The purpose of this standard is to allow the calculation of the admissible load and to indicate it, under certain defined conditions, based on the assigned intensity, to serve as guidance to users and to help designers to choose the assigned power. necessary in transformers intended for new installations. A base outdoor cooling air temperature of 20°C is assumed. The curves are provided for this temperature and also for external cooling air temperatures of 10 °C and 30 °C. Deviations from these temperatures are considered acceptable taking into account that the additional life consumption that exists when the cooling air temperature is higher is compensated by the reduced life consumption when the external cooling air temperature is lower. . In practice, continuous uninterrupted operation at full rated power is not common and this standard gives recommendations for daily cyclic loads taking into account variations in ambient temperature with the seasons. The daily life consumption due to thermal effects is compared with the "normal" life consumption that would result when the dry type transformer was operating at rated voltage and current with an outside cooling air temperature of 20 °C. The load curves in Figures 5.1 to 5.12 show the allowable loads that would result in a normal daily life consumption for winding insulation systems intended for temperatures of 105,120,130,155,180 and 220 "under the following conditions: a) continuous service at different temperatures of the external cooling air; b) cyclical service with different temperatures of the external cooling air. NOTE - It is assumed that the transformer is adequately ventilated and that the increase in losses resulting from an overload will not modify the temperature of the external cooling air. .