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On-site partial discharge (PD) measurement is required to ensure proper installation of extra high voltage (EHV) cable systems accessories. To achieve high sensitivity and good localization, two problems have to be overcome. First, the strong high frequency attenuation in long XLPE cables requires that the sensors be located along the cable, preferably directly at the accessories. Secondly, the detection system must be able to distinguish internal PD from other pulses. This paper describes a solution based on directional coupling sensors and a data visualization system, which displays phase-amplitude diagrams for individual PD sources which are identified by the direction of pulse propagation. It has been applied to on-site measurements, type and routine testing of HV cable joints and stress cones. Due to the reliable discrimination between internal PD from the accessory measured and from other pulses, testing can be done in unshielded rooms even using terminations with internal PCI and corona. The method works independently well on line voltage, resonance sources, oscil1,ating voltages and 0.1 Hz. cosine-square voltage. It has been used to verify the cable accessories installed in the 6.3 km long 380 kV cable system in Berlin, Germany

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The diagnostic examination of partial discharges (PD) is regarded a powerful, non-destructive and sensitive diagnostic tool for the condition assessment of insulating systems. Two major tasks of PD measurements may be distinguished, (i) providing evidence of PD (detection) and (ii) the location of the PD. Particularly with regard to the question "Where is the PD source?", the possibility to geometrically localize the flaw, by means of arrival times of the acoustic signals, gets an extremely interesting option. For the estimation of the PD site precise measurements of acoustic arrival times and robust positioning algorithms are essential. The averaging of acoustic PD signals (either with an electric or an electromagnetic UHF PD trigger signal) helps to enhance the acoustic sensitivity. The acoustic detection limit is hence lowered significantly and the determination of the arrival times is made possible for weaker PD. Supplementary steps, like automatic arrival time determination or additional wavelet-based de-noising further improve the overall location accuracy. Regarding the solution algorithms a new approach within the acoustic signal processing, which works with pseudo-times, allows for the use of robust direct GPS (Global Positioning System) solvers instead of the previously used iterative algorithms.

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