Experiences with oil-insulated transformers

The current from the St. Croix Power Company's plant is carried underground at 25,000 volts into the heart of the business district, and is there stepped down in the St. Paul Gas Light Company's Cedar street station for use in six-phase synchronous converters and for 2200-volt alternating-current distribution. The transformers for the synchronous-converters are six in number, with one spare transformer, all of 300-kw. rating, designed for 22,500 volts on the high-tension end and 78 volts supply to the converters. In addition to these there are four 200-kw. transformers with the same primary voltage but with secondaries having 25 extra taps, brought out at one terminal, with 20 volts between taps; these giving a range of voltage from 2100 to 2600 volts. These transformers are connected on the Scott system to change from three- to two-phase current, an extra primary tap being provided to give the right ratio.