Abstract
The impacts caused by the polarity reversal of the applied voltage on space charge dynamics and electric field enhancement across an oil gap have been studied in an oil gap and single-layer pressboard composite insulation system. The experimental results validate that the electric field enhancement across the oil gap immediately after the application of the reversed electric field is directly dependent on the number of residual charges within the insulation system at the moment of the application of the reversed stress. Therefore, the electric field enhancement in the system is strongly dependent on the magnitude of the applied electric field, the duration of polarity reversal and the degradation of the mineral oil. An estimation of the enhanced electric field immediately after polarity reversal based on the charge decay characteristics has been proposed and successfully applied to calculate the electric field enhancement in an aged oil sample under 20 kV/mm, which cannot be accurately measured due to the very fast space charge dynamics in the aged oil under a strongly enhanced electric field.
Highlights
IntroductionISSN 0914-4935 © MYU K.K. Sensors and Materials, Vol 29, No 8 (2017)
ISSN 0914-4935 © MYU K.K.Sensors and Materials, Vol 29, No 8 (2017)are immersed in a large quantity of insulating oil
The proposed space charge dynamics during the polarity reversal operation is verified by pulsed electroacoustic (PEA) measurements in a fresh oil sample
Summary
ISSN 0914-4935 © MYU K.K. Sensors and Materials, Vol 29, No 8 (2017). Are immersed in a large quantity of insulating oil. Under such complex conditions, space charge characteristics under polarity reversal stress are still poorly understood and difficult to estimate. The pulsed electroacoustic (PEA) technique has been used to investigate space charge dynamics in an oil-impregnated pressboard with a thickness of 1 mm combined with a 0.5-mm-thick oil film under different polarity reversal stresses at room temperature. A method for estimating the space charge distribution, based on space charge characteristics, is proposed and validated
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