With the rapid transition of overhead lines to covered conductors, line break fault occurs more frequently in resonant grounding systems. Line break fault, especially with earthing, requires ...comprehensive study. There are significant advantages for the detection of line break fault using steady-state voltage characteristics on both sides of the fault point. In this paper, a model is built for different types of single-phase line break fault in resonant grounding systems. Based on the fundamental analysis of single-phase line break fault without earthing, the single-phase line break fault with earthing at system/load side is also comprehensively studied. The neutral voltages are derived from the proposed model. The magnitudes, angles, and phase sequences of the three-phase voltages and line-to-line voltages are mathematically derived for both upstream and downstream of the fault point. The difference between single-phase line break fault and single-phase-to-earth fault is identified. The analysis is verified in the simulations. Built upon the analysis in this paper, the detection and location approaches for line break fault in resonant grounding systems can be further studied.
An innovative methodology is proposed for measuring the resistance of substation grounding grids located in congested areas, particularly those in urban regions. The significant innovation is the use ...of auxiliary current and potential circuits vertically arranged on the ground. The feasibility of using the Fall of Potential (FoP) Method is experimentally investigated using the reduced model technique and an appropriate measuring electrode setup is proposed. The possibility of measurement using the two auxiliary electrodes, positioned in relation to the grid under test, obeying a ratio of 76%, is also evaluated. The depth of these measuring auxiliary electrodes for reliable measurements was determined from a theoretical study, a series of computer simulations, an experimental study in a reduced model, as well as measurements on a 100 m2 grounding grid. The results show the feasibility of using the FoP Methodology as well as the two auxiliary electrodes whose distances to the grid obey the proportion of 76%.
•It is possible to use auxiliary circuits vertically installed in the ground to measure the grounding resistance.•The novel methodology aims to attend situations where classic methodologies do not apply.•The difficulties and challenges for measuring a ground resistance using the new methodology are similar to those found in conventional methodologies.•The reduced model technique has proven effective for studying the positioning of auxiliary measurement circuits.
The grounding electrode buried in soil is prone to corrosion affected by soil and leakage current. The surface of corroded grounding electrodes is wrapped with corrosion product, which affects the ...normal current dissipation process and weakens the grounding performance. The accurate analysis of the grounding performance with corrosion layer can lay a solid theoretical basis for the safety of the power system. In this study, the corrosion layer is regarded as a layer of conductive medium between the electrode and soil. The leakage current along the electrode and the charge on the interface are analysed by coupling point matching method with boundary element method. Finally, the leakage current, grounding resistance, ground potential rise (GPR) and the step voltage of the two typical electrodes with corrosion layer are investigated. The results show that the corrosion layer causes the reduction of the leakage current at the end of the electrode and the enhancement of the leakage current in the middle location. Furthermore, the corrosion layer causes the increase of the grounding resistance and GPR, and the decrease of the step voltage. In addition, the influence of the reduced radius on the grounding performance is much smaller than that of the corrosion layer.
This article presents a performance comparison of the solid, low impedance, high impedance, frequency-selective, and isolated grounding systems. A grounding system (for any power system component) is ...designed as an impedance (<inline-formula><tex-math notation="LaTeX">\bar{Z}_{G}</tex-math></inline-formula>) that connects the neutral point to the ground. The impedance <inline-formula><tex-math notation="LaTeX">\bar{Z}_{G}</tex-math></inline-formula> is constructed using a combination of <inline-formula><tex-math notation="LaTeX">R</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">L</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">C</tex-math></inline-formula> elements. The values and combination type (series or parallel) of <inline-formula><tex-math notation="LaTeX">R</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">L</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">C</tex-math></inline-formula> determine the possible influence of <inline-formula><tex-math notation="LaTeX">\bar{Z}_{G}</tex-math></inline-formula> on ground currents and potentials. Each grounding system is related to a system voltages level, a specific combination of <inline-formula><tex-math notation="LaTeX">R</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">L</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">C</tex-math></inline-formula>, and a range of <inline-formula><tex-math notation="LaTeX">R</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">L</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">C</tex-math></inline-formula> values. The solid, low impedance, high impedance, frequency-selective, and isolated grounding systems are designed for a <inline-formula><tex-math notation="LaTeX">3\phi</tex-math></inline-formula> transformer and a <inline-formula><tex-math notation="LaTeX">3\phi</tex-math></inline-formula> synchronous generator in order to compare their influences on ground currents and potentials during ground faults. The transformer and generator are tested for line-to-ground and double line-to-ground faults with all designed grounding systems. Test results show that some grounding systems can reduce ground currents only, while others can reduce ground potentials only. Such capabilities can be used to fulfill certain system and operation requirements (e.g., service continuity, ground capacity, etc.).
