Improved Modelling of PDIV Evolution Over Time Under Multiple Ageing Factors for Insulation of Inverter-Fed Electrical Machines

This article describes research to model PDIV evolution under multi-factor stressing of the insulation system of an electrical machine. An attempt is made to establish whether a change of PDIV could be used to predict remaining life. Twisted pairs are used as samples of electrical motor insulation. They undergo accelerated ageing by exposure to high temperatures and the constant influence of inverter-style square-wave voltage. The ageing process lasts between weeks and months during which PDIV is measured periodically. The dedicated method of PDIV measurement with inverter-style voltage is presented. The evolution of PDIV is successfully modelled using an Inverse Power Model – observation and modelling of PDIV evolution is a novelty in the field. The ageing tests are performed according to the Design of Experiment method. The evolution of the parameters of the model at different factor levels can be extrapolated from the model obtained.