Patent ID: 7738221

Claim:
A power transformer protection system, comprising: a first Rogowski coil positioned to sense a primary current associated with a primary of the power transformer and to output a primary signal indicative of the primary current; a second Rogowski coil positioned to sense a secondary current associated with a secondary of the power transformer and to output a signal indicative of the secondary current; a protection relay configured to isolate the power transformer when the protection relay is activated; and a controller operable to activate the protection relay, wherein the controller is further operable to compare the output of the first Rogowski coil and the output of the second Rogowski coil to obtain a differential first time derivative of current, to sample the differential first time derivative of current based on a sampling rate, to detect an inrush condition when a predetermined number of sequential samples of the differential first time derivative of current are within a predetermined range, and to prevent activation of the protection relay in response to detecting the inrush condition.