Stability analysis and improvement of direct measurement method for stray capacitance in AC motors
CHENG Yuanhui
LIU Ruifang
ZHANG Tianhe
LI Zhihao
CHEN Like
ZHONG Hui
XU Kepeng
Abstract：In the modeling of bearing currents in variable-frequency AC motors,the direct measure-ment of stray capacitance often yields unstable results due to fluctuations in terminal capacitance data.To address this issue,this paper proposes a short-circuit method for measuring stray capacitance.First,the generation mechanism of bearing currents in variable-frequency drive systems is analyzed,along with a description of the lumped-parameter bearing current model and the associated stray capaci-tance parameters.Second,the direct measurement method is employed to determine motor stray ca-pacitance,and the impact of terminal capacitance fluctuations on the stability of both the measured ca-pacitance and its derivative are assessed.Finally,the short-circuit method is introduced for extracting stray capacitance,on which the influence of terminal capacitance fluctuations is examined.Experimen-tal results indicate that in the direct measurement method,terminal capacitance fluctuations signifi-cantly impair the stability of the measured stray capacitance and its derivative,resulting in discontinui-ties and high variability of stray capacitance.In contrast,the short-circuit method yields stray capaci-tance values and derivatives that are unaffected by sensitivity intervals and show no data fluctuations.These findings demonstrate that the short-circuit method is more suitable for measurement of stray ca-pacitance in AC motors.
Keywords：variable-frequency drivestray capacitancebearing voltagebearing currentdirect mea-surement methodshort-circuit method
Publication Date：2025-06-30
Online Publishing Date：2025-08-21(First online date of this platform, not the publication date of the document)
Pages：7( 130-136 )