High voltage mobile substation

View of the core and coils of one of the highest voltage mobile substations ever built, constructed by the Allis-Chalmers Manufacturing Company for the United States Department of Interior, Bonneville, Oreg. Tap changing mechanism provides low voltages from 2.4 kv to 13.8 kv from a 31-kv to 110-kv 3-phase line. Delta and Y connections are provided together with 4 plus 2 1/2 and 6 minus 2 1/2 per cent voltage taps. The forced-oil-cooled transformer together with high and low voltage switchgear will be trailer-mounted to provide a 2,500-kva emergency tie-in substation for a large West coast network. At the left is shown the low voltage side and at the right the high voltage side of the horizontally mounted unit