An experimental study about the weight of the (dv/dt) factor characterizing inverter-like voltages during pre-selection tests on copper enameled wires for adjustable speed drives motors

Pre-selection tests on enameled copper wires to be adopted for windings of inverter driven rotating machines are generally performed applying quasi-square wave voltages to suitable specimens. This work experimentally investigates the influence of the factor "dv/dt" (or of the rise-time) characteristic of such quasi-square waves on the output of the above pre-selection tests. The aging test campaign, carried out on twisted pairs, evidenced that the longer the test voltage rise-times (i.e. the lower its "dv/dt" factor) the shorter is the specimens lifetime. Besides, the monitoring of partial discharges (PD) during the agings showed that this lifetime shortening was consistent with an increased occurrence (number) of PD. Therefore, in the experimental context, the insulation degradation could be considered primarily influenced by the effects of PD.