IEEE C57.94-1982 (R2006) pdf free.IEEE Recommended Practice for lnstallation，Application, Operation, andMaintenance of Dry-Type General Purpose Distribution and PowerTransformers.
IEEE C57.94 following American National Standards referred to in this recommended practice are superseded by arevision approved by the American National Standards Institute, the latest revision shall be used.
[1]ANSI C2-1981,National Electrical Safety Code2
[2] ANSI C57.12.50-1981，American National Standard Requirements for Ventilated Dry-Type DistributionTransformers 1 to 500kVA, Single Phase: and 15—500kVA,Three-Phase with High Voltage 601—34500 Volts, LowVoltage 120—600 Volts
[3]ANSI C57.12.51-1981 American National Standard Requirements for Ventilated Dry-Type Power Transformers,501 kVA and Larger, Three-Phase, with High-Voltage 601 to 34 500 Volts, Low-Voltage 208Y/120 to 4160 Volts
[4]ANSI C57.12.52-1981，American National Standard Requirements for Sealed Dry-Type Power Transformers,501 kVA and Larger, Three-Phase, with High-Voltage 601 to 34 500 Volts, Low Voltage 208Y/120 to 4160 Volts
[5] ANSI C57.12.70-1978,American National Standard Terminal Markings and Connections for Distribution andPower Transformers
[6]ANSI C57.12.80-1978,American National Standard Transformer Terminology
[7] ANSI C57.96-1959，American National Standard Guide for Loading Dry-Type Distribution and PowerTransformers (Appendix to ANSI C57.12 standards)
[8]ANSI C62.2-1980，American National Standard Guide for Application of Valve-Type Lightning Arresters forAlternating Current Systems
[9] ANSI C84.1-1977,American National Standard Voltage Ratings for Electric Power Systems and Equipment(60 Hz) (includes supplement ANSI C84.1a-1980)
[10] ANSIIEEE C57.12.01-1979,IEEE Standard General Requirements for Dry-Type Distribution and PowerTransformers
Dry-type transformers are designed for operation at altitudes not to exceed 1000 m (3300 ft). Operation at greateraltitude requires special precaution.The reduced air density at higher altitudes adversely affects the dielectric strengthof the transformers which depend on air for insulation.Special designs incorporating larger clearances may berequired for high altitude operation.Additional information and correction factors are covered in ANSIEEEC57.12.01-1979 [10].Reduced air density at high altitudes increases the temperature rise of transformers. Thecapability to dissipate heat losses is reduced and, therefore, transformer loading capability may be reduced.Additionalinformation and data on this is contained in ANSI C57.96-1959[7].
ON-OFF switching of loads, such as full voltage starting of motors can place severe mechanical stress on the windingconductors and support components. Where this type of loading is anticipated,transformer specifications shoulddescribe loading duty.Special design measures may be necessary to restrain the mechanical forces.
Operation at voltages in excess of rating may cause core saturation and excessive stray losses. This can result inoverheating and abnormally high noise levels. Special care should be taken where overexcitation is anticipated.See ANSI/IEEE C57.12.01-1979 [10].
Where dry-type transformers are connected to lines subject to lightning exposure or other voltage surges, carefulcoordination of transformer BIL levelsand protective surge arresters must be made. The ANSI Surge AttesterApplication Guide，ANSI C62.2-1980 [8]， and manufacturer’s surge attester product data provides specificinformation on over-voltage protection of dry-type transformers. Transformers in systems having solid state control,which may cause voltage transients and distorted current wave forms require special consideration.IEEE C57.94 pdf download.