Ageing properties of polyimide and polyester films: Experimental results and discussion

Adjustable Speed Drives generate square voltage waveforms. These specific stresses may introduce defects during the operation of rotating machines particularly with regard to their electrical insulation. Indeed, insulation materials initially designed for applications with 50 Hz sine waves am used under square wave without any specific changes in regard of the new voltage generated. Lifetime determination is one of the simplest way to appreciate induced changes when voltage is modified. These measurements are performed on samples (25 μm thick) of Polyimide (Kapton^TM) and Polyethylene Terephthalate for square voltage waveforms with a magnitude between 500 and 700 V peak at two frequencies (3 and 10 kHz) and for the same voltage front (around 1 kV/μs). Results of such study are presented