Use of equivalent annual ambient temperature in overloading transformers and voltage regulators

In the “Interim Report on Guides for Overloading Transformers and Voltage Regulators,”¹ reference is made to the use of equivalent annual ambient temperatures in determining the loading of transformer equipment. This paper is to show a method of calculating the equivalent annual ambient temperature from readily available climatological data to avoid difficulties in other methods that have been proposed. An outline is given also of conditions under which the equivalent annual ambient temperature may be applied in determining permissible overloads for transformers.