IEEE C57.12.59-2001 pdf download IEEE Guide for Dry-Type Transformer Through-Fault Current Duration
1.Overview
11 Scope
This guide applies to dry-type transformers designated as Category I and Category Il in IEEE StdC57.12.01″-1998.’ Category Ill transformers have not been included since these are not commonly manu-actured 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 magnitude to clearing time. It is desirable that these characteristic curves be coordinated with comparable curvesapplicable 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 protectivedevices that limit the exposure time of dry-type transformers to short-circuit currents. This guide is notintended 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*or fault-current magnitudes near the maximum short-circuit current rating of the transformer. mmechanicaeffects are more significant than thermal effects. The maximum symmetrical short-circuit current should notexceed 25 times normal base current in accordance with IEEE Std C57.12.01-1998. At lower fault-currentmagnitudes approaching the overload range, mechanical effects are less important unless the frequency andduration of fault occurrence is high enough to promote mechanical degradation. The point of transitionbetween mechanical concern and thermal concern cannot be precisely defined; mechanical effects tend tohave 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 aresuperseded by an approved revision, the revision shall apply.
IEEE C37.91”-2000, IEEE Guide for Protective Relay Applications to Power Transformers.2.2.3
IEEE C57.12.01-1998, 1EEE 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, 1EEE Guide for Loading Dry-Type Distribution and Power Transformers.
3. Definitions
For the purposes of this guide, the following terms and definitions apply. The Authoritative Dictionary ofEEE Standards Terms B114 should be referenced for ters not defined in this clause.
3.1 normal base current: Rated current of a transformer corresponding to its rated voltage and rated basekVA.
3.2 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 Il 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.
4.Transformer coordination
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 Il trans-formers as defined in IEEE Std C5712.01-1998 and adopted in Table 1.
For Category l, a single curve applies that reflects both thermal and mechanical damage considerations.