A study of electrical characteristics of mineral transformer oils with reduced and increased viscosity

Recently has been submitted for publication the revision of IEC 60296, which concerns specification for unused mineral oils to be employed in switchgear and transformers. For the transformers, the IEC 60296 Standard, in comparison with the past Edition, introduces oils with a reduced viscosity having obviously also a decreased flash point. At the same time a new Standard (Project IEC 60076) is now under development, actually in circulation as Committee Draft: "Guide for design and application of liquid-immersed power transformers using high-temperature insulation materials". This Guide, among others, include also mineral oils (called HTM-240 and HTM-205) having a much higher flash points, up to 240°C, accompanied with acceptable increases in their viscosities. It seems to be a very interesting point to investigate how change the electrical properties of these new mineral oils having increased and reduced viscosities.