New challenges in aging modeling - pulse stress

The transformer population in service is getting older; hence more attention is focused to transformer diagnostics. Through decades a great advances have been achieved in degradation understanding and diagnostic methods. However the quality of electrical energy is slightly changing recently. As power electronics is used in vast majority of electric drives, and also DC power lines are built or designed at least, it is necessary to focus on different degradation phenomena acting in electric insulation systems. More high order harmonics are appearing in the power network, causing additional stresses on insulation system. While study the aging of EIS more attention must be paid to multifactor aging models including the influence of power electronics in power network. As an example combined multifactor aging model for paper-oil insulation system used in HV power transformers is described in this article. The model is respecting the thermal and pulse voltage stress.