Effect of Al2O3 nanorods on dielectric strength of aged transformer oil/paper insulation system

摘要

With the commencement of high voltage alternating current (HVAC) and high voltage direct current (HVDC), the demands on insulating reliability of power transformer is getting more and more imperative. The mineral oil (MO/TO) in conjunction with paper is the main insulation components in oil-immersed transformers; their insulation properties play a significant role in the safe and stable operation of power transformers. To strengthen the insulation level of ultra-high voltage transformer and to reduce its size and weight, it is imminent to enhance the insulating performance of transformer oil and oil-impregnated cellulose. Recently, a unique novel effort of suspension of nanoparticles (NPs) into mineral oil (MO) has been carried out and the results have exhibited improved insulation characteristics of transformer oil. The Al2O3 nanoparticles with favorable features were prepared in our lab to develop transformer oil/paper insulation system with better insulation performance. The transformer oil-based nanofluids (NFs) were prepared with nanorod shape, oleic acid (OA) surface modification and 0.8 g/L concentration of NPs. The pressboards were cut into the desired sizes (85 mm.55 mm). The thickness of the pressboards was 2 mm applied in flashover tests. The prepared pressboards were put into an oven at 105 degrees C for almost 48 h to carry out the hot air drying operation. Then they were put in the vacuum drying at 85 degrees C for 48 h. The impregnated pressboards were prepared by impregnating them into dried oil and NF under vacuum beneath 1 kPa at 80 degrees C for almost 48 h to obtain the oil-impregnated pressboard (OIP) and nanofluid-impregnated pressboard (NIP) respectively. Additionally, the prepared insulation system samples of liquid (MO and NFs) and solid (OIPs, NIPS) were thermally aged at 130 degrees C for 30 days. The effect of alumina NPs on thermal aging of transformer oil and pressboard were also investigated. The results showed that Al2O3 NPs can slow