scope:

This guide applies to dry-type transformers designated as Category I and Category II in IEEE Std C57.12.01-1998.¹ Category III transformers have not been included since these are not commonly manufactured and may require special consideration depending on the manufacturer's recommendations.

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 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 dry-type transformers to short-circuit currents. This guide is not intended to imply overload capability.

¹Information on references can be found in Clause 2.