Induced Losses in Steel Plates in the Presence of an Alternating Current

Abstract
The presence of current-carrying conductors near conducting surfaces induces eddy-current flow in the conducting surfaces and causes resistive and reactive losses to be reflected to the source of supply. In the heavy current field such losses appear in bus-bar installations, rotating equipment, transformers, and other electrical equipment. In large power transformers in which the low-voltage connections may carry 6,000 amperes rms or more, the resulting magnetic field intensity is 220 oersteds or more at a distance of 3 inches. Test data are presented for two conditions: 1. a single lead parallel to a conducting magnetically permeable surface of typical steel transformer tank plate material and 2. a single lead parallel to the same surface covered with 1/4-inch-thick aluminum plate. A unique test fixture design is descibed with which data have been obtained to establish a correlation between current, conductor-to-plate spacing, and loss. It is shown that loss is not a function of current squared when considering steel alone, but is a function of current to a power less than two, with the power a function of conductor-to-plate spacing. Test data are compared with values calculated from a previous paper relating current in a current filament to induced loss in a semi-infinite solid.1 Electrical and magnetic characteristics are presented for the steel-plate and aluminum-shielding material used in the tests.

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