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.