1,720,962 research outputs found
fault location in Power Network based on Electromagnetic Time Reversal
No full textThe research investigates a new method based on electromagnetic time-reversal (EMTR) theory for locating faults in power networks. This method was developed first in the field of acoustics and was more recently applied to electromagnetics. The basic idea of the EMTR is to take advantage of the reversibility in time of the wave equation. The transients observed in specific observation points of the system are time-reversed and transmitted back into the system. The time-reversed signals are shown to converge to the source (fault) location.21 Settembre 201
best PhD poster Award, EEEIC15
No full textThe undergrounding of HV subtransmission networks in urban/suburban areas is bound to increase fault currents, especially for ground faults if system neutral is solidly grounded. A parametric fault analysis based on symmetrical components is applied to a sample HV system with three lines and two EHV points of supply, based on a simple meshed Italian subtransmission network. Results are then validated by detailed three-phase ATP-EMTP simulations. Values yielded by the parametric study confirm the expected increase of all fault levels, reaching up to 36% and 69% for three-phase and 1-phase-to-ground faults, and even 104% for the ground current of phase-to-phase-to-ground faults. All calculated values are however tolerable, with fault currents well within the operating envelope of devices and components; cross-bonded sheaths also significantly relieve substation grounding mats. Some consequences of undergrounding such as reduction of earth-fault factor may be actually beneficial
Optimal power flow application to EHVAC interconnections for GW-sized Offshore Wind Farms
No full textOperation of long EHVAC cable interconnectors requires controlling voltage/reactive power profiles. With reference to a hypothetical 200 km long 400 kV-50 Hz cable system, connecting to the grid three large OWFs with 2 GW total capacity, the paper compares results yielded by a dedicated algorithm with those of a standard OPF software. A parametric study of the interconnector was carried out, considering different dispatch scenarios and boundary conditions (network connection point voltages). Several cases were ran for an enlarged, meshed test system including the interconnector. Results show that solutions yielded by OPF and by the authors' algorithm are very close, confirming the effectiveness of the latter but also its possible replacement by a standard OPF when dealing with non-radial cable system topologies
Protection system studies for ENEL Distribuzione's mv loop lines
No full textThe paper describes some of the fault studies performed for the protection system of ENEL Distribuzione's experimental MV loop lines. The system consists of a pilot relaying scheme using directional overcurrent relays for ground and phase fault detection. With reference to an actual implementation (a MV distribution network including a loop line, in Southern Italy), attention is focused on phase fault detection, aiming at the determination of magnitude and phase angle settings for relays. The effects of fault location and fault resistance are investigated by detailed simulations, resulting in tentative phase relay settings for the new protection scheme
An alternative method for locating faults in transmission line networks based on time reversal
No full textWe present an alternative method based on the time-reversal process to locate faults in transmission line networks. The proposed procedure considers different media for the forward and the backward propagation phases. Specifically, the transverse branch representing the fault is removed from the circuit in the backward propagation since its location represents the solution of the process and, therefore, is not known in advance. The advantage of the proposed method is twofold. First, the proposed backward model requires only one simulation for the time-reversed backward propagation phase, thus reducing significantly the computational burden. Second, we demonstrate that this modified backward propagation medium satisfies a property such that the fault location can be identified by computing, in the frequency domain, the argument of the voltage along the line. The theory is first formulated for the case of a lossless homogeneous single-phase transmission line; then, its applicability is extended to lossy inhomogeneous transmission line networks. A single-phase inhomogeneous transmission line and an inhomogeneous Y-shape network are specifically considered to support this claim. We show that the proposed procedure can provide high fault location accuracy (i.e., in the range of m), using only one observation point. Furthermore, we propose a criterion to link the bandwidth of the sampling system to the desired fault location accuracy
Modelling of battery energy storage systems under faulted conditions: Assessment of protection systems behaviour
No full textThe paper present a preliminary study of the protective relays of a 10 MW sized battery energy storage system (BESS) recently installed by TERNA, the Italian TSO. A complete model of the system, including inverters, has been implemented in ATP-EMTP in order to assess the behaviour of protective relays during symmetric and asymmetric faults. Results show that ground fault protection of MV feeders can be performed by zero-sequence non-directional overcurrent relays, obtaining a correct fault selection even for fault resistances in the kΩ range. Phase-to-phase and three-phase fault selection can be performed by means of overcurrent relays: an inverter current limiting control under fault conditions has to be implemented to avoid the system shutdown. Lastly, HV-level faults have been simulated during BESS-supplied, islanded operation, evidencing very low fault current contributions, depending on the actual share of battery modules operating at the time of fault, with less modules giving worst results
Detection of cross-country faults in medium voltage distribution ring lines
No full textThe paper deals with the protective relaying of MV rings recently introduced by e-distribuzione, the largest Italian Distribution System Operator (DSO). The paper refers to an existing MV distribution system which includes a loop line. Attention is focused on Cross-Country Faults (CCFs), i.e. two Line-to-Ground Faults simultaneously occurring in two different phases at different locations. A large number of detailed ATP-EMTP simulations of CCFs are carried out, evidencing a few critical CCF combinations not detected by the presently adopted protective relays. Results point out that such maloperations only occur in mixed overhead-cable rings, while all-cable loop lines are not affected. Lastly, it is also shown that CCF detection is not a problem in mixed overhead-cable rings if the overhead lines are equipped with a ground conductor. The above results could be taken as guidelines for new ring lines
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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