Method for voltage-sag-source detection by investigating slope of the system trajectory

A method of determining the voltage-sag-source direction is proposed. The slope of a line fitting two parameters during the disturbance is employed for the detection. A least-squares method is used to perform the line fitting. The voltage-sag-source direction is determined by examining the sign of the slope. The method is verified to be promising by theoretical analysis, simulations and actual field measurements. Simplicity, ease of implementation and robustness are the advantages of the method.