Short-circuited sample

There are several methods to determine and compare the resistance to partial discharges. Some tests are done on finished cables, such as the U-bend test, and others are done on laboratory samples molded from the insulation, that are subjected to partial discharges created by sharp objects, such as needles under high voltages. The tests compare either the energy required or the length of time required to erode or fail (short circuit) samples of similar thickness. 

For example, the current response of a short-circuited sample to a pressure pulse (LIPP, PWP) of amphtude p and duration r is given by (Ferreira and Gerhard-Multhaupt 1990)... 

Figure 29 shows the non-uniform optical pattern on film due to mechanical birefringence with no field and the Kerr measurement after the short-circuited sample is irradiated with high-energy electrons. Whereas the peak electric field in Fig. 25 is -160 kV/cm, the peak field due to the trapped electrons in Fig. 27 is -1.5 MV/cm, which led to the spark discharge treeing pattern shown. 

Introduction Types of metal-enclosed bus systems Design parameters and service conditions for a metal enclosed bus system Short-circuit effects Service conditions Other design considerations Skin effect Proximity effect Sample calculation for designing a 2500 A non-isolaled phase aluminium busbar systern... 

Figure 20-9 shows the negative effect of uninsulated heating elements on corrosion protection. In a 250-liter tank, an electric tube heating element with a 0.05-m surface area was screwed into the upper third without electrical separation, and in the lower third a tinned copper tube heat exchanger with a 0.61 -m surface area was built in. The Cu heat exchanger was short-circuited for measurements, as required. For cathodic protection, a potential-controlled protection system with impressed current anodes was installed between the two heating elements. The measurements were carried out with two different samples of water with different conductivities. 

Figure 5.3 Schematic representation of the penetration profile for bulk, grain boundary, and dislocation diffusion in a polycrystalline solid. The initial part of the curve is bell shaped, and the part due to short-circuit diffusion is made up of linear segments. The insets show the distribution of the tracer in the sample.

The measurement of properties such as the resistivity or dielectric constant of PS requires some kind of contact with the PS layer. Evaporation of a metal onto the PS film-covered silicon sample produces a metal/PS/Si sandwich, which behaves like an MIS structure with an imperfect insulator. Such sandwich structures usually exhibit a rectifying behavior, which has to be taken into account when determining the resistivity [Si3, Bel4]. This can be circumvented by four-terminal measurements of free-standing PS films, but for such contacts the applied electric field has to be limited to rather small values to avoid undesirable heating effects. An electrolytic contact can also be used to probe PS films, but the interpretation of the results is more complicated, because it is difficult to distinguish between ionic and electronic contributions to the measured conductivity. The electrolyte in the porous matrix may short-circuit the silicon filaments, and wetting of PS in-... 

The short circuit photocurrent density (320-400 nm illumination, lOOmW/cm ) of the sample anodized in 1 1 DMSO and ethanol containing 4% HF solution, Fig. 5.43 curve (a), is more than six times the value for the sample obtained in a 1% hydrofluoric acid aqueous solution, Fig. 5.43 curve (b). 

Figure 13 Dependence on 10-MeV-proton and 1-MeV-electron fluence of the remaining factor of short circuit current (Isc) for Si-BSFR solar cells. Circles and squares represent the results for samples irradiated with 10-MeV protons and 1-MeV electrons, respectively. Broken lines represent the fitting results based on a model mentioned in the text.

Fig. 23. Time dependence of steady-state I-V behaviour (scan rate 100 mV/s) for (a) polymer-coated n-GaAs electrode (area —0.1 cm2) and (b) bare n-GaAs photoanode in contact with the I /I (0.5/0.5 M) redox electrolyte (pH = 5). The illuminated electrode (light intensity 53mW/cm2) was maintained at approximately short-circuit condition (0.3 V vs. SCE) for the duration shown, after which the potential scans were initiated. The initial level of the I-V curve for the bare electrode was dose to that seen at 0 min for the coated sample. The electrolyte was stirred in all cases...

In the TSDC considered here, a sample is cooled to a low temperature ( 100K) and illuminated with 3 X 10 lx hght for a time tp ( 4min) in the presence of an applied DC field (E = 5 X 10" V/cm). Then, the light and voltage are switched off the structure is short-circuited and, after a delay period necessary for sample relaxation (to reach equihbrium between the free and the trapped carriers), the sample is heated in the darkness at a constant rate Vt while the TSDC is measured. We preferred TSDC experiments because of the absence of noise due to a voltage source and the strongly reduced influence of the intrinsic conductivity. 

This, however, requires that effluent samples be gathered over a long period. Such sampling schedules are difficult to set up since short circuiting or severe mixing can cause both... 

Hippel 1954b). The values of e and e" were derived from microwave theory by placing a sample of material against the end of a short-circuited transmission line, such as a waveguide or a coaxial line. This technique has applicability to high and low loss materials and in the present day has found applicability for the measurement of powders, grains and pulses (Nelson 1972,1991). 

Figure 2 shows the structure of this sensor which is similar to that of the potentiometric sensor reported earlier (10). The only difference is that in this sensor a short circuit current between the sensing electrode and the counter electrode is measured with an ammeter. The proton conductor, antimonic acid (Sb205 2H20), was prepared from antimony trioxide and hydrogen peroxide according to a method described elsewhere (7,14). The sample powder was mixed with... 

Sensing performance for H-,. Sensing performance of the amperometric sensor was examined for the detection of H2 in air. Figure 3 shows the response curve for 2000 ppm H2 in air at room temperature. The response was studied by changing the atmosphere of the sensing electrode from an air flow to the sample gas flow. With air the short circuit current between two electrodes was zero. On contact with the sample gas flow, the current increased rapidly. The 90% response time was about 10 seconds and the stationary current value was 10yUA. When the air flow was resumed, the current returned to zero within about 20 seconds. 

The short circuit current of the sensor cell was in direct proportion to the sample gas concentration. 

The experiments demonstrate the development of a streaming potential in consolidated bentonite clay when flushed by a NaCl-solution of either low or high concentration. The streaming potential measured in our experiments is at least 5 to 10 times larger than values reported for bentonite in the literature. Apparently this is caused by a very low electric conductivity of the bentonite samples studied. This low conductivity might be ascribed to overlapping diffuse double layers on the clay particles, caused by the high compaction and the presence of monovalent ions in the equilibrium solution. The bentonite, thus compacted, will be a very effective medium for active application of electroosmosis. Compared with electrically shorted conditions, chemical osmosis will be reduced when the clay is not short-circuited. 

Figure 12.5 Switching dynamics probed across the wedge sample with PFM. Note that the tip did not touch the Pt electrode for switching in order to avoid tip-sample short circuit.

There are at least two ways to obtain information by t.s.c. The first is that for the global spectra where the polymeric film is polarized by a static electric field at the polarization temperature Tp and then quenching down to the freezing temperature. With the field turned off and the sample short circuited the depolarization current due to dipolar reorientation is measured as the temperature increases from T0 to the final temperature Tf > Tp. 

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