grounded.


Table 12. Voltages touch, step, Rg, GPG Mesh 1 - Mesh 2 grounded




The potential distribution on the ground surface of grid 1, where the source distribution substation is located, and grid 2, which represents the ground grid of the building closest to the substation, is calculated. The calculations are made assuming that the ground mesh of the building is connected to the ground meshes of the surrounding buildings; it is assumed that the meshes of the structures have the same characteristics and technical parameters equal to mesh 1. The simulation for the two meshes is done by varying their distance, starting from 10 to 60 meters, obtaining TTV=2489.47 V and TSV=8857.39V. In the situation in urban areas, the MTV in the neighboring building for d = 30 presents high values; however, the stepped voltages in the space between the substation and the adjoining installation are higher voltages for the grids connected. The transfer of dangerous potentials and the technical parameters of the mesh and the ground depend mainly on the value of the fault current. A considerable distance between nearby meshes does not guarantee a decrease in the transfer of dangerous potentials. In electrical substations, the resistivity value of the surface layer is an important parameter to take into account; its value directly influences the TTV and TSV values of the substation and, therefore, the transferred potential gradients.


4.            Conclusions


Based on the scenarios presented in this study with variables of resistivity of the surface layer and different configurations, the variation of the GPG has been determined against several strategies. Technical parameters that appear in GS designs have been related and evaluated, observing how these influence the GPG.

This article presents the simulation and analysis of real potential transfer scenarios between electrical substations and metallic structures. Based on them, results have been obtained that reflect the values of dangerous transfer voltages to metallic structures near a substation, exceeding the TTV and TSV allowed in a GS. Measures and procedures taken into account to reduce transfer voltages in the design and construction of GS are indicated.

The values of short-circuit currents, soil resistivity, distances, and location between nearby metal structures, among other design parameters, influence the transfers of electrical potentials between a substation and adjoining metal structures. It is essential to consider the GPG generated in a GS outside the substation area, the interference effects of potentials generated by the existence of metal structures, and the GS close to the substation.

In nearby grids, an analysis is made of the potentially  dangerous situations that may appear when transferring the potentials generated by the ground fault currents to the grids and nearby ground equipment and the personnel

protected by them. In designs of cathodic protection systems for pipelines in oil stations, interferences between GS’s connected to the substation grid with cathodic protection systems are avoided as much as possible. Otherwise, the problem should be deepened, proposing suitable solutions to this interference, which would prevent compromising the effectiveness of the cathodic protection system.

Detailed scenario analysis is performed when the nearby grid is with other grounded objects; these circumstances are necessary for installing substations in urban areas. The analysis carried out in the document has shown that in case of ground faults in an unintentional connection of ground networks, it can cause high TTV and TSV in nearby meshes, which can lead to severe risks for the human being who transmits them.




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