The recommended process and criteria for developing V/Hz curves for relay protection purposes for power transformers directly connected to generators are provided in this recommended practice.

This recommended practice applies to liquid-immersed power transformers that are connected to generators subjected to significant short duration increases in the volts per hertz (V/Hz) ratio.

The main purpose of this recommended practice document is to provide a procedure for developing design-specific V/Hz operational limits versus time curves for users of power transformers directly connected to generators. More accurate and more design-specific V/Hz curves should aid users in the proper design and settings of protective relay protection systems of power transformers.