Article

Analysis of frequency distribution of ground fault-current magnitude in transmission networks for electrical safety evaluation

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Abstract

Ground Potential Rise (GPR) evaluation under fault conditions is important for the evaluation of electrical safety risk to human beings who are present in and around electric installations. Current national and international standards recommend such evaluation is based on a set of ‘worst-case’ conditions that include a simplified fault current calculation procedure based on assuming a maximum value. Accordingly, this approach may lead to over-design of grounding systems in certain cases by overestimating individual risk. To address this and move towards a comprehensive probabilistic assessment of risk, a more detailed model of the electric network is required for fault current magnitude evaluation. This paper describes the application of the multi-conductor method to determine fault current distribution on transmission networks. First, a model of a portion of the UK transmission network is built and the fault current and its distribution among the phases, ground wire and ground is evaluated for three example fault positions. It is found that the position of the fault along the line, substation bus section status and proximity to generation affect greatly the current distribution. Then, a transmission model based on the national network is built, and the effects of system loading and generation on fault current magnitude were also considered. A complete frequency distribution of fault current magnitude is obtained and the results demonstrate the value of such description for the probabilistic assessment of human safety in grounding system design.

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... -Although different national standards vary in safety criteria [18,[21][22][23], it is commonly accepted that consistent utilization of the standards includes comfortable safety margins (because they apply classical deterministic "worstcase" theory which assumes pessimistic values for all random variables present in the danger assessment and assume that all unfavorable situations will occur simultaneously) [22][23][24][25][26]. ...
... -On the other hand, state-of-the-art knowledge on hazardous voltages calculation used in detailed computer simulations of earthing system, and, particularly, probabilistic methods application (with parameters extracted from historical system fault data) [22][23][24][25][26] enable more accurate and objective treatment of practically all (random) variables present in the danger assessment. The adequacy of calculating the permissible values of prospective touch and step voltages using feet resistance estimates according to various national standards might be called into question in such studies (further referred to as state-of-the-art safety studies), especially at low values of h s . ...
... , and R f,s (h s , K, D), for different D. One example of the suggested application of (26) in (21) is available in Section 4.5.1 of this paper. In [28], this author proposed a simple extension of formula (25) to the cases where there is a surface layer, which is declared only for 0.3 m ≤ D ≤ 1 m, and expressed the resistance of the feet in parallel modifying the resistance of one foot placed on the surface of the soil of the same structure. ...
Article
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This paper concerns the human feet resistance estimates in safety studies of earthing systems, taking into account small effective thicknesses of the surface layer and mutual resistance between the feet. Based on simulations using the finite element method, performed to determine the variation of the feet resistance to earth with the following parameters: resistivity of natural soil, surface layer resistivity and thickness, and separation distance between the feet, the available literature was analysed; then expressions for the surface layer derating factor based on the one-foot model are suggested that best match the simulation results. Simple correction factors are also proposed for calculating the earth resistance of two feet in parallel and in series that take into account the mutual interference of the feet for different separation distances between the feet. The influence of inaccuracies in feet resistance assessment on estimates of permissible prospective touch and step voltages is discussed in various cases, taking into account that resistance of the human body depends on the applied voltage and current path. (Submitted to Electrical Engineering, Archiv für Elektrotechnik, on March 9th, 2022)
... This places a responsibility on designers and researchers to maintain a robust system throughout its operational lifespan. Designers strive to establish a secure path for fault conditions back to the source (Nassereddine et al. 2014b;Nassereddine et al. 2013a), which may involve directing the fault current to Earth or a return conductor (Buccheri and Mangione 2008) The magnitude of the fault current can exceed the load current by more than 10 times (Coppo et al. 2019). To ensure that the voltage rise stays below dangerous levels, the high current must be absorbed by a low-resistance path (Dladla, Nnachi, and Tshubwana 2022;Lee and Chang 2005). ...
... To measure the EPR and earth grid resistance, a zero-reference point is required. This can be achieved by using a spare communication wire terminated at a remote area (Coppo et al. 2019;IEEE 80-2013;Nassereddine et al. 2013b;. The paper introduces equation 7 to compute the earth grid resistance at location 'i' when the voltage IoT is present. ...
