Provides guidance on determining the acceptable relationship between transformer rating and proposed load cycle when considering the effect of operating temperatures on life expectancy due to insulation deterioration and thermal ageing. Includes recommendations for loading above the nameplate rating and guidance for choosing appropriate rated quantities and loading conditions for new installations. It applies to the same range of transformers complying with AS 2374.1-1997. This Standard is technically equivalent to and reproduced from IEC 354:1991 and includes Australian informative appendices on determination of the thermal time-constant and indirect measurement of winding hot-spot temperature.