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ANSI C57.12.22

93rd Edition, January 1, 1993

Complete Document

Transformers - Pad-Mounted, Compartmental-Type, Self-Cooled Three-Phase Distribution Transformers With High-Voltage Bushings, 2500 kVA and Smaller: High Voltage, 34 500 Grd Y/19 920 Volts and Below; Low Voltage, 480 Volts and Below

Includes all amendments and changes through Reaffirmation Notice , 1998

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The Accredited Standards Committee on Transformers, Regulators, and Reactors, C57, has for many years been developing and correlating standards on transformers and regulators. The data used in this work have been gathered from many sources, including the standard of the Institute of Electrical and Electronics Engineers and the National Electrical Manufacturers Association, reports of committees of the Edison Electric Institute, and others.

This standard and the companion standard on single-phase transformers (ANSI C57.12.21) were prepared by the Subcommittee on Distribution Transformers, Overhead and Pad-mounted, C57.12.2.

Suggestions for improvement of this standard will be welcome. They should be sent to the American National Standards Institute, 1430 Broadway, New York, 10018.


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.

This standard covers certain electrical, dimensional, and mechanical characteristics and takes into consideration certain safety features of three-phase, 60 Hz., mineral-oil-immersed, self-cooled, padmounted, compartmental-type distribution transformers with high-voltage bushings. These transformers are rated 2500 kVA and smaller, with high voltages of 34 500 GrdY/19 920 volts and below, and with low voltages of 480 volts and below. These transformers are generally used for step-down purposes from an underground primary cable supply.

NOTE—Refer to latest federal regulations concerning PCB contamination in transformers.

This standard covers the bushing and terminal arrangements for radial feed systems. Either certain minimum dimensions (see figures 1-3) or certain specific dimensions (see figures 4-6) shall be specified.

This standard does not cover the electrical and mechanical requirements of any accessory devices that may be supplied with the transformer.