The Partial Discharge Characteristics of Oil-Paper Needle-Plane Insulation Defects Under Pulsating DC Voltage

The converter transformer plays a crucial role in HVDC transmission systems, with its valve-side windings exposed to complex composite waveforms, including power frequency, DC, harmonics, and pulses. These DC and pulsating components have a significant impact on the oil-paper insulation within the transformer. Thus, understanding partial discharge characteristics under DC pulsating voltages is essential for accurately assessing transformer health. The most common cause of partial discharges in transformers is sharp metal burrs that result in tip discharges in oil. This paper details the development of a DC pulsating voltage generation device and the establishment of an ultra-wideband partial discharge detection system using the pulse current method. The study explores tip discharge characteristics in oil under DC pulsating voltages, revealing that these discharges are influenced by both pulsating and DC components. When the pulsating component is small, discharge pulses appear in a single form; with larger pulsations, discharges occur at both the rising and falling edges, with pulse directions opposite at each position. Additionally, increasing the DC component's amplitude leads to a rise in both discharge frequency and amplitude.