Remote Fault Estimation and Thevenin Impedance Calculation from Relays Event Reports

One of the typical features in modern relays is the generation of event reports during a disturbance. Event reports are records of regularly taken samples of the line currents and voltages as seen by the relay during a disturbance. This paper describes a software tool developed for the use of these event reports to perform the tasks of fault classification and estimation. The program estimates the 60 Hz values of currents and voltages by applying DFT (discrete Fourier transform) to the samples recorded by the relay every quarter of a cycle. Using these values the program performs the following calculations: 1) classification of fault, 2) estimation of the fault distance from the relay location and 3) Thevenin´s impedance of the system at the fault point as well as a Thevenin´s equivalent impedance of the system in front and behind the relay. The program was initially tested with data generated from ATP simulations and later with data from relays installed in an operating electrical network. The results show that the software is highly reliable, providing accurate estimation of faults and Thevenin´s equivalent impedances