Electrically Manipulated Water Accumulation in Insulating Oil: Insights From Molecular Dynamics Simulations

To reduce the potential threat of water in electrical equipment, it is crucial to study the mechanisms of water accumulation in insulating oil under electrical manipulation. This study established an oil-water mixture model using molecular dynamics simulations to quantitatively explore the dynamic evolution of water clusters under different electric fields. Key findings indicate that under a direct current (DC) electric field, polar water molecules align with the field. At DC electric field strengths (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub>) below 0.50 V/nm, interactions between water molecules strengthen, leading to tighter aggregation and increased nucleation and growth rates. As the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> increases, polarization intensifies, enhancing oil-water interactions, restricting water mobility, and inhibiting new nucleation. Existing droplets stretch and grow rapidly, with reduced internal density, causing structural instability. Under an alternating current (AC) electric field, water molecule orientation adjusts periodically. At electric field amplitudes (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>) below 0.50 V/nm, weak polarization and depolarization effects reduce water molecule migration. However, stronger intermolecular attraction tightens molecular aggregation, leading to increased collision frequency, which subsequently enhances nucleation and growth rates. As a result, the formed water clusters tend to hover near the center of the electric field. As <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> exceeds 0.50 V/nm, stronger periodic polarization enhances aggregation, resulting in more vigorous motion and the formation of larger, more stable droplets. Relatively speaking, the AC field shows stronger dynamic regulation, accelerating water molecule aggregation and nucleation, particularly at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>=2.00 V/nm. This study provides key insights into the dynamic behavior of water in electrical equipment.