Partial discharge diagnostics on 3.3 kV, 1.2 kA IGBT modules

The insulated gate bipolar transistors (IGBT's) are a new class of semiconductor devices which, for their performances in terms of driving, switching behaviour, etc., are nowadays widely adopted in adjustable speed drives and are increasingly replacing traditional components like SCR and GTO thyristors. Large effort is dedicated in the literature in order to investigate on their long term behaviour, which limits their employment in high reliability demanding applications, like railway traction. In the present paper, in order to investigate on the long-term performances of the electrical insulation of such devices, an experimental activity has been carried out on two types of commercial IGBT modules produced by two different manufacturers. The IGBTs have been subjected to typical working cycles occurring in a traction converter and the effect of the application of such stresses has been studied by recording, at different ageing stages, the partial discharge activity occurring in each module. A characterization of the first stages of the ageing process has thus been achieved.