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This paper presents an experimental work investigating the failure data of oil-impregnated paper under pulsating DC voltage. The failure data of the oil-impregnated paper specimens were obtained through constant voltage stress tests; the Weibull distribution was used to estimate the statistical distribution of failure data. The exponential function (EF) and the inverse power function (IPF) were used to modify the Weibull distribution of failure data, so as to obtain two dual-variable Weibull failure distributions (WFDs), which were used to analyze failure data of oil-paper specimens obtained under pulsating DC and individual DC and AC voltages. Their adequacies were evaluated by using failure data obtained through the constant stress tests under various voltages. Both EF-modified and IPF-modified WFDs show more adequacy for failure data of oil-paper insulation under DC and pulsating DC voltages than AC voltages. The EF-modified WFD was more adequate than IPF-modified WFD in estimating the statistical distribution of failure data. [ABSTRACT FROM PUBLISHER]

The oil-paper insulation of valve-side windings in a high voltage direct current (HVDC) converter transformer is subjected to both complicated voltage and severe thermal stresses. Partial discharge (PD) occurring in oil-paper bounded cavities is influenced by voltage stress type as well as temperature. This paper presents PD behaviors in an oil-paper bounded gas cavity under pulsating DC voltages. The voltage across the gas cavity and PD inception voltages at different test conditions are analyzed. Influences of temperature on statistical PD distributions and parameters are also presented. A numerical model is used to interpret PD behaviors under pulsating DC voltages and various temperatures. Experimental results and theoretical statements show that the temperature exhibits a great influence on the behaviors of cavity discharge under pulsating DC voltages. Volume resistivity, gas pressure, charge decay time constant, and electron generation rate are the primary parameters influencing PD behaviors at different temperatures. [ABSTRACT FROM PUBLISHER]

This communication proposed an ultra-high frequency (UHF) stacked Hilbert antenna array to broaden bandwidth and increase gain of Hilbert fractal antenna. Two parasitic curves were added to improve the third order Hilbert curve and stacked structure was applied to the new antenna element. The UHF stacked Hilbert antenna was designed as antenna array that involved 2 \times 2 elements and fed by the Wilkinson's four-way power divider. Measurement results show that the UHF stacked Hilbert antenna array achieves a maximum gain of -1 dBi and exhibits a wide impedance bandwidth. Actual partial discharge (PD) experiments were carried out for typical artificial insulation defect models, while the proposed antenna array and an existing Hilbert fractal antenna were both used for PD measurements. The proposed antenna array was superior in this respect and effective for UHF online monitoring of PDs in electrical apparatus. [ABSTRACT FROM PUBLISHER]