E&S Earthing Solutions has received a number of requests regarding the new and miraculous “Smart Ground Meter” that is listed in the recently updated IEEE Std. 81-2012. The recent revision of standard 81 is very concerning in that the standard removes all mention of long-standing earth meter requirements that had been found in IEEE std. 81-1983 Section 7.4.2. In fact, the new standard has removed any physical requirements for metering and spends a great deal of time endorsing the new “Smart Ground Meter”.
The “Smart Ground Meter” is a very expensive new product developed by Sakis Meliopoulos, and claims to be able to conduct earthing/earthing tests that seem to break the laws of physics. It should be noted that Meliopoulos also happens to sit on the standards board that approves standard 81. This conflict of interest is apparent when reading the new and highly compromised IEEE 81-2012 standard.
While we at E&S have not been able to view this new meter in action, when we asked for documentation proving the miraculous claims the meter manufacturers make, we were told that the evidence had not yet been released for public review. We have since sent a request to IEEE for a review of this standard, which we have yet to see a reply.
It is E&S Earthing Solutions official position that IEEE Std. 81-2012 should be withdrawn immediately.
The following is the official statement from Safe Engineering Services in Montreal Canada, the originators of many of the earth tests listed in IEEE Std. 81 and the only independent company we know of that have so far been able to see the “Smart Ground Meter” in action:
From Safe Engineering Services:
Comments on the Smart Ground Meter, which was designed to measure soil resistivity and earthing system impedance:
1. Soil Resistivity. Soil resistivity is measured by causing a current to circulate between successive pairs of electrodes, while the resulting potential difference is measured between other pairs of electrodes. Other soil resistivity meters used by earthing system designers and geophysicists display the resulting measured values, so that the user can interpret the data with software or graphical methods and, most importantly, see how and to what degree the soil model chosen for the earthing analysis or other application matches the measured data. The Smart Ground Meter, on the other hand, does not provide this measured data in any readily accessible form, so the user is left in the dark. Worse yet, the Smart Ground Meter makes the fundamental assumption that the soil consists of only two horizontal layers and produces as output the parameters of these two layers only, no matter to what degree the measured data indicates that more than two soil layers are present. In addition to the top and bottom layer resistivities and top layer thickness, the Smart Ground Meter provides graphs of probability versus percent error for each of these parameters, thus underscoring the expectation that the results are inherently erroneous and uncertain! If you think about it, this error estimate is silly, given that there is no way the Smart Ground Meter or any other instrument or method can know anything about the accuracy of the resistivity of the “bottom” soil layer, since major changes can always occur at depths beyond those that can be detected by the electrode spacings used; furthermore, when multiple soil layers are present (e.g., high resistivity soil, then wet soil at the water table, then rock, etc.), one wonders which two layers the instrument is reporting. If multiple layers are combined, one wonders how the instrument can make a judgment as to how combining these layers will affect the performance of an earthing system! In a nutshell, the Smart Ground Meter presents as output the parameters of a two-layer soil, no matter what the soil structure really is, and does not provide ready access to the raw data required for a proper analysis of the data with recognized interpretation methods.
2. Grid Impedance. The developers of the Smart Ground Meter have claimed that it provides two important advantages over standard instruments and methodologies, such as those described in IEEE Standard 81.2:
a. It purportedly allows the resistance of an earthing system to be readily determined using electrodes placed at substantially lesser distances from the earthing system under test than is the case with other equipment and methods;
b. It purportedly allows the resistance of the earthing system to be deduced accurately, despite connections to transmission line shield wires and other such earth return conductors leaving the facility under test. This is achieved by injecting test currents at a number of different frequencies, it being assumed that the reactance detected at higher frequencies represents that of the earth return conductors.
