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Latest addition to SES’ Powerful Software Packages















































































































































































The AutoGroundDesign engineering tool is the only fully automated software package 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 gives minimum impedance, 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 meet safety constraints, while reducing the overall cost of the grid. Extensive collections of predefined grids have been analyzed, constructed and can be easily updated by the user. A strategy has been devised to quickly find an appropriate grid, while at the same time minimizing the size of the database. The time devoted to design a safe and cost-effective grounding grid is minimized by the use of such automation techniques and appropriate databases.

1. Introduction

The design of grounding systems is often based on rough guidelines, derived from engineering experience. It is frequently a trial-and-error procedure and can be quite time-consuming, since it is too difficult to account for the large number of variables (topology and dimensions of the grounding system, burial depth, type and characteristics of the soil structure and material used for the grid’s conductors, whether or not grounding rods are attached to the grid, 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 arbitrary shape grounding systems. The screen to specify the vertices of any horizontal arbitrary grounding system is shown below.

2. Features

AutoGroundDesign has the following unique features:

3. 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 and 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. This was more pertinent, since SES has developed a new and unique automated design method that promises to reduce considerably the time needed to determine an adequate design for grounding systems. However, AutoGroundDesign was restricted to rectangular grids buried in multilayered soils. This version didn’t have a soil resistivity measurement and fault current distribution analysis modules. The soil structure characteristics and grounding grid fault current had to be specified by the user. These steps were quite inconvenient.

In the 2005 release of AutoGroundDesign, the soil resistivity measurement analysis, fault current distribution analysis and safety computation assessment modules have been integrated into the AutoGroundDesign specialized package. A new iterative approach and improved observation point selection procedure that speed up computation time have been introduced into this package. Moreover, metallic plates have been introduced and a robust and flexible grid and rod creation procedure that allows the specification of unequally spaced grids and rods were added as well. However, AutoGroundDesign was still restricted to rectangular grids.

Finally, SES is pleased to announce that in 2012, AutoGroundDesign can handle horizontal arbitrary shape grounding systems.

4. 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 all design requirements are not met or if these requirements are exceeded by a considerable margin suggesting possible 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.

Some of the unique strategies and techniques used in AutoGroundDesign are as follows:

5. Automated Grounding System Design Structure

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

Automated Grounding Design Central Module

This core and controlling module has a simple interface that allows a user 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 that meets 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. Since it is assumed that the grid is an equipotential structure, the locations of the current injection points within the ground network do not play a significant role, i.e. the longitudinal impedances of the ground conductors can be neglected.

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 many horizontal layers, as well as vertically and exponentially layered soil models.

Fault Current Distribution Analysis Module

This module calculates the fault current distribution in multiple terminals, transmission lines and distribution feeders using minimum 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, user’s own standard or a hybrid combination of these standards. 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 earth surface covering layer), body resistance, optionally specified foot resistance and resistance of protective wear, such as gloves or boots, and 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.