Apparatus and method for fault detection and location determination

#This application relates to fault detection and, more specifically to determining fault location and/or direction of faults in electrical networks.

#Various approaches have been used over the years to detect and/or locate electrical faults in electrical networks. In some of these approaches, a reactance algorithm is used to detect and/or locate the faults. More specifically, the magnitudes of the voltage and current of faulted phase and the phase angle between the voltage and the current are determined. Since the voltage and current data are typically obtained from a data sampling device, calculation of the phase angles and the difference in the phase angles requires a steady-state pure sinusoidal segment of voltage and current for at least two power cycles (due to the theoretical requirement of digital signal processing in the calculation of the magnitude and phase angle of a digitized signal). Then, once these values are obtained, a determination as to where a fault exists may be made. In other words, the above-mentioned previous approaches must wait until after the onset of fault through the transient period of fault behavior, for the occurrence of a post-fault steady state voltage and current and only then, after obtaining these values, calculate the magnitude and phase angle for the voltage and current and thereby locate a fault.

#Unfortunately, a large portion of permanent faults and the most transitory/intermittent faults (which are often the precursors of permanent faults) do not produce the desired long post-fault steady-state behavior. Instead, these faults quickly disappear right after a short-lived transient period without reaching a steady state. The majority of short-lived, transient-period only faults, whether they are permanent, transitory, or intermittent, last only about one cycle length of time. For example, underground insulation breakdown intermittent faults (for underground cable) or overhead power lines typically last less than one cycle, most often for about ½ cycle or less. These sub-cycle faults, which may lead to permanent faults, need to be located or loss of electric service may occur as the intermittent faults develop into permanent faults. The conventional fault location approaches described above are incapable of locating sub-cycle faults. In fact, in most cases, these faults are simply ignored by these previous approaches. Therefore, determination of distance to such a sub-cycle fault (intermittent or permanent) is not attempted.

#FIG. 1 comprises a block diagram of a system that determines a distance to a fault according to various embodiments of the present invention;

#FIG. 2 comprises a flowchart of one approach that determines a distance to a fault according to various embodiments of the present invention;

#FIG. 3 comprises a block diagram of an apparatus that determines a distance to a fault according to various embodiments of the present invention;

#Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.

#Approaches are provided that locate sub-cycle faults (both permanent and intermittent) in electric power circuits. The approaches described herein sometimes employ injection approaches and calculate the source impedance under fault conditions. Then, a calculation of the line inductance to the faulted location is made and this line inductance may be multiplied by the known distance/inductance factor of the line to determine the actual physical distance (e.g., in meters, feet, and so forth) from a measuring device to the fault. Additionally, a determination can be made as to whether the fault is upstream or down stream of the measuring device. A determination may also be made as to whether the fault is at the same or different line in the same bus, or at same bus line or different bus line of multi-bus configuration, based at least in part upon a polarity of the determined source inductance.

#In many of these embodiments, the calculation of source inductance and fault distance is accomplished by using the voltage and current signals measured at, for example, a substation (or some other suitable location) and by applying a time domain differential equation to inversely obtain the inductance from the transient waveform represented by the signals. Advantageously, the approaches described herein do not require prior information concerning the impedance of the circuit. In this respect, the source inductance of a substation circuit can be obtained and the source inductance is used for faulted phase identification and, consequently, for classification of faults. The approaches described herein can utilize time domain signal analysis since the signal itself, in transient or steady-state, reveals the circuit and the circuit components from which the signal is obtained and analyzed.