Investigation of the Static Electrification Phenomenon in Power Transformers with the Streaming Model Test Setup

Several insulation damages of large high voltage power transformers in the
past were attributed to static electrification. Since the first failures occurred lots of
investigations were done. Most of the research concentrated on the conventionally for
insulation in power transformers used mineral oil-cellulose couple. The goal of the
presented research activity is the investigation of the electrostatic charging behaviour of
not so well studied liquid-solid couples, which are also used in transformers for insulation.
This paper presents the streaming model test setup which was built up for the simulation
and the measurement of the static electrification phenomenon in power transformers.
Additionally first results are shown concerning the electrostatic charging behaviour of
mineral oil-aramid in comparison to that of mineral oil-cellulose as a function of flow
velocity and system temperature. For both investigated liquid-solid couples electrostatic
charging tendency increased with rising flow velocity and reached highest values for a
combination of high temperature and high flow velocity. The mineral oil-cellulose couple
showed higher charging than the mineral oil-aramid couple which is linked to the higher
surface roughness of the investigated cellulose.