NEN - NPR 10354
Power transformers - Loading guide for oil-immersed transformers
|Publication Date:||1 July 1992|
|ICS Code (Transformers. Reactors):||29.180|
This guide is applicable to oil-immersed transformers complying with IEC 76. It indicates how, within limits, transformers may be loaded above rated conditions. For furnace transformers, the manufacturer should be consulted in view of the peculiar loading profile. This guide provides guidance for the specification and loading of power transformers from the point of view of operating temperatures and thermal ageing. It provides recommendations for loading above the nameplate rating and guidance for the planner to choose appropriate rated quantities and loading conditions for new installations. The guide gives mathematical models for judging the consequence of different loadings, with different temperatures of the cooling medium, and with transient or cyclical variation with time. The models provide for the calculation of operating temperatures in the transformer, particularly the temperature of the hottest part of the winding. This hot-spot temperature is, in turn, used for evaluation of a relative value for the rate of thermal ageing. This guide further presents recommendations for limitations of permissible loading according to the results of the temperature calculations. These recommendations refer to different categories of transformers by size and importance, and also to different types of loading duty - continuous loading, normal cyclic undisturbed loading or temporary emergency loading.