Studies on compatibility of silicone oil with pressboard insulation

The paper oil insulation system is an integral and essential part of large power transformers. The failure of power transformers under combined stresses and fast transients has made it necessary to look for an alternate liquid insulant. In this study, silicone oil was investigated for use as a liquid insulant. The samples of pressboard are subjected to dielectric tests like electric strength, surface electric strength under AC, DC and combined AC/DC voltages, dielectric dissipation factor and others. The variation of dielectric constant, dissipation factor of silicone oil has been studied over a range of frequency. The surface electric strengths of cellulosic insulation with silicone oil and with mineral oils have been compared. Some very interesting results on the performance of silicone oils have been observed and discussed.