Executive Summary

Electric grounding is a common safe work practice for all types of electrical equipment in industrial facilities. In the case of accidental energization of transmission lines, high step and touch potentials can result, causing fatal injuries. The main purpose of a grounding grid is to mitigate overvoltages and to provide adequate protection for the working personnel against electric shocks. However, one must be aware of certain shock hazards which have frequent occurrence in substations, making it imperative to ground all conductive structures for effective mitigation.

A ground grid/mat study can be conducted to evaluate these potentials and provide optimal levels of protection through minimization.

Objective

The main goal of a grounding grid/mat study is to analyze the step and touch potentials and prevent the occurrence of shock related incidents.

Brief Study Methodology

A ground grid/mat study evaluates the effects of step and touch potentials within a power system and analyzes its impacts on the system operation. Data collection procedures are performed as per NEC requirements including the inspection of soil characteristics and effect of various environmental factors.

The maximum ground currents at each point are first calculated, which precede the evaluation of the step and touch potentials at the margin as well as internal voltages for each substation grid. The grounding grid is then designed and modelled on power systems software. Once a comprehensive model is developed, what follows is the calculations for grounding resistance. Adjustments are made as a final step to ensure the best grid design with minimal levels of the step and touch potentials.

Expected Study Outcomes & Recommendations

Ground Grid/Mat studies are performed as per the latest IEEE-80, NEC, ANSI & NFPA standards. Study outcomes and recommendations are expected to improve your facility in the following areas:

• Reliability and safety of the system is expected to increase.
• Optimal protection for working personnel against step and touch potential hazards.
• Reduced lead time for design of the grounding grid.
• Cost savings in the material sizing for grounding rods and conductors.
• Effective dissipation of the grounding fault currents.
• Electrical grounding safety as per OSHA requirements.

Study Deliverables

The proven expertise of our team of certified professional engineers will aid in the evaluation of your system and deliver state-of-the-art grounding solutions for your power system’s protection. We work closely with our clients in collecting the data, modeling the system, simulating the worst case conditions and abnormalities, plotting the step and touch potentials & offering recommendations in compliance with the latest industrial standards.

AllumiaX, LLC provides independent and third-party engineering support by presenting comprehensive deliverable reports backed by industry standards and best practices, analysis work based on industry-leading software (ETAP), and proven results based on accurate modelling and calculations. The reports are expected to include the following deliverables:

• A comprehensive grounding grid model of the facility in modern power systems software.
• Calculations for step and touch potentials (both internal and external).
• Accurate models of the step and touch potentials on 2D and 3D plots.
• Evaluation of the potentials at the earth surface.
• Evaluation of various ground grid configurations to determine the worst case scenario.
• Recommendations for the reduction of step and touch potentials below standard limits.
• Tabulated results of the study in compliance with NEC, IEEE ,ANSI & NFPA standards.

References

• NFPA 70, “National Electric Code” ,2017
• NFPA70E, “Standard for Electrical Safety in the Workplace”, 2017
• IEEE Std 80-2013 - IEEE Guide for Safety in AC Substation Grounding
• IEEE Std 953 - Grounding of Industrial Power Systems
• IEEE Std 3003.2 - Recommended Practice for Equipment Grounding and Bonding in Industrial and Commercial Power Systems