IEEE C57.109-1993

This guide applies to transformers referenced in IEEE Std C57.12.00-1993 as Categories I, II, III, and IV.

Protective devices such as relays and fuses have well-defined operating characteristics that relate fault magnitude to operating time. These characteristic curves should be coordinated with a comparable curve(s)applicable to transformers that relate duration and fault magnitude to withstand capability. This guide sets forth recommendations believed essential for the application of overcurrent protective devices applied to limit the exposure time of transformers to short-circuit currents [see IEEE Std C37.91-1985 (Reaff 1991)]. This guide is not intended to imply overload capability.

Revision Standard - Superseded. Recommendations believed essential for the application of over current protective devices applied to limit the exposure time of transformers to short-circuit current are set forth. Transformer coordination curves are presented for four categories of transformers. There is no intent to imply overload capability