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Published in Heinz P. Bloch, Kenneth E. Bannister, Practical Lubrication for Industrial Facilities, 2020
Heinz P. Bloch, Kenneth E. Bannister
The magnitude of the breakdown voltage depends on many factors, such as the shape of the electrodes and the thickness and dielectric strength of the insulation between them. In accordance with the ASTM method D 877 or D 1816, the dielectric strength of an insulating oil is evaluated in terms of its breakdown voltage under a standard set of conditions. Because of the marked effect of contamination on test results, special care must be exercised in obtaining and handling the sample. The sample container and test cup must be absolutely clean and dry, and no foreign matter must come in contact with the oil.
Basic electronics
Published in Raymond F. Gardner, Introduction to Plant Automation and Controls, 2020
Normal diodes can be damaged when reverse-biased breakdown occurs; however, the Zener diodes are carefully doped with just enough impurities to make the breakdown voltage both predictable and constant. Zener diodes are designed to operate continuously in the reverse-bias polarity and the resulting voltage drop across the Zener diode is always the breakdown voltage. Because these diodes are designed to produce a fixed voltage level, they can be used to set or “regulate” voltage to other parts of the electronic sub-circuit, behaving like an inexpensive voltage regulator. Another function of a Zener diode is to prevent voltage surges from reaching sensitive parts in a circuit. Figure 3.13 shows a Zener diode properly installed in the reverse-bias direction in a dc circuit.
AlGaN/GaN HEMTs for High Power Applications
Published in D. Nirmal, J. Ajayan, Handbook for III-V High Electron Mobility Transistor Technologies, 2019
Since GaN is highly sensitive material, the passivation of the top layer is necessary to reduce the surface effects. Severe deterioration in the power performance is observed in GaN HEMT with poor passivation. In conventional GaN-based HEMT, SiO2 or Si3N4 are used as the passivation agent to reduce the surface effects and associated trapping effects. These trapping effects are assumed to be associated with surface states created by dangling bonds, threading dislocations accessible at the surface and ions absorbed from ambient environment. In order to reduce this degradation more effectively, High-k passivation layers are introduced by Binola et al. By increasing the permittivity or by increasing the thickness of the passivation layer, the breakdown voltage increases because of the weakening of the electric field at the drain edge of the gate [23]. Thus by using high-k material and thick passivation layer, breakdown voltage can be increased.
A novel 4H-SiC MESFET by lateral insulator region to improve the DC and RF characteristics
Published in International Journal of Electronics, 2018
Zohreh Roustaie, Ali A. Orouji
A power device has an important parameter – the breakdown voltage. The breakdown voltage of the device can limit its power density. The electric field is directly related to the breakdown voltage. By the improvement of the electric field distribution in the device, the breakdown voltage will increase. Studies so far show that breakdown occurs in the corner of the gate near drain while it is caused by accumulation of the electric field in this part of the device (Razavi et al., 2013; Zhu et al., 2007). By increasing the drain–source voltage, the maximum electric field in the channel increases at the corner of the gate near the drain and at this point the carriers accelerate. At this time, the electron–hole pair is created and because of the multiplication of the electron–hole pair acts like a positive feedback and constantly by increasing the number of electron–hole pair a breakdown occurs.
Numerical and Experimental Investigation of the Channel Expansion of a Low-Energy Spark in the Air
Published in Combustion Science and Technology, 2019
K. V. Korytchenko, S. Essmann, D. Markus, U. Maas, E. V. Poklonskii
Optical access to the discharge was achieved via quartz glass windows (55 mm clear diameter) in each flange. The optical setup is shown in Figure 4. A schlieren setup was used to investigate the temporal evolution of the hot gas kernel that formed during the discharge, as well as the pressure wave that formed at the perimeter of this kernel. The setup consisted of two 500 mm focal-length field lenses and a vertically oriented razor blade as the schlieren stop. A spark flash lamp (Nanolite KL-L) with a very short flash duration of less than 25 ns was used as a light source in order to freeze the position of the pressure wave on the schlieren images, which were recorded on a CCD camera (LaVision Imager ProPlus 2M). The spatial resolution of the images was 50 pixels/mm. As will be seen later, the time scale on which the kernel expands necessitates that schlieren images be taken as early as a few hundred nanoseconds after the beginning of the discharge. However, intrinsic delays of the equipment used allowed images to be taken no earlier than 6.5 µs when triggering them by means of the discharge current. Therefore, the discharges were triggered by means of ultraviolet radiation from a laser (frequency-quadrupled Nd:YAG laser at 266 nm, 7 ns pulse duration, 50 mJ pulse energy, cf. Figure 4). The voltage chosen was close to but below the natural breakdown voltage; thus, the probability of discharges occurring spontaneously was low enough that no discharges were recorded in a time interval of several minutes. The natural breakdown voltage depends on the properties of the gas, the pressure, and the electrode distance. If the voltage applied is high enough, free electrons present in the inter-electrode region are sufficiently accelerated in the electric field that an electron avalanche is created, eventually leading to a breakdown due to the Townsend mechanism (Townsend, 1915). By decreasing the voltage, the limited number of start electrons may make the probability of a breakdown so remote that, ultimately, no discharges will occur under otherwise normal conditions. Using ultraviolet radiation, a large number of free electrons are generated at a specific point in space and time. The unfocussed laser beam partially hits the electrode tips, where electrons are emitted from the metal surface due to the photoelectric effect. Electrons may also become free from molecules in the gas phase due to multi-photon ionization, though this process is likely of minor importance. This temporarily reduces the electric field strength required for a breakdown, allowing a precisely timed generation of discharges to take place. The number of free electrons generated depends on the laser irradiance and the beam path. The laser energy chosen was as low as possible, so that pre-heating of the gas would not interfere with the experiment, but was high enough to reliably trigger discharges. This was confirmed by comparing experimentally obtained kernel and pressure wave radii with and without laser triggering at the same discharge energy for time intervals where this was possible (>6.5 µs). No significant differences were found between the two cases. Further details on this triggering method can be found in work (Essmann et al., 2017).