Časovno odvisna simulacija toka odklopnika brez obloka in naraščajočo upornostjo

There has been intensive research and development in the field of Circuit breakers, whether DC and AC, or low voltage and high voltage. The result of this has led to the production of highly reliable circuit breakers that accompany a built-in arc extinguishing system. However, the purpose of this study is to give the basics for arc-free current breaking with fast interruption of fault currents, e.g., in surge protective devices (SPD) for AC and DC systems, by means of a time-dependent resistor with fast rising resistance. This investigation shall illustrate how the current can be driven almost to zero with a steadily time increasing resistance, and interrupted completely without an electric arc. The basic aim of the conducted transient circuit simulations is to determine suitable time functions for the current or resistance and necessary initial and final resistances. This paper will discuss the "optimisation conditions", a switching time as short as possible, small switch-off overvoltage, and possibly an energy conversion in the resistor as low as possible is set using ATP-EMTP and analytical calculations.Na področju odklopnikov, bodisi enosmernega ali izmeničnega toka, nizke ali visoke napetosti, poteka veliko raziskav, kar rezultira v proizvodnji zelo zanesljivih odklopnikov, ki spremljajo vgrajeni sistem za gašenje obloka. Namen tega članka je pokazati osnove za odklop električnega toka brez obloka s hitrimi prekinitvami okvarnih tokov, npr. v prenapetostnih zaščitnih napravah za izmenične in enosmerne sisteme s pomočjo časovno odvisnega upora s hitro naraščajočo upornostjo. Ta študija ponazarja, kako lahko električni tok prekinemo z enakomerno naraščajočo upornostjo in kako ga lahko popolnoma prekinemo brez električnega obloka. Glavni cilj izvedenih simulacij je določitev ustreznih časovnih funkcij za električni tok ali upor ter potrebne po začetnih in končnih upornostih. V članku so predstavljeni »optimizacijski pogoji«: čim krajši preklopni čas, majhna izklopna prenapetost, in morebitna čim nižja pretvorba energije v uporu, ki je določena z uporabo ATP‐EMTP in analitičnih izračunov

Absorption of sunscreens across human skin: an evaluation of commercial products for children and adults

Aims Topical sunscreens are routinely applied to the skin by a large percentage of the population. This study assessed the extent of absorption of a number of common chemical sunscreen agents into and through human skin following application of commercially available products. Methods Sunscreen products were applied to excised human epidermis in Franz diffusion cells with the amount penetrating into and across the epidermis assessed by h.p.l.c. for 8 h following application. Results All sunscreen agents investigated penetrated into the skin (0.25 g m(-2) or 14% of applied dose), but only benzophenone-3 passed through the skin in significant amounts (0.08 g m(-2) or 10% of the applied dose). With one exception, suncreen agents in corresponding products marketed for adults and children had similar skin penetration profiles. Conclusions Whilst limited absorption across the skin was observed for the majority of the sunscreens tested, benzophenone-3 demonstrated sufficiently high penetration to warrant further investigation of its continued application