Impact of Propagation Losses on Fault Location Accuracy in Full Transient-Based Methods

Abstract

This paper studies how propagation and termination losses affect full transient-based fault location techniques. Their accuracy is discussed in terms of both location uncertainty, caused by a limited spatial resolution, and systematic errors, caused by a bias in the fault-location metrics. This last case is proven to be by far likelier when propagation losses are higher than the dissipation in line termination loads. Two different location metrics are studied, namely correlation and normalized projection, as found in the literature, with correlation proven to be unbiased, since it benefits from two location mechanisms, namely frequency and time-decay matching of a line resonances, as opposed to projection, which only relies on the former mechanism. A numerical analysis of realistic lossy overhead lines confirms theoretical predictions about biased fault location and loss of spatial resolution and the role played by the frequency content of transient data. When applied to the modal analysis of a three-phase transmission line, these results help explaining why faults are located with widely variable accuracy depending on their distance and the bandwidth of the recorded transient, confirming that wide-band transient sampling does not necessarily results in the best location accuracy.

On the Spatial Resolution of Fault-Location Techniques Based on Full-Fault Transients

“…Given that propagation losses significantly increase with the frequency, TBM can present super resolution most likely below the MHz range. Results of TBM applied to lossy lines are found in the EMTR literature [11], [12] and in [18], where the reported location accuracy is consistent with the super-resolution property.…”

“…Therefore, only termination losses will be explicitly discussed in the rest of the paper, in order to reduce the number of parameters involved, with no loss of generality in our conclusions. The spatial resolution in (16) would depend on the fault distance L only for significant propagation losses, compared to losses in the line terminations, as discussed in [18]. This paper will not explore this case, since it focuses on the spatial resolution of TBM, thus close to the actual fault position.…”

Surge Compression for Improved Fault Location Accuracy in Full Transient-Based Methods

“…Since these results were obtained by filtering out the ground mode, it could appear as contradictory to observe ground-mode related contributions. In fact, it was proven in [25] that PG faults act as modal couplers, thus scattering energy among ground and aerial modes at each interaction with the fault. The increasing number of echoes grouped into clusters in Fig.…”

“…Both TBM approaches have been shown to effectively estimate a fault position from its full transient, but the use of an a posteriori normalization in projection-based TBM was proven to be susceptible to location biases, particularly so in presence of non-negligible propagation losses [25]. For this reason, this paper will focus only on the case of transient correlation, but the ideas here discussed can also be applied to projection-based methods, such as EMTR.…”

“…These results prove that faults can be located with a higher accuracy than currently possible with TBM, without increasing either the complexity of the post-processing currently applied in TBM, or requiring higher sampling rates. The most practical impact could be expected for lines with high-frequency propagation losses: in this case a higher sampling rate may paradoxically reduce the location accuracy, as proven in [25]. It is therefore of practical interest to be able to increase the location accuracy without relying on higher sampling rates, a standard solution adopted in TWM [14], [20], [26].…”