2005 Users Group Conference Proceedings

Article Abstract

User Contributions

This paper outlines practical methods for testing of grounding systems using current injection. Injection testing enables comprehensive testing of grounding systems. Many important grounding system parameters can be measured, including impedance, touch, step, and transferred voltages, ground potential rise contours, current splits in overhead ground wires, OPGW and cable screens. Injection testing is also suited to specific situations such as mining installations or power stations supplied by gas or oil.  The latter cases require specific grounding measures for safety reasons and injection testing can confirm such issues.  Injection testing also allows identification of any transferred voltages, for example, onto farm fences, water and gas pipelines, telecommunications and railway signalling circuits etc.  Injection test methods can also be used to measure induced voltages into other services in a transmission line right-of-way.

Importance of using MALZ and Finite Volumes of Different Resistivities for the Grounding Analysis of Large Hydroelectric Generating Plants

Gilles Allard

Ingénierie de Production, Hydro-Québec Équipement, Hydro-Québec, Montreal, Canada

This paper describes the evolution of Hydro-Quebec grounding analyses of the Eastmain hydroelectric complex (two power plants and two substations for a total of 1250 MW generating capacity) using a 7 km long wire electrode immersed in the upstream reservoir. The analysis began in 2002 using the finite volumes option in MALT and was analyzed again in 2005 using the MALT and the MALZ new adaptive patch algorithms. The results are also compared to a preliminary study made in 1995 using a software package that supports a standard 2 layer soil model only. The paper addresses the following topics: How the computed results change when the analysis module changes from MALT to MALZ; Why finite volumes are useful to analyze large hydroelectric power stations; Why MALZ is best suited for this kind of analysis (circulating currents); And how the new adaptive patch algorithms facilitated the task.

Soil Resistivity Measurement, Substation Grounding Design and Ground Impedance Measurement, Using Program CDEGS

C. Cespedes and  J. Quijada

Div. Subestaciones De Transmision,  Dpto. Ingenieria De Subestaciones, Caracas, Venezuela

The calculations of grounding grid in this paper are made through two methodologies, the IEEE STD 80 - 2000, and the one based on the electromagnetic method, that  uses the representation of soils with models of two or more layers.  A computational tool for the  designing  the substation Macagua 115/13.8 kV of C.V.G. EDELCA was used. Using the program CDEGS (Current Distribution, Electromagnetic Fields, Grounding and Soil structure analysis) allows to obtain safe values of voltage through suitable geometric configurations of the electrodes of the grounding grid; as well as, the values of currents that flow to earth, in case of a fault of the system. The soil resistivity measurements was made, resulting the representative parameters of the behavior of the soil, and  measurements in field using the Method of Fall of Potential recommended by IEEE STD 81 – 1983.  The verification of the results obtained through the determination of the ground resistance and the touch and step voltage were done. According to the analysis of results, it is possible to conclude that using the two-layer soil model of soil results in measurements obtained reproducing the behavior of the grounding grid.

Safety and Operation of Double Circuit Underground Transmission Lines Duct Banks

Marcia Eblen

Pacific Gas & Electric Company, San Ramon, California, U.S.A

With the advent of solid dielectric high voltage cable (115kV and 230kV), underground transmission systems are a reality.  Many installations include more than one circuit in each duct bank.  In order to reduce cable size, shield grounding schemes have been modified to include cross-bonding, single point grounding, segmented grounds, and combinations there of all using sheath voltage limiters (SVL) to reduce the voltage stress on the cable shielding system during normal operation and switching transients.  With conductors of adjacent circuit only inches apart, induced voltages become a concern for two major areas:

1. Safety-What are the hazards for maintenance personnel when entering a vault with both circuits energized and when only one circuit is energized?

2. Operation-SVLs are used to protect the cable sheath but are not designed to withstand fault current.  What is the expected impact on the SVL system during a fault event?

To investigate these questions, a real circuit condition and hypothetical fault events will be modeled using TRALIN and SPLITS.

Detailed & Unique Modeling Projects using CDEGS

W.K. Daily

Austin Energy, Austin, Texas, U.S.A

The purpose of this paper is not necessarily to discuss a particular project or the specifics of a particular project, but instead discuss the unique capabilities of the CDEGS software by looking at several difficult and interesting projects completed by this author over a span of 20 plus years of experience using the software. This includes a timeframe when the CDEGS Software was not near as user friendly as it has evolved into today.

Practical Testing of Grounding Systems by Current Injection

Tony Mitton and Robin Watson

Mitton Consulting Ltd, Christchurch, New Zealand