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Global Earthing Systems (GESs) are defined by international standards IEC 61936-1 and EN 50522 as an equivalent Earthing System (ES) created by the interconnection of local ESs. Thanks to this interconnection, just a percentage of the total fault current is injected to ground in a single ES, reducing the risk of electrocution. However, even if several experiments and models proved this effect, the...
Arrays of photovoltaic (PV) modules, mounted on metallic structures, always create stray capacitances between active conductors and ground. Thus, leakage currents flowing in these ground capacitances are formed. If the number of PV modules array is high, these currents can reach some amperes. Noticeable leakage currents can cause several problems related to the proper operation of electrical installation...
Both EN 50522 and IEEE Std. 81 propose the Fall of Potential Method (FPM) to carry out the measurement of the resistance to earth of an Earthing System (ES). However, in urban areas, the recommended distances between the ES and auxiliary electrodes are not easy to respect, due to the presence of buildings and tarmac. Moreover, unknown buried metallic parts, as well as the interconnection among the...
Common solids (e.g. flour, sugar, etc.) can be suspended and transported in air via pneumatic conveying systems. Finely divided solid substances dispersed into a dust cloud (e.g. into a silo) can form a potential explosive atmosphere, if in the right concentration with the oxidizing agent (e.g. air). In addition, it is known that the pneumatic handling of substance, which allows its transport at a...
This paper discusses fundamental electrical safety issues, and the protection against electric shock of persons interacting with electric vehicles. The safety of users may be challenged by the vehicle's increased operating voltages, at different frequencies, possibly making more complex the protection against direct and indirect contacts. The electric safety of the vehicle is herein examined in both...
In recent decades, most electrical appliances have been deeply transformed with the addition of power electronics. In case of failures, the fault current is no longer sinusoidal and the effects on human beings are, up to now, not well known. Non sinusoidal currents can be decomposed in a series of sinusoidal currents: for this purpose, the IEC Standard 62423 defines a test waveform for F type residual...
International Standards IEC 61936-1 and EN 50522 define a Global Earthing System (GES) as the earthing network, created by the interconnection of local earthing systems, that should guarantee the absence of dangerous touch voltages. This is achieved through two effects: the division of the earth fault current between many earthing systems and the creation of a quasi equipotential surface. The second...
In this paper the electrical safety of DC urban traction systems is analysed, with particular focus on fault current detection and on dangerous voltages which could arise in case of fault. For the discussion the tram network of Turin, Italy, is used as a case study. Firstly the structure of the DC traction power supply is described; then the safety of the system is analysed, examining possible types...
International Standards IEC 61936-1 and EN 50522 define a Global Earthing System (GES) as the earthing network, created by the interconnection of local earthing systems, that should guarantee the absence of dangerous touch voltages. Despite that, Standards do not provide any official practical guidelines for its identification. The official classification of GES areas would lead to a simplification...
This paper presents the results of field measurements of touch voltages occurring in buildings under ground-fault conditions, as well as of resistance-to-ground of edifices of different nature (i.e. masonry, reinforced concrete). The goal of this experimental study was to confirm that ground-fault potential profiles and touch voltages in buildings do depend on the make-up of the structure, the floor...
Building structures are systems of connected parts designed to support continuous persons' occupancy. Safety of persons against electrical indirect contact under ground-fault conditions depends on the potential gradient established by the fault current within the structure.
Aeronautical ground lighting (AGL) systems have been developed to deliver warnings and status indications to pilots and maneuvering area vehicle drivers on runways. Their role in preventing the hazard of runway incursions, present in the aviation industry, is therefore crucial. AGL systems basically consist of: a primary series lighting circuit, which is supplied at constant current and high-voltage...
The object of this paper is to review various methods of determining the extent of hazardous areas in industrial facilities where explosive gas or vapor atmospheres may be present. Three different approaches are analyzed and compared. The first one is recommended in North American Standards, such as APl500 [1], APl505 [2] and NFPA 497 [3]. The second is one of the proposals for the second edition...
Lightning strikes can affect photovoltaic (PV) generators and their installations, involving also the inverter's electronics. It is therefore necessary to evaluate the risk connected to lightning strikes in order to adopt the correct protective measures for the system. The Standard IEC (EN) 62305-2 reports the procedures for the risk calculation and for the choice of proper lightning protection systems...
After twelve years of operation, the lightning location system installed in Italy by CESI s.p.a. (named CESI SIRF®) collected over fifteen millions of lightning data. The present paper shows the methodology applied to these data, in order to evaluate the ground flash density (Ng) in Italy, under the supervision of the Italian Standards (CEI). A critical step was to take into account all data losses...
The safety and protection of workers is a duty of their employer. In case of presence of hazardous areas due to the risk of explosion, an area classification has to be performed to identify the shape and size of the locations where an explosion may happen. Two typical cases that can produce hazardous areas are gas emissions from a containment system, because of normal operation or because of a failure,...
The installation of surge protective devices (SPD) can provide adequate lightning protection for equipment inside a structure. To this end, the main SPD characteristics are the SPD protection factor and its protection level. This paper shows that a coordinated SPD system, characterized by both the nominal discharge current and the impulse current, can have different protection factors for each equipment...
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