Angularly resolved field mapping in transformer oil

The authors report angularly resolved measurements of the electric field in transformer oil around two overlapping pressboard barriers, a geometry relevant to HVDC transformer design. Measurements have been performed at room temperature and at 80°C and the data are compared with the results of electrostatic calculations. It is concluded that the Kerr electro-optic field mapping technique has been developed into a versatile engineering tool for investigations concerning HVDC converter transformer insulation. The present study of oil/pressboard insulation shows that traditional electrostatic field mapping gives a reasonable picture of stress levels, provided the resistivity ratio between oil and pressboard is not chosen too high