Patent ID: 7403364

Claim:
An apparatus, comprising: a d-q component transformer configured to generate a d-q voltage value from a plurality of phase voltage signals corresponding to phase voltages in a power system and to generate a d-q current value from a plurality of phase current signals corresponding to phase currents in the power system; a first voltage filter configured to generate a first voltage sample from the d-q voltage value, the first voltage sample corresponding to the d-q voltage value at a first point in time; a second voltage filter configured to generate a second voltage sample from the d-q voltage value, wherein the second voltage sample corresponds to the d-q voltage value at a second point in time that precedes the first point in time; a first current filter configured to generate a first current sample from the d-q current value, the first current sample corresponding to the d-q current value at the first point in time; a second current filter configured to generate a second current sample from the d-q current value, wherein the second current sample corresponds to the d-q current value at the second point in time; a power value generator configured to generate a delta d-q power value from the first and second voltage samples and the first and second current samples; a fault detector configured to detect a fault condition in a power system by comparing the d-q voltage value to an under-voltage limit value; a characterizer circuit configured to determine a characteristic of the fault condition responsive to the delta d-q power value; and a control circuit configured to control a power system component responsive to the characteristic of the fault condition.