Device measures substation ground impedance on-line

Substation owners can now receive information to confirm system design specifications, while ensuring safety, with the new digital version of the Smart Ground Multimeter (SGM). Developed with support from EPRI and manufactured by Hood-Patterson & Dewar, Inc., Decatur, Ga., the unit provides a more accurate way to measure substation ground impedance than the conventional fall-of-potential method.

Under the fall-of-potential method, measurements must be made on de-energizing, isolated grounding systems—a task nearly impossible at existing facilities without interrupting the customer’s power supply. In contrast, the SGM can easily measure the ground impedance on both energized and de-energized substation ground systems. It works by injecting transient ground potential differences around the grounding system, as well as the injected electrical current. After it measures ground potential differences, these measurements are then processed by computer software that filters out electronic noise. Then, it corrects for errors and estimates the test substation ground mat impedance. For more information, contact Lyn Cosby or J.B. Franklin at Hood-Patterson & Dewar at (404) 296-5990.