Challenges related to development of an on-line PD detection and localisation system

Partial discharge detection and localisation is a well-established off-line tool for diagnosing medium voltage cables [1-3]. For on-line application a number of new problems have to be solved, not only related to sensor coupling and high noise levels. In this paper a few additional consequences are discussed. The electric field in a belted cable is elliptical. The amount of field eccentricity influences PD patterns, due both to the PD excitation itself and to the coupling and propagation of the signal to the cable conductors. Further, the impedances seen by the propagating pulses at the cable end can vary, depending on the substation equipment. Therefore, localisation techniques based on reflectometry become unreliable, and signal detection at both cable ends is preferred. This implicates the need of synchronisation of the two set-ups and a communication channel between them. This paper discusses the feasibility to use the cable under test for these purposes.