Abstract: Provided is an apparatus and method for providing to a differential relay an operational vector-group compensation setting pair that automatically provides correction for a phase shift occurring between currents of at least two windings of a power transformer. The method includes calculating a first and second plurality of phasors using secondary currents derived from respective first and second winding of the at least two windings. The method also includes selecting one pair of vector-group compensation settings based on operate current values calculated using different pair combinations of the vector-group compensation settings applied to the first and second plurality of phasors.

Abstract: Provided are methods for controlling operation of a voltage regulator of a single-phase of a three-phase power system to regulate a measured voltage. One of the methods includes recording a first elapsed time between detecting a first excursion of the measured voltage from an in-band area to an out-of-band area, and a first return of the measured voltage to the in-band area. The method also includes recording a second elapsed time period (dip period) between detecting the first return and a second excursion of the measured voltage from the in-band area to an out-of-band area. If the second elapsed time period is less than a predetermined dip time period, causing a tap position change of the voltage regulator upon expiration of a countdown period initiated upon detecting the first excursion, thereby adjusting the measured voltage to the in-band area while allowing a voltage drop of limited length.

Abstract: Provided is an apparatus and method for providing a voltage reduction for single-phase voltage regulator operation in a three-phase power system. The voltage regulator includes a plurality of tap positions selectable to adjust a voltage at a load to an in-band area. The method includes determining a measured voltage and current at the voltage regulator, determining a line voltage drop between the voltage regulator and the load if the measured voltage in the OOB area above the in-band area, and utilizing the measured voltage to lower the voltage at the load if there are no available taps. The method also includes utilizing the measured voltage less the line voltage drop to determine the tap change if there are available taps.

Abstract: Provided is an apparatus and method for providing to a differential relay an operational vector-group compensation setting pair that automatically provides correction for a phase shift occurring between currents of at least two windings of a power transformer. The method includes calculating a first and second plurality of phasors using secondary currents derived from respective first and second winding of the at least two windings. The method also includes selecting one pair of vector-group compensation settings based on operate current values calculated using different pair combinations of the vector-group compensation settings applied to the first and second plurality of phasors.