Copper contaminated insulating mineral oils-testing and investigations

Reactions between the liquid insulation and the copper conductors in power transformers and other electrical apparatus may lead to the formation of dissolved and suspended copper in the insulating oil. In this work a study concerning the correlation between the copper form and the dielectric properties of the fluid is presented. In particular, to determine the total copper content in oil and consequently to discriminate by subtraction the presence of particulate copper, we optimized a method of oil mineralization. Moreover, by filtering the oils with PTFE filters (0.45, 1 and 5 μm), the dimension of suspended copper content has been quantified and discriminated from the dissolved one: in such way, we investigated the influence of particulate copper on the characteristics of the oils and we determined the physical form that mostly affect the dielectric properties.