Breakdown characterization of transformer mineral oil on the pulsed and AC condition

Since the invention of electrical energy, their consumption increased over time and nowadays, with electric cars and smart cities, the demand for electrical energy increased exponentially as the energy should be on 24/7, not only in the daylight as was in the past. Generally, electric cars transport people daily, and at night, connected to battery chargers fed by the AC mains. These revolutionary lifestyles are changing the electric demand. Nowadays we have found different ways to generate electrical energy (hydroelectric, thermoelectric, aeolian, solar); many of these central generations are far from consumer and use transmission lines to connect that, and transformers are used for almost all of that to increase or decrease voltage/current. Transformers are composed of three elements in their construction: copper winding, magnetic core, and oil. The oil used as insulation material for winding also cools down the device, transferring the heat from winding and magnetic core to the outside through the metal structure and circulating it by the convection process. In this work, we characterized the mineral oil voltage breakdown (BD) at room temperature as liquid insulators in transformers. On the pulsed condition, we reached a dielectric strength of order of 27.5 kV/mm, while under alternate current AC conditions, the dielectric strength was only around 5 kV/mm, testing with the same pair of electrodes. With the pulsed testing, the BD has a higher value due to less stress on the material than the AC 60 Hz continuous voltage application.