An Extension of the Standard-Based Approach in the Assessment of Liquid Dielectrics Behavior

An increasing number of dielectric fluids intended for use in transformers are appearing on the market. Due to the growing awareness of sustainable development and the serious environmental risks posed by any mineral oil spills, transformer manufacturers are constantly working on alternative dielectric liquids. Therefore, it is crucial to test those liquids thoroughly. Commonly performed tests are also focused on dielectric strength under both lightning impulse (LI) breakdown voltages (IEC 60897) and breakdown voltages at power frequency (IEC 60156). In this article, the authors propose an extension of the standard list of tests by including the measurement of partial discharges at power frequency and acceleration voltage at the LI of both polarities. In the first case, a standard international electrotechnical commission (IEC) TR 61294 is adopted while in the second one, the methodology is enlargement of the provisions of IEC 60897 by the mentioned acceleration voltage measurements. In both cases, these additional tests enable a more comprehensive evaluation of dielectric liquids under consideration, especially in the case of newly ester liquids introduced in the market. The results show that the proposed approach is worth to be further considered in terms of the use of a given liquid in a power transformer.