Investigations on the Impact of Paper Moisture on Nanoparticles Dispersed Oil-Paper Insulation Using Lightning Impulse Parameters

This article presents a novel approach to accurately measure moisture levels in power transformer oil-paper insulation by analyzing dielectric response currents under standard and nonstandard lightning impulse (NSLI) voltages. Laboratory-prepared samples emulating transformer paper insulation with varying moisture levels are impregnated in different oils (mineral, vegetable, or their nanofluids) and are subjected to lightning impulse testing. Response currents are recorded, and transfer functions are evaluated by examining applied voltage and response current. Five coefficients (three from the numerator, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${a}2$</tex-math> </inline-formula>, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${a}1$</tex-math> </inline-formula>, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${a}0$</tex-math> </inline-formula>, and two from the denominator, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${b}1$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${b}0$</tex-math> </inline-formula>) are found sensitive to moisture content variations. Therefore, empirical relationships between these coefficients and paper moisture content (%pmc) are developed and are validated using newly prepared samples with different moisture contents, yielding maximum errors below 2.75% for NSLI and 3.5% for SLI. These findings offer valuable insights into transformer insulation conditions, enabling timely preventive measures to mitigate transformer failure.