Distribution Substation Transformers: Understanding North American Standards Defining Transformer Performance, Testing, Installation, and Maintenance

This article will discuss the key applicable North American standards defining performance, testing, installation, and routine field maintenance of liquid-immersed distribution substation transformers. These transformers, typically applied in commercial and industrial power systems, can be installed either in outdoor or indoor locations, applied as remote or close-coupled to either primary or secondary switchgear, or both. Typical ratings for these distribution substation transformers range from 112.5 kVA through 10,000 kVA three-phase, at 50 or 60 H, with primary voltage at 34,500 V and below and secondary voltage at 6,900 V and below. Not included in the scope of this article are dry-type distribution transformers, pad-mounted distribution transformers, or power transformers with ratings up to 100,000 kVA and 230 kV. Recommendations based on these standards for selection, installation, and factory/field-testing industry users should specify to maximize reliability, operational efficiency, and safety will follow.