... From the above analysis, it can be seen that the amplitude of the steady-state component of the grounding current gradually decreases, resulting in less obvious fault characteristics. However, when the amplitude of the transient component of the grounding current gradually increases, the fault information is easier to extract [6]. The initial phase angle of the fault directly affects the amplitude of the transient component of the grounding current. ...
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To reduce the error of single-phase ground fault and improve the security and stability of distribution network operation, an online monitoring method for single-phase ground fault in a medium voltage distribution network based on multi-measuring point information is proposed. Based on the analysis of single-phase grounding transient characteristics, the fault location is determined from the information of multiple measuring points according to the characteristics analysis results to realize the fault subsection location, identify the fault line section, and improve the location accuracy. Based on the fault location results, fault monitoring is realized through the “four-in-one” intelligent distribution terminal. The experimental results show that the accuracy of the monitoring results of this method is kept above 95%, and the monitoring error value of grounding fault is kept at about 1%, so the monitoring results have high reliability.
... Membership functions are determined for each range of the conditions. Studies [13,[17][18][19][20] were concerned with the location of a single-phase ground fault depending on the network operation. A complex admittance matrix method was proposed as a location tool. ...
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The paper addresses the issue of identification of the type of single-phase ground fault in medium voltage networks operating mainly with an isolated neutral. By analyzing the published research, the most promising methods for detection of a single-phase ground fault were selected. Further, using the selected parameters, algorithms were designed to determine the parameters, process them, and use them to identify the type of a single-phase ground fault. The algorithm developed by the authors was formalized for the application on the basis of microprocessor-based protection systems using digital signal processors. The operation process was modeled using real oscillograms of single-phase ground fault. The use of high-frequency zero-sequence current and voltage components, as well as the root-mean-square value of the zero-sequence voltage, made it possible to design an algorithm that identifies any of the possible single-phase ground fault types (bolted, arc, or contact resistance ones). The first part of the article gives an overview of the state-of-the-art of research in the field of detection and identification of single-phase-to-earth faults. In the second part, the parameters of emergency operating conditions are analyzed and the key parameters are determined based on them. The third part contains a description of the single-phase fault identification algorithm developed by the authors and the output oscillograms. The fourth part makes conclusions on the applicability of the algorithm.
... Most of today's distribution networks are low-current grounding systems, and the detection of grounding faults has always been a technical problem plaguing the operation of distribution networks [1]. In recent years, with the wide application of power electronics technology and the increase of various nonlinear loads, harmonic pollution in power system has become increasingly serious, which has become a public hazard affecting power quality [2]. ...
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In order to realize the accurate judgment of the ground fault and improve the fault discrimination effect, this paper proposes a low-current ground fault discrimination method for the primary and secondary fusion complete sets of equipment under the calculation of three-phase asymmetric harmonic power flow. The three-phase asymmetric harmonic power flow calculation is carried out, the ground fault line selection model is constructed according to the calculation results, and the faulted line is obtained by the zero-sequence active component method and the zero-sequence reactive power component method; the wavelet packet transform method is used to extract the transient zero-sequence power direction, and use it as a line selection criterion to identify whether a ground fault occurs. The amplitude characteristic enhancement value of each section is obtained by calculation. According to the distribution characteristics of the zero-sequence current amplitude of the faulted feeder, the corresponding section is selected as the fault section, and the mutation logic array is used in the determined fault section to realize the low-current grounding fault judgment. The experimental results show that the method has high judgment accuracy in practical application, and the highest value is 98.5 %, which indicates that the method can accurately judge the fault line and determine whether ground fault occurs.
... A method based on EMTP-ATP program has been presented in 3 [27] to determine the value of currents flowing into substations grounding. The application of the multi-conductor method has been described in [28] The proposed method in [1] takes into account all the mentioned parameters except one of them. In [8], the authors assumed that the short-circuit current passing through the phase conductor is known, while in the proposed method in this paper, the currents passing through the phase conductors are taken unknown that include in the final proposed formula. ...
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