IEEE C57.12.56:1986 pdf download.IEEE Standard Test Procedure for Thermal Evaluation of Insulation Systems for Ventilated Dry-Type Power and Distribution Transformers.
IEEE C57.12.56 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 1111 and ANSI C57.12.51-1981 121, and whose highest voltages exceed nominal 6000 V.
NOTE — In this standard, the term transformer shall be considered to mean i’entilated dry-type transformer unless quahhed by other descriptive terms.
1.2 Purpose
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 he used as a basis for a loading guide
3) For comparative evaluation of different insulation systems
1.3 References
[l] ANSI C57.12.50-1981, American National standard Ventilated Dry-Type Distribution Transformers, 110500 kVA. Single-Phase, and 15 to 5(X) kVA, Three-Phase, with High-Voltage 6() I to 34 500 Volts, Low-Voltage 12010 6000 Volts
[2] 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 34500 Volts, Low-Voltage 208Y/l20to 4160 Volts.
[3] ANSI/ASTM D149-81, Standard Test Methods for Dielectric Breakdown Voltage and Dielectric Strength of Electrical Insulating Materials at Commercial Power Frequencies.
[4] ANSIJIEEE C57.98- 1986. IEEE Guide for Transformer Impulse Tests.
[5] ANSI/IEEE Std 4-1978, IEEE Standard Techniques for High-Voltage Testing.
[6] ASTM El 04-51 (RI 971), Standard Recommended Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions.
[7] IEEE Std 1-1969, IEEE General Principles for Temperature Limits in the Rating of Electric Equipment.
[8] IEEE Std 101-1972, IEEE Guide for the Statistical Analysis of Thermal Life Test Data.
[9] IEEE Std IOIA-1974, Simplified Method for Calculation of the Regression Line (Appendix to IEEE Guide for the Statistical Analysis of Thermal Life Test Data. IEEE Std 101-1972).
[10] MANNING, M. L. The Electrical Insulation Challenge for Dry-Type Transformers. Insulation! Circuits, Sept 1973, vol 19, no 10, pp 87-92.
1.4 Applicable Document in Preparation5
2. Basic Considerations
2.1 General
Two test methods are developed to provide a means for evaluating insulation systems as a function of thermal aging and are an extension of ATEE 65I956.6 Thermal Evaluation of Ventilated Dry-Type Power and Distribution Transformers.
One method is based on retention of a dielectric withstand voltage equal to a percentage of the initial 50/60 Hz dielectric withstand c capability of the test sample.
The second method is based on the retention of the basic impulse insulation level7 by impulse testing. or by related [10] 50/60 Hz voltage withstand capability tests on models. See 3.7.
2.2 Intent
The intent of these test methods is to have each component of the insulation system tested under conditions that are as nearly as possible the same as those in the actual transformer. Thus, each of the components is evaluated in accordance with its actual function.
2.3 Aging Factors
The primary aging factors shall be temperature and time. Although the primary aging factors are temperature and time, the criterion of failure of these high-voltage insulation systems is assumed to be voltage related to the initial dielectric strength orto the rated basic impulse voltage level. IEEE C57.12.56 pdf download.