IEEE C37.112:1996 (R2007)

New IEEE Standard - Superseded.
The inverse-time characteristics of overcurrent relays are defined in this standard. Operating equations and allowances are provided in the standard. The standard defines an integral equation for microprocessor relays that ensures coordination not only in the case of constant current input but for any current condition of varying magnitude. Electromechanical inverse-time overcurrent relay reset characteristics are defined in the event that designers of microprocessor based relays and computer relays want to match the reset characteristics of the electromechanical relays.

The scope of this standard includes the review of carious existing analytic techniques used to represent relay operating characteristic curve shapes and proposed analytical (formula) representation of typical operating characteristic curve shapes to foster some standardization of available inverse-time relay characteristics provided in microprocessor or computer relay applications.
The purpose of this standard is to provide an analytic (formula) representation of typical relay operating characteristic curve shapes of various inverse-time relays to facilitate representation by microprocessor-type relays and promote a degree of standardization in the inverse shape of a selected curve.