IEEE Std C57.100 pdf free download

IEEE Std C57.100 pdf free download.Thermal Evaluation of Insulation Systems for Liquid-Immersed Distribution and Power Transformers.
4. Aging influences The primary aging factors employed in this procedure are temperature and time. Since few transformers operate for extended periods at constant temperatures, provision is made for thermal cycling in this procedure. For the sealed tube test procedure and the dual temperature test described in Annex A, Annex B and Annex C, cyclical loading is not part of the standard test method. 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 in actual service may differ greatly from the life determined by the essentially continuous loading procedure prescribed in this standard.
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 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. Because of the nature of this test, the word failure, as used herein, assumes a special connotation. It is used here to describe an insulation breakdown such that a service outage would result if it occurred in the field. Consequently, some of the criteria of failure that are commonly used in tests on new transformers do not apply. For example, minor disturbances in the oscillograms obtained on impulse tests or increases in the leakage current on applied potential tests are not necessarily indicative of failure as defined here. Specific instructions for the treatment of such marginal cases are given in 10.3. If a test sample should fail prematurely, that is, long before its anticipated life expectancy and if subsequent examination conclusively shows the failure to be the result of defects in material or workmanship, rather than thermal degradation, failure of this sample may be ignored in determining the test results and another sample substituted for it.IEEE Std C57.100 pdf download.