IEEE C57.12.59-2001 pdf download

IEEE C57.12.59-2001 pdf download.IEEE Guide for Dry-Type Transformer Through-l Fault Current Duration
This guide applies to dry-type transformers designated as Category I and Category II in IEEE Std C57.12.01″- 1998. Category III transformers have not been included since these are not commonly manu- factured and may require special consideration depending on the manufacturer s recommendations.
1.2 Purpose Protective devices, such as relays and fuses, have well-defined operating characteristics that relate fault mag- nitude to clearing time. It is desirable that these characteristic curves be coordinated with comparable curves applicable to dry-type transformers that relate duration and fault magnitude to withstand capability.
This guide sets forth recommendations believed essential for the application of overcurrent protective devices that limit the exposure time of drytype transformers to short-circuit currents. This guide is not intended to imply overload capability.
1.3 General The magnitude and duration of fault currents are of utmost importance in establishing a coordinated protection practice for transformers, as both mechanical and thermal effects of fault currents must be considered. For fault-current magnitudes near the maximum short-circuit current rating of the transformer, mechanical effects are more significant than thermal effects.
The maximum symmetrical short-circuit current should not exceed 25 times normal base current in accordance with IEEE Std C57.12.01-1998. At lower fault-current magnitudes approaching the overload range, mechanical effects are less important unless the frequency and duration of fault occurrence is high enough to promote mechanical degradation.
The point of transition between mechanical concern and thermal concern cannot be precisely defined; mechanical effects tend to have a more prominent role in larger kVA ratings because the mechanical forces are greater.
2. References This guide is to be used in conjunction with the following publications. If the following publications are superseded by an approved revision, the revision shall apply. IEEE C37.91″-2000, IEEE Guide for Protective Relay Applications to Power Transformers.2.3 IEEE C57.12.01-1998, IEEE Standard General Requirements for Dry-Type Distribution and Power Trans- formers Including Those with Solid-Cast and/or Resin-Encapsulated Windings.
IEEE C57.96″-1999, IEEE Guide for Loading Dry-Type Distribution and Power Transformers.
3. Definitions For the purposes of this guide, the fllowing terms and definitions apply.
The Authoritative Dictionary of IEEE Standards Terms [B 1]+ 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 base kVA. 3.2 transformer short-circuit impedance:
1.) For Category I transformers, the transformer expressed in percent of rated voltage and rated base kVA of the transformer.
2.) For Category II transformers, the sum of transformer impedance and system short circuit impedance at the transformer location, expressed in percent of rated voltage and rated base kVA of the transformer.
4. Transformer coordination
For the purposes of coordination of overcurrent protective devices, with transformer short-circuit withstand capability, Figure 1 and Figure 2 are presented as protection curves for Category I and Category II trans- formers as defined in IEEE Std C57.12.01-1998 and adopted in Table 1. For Category I, a single curve applies that rflcts both thermal and mechanical damage considerations. For Category II, 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 a solid and a dotted portion, the solid portion represents a total fault duration beyond which thermal damage to insulation adjacent to current carrying conductors and anneal-softening of aluminum may occur, while the dotted portion represents a total fault duration beyond which cumulative mechanical damage may occur.
The increasing significance of mechanical effects for higher kVA transformers is reflected in these curves. The frequency of faults varies with different transformer applications. Applications characterizing frequent and infrequent 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.IEEE C57.12.59 pdf download.EEE C57.12.59-2001 pdf download