SUSCEPTIBILITY OF HIGH DENSITY CELLULOSIC TRANSFORMER INSULATION TO PARTIAL DISCHARGES

The construction process of high-voltage high-power transformers is both time and resources consuming. Starting from the design phase through the assembly up to the impregnation, great care must be taken so that the final product will be able to operate reliably for the period of e.g., 40 years. To verify if such requirement will be fulfilled, each finished transformer after manufacturing is subjected to factory testing. One of the demands is that the partial discharges measured in a transformer do not exceed values given in a IEC or IEEE standard. It has been observed that a transformer which show high PD activity when tested shortly upon impregnation shows lower or no PD activity after some days of standing time. It can be easily understood that such a complicated structure might present…