1.1 This guide is applicable to oil-immersed transformers of types ON and ON/OB complying with IS : 2026-1962*.
1.1.1 IS : 2026-1962* does not take into consideration either temperatures different from normal or variations in the load ( which only exceptionally correspond to uninterrupted continuous operation at rated kVA).
1.2 This guide indicates how oil-immersed transformers may be operated for different ambients and duties without exceeding the acceptable limit of deterioration of insulation through thermal effects.
For very large transformers, for example, 100 MVA and above, the advice of the manufacturer should be followed. (For additional limitations requiring reference to the manufacturers, see 3).