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Transformers in this standard are generally for larger distribution customers often with special voltages or installation requirements like convention centers with large chiller plants and extensive exhibit space. There is often a desire to serve these transformers from underground systems using side-mounted bushings on the primary. This standard seeks to define the small power transformer that is applied as more than just a limited scope version of the power transformers covered by IEEE Std C57.12.10 and as more than a large distribution class transformer covered by IEEE Std C57.12.10 and as more than a large distribution class transformer covered by IEEE Std C57.12.34.

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Characteristics relating to performance, limited electrical and mechanical interchangeability, as well as safety of the equipment described, and to assist in the proper selection of such equipment, are set forth in this standard. Specific rating combinations are described in the range from 750/1000 kVA to 7500/10,000 kVA inclusive, with high-voltage 601 V to 34 500 V inclusive and low-voltage 208Y/120 V to 4160 V inclusive. This standard describes certain electrical and mechanical requirements and takes into consideration certain safety features of 60 Hz, two-winding, three-phase, ventilated dry-type transformers with self-cooled ratings 501 kVA and larger, which are generally used for step-down purposes. Clause 9 through Clause 11 describe other requirements or alternatives that may be specified for some applications and lists forced-air-cooled ratings for certain sizes. Keywords: ambient temperature, basic lightning impulse insulation level (BIL), construction, current transformer, dry-type, electrical, forced-air cooled, grounding, insulation level, jacking, limiting temperature, mechanical, percent impedance voltage, performance, rating, self-cooled, surge arresters, taps, temperature device, temperature rise, tests, transformer, transformer enclosure, unit substation, winding temperature.

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The clause that addresses direct measurement with fiber-optic detectors is expanded and an annex detailing examples of installation techniques for fiber-optic probes is added in this amendment.

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This recommended practice provides calculation methods to conservatively evaluate the feasibility for an existing installed dry-type or liquid-filled transformer, to supply nonsinusoidal load currents as a portion of the total load. This recommended practice also provides necessary application information to assist in properly specifying a new transformer expected to carry a load, a portion of which is composed of nonsinusoidal load currents. A number of examples illustrating these methods and calculations are presented. Reference annexes provide a comparison of the document calculations to calculations found in other industry standards. Suggested temperature rise calculation methods are detailed for reference purposes.

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Conformance tests and requirements for the integrity of above-grade pad-mounted enclosures for application in coastal environments that contain apparatus energized in excess of 600 V and that may be exposed to the public are described. These include, but are not limited to, the following types of equipment enclosures: pad-mounted capacitors or inductors, pad-mounted distribution transformers, pad-mounted junction enclosures, pad-mounted metering equipment, pad-mounted switchgear, and pad-mounted voltage regulators. Keywords: enclosure integrity, IEEE C57.12.29, pad-mounted equipment, switches, transformers, voltage regulators.

Electric transformers.