IEEE C57.12.21

Abstract

Foreward<br>The Accredited Standards Committee on Transformers, Regulators, and Reactors, C57, has for a number of years been developing and correlating standards on transformers and regulators. The data used in this work have been gathered from many sources, including the standards of the Institute of Electrical and Electronics Engineers and the National Electrical Manufacturers Association, reports of committees of the Edison Electric Institute, and others. <br>This standard was prepared by the Working Group of the Subcommittee on Distribution Transformers, Overhead and Pad-Mounted, C57.12.2, and is a revision of the 1986 edition. Added to this revision are sections on storage and installation with emphasis being placed on the actual position when stored and the consideration of the angle of tilt when installed.<br>Scope<br>This standard is intended for use as a basis for determining performance, interchangeability, and safety of the equipment covered, and to assist in the proper selection of such equipment. <br>This standard covers certain electrical, dimensional, and mechanical characteristics and takes into consideration certain safety features of single-phase, 60 Hz, mineral-oil-immersed, self-cooled, padmounted, compartmental-type distribution transformers with high-voltage bushings. These transformers are rated 167 kVA and smaller, with high-voltages of 34500 GRD/19900 volts and below for operation between one phase and grounded neutral, and low-voltage of 240/120 volts. These transformers are generally used for step-down purposes from an underground primary cable supply. <br>NOTE&#8212;Refer to latest federal regulations concerning polychlorinated biphenyl (PCB) contaminations in transformers. <br>This standard covers bushing and terminal arrangements for both radial and loop feed systems. <br>This standard does not cover the electrical and mechanical requirements of any accessory devices that may be supplied with the transformer.