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AutoGroundDesign


Automated grounding (earthing) analysis of systems with horizontal arbitrary shape and made of bare buried conductors that are electrically small enough to be considered equipotential including the capabilities to automatically configure and dimension grounding systems and various standard types of electrodes that meet a specific earth resistance target.




Technical Description

The AutoGroundDesign software package is the only fully automated software tool that can analyze and design grounding systems without the intervention of the user between various phases of the design.

This software package offers powerful and intelligent functions that help electrical engineers design safe horizontal, arbitrarily shaped grounding installations quickly and efficiently. A multiple-step approach is used for the automated grounding system design. A grid consisting of a buried metallic plate, which provides the lowest resistance, touch and step voltages, is used as a starting point to determine if safety limits can be achieved. If yes, a grounding system consisting of a minimum number of conductors is computed. From these results, a preliminary design is then selected based on the SES reference database, other intelligent rules, or as specified manually by the user. Next, the initial design is refined recursively using rule-based techniques and algorithms to improve its performance and satisfy safety constraints, while reducing the overall cost of the grid. Extensive collections of pre-defined grids have been analyzed and constructed. A strategy has been devised to quickly identify an appropriate grid, while at the same time minimizing the size of the database. The time devoted to designing a safe and cost-effective grounding grid is minimized by the use of these automation techniques and appropriate databases.



The component-based nature of the software package allows you to focus on your immediate needs, from the computation of the resistance of a simple grid to a complete safety analysis of the complex grounding system of a substation. Simply add more components as your needs evolve. Typical AutoGroundDesign packages include:

This package includes everything found in the Uniform Soil package and adds a powerful module which computes the distribution of fault current between the grounding system and other metallic paths such as overhead ground wires, shield wires, neutral conductors, or cable sheaths and armors.

This package includes everything found in the Uniform Soil package and adds the ability to model soil structures composed of two horizontal layers. It also adds a resistivity measurement analysis module that converts measured data into a suitable soil model.

This package includes everything found in the Uniform Soil package and adds the ability to model soil structures composed of two horizontal soil layers and a third added surface layer to enhance safety in the vicinity of the substation. It also adds a powerful module which computes the distribution of fault current between the grounding system and other metallic paths such as overhead ground wires, shield wires, neutral conductors, or cable sheaths and armors. Note that the resistivity measurement analysis module that converts measured data into a suitable soil model is not included in this package.

This package combines all the features found in the preceding two packages that support horizontal two-layer soils.

This package includes everything found in all preceding packages and adds the ability to model soil structures composed of any number of horizontal soil layers (multilayer soils). Note that this package cannot be ordered without the resistivity analysis or fault current distribution modules.

All packages above include utilities (e.g., a conductor ampacity computation module (SESAmpacity), graphic servers, text editors, etc.).


Background

A grounding system design requires several iterations before obtaining a safe configuration. Therefore, it can be quite time consuming. It is difficult to account for the large number of variables e.g., topology and dimensions of the grounding system, burial depth, type and characteristics of the soil structure and material used for the grid’s conductors (horizontal wires and grounding rods, etc.) that can affect the grounding system performance. The AutoGroundDesign specialized software package offers powerful and intelligent functions that help electrical engineers design safe grounding systems quickly and efficiently without the intervention of the user between various phases of the design. AutoGroundDesign takes into account the full complexity of the system with strategies and techniques that have been developed to allow the automated design to be applied to horizontal arbitrarily shaped grounding systems.

This is the ideal tool to examine, enhance and optimize a large number of existing substations that require updates due to increased fault levels or new safety standard requirements. It can also be used as the first step in a more complex design cycle requiring manual interventions.

The screen to draw or specify the vertices of any horizontal arbitrary grounding system is shown below:




Features

AutoGroundDesign has the following unique features. It:

  • Generates grounding system designs based on a simple description of the substation site. The data entry requirements are reduced to a minimum, i.e., environment settings, soil data, grounding grid zone, fault current in the grid, safety-related data, as well as automated design parameters and controls.
  • Models grounding systems and evaluates their performance. It is well suited to analyze and design a grounding grid as long as the longitudinal impedances of the ground conductors can be neglected.
  • Analyzes and designs horizontal arbitrarily shaped grounding grids consisting of horizontal and vertical arrangements of bare conductors buried in uniform and multilayered soils. This is achieved with an automatic meshing method that accounts for any polygonal shape.
  • Presents a user-friendly interface, simplifying the specification of the horizontal arbitrary grounding zone. The shape of this zone can be defined and displayed dynamically from the interface. Each vertex can be moved by dragging it to a new position and the data is updated immediately in the data grid and vice versa.
  • Carries out automated designs with several procedures, such as Automatic, Midpoint, and Linear methods. These procedures will specify the progress of the automated design process appropriately, using ground grid databases, smart search algorithms and techniques, as well as examining performance and evaluating criteria and constraints more efficiently.
  • Offers three other modes of operations, namely, the Estimator, Configuration and Dimension Predictor modes that allow users to quickly and accurately estimate the resistance of various grounding systems (such as grids, plates, array of rods, star electrodes, circular rings, etc.) or to predict the size (dimension) or configuration of the grounding system that meets that resistance.
  • Includes intermediate results from the grounding, soil resistivity and fault current distribution analyses as an integral part of - and enabling an examination and better understanding of - these results and all steps involved in the automated design process.
  • Features efficient and intelligent design techniques which have been developed to generate different types of observation points in order to accurately carry out computations while also minimizing computation time during the iterative design steps. At the final computation step, a complete set of observation points can be defined either automatically or by the user, to produce conventional rectangular 3D and spot 2D plots that are useful for exploring the computation results.




Program Development History

SES implemented the first automated grounding grid design software in the early 90’s. It had a character-based (DOS-based) menu interface and was called AutoGrid. It was restricted to rectangular grids buried in uniform or two-layer horizontal soils. Computation time was the main obstacle to the systematic use of this automated feature.

In 2004, SES developed the first version of a Windows-based specialized package called AutoGroundDesign. In the 2005 release of AutoGroundDesign, the soil resistivity measurement analysis, fault current distribution analysis and safety computation assessment modules were integrated into the AutoGroundDesign specialized package. A new iterative approach and improved observation point selection procedure, which resulted in faster computation times, were introduced into the package. Furthermore, metallic plates were introduced, as well as a robust and flexible grid and rod creation procedure, allowing for the specification of unequally spaced grids and rods. AutoGroundDesign, however, was still restricted to rectangular grids. Finally, in 2012, AutoGroundDesign was able to handle horizontal arbitrarily shaped grounding systems.




Grounding System Design Technologies and Procedures

Consider the traditional process of designing a substation grounding system. Based on experience and on the substation ground bonding requirements, a preliminary grounding system configuration is developed and analyzed. The calculated results are examined to determine if all design requirements are met. If not all design requirements are satisfied, or if they are exceeded by a considerable margin thereby suggesting the possibility of significant savings, design modifications are made to the grounding system and the design analysis is started again.

To produce an optimized design, better knowledge of the soil structure and the actual fault current flowing into the substation is needed. Also, a large number of factors such as the geometrical proportions of the grid, its depth, the type of grid conductors and whether or not grounding rods are attached to the grid are essential.

A multiple-step approach is used for the automated grounding system design.

  • First, a grounding system consisting of a buried metallic plate is used as a reference. This gives the minimum ground resistance achievable for a grid of a given size, and determines whether the desired ground resistance and safety limits would be achievable with a solid plate. If not, then the whole process is stopped and the user is informed that the design process is impossible without additional mitigation measures.
  • Second, a grounding system consisting of a minimum number of conductors—for example, the conductors along the grid periphery with or without a few conductors inside the grid—is analyzed to see whether the desired ground resistance and safety limits can be achieved with a sparse grid. If yes, the design process is completed quickly without the need to refer to the reference design database and smart iterative techniques.
  • Third, an appropriate preliminary grid design is selected based on an SES reference database and other intelligent rules, or as specified manually by the user. The use of the reference database is based on the input data provided by the user, such as the size and the geometrical proportions of the grid, the soil structure type, the fault current injected, and the required safety criteria.
  • Finally, the initial design is refined recursively using rule-based techniques and smart algorithms to improve its performance and meet safety constraints, while reducing the overall cost of the grid.



Automated Grounding System Design Structure

The automated grounding system design software integrates the following modules and has the structure shown below:

Automated Grounding Design Central Module

This core and controlling module has a simple interface that allows users to establish an automated grounding system design quickly and efficiently. The ultimate objective of this module is to manage and coordinate input data, safety criteria and progress decisions in order to obtain a grid design meeting all requirements. The overall automated design parameters are controlled by this module to select the methodology used to obtain the initial design of the grounding systems, specify which grid database methodology is to be used for the automated design, and specify the maximum number of design iterations as well as the rate at which the design of the grid evolves.

Grounding Analysis Module

This module is used to analyze power system ground networks subjected to AC or DC power frequency currents discharged into various soil structures. It computes the safety performance of the grounding grid, in terms of GPR, touch and step voltages.

Soil Analysis Module

This module is dedicated to the development of equivalent earth structure models based on measured soil resistivity data. It can generate models with horizontal multilayer soils.

Fault Current Distribution Analysis Module

This module calculates the fault current distribution in multiple terminals, transmission lines and distribution feeders using minimal information and a simple set of data concerning the network. It provides the actual fault current flowing into a grounding grid, as well as currents in the shield wires, tower structures and cable sheaths. Self and mutual impedances of the shield wires and cable sheaths are also computed and available.

Safety Module

This module generates safety threshold values based on IEEE Standard 80, IEC Standard 479, the user’s own standard, or a combination of these. The computed safety voltage limits are used to decide whether to stop or continue the design process. The parameters to determine the safety voltage limits are: fault clearing time, earth surface covering layer (e.g., crushed rock) resistivity and thickness, equivalent subsurface layer resistivity (this is the resistivity of the soil beneath the layer that covers the surface of the earth), body resistance, optionally specified foot resistance and resistance of protective wear, such as gloves or boots, and a fibrillation current threshold computation method.

View, Plot and Report Tools

A CAD-based module is used to view or edit three-dimensional grounding grids consisting of straight-line segments. The line segments represent either metallic conductors or observation profiles. They can be viewed from any direction, in a variety of ways. Another report and graphics module serves as a powerful output processor to display the computation results in various graphical or print formats. This module also has the capability to view the input data and even launch the grounding analysis module.

Finally, a third graphics module simultaneously displays 2D or 3D computation results directly over the grounding grid system configuration.