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Newburyport, MA, United States

Lang M.J.,Mersen | Jones K.,Project Integration Inc.
IEEE Transactions on Industry Applications | Year: 2012

Recent testing with various electrode configurations and insulating barriers suggests that 250-V equipment omitted from arc flash hazard analyses has the potential for burn injury. Research into the sustainability of arcs at these voltages shows that assumptions about the magnitude of these hazards need to be revised. This research enhanced the work of previous efforts by focusing on the sustainability of arcs with fault currents lower than 10 kA. Gap lengths between electrodes, electrode shape, electrode material, and voltage variations are studied for their effects on arc sustainability. A modified barrier design representative of the space around panelboard bus bars is also studied. © 2011 IEEE. Source

Walsh P.R.,Mersen | Price M.M.,American Electric Power
IEEE IAS Electrical Safety Workshop | Year: 2016

Mitigation of arc flash incident energy is important to increase safety. One method is to reduce the duration of the arc flash by using protective relays to sense an arc flash fault. This method requires a supply-side overcurrent protective device that will respond to the protective relaying fast enough to mitigate the incident energy. In many existing installations, MV transformer primary fuses are already installed to provide transformer protection. Before the development of a MV controllable fuse, the MV fuse would have to be replaced with a MV circuit breaker or circuit switcher to have relay control of the MV protective device. This replacement would have significant equipment/construction costs and would require extensive equipment outage time. The MV controllable fuse method uses the existing fusegear protecting the primary side of the transformer. The protective relaying senses the arc fault and signals the controllable fuse to change to a faster acting timecurrent response. Incident energies can be reduced from 200 Cal/cm2 to below 8 Cal/cm2 on the transformer secondary. This paper reviews an installation using a MV controllable fuse to mitigate the incident energy on the equipment connected to the transformer secondary. © 2016 IEEE. Source

Catlett R.,ABB | Lang M.,Mersen | Scala S.,Superior Power Products
IEEE IAS Electrical Safety Workshop | Year: 2016

As industry pursues safer workplaces with arc flash mitigation programs, they face major challenges in effectively reducing incident energies on the secondary of medium voltage to low voltage (MV-LV) transformers. When an arc fault occurs on the transformer secondary, primary currents can be below the short circuit range of the primary protection. Typical E-rated fuses can take over 2 seconds to clear while high side device 51 relays will have a waiting period before initiating a breaker trip. Solutions that adjust the LV main breaker's (if applied) protective functions for faster response, do not address arc fault issues on the bus connecting this main breaker to the transformer secondary. This paper presents a method of applying a high speed grounding switch (HSGS) at a location between the MV Erated fuse load terminal and the transformer's primary connection. Since the transformer's primary voltage is reduced to zero in milliseconds, the low voltage arc flash event collapses quickly to limit incident energies to less than 1.2 cal/cm2. Applications can include MV-LV transformers up to 5000kVA. © 2016 IEEE. Source

Olmos L.,French National Center for Scientific Research | Olmos L.,Universidad Michoacana de San Nicolas de Hidalgo | Chaix J.-M.,French National Center for Scientific Research | Nadler S.,Ecole Nationale Superieure des Mines de Saint - Etienne CMP | And 3 more authors.
Granular Matter | Year: 2016

X-ray microtomography experiments were performed in order to evaluate the densification of silica sand submitted to horizontal sinusoidal vibrations carried out at constant frequency (50 Hz) with controlled acceleration and deceleration Γ. Packing homogeneity was characterized using relative density distribution through 3D images of the relaxed samples. Information obtained from the images allowed us to evaluate data at grain scale: porosity and pore size distribution, number of contacts per particle, particle shape and size distribution were evaluated and linked to the densification process. Based on the internal analysis of samples, the results confirm and extend the conclusions of previous works regarding the 3-layer densification under vibration and the proposed optimized vibration cycle to get dense and homogeneous samples. They extend them to different initial packings. Additionally, significant correlations are found between density and local particle packing characteristics such as pores size distribution, or the number of contacts per particle. © 2016, Springer-Verlag Berlin Heidelberg. Source

Nadler S.,Ecole Nationale Superieure des Mines de Saint - Etienne CMP | Bonnefoy O.,Ecole Nationale Superieure des Mines de Saint - Etienne CMP | Chaix J.-M.,CNRS Materials Science and Engineering | Thomas G.,Ecole Nationale Superieure des Mines de Saint - Etienne CMP | Gelet J.-L.,Mersen
European Physical Journal E | Year: 2011

Numerical and experimental studies have been undertaken to analyze three parameters controlling the compaction of granular media submitted to sinusoidal horizontal vibrations. We have characterized the influence of the dimensionless acceleration Γ, the geometry of the container and the friction coefficients on the grain velocities and on the packing densities. Above a critical acceleration Γcrit, the velocities increases with Γ. For low values of Γ, the surface layers are compacted, whereas the bottom layers remain at their initial density. For high values of Γ, the bottom layers get compacted, the surface layers are fluidized so that the bulk dynamic and relaxed densities decreased. In the same way, the effect of the dimensions of the container and of the friction coefficients on the packing properties has been studied for given heights of sand, acceleration and frequency. It has been shown that the influence of the two last parameters is similar to that of acceleration. The numerical results given by the Discrete Element Method appear to be in good agreement with experimental results. © EDP Sciences. Source

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