This guide is applicable to oil-immersed transformers complying with MS ...* and operated within the limitations referred to in clause 3.
For very large transformers, e.g. 100 MVA and above, the advice of the manufacturer should be followed.
MS ...* 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 power).
This guide indicates how oil-immersed transformers may be operated in different conditions of ambient temperature and service, without exceeding the acceptable limit of deterioration of insulation through thermal effects.
For transformers with forced oil circulation, the guide is rather conservative and the loads indicated may probably be exceeded, but again the manufacturer should be consulted.