Glass Fibre Insulated Wire Assessment under Partial Discharges Activity via Dielectric Dissipation Factor Measurements

This experimental study evaluates the ageing rate associated with partial discharges (PD) activity for a Type-II insulated wire (i.e., Glass fibre), relying on the dielectric dissipation factor (DDF) and capacitance tip-up measurements. The employed specimens model the turn-to-turn insulation for low-voltage electrical machines. The turn-to-turn insulation was investigated because is the weakest point of the whole insulation system. The repetitive partial discharge inception voltage (RPDIV) is determined for unipolar and bipolar square waveform excitations with different rise times and frequencies. Then, the samples are stressed constantly under RPDIV at several exposure times for ageing purposes. The DDF and capacitance tip-up measurements are performed at the end of each ageing cycle. The reported findings enable the definition of indicators for the PD activity through the selected diagnostic markers (i.e., DDF and insulation capacitance). In addition, the proposed approach can provide reliable information on the Glass fibre ageing level associated with PD activity, comparing the harmfulness of different steep-fronted square waveforms.