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The paper presents the layout of two opposing thyristors working as an Arc Eliminator (AE). The presented solution makes it possible to protect an electrical apparatus against the effects of an arcing fault. An Arc Eliminator is assumed to be a device cooperating with the protected apparatus. Thyristors were used because of their speed of operation and a relatively lower cost compared to other semiconductors with the same current-carrying capacity. The proposed solution, as one of the few currently available, makes it possible to eliminate the fault arc—both at short-circuit currents and current values to which overcurrent protections do not react. A test circuit was designed and made to study the effectiveness of the thyristor arc eliminator. A series of tests was carried out with variable impedance in the arc branch, including the influence of circuit inductance on arc time. It was found that the thyristor arc eliminator effectively protects devices powered from a low voltage power network against the effects of a fault or arc fault. The correctness of system operation for a wide range of impedance changes in the circuit feeding the arc location was demonstrated.

Welding tendency for selected contact materials under different sWitching conditions Tendencja sczepiania wybranych maTeriałów sTykowych w różnych warunkach łączeniowychThe flow of significant current through electric contacts may lead to contact welding. In a.c. circuits this phenomena is not only dependent on properties of contact material (i.e. resistance to welding) but on the phase in which current is switched on. Welding tendency for contact materials made from AgNi, AgCdO and AgSnO 2 was evaluated based on selected phase at which make operation took place. The test circuit was protected by overcurrent apparatus to simulate real working environment. It is observed that welding tendency for the selected contact materials is contingent to current phase at which make operation is done.

IntroductionElectromagnetic relays are commonly used to connect circuitry with moderate values of the switching current (i. e. the medium current circuits) at a voltage not exceeding 1000 V. They are used inter alia as actuators in the building automation systems (eg. KNX, LCN, LonWorks) or in drivers and the programmable relays (Easy, NEED). They differ among themselves with a structure, purpose, and technical parameters. In regard to the contacts of connectors made of different materials, in literature, there are often presented results of research carried out as well in normal operation as in terms of specific exposures. These studies, however, are often focused on the low voltage (<50 V) direct current circuits [8]. Similar research were performed by Morin [16], Neuhaus [17] or Doublet [6], who independently conducted similar work for contacting materials for low voltage direct current circuits. Research related to processes of switching in circuits of medium voltage alternating current are focused on current ranges from a few to several kA [1,9]. A noticeable is the lack of research in the field of low-and medium current AC switches at currents close to normal and short-circuit working conditions which may occur in low voltage electrical installations, that usually do not exceed 1 kA. Within the scope of modeling simulation studies are being conducted on the heating rail and contact connections with complex shapes, configurations and utilizing a variety of conductive materials [10].Relays for connecting the receiving circuits are exposed to unfavorable processes. These phenomena may include closing overload and short-circuit currents, which may lead to shortening the life ofrelays or, in extreme cases, their total damage. The article describes the impact of switching short-circuit on the change of the contact resistance. Relays with three different contacting materials have been investigated.Contact resistance of the connector is the important performance parameter. It is important that during the utilisation of the relay this resistance reaches values as small as possible and simultaneously do not differed significantly in time. Among other things, associated with its heating the safe working load of the relay depends on its value [15]. The contact resistance value is dependent on [7,14]:shape resistance -The resultant value of contact resistance (transition) is equal to:The tarnish resistance R n is difficult to determine analytically, since it depends on multiple, sometimes random, factors including: temperature, humidity, contact material. The shape resistance R k mainly depends on the resistivity and hardness of the contact material. To its description the single-point model with elliptical, equipotential current flowlines is often used [5,7]. The actual contact area is much smaller than the apparent (nominal) surface of the contact point. This model can be considered correct, at low contact pressure forces used in relays.The value of the contact resistance is affected by the material used for the con...

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Convection forces can cause significant segregation within the liquid during directional solidification, influencing the structure of the mushy zone and the type and distribution of phases present in the solidified alloy. The solidification behavior of AlSiFeMn alloys with strong convection was investigated via experimental results combined with thermodynamic calculations. Experimental specimens were processed in a directional solidification facility with forced melt flow, resulting in high levels of elemental segregation across samples. The resulting local compositions were located on phase diagrams Al-Si-Fe, Al-Si-Mn and Al-Fe-Mn for prediction of the variation in solidification behavior. Phase mass fraction diagrams created in Thermo-Calc showed the effect of segregation on the characteristic temperatures, mushy zone length and the order of occurring phases precipitating across specimens. These findings were used to create 2D maps for visualization of the mushy zone, mass fraction of α-Al dendrites, β-Al 5 FeSi, Al 15 Si 2 Mn 4 and their spatial location. The specimen centers showed enrichment in AlSi-eutectic but for β-Al 5 FeSi and Al 15 Si 2 Mn 4 results are ambiguous. Fe-phases start to grow mainly behind the dendrites tips and in general may flow between them. Mn-rich phases start to precipitate at higher temperatures than β and in many places before α-Al and in this way may flow in the melt above the mushy zone.

This paper presents a method to limit the arc energy and hence the hazard risk category value according to IEEE 1584 by using a system of two oppositely connected multi-sectional thyristor branches. A test circuit for testing the effectiveness of a thyristor arc eliminator was designed and constructed. Arc ignition inside electrical switchgear can be a source of danger for technical personnel. The arc energy calculated according to the algorithms in IEEE 1584 can be significantly reduced by using multi-sectional arc eliminator MSAE. For the actual measuring object, the calculation of the hazardous arc flash zone and the hazard category was carried out for the system not equipped with an arc eliminator, and then the same was performed in a system with an arc eliminator. In parallel, the pressure inside the closed polyvinyl chloride (PVC) electrical box enclosure was measured and then compared with the calculated pressures that could occur during an arc fault. It was found that a Multi-Sectional Arc Eliminator (MSAE) effectively protects devices supplied from low voltage networks against the effects of short circuit or arc fault, such as the sudden increase of gas pressure inside the switchboard, which may cause it to break, significantly reduce the loss of electrode material, limit the spread of hot electrode material outside the switchgear, and also significantly reduces the energy of the electric arc.