Extraction of low molecular weight acids from transformer liquids using water extraction technique

Acidity has been recognised to be an excellent marker of the transformer insulation system. In the recent decade, a sub-group of the acids, known as low molecular weight acids (LMA), have been identified to be the cause of acid catalysed degradation of the paper insulation. Due to the unavailability of a standard method, LMA in transformer oil is commonly measured through a water-extraction process where LMA is extracted into water prior to the titration. This contribution investigates the effects of some key parameters of the extraction process including stirring speed, stirring duration and the separation period. Experiments are conducted with two types of transformer liquids including a mineral oil and a synthetic ester. Results indicate that the best extraction efficiency for the transformer liquids can be reached at a stirring speed of 650 rpm. Furthermore, it is found that the LMA extraction is completed within 1 hour and 3 hours of stirring for the mineral oil and the synthetic ester, respectively. The mineral oil had higher LMA extracted in water than the synthetic ester in a wide range of initial acidity concentration. This is due to a residual amount of LMA remaining in the ester liquid irrespective of the initial acidity