Determination of the environmental conditions for the accelerated ageing of MV-PILC cables

The accelerated artificial ageing of dielectric materials requires a specially designed laboratory setup and well defined environmental and technical conditions in order to obtain a suitable and realistic ageing factor. The ageing factor (AF) is to be chosen in a way that faults in at least a great number of the test samples happen within the expected project duration. Otherwise, the time schedule of the accelerated ageing process must enable a good extrapolation to the ageing scenario under real load conditions. By a defined pre-test schedule and through a monitoring of specific parameters like the partial discharges (PD) and tan(delta) of the cable samples or the fault rate, the best suitable operating point of the artificial ageing systems is determined. In order to define the environmental and technical conditions, a pre-test has been done. This, together with its main results is described in this paper, as well as the principles of he realized accelerated ageing system specialized for paper insulated lead covered (PILC) cables, with a highly sensitive and selective PD-detection/localization and tan(delta) measurement. It is shown that it facilitates the monitoring of the entire ageing process and therefore the later development of sophisticated diagnostic criteria based on the physical ageing process.