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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. [ABSTRACT FROM AUTHOR]

Based on the plasma modified model and photoionization optimization model, this article constructs a low temperature and subatmospheric pressure air streamer discharge model. Through the model, the characteristics of streamer discharge under high-frequency square wave voltage are studied. Streamer discharge exhibits a different discharge pattern from dc voltage in the voltage drop stage and low-level stage. In addition, duty cycle and rise (fall) time have different effects on parameters, such as electron density, positive ion density, electric field, space charge density, photoionization rate, and streamer propagation velocity. [ABSTRACT FROM AUTHOR]

Air breakdown in sub- and supersonic flows induced by the subcritical streamer discharge and the effect of the initiator shape on breakdown conditions are studied. Experiments with varying the electric field strength and air pressure show that the ability of electromagnetic vibrators to initiate air breakdown has a resonant character. Placing a small electromagnetic vibrator in a microwave beam allows one to initiate air breakdown with a field strength in the microwave beam which is significantly smaller than the critical breakdown strength. The dependencies of the critical intensity of the electric field on the pressure and location of the initiator are reported. The dependence of the field amplification coefficient at the vibrator edge on the screen dimensions is presented at different lengths and widths of the screen. [ABSTRACT FROM AUTHOR]

In atmospheric radio-frequency (RF) discharges, two discharge modes, namely α and y modes, have been deeply discussed by experimental measurements and computational data, and another mode, known as Ω mode, has also been reported in the electronegative gas. In this paper, we present a fluid model to investigate the formation and dynamics of Ω mode in atmospheric RF discharges but controlled by dielectric barriers with pure helium as working gas. The simulation results show that the Ω mode can be observed right after the breakdown event, and only sustained in a very narrow voltage range; then, the discharge will enter into the α mode as the applied voltage is further increased. Compared with the α mode, the numerical data reveal that in the Ω mode, a relatively larger electric fields are sustained in the bulk plasma to ensure the continuity of discharge current due to the lower electron density, consequently the Ohmic heating and ionization processes mainly take place in the central region of discharge gap. [ABSTRACT FROM PUBLISHER]

The concept of effective diffusion length, as a means to characterize diffusion losses in calculations of microwave breakdown in radio frequency (RF) devices with inhomogeneous electric fields, is discussed in detail with emphasis on geometrical situations where the inhomogeneity of the microwave electric field plays an important role for the breakdown threshold. In particular, good analytical approximations are found for the microwave breakdown threshold field, in a number of different geometrical situations. Finally, an explicit experimental example demonstrates how the effective diffusion length in a coaxial resonant filter structure can be inferred from a set of breakdown threshold data obtained for different pressures. [ABSTRACT FROM PUBLISHER]