PD diagnosis on medium voltage cables with oscillating voltage (OWTS)

Detecting, locating and evaluating of partial discharges (PD) in the insulating material, terminations and joints provides the opportunity for a quality control after installation and preventive detection of arising service interruption. A sophisticated evaluation is necessary between PD in several insulating materials and also in different types of terminations and joints. For a most precise evaluation of the degree and risk caused by PD it is suggested to use a test voltage shape that is preferably like the same under service conditions. Only under these requirements the typical PD parameters like inception and extinction voltage, PD level and PD pattern correspond to significant operational values. On the other hand the stress on the insulation should be limited during the diagnosis to not create irreversible damages and thereby worsening the condition of the test object. The paper introduces an oscillating wave test system (OWTS), which meets these mentioned demands well. The design of the system, its functionality and especially the operating software are made for convenient field application. Field data and experience reports was presented and discussed. This field data serve also as good guide for the level of danger to the different insulating systems due to partial discharges.