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The groundings of the power distribution, signaling, and power systems of a railway system are individually performed to realize fail safe, and the groundings are often installed in close proximity. Thus, when a grounding electrode is invaded by a lightning current, its ground potential rises together with the potential of the adjacent grounding electrodes; hence, there is a possibility of a large overvoltage being applied to the connected devices. In this paper, we have investigated the potential spread between two rod-shaped electrodes widely used in the grounding of the power, signal, and distribution systems of a railway system using the finite-difference time-domain method. The results of this paper are organized in such a way that the extent of the potential spread to the neighboring grounding electrodes can be understood from information such as the grounding resistivity at the installation location of the ground electrode and the wavefront duration of the lightning current, and these findings will be useful for grounding design. We also investigate the effect of the insulator between two neighboring electrodes to prevent the potential spread. [ABSTRACT FROM AUTHOR]

This paper suggests an advanced approach in the verification of the adequacy of a grounding system (GS) located in a common zone of influence with other GSs, taking into account the mutual interferences between the GSs. In fact, the presence of other GSs can transfer inadmissible touch and step voltages on the testing GS, particularly sensitive for critical power systems as data centers and hospitals. The safety of a local GS or of a global GS (GGS) does not admit uncontrolled interferences. Simulation programs assume a relevant importance, because they allow analyzing the interferences of GSs, particularly in operational difficulties for the tests. GSs have to maintain within the installation lifetime their characteristics of integrity and continuity and their safety performances; hence, they require a management program. This paper highlights the relevance of intrinsically safe GSs that guarantee safe touch/step voltages lower than permissible permanent voltages such as GGSs. GSs in city centers and urban and industrial areas evolve in time. Each installation of a new GS can influence the performance of the GSs existent in the area. Inspections and measurements are also necessary, following variations that can influence essential requirements. [ABSTRACT FROM AUTHOR]

The International Electrotechnical Commission Standard 61936-1 “Power installations exceeding 1 kV a.c.” defines the “global grounding system” (GGS) as an equivalent grounding system that ensures “no dangerous touch voltages.” This paper deals with an analysis of the parameters that characterize the behavior of grounding systems (GSs) operating in the same zone of influence (ZOI) and proposes to recognize four levels of “globality.” With this aim, the geometric criterion and the safety criterion are introduced to identify the ZOI. The safety criterion allows for identifying a GGS and characterizing the global ZOI of a GGS. This paper highlights the relevance of recognizing what is intrinsically safe for a GS that guarantees safe touch/step voltages lower than permissible permanent voltages. An integration of many coexisting GSs for constitution and extension, naturally, can reach the level of an intrinsically safe GS and, hence, of a GGS. [ABSTRACT FROM AUTHOR]

This paper presents the results of field measurements of touch voltages occurring in buildings under ground-fault conditions, as well as resistance-to-ground of edifices of different nature (i.e., masonry, reinforced concrete, etc.). The goal of this experimental study was to confirm that ground-fault potential profiles and touch voltages in buildings do depend on the make-up of the structure, the floor material, the configuration and location of the grounding electrodes with respect to the point of touch, and the presence of metalwork (e.g., metal pipes) bonded to the ground system. The results of the above measurements, involving buildings of different construction type, are herein presented and discussed, and were obtained following the analytical models illustrated in Part I of this paper. [ABSTRACT FROM AUTHOR]

Global earthing systems (GESs), which are created by the interconnection of local earthing systems, should guarantee the absence of dangerous touch voltages. According to international standards, one of the reasons for this safety characteristic of GESs is that medium-voltage and low-voltage grounding systems form a quasi-equipotential area. Typical examples of GESs are in city centers due to the high number of interconnected grounding systems in the area. For this reason, in addition to ground grids, other metallic parts with different primary functions shall be also considered, e.g., water and gas pipes, tramway tracks, and building foundations can modify the electric potential distribution in the area. In this paper, a model based on the Maxwell's subareas method (MaSM) is used to evaluate how buried metallic parts, which are not intentionally connected to ground grids, modify the electric potential on the soil surface. First, the MaSM model is validated with experimental measurements on a simple electrode configuration. The measured voltages are compared with the MaSM results and with the results obtained with a finite-element method model simulated with COMSOL Multiphysics. Then, the simulations are carried out on a realistic urban test case. [ABSTRACT FROM AUTHOR]

The adequacy of grounding systems has to be periodically verified in operational time. With urban development and building growth adjacent to power systems as high-voltage/medium-voltage substations, it is very rare to have an area around with sufficient accessibility for installing potential and current electrodes. This paper discusses a safety criterion to verify the effectiveness of a grounding system. This criterion suggests conservative tests for both ground potential rise and touch and step voltages that allow to verify the grounding systems' effectiveness in areas with reduced accessibility and to monitor its evolution in time. [ABSTRACT FROM AUTHOR]

Each grounding system (GS) needs periodical measurements to control its adequacy to the safety conditions. The tests of step and touch voltages are the sole measurements available in urban or industrial areas with reduced accessibility. In fact, in these areas, the classic measurements used to verify the electrical characteristics of the GS generally present some operational difficulties. The auxiliary current electrodes can only be located at short distances, and thus, the test methods and techniques result in conservative values in comparison with the prospected true values measurable by adopting a remote auxiliary electrode. The locations of auxiliary current electrodes at short distance make it easier to keep them permanently installed and to permit the monitoring of the adequacy of GS. This paper presents the measuring touch/step voltages procedure that provides conservative results showing some case studies done in GS of high voltage/medium voltage substations. It is essential to have the map of the constitution and configuration of the GS to know its data and the location of the various equipment and buildings, the presence of extraneous conductive parts inside, and in proximity of the substation, such as other GS. The field measurements require a good experience of the operator that can be learned by carrying out measurements in cases of GS with influence zone accessible, so that it is possible to compare the traditional method with a remote electrode and the method at short distance. [ABSTRACT FROM PUBLISHER]

Grounding systems (GSs) must be tested periodically in order to maintain the touch voltage (TV) and step voltage (SV) below a safe value in all of the zones of the installation. Measurements of the ground resistance and of the TV and SV are typically done by the fall-of-potential (FoP) method, locating the auxiliary current electrode at remote distance to test the effective behavior of the GS. In urban areas, it could be very complicated or impossible to install the auxiliary current electrode as required, not having area around with sufficient accessibility. At this aim, this paper describes a methodology of using multiple current electrodes at short distances, modifying the classic FoP practice, so that the measurements of TV and SV are always conservative. The adequacy of a GS is verified if the values of the TV and SV, tested inside and in the vicinity of the GS, are below the permissible limits, regardless if they are true or conservatively increased. Thus, the measured TV and SV by the suggested method, always conservative, allow verifying the adequacy of GSs, in the cases where it is impossible to locate the remote auxiliary electrode. [ABSTRACT FROM AUTHOR]

To date, there has not been a completely satisfactory comparison between theory and experiment for a ground system that is excited by a current with a submicrosecond rise time. This requires careful definitions of both the measured and calculated voltages because the electric field is no longer conservative and voltages become path dependent. An experiment performed by EdF in the late 1970s has been carefully analyzed and compared with a simulation using full-wave theory. The comparison is excellent, and this example can now be used as a “gold standard” to which approximate grounding theories can be compared. [ABSTRACT FROM AUTHOR]