Recommendations for Selection, Installation and Maintenance of Substation Transformers

Abstract

For the past several years, there has been confusion surrounding both factory and field testing of liquid filled distribution substation transformers installed in industry. With the advent of new ester-based fluids, new standards have been developed that impact selection, installation and maintenance of liquid-filled transformers. This article will focus on established standards for both factory and field testing and recommended tests during scheduled rotational outages. Typical ratings for distribution substation transformers applied in process industries range from 112.5 kVA through 10,000 kVA three-phase, at 50 or 60 Hertz, with primary voltage at 34,500 volts and below and secondary voltage at 4,160 volts and below. Not included in the scope of this paper are dry-type distribution transformers, pad-mounted distribution transformers or power transformers with ratings up to 100,000 kVA and 230 kVA. Field testing recommendations focus on dissolved gas analysis (DGA) testing and understanding/trending test results will be covered. A case study outlining recent testing, results and lessons learned for an integrated paper mill in the U.S. Pacific Northwest will be reviewed.