This paper presents partial discharge trends of various developing faults such as drying out of impregnated paper cables, moisture ingress, earth screen damage, etc. These trends were measured over either weeks, or months, by PD-OL (PD Online with Location), which measures and locates PD activity. The presented cases are results from continuous measurements on more than 150 cable connections.

The paper also briefly discusses the principles behind the measurement technique, the centralized data processing, and the internet portal. PD-OL is a mature and unique diagnostic and monitoring tool for medium-voltage power cable connections, up to several kilometers length for any desired period of time (hours, weeks, years). The network owner can monitor the actual health of their cable systems via the internet, backed up by a warning service.

The results show that PD-OL is an economical and reliable alternative for off-line PD measurement methods, while offering so much more.