A novel out-of-step detection algorithm using angle of power signal

The electric power system maintains a dynamic and delicate balance between generation and load in normal operation condition. A disturbance, such as a sudden change of load, a power system fault, or a trip of a large generation unit, may break the balance, cause the oscillations among the generator rotor angles and force the generators to adjust to a new operating condition. The adjustment will not happen instantaneously due to the inertia of the generator prime movers. The oscillation will cause either stable and/or unstable power swings. During a power swing, the impedance trajectory seen by a distance relay may enter the fault detection zones and cause unwanted relay operation. Distinguishing stable and unstable power swing is one of the challenging tasks. This paper presents a wavelet based energy function for distinguishing stable and unstable power swing using Wavelet based Power Angle criteria.