ABSTRACT
Given a daily (repeating) load and ambient profiles, and the top-oil and winding time constants, it is possible to calculate the temperatures of the top oil and hottest spot for any point of time during a cycle. The greatest thermal degradation of cellulose insulation occurs at the location of the hottest spot. With respect to loading, the requirements of concern are those that define the transformer's thermal characteristics. The cooling class affects the design of the cooling package. Different cooling classes have different thermal profiles. Consequently, the operator must understand the cooling classes and their thermal profiles in order to confirm that a given transformer is responding properly. Thermal profiles show the relationships between different temperatures inside a transformer. Operators must understand these thermal profiles for given cooling classes in order to understand a transformer's thermal response to a given load. The thermal rating of a power transformer differs from the thermal rating of other current-carrying elements in a substation.
