Detection of high impedance faults in medium voltage distribution networks

A Cross-Country Fault (CCF) is the simultaneous occurrence of a couple of Line-to-Ground Faults (LGFs), affecting different phases of same feeder or of two distinct ones, at different fault locations. CCFs are not uncommon in medium voltage (MV) public distribution networks operated with ungrounded or high-impedance neutral: despite the relatively small value of LGF current that is typical of such networks, CCF currents can be comparable to those that are found in Phase-To-Phase Faults, if the affected feeder(s) consists of cables. This occurs because the faulted cables’ sheaths/screens provide a continuous, relatively low-impedance metallic return path to the fault currents. An accurate evaluation is in order, since the resulting current magnitudes can overheat sheaths/screens, endangering cable joints and other plastic sheaths. Such evaluation, however, requires the modeling of the whole MV network in the phase domain, simulating cable screens and their connections to the primary and secondary substation earth electrodes by suitable computer programs, such as ATP (which is the acronym for alternative transient program) or EMTP (the acronym for electromagnetic transient program), with substantial input data being involved. This paper presents a simplified yet accurate circuit model of the faulted MV network, taking into account the CCF currents’ return path (cable sheaths/screens, ground conductors, and earthing resistances of secondary substations). The proposed CCF model can be implemented in a general-purpose simulation program, and it yields accurate fault currents estimates: for a 20 kV network case study, the comparison with accurate ATP simulations evidences mismatches mostly smaller than 2%, and never exceeding 5%.

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Lightning Performance of Medium Voltage Distribution Networks

Lecture Notes in Electrical Engineering - Proceedings of the 21st International Symposium on High Voltage Engineering ◽

10.1007/978-3-030-31676-1_144 ◽

2019 ◽

pp. 1544-1554

Author(s):

V. Vita ◽

C. A. Christodoulou ◽

L. Ekonomou

Keyword(s):

Distribution Networks ◽

Voltage Distribution ◽

Medium Voltage

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Analysis of High Impedance Faults Current Using Fourier, Wavelet and Stockwell Transforms

10.48011/sbse.v1i1.2290 ◽

2020 ◽

Author(s):

Gabriela N. Lopes ◽

Luiz H. P. C. Trondoli ◽

José Carlos M. Vieira

Keyword(s):

Distribution Systems ◽

Test Field ◽

Medium Voltage ◽

Detection Techniques ◽

Promising Tool ◽

High Impedance ◽

Random Behavior ◽

Key Characteristics ◽

High Impedance Faults ◽

High Degree

Detection of high impedance faults (HIFs) in distribution systems is a challenging task, which has attracted the interest of the researchers for decades. The HIF current random behavior and its lowmagnitude cause difficulties for a reliable detection by traditional protection methods. Therefore, the hazards for grid devices, people and animals safety, associated with HIFs, motivate the research of new detection techniques. However, there is no fully efficient solution for this problem. In this context, this paper aimed to characterize HIFs by a set of real measurements considering different type of soils employing Fourier (FT), Wavelet (WT) and Stockwell Transforms (ST). The measurements were performed at the fault spot in a medium voltage test field specially built for this purpose. The idea is to highlight key characteristics of the HIF current waveforms pointed out by each of transform and assess which ones can be used as a promising tool for HIF detection. The results showed that the HIF current can be characterized by the interharmonic behavior during the fault, extracted by FT and by the high degree of energy variations at specific decomposition levels of WT and ST.

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