Abstract:
Power transformer is one of the most expensive components in electrical network. Frequent breakdown of power transformers are reported mainly due to the failure of electrical insulation. Many researchers are working towards improving the electrical insulation properties of transformer oil. Present nano technology confirms that addition of nano fillers in the transformer oil provide superior electrical insulation properties. Recent concern towards environmental and fire safety of transformer operation has led to the development of natural ester based liquid insulation for power transformers. Hence it is important to evaluate the electrical insulation characteristics of nano modified natural ester based liquid insulation system. In this work, laboratory experimental works are carried out to understand the electrical insulation parameters such as power frequency breakdown voltage (BDV), volume resistivity, dielectric loss factor, relative permittivity, flash point, fire point, viscosity and lightning impulse streamer propagation characteristics of corn oil filled with SiO2 nano fillers at different %wt concentration such as 0.01%, 0.05% and 0.1%. Lightning impulse withstand tests are conducted at both needle/plane and needle/sphere electrode geometry with 1.2/50 μs waveform at both positive and negative polarity. It is noticed that addition of SiO2 nano filler at lower %wt concentration in the range of 0.01% - 0.05% has significant influence in improving the BDV, volume resistivity, flash point, fire point, lightning impulse withstand and breakdown strength of corn oil. Results also reveal that the nano modified corn oil considerably reduces the dielectric loss factor and lightning streamer propagation velocity. Improvement in dielectric, thermal and LI streamer characteristics gives confident that nano modified corn oil may be considered for transformer applications.
