Behaviour of rape-seed-oils under impulse voltages

This paper deals with the breakdown behaviour of vegetable rape-seed-oils under impulse conditions. The investigations were carried out in homogeneous fields of plane-plane and inhomogeneous fields of rod-plane electrode configurations using lightning impulse (1.2/50 μs) and switching impulse (250/2500 μs) voltages up to 600 kV. Electrode distances varied between 5 and 50 mm respectively. To get an overview concerning the electrical properties of rape-seed oils under incipient breakdown stress, both statistical and optical experiments were made. Optical investigations used strong inhomogeneous fields with point-plane electrode configurations. The results are close to experiments in insulating mineral oil. Beyond a critical field strength, positive and negative streamers occur with similarities to streamers in mineral oil. A primary and a secondary propagation mode can be distinguished. Statistical experiments reveal that from the dielectric point of view, it is in principle possible to use rape seed oils as insulating material in power transformers. High-voltage-capacitors constructed in the past sometimes used rape seed oils as dielectric and seem to support this theory