Optical Signal Characteristics of Power Frequency Arc in Transformer Oil

Timely detection of internal arc faults in transformers is conducive to reducing the fault's energy and the possibility of combustion and explosion. The optical signal detection method of partial discharge in transformer oil is a relatively mature technology that is expected to detect high-current power frequency arcs in oil further. However, there are significant differences in the development processes of partial discharges and arcs, which result in different optical signals. Currently, there are no studies on the optical signal characteristics of high-current power frequency (50 Hz) arcs in oil. In this letter, the optical characteristics of the arc in oil are measured, and the gap is filled. It is found that at the initial moment of arc development (0∼5 ms), the optical signals in the ultraviolet, visible, and near-infrared wavelengths are all strong. After 5 ms, the near-infrared and visible lights are dominant. The optical signal is presented as four peaks with an interval of about 10 ms. After about 40 ms, the optical signal is difficult to transmit due to the numerous bubbles at the interface and the darken of oil. Therefore, it is recommended to use a photodetector containing near-infrared and visible wavelengths to detect power frequency arc faults in oil. Further, it is urgent to study the propagation and reflection characteristics of optical signals in transformer tanks and to guide the selection of sensor sensitivity and position.