Читать книгу Alternative Liquid Dielectrics for High Voltage Transformer Insulation Systems - Группа авторов - Страница 42

The quality of the dielectric insulating oil is studied and assessed by performing the AC breakdown voltage (ACBDV) test. It is conducted using BAUR DTA 100C as per the standard IEC 60156. ACBDV of insulating liquid is the prime parameter in defining its electric characteristics. The ACBDV is affected adversely by conducting particles, moisture content, and air/gas bubbles formed in the transformer insulating liquid. The measured ACBDV indicates the integrity of the oil and gives a superior value when the oil is impurity free. The oil acts as an insulating agent and a coolant in a power transformer. Apart from the solid insulation like kraft paper and pressboard, the composite oil–paper system gives an effective insulation system to the transformer. Some studies reported enhanced values of NEOs to conventional MO in comparison [47]. Some natural esters have an ACBDV of more than twice the values of the conventional oil, which indicates that natural esters can provide better resistance to high electrical stress in comparison to MO [52]. There is a huge variation in the level of water solubility of natural ester and MO, and ACBDV greatly depends on these moisture levels [53]. The tests conducted on samples of NEOs have a higher value of water content in comparison to conventional oil. This happens because of the chemical structure of the natural esters, which has higher saturation limits in water content than that of MO. Water content level of 200 ppm in NEO has a relative humidity value of 26.7%, which is equivalent to 10 ppm of water content in MO [54]. It is observed from Figure 2.5 that the ACBDV of NEOs like pongamia, jatropha, and palm oil is better than MO. Hence, with all these evidences, it is clear that NEO has comparatively higher moisture saturation levels than MO, and performance of NEO is significantly better than MO.