Partial discharge diagnostics of long and branched medium-voltage cables

On site partial discharge (PD) methods have become successful tools to diagnose and monitor cable circuits. This paper describes the background of these methods, some fundamentals and challenges. The first section gives a brief introduction to and definition of the 0.1 Hz or very low frequency (VLF) PD methods. The next section discusses more general items and misconceptions on PD diagnostic testing and its role within condition based maintenance (CBM). The section 'Reflection based 0.1 Hz PD test method' summarises the principle of this method. Finally, the section 'Multi sensor 0.1 Hz PD test method' describes a method to meet the challenge of testing long and branched medium-voltage cables.