Oil impregnated paper condition assessment using time spectroscopy method

The condition assessment of power transformers insulation using dielectric spectroscopy in frequency domain is a very useful method. Unfortunately, this method has a main deficiency due to the long measurement time, especially at low electric field frequencies and also to the expensive cost of the equipments. Another easier method which also permits to obtain the complex relative permittivity components and loss factor is the time spectroscopy method, which is based on the absorption/resorption currents measurements. This paper presents a study concerning the assessment of mineral oil impregnated paper condition using the time spectroscopy method. The values of complex permittivity components and loss factor for oil impregnated paper samples subjected to accelerated thermal stresses (at T = 135 °C and 155 °C) were determined and used to evaluate the insulation condition. Moreover, the condition of aged samples was analyzed using other parameters like polymerization degree and water content.