Search results for "fault"
showing 10 items of 610 documents
Evidence of Roman Earthquake Surface Faulting at Santa Venera al Pozzo (Catania, Southern Italy): a probable seismic event in 251 AD?
2018
The record of historical seismicity of Catania (Southern Italy) and its neighbourhood during the first millennium AD is largely incomplete due to the scarcity of sources reporting information on earthquake damage, whereas on the contrary numerous historical sources provide plentiful description of past Etnean eruptions affecting the Catania area. This study provides new insights on the Catania seismic history, which was struck by large earthquakes during its recent history (e.g. 1169, 1542, 1693, 1818 earthquakes). During the first millennium, the only documented earthquake occurred in 251 AD, a year before of the big Etna eruption of 252 AD (Guidoboni et al., 2014). This earthquake left we…
Development of “Design of Experiments” for modelling direct expansion air-conditioning systems under variable cooling loads and faulty operating cond…
2019
Air conditioning systems are widely adopted in the building sector and are generally responsible for high energy consumption. Part of this consumption is related to the poor maintenance adopted by plant owner over time, which causes energy performance degradation. Typical faults, such as fouling or improper refrigerant charge have been shown to heavily impact on energy consumption of these systems. In order to support cost-effective maintenance schedule, Fault Detection and Diagnosis Technique are under investigation in the world. However, in order to devise a diagnostic method a preliminary modelling of air conditioning system is due. To this aim, a test procedure which requires the least …
On the reliability of thermoeconomic diagnosis of fouled evaporators: assessing the influence of geometries, operating conditions and reference state
2015
Thermoeconomic diagnosis of refrigeration systems is a pioneeristic approach, which has been proven to achieve good performances (under favorable conditions) for the detection of specific faults such as condenser and evaporator fouling and compressor valve leakage. In this paper the sensitivity of performance in detecting fouled Direct Expansion (DX) coils is investigated; the examined parameters are the temperature and relative humidity of coil inlet air and the sensible/latent heat ratio of the coil (varied by considering different numbers of rows). As the thermoeconomic model requires splitting the specific exergy of cooling air into “mechanical”, “thermal” and “chemical” fractions, and …
Short-circuit Calculations in Hybrid AC/DC Microgrids
2022
In this paper, the issues related to short-circuit calculations in hybrid AC/DC microgrids are discussed. The reference standard for short-current calculations in DC systems is the IEC 61660, which provides a mathematical formulation of the problem. The standard only includes radial DC grids and does not consider a more complex system, such as meshed DC systems or a hybrid AC/DC microgrid. This paper proposes a generalized approach that can be used independently of the characteristics of the hybrid system. The proposed approach is applied to two test microgrids and the results are compared with those obtained simulating the same grids with Neplan 360.
Safety Concerns on Ground Fault Application Transfer Phenomenon in HV Installations
2007
When a fault to ground occurs in HV/MV substations supplied by a combined overhead-cable line, most of the fault current can be transferred and injected into the soil several kilometers far away from the fault location. This phenomenon is called "fault application transfer" and mostly concerns transition stations, where cables are connected to the overhead line. If the transition station is a dead-end steel pole structure, usually accessible to the general public, the local ground electrode could be inadequate to maintain ground potential rise within safety limits. Hence, dangerous touch and step voltages may appear at exposed locations. In the paper results of various computer simulations …
A New Mathematical Approach for Faults Identification and Location in Distribution Systems
2009
The paper presents a new methodology for fault identification and location in electrical distribution systems, based on the use of a lumped parameter representation of the faulted line and on a matrix approach. Utilities are quite interested in such items, since the new required quality standards put severe constraints on faults management and clearance.
Results of the research on global earthing systems: A contribution to the problem of their identification
2013
The paper presents a study on the factors that can have influence on the rise of a Global Earthing System. The first part of the work deals with: - the definition of proximity, interconnection and quasi-equipotential; - the influence of the presence of HV/MV stations on the dangerous voltages and on the permissible voltage limits; - the dependence of the hazardous condition for persons on the different kind of fault; - the effects on safety of the coexistence of HV, MV and LV systems. In the second part, starting from the discussion on the themes above-mentioned and on the results of the studies, measurement campaigns and simulations on interconnected earthing systems done in the last fifte…
Ground Fault Current Distribution in Substations Supplied by Nonuniform Multi-Section Lines
2007
he paper presents a general method for computing the distribution of substation ground fault current. The feeding line can be entirely homogeneous along its whole length or consisting of two or more different sections, i.e. part overhead and part underground cable. Based on the two-port theory, the proposed method allows to take into account all the relevant conductively and inductively coupled parameters which take part to the distribution of the fault current and can be easily implemented in a computer program. Numerical examples demonstrate the high efficiency of the proposed method.
Practical tables for the design of the grounding systems in distribution networks in presence of metallic interconnection
2009
The present paper deals with the dependence of the ground current, due to a single-line-to-ground fault in a secondary substation, on the electrical and geometrical parameters of a Medium Voltage distribution network in which a metallic interconnection between the grounding systems is realized. Examining different situations, some easy-to-use tables are provided for a practical approach to the design of the ground electrodes of the secondary substations in these networks. The relevance of the work is due to the lack in the international standards of specific indications on how to consider the presence of the interconnection elements in distribution networks.
Approccio allo Sviluppo di Sistemi Diagnostici per il Funzionamento Fault Tolerant delle Micro-grid
2009
Il progressivo aumento del livello di penetrazione della generazione distribuita(GD) è destinato a provocare un profondo mutamento nelle esistenti reti di distribuzione che non sono più considerate come terminazioni passive del sistema elettrico complessivo. Una soluzione possibile è quella relativa alla realizzazione di piccole reti, le micro-grid, che riproducono, al loro interno, la struttura del sistema di produzione e distribuzione dell’energia elettrica. Per ottenere una adeguata affidabilità della micro-grid risulta importante la individuazione e la gestione dei guasti ai fini del perseguimento dell’esercizio "fault tolerant" della micro-grid stessa. Nel presente lavoro, dopo aver in…