Analysis of the grid harmonics and their impacts on distribution transformers

Widespread application of power electronics in industrial and residential loads has increased the harmonics of the gird significantly. The grid harmonics have destructive impacts on the gird components including distribution transformers. Studying the impacts of current harmonics on distribution transformers is crucial for grid design and maintenance. Therefore, this paper studies the effect of gird harmonics on eddy current loss, other stray losses, hottest spot temperature, and lifetime of distribution transformers. The current harmonics of six 100KVA transformers at a provincial power distribution center are measured in a one week test period and the impacts of grid harmonics on the investigated transformer are thoroughly discussed.

I. Nomenclature

load loss

winding eddy-current loss

other stray loss

cupper loss

per unit load loss at rated conditions

per unit other stray loss at rated conditions

per unit winding eddy-current loss at rated conditions

per unit copper loss at rated conditions

per unit rms load current

harmonic order

highest significant harmonic number

per unit rms current at harmonic

rms fundamental load current

harmonic loss factor for winding eddy currents

harmonic loss factor for other stray losses

per unit rms load current

maximum permissible load current at rated conditions

top-oil-rise over ambient temperature

top-oil-rise over ambient temperature at rated conditions

no load loss

hottest-spot conductor rise over top-oil temperature

rated hottest-spot conductor rise over top-oil temperature

winding-rise over ambient temperature

ambient temperature

transformer hottest spot temperature

aging acceleration factor