Study of water molecules state in transformer oil via FT-IR spectrum and molecular dynamic simulation

Mineral transformer oil has been widely used in the power transformers due to its good insulating property and thermal conductivity. It is well-known that water molecules in the oil have detrimental effect on its conduction and breakdown strength and tend to cause accelerated aging of oil and paper insulation system. The relation of the total amount of water to the electrical properties of oil has been widely investigated. A turning point of moisture content has been found that beyond this point the abrupt decrease of AC breakdown strength of oil is alleviated and keep almost constant with the further increasing of moisture content. Water state in saturated and unsaturated hydrocarbons and aromatic hydrocarbons have been studied and indicated that the state of water molecules is closely related to the electrical conductivity of hydrocarbons. Therefore, it is of great importance to investigate the water state in the mineral transformer oil with different moisture contents. In this paper, mineral transformer oil was treated at different humidity and Fourier transform infrared spectrometer (FT-IR) was used to characterize the water state of oil samples with different moisture contents. Moreover, the water state in the oil samples was investigated using a molecular dynamics simulation. By analyzing the formation of hydrogen bonds and the diffusion behavior of water molecules, it is found that the hydrogen bond energy is greatly changed by varying the moisture content of mineral oil, which lead to the change of the state of water clusters.