IEEE C37.114-2014 IEEE Guide for Determining Fault Location on AC Transmission and Distribution Lines.
4. Two-terminal data methods 4.1 Background Present communications technology allows for use of data from both ends of the transmission line. The calculation of fault location using data from two ends is fundamentally similar to the single-ended methods except now a means exists to determine and reduce or eliminate the effect of fault resistance and other similar factors that tend to throw off the accuracy of the estimate. These factors, such as nontranspositions, strong or weak sources, loading, and others, have been discussed earlier. There have been many articles on variations of the fundamental techniques aimed at improving the accuracy in locating faults. Details of many of these variations can be found in the articles referenced in this guide (i.e., Girgis, Hart, and Peterson [B10], Hart, Novosel, and Udren [B15], Kezunovic [B24], Lawrence, Cabeza, and Hochberg [B31], Novosel, et al. [B38], and Tziouvaras, Roberts, and Benmouya [B61]. Positive, negative, or zero sequence components may be used and the choice depends on the type of fault and on the extent of system imbalances such as mutual coupling (Makki, et al. [B35]). Positive-sequence components are present in all fault types which simplifies automation because the fault type does not need to be calculated. Negative-sequence components are useful for mitigating the effects of mutual coupling and are present in most fault types except for balanced three-phase faults (Turner [B60]). Zero-sequence components are also useful especially when system imbalances are properly mitigated but are only present in unbalanced fault types. The main drawback is the fact that data from both ends must be gathered at one location to be analyzed, whereas the one-terminal location can be done at the line terminal by the relay or other device collecting the data. Effective two-terminal fault location requires an efficient means of collecting oscillographic or phasor data from electronic devices at each end of a line following a fault and processing that data automatically.
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