Camilo tells us:
Project_description: My project is Ground measurement of a large oil plant with an energized substation! Is there any standard related to this? I’m worry of energizing the ground in an explosive atmosphere … there’s no way how to guarantee that all metalic structures within explosive areas are perfectly bonded, thus not having DOP (Difference of potential).
Concerns: I´m worried because since its a large grounding system, the common earth ground tester is useless because it injects little current, and then it will be hard to find the potential plateau. I will use an AC generator of 127V. The concern it that when I energize the grounding, the ethanol pipes that is also grounded might develop a potential difference in some loose connections (if they exist).. the ethanol tanks are far and they are connected to the main ground by these metallic pipes… If a DOP appears, it might cause sparks inside the tanks or pipes, and that could lead to an explosion.
Thank you for your question regarding ground resistance measurements at oil plants. It is our pleasure to help.
Taking measurement for resistance-to-ground of existing facilities is always a difficult process, especially when the grounding system is in use and bonded to hundreds, if not thousands, of objects. Having to measure an oil plant with explosive hazards only compounds the problem. You are correct that the typical ground resistance meter does not have the power to properly measure even a relatively small facility, let alone a giant compound such as an oil plant.
E&S Grounding Solutions recommends the use of true Direct-Current (DC) meters. Not only do Direct-Current (DC) meters work better for measurements in the earth/soil, but they have a far lower spark hazard. The meter we use is by Advanced Geosciences Incorporated (AGI) and uses an 800-Volt p-p DC power source, which requires an extra car battery to power it. This meter has more than enough power to make the measurements you need, and because it is DC, you should not have to worry about explosion hazards. We also recommend using test-lead cables instead of standard wire.
Even if you have the correct meter, you are really in for quite a job. The test you are trying to conduct will require very long test-lead cables that are at least 3X the diagonal length of the compound, with a 10X length preferred. You will also need to take Wenner 4-point Soil Resistivity Data, have accurate Direct Current Ammeters, and will need to be able to remove as much of the interconnected metallic objects from the ground grid as possible. This is to mention only a few of the requirements needed to do a resistance test. An impedance test is far more complex.
In our experience, the best way to validate existing large scale grounding grids that are in use, is to conduct a series of Direct-Current (DC) Point-to-Point Continuity tests around the compound, conduct Soil Resistivity measurements, and couple that with extensive computer modeling. This not only provides accurate resistance and impedance data, but further confirms that the grid is sound, in good condition, and effective; which is something a standard ground resistance test does not do.
E&S Grounding Solutions is of course more than happy to help you out with this difficult and time-consuming project, but if not us, please get someone with the proper test equipment, computer systems, and expertise. Bad grounding, especially in explosion hazard environments, can result in life-threatening situations. Please feel free to contact our Engineering Department directly and one of our engineers will be happy to speak with you about your project, free of charge.
The Engineering Team at E&S Grounding Solutions