IEEE C57.94-2015 pdf free.IEEE Recommended Practice for Installation, Application, Operation, and Maintenance of Dry-Type Distribution and Power Transformers.
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.
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 C57.12.01.
Where dry-type tansformers are connected to lines subject to lightning exposure or other voltage surges, careful coordination of transformer Basic Impulse Levels and protective surge arresters must be made. The IEEE surge arrester application guides, IEEE Std C62.2 and IEEE Std C62.22, and manufacturer’s surge arrester product data provides specific information on overvoltage protection of dry-type transformers. Transformers in systems having solid state control that may cause voltage transients and distorted current waveforms require special consideration.
IEEE Std C57.142 provides information regarding occurrence and mitigation of switching transients
induced by transformers, switching devices, and system interaction.
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,excesive 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 de-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.
Sealed dry-type transformers are 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 liquidimmersed transformers. Sealed dry-type transformers containing insulating gases that condense at low temperatures must be applied with caution where the transformer is left deenergized for appreciable periods of time. A supplementary heat source may be required to vaporize the gases prior to energizing the transformer. See 7.3.3.IEEE C57.94 pdf download.