Sensitive low field Kerr electro-optic measurements in transformer oil

A frequency-selective amplifier was used to make sensitive Kerr electro-optic field mapping measurements with a small signal AC voltage superimposed on a DC level. With several different electrode materials, including brass, stainless steel, and aluminium, the authors have observed very significant levels of field distortion due to positive space charge on the order of 400 μC/m³. It was possible to measure field strengths as low as 100 V/cm with typical average field strengths tested over the range of 500 V/cm to 29 kV/cm. The transient evolution of these fields was also measured, showing the transition from a uniform to a highly nonuniform field on a time scale on the order of 60 s