IEEE C57.12.00-2010 pdf download IEEE Standard for General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers
For multi-winding transformers or autotransformers, 4.1.6.1 applies only to specific loading conditionsused as the basis of design. These loading conditions involve simultaneous coordination of kVA input andoutput,load power factors, and winding voltage combinations (see item j) of 4.3.3]. Differences in loadingand voltage regulation for various output windings may prevent simultaneous achievement of 105% voltageon all output terminals. In no case shall the kVA outputs specified for any loading condition requirecontinuous loading of any input winding in excess of its rating.
4.1.6.2 Maximum continuous transformer operating voltage
The maximum continuous transformer operating voltage should not exceed the levels specified in ANSlC84.1. System conditions may require voltage transformation ratios involving tap voltages higher than themaximum system voltage for regulation purposes. However, the appropriate aximum system voltageshould be observed under operating conditions.
4.1.7 Outdoor operation
Unless otherwise specified, transformers shall be suitable for outdoor operation.
4.1.8 Step-down operation
Unless otherwise specified, transformers shall be designed for step-down operation
4.1.8.1 Generator step-up transformers
Transformers identified as generator step-up transformers shall be designed for step-up operation.
4.1.8.2 System tie transformers
Transformers identified as system tie transformers or autotransformers shall be designed for stcp-downoperation, or step-up operation, or both, as specified by the user.
4.1.9 Tank or enclosure finish
Temperature limits and tests shall be based on the use of a nonmetallic pigment surface paint finish. Itshould be noted that metallic-flake paints, such as aluminum and zinc, have properties that increase thetemperature rise of transformers, except in direct sunlight.
4.2 Loading at other-than-rated conditions
IEEE Std C57.9ITM B28] provides guidance for loading at other-than-rated conditions including thefollowing:
IEEE Std C57.91 (B28) is an IEEE guide, and as such, it does not specify mandatory requirements. Itprovides the best known general information for loading of transformers under various conditions based ontypical winding insulation systems. It is based upon the best engineering information available at the timeof preparation. The guide discusses limitations of ancillary components other than windings that may limitthe capability of transformers. When specified, ancillary components and other construction features (suchas cables, bushings, tap changers, oil expansion space, etc.) shall be supplied in a manner that will not limitthe loading to less than the capability of the windings.
4.3 Unusual service conditions
Conditions other than those described in 4.1 are considered unusual service conditions and, when prevalent.
should be brought to the attention of those responsible for the design and application of the apparatus.
Examples of some of these conditions are listed in 4.3.3.
4.3.1 Unusual temperature and altitude conditions
Transformers may be used at higher or lower ambient temperatures or at higher altitudes than thosespecified in 4.1.3, but special consideration should be given to these applications. IEEE Std C57.91 (B28provides information on recommended practices.