Existing fault handling methods struggle to simultaneously meet the high demands of flexible DC distribution networks for fast response, selectivity, functional coordination, and techno-economic performance. To address this challenge, a fault handling method based on a novel function-integrated multi-port DC circuit breaker (FIMP-DCCB) is proposed. First, a topology design is presented for FIMP-DCCB that integrates current limiting, fault clearance, and fault-property identification. Then, an efficient fault handling strategy is proposed, comprising a fault current pre-transfer strategy to reduce the current-limiting delay, a distribution line/bus short-circuit fault clearing method based on the functional coordination of ‘current limiting, fault clearance, and fault-property identification', and a backup fault-handling strategy for UFD failure. Finally, by establishing the equivalent model and low-voltage physical circuit, the working principle of FIMP-DCCB is analyzed. The proposed FIMP-DCCB is further compared with typical DCCBs to show technical and economic advantages.
The C4F7N/CO2 gas mixture possesses excellent dielectric strength and low environmental impact, serving as a promising SF6 alternative for gas-insulated switchgear (GIS). However, metallic particle contaminants can be released by mechanical operations during GIS erection; these particles move under electric fields and readily trigger gas-gap breakdown or surface flashover, but the motion mechanisms of the particles in the C4F7N/CO2 gas mixture remain unclear. In this study, a transparent GIS test platform was established, and a YOLO object detection algorithm combined with the DeepSORT tracking method was adopted to achieve full-process trajectory tracking of the particle. This study investigated the linear metallic particles in the DC-GIS filled with 10%C4F7N/90%CO2 gas mixture, in comparison with SF6. Results show that “firefly motion” is the key factor dominating particle adsorption onto insulators. Compared with SF6, the C4F7N/CO2 gas mixture exhibits lower firefly motion duration and adsorption probability. Reducing the gas pressure decreases the firefly motion duration and adsorption probability. Increasing the voltage amplitude intensifies particle motion, while the adsorption probability decreases. Compared with positive polarity, negative polarity induces higher firefly motion duration and adsorption probability. Increasing the particle length and radius increases the firefly motion duration and adsorption probability. This study provides a reference for theoretical studies on particle contamination prevention in the C4F7N/CO2 gas mixture.
Metallized polypropylene film capacitors (MPPFCs) are widely employed in power transmission and renewable energy systems as key components for filtering and reactive power support. However, harmonic voltages introduce additional losses and accelerated aging, which threaten their insulation integrity and long-term reliability. This paper proposes a non-uniform loss calculation method for MPPFCs based on segmented modeling. A wideband distributed equivalent circuit model is established to analytically derive the plate voltage/current distribution and loss characteristics under harmonic excitation, enabling spatially resolved characterization of loss distribution along the electrode structure. Model parameters are identified through dielectric response testing, and experimental studies are conducted (up to 1 kHz) to evaluate loss distribution, temperature rise, and reliability degradation, while higher-frequency behavior is analyzed based on the proposed model. The results show that harmonic voltage leads to highly non-uniform current distribution, with plate loss becoming dominant and increasing sharply with frequency. Temperature rise exhibits nonlinear behavior, where larger capacitance values result in faster heating and higher steady-state temperatures, eventually causing thermal runaway. Long-term harmonic stress increases the equivalent series resistance (ESR), consistent with microscopic evidence of electrode oxidation and polymer degradation observed by scanning electron microscope (SEM) and energy-dispersive X-ray spectrometer (EDS). These findings provide new insights into the reliability assessment of capacitors under harmonic-rich operating conditions, and can serve as a reference for the design and lifetime evaluation of power delivery equipment.
The skin effect is a familiar subject to power system engineers and researchers. It plays an important role in the accurate modeling of power systems components, such as transmission lines subjected to switching operations and electromagnetic transients. The frequency-dependent internal impedance of solid or tubular cylindrical conductors can be easily expressed in closed form using Bessel functions (of integer order) when the material medium is homogeneous. However, in general, for inhomogeneous media, the impedance can only be evaluated using numerical methods. Based on Maxwell's equations, applied to radially inhomogeneous conductors, we show for the first time that Bessel functions (of complex order) can still be employed to describe and compute the per-unit-length skin-effect internal impedance of inhomogeneous cylindrical conductors provided that their conductivity follows a certain well-defined type of radial profile. The theory is illustrated with some examples of conductivity profiles, with the resulting internal impedance plotted against the frequency in the range 0 to 50 kHz.
