Patent ID: 8045307

Claim:
A protective relay for providing protective control to a power system carrying three-phase power, the protective relay comprising: a processor; at least one computer readable medium; program instructions stored on the at least one computer readable medium and executable by the processor to perform a fault detection method comprising: receiving a first set of signal values representative of the voltage properties of each phase of the three-phase power system and a second set of signal values representative of the current properties of each phase of the three-phase power system; processing said first set of signal values to produce a first set of processed signals representing the current change for each respective phase of the three phase power; processing said second set of signal values to produce a second set of processed signals representing the voltage change for each respective phase of the three phase power; determining a maximum value of said first set of processed signals and a maximum value of said second set of processed signals; dividing said maximum value of said first set of processed signals by a first threshold value resulting in a first quality value; dividing said maximum value of said second set of processed signals by a second threshold value resulting in a second quality value; selecting the set of processed signals having the larger quality value; and using said selected set of processed signals to determine whether a fault condition exists on any phase of the three phase power.