IEEE C57.100-2011 pdf free download.IEEE Standard Test Procedure for Thermal Evaluation of Insulation Systems for Liquid-Immersed Distribution and Power Transformers.
3. Definitions For the purposes of this document, the following terms and definitions apply. The IEEE Standards Dictionary: Glossary of Terms & Definitions should be referenced for terms not defined in this clause. 4 3.1 Industry-proven insulation system Decades of operating equipment manufactured using an insulation system including thermally upgraded kraft paper, cellulosic pressboard, and mineral oil has shown that a minimum life expectancy of at least 20.5 years (180 000 hours) may be assumed if the hottest-spot temperature, at rated load as defined in IEEE Std C57.12.00, is maintained. This proven insulation system includes a manufacturing process, which provides initial drying to a moisture content of 0.25% to 0.50% moisture by weight, and after processing, the insulation system will be sealed to prevent the ingress of air (oxygen) and moisture. The minimum life expectancy curve from IEEE Std C57.12.00 to be used for comparison purposes is repeated here by Equation (1) and displayed in Figure 1.
It is recognized that environmental conditions, such as corrosive atmosphere and excessive vibration, can affect actual service life. It seems appropriate to evaluate such extraneous influences separately from the effects of temperature, and they are therefore not included in this procedure. However, for all insulation system testing covered under this requirement, moisture content of the insulation system should be monitored at the beginning of the testing, as it should be representative of the upper limit of factory oil processing equipment (typically in the range of 0.25 to 0.50% moisture by weight of the solid). 5. Minimum life expectancy The load on most transformers is cyclic, with both daily and annual cycles. For this reason, the peak thermal loading (which develops the highest temperature in the transformer windings) occurs on relatively few days during the year and for a relatively small portion of each of these days. Thus, the cumulative time at or above the rated hottest-spot temperature is considerably less than the total elapsed time. Further, it is generally agreed that thermal degradation of insulation is a function of both temperature and time at the temperature. Consequently, the life expectancy (elapsed time) in actual service may differ greatly from the life determined by the essentially continuous loading procedure prescribed in this standard. Experience and experimental evidence indicate that an insulation system capable of operating 180 000 hours, (approximately 20.5 years) at rated hottest-spot temperature should give satisfactory life expectancy under the normal operating conditions described in the preceding paragraph.
6. Criteria for end of life—Distribution transformer and power transformer model In these tests, the life of a particular test specimen is considered to be ended when thermal the degradation of the insulation system has progressed to a point such that the test specimen cannot withstand any one of a series of tests intended to simulate the abnormal currents or voltages that are commonly experienced in actual service. The degradation or aging is produced by a series of temperature cycles, each consisting of a specified time at a specified hottest-spot temperature followed by a return to approximately ambient temperature. Such a series of temperature cycles, followed by end of life tests, will hereafter be referred to as a test period. Since it is impractical to determine the exact point in the test period procedure when the sample reached the level at which it could not withstand the end-point tests, its life at the test temperature should be considered to be the duration of one test period multiplied by the number of periods to failure less one half of one period.