What is the transformer oil name used in modern grids?

There is no single universal name. Modern grids commonly use mineral insulating oils specified to IEC 60296, often sold under well known trade names that differ by region and supplier. Increasingly, utilities also deploy ester based fluids such as natural esters (for biodegradability and higher fire point) and synthetic esters (for strong fire safety and stable properties), plus silicone fluids in specialized fire safe designs. When someone asks for the transformer oil name, the most correct answer is the oil family and applicable standard, then the approved brand or product name on the utility’s qualified list.