The flashover and breakdown faults induced by surface defects of aramid insulation pull rods (ARIPRs) seriously threaten the safe operation of high voltage gas-insulated switchgear. To accurately ...detect the surface defects of AIPRs, this paper proposed a high-sensitivity detection method based on the photon counting technique. The photon counting characteristics of AIPR samples under different voltages and defect sizes of grounding burrs were investigated, and the influence of defects was also explained by simulation analysis. Results reveal that the defects make the photon number increase sharply, and the increased amplitude is positively correlated with the defect size. The investigation of the feature of photons indicates that it is possible to determine the quantitative relationship between photon counting results and defect size. In this regard, the photon counting method provides a new approach for the offline detection of surface defects of GIS aramid insulation pull rods.
The topology and breakpoints of the grounding grid will directly affect its working performance. This paper proposed a resistivity reconstruction method based on magnetic detection electrical ...impedance tomography (MDEIT) to measure the topology and breakpoints of the grounding grid. First, this paper describes the forward problem of grounding grid detection in MDEIT, and calculates the magnetic-field distribution above the grounding grid. Then, the resistivity reconstruction method based on the least squares method is proposed. Finally, this paper verifies the feasibility of the proposed method by a numerical example, which shows that the proposed method can be applied to measure the topology and breakpoints of the grounding grid.
•Lightning response of grounding electrodes is assessed using FDTD.•The FDTD simulations modeled the soil as a Debye medium.•MATLAB function invfreqs to identify the poles corresponding to soil ...resistivity is consistent.•6 poles are enough to represent the frequency-dependence of soil parameters.•4 poles are enough to determine grounding impulse impedance.
This paper considers an evaluation of the influence of the frequency-dependence of soil parameters on the lightning response of horizontal grounding electrodes by means of the finite-difference time domain (FDTD) electromagnetic model. The FDTD simulations assumed the soil modeled as a multipole Debye medium and the response of grounding electrodes due to lightning return stroke currents with typical front time parameters of negative first and subsequent strokes was assessed. The results in terms of the ground potential rise (GPR) and grounding impulse impedance (ZP), were compared to those provided by the application of the Hybrid Electromagnetic Model (HEM), a frequency domain model widely applied for lightning related problems, and revealed the top quality of the modeled approach in FDTD. The largest percentage variations of the calculated impulse impedance compared to HEM were around 6 % and 10 % for first and subsequent stroke currents, respectively.
This paper proposes a generic power flow algorithm for bipolar DC microgrids based on the Newton–Raphson (NR) method. The bipolar DC microgrid has gained considerable attention for its effectiveness ...and reliability with regard to power supply. To date, however, power flow algorithms for bipolar DC networks have not been fully investigated and generalized, although power flow analysis is an essential tool, with diverse applications ranging from network design to real-time control. In this study, a current injection-based power flow algorithm is established that considers the grounding scheme and voltage control method of energy source. Six bus types are defined, depending on the grounding scheme and voltage control combination. The unknown pole voltages and equations to be iteratively solved are identified. Afterwards, the unknown pole voltages are updated via a single NR method, which makes the proposed method straightforward and efficient. The case study validates that the proposed power flow algorithm can find the bus voltages of each pole sufficiently close to the simulation results of PSCAD/EMTDC, while having a low computational burden.
•Generic power flow algorithm for bipolar DC microgrids is proposed.•Proposed algorithm considers grounding schemes and control modes of energy sources.•Proposed algorithm aids various power system applications for bipolar DC microgrids.•Developed method has high accuracy and low computation time with single NR method.
The emerging vision-and-language navigation (VLN) problem aims at learning to navigate an agent to the target location in unseen photo-realistic environments according to the given language ...instruction. The main challenges of VLN arise mainly from two aspects: first, the agent needs to attend to the meaningful paragraphs of the language instruction corresponding to the dynamically-varying visual environments; second, during the training process, the agent usually imitate the expert demonstrations, i.e ., the shortest-path to the target location specified by associated language instructions. Due to the discrepancy of action selection between training and inference, the agent solely on the basis of imitation learning does not perform well. Existing VLN approaches address this issue by sampling the next action from its predicted probability distribution during the training process. This allows the agent to explore diverse routes from the environments, yielding higher success rates. Nevertheless, without being presented with the golden shortest navigation paths during the training process, the agent may arrive at the target location through an unexpected longer route. To overcome these challenges, we design a cross-modal grounding module, which is composed of two complementary attention mechanisms, to equip the agent with a better ability to track the correspondence between the textual and visual modalities. We then propose to recursively alternate the learning schemes of imitation and exploration to narrow the discrepancy between training and inference. We further exploit the advantages of both these two learning schemes via adversarial learning. Extensive experimental results on the Room-to-Room (R2R) benchmark dataset demonstrate that the proposed learning scheme is generalized and complementary to prior arts. Our method performs well against state-of-the-art approaches in terms of effectiveness and efficiency.
There has been a growing demand of electric power in many urban agglomerations. To address this demand, 110-kV power networks are regularly expanded inside and around cities in Poland. These power ...networks are often constructed as underground cable lines. The 110-kV cable lines are usually designed as three single-core cables laid in a common route. In case of long 110-kV cable lines, the cross-bonding method is applied to the connection of metal sheaths of these cables. Additionally, one or more earth continuity conductors are laid along the main cable line and earthed at both their ends. These earth continuity conductors can be uninsulated and can cause electric shock hazard (danger step voltages). The problem defined in this paper consists of an attempt to calculate the expected step voltages for different considered earth continuity conductor arrangements in 110-kV cable lines and to compare the obtained results to admissible values of the voltages found in an appropriate standard. Protection against electric shock, calculation of earthing resistance, and step voltages, as well as simulation studies in case of sample 110-kV cable lines have been described in the paper. The results show the analyzed layouts of 110-kV cable lines have significant impact on the values of voltages occurring in and around earth continuity conductors. The maximum values of earth electrode voltage (and in this way expected touch voltages), as well as step voltages occur in the layout of single cable line and single earth continuity conductor arranged in parallel.
Bentonite is low resistance water retaining conductive clayey material often used as grounding enhancement material, particularly in a troubled environment. Due to its unique property, bentonite ...retains water and dissipate unwanted electrical current to ground. However, bentonite's water retention capacity would inevitably induce corrosion to the grounding electrode and may jeopardize the grounding system's performance in the long run. This study presents bentonite properties on copper electrodes' corrosion behavior. In this study, copper corrosion behavior buried in Andrassy bentonite specimens was investigated under varying relative humidity conditions using the vapor equilibrium technique. The corrosion rate was calculated at equilibrium, and FESEM later characterized the corroded surfaces. The copper corrosion rate in Andrassy bentonite was found to be between 2.2 and 2.8 × 10-3 mm/year. Test results showed that more water might not necessarily induce and expedite copper corrosion. However, it was noted that copper corrosion was somewhat limited under extremely dry conditions and very wet conditions. On the other hand, RH = 75% was the optimum copper corrosion condition to occur. It is believed that the corrosion of copper specimen may be influenced by other complex mechanism presence of such as chemicals species and microbes contained within the bentonite and surrounding environment.
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