Both of these claims are based on flawed assumptions. According to its developers, the Smart Ground Meter does not need electrodes extending very far from the earthing grid because it does not measure the resistance of the earthing grid with respect to a remote point, as IEEE Standard 81.2 recommends. Rather, it examines differences in measured resistance with respect to successive electrodes that are much closer to the earthing grid. Based on the assumption that the outermost electrodes are within the zone of influence of the bottom soil layer and must therefore reflect an apparent resistance function that corresponds to that of a soil whose deeper layers no longer change in resistivity, the Smart Ground Meter extrapolates the apparent resistance differences to obtain an absolute resistance. There are two problems with these assumptions:
a. The soil resistivity can change, sometimes dramatically, at depths which are detected only by electrodes located far away from the earthing system under test. Deep soil resistivity (e.g., at depths on the order of the length of the earthing system) can have a significant effect on grid resistance and therefore on GPR, touch voltages and step voltages.
b. The presence of buried metallic structures in the soil can have a pronounced effect on local earth potential gradients and thereby adversely affect an instrument that depends heavily on voltage or resistance gradients.
The Fall-of-Potential method recognized by IEEE Standard 81.2 is much more robust because it requires large electrode spacings and it does not depend on local earth potential gradients.
Furthermore, the Smart Ground Meter assumes that the earthing grid under test has negligible reactance, as contrasted with the neutral wires and shield wires leaving the facility under test, which are assumed to behave like inductive chokes as the frequency increases, thus making it possible to detect the grid resistance, which is purportedly not changing. Grounding grids, however, do not have negligible reactance, particularly when they are large and the soil resistivity is low to moderate. Indeed, the grid impedance may be more reactive than resistive! Thus, as the frequency rises, the portion of the earthing system that is most effectively dissipating current into the earth shrinks and its apparent resistance increases, a fact to which the Smart Ground Meter is oblivious, attributing this change in resistance as the shedding of a earthing contribution from neutral and shield wires. When you think about it further, you wonder how any meter could possibly tell the difference between buried conductors connecting one part of an earthing system to another from overhead neutral wires connecting a small earthing system to a large number of closely spaced distribution poles… unless you have a clamp-on ammeter probe measuring how much current is flowing in those overhead neutral wires!
I know of one utility that invited the developer of the Smart Ground Meter to carry out a series of earth resistance tests of substations and power line structures (with and without the neutrals/overhead earth wires connected) using the Smart Ground Meter, as they were having difficulty obtaining satisfactory test results on their own. During this 3-day test, the Smart Ground Meter failed to provide similar earth resistances with and without the neutrals/overhead earth wires connected. Other utilities have found the instrument to fail to properly measure earth resistance as advertised, which is not surprising, in light of the theoretical shortcomings discussed above. Any company would be strongly advised to have the instrument tested before purchasing it. I would expect the instrument to be particularly failure-prone for large earthing systems, especially in low to moderate soil resistivities, and also small distribution substations and poles in high resistivity soils. I have seen firms advertising that the instrument can be used to test earthing systems in congested urban areas: I would love to see a distribution pole earth tested on a city street, in an area where the water mains are metallic! One utility representative was so annoyed by the poor performance of the meter that he offered to discuss his experience with the meter with anybody who expressed an interest. He indicated that he knows of other organizations that have found the meter to fail to measure earth impedance correctly.
I would therefore strongly recommend against the use of the Smart Ground Meter for both soil resistivity and grid impedance tests, as it makes flawed assumptions in developing the soil models and grid resistances it computes and hides from the user the measurement data that would allow an experienced practitioner to come up with soil models and grid impedances, based on sound interpretation methods.
Disclaimer: The discussion above is based on comments made to the undersigned by users of the Smart Ground Meter, on the author’s own encounters with the meter, and on technical publications describing the methodology used by the instrument. It is entirely possible that some of the limitations (e.g., the two-layer limitation for soil resistivity measurements and the use of test electrodes close to the earthing grid depending upon measurement of earth potential gradients for earth impedance measurements) described above have been addressed in a recent version of the instrument and that some of the initial claims made about the capabilities of the instrument have been recanted; however, the author is not aware of such changes.
Robert D. Southey, Eng.
Director, Applied R&D
Safe Engineering Services & technologies ltd.
3055 Boul. Des Oiseaux, Laval, Quebec, Canada, H7L 6E8
Tel.: (450) 622-5000; Fax: (450) 622-5053
Web Site: www.sestech.com