Development of a Method for Evaluation of the Life Curve of the HV and EHV Cable Polymeric Insulation: The First Results and Fields of Application

摘要

A test procedure and an experimental setup are presented that enable derivation of the "life curve," i.e., the electrical tree induction period vs. applied voltage dependence for the low-density cross-linked polyethylene insulation. The developed equipment allows testing samples of materials both made in a laboratory and cut out from commercially manufactured cables at room temperature and at long-term permissible and overload temperatures. The fact of the electrical tree inception is established by light microscopy directly during simultaneous high-voltage test of ten samples. The optical system and the applied microma-nipulation technique provide spatial resolution of approximately 1.5 μm, high-precision delivery of the microelectrode to the area of interest inside the sample, a permanent and reliable contact between the micro-electrode and the material, and preservation of the residual mechanical stress field. The obtained results can be applied to development of new high-voltage cables with polymer insulation. The derived "life curve" enabled-using the corresponding mathematical model-calculation of the electric insulation thickness, which reaches 19-20 mm for the 220-kV cables.