File:Ohio Insulator Test Transformers.JPG

This photo is not of high quality as it was copied from an article written by A. O. Austin that was presented at the International High-tension Congress in Paris on June 5-6, 1929. The title of the article was "A Laboratory for Making Lightening and Other Tests Upon Full Sized Insulator Strings and Towers." The photo shows the three test transformers in the center bay of the horse barn that A. O. Austin purchased from the estate of O. C. Barber in 1926. The midpoint of the high-voltage winding of each transformer is connected to the core and tank. Therefore, when the transformers were connected in series, each tank had to be insulated from ground and the other transformer tanks. The highest voltage transformer required the highest porcelain tile insulating pier. The left side of the lower transformer tanks shows four low-voltage bushings. There are actually 16 low-voltage bushings on each transformer, 12 not shown in the photo. Each transformer had four low-voltage primary windings, each winding with two taps accounting for the 16 bushings. These windings could be connected in a variety of series-parallel connections with one side of at least one winding connected to the tank potential. A. O. Austin devised a scheme for "Multiple Excitation" by mounting an AC generator below each transformer tank (not shown) in the top center of each insulating pier. The generator being at tank potential had to be driven by an insulated shaft connected to a synchronous motor mounted on the ground in the center of each pier (also not shown). The motors were synchronized so that the output of each generator was in the phase so that all the high-voltage winding voltages were in phase. This was claimed to give very good regulation and is described in the Paris paper. The platforms shown at the base of each transformer tank were used to mount storage batteries that were necessary to provide the DC field excitation for the AC generators.