Fault Location Process Overview
The Fault Location process is as follows:
• When the system receives a message of a fault occurrence, the FLA automatically retrieves fault information from relays and fault indicators (if available) and logs a new event in the Work Agenda.
• FLA uses fault information and circuit parameters to calculate potential fault locations for fault events. Potential fault locations are displayed in the Viewer.
• When the FLA tool is started, it displays analysis details about fault events, including SCADA measurements and probable fault locations.
• If more than one fault location is identified for a specific fault event, the user may have to correct a calculated fault location after the actual fault location is identified by crew members on site.
Fault Location Algorithm
The algorithms used by FLA are different from those used for a regular short-circuit analysis. When performing a short-circuit analysis, where you are determining fault currents, you have more information since you know where the fault is. In that case, the model is solved with a known fault type at a known location. The fault currents at the target location are determined by the source voltage, source impedance, and all conductor impedances along the path to the fault.
With FLA, only the fault currents at the fault reporting device are known and the fault location must be extrapolated. If available, FLA can utilize fault voltage recorded at fault reporting device in conjunction with the fault currents to further improve the analysis.The short-circuit analysis is performed with the fault placed at the breaker and the fault currents determined for that scenario. These should be higher than the fault currents reported by SCADA. For example, if SCADA is reporting 2500 Amps at the breaker and the solution is reporting 3000 Amps, we know that there is more impedance in the path to the fault that would account for the 500 Amps difference. We calculate the impedance that would cause the difference and trace down the feeder summing up conductor impedances until we arrive at a location that equates to the target impedance.
One significant difference between the two scenarios is that by placing the fault at the breaker, we are removing all downstream load from consideration. Whereas in FLA, the fault is actually downstream, so the breaker fault currents will have a component that is for the load that is between the breaker and the fault. The assumption that is made is that component is insignificant; however, in reality, the further down the feeder the FLA fault is, the more significant that component becomes. This may or may not have a significant impact on the results because the fault will pull down the breaker voltage.