Ageing of used composite insulation systems under different voltage stress

This paper describes the assessing the lifetime curves of composite insulation under different kind of voltage stress. This covers several areas that are important for using the electrical insulation properly. First one is the composite insulation. The use of this kind of insulation is rising, new types of composites are being invented and investigated with the aim for the best achievable properties. These insulation structures are inhomogeneous that causes problems with PD etc. This kind of insulation has its use in high voltage applications as is large rotating machines (e.g. turbo and hydro generators). This composite was aged by a different kind of voltage applied. First, the AC voltage was applied, as it is the most commonly used voltage. The composite was also subjected to the DC voltage, as it is rising, thanks to the usage of power electronics in DC drives, which generates voltage spikes. This brings new problems that shorten the lifetime of the electrical machines.