12-12-05 -- T&D Worksite Shock Protection Research Project Enters Test Phase
Bethesda, MD -- The Electrical Contracting Foundation’s research project on T&D Worksite Shock Protection (WSP) is preparing to begin testing. The University of Kansas research team is currently setting up dry and wet laboratories for small-scale modeling, to supplement actual field testing on transmission and distribution systems at Kansas City Power and Light, and at A.B. Chance high-voltage testing facilities in Centralia, MO.
These were among the developments discussed by the project’s steering committee at its November 29, meeting in Chicago. It was attended by fifteen members representing a broad spectrum of electric utilities, line constructors, and equipment manufacturers. Lead researcher Thomas Glavinich, P.E., D.E., reported on preliminary arrangements and testing plans.
Protecting People on the Ground
The aim of the project is developing equipotential grounding techniques to protect workers on the ground, and the general public, from electrical shock hazards associated with working on energized overhead T&D systems. In addition to direct contact with live conductors and equipment, these hazards include electrical and magnetic induction, and static effects caused by working under dusty conditions, such as those found in mining, or powerline construction and maintenance operations in desert areas.
Dr. Glavinich summarized the goal of this project as “doing an IEEE 80 [Substation Grounding Standard] on the fly. When you’re building a power substation, you can spend a long time designing a ground grid to reduce step and touch potentials. We don’t have that luxury when there are crews out there moving along the line.” The University of Kansas research team has even coined a new term to describe the real-time evaluation of personnel safety factors by line workers in the field: RACS, which stands for ‘Rapid Assessment of Conditions for Safety.’
Agreement Reached on Testing Scenarios
The steering committee reached two important decisions at the Chicago meeting that will shape the test program. The first was to simplify the test program by reducing the number of variables, using a single-phase distribution line fed by a grounded source for evaluating step and touch voltages. This approach should give results equivalent to modeling many possible configurations of three-phase power systems operating at different voltages.
The second major decision was to rely on laboratory testing and mathematical modeling to supplement actual field testing on energized power systems. Scale model testing offers a number of advantages:
- It’s faster, safer, and less expensive than field-testing.
- Provides a controlled environment for studying particular scenarios (e.g., known resistivity for homogeneous or layered earth)
- Allows researchers to change one or more variables while holding other conditions constant.
- It has historically been used to study grounding and ground grids.
- Allows testing many different configurations and combinations of grounding electrodes.
“Another problem with fault-testing at actual system voltages is lack of repeatability,” explained Dr. Glavinich. “After staging a fault, you change the soil moisture content, structure, ionization, and so forth so that repeating the test often gives different results. The same is true when trying to replicate the tests at different locations in different seasons or weather conditions.”
In the actual field testing at KCPL and A.B. Chance, specially-designed metal test legs will be used to simulate the flesh-and-blood legs of actual ground workers, to measure step voltage and gradients near power poles under a variety of fault scenarios.
Focus on Equipotential Grounding
This Foundation research project is focusing on the safety benefits equipotential grounding, a protection technique that involves connecting together all metal objects near a powerline worksite (including trucks, metal poles, protective ground mats, nearby fences, etc.) so they are at the same potential, or voltage to ground. Doing this properly reduces the risk of electric shock due to voltage differences, and also induction from energized lines and equipment.
Temporary grounding jumper assemblies (TGJAs), used to join metal objects together, are key components of these equipotential grounding systems for personnel safety in line construction operations. For this reason, the Foundation research project also plans to investigate practical ways for line crews to test and evaluate the performance of these key safety components in the field.
One outcome of the Electrical Contracting Foundation’s research project on T&D Worksite Shock Protection is expected to be a ‘National Electrical Installation Standard (NEIS)’ on the testing and proper application of these TGJAs. NEIS are a series of ANSI-approved standards for electrical construction techniques, published by the National Electrical Contractors Association (NECA).
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The Electrical Contracting Foundation (ELECTRI’21), established in 1988, is the primary research arm of the electrical construction industry. Foundation research projects are intended to improve the productivity, professionalism, and competitiveness of electrical contractors. To learn more about the Electrical Contracting Foundation, please visit www.electri21.org.
The National Electrical Contractors Association, founded in 1901, is the leading representative of a segment of the construction market comprised of over 70,000 electrical contracting firms. To learn more about the industry and NECA’s services, please visit www.necanet.org.