Results 1 - 10 of 1890
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[en] Highlights: • An innovative TENG superimposed electrode layers is presented. • Utilizing the edge effect of two charged parallel plates. • One with part of the Al electrode extended as the contact point is proposed. • The Isc for TENG stacked with four layer electrodes can enhanced remarkably. • The volume can be reduced by 50–80% compared to the traditional TENG. Traditional methods enhancing the output performance of triboelectric nanogenerator (TENG) are mainly by increasing the number of single TENGs mechanically after controlling the materials surface structures and/or chemical modifications. We present an innovative TENG superimposed electrode layers by utilizing the edge effect of two charged parallel plates with poly-l-lactide (PLLA) slice and silicone sheet as the triboelectric materials and the extended part of Al electrode as the connection. When the gap distance (d) between the upper and lower friction surfaces is 1.5 cm, the d/L (L is the lateral size of TENG) is greater than 0.4, the short-circuit current (Isc) of TENG stacked with four layer electrodes was 3 times larger than that of TENG with one layer electrode. The Isc reaches a saturation when the number of superimposed electrode layers was beyond eight, corresponding to 3–5 times larger than that with one layer electrode. While the obtained Isc was 2–5 times larger than that with one layer electrode, the volume of TENG based on superimposed electrode layers can be reduced by 50–80% compared to the traditional TENGs stacked the number of single TENGs. This simple, novel method paves a way for enhancing output current, more miniaturization of the TENG.
[en] A method of increasing the sensitivity of protection from single-phase short-circuits to ground by acting on the signal with brief dummy grounding of the neutral is described. After determining the damage, the neutral is again grounded through a high resistance and an arc-quenching reactor. An increase in the protection sensitivity is thereby obtained, the damage detection time is shortened, and the probability of the single-phase short-circuit to ground converting into double and multipoint earth faults is reduced.
[en] We report on the key role of the acoustical impedance ratio between the solid and the host fluid in the transmission properties of slit arrays. Numerical calculations predict huge sound screening effects up to 60 dB for low impedance ratio values. The screening band appears over a broad frequency region and is very robust against dissipative losses of the material as well as against the sound incident angle. This counterintuitive result is discussed in terms of the hydrodynamic short circuit, where the fluid and the solid at the radiating interface vibrate out of phase, resulting in a huge sound blocking effect.
[en] Long-lasting problems concerning peculiar statistical behaviour of high populated electron avalanches have been analysed. These avalanches are precursors of streamer breakdown in gases. The present streamer theory fails in explaining severe systematic deviations from the Furry statistics that is believed to be a governing statistical law. Such a deviated behaviour of high populated avalanches seems to be a consequence of a special pre-breakdown mechanism that is rather different from that known so far in discharge physics. This analysis tends towards formulating a modified theoretical concept supplementing the streamer theory by a new statistical view of pre-streamer states. The correctness of the concept is corroborated by a series of experiments
[en] Methods are proposed for measuring the resistance and impedance of the welding circuit in contact machines; the machine may be switched on in short-circuit mode. Methods are outlined for measuring and calculating the basic electrical parameters.
[en] Magnetic tunnel junctions may experience failure due to local shortcuts in the insulating layers of such devices. The quality of the insulating layers of these devices must be analyzed. We use electrodeposition to decorate pinholes and analyze the density of pinholes and pinhole precursors. Electrical breakdown measurements can also be performed on magnetic tunnel junctions to predict the probability of such devices failing. We discuss both experimental methods and compare the results obtained. It is observed that the two methods yield the same results for the areal defect density. [copyright] 2001 American Institute of Physics
[en] A current-limiting coil with a core made of superconducting high-Tc material is tested with a view to application as a short-circuit current limiter in a three-phase network. According to the current limiter concept, the coil core is a superconductor during rated current operation, and thus keeps the coil inductance low by means of the screening effects. Under overload conditions, the magnetic field of the core winding reduces the core to normal conductivity, which eliminates the screening effects, increases the inductance, and thus results in current limitation. (orig.)
[de]Im Hinblick auf die Anwendung zur Kurzschlussstrombegrenzung in Drehstromnetzen wird eine Drossel mit einem Kern aus supraleitendem Hoch-Tc-Material untersucht. Das Strombegrenzerkonzept sieht vor, dass der Drosselkern im Betrieb mit Nennstrom supraleitend ist und durch seine Abschirmstroeme die resultierende Induktivitaet der Drossel niedrig haelt. Bei Ueberlast versetzt das Magnetfeld der Wicklung den Kern in den normalleitenden Zustand. Dadurch verschwinden die Abschirmstroeme, verbunden mit einem Anstieg der resultierenden Induktivitaet, die den Strom begrenzt. (orig.)
[en] Power evacuation and feeding of the auxiliaries directly from the 400 kV grid are sensitive points governing the security of 1300 MW PWR Nuclear Power Plants of the French Program. These two different functions are provided by two specific types of transformers. - Banks of 3 single-phase 550 MVA - 400 kV/20 kV transformers. - Three-phase 96 MVA - 400 kV / 3 x 6.8 kV transformers. These passive elements must have a never failing reliability and assure a continuous service in spite of electric, thermal and mechanical stresses that may occur during the lifetime of the power plant. Dielectric and thermal tests carried out in the manufacturers test floors insure these stresses withstand capabilities of transformers. In France, high short-circuit power for the 400 kV network added to often low impedance voltages for transformers impose on them very high stresses during short-circuits. Calculation and experimentation on scale or partial models are not sufficient to insure short-circuit currents withstand capabilities of transformers. The margin of uncertainty dependent on obligatory extrapolations for this kind of complex systems [steel, magnetic sheets, copper, oil, paper and transformerboard] can be reduced in a significant way only by real scale tests on prototypes. These tests that need both high power and voltage cannot be performed in manufacturers test floors. So, in France they are carried out at the EDF Les Renardieres Laboratory. Following paper deals with SHELL TYPE TRANSFORMERS which, particularly thanks to their interleaved rectangular windings display a great resistance to short-circuit stresses
[en] Micro fluidic chip is mainly driven electrically by external electrode and array electrode, but there are certain disadvantages in both of ways, which affect the promotion and application of micro fluidic technology. This paper discusses a scheme that uses the conductive solution in a microchannel made by PDMS, replacing electrodes and the way of dielectric breakdown to achieve microfluidic chip driver. It could reduce the driving voltage and simplify the chip production process. To prove the feasibility of this method, we produced a micro fluidic chip used in PDMS material with the lithography technology and experimented it. The results showed that using the dielectric breakdown to achieve microfluidic chip driver is feasible, and it has certain application prospect.
[en] Current-limiting reactors (CLR) are known to have a significant effect on transition processes during short circuits (SC) leading to excesses beyond the permissible values of the transient recovery voltage (TRV) at the terminals of breakers for short-circuit currents, which in turn can lead to failure of the breakers. It is shown that the traditional (generally accepted) method for calculating transient recovery voltages based on using a circuit with the reactor replaced by lumped parameters is not suitable for magnetized CLR, and in the case of uncontrolled CLR can yield erroneous results. It is argued that there is a need to account for the distribution of the winding parameters of current-limiting reactors in calculations of the TRV at the contacts of breakers as they interrupt short circuits and relevant analytic expressions are derived.