•HFACS-Ground which is useful for grounding accident analysis is developed.•Type of knowledge that can be extracted from accident and incident reports is analyzed.•Accident reports are reliable and ...useful source for evidence-based risk modeling.•Mandatory incident reports are considered reliable for evidence-based risk modeling.•Voluntary incident reports, at their current form, are unreliable source for risk modeling.
This paper presents study of 115 grounding accident reports from the Safety Investigation Authority of Finland and Marine Accident Investigation Branch of the UK, as well as 163 near-miss grounding reports from ForeSea and Finnpilot incident databases. The objective was to find the type of knowledge that can be extracted from such sources and discuss the usability of accident and incident reports for evidence-based risk modeling. A new version of Human Factors Analysis and Classification System (HFACS) is introduced as a framework to review the accident reports. The new positive taxonomy as Safety Factors, which are based on high level positive functions that are prerequisite for safe transport operations, is used for reviewing the incident reports. Accident reports are shown as a reliable source of evidence to extract the most significant contributing factors in the events. Mandatory incident reports are considered useful for understanding the effective barriers as risk control measures. Voluntary incident reports, though, are seen as not very reliable in their current form to be used for evidence-based risk modeling.
Weakly-supervised phrase grounding aims to localize a specific region in an image that corresponds to the given textual phrase, where the mapping between noun phrases and image regions is not ...available in the training stage. Previous methods typically exploit an additional proxy task (e.g., phrase reconstruction or image-phrase alignment) to provide supervision for training, since the lack of region-level annotations in the weakly-supervised setting. However, there exists a significant gap in optimization objectives between the proxy tasks and the target grounding task, which may result in low-efficient optimization for the target model. Therefore, in this paper, we propose a novel dual reinforcement learning framework to directly optimize the phrase grounding model. Specifically, we consider the duality of phrase grounding and phrase generation tasks. These two tasks form a closed loop that can provide quality feedback signals to measure the performance of each other. In this way, we can measure the correctness of the localized regions and thus be able to optimize the grounding model directly. We design two reward functions to quantify the feedback signals and train the models via reinforcement learning. In addition, to relieve the training difficulty of our framework, we present a heuristic algorithm to generate pseudo region-phrase pairs to warm-start our models. We perform experiments on two popular phrase grounding datasets: ReferItGame and Flickr30 K Entities, and the results demonstrate that our method outperforms the previous methods by a large margin.
Due to multiple operation modes and corresponding mode transitions of microgrids (MGs), the MG grounding design is challenging. An MG may lose its grounding provided by the main distribution grid ...when it transitions to the islanded operation, resulting in potential hazards to both equipment and personnel. Existing transformer-based grounding schemes are bulky and have low control capability, which leads to poor transition performances and may affect the operation and protection of the whole distribution grid in the grid-connected mode. Power inverters have been applied as interfaces of distributed energy resources (DERs), which can potentially serve as groundings for future MGs. In this article, a novel DER inverter-based MG grounding scheme is proposed to realize flexible grounding in MGs. The detailed grounding structure and control methods are discussed. The proposed grounding scheme is verified on a realistic MG model through simulation. The proposed control strategies are demonstrated on a converter-based hardware testbed.
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