Loading of Sealed Dry-Type Transformers

The winding temperature rises of a representative sealed dry-type transformer 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 considering a variety of transformer geometries. Aging rates used for these temperatures are those of presently used materials as determined by several investigators. Aging curves for these overload cycles are then computed and the allowable loads determined for normal life expectancy as well as for a few specified per-cent loss of life criteria.