Partial discharges testing of power modules

IGBT hybrid power modules used in high voltage applications (ex. railway traction systems) are built using several dielectric materials. This stack may be a source of partial discharges. Up to now these modules are tested as regards partial discharges using a normalized test (EIC 270), which despite its quality is not representative of the real applied stresses endured during normal operating conditions, as it does not stress all the materials present in the stack. A new method for determining partial discharges activity in such power modules has been developed. Application of this test to IGBT modules leads to a PD ignition threshold lower than the one found using the normalized test. In this paper the different results obtained up to now in this field are summarized and discussed. Additionally, the test is modified in order to apply it to different structures in order to identify the possible cause of PD developments in such power modules.