Photovoltaic (PV) panels and their grid-connection circuitries have to be grounded to comply with various standards and industrial codes. Objectives of grounding a PV system include limiting ground ...currents and potentials, supporting the operation of protective devices therein, and preventing the accumulation of static charges on PV panels. These objectives can be translated into design constraints for an impedance to connect a PV system to the ground. This paper presents the design and performance assessment of a frequency selective grounding (FSGR) for grid-connected PV systems. The proposed FSGR is composed of a parallel <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> circuit, which provides a resistive path for dc currents and a low capacitive impedance path for harmonic currents. The FSGR is designed and experimentally tested for a 2 kW, <inline-formula><tex-math notation="LaTeX">3\phi</tex-math></inline-formula>, laboratory grid-connected PV system under fault and non-fault conditions. The performance of the proposed grounding is also compared with the solid grounding under similar conditions to further assess its capabilities. Experimental results show that the FSGR can reduce ground currents, limit ground potentials, and reduce the dc leakage currents. These observed features are complimented with minor effects on the operation of protective devices in a grid connected PV system.
Visual grounding is a task that seeks to predict the specific location of an object or region described by a linguistic expression within an image. Despite the recent success, existing methods still ...suffer from two problems. First, most methods use independently pre-trained unimodal feature encoders for extracting expressive feature embeddings, thus resulting in a significant semantic gap between unimodal embeddings and limiting the effective interaction of visual-linguistic contexts. Second, existing attention-based approaches equipped with the global receptive field have a tendency to neglect the local information present in the images. This limitation restricts the semantic understanding required to distinguish between referred objects and the background, consequently leading to inadequate localization performance. Inspired by the recent advance in knowledge distillation, in this paper, we propose a DUal knowlEdge disTillation (DUET) method for visual grounding models to bridge the cross-modal semantic gap and improve localization performance simultaneously. Specifically, we utilize the CLIP model as the teacher model to transfer the semantic knowledge to a student model, in which the vision and language modalities are linked into a unified embedding space. Besides, we design a self-distillation method for the student model to acquire localization knowledge by performing the region-level contrastive learning to make the predicted region close to the positive samples. To this end, this work further proposes a Semantics-Location Aware sampling mechanism to generate high-quality self-distillation samples. Extensive experiments on five datasets and ablation studies demonstrate the state-of-the-art performance of DUET and its orthogonality with different student models, thereby making DUET adaptable to a wide range of visual grounding architectures. Our code are available on DUET.
•Propagation time between grounding electrodes affects ground potential rise.•The grounding resistance model considering the propagation time is represented by self-grounding resistances and current ...sources given by mutual grounding resistances and injection currents.•The proposed grounding resistance model can be realized in the EMTP.
The velocity of electric field in the soil is sufficiently lower than that in the air. Conventional grounding resistance models based on an electric circuit theory ignore the propagation time between grounding electrodes (GEs). If the GEs are connected using an aerial lead conductor, the propagation time along the lead conductor is apparently different from that along a grounding conductor (GC) in the soil. The propagation time of mutual grounding resistance between GEs should be considered in accurate lightning surge analysis. This paper proposes a simulation model of the mutual grounding resistance considering the propagation time between GEs.
In this work, we explore neat yet effective Transformer-based frameworks for visual grounding. The previous methods generally address the core problem of visual grounding, i.e. , multi-modal fusion ...and reasoning, with manually-designed mechanisms. Such heuristic designs are not only complicated but also make models easily overfit specific data distributions. To avoid this, we first propose TransVG, which establishes multi-modal correspondences by Transformers and localizes referred regions by directly regressing box coordinates. We empirically show that complicated fusion modules can be replaced by a simple stack of Transformer encoder layers with higher performance. However, the core fusion Transformer in TransVG is stand-alone against uni-modal encoders, and thus should be trained from scratch on limited visual grounding data, which makes it hard to be optimized and leads to sub-optimal performance. To this end, we further introduce TransVG++ to make two-fold improvements. For one thing, we upgrade our framework to a purely Transformer-based one by leveraging Vision Transformer (ViT) for vision feature encoding. For another, we devise Language Conditioned Vision Transformer that removes external fusion modules and reuses the uni-modal ViT for vision-language fusion at the intermediate layers. We conduct extensive experiments on five prevalent datasets, and report a series of state-of-the-art records.
A rigorous full-wave approach based upon the finite-element method (FEM) is used for the analysis of grounding systems taking the frequency dependence of soil electrical parameters into account. The ...method uses minimum approximations to model the transient behavior of grounding systems. In this analysis, frequency dependence of the soil conductivity and relative permittivity is represented using available analytical formulae obtained from experimental data. It is shown that there are cases in which the frequency dependence of the soil conductivity and relative permittivity can affect the transient behavior of grounding systems. Our simulation results show that the effect of frequency dependence is more pronounced for grounding systems buried in low conductive soils in contrast with those buried in highly conductive soils and especially when these systems are subjected to lightning subsequent return stroke currents. In practice, it seems legitimate to disregard the frequency dependence of the soil conductivity and relative permittivity for grounding systems buried in highly conductive soils subjected to lightning first return stroke currents. Within this context, it is shown that the soil conductivity, length of grounding electrode, and the frequency content of the injected current are the main factors contributing to the beneficial effect of the frequency dependence of soil electrical parameters.
This work presents the mutual influence of nearby grounding structures on each other in terms of safety parameters. To epitomise mutual influence, primarily a mathematical model of the double circuit ...transmission line, cling to the tower, close by a substation is considered. The model estimates the ground fault current venting into the encompassing soil, in case of single-phase to ground fault at the tower, when mutual resistive effects of both groundings are taken into account and when they are ignored. Neglecting these effects leads to a false estimation of safety parameters such as ground-fault current and touch voltages, which are frequently used in grounding design. It may lead to unnecessary expenditures on the safety design of the grounding system. For verification purposes, the practical application of the model is exhibited. Also, an interactive model between substation grounding (grid model) and nearby tower grounding (rod model) is examined in terms of safety parameters. To further validate, an experimental set up is built for two nearby groundings. Experimental results obtained through it are compared with the results of the finite-element method and analytical method and are found to be favourable. Touch, step, and ground potential distribution profiles with and without considering nearby grounding are also presented.
Comprehensive understanding of video content requires both spatial and temporal localization. However, there lacks a unified video action localization framework, which hinders the coordinated ...development of this field. Existing 3D CNN methods take fixed and limited input length at the cost of ignoring temporally long-range cross-modal interaction. On the other hand, despite having large temporal context, existing sequential methods often avoid dense cross-modal interactions for complexity reasons. To address this issue, in this paper, we propose a unified framework which handles the whole video in sequential manner with long-range and dense visual-linguistic interaction in an end-to-end manner. Specifically, a lightweight relevance filtering based transformer (Ref-Transformer) is designed, which is composed of relevance filtering based attention and temporally expanded MLP. The text-relevant spatial regions and temporal clips in video can be efficiently highlighted through the relevance filtering and then propagated among the whole video sequence with the temporally expanded MLP. Extensive experiments on three sub-tasks of referring video action localization, i.e., referring video segmentation, temporal sentence grounding, and spatiotemporal video grounding, show that the proposed framework achieves the state-of-the-art performance in all referring video action localization tasks.
Impulse performance of grounding grid is needed for lightning protection design of power system. This paper describes an impulse test facility established for the full-scale grounding grid (50 m long ...and 52.5 m wide) in a 110 kV substation. Test method is presented, including configuration of current injection and return point, measurement of potential rise and longitudinal current. Impulse test is carried out with 2.6/50 and 8/20 μ s current waveform, and the maximum current amplitude is 4 kA. A Current Distribution, Electromagnetic fields, Grounding and Soil structure simulation for the tested grounding grid is also adopted. Impulse performance of full-scale grounding grid is affected by soil ionization and conductor inductance. There is steeper peak on the potential rise waveform near the injection point with shorter wave front current, which leads to more uneven potential rise distribution. Partial soil ionization could increase the current dispersing into the soil at partial area of the grounding grid, and the longitudinal current flowing to the next area decreases. These two factors pose a high potential difference hazard to the secondary equipment via the secondary cable.
Abstract
In this paper, I give an argument for the view that non-fact entities – such as physical objects, abstract objects, events and so on – can ground other entities. Roughly put, the argument is ...as follows: those who accept this view can provide a more plausible account of the grounds of identity facts than those who deny this view.
The impact of frequency dependence of soil parameters on the lightning response of grounding systems is particularly significant, especially for systems with high soil resistivity. However, ...incorporating this behavior in the time domain can be challenging. To address this issue, various approaches in the literature have been explored and compared in this paper. Furthermore, the author has made notable enhancements to a recently developed method designed for this specific task. To validate the effectiveness of these improvements, a comprehensive comparison was conducted against alternative approaches. The study demonstrates that the developed method, which includes frequency dependence of soil parameters in time domain simulation, exhibits higher accuracy in simulating the lightning response of grounding systems. This holds true even for systems with large dimensions and strong frequency-dependent behavior, such as grounding systems with high soil resistivity exposed to fast lightning impulses. Additionally, the model also incorporates the phenomenon of soil ionization.
