Increasing deployment of power-electronic loads has intensified the need for short-horizon forecasting of voltage harmonic distortion at low-voltage points of common coupling. This study develops a telemetry-first framework for forecasting phase-wise voltage total harmonic distortion (UTHD) and its compliance margin using routinely retained 10 min power-quality indices. Independent histogram-based gradient-boosting regressors (HGBRs) were trained for 10, 30, 60, and 120 min horizons using leakage-controlled chronological validation and were benchmarked against persistence, seasonal and climatological references, Ridge, autoregressive integrated moving average (ARIMA), bidirectional long short-term memory (BiLSTM), target-history-only HGBR, XGBoost, and LightGBM. Forecast uncertainty was quantified using symmetric conformal prediction with calibration-only selection of adaptive residual parameters. Across the three Córdoba phases, the common-feature HGBR achieved mean MAEs of 0.198, 0.225, 0.232, and 0.258 percentage points at 10, 30, 60, and 120 min, respectively, and consistently outperformed persistence. The selected conformal configuration achieved mean empirical coverages of 90.55–88.77% for nominal 90% intervals and 95.15–94.17% for nominal 95% intervals across increasing horizons. These findings show that index-level telemetry can support accurate multi-horizon UTHD forecasting with empirically calibrated predictive uncertainty for forecast-informed harmonic monitoring.
Arc erosion induced by lightning-triggered power-frequency follow currents is a primary cause of insulated conductor breakage. However, significant thermal–mechanical differences remain between laboratory low-current tests and field high-current faults, and existing models fail to quantitatively characterize the transition of damage mechanisms under different currents. This study compares the fracture morphologies of two types of broken samples using scanning electron microscopy. The laboratory low-current samples exhibit an oxygen content as high as 41.22% at the fracture surface, accompanied by a reef-like progressive melting morphology, indicating thermal erosion dominance. In contrast, the field high-current samples display extremely low oxygen content, numerous cracks and pores, and pronounced mechanical fracture features. To quantitatively reveal these mechanisms, a magnetohydrodynamic arc ablation model coupled with material phase change was established using a JKLYJ-70 insulated conductor, and simulations were conducted for a typical fault current of 5 kA. Results indicate a maximum arc temperature of 12,974 K. The axial temperature distribution exhibits a “higher-at-ends, lower-in-middle” profile, while the radial temperature distribution approximates a Gaussian distribution. The peak electrodynamic force on the conductor surface reaches 3951 N, significantly exceeding other force components. Theoretical predictions indicate that the breakage time under pure thermal effects is 14.8 s, which is shortened to 2.8 s after incorporating the electrodynamic force, representing a reduction of 81.1%. Further calculations identify a theoretically predicted critical current threshold of approximately 1.45 kA. Above this threshold, the electrodynamic force is dominant, and mechanical fracture occurs prior to melting. Below this threshold, thermal accumulation and melting erosion are dominant, requiring the conductor to reach its melting point before breakage. This threshold reveals the critical condition for the transition from thermal-dominated to force-dominated breakage under thermal–mechanical coupling, providing a general modeling approach for high-temperature arc–conductor interaction analysis and a theoretical basis for differentiated protection design in electrical engineering.
This study investigates the effect of die geometry on the deformation behavior of a disc-shaped billet during cyclic pressing with alternating deformation directions. Each complete cycle comprised two successive passes with a 90° change in the pressing direction. Two cross-channel die configurations were considered: aligned and offset channels. Numerical simulations were performed in DEFORM-3D using the built-in material model for AA5049 aluminum alloy. After one pressing cycle, the offset-channel die resulted in a greater accumulation of equivalent strain: the proportion of the analyzed cross-section with strain values above 0.15 mm/mm increased from 36.78 to 53.80%, while the proportion of regions with values above 0.30 mm/mm increased from 13.43 to 21.08%. Effective stress levels remained comparable for both configurations, whereas offset channels increased the proportion of material subjected to compressive mean stresses. AA3003 aluminum alloy was used for experimental investigation of the structural effects of changes in die geometry, with particular attention to the evolution of the deformation substructure during plastic deformation. Specimens subjected to ten deformation cycles were examined by transmission electron microscopy. The selected TEM regions showed geometry-dependent differences in cell/subgrain morphology and substructure fragmentation. The characteristic cell/subgrain dimensions were 0.476 ± 0.027 µm for aligned channels and 0.457 ± 0.014 µm for offset channels. Because the uncertainty intervals overlap and no significance test was performed, these values are not interpreted as evidence of a statistically significant size difference. The results demonstrate that channel geometry affects the strain and stress distributions as well as the formation of the deformation substructure. Given the differences in alloy composition and number of deformation cycles, the numerical and experimental results were compared qualitatively.
A novel single-stage driver configuration that combines a modified buck–boost converter with a Class-D series resonant topology is implemented for high-power LED applications. Operating in the discontinuous conduction mode (DCM), the integrated buck–boost stage inherently guarantees a high power factor (PF) alongside minimized total current harmonic distortion (THDi). To power four independent LED strings, the resonant stage interacts with a 1:1 transformer, which successfully delivers autonomous current-balancing capabilities without requiring auxiliary current control loops. The proposed architecture effectively mitigates stage-to-stage conversion losses. Furthermore, soft-switching performance is achieved across all components, featuring zero-voltage switching (ZVS) during turn-on for active switches and zero-current switching (ZCS) during turn-off for diodes. The steady-state behavior of the topology is thoroughly analyzed, followed by the formulation of mathematical equations to guide component selection. To validate the theoretical framework, a 100 W experimental prototype was constructed and evaluated. Initial assessments under rated loading conditions—consisting of four parallel channels, each containing twenty-five series-connected 1 W LEDs—demonstrated a PF of 0.996, a THDi of 5.58%, and an overall power conversion efficiency of 89.6%. Subsequent robustness tests utilizing asymmetrical string arrangements (23, 24, 26, and 27 LEDs per channel) confirmed nearly uniform current distribution across all branches, thereby substantiating the self-governing current-sharing mechanism of the proposed circuit.
