The influence of combined strain and constructive solutions for stator insulation of rotating electrical machines on duration of their reliable exploitation

In the paper results of the examination of ageing of stator insulation of rotating electrical machine are presented. Results of experiments given within this paper have been recorded over the 20 years' period. The paper has predominantly experimental character. The experimental procedure has been improved over time and the obtained results were repeatable with a measurement uncertainty less than 5%. The experiments were performed on the samples taken from coil windings of standard type and whole coil windings. The samples are taken from the coil winding characteristic parts. The tests were carried out on the new and on the samples (coil windings) that were in use for several years. Under the well-controlled laboratory conditions, the impact of the technological process for the coil winding production, the time of use and the combined strain (temperature, humidity, mechanical strain and overvoltage strain) was tested on the conductor insulation of the coil winding. The parameters considered in this examination are the polarization index, the coefficient of proportionality and the lifetime exponent. By comparing results obtained on the samples with the results obtained on the whole coil windings, the effect of spatio-temporal increase in probability was noticed. From presented results, it can be concluded how the synergy of technological process of coil winding production, the time and the conditions of exploitation affect the rotating electrical machine lifetime.