Design and constructional features of a 275-kV special-duty transformer bank

The paper discusses the special features of a 275-kV bank of single phase transformers developed for use in a new research station for proving high-power circuit-breakers. After a review of the specification for the transformers, the basic design is dealt with in some detail. The abnormally low impedance, which is constant on all voltage ratios, was achieved by adopting ashell-type construction with interleaved windings; the special measuresused to produce this winding design for an insulation level of 1250 kV(full-wave impulse) are examined. Some of the manufacturing techniques are described, and, in particular, reference is made to radiography used as an inspection tool to check the totally shrouded windings. The drying and impregnating processes are discussed, and a typical log of relevant data is reproduced. Finally, impulse-voltage test results on sample windings and the finished transformers are examined.