Three-phase arc

Uses. The standard three-phase arc furnaces are available in sizes from 200 kg to 500 t and shed diameters of 1—12 m. Eumace transformer... 

The Occupational Safety and Health Administration will deem the results of this method reasonable when the employer adjusts them using the conversion factors for three-phase arcs in open air or in an enclosure, as indicated in the program s instmctions. 

Class of equipment Single-phase arc mm (inches) Three-phase arc mm (inches)... 

For three-phase arcs in open air and in enclosures, the arc gap will generally be dependent on the spacing between parts energized at different electrical potentials. Documents such as IEEE Std 1584b-2011 provide information on these distances. Employers may select a reasonable arc gap from Table 5, or they may select any other reasonable arc gap based on sparkover distance or on the spacing between (1) live parts at different potentials or (2) live parts and grounded parts (for example, bus or conductor spacings in equipment). In any event, the employer must use an estimate that reasonably resembles the actual exposures faced by the employee. 

In the electric arc furnace method, the raw material is melted by a three-phase arc in a container lined with MgO or AI2O3 (available Si02). The wiring voltage between two electrodes (electrodes introduced vertically into the container and almost touching the material) is generally 75V-180 V. To maintain a constant current, the distance between the electrodes and molten material must be adjusted automatically. 

Open-Arc Furnaces. Most of the open-arc furnaces are used in melting and refining operations for steel and iron (Fig. 1). Although most furnaces have three electrodes and operate utilizing three-phase a-c power to be compatible with power transmission systems, d-c furnaces are becoming more common. Open-arc furnaces are also used in melting operations for nonferrous metals (particularly copper), slag, refractories, and other less volatile materials. 

Submerged-Arc Furnace. Furnaces used for smelting and for certain electrochemical operations are similar in general design to the open-arc furnace in that they are usually three-phase, have three vertical electrode columns and a shell to contain the charge, but dkect current may also be utilised They are used in the production of phosphoms, calcium carbide, ferroalloys, siUcon, other metals and compounds (17), and numerous types of high temperature refractories. 

The first successful direct-arc electric furnace, patented by Heroult in France, was placed in operation in 1899. The patent covered single- or multiphase furnaces with the arcs placed in series through the metal bath. This type of furnace, utilizing three-phase a-c power, was historically the most common for steel production. 

The first direct-arc furnace in the United States was a single-phase two-electrode rectangular furnace of 4-t capacity at the Halcomb Steel Company (Syracuse, New York), which made its first heat in 1906. A similar but smaller furnace was installed two years later at the Firth-Sterling Steel Company in McKeesport, Pennsylvania. In 1909, a 15-t three-phase furnace was installed in the South Works of the Illinois Steel Company, in Chicago, Illinois, which was, at that time, the largest electric steelmaking furnace in the world. It was the first round instead of rectangular furnace and operated on 25-cycle power at 2200 V. 

Single-or three-phase Single-phase reactors are used in the neutral circuit either to limit the ground fault currents or as arc-suppression coils (Section 20.5). Similarly, three-phase reactors are used for three-pha.se applications. 

Standard Open or Totally-Enclosed Fan-Cooled (TEFC) generators and motors are acceptable in Division 2 areas if they do not contain brushes or other arcing contacts or high-temperature devices. Three-phase TEFC motors are acceptable in Division 2 locations, but singlephase motors usually contain arcing devices and are not acceptable... 

S)-ibuprofen by means of ionic liquid flow within a microfluidic device. (B, Bottom) Photographs of the three-phase flow in the microchannel (a) center near the inlets of the microchannel, (b and c) arc of the microchannel, and (d) center near the outlets of the microchannel. Flow rates of the aqueous phase and the ionic liquid flow phase in (a-d) were 1.5 and 0.3 mL/h, respectively. (Reprinted from Huh, Y.S., Jun, Y.S., Hong, Y.K., Hong, W.H., and Kim, D.H., /. Mol. Catal. B, 43, 96-101, 2006. Copyright 2006 Elsevier. With permission.)... 

In three-phase systems the top phase. T. is an oleic phase. Ihe middle phase. M. is a inicroeuiulsion. and Ihe bottom phase. B. is an aqueous phase. Microcmulsions that occur in equilibrium with one or two other phases arc sometimes called "limiting mieroemulsions. because they occur at Ihe limits of the single-phase region... 

Example 13.2. It is instructive to relate the film pressure to a three-dimensional pressure (Fig. 13.5). On the barrier of length l the film exerts a force nl. In the three-dimensional case we estimate the force from the pressure P which acts upon a surface Id, where d is the thickness of the monolayer. This force is Pld. If the forces are set equal, we obtain P = Tt/d. Typical values for a monolayer in the Li phase arc d 1 nm and 7r = 10-3 N/m. Then we estimate a three-dimensional pressure of P = 106 N/m2 = 10 atm. 

Bias-dependent measurements were performed in order to check to what extent the mechanism depends on the electrical operation conditions. Fig. 43 shows double-logarithmic plots of the electrode polarization resistance (determined from the arc in the impedance spectrum) versus the microelectrode diameter observed at a cathodic bias of —300 mV and at an anodic bias of +300 mV respectively. In the cathodic case the electrode polarization resistance again scales with the inverse of the electrode area, whereas in the anodic case it scales with the inverse of the microelectrode diameter. These findings are supported by I-V measurements on LSM microelectrodes with diameters ranging from 30-80 pm the differential resistance is proportional to the inverse microelectrode area in the cathodic regime and comes close to an inverse linear relationship with the three-phase boundary (3PB) length in the anodic regime [161]. 

Phenyl THphenylgcrmyl Tellurium2 2.56 g (6.25 mmol) of diphenyl ditellurium are dissolved in a mixture of 3 ml of benzene plus 9 ml of ethanol, the solution is heated on a water bath, and, at reflux, a solution of 0.38 g (10 mmol) of sodium borohydride in 9 ml of 1 molar aqueous sodium hydroxide is added dropwise. When the red color of the mixture has faded, 5.1 g (15 mmol) of solid chlorotriphenylgermane are added quickly, the mixture is stirred for 5 min, and poured into 50 ml of water. The resultant mixture is extracted with three 70 ml portions of diethyl ether, the organic phases arc combined, dried with anhydrous sodium sulfate, filtered, and evaporated to dryness. The residue is recrystallized from hexane yield 3.9 g (61 %) m.p. 107°. Examples of similarly prepared compounds are ... 

Data on gas phase dispersion in three-phase sparged columns arc scarce. For two-phase systems a few correlations arc available [64, 67, 71, 72] which are shown... 

Figure 1.9 Arc energy A, nitrous oxide production S and yield y of nitrous oxides in a contactor with contacts operated in air at normal ambient pressure, switching off a three-phase system with 1000 V, 260A rms at 50cps, versus the ratio resistance R to impedance Z (or versus the phase angle

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