A Novel Out-of-step Splitting Protection Based on the Wide Area Information

Abstract

Using the wide area information obtained from phasor measurement units, a novel out-of-step splitting protection is proposed. In order to analyze the different characteristic of bus voltage phase angles, a new coordinate system is introduced. In this coordinate system, all of the converted bus voltage phasor ends are stable, while only the common beginning is moving during the out-of-step oscillation process. Its conformal property guarantees the voltage phase angle differences in the old and new coordinate systems are equal. After the coordinate transformation, the formula about the converted power network neutral point trajectory is derived. The intersection of the trajectory and the broken line which connects the bus voltage phasor ends is the out-of-step center. All of the buses are divided into two parts by the out-of-step center. Through a series of proofs, it is found that the absolute values of the bus voltage phase angles in one part are always smaller than 110°, while the voltage phase angles of the rest buses vary from −180° to 180°. These different characteristics could be used to group these buses and locate the out-of-step center. It is very simple because only the voltage phase angle information is applied, and there are no complex mathematical operations. Finally, a novel out-of-step splitting protection scheme is given. The digital simulation results prove the proposed scheme is efficient.