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A three-dimensional model based on molecular dynamics has been developed to describe the formation of a single cathode spot in vacuum arcs. The formation of the cathode spot is assumed to be controlled by the plasma ions, the effect of which is simulated in LAMMPS through the process of ion bombardment. The cathode is represented by structured copper atoms, while the ions are continuously injected into the domain with a certain velocity towards the cathode surface. Ion bombardment leads to the appearance of a crater, which is caused by the accumulation of pressure effect against the relaxation of substrate temperature. The size of the crater is found to be determined by the spatial distribution of the injected ions. The formation of the cathode spot is also scrutinised by electron emission from the cathode surface with variable surface temperature during the cathode spot development process. In addition, the evaporated atoms forming the metal vapour are observed. This study provides a description of the formation of the cathode spot at microscale, which shall be helpful to further studies of the arc rooting and arc contact (electrode) erosion in vacuum environment. [ABSTRACT FROM AUTHOR]

Due to the uncertainty of user's behaviour and other conditions, the design of energy efficiency improvement methods in buildings is challenging. In this paper, a building energy management method based on deep reinforcement learning is proposed, which solves the energy scheduling problem of buildings with renewable sources and energy storage system and minimises electricity costs while maintaining the user's comfort. Different from model-based methods, the proposed DRL agent makes decisions only by observing the measurable information without considering the dynamic of the building environment. Simulations based on real data verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The key concern for transformers experiencing ferroresonance is whether the energy transferred into the transformer body during core saturation by the nonsinusoidal currents is damaging. Saturation and the consequent incompetency of the core to contain the flux manifests itself as current induced in parts of the transformer body not foreseen to conduct current. Sustained ferroresonance may last for minutes (or even hours), when no intervening operations are carried out, and may cause local overheating and thermally degrade surrounding insulation. In this paper, transient electromagnetic analysis was conducted by using 2-D finite-element models of a 240-MVA 400/132/13-kV autotransformer. As a continuing effort, the main objective of modeling is to visualize the flux flow in parts where transformer designers have not anticipated its presence. A quantitative assessment of the flux, the induced currents, and the power dissipated in these parts has been carried out to determine the degree of risk imposed on a transformer under ferroresonance. Index Terms--Failure mechanisms, ferroresonance, finite elements, transformers.

Frequency-response analysis (FRA) has been accepted as one of the most sensitive tools to detect mechanical faults of power transformers. Correct interpretation of FRA responses is crucial when assessing the integrity of a transformer. Transformer FRA responses have distinctive frequency regions which are predominated by core, windings, and measuring setup. This paper addresses one of the major factors that affect the FRA responses: the winding structure itself. In terms of the structures of single winding, they can be categorized into windings with either high- or low-series capacitance in proportion to the shunt capacitance. Correspondingly, the FRA responses of windings of high series capacitance exhibit the increasing trend of magnitude, while windings of low series capacitance display a steady magnitude trend with the features of resonances and quasi-antiresonances or antiresonances. For a winding made of two concentric winding coils, the pattern of alternating resonances and antiresonances would be exhibited on its FRA response. Index Terms--Diagnosis, frequency-response analysis (FRA), interpretation, power transformers.