The AutoGroundDesign package performs automated analyses of grounding (earthing) systems of any arbitrary perimeter and identifies an economical grid configuration complying with user defined safety criteria that can be used as the design for grounding grids that are electrically small enough to be considered equipotential.

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Technical Description

The only fully automated software tool capable of analyzing and designing grounding systems with no user intervention between design phases, AutoGroundDesign’s powerful and intelligent functions help electrical engineers to safely and efficiently design horizontal, arbitrarily shaped grounding installations.

A multiple-step approach is used for the system design, beginning with the manual specification of parameters related to the grounding system, soil and fault current data, and safety criteria. Then the automated design process begins, starting with a grid consisting of a buried metallic plate (which provides the lowest resistance, touch and step voltages) to determine if required safety limits are achievable. 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 to satisfy safety constraints, while reducing the overall cost of the grid. These steps are described in greater detail below.

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.

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The component-based nature of the software package allows you to focus on your immediate needs, which may initially be, for example, to compute the resistance of a simple grid. Then as your needs evolve, for example to performing complete safety analyses of complex grounding systems of substations, you can consider upgrading to a software package with more sophisticated capabilities.

Two AutoGroundDesign packages are available:

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

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Background

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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 — and enabling an examination and better understanding — of these results and all steps involved in the automated design process.
• Features efficient and intelligent 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.

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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, knowledge of the soil structure and the actual fault current flowing into the substation is required. Also, a large number of factors such as the geometrical proportions of the grid, its depth, the type of grid conductors and whether 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. If no manual modifications (e.g. conductor locations) need to be made to the refined grid, then the refined grid may be used as the basis of the final design. A software package such as AutoGrid Pro or MultiGround would be required if manual modifications to the design are required.

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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. This module manages and coordinates input data and is used to calibrate the iterative process for automatically designing a grounding grid, with the ultimate objective of providing a design that meets all requirements and yet is not overly conservative, and therefore cost-effective. The design parameters include the selection of the methodology to obtain the initial design of the grounding system, to specify which grid database methodology is to be used for the automated design, to specify the maximum number of design iterations, and the rate at which the design of the grid evolves with every iteration.

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 apparent resistance or resistivity. 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. Terminals with multiple blocks can be defined, where each block can have different line parameters, and other characteristics such as span length values and the positions of neutral and phase conductors can likewise vary from one block to the next. 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 for two geometrical zones (inside and outside the grid), representing areas with typically different safety thresholds. 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 (editing requires an AutoGrid Pro or AutoGround/MultiGround software package) 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 in SESCAD. AutogroundDesign also features an embedded 3D viewer to view the resulting grid.

In addition, computational results as printed in the output file can be viewed and plotted via the View Design Summary button, and plots and reports of the computation results can be viewed by launching SESSystemViewer or GRServer using the corresponding buttons.

GRServer 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.

Lastly, SESSystemViewer displays 2D or 3D computation results directly over the grounding grid system configuration.