Loading of Ventilated Dry-Type Transformers

This is a continuation of the previously published data on the loading of sealed dry-type transformers.1 With the same representative core and coils as were used in the previous work, and the sealed tank replaced with a louvered casing, the winding temperature rises are measured for a variety of loads following several steady-state conditions. These data are converted to hottest-spot temperatures utilizing previously published hottest-spot increments and the allowable limits specified in the standards. Aging rates are those for the presently used materials in ventilated dry-type transformers. Insulation aging is computed for various overload cycles and the allowable loads determined for normal life expectancy as well as a few specified per cent loss-of-life criteria.