IEEE C57.12.56:1986 (R1998)

New IEEE Standard - Superseded.
This IEEE Standards product is part of the C57 family on Power Distribution and Regulating Transformers. A test procedure for determining the temperature classification of ventilated dry-type power and distribution transformer insulation systems by test rather than by chemical composition is established. The intent is to provide a uniform method for providing data for selection of the temperature classification of the insulation system, for providing data that may be used as a basis for a loading guide, and for comparative evaluation of different insulation systems. Voltage-withstand endpoint criteria are related to the impulse voltage distribution within the coil or to the initial voltage-withstand of the coil. A relationship between impulse withstand of the insulation and short-term 60-Hz-withstand is identified so that 50/60--Hz testing of model coils is possible.

This standard is intended to establish a uniform method for determining the temperature classification of ventilated dry-type power and distribution transformer insulation systems by test rather than by chemical composition. These insulation systems are intended for use in transformers listed in ANSI C57.12.50-1981 [1] and ANSI C57.12.51-1981 [2], and whose highest voltages exceed nominal 600 V.
NOTE — In this standard, the term transformer shall be considered to mean ventilated dry-type transformer unless qualified by other descriptive terms.
The purpose of this standard is to establish a uniform method
1) For providing data for selection of the temperature classification of the insulation system
2) For providing data which may be used as a basis for a loading guide
3) For comparative evaluation of different insulation systems