1987IEC 60076-3-1:1987 Power transformers. Part 3: Insulation levels and dielectric tests. External clearances in air
IEC 60076-3-1:1987 Power transformers. Part 3: Insulation levels and dielectric tests. External clearances in air was changed to IEC 60076-3:2000 Power transformers - Part 3: Insulation levels, dielectric tests and external clearances in air.