Series arc faults can cause fire hazards in dc distribution systems. During a series arc fault, the line impedance usually increases rapidly and the arc current includes high-frequency components. To capture the arc-induced high-frequency signals, parallel capacitors are added to the circuit. The characteristics of the currents through these capacitors permit fault detection and localization. This paper determined that a Rogowski coil could be constructed with adequate bandwidth to cover the relevant frequency band of 1 kHz-1 MHz, found that the amplitude of the pulse and the difference in the integrated fast Fourier transform of the current signal are well correlated with the series fault, described experiments to demonstrate that, over the range tested, the two parameters are robust with respect to the pressure of the atmosphere in which the arc forms, the electrode material, the speed at which the electrodes separate to initiate the arc, the switch operation, the load-type and the load change, and demonstrated that within the well-known limits of traveling wave localization, such localization can be used based on the capacitor current pulse information after it has been validated by the spectrum analysis as a fault and not a spurious signal. The proposed approach was demonstrated in two low-voltage dc cable circuits.

Dielectric materials with high thermal conductivity (TC) can enable disruptive performance enhancement in the areas of electronics packaging, thermal management, energy storage, cabling, and heat sinks. There have been widespread global efforts over the past decade on developing novel nanocomposite dielectric materials. As a baseline, legacy polymers and epoxies used in the abovementioned applications have very low thermal conductivities ranging from 0.1-0.5 W·m ^-1 ·K ^-1 . Recent advances have led to the commercial availability of polymeric materials with thermal conductivities approaching 10 W·m ^-1 ·K ^-1 . Importantly, several fundamental studies report novel nanocomposites with thermal conductivities > 50 W·m ^-1 ·K ^-1 . This article summarizes progress in the development of such materials with a focus on developments that show promise for improved practical dielectrics. This review highlights that high TC alone is inadequate to characterize the suitability of any material for the above applications. Other thermal properties, such as thermal diffusivity, glass transition temperature, and the ratio of the in-plane to out-of-plane TC, are important to quantify the thermal performance of novel nanocomposites. In addition, characterization and understanding of mechanical properties (coefficient of thermal expansion (CTE), tensile strength and elastic modulus) and electrical properties (dielectric strength and dielectric permittivity) are critical for holistic multifunctional assessments of these materials. There are other parameters and properties that influence performance, life, and manufacturability, such as viscosity and moisture absorption. This study reviews all the above aspects of nanocomposite dielectric materials reported in the literature. More specifically, we analyze various filler-polymer combinations, and the influence of approaches to incorporate fillers in the polymer on the thermal, mechanical, and electrical properties. While the addition of fillers leads to huge enhancements in TC, the TC is highly anisotropic, with out-of-plane TC lower than in-plane TC by an order of magnitude. It is seen that most present-day materials are still inadequate for future applications due to their low glass transition temperatures; specific promising materials are highlighted. While the addition of fillers reduces the CTE, further reduction is needed to favorably improve the mechanical performance of these materials. While the electrical insulating properties of these composite materials are adequate, there is very little data reported on other electrical properties. In summary, while there is an understandable focus on enhancing the TC, other properties are underreported, and there is insufficient information to support the assessment of most novel materials for practical applications. Overall, this study summarizes the state-of-the-art dielectric nanocomposites and outlines directions for future research to bridge the gap between basic materials science and applications.

Partial discharge (PD) is a phenomenon often occurring in insulation system defects (cavities), which can significantly affect life and reliability. While broad knowledge on PD phenomenology of high-frequency transformers (HFT) has been achieved under ac sinusoidal voltage, much less work has been done to infer PD behavior under emerging high frequency pulsewidth modulation (PWM) operation conditions. An impediment has been the limited appropriate test equipment. A recently developed novel ±5 kV GaN-based high-frequency PWM supply with controllable dV/dt , voltage level and frequency has been developed. This article explores the application of these measurements to the testing of materials in this electrical environment. Two commonly used windings for HFT were tested under different applied voltage magnitudes, frequencies, and slew rates. According to the test results, at high frequency (up to 50 kHz) the electric field generated by space charge deposited by PD occurring during previous PWM pulses plays an important role in PD behavior. The frequency dependent permittivity of the insulation material can also affect PD measurement results.

Arc faults threaten the safe operation of photovoltaic (PV) systems. An arc fault detection and localization approach using parallel capacitors is proposed. A PV system has been analyzed and tested with five capacitors paralleled with the branches in the system. Series and parallel arc faults at nine locations have been tested in the system. When an arc occurred, current pulses were generated in the capacitors and their amplitudes and polarities were obtained through Hall current sensors. Discrete wavelet transformation was performed on the capacitor currents and the distributions of their amplitudes, frequency spectrums, and polarities are here reported. The results indicate that the distributions are unique under different fault types and locations, which could be used to detect and localize arc faults in PV systems. Moreover, the amplitudes of the capacitor currents can also help to localize a series arc fault within a PV string. Finally, the proposed approach is validated by a double-fault test.