IEEE Std C57.94 pdf free download

IEEE Std C57.94 pdf free download.Installation, Application, Operation, and Maintenance of Dry-Type Distribution and Power Transformers.
4. Application
4.1 Fire protection
Dry-type transformers are generally applied in locations where minimum fire hazard is essential. They are constructed of materials designed to operate at high temperatures.
4.2 Unusual operating conditions
4.2.1 High altitude operation
Dry-type transformers are typically designed for operation at altitudes not to exceed 1000 rn altitude. The reduced air density at higher altitudes adversely affects the dielectric strength of the transformers, which depend on air for insulation. Operation at these higher altitude levels may require special design techniques to meet the required dielectric insulation test levels. Additional information and correction factors are covered in IEEE Std C57.12.0l. Reduced air density at higher altitudes also increases the temperature rise of a transformer. The capability to dissipate heat losses is reduced and, therefore, transformer loading capability may be reduced. Additional information and data on this subject is contained in IEEE Std
C57.96.
4.2.2 Impact loading
ON-OFF switching of loads such as full voltage starting of motors can place severe mechanical stress on the winding conductors and support components. Where this type of loading is anticipated, transformer specifications should describe loading duty. Special design measures may be necessary to restrain the mechanical forces.
4.2.3 Over excitation
Operation at voltages in excess of rating may cause core saturation and excessive stray losses. This can result in overheating and abnormally high noise levels. Special care should be taken where over excitation is anticipated. See IEEE Std C57.12.0l.
4.4 Transient voltage protection
IEEE Std C57. 142 provides information regarding occurrence and mitigation of switching transients induced by transformers, switching devices, and system interaction.
4.5 Environmental considerations
4.5.1 Ventilated and non-ventilated dry-type transformers
Ventilated dry-type transformers are normally designed for installation in dry environments. However. with additional environmental protection, they can be designed for not only outdoor installation, but for environments containing contaminants including dust, fertilizer, excessive moisture, chemicals, corrosive gases. oils, or chemical vapors. Designs will operate successfully where humidity is high. but under this condition it may be necessary to take precautions to keep them dry if they are dc-energized long enough to reach ambient temperature. When installed indoors, precautions should be taken to guard against accidental entrance of water such as might be the result of an open window, a break in a water or steam line, or from the use of water near the transformer.
4.5.2 Sealed dry-type transformers
Sealed dry-type transformers arc not affected by moisture and other contaminants as are other types of dry- type transformers. In general, they may be installed in any environment suitable for liquid-immersed transformers. Sealed dry-type transformers containing insulating gases that condense at low temperatures must be applied with caution where the transformer is left dcenergizcd for appreciable periods of time. A supplementary heat source may be required to vaporize the gases prior to energizing the transformer.
4.6.2 Removal
When located inside buildings, transformer rooms, or enclosures, means should be provided to permit the removal and replacement of a unit in the event of a failure. A route should be available that provides entrances, doorways, and passages with sufficient clearances to permit removal of the transformer. Electrical and mechanical connections of the transformer to other electrical equipment should be of a type that will permit the removal of the transformer without removal or major disassembly of the other equipment.IEEE Std C57.94 pdf download.