Modeling Humidity Impact on PDIV for Turn-to-Turn Insulation of Inverter-Fed Motors at Different Temperatures
Hadi Naderiallaf, Yatai Ji, Paolo Giangrande, Michael Galea
Abstract
This paper models the partial discharge inception voltage (PDIV) as a function of ambient humidity ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ) at various temperatures ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ts</i> ) using Schumann’s streamer inception criterion (SCSIC) for turn-to-turn insulation, which is the most vulnerable part in inverter-fed motors’ insulation system. The Schumann constant (i.e., the natural logarithm of the critical electron number defining the Townsend-to-streamer discharge transition, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> ) varies with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> , showing distinct patterns at low and high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ts</i> . The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> equations are derived across a wide range of relative humidity (RH) levels (20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%) at four <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ts</i> (25°C, 40°C, 60°C, and 90°C). These equations can be used in finite element analysis software to predict PDIV under varying <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> with outstanding accuracy. Additionally, a novel approach is presented for partial discharge (PD) phenomenology under <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> variations at different <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ts</i> using SCSIC-derived streamer inception parameters (SIPs): critical field line length (CFLL), air effective ionization coefficient (α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ), partial discharge (PD) inception field ( <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">inc</sub> ) and firing voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">firing</sub> ). Notably, at high Ts (e.g., 90°C), a transition phase emerges concerning RH, leading to significant SIP changes due to the disappearance of a critical region (CritR) in α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> at specific electric field intensities. The developed humidity-dependent PDIV model supports insulation designers in achieving PD-free designs that account for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> variations and sheds light on SIPs variations concerning <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> changes.