I. Introduction
Partial Discharge (PD) can reflect the severity of equipment insulation damage [1], [2]. Optical measurement is a non-electrical measurement method that reflects the characteristics of PD by detecting the optical radiation in the PD process, which has the advantages of anti-electromagnetic interference performance and high sensitivity [3], [4]. The optical signal obtained by the optical measurement method or the electrical signal converted by the optical sensor is often used in PD spectral analysis, discharge pattern identification, discharge localization and other studies [5]–[9]. Fluorescent fibers are commonly used sensors in photometric measurement methods which have the characteristics of good insulation, not easy to damage, aging resistance, while not interfering with the operating equipment and have good stability [10], [11].