IEEE 638:2013 pdf free download – IEEE Standard for Qualification of Class 1E Transformers for Nuclear Power Generating Stations
5.3 Thermal life qualification
When thermal aging effects based on qualified life of insulation and support systems have beendemonstrated to be negligible, seismic tests may be performed without prior thermal aging.
When thermal aging effects based on qualified life cannot be demonstrated to be negligible, then thermalaging of the transformer under qualification shall be performed prior to seismic testing of the referencedtransformer. The following approach may be used to evaluate the thermal life of the transformer.
Due to limitations related to physical size,energy requirements，and elapsed time，thermal aging of acomplete transformer may not be practical. Also，because of the probable inability of thermal agingprocedures to condition a complete transformer to a known end of qualified life, attempting to thermallyage a complete transformer prior to qualification testing is most likely not practical. Therefore, in lieu ofthermally aging a complete transformer, it is acceptable to thermally age windings, components, or validinsulation system models and materials (accurately representing transformer designs to be qualified) todetermine the thermal effects expected to accrue during the transformer’s operating life.
Acceptable aging procedures and end-point testing are outlined in IEEE Std C57.12.60 or IEEEstd C57.100.Other thermal aging procedures may be used provided that justification is agreed uponbetween manufacturer and user. The data used to support the thermal aging procedures shall be pertinent tothe application and shall be available in an auditable form.
5.4 Thermal analysis calculation
Transformer loading guides IEEE Std C57.91 and IEEE Std C57.96 include procedures for calculatingconservative estimates of the fraction of transformer life expectancy that is expended under varioustemperature and/or loading conditions. Operation of a transformer at less than the rated insulation systemtemperature will reduce aging of the insulation system during its design life， as shown in the above-referenced loading guides. The effects of nonsinusoidal loading, if applicable, should be accounted for inthe thermal analysis calculations. IEEE Std C57.110 includes procedures for calculating the effects ofnonsinusoidal loading on a transformer’s loading capability. When a thermal analysis calculation is performed, the above-referenced standards and guides that are applicable for the particular transformerbeing qualified shall be utilized.
6.2 Test unit
lt is the intent of this clause to require testing of a full-size production-line transformer that incorporatesessential components and accessory equipment. The qualification tests that verify the performance requiredby the user’s specification are the routine and design tests.Routine tests shall be conducted on eachtransformer manufactured and on the prototype transformer used for design tests. Design tests (includingtemperature test, impulse test, and short-circuit test), as defined in appropriate IEEE standards, plus seismictests as defined in IEEE Std.344,are conducted on the prototype transformer.
The prototype transformer chosen for such tests shall be a representative unit of a design family in that itshall have the same design features and material specifications as other members of that design family.Operating stresses and electrical/structural loads shall be no less severe than those for all transformers inthe design family to be qualified. Design test reports shall identify all materials，test methods (includingquality control), and features not specifically representative of the transformer being qualified and justifydifferences in each parameter by analysis, operating experience, or independent testing.