IEEE Std C57.12.59 pdf free download

IEEE Std C57.12.59 pdf free download.Dry-Type Transformer Through-Fault Current Duration.
For Categories II and Ill, two curves apply, one of which reflects both thermal and mechanical damage considerations, while the other reflects primarily thermal damage considerations only. On curves that have both a solid and 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 curves in Figure 1, Figure 2, and Figure 3 are based upon maximum symmetrical short-circuit current magnitude of dry-type transformers not to exceed 25 times base current limited to a shortcircuit current duration of 2 s.
For Category I transformers, the symmetrical short-circuit magnitude will normally be limited only by the transformer impedance.
For Category II and Category III transformers, the symmetrical short-circuit current is calculated based on the sum of the transformer impedance plus a value of system impedance specified by the user. See IEEE Std C57.12.01 for additional details. NOTE- Refer to IEEE Std C57.96 [B1]5 for loading capabilities at durations longer than 100 s for Categories II and III transformers.
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 judgment and favorable historical field experience; they provide a uniform minimum standard for all dry-type transformers. For an explanation of how the curves are derived, refer to Annex A. The per-unit short-circuit currents shown in Figure 1, Figure 2, and Figure 3 are the balanced transformer winding currents. The line currents that relate to these winding currents depend upon the transformer connection and the type of fault present. Application engineers shall relate the winding currents to the currents seen by the protective devices in order to protect the transformer within its capability.
4.2 Category I transformers The recommended duration limit is based on the curve in Figure 1. The curve reflects both thermal and mechanical damage considerations and should be applied as a protection curve for faults that will occur frequently or infrequently.
4.3.1 Faults that occur frequently
The curve in Figure 3a, reflecting both thermal and mechanical damage considerations, should be applied as a protection curve for faults that will occur frequently (typically more than five in a transformer lifetime.) It is dependent upon the short-circuit impedance for fault currents above 50% of the maximum possible and is keyed to the I2t of the worst-case mechanical duty (maximum fault current for 2s) as shown by the dashed curve for a few impedances. The remaining portion matches thermal protection curves for faults below the 50% level.
4.3.2 Faults that occur infrequently
The curve in Figure 3b reflects primarily thermal damage considerations. It is not dependent upon short-circuit impedance of the transformer and may be applied as a protection curve for faults that will occur only infrequently (typically not more than five in a transformer lifetime). This thermal damage curve may also be used for backup protection where the transformer is exposed to frequent faults normally cleared by high-speed relaying.IEEE Std C57.12.59 pdf download.