Optical Partial Discharge Detection on Cable Accessories using Photomultiplier Modules and Silicon Photomultipliers

Inhalt:
The measurement and analysis of partial discharges (PD) is well known to be an indicator of defective insulation and a cause of insulation ageing and degradation. Due to their immunity to electromagnetic disturbances, optical fiber sensors are suited well for the use in high voltage surroundings. In this work optical PD detection methods based on a fluorescent silicone fiber as optical sensing element in combination with two kinds of photodetectors, photomultiplier tube (PMT) modules and silicon photomultipliers (SiPM), are presented and compared. Due to their much better cost efficiency, SiPMs are a highly interesting alternative to the sensitive PMT modules. The predominant noise signals in PMTs and SiPMs are sporadically occurring pulses, described as dark count rate (DCR), which can lead to a false PD detection. While the very sensitive PMT modules come with a very low DCR of below 10 counts per second, the much cheaper SiPMs show rates of around 100 thousand counts per second and thus require specific analogue and digital signal processing. To further reduce the false positives, an approach is presented measuring light pulses using two photodetectors on the same sensor fiber coincidentally. Measurements were performed with a tip-plane geometry in a lightproof test setup, as well as on lightproof cable accessories with a transparent silicone as insulating material and an embedded fluorescent fiber sensor. The acquired data are compared with simultaneously recorded electrical PD signals. The behavior of optically detected PD pulses in terms of amplitude and phase-relation to the reference voltage is compared with the electrically measured pulses. Both PMT and SiPM measurements show promising results for the use in future PD monitoring systems.