IEEE C57.12.59-2001 pdf free download.IEEE Guide for Dry-Type Transformer Through-Fault Current Duration.
For the purposes of this guide, the following terms and definitions apply.The Authoritative Dictionary ofIEEE Standards Terms [B1]’ should be referenced for terms not defined in this clause.
3.1 normal base current: Rated current of a transformer corresponding to its rated voltage and rated basekVA.
transformer short-circuit impedance: 1.) For Category I transformers, the transformer expressed inpercent of rated voltage and rated base kVA of the transformer. 2.) For Category ll transformers, the sum oftransformer impedance and system short-circuit impedance at the transformer location, expressed in percentof rated voltage and rated base kVA of the transformer.
For the purposes of coordination of overcurrent protective devices, with transformer short-circuit withstandcapability,Figure 1 and Figure 2 are presented as protection curves for Category I and Category ll trans-formers as defined in IEEE Std C57.12.01-1998 and adopted in Table 1.
For Category l, a single curve applies that reflects both thermal and mechanical damage considerations.
For Category ll, two curves apply, one of which reflects both thermal and mechanical damage consider-ations,while the other reflects primarily thermal damage considerations only.On curves that have both asolid and a dotted portion, the solid portion represents a total fault duration beyond which thermal damage toinsulation adjacent to current-carrying conductors and anneal-softening of aluminum may occur, while thedotted portion represents a total fault duration beyond which cumulative mechanical damage may occur.Theincreasing significance of mechanical effects for higher kVA transformers is reflected in these curves. Thefrequency of faults varies with different transformer applications.Applications characterizing frequent andinfrequent faults are presented in the annex of IEEE Std C37.91-2000.The short-time thermal load capability of dry type transformers is summarized in Table 2.
The validity of these damage-limit curves cannot be demonstrated by test, since the effects are progressive over the transformer lifetime. The curves are based principally on informed engineering judgement andfavorable historical field experience.IEEE C57.12.59 pdf download.