Study of Nano-oil Preparation Conditions for Experiments to Determine Electrical Strength

The paper presents the results of experiments to determine the breakdown voltage of liquids containing carbon nanotubes added to mineral insulating oil used in electrical transformers. The liquid was obtained in various ways, including using an ultrasonic disperser. The experimental results showed that the addition of carbon nanotubes in various concentrations inevitably leads to a decrease in the electrical strength of the insulating liquid. At low concentrations, the electrical strength values approximately correspond to the values of pure liquid, however, with increasing concentration, the electrical strength of all nanofluids decreases. It has been shown that the nanofluid preparation technology has a strong influence on its breakdown voltage. As a result of experimental studies, it was revealed that the characteristics of nano-oil are influenced by: the power and duration of ultrasonic exposure; the depth and duration of vacuum exposure to nano-oil after its preparation; the rate of voltage rise on the test setup and the time between measurements. The most stable oil samples, according to the results of breakdown voltage measurements, were obtained by adding pre-crushed nanotubes to the transformer oil volume. The nanotubes were ground in a high-energy planetary centrifugal ball mill AGO-2 with steel drums and balls for 45 seconds. The oil was exposed to ultrasound for 30 minutes at a power of 1 kW. Next, the nano-oil was poured into measuring cells, which were placed in a degassing chamber. Degassing was carried out while simultaneously stirring the nano-oil with a magnetic stirrer to avoid the formation of agglomerations. Degassing was carried out for 24 hours at a vacuum level of 0.03 mbar.