Traveling Wave Faults

Power Grid Fault Locator and Detection

Faults in power grid transmission lines often occur in remote locations, and repairing them can be time consuming, especially if the location of the fault is unknown. Traveling-wave fault location is a method of estimating the location of a fault based on measuring the difference in arrival times of fault artifacts at the two ends of a faulted line.

Using Precision Time to Find Power Grid Faults

Most faults generate a waveform containing a significant amount of high-frequency energy. This can be caused by the primary event initiating the fault, such as a lightning strike or tree hit and the resulting arc; or it can be caused by a break in the line due, for example, to snow, ice, and/or wind loading. This high-frequency energy can often be detected with excellent resolution in the time domain. This event ‘signature’ propagates down the transmission line at nearly the speed of light. Therefore, the ‘signature’ will be received at the ends of the line at times equal to the time of the fault event, plus the propagation delay along the line. If the arrival times at both ends of the line can be measured, then the location of the fault can be estimated. With a good fault signature and accurate time, the fault can be localized to the nearest transmission tower, expediting dispatch of repair crews.

Accuracy

Because fault waveforms travel at the speed of light, or very nearly, this application imposes the most stringent requirements of all those listed. If, for example, towers are located 500 meters apart, and the goal is to locate a fault to the nearest tower, then the maximum time error which can be tolerated (between the two clocks at the ends of the line) is the amount of time it requires the signal to travel 500 meters. At the speed of light, this is about 1.7 us. Since there are also other sources of error, it is best to keep the error well below this. GPS and other precise sources of time can provide accuracy of 100 nanoseconds (0.1 us) or better, so this requirement can be met, with proper care in application.

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