This paper dealt with the measurement and analysis of partial discharge (PD) under high voltage direct current (HVDC) in SF6 gas. Electrode systems such as a protrusion on conductor (POC), a protrusion on enclosure (POE), a crack on epoxy plate and a free particle (FP) were fabricated to simulate the insulation defects. The analysis system was designed with a Time-Frequency (T-F) map algorithm programed based on Lab VIEW. This can arrange the acquired PD pulses into frequency and time domain. A HVDC power source is composed of a transformer (220 V/50 kV), a diode (100 kV) and a capacitor (50 kV, 0.5 μF). The gap between the electrodes is 3 mm, and the SF6 gas was set at 5 bar. PD pulses were detected by a 50 Ω non-inductive resistor. In the analysis, PD pulses were distributed below 0.5 MHz and 20 ns ∼ 35 ns for the POC, 0.7 MHz ∼ 1.7 MHz, below 0.6 MHz and 10 ns ∼ 40 ns and 60 ns ∼125 ns for the POE, below 0.1 MHz and 135 ns ∼ 215 ns for the crack, and below 1.6 MHz and 250 ns for the FP.

To operate organic light emitting device (OLED) with alternating current (AC) power source without AC/DC(direct current) converter, we fabricated the fluorescent OLED and measured the emission characteristics with AC and DC. The OLED operated by AC showed higher maximum current efficiency of 8.2 cd/A and maximum power efficiency of 8.3 lm/W. But current efficiency and power efficiency of AC driven OLED showed worse than DC driven OLED at high voltage above 10 V. This result can be explained by the peak voltage of AC was  times than DC, In case of low driving voltage the emission characteristics were improved by the peak voltage of AC, but in case of high driving voltage the emission efficiencies were decreased by the roll off phenomena. Finally, serial OLED arrays using twelve OLEDs driven by AC 110 V showed average voltage of 9.17 V, voltage uniformity of 99.0%, average luminance of 1,175 cd/㎡, luminance uniformity of 94.